全文获取类型
收费全文 | 4949篇 |
免费 | 124篇 |
国内免费 | 20篇 |
专业分类
管理学 | 733篇 |
民族学 | 25篇 |
人口学 | 660篇 |
丛书文集 | 29篇 |
理论方法论 | 428篇 |
综合类 | 215篇 |
社会学 | 1985篇 |
统计学 | 1018篇 |
出版年
2023年 | 23篇 |
2022年 | 16篇 |
2021年 | 23篇 |
2020年 | 70篇 |
2019年 | 95篇 |
2018年 | 154篇 |
2017年 | 191篇 |
2016年 | 176篇 |
2015年 | 111篇 |
2014年 | 112篇 |
2013年 | 664篇 |
2012年 | 314篇 |
2011年 | 234篇 |
2010年 | 113篇 |
2009年 | 80篇 |
2008年 | 105篇 |
2007年 | 93篇 |
2006年 | 84篇 |
2005年 | 611篇 |
2004年 | 329篇 |
2003年 | 175篇 |
2002年 | 90篇 |
2001年 | 140篇 |
2000年 | 90篇 |
1999年 | 49篇 |
1998年 | 49篇 |
1997年 | 42篇 |
1996年 | 33篇 |
1995年 | 36篇 |
1994年 | 41篇 |
1993年 | 35篇 |
1992年 | 50篇 |
1991年 | 55篇 |
1990年 | 35篇 |
1989年 | 36篇 |
1988年 | 44篇 |
1987年 | 19篇 |
1986年 | 27篇 |
1985年 | 41篇 |
1984年 | 32篇 |
1983年 | 40篇 |
1982年 | 27篇 |
1981年 | 24篇 |
1980年 | 23篇 |
1979年 | 25篇 |
1978年 | 41篇 |
1977年 | 21篇 |
1976年 | 27篇 |
1975年 | 27篇 |
1968年 | 15篇 |
排序方式: 共有5093条查询结果,搜索用时 15 毫秒
231.
232.
Nils Chr Stenseth Ottar N. Bj?rnstad Takashi Saitoh 《Researches on Population Ecology》1998,40(1):85-95
We interpret gradients in population dynamics of the gray-sided vole from the southwestern part of the island of Hokkaido
to its northeastern part within the framework of a phenomenological model involving the relative length of summer and winter.
In Hokkaido, as in other northern regions, both spring and fall is considered as short transition periods between the two
main seasons — summer (the primary breeding season) and winter (the non-reproductive or secondary breeding season). We show
that the geographic transition in dynamics may be understood as the combined consequence of different patterns of density-dependence
during summer and winter, and geographically varying season lengths. Differences are shown to exist between summer and winter
with respect to strength of density-dependence. Direct density-dependence, in particular, is stronger during winter than during
summer. A model is presented to show how relative lengths of seasons can induce both stable and periodically fluctuating population
dynamics. The results are compared and contrasted with what is otherwise known about the gradient in rodent dynamics in Fennoscandia. 相似文献
233.
Natural hybridization among wingless carabid beetles of the subgenusOhomopterus (Carabidae, genusCarabus) is reviewed, and its significance in the evolution of this subgenus discussed. Natural hybridization occurs between parapatric
species of similar size. Two case studies of natural hybridization suggest that natural hybridization could have affected
the evolution of this subgenus in different ways. When there is a large difference in genital morphology between hybridizing
species, interspecific copulation often results in genital injuries that causes mortality of copulating individuals, and hence
reduces the fitness of hybridizing individuals greatly. In such a case, hybridization may be effective in maintaining the
parapatric distribution of the two species, and in the long term, may promote reinforcement selection for traits which are
effective in prezygotic reproductive isolation. When the morphological difference in genitalia is not so large as to cause
genital injury, a hybrid population may be established at the intermediate zone between two parental species, provided that
the immigration rates of the two species into the intermediate zone are small. Thus, natural hybridization may have contributed
to both divergence and reticulate evolution in this subgenus. 相似文献
234.
