全文获取类型
收费全文 | 23820篇 |
免费 | 417篇 |
国内免费 | 1篇 |
专业分类
管理学 | 3086篇 |
民族学 | 172篇 |
人才学 | 3篇 |
人口学 | 3612篇 |
丛书文集 | 59篇 |
理论方法论 | 1675篇 |
综合类 | 424篇 |
社会学 | 10930篇 |
统计学 | 4277篇 |
出版年
2023年 | 89篇 |
2022年 | 78篇 |
2021年 | 105篇 |
2020年 | 276篇 |
2019年 | 310篇 |
2018年 | 2032篇 |
2017年 | 2174篇 |
2016年 | 1449篇 |
2015年 | 367篇 |
2014年 | 439篇 |
2013年 | 2646篇 |
2012年 | 906篇 |
2011年 | 1468篇 |
2010年 | 1353篇 |
2009年 | 1019篇 |
2008年 | 1089篇 |
2007年 | 1248篇 |
2006年 | 306篇 |
2005年 | 507篇 |
2004年 | 462篇 |
2003年 | 445篇 |
2002年 | 322篇 |
2001年 | 347篇 |
2000年 | 315篇 |
1999年 | 283篇 |
1998年 | 209篇 |
1997年 | 177篇 |
1996年 | 252篇 |
1995年 | 196篇 |
1994年 | 209篇 |
1993年 | 174篇 |
1992年 | 208篇 |
1991年 | 221篇 |
1990年 | 205篇 |
1989年 | 178篇 |
1988年 | 208篇 |
1987年 | 185篇 |
1986年 | 147篇 |
1985年 | 182篇 |
1984年 | 181篇 |
1983年 | 158篇 |
1982年 | 119篇 |
1981年 | 91篇 |
1980年 | 101篇 |
1979年 | 117篇 |
1978年 | 88篇 |
1977年 | 77篇 |
1975年 | 63篇 |
1974年 | 66篇 |
1973年 | 60篇 |
排序方式: 共有10000条查询结果,搜索用时 437 毫秒
991.
Thrushes (Turdus spp., Turdidae) are among the most common frugivorous birds in urban areas around the world, where they disperse the seeds
of a variety of plant species. We studied the abundance, habitat use, foraging behavior and diet of four thrush species (Turdus rufiventris, T. amaurochalinus, T. leucomelas, and T. albicollis) in a suburban area in south Brazil. Abundance, habitat use and foraging behavior were based on birds surveyed along a 3,240 m
transect crossing open (formed by lawns, streets, and buildings) and forested areas. Diet was based on fecal samples collected
from mist-netted birds. Turdus rufiventris was the most abundant species, followed by T. amaurochalinus, T. leucomelas, and T. albicollis. All species used forest fragments more frequently than expected by chance. A total of 91.8% (n = 147) of the fecal samples contained fruit remains, while 42.2% contained only animal matter. Most of the foraging records
were on the ground, where birds got mainly invertebrates. Fruits and invertebrates were eaten more frequently in open than
in forested areas. A total of 25 seed morfospecies were found in the droppings, including five exotic plant species. Thrushes
overlapped widely in the fruit composition of their diets. The high abundance and degree of frugivory, coupled with the frequent
use of forest patches, indicate that thrushes are among the great bird contributors to the seed dispersal occurring in urban
forest patches, potentially influencing the vegetation dynamics of such habitats so important for the maintenance of the biodiversity
in urban areas. 相似文献
992.
Abstract CLASS is a production scheduling system, that is designed to function in either a stand-alone manner, or in conjunction with an MRP system. MRP systems innately do not have 'closed loop’ capability in the sense of being able to produce master schedules and order releases that are consistent and that respect capacity constraints. True closed loop performance requires detailed scheduling. In addition to interfacing with MRP systems, CLASS is designed to produce schedules that can be used in conventional shops or can be downloaded to automated facilities. The design goals for the system, its internal architecture, and its role in manufacturing control systems are described. The modelling and decision capabilities 相似文献
993.
