全文获取类型
收费全文 | 25316篇 |
免费 | 431篇 |
专业分类
管理学 | 3199篇 |
民族学 | 128篇 |
人才学 | 6篇 |
人口学 | 2370篇 |
丛书文集 | 130篇 |
教育普及 | 2篇 |
理论方法论 | 2210篇 |
现状及发展 | 1篇 |
综合类 | 314篇 |
社会学 | 12099篇 |
统计学 | 5288篇 |
出版年
2023年 | 121篇 |
2021年 | 127篇 |
2020年 | 380篇 |
2019年 | 580篇 |
2018年 | 636篇 |
2017年 | 869篇 |
2016年 | 613篇 |
2015年 | 469篇 |
2014年 | 586篇 |
2013年 | 4246篇 |
2012年 | 864篇 |
2011年 | 779篇 |
2010年 | 616篇 |
2009年 | 582篇 |
2008年 | 620篇 |
2007年 | 653篇 |
2006年 | 593篇 |
2005年 | 553篇 |
2004年 | 535篇 |
2003年 | 504篇 |
2002年 | 511篇 |
2001年 | 637篇 |
2000年 | 546篇 |
1999年 | 516篇 |
1998年 | 419篇 |
1997年 | 387篇 |
1996年 | 389篇 |
1995年 | 365篇 |
1994年 | 348篇 |
1993年 | 334篇 |
1992年 | 412篇 |
1991年 | 396篇 |
1990年 | 359篇 |
1989年 | 354篇 |
1988年 | 330篇 |
1987年 | 305篇 |
1986年 | 306篇 |
1985年 | 338篇 |
1984年 | 335篇 |
1983年 | 340篇 |
1982年 | 269篇 |
1981年 | 229篇 |
1980年 | 240篇 |
1979年 | 253篇 |
1978年 | 222篇 |
1977年 | 207篇 |
1976年 | 185篇 |
1975年 | 173篇 |
1974年 | 150篇 |
1973年 | 123篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
Diane Hope Weixing Zhu Corinna Gries Jacob Oleson Jason Kaye Nancy B. Grimm Lawrence A. Baker 《Urban Ecosystems》2005,8(3-4):251-273
We explored variations in inorganic soil nitrogen (N) concentrations across metropolitan Phoenix, Arizona, and the surrounding
desert using a probability-based synoptic survey. Data were examined using spatial statistics on the entire region, as well
as for the desert and urban sites separately. Concentrations of both NO3-N and NH4-N were markedly higher and more heterogeneous amongst urban compared to desert soils. Regional variation in soil NO3-N concentration was best explained by latitude, land use history, population density, along with percent cover of impervious
surfaces and lawn, whereas soil NH4-N concentrations were related to only latitude and population density. Within the urban area, patterns in both soil NO3-N and NH4-N were best predicted by elevation, population density and type of irrigation in the surrounding neighborhood. Spatial autocorrelation
of soil NO3-N concentrations explained 49% of variation among desert sites but was absent between urban sites. We suggest that inorganic
soil N concentrations are controlled by a number of ‘local’ or ‘neighborhood’ human-related drivers in the city, rather than
factors related to an urban-rural gradient. 相似文献
23.
A sample size justification should be given for all clinical investigations. However, sometimes the objective of a trial is to estimate an effect with a view to planning a later definitive study. This paper describes the calculations for designing studies where one wishes to adopt an estimation approach through using confidence intervals around the overall response. Calculations are given for data anticipated to take a Normal form. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
24.
Craig H. Mallinckrodt Christopher J. Kaiser John G. Watkin Michael J. Detke Geert Molenberghs Raymond J. Carroll 《Pharmaceutical statistics》2004,3(3):171-186
The last observation carried forward (LOCF) approach is commonly utilized to handle missing values in the primary analysis of clinical trials. However, recent evidence suggests that likelihood‐based analyses developed under the missing at random (MAR) framework are sensible alternatives. The objective of this study was to assess the Type I error rates from a likelihood‐based MAR approach – mixed‐model repeated measures (MMRM) – compared with LOCF when estimating treatment contrasts for mean change from baseline to endpoint (Δ). Data emulating neuropsychiatric clinical trials were simulated in a 4 × 4 factorial arrangement of scenarios, using four patterns of mean changes over time and four strategies for deleting data to generate subject dropout via an MAR mechanism. In data with no dropout, estimates of Δ and SEΔ from MMRM and LOCF were identical. In data with dropout, the Type I error rates (averaged across all scenarios) for MMRM and LOCF were 5.49% and 16.76%, respectively. In 11 of the 16 scenarios, the Type I error rate from MMRM was at least 1.00% closer to the expected rate of 5.00% than the corresponding rate from LOCF. In no scenario did LOCF yield a Type I error rate that was at least 1.00% closer to the expected rate than the corresponding rate from MMRM. The average estimate of SEΔ from MMRM was greater in data with dropout than in complete data, whereas the average estimate of SEΔ from LOCF was smaller in data with dropout than in complete data, suggesting that standard errors from MMRM better reflected the uncertainty in the data. The results from this investigation support those from previous studies, which found that MMRM provided reasonable control of Type I error even in the presence of MNAR missingness. No universally best approach to analysis of longitudinal data exists. However, likelihood‐based MAR approaches have been shown to perform well in a variety of situations and are a sensible alternative to the LOCF approach. MNAR methods can be used within a sensitivity analysis framework to test the potential presence and impact of MNAR data, thereby assessing robustness of results from an MAR method. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
25.