Evgeny D. Maslennikov Alexey V. Sulimov Igor A. Savkin Marina A. Evdokimova Dmitry A. Zateyshchikov Valery V. Nosikov 《Journal of applied statistics》2015,42(1):71-87
The article focuses on the application of the Bayesian networks (BN) technique to problems of personalized medicine. The simple (intuitive) algorithm of BN optimization with respect to the number of nodes using naive network topology is developed. This algorithm allows to increase the BN prediction quality and to identify the most important variables of the network. The parallel program implementing the algorithm has demonstrated good scalability with an increase in the computational cores number, and it can be applied to the large patients database containing thousands of variables. This program is applied for the prediction for the unfavorable outcome of coronary artery disease (CAD) for patients who survived the acute coronary syndrome (ACS). As a result, the quality of the predictions of the investigated networks was significantly improved and the most important risk factors were detected. The significance of the tumor necrosis factor-alpha gene polymorphism for the prediction of the unfavorable outcome of CAD for patients survived after ACS was revealed for the first time. 相似文献
235.
Certain motor vehicle safety standards stipulate a collision test speed and a set of performance criteria that vehicles must satisfy during or after the collision test. For example, Federal Motor Vehicle Safety Standard 301 requires a 30 mile per hour (mph) barrier collision and specifies a certain maximum allowable limit on the total spillage of fuel. Vehicle designs are required to meet this standard; however, when collision tests are conducted at speeds higher than the standard, vehicles do not always satisfy the performance criteria. This paper develops a mathematical model for estimating the probability of meeting the standard by using a Bayesian framework to incorporate engineering judgment with collision test results. The model is based on the idea that there are random features to a vehicle's ability to meet performance standards in a collision, especially at such elevated speeds. Example calculations are included to illustrate the estimation of the probability of meeting the standard and to compare it with a maximum likelihood approach. 相似文献
236.
Marisa?C.?Young Jean?E.?WallaceEmail author 《Journal of Family and Economic Issues》2009,30(3):305-319
This study examines whether men and women invest in different determinants of productivity and whether these investments affect
productivity and salary in different ways. Hypotheses are tested from human and social capital theories that include more
direct measures for family responsibilities and family-friendly firm arguments. Data from 670 law firm lawyers were used given
they report a standardized measure of productivity in billable hours. Despite men investing more in their careers and women
investing more in their families, both report similar productivity and their productivity is affected similarly by these factors.
In addition, equally productive men and women are paid the same. The findings further our understanding of productivity and
salary and the relevance of family responsibilities and family-friendly firms.
Marisa C. Young is a second year Ph.D. student in Sociology at the University of Toronto. She is currently working on a federally funded project titled “Investigating Neighbourhood Effects on Mental Health.” Her dissertation research examines neighbourhood effects on the gendered distribution of housework, work-family conflict, and mental health. Jean E. Wallace, Ph.D., is a Professor of Sociology at the University of Calgary. She has studied professionals’ work attitudes, experiences, and organizational settings for over 20 years, with a recent shift in focus from lawyers to physicians. Her current research interests include well-being, work-life balance, job stress, and coping strategies. 相似文献
Jean E. Wallace (Corresponding author)Email: |
Marisa C. Young is a second year Ph.D. student in Sociology at the University of Toronto. She is currently working on a federally funded project titled “Investigating Neighbourhood Effects on Mental Health.” Her dissertation research examines neighbourhood effects on the gendered distribution of housework, work-family conflict, and mental health. Jean E. Wallace, Ph.D., is a Professor of Sociology at the University of Calgary. She has studied professionals’ work attitudes, experiences, and organizational settings for over 20 years, with a recent shift in focus from lawyers to physicians. Her current research interests include well-being, work-life balance, job stress, and coping strategies. 相似文献
237.