Paul S. Appelbaum 《Accountability in research》2013,20(2-4):265-276
Concern about the participation of incompetent subjects in psychiatric research has grown in the last several years. In response, the National Bioethics Advisory Commission (NBAC) recommended in its recent report that all investigations involving persons with mental disorders that may be associated with cognitive impairment that may pose greater than minimal risk to subjects utilize independent assessors to verify the capacities of subjects prior to entry into the study. This recommendation poses several problems for the conduct of research and the protection of research subjects. First, it fails to target that group of subjects most likely to be at risk for incapacity. Second, it focuses on too broad a range of research projects, many of which pose little risk to participants. The substantial costs of this approach are therefore not likely to be outweighed by concomitant benefits. In place of the NBAC recommendation, the author proposes a more flexible system of capacity assessment, designed to balance the costs with a greater likelihood of achieving meaningful protection for research subjects with mental disorders. 相似文献
994.
The usual formulation of subset selection due to Gupta (1956) requires a minimum guaranteed probability of a correct selection. The modified formulation of the present paper includes an additional requirement that the expected number of the nonbest populations be bounded above by a specified constant when the best and the next best populations are ‘sufficiently’ apart. A class of procedures is defined and the determination of the minimum sample size required is discussed. The specific problems discussed for normal populations include selection in terms of means and variances, and selection in terms of treatment effects in a two-way layout. 相似文献
995.
We consider the problem of UMVU estimation of a U-estimable function of four unknown truncation parameters based on two independent random samples from two two-truncation parameter families. In particular, we obtain the UMVU estimator of functional, P (Y > X). Also the confidence intervals for some parametric functions are obtained. 相似文献
996.
Significant advances have been made to understand the interrelationship between humans and the environment in recent years,
yet research has not produced useful localized estimates that link population forecasts to environmental change. Coarse, static
population estimates that have little information on projected growth or spatial variability mask substantial impacts of environmental
change on especially vulnerable populations. We estimate that 20 million people in the United States will be affected by sea-level
rise by 2030 in selected regions that represent a range of sociodemographic characteristics and corresponding risks of vulnerability.
Our results show that the impact of sea-level rise extends beyond the directly impacted counties due to migration networks
that link inland and coastal areas and their populations. Substantial rates of population growth and migration are serious
considerations for developing mitigation, adaptation, and planning strategies, and for future research on the social, demographic,
and political dimensions of climate change. 相似文献
997.
Santiago Budría 《Social indicators research》2011,102(3):409-437
This paper asks whether educational mismatches can account for the positive association between education and wage inequality
found in the data. We use two different data sources, the European Community Household Panel and the Portuguese Labour Force
Survey, and consider several types of mismatch, including overqualification, underqualification and skills mismatch. We test
our hypothesis using two different measurement methods, the ‘statistical’ and the ‘subjective’ approach. The results are robust
to the different choices and unambiguously show that the positive effect of education on wage inequality is not due to the
prevalence of educational mismatches in the labour market. 相似文献
998.
999.
Thomas A. Weber 《Theory and Decision》2010,69(2):257-288
We consider a confidence parametrization of binary information sources in terms of appropriate likelihood ratios. This parametrization
is used for Bayesian belief updates and for the equivalent comparison of binary experiments. In contrast to the standard parametrization
of a binary information source in terms of its specificity and its sensitivity, one of the two confidence parameters is sufficient
for a Bayesian belief update conditional on a signal realization. We introduce a confidence-augmented receiver operating characteristic
for comparisons of binary experiments for a class of “balanced” decision problems, relative to which the confidence order
offers a higher resolution than Blackwell’s informativeness order.
Where observation is concerned, Chance favors only the prepared mind. —Louis Pasteur (1822–1895).相似文献
1000.
This paper considers settings where populations of units may experience recurrent events, termed failures for convenience,
and where the units are subject to varying levels of usage. We provide joint models for the recurrent events and usage processes,
which facilitate analysis of their relationship as well as prediction of failures. Data on usage are often incomplete and
we show how to implement maximum likelihood estimation in such cases. Random effects models with linear usage processes and
gamma usage processes are considered in some detail. Data on automobile warranty claims are used to illustrate the proposed
models and estimation methodology. 相似文献