Estimated associations between an outcome variable and misclassified covariates tend to be biased when the methods of estimation that ignore the classification error are applied. Available methods to account for misclassification often require the use of a validation sample (i.e. a gold standard). In practice, however, such a gold standard may be unavailable or impractical. We propose a Bayesian approach to adjust for misclassification in a binary covariate in the random effect logistic model when a gold standard is not available. This Markov Chain Monte Carlo (MCMC) approach uses two imperfect measures of a dichotomous exposure under the assumptions of conditional independence and non-differential misclassification. A simulated numerical example and a real clinical example are given to illustrate the proposed approach. Our results suggest that the estimated log odds of inpatient care and the corresponding standard deviation are much larger in our proposed method compared with the models ignoring misclassification. Ignoring misclassification produces downwardly biased estimates and underestimate uncertainty. 相似文献
26.
Professor Stephen Senn Dr Dipti Amin Professor Rosemary A. Bailey Professor Sheila M. Bird FFPH Dr Barbara Bogacka Mr Peter Colman Dr rew Garrett Professor rew Grieve Professor Sir Peter Lachmann FRS FMedSci 《Journal of the Royal Statistical Society. Series A, (Statistics in Society)》2007,170(3):517-579
27.
28.
Has the image of Che Guevara lost its power to evoke radical politics in the face of pervasive commodification? The commercialization of this 1960s political icon has called into question the power of the market to shape collective memories. Meanwhile, antisystemic movements of the left continue to erect his image at protest events. In light of this contest over how Che Guevara is remembered, we investigate, using data from a survey of Spanish citizens, who is most likely to recall him. We find qualified support for the theory of generational imprinting—Che is more often recalled by those generations who saw him rise to prominence during their formative years, although prominent as a collective symbol rather than as a living person. Our results also corroborate the claim that historical figures or events are more salient for, and therefore more likely to be remembered by, some subgenerational units than others. Thus, although the younger generations are in general more likely than their elders to recall Che, he is most frequently remembered by the highly educated leftists who espouse postmaterialist and posttraditionalist values and identify more with their local regions than with the nation of Spain. These patterns suggest that, in contrast to the dire predictions of mass culture theorists, the memory of Che Guevara has become increasingly tied to markers of social, ethnic‐regional, and political identity. 相似文献
29.
The 1998 Korean Survey of Family Income and Expenditures was used to examine the overall consumption and saving behavior of Korean baby boomers and compared the differences in consumption and saving behavior between older and younger boomers. The t -test results indicated that the younger boomers allocated a significantly higher percentage of their expenditures on food away from home, household appliances, transportation and communication than did the older boomers, whereas the older boomers spent higher amounts and allocated larger budget shares on their children's education than did the younger boomers. The results of Ordinary Least-Squares (OLS) regression analysis showed that, holding other factors constant, older boomers not only spent significantly more in the total consumption expenditures and education expenditures, but older boomers also saved significantly less than did younger boomers. 相似文献
30.
We examine the labor-cost savings associated with privatization by comparing earnings and employment trends of public and
private sector refuse workers. Findings suggest that high union earnings for workers in the public sector are a source of
labor-cost savings in the refuse industry. Evidence on job changers does not indicate that earnings for this group of workers
are a compensating differential. Metropolitan area employment findings suggest that municipalities are less likely to use
union refuse workers in the public sector when a relatively small percentage of area residents belong to a union.
The authors thank Jacqueline Agesa, Keith Bender, Maria Crawford, and Richard Perlman for valuable suggestions. Research assistance
from Eric Blackburn is greatly appreciated. 相似文献