Hagelin John S. Rainforth Maxwell V. Cavanaugh Kenneth L. C. Alexander Charles N. Shatkin Susan F. Davies John L. Hughes Anne O. Ross Emanuel Orme-Johnson David W. 《Social indicators research》1999,47(2):153-201
This paper reports the results of a prospective experiment in which a group of approximately 4,000 participants in the Transcendental Meditation and TM-Sidhi programs of Maharishi Mahesh Yogi assembled in Washington, D.C., from June 7 to July 30, 1993. It was hypothesized that levels of violent crime in the District of Columbia would fall substantially during the Demonstration Project, as a result of the group's effect of increasing coherence and reducing stress in the collective consciousness of the District. A 27-member Project Review Board comprising independent scientists and leading citizens approved the research protocol and monitored the research process. Weekly crime data was derived from database records provided by the District of Columbia Metropolitan Police Department (DCMPD), which are used in the FBI Uniform Crime Reports. Statistical analysis considered the effect of weather variables, daylight, historical crime trends and annual patterns in the District of Columbia, as well as trends in neighboring cities. Consistent with previous research, levels of homicides, rapes and assaults (HRA crimes) correlated with average weekly temperature. Robberies approximately followed an annually recurring cycle. Time series analysis of 1993 data, controlling for temperature, showed that HRA crimes dropped significantly during the Demonstration Project, corresponding with increases in the size of the group; the maximum decrease was 23.3% (p < 2 × 10–9) [24.6% using a longer baseline, with 1988--1993 data (p < 3 × 10–5)], coincident with the peak number of participants in the group during the final week of the assembly. When the same period in each of the five previous years was examined, no significant decreases in HRA crimes were found. Robberies did not decrease significantly. However, a model that jointly estimated the effect of the Demonstration Project on both HRA crimes and robberies showed a significant reduction in violent crimes overall of 15.6% (p = 0.0008). Further analysis showed that the effect of the coherence-creating group on reducing HRA crimes could not be accounted for by additional police staffing. The time series analysis for HRA crimes gave results that are highly robust to alternative model specifications, and showed that the effect of the group size was cumulative and persisted after the Demonstration Project ended. Also, calculation of the steady state gain based on the time series model predicted that a permanent group of 4,000 coherence-creating experts in the District would have a long-term effect of reducing HRA crimes by 48%. 相似文献
238.
Summary ‘Predator-foolhardiness’ (Lloyd andDybas, 1966b) in an epidemic population of the sugarcane cicada,Mogannia minuta was tested by counting the number of successful and failed trials of hand-capturing of adults in the centre and periphery
of a heavily infested area. Males frequently failed to escape from capture in the outbreak area but they did not in the peripheral
zone. Females could escape well irrespective of the density. It was considered that the ‘predator-foolhardiness’ of males
is not due to genetic differentiation through the process of outbreak but to the effect of massive chorus on the escape behaviour.
The work was supported in part by Grant-in-Aid No. 439017 from the Ministry of Education, Science and Culture. 相似文献
239.
Residential preferences and population distribution 总被引:2,自引:1,他引:1
Public opinion research has revealed decided preferences for living in rural areas and small towns, and proponents of population deconcentration have interpreted this as support for their policies. This study, based on a national sample, yielded similar results, but when we introduced the additional possibility of a preference for proximity to a larger city, then the rural areas preferred were found, for most respondents, to be those within the commuting range of a metropolitan central city. Although persons wishing to live near large cities were found to be looking for the same qualities of living sought by those who prefer a more remote location, these findings are not, in general, consistent with the argument that public preferences support strategies of population dispersal into nonmetropolitan areas. Instead they indicate that most of those who wish to live in a different location favor the peripheral metropolitan ring areas that have, in fact, been growing rapidly by in-migration. 相似文献
240.
With increasing demand for low-density recreational services and limited supply of facilities to provide them, congestion is becoming an important management problem. The purpose of this paper is to outline a model of congestion, estimate the effect of it upon individual willingness to pay for wilderness experiences, and illustrate how these results might be used for efficient management. A survey of users of the Spanish Peaks Primitive Area indicates that their revealed willingness to pay is significantly affected by encroachments upon the solitude they experience during their trip. Consequently, congestion effects for such services can be measured and used in the formation of administrative policy. 相似文献