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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
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Bankrupt Rhetoric: How Misleading Information Affects Knowledge about Social Security 总被引:2,自引:0,他引:2
Most citizens know little about politics. Scholars often attributepolitical ignorance to individual-level factors, but we concentrateon the quality of the information environment. Employing a combinationof experimental methods and content analysis, we code statementsfrom the 199899 debate over Social Security reform aseither misleading or not misleading. Then, using surveys conductedduring the debate, we examine the impact of individual- andenvironmental-level variables on political knowledge about theprograms future. We show that misleading statements aboutSocial Securitys future cause some citizens to get animportant fact about the program wrong. More precisely, manycitizens mistakenly believe that Social Security will run outof money because political elites occasionally use words thatlead to overly pessimistic assessments of the programsfinancial future. Our findings have important implications forpolicymakers who are attempting to remake Americas largestfederal program, scholars who study citizen competence, andcitizens in a representative democracy. 相似文献
5.
William A. Mueller D.M.D. 《Child and Adolescent Social Work Journal》1993,10(5):395-401
Dental caries in children is now recognized as a preventable disease. The use of fluoride and sealants has produced a major reduction in caries prevalence among school aged children in the United States and other countries. A portion of the child population who are educationally and socioeconomically disadvantaged are not fully receiving these benefits. Public policy, insurance and medicaid groups must be made aware of these preventative measures and strategies developed to implement them. 相似文献
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Jason P. Fine David V. Glidden Kristine E. Lee 《Journal of the Royal Statistical Society. Series B, Statistical methodology》2003,65(1):317-329
Summary. We propose a simple estimation procedure for a proportional hazards frailty regression model for clustered survival data in which the dependence is generated by a positive stable distribution. Inferences for the frailty parameter can be obtained by using output from Cox regression analyses. The computational burden is substantially less than that of the other approaches to estimation. The large sample behaviour of the estimator is studied and simulations show that the approximations are appropriate for use with realistic sample sizes. The methods are motivated by studies of familial associations in the natural history of diseases. Their practical utility is illustrated with sib pair data from Beaver Dam, Wisconsin. 相似文献
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A survey of the extant literature addressing the factors that drive African American municipal employment offers two broad types of explanations: (1) Black political power and (2) institutional. A comparative assessment of the performance of each of these explanations fills a gap in the literature by illuminating the differences of these distinct perspectives when it comes to employment of Blacks in the public sector. Focusing on six Florida cities from 1960 to 2000, this study tests the predictive power of each of these explanations comparatively for four city departments. The findings indicate that the Black political power explanation performs better than the institutional explanation as a predictor of Black employment. 相似文献
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Past studies have found equivocal support for the ability of young infants to discriminate infant‐directed (ID) speech information in the presence of auditory‐only versus auditory + visual displays (faces + voices). Generally, younger infants appear to have more difficulty discriminating a change in the vocal properties of ID speech when they are accompanied by faces. Forty 4‐month‐old infants were tested using either an infant‐controlled habituation procedure (Experiment 1) or a fixed‐trial habituation procedure (Experiment 2). The prediction was that the infant‐controlled habituation procedure would be a more sensitive measure of infant attention to complex displays. The results indicated that 4‐month‐old infants discriminated voice changes in dynamic face + voice displays depending on the order in which they were viewed during the infant‐controlled habituation procedure. In contrast, no evidence of discrimination was found in the fixed‐trial procedure. The findings suggest that the selection of experimental methodology plays a significant role in the empirical observations of infant perceptual abilities. 相似文献
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中德婚姻市场供需情况的比较研究 总被引:11,自引:0,他引:11
本文从概念、形成机制、度量方法、后果及其解决途径等方面探讨了婚姻挤压问题 ,考虑到婚姻挤压对婚姻寿命、初婚人数及其性别差异的影响而创立了婚姻寿命指数与初婚挤压指数两指标 ,提出了婚姻市场类型的划分标准。通过对中德两国婚姻市场的历史与现状的考察 ,揭示了中德两国婚姻挤压产生的原因、类型、差异和未来的变化趋势 ,并对如何化解中国未来婚姻市场的供求矛盾提出了对策与建议 相似文献