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291.
Leland B. Deck Ellen S. Post Eric Smith Matthew Wiener Kathleen Cunningham & Harvey Richmond 《Risk analysis》2001,21(5):821-821
As part of its periodic re-evaluation of particulate matter (PM) standards, the U.S. Environmental Protection Agency estimated the health risk reductions associated with attainment of alternative PM standards in two locations in the United States with relatively complete air quality data: Philadelphia and Los Angeles. PM standards at the time of the analysis were defined for particles of aerodynamic diameter less than or equal to 10 microm, denoted as PM-10. The risk analyses estimated the risk reductions that would be associated with changing from attainment of the PM-10 standards then in place to attainment of alternative standards using an indicator measuring fine particles, defined as those particles of aerodynamic diameter less than or equal to 2.5 microm and denoted as PM-2.5. Annual average PM-2.5 standards of 12.5, 15, and 20 microg/m3 were considered in various combinations with daily PM-2.5 standards of 50 and 65 microg/m3. Attainment of a standard or set of standards was simulated by a proportional rollback of "as is" daily PM concentrations to daily PM concentrations that would just meet the standard(s). The predicted reductions in the incidence of health effects varied from zero, for those alternative standards already being met, to substantial reductions of over 88% of all PM-associated incidence (e.g., in mortality associated with long-term exposures in Los Angeles, under attainment of an annual standard of 12.5 microg/m3). Sensitivity analyses and integrated uncertainty analyses assessed the multiple-source uncertainty surrounding estimates of risk reduction. 相似文献
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293.
Eric Blyth Marilyn Crawshaw† Jean Haase‡ Jennifer Speirs§ 《Child & Family Social Work》2001,6(4):295-304
In this paper the authors, all experienced social workers with research and practice interests in assisted conception, review practices concerning access to genetic origins information in adoption, and consider to what extent these may be relevant for practice in donor‐assisted conception. The paper concludes with policy and practice recommendations that take account of the views of donor offspring and their desire for increased information about their genetic heritage. 相似文献
294.
To identify patterns that can be used to predict vegetation and landscape characteristics in urban environments, we surveyed the species composition and size of woody plants, as well as the landscape structure of forest canopies, along a forest-to-urban gradient near Oxford, Ohio, USA. The gradient included six sites of increasingly urban land-use: a preserve, a recreational area, a golf course, a residential subdivision, apartment complexes, and a business district. We recorded species identity and stem diameter for all woody plants greater than 3 cm diameter at breast height (DBH) to examine the distribution of individual species as well as overall community composition. We used digitized aerial photographs to compare the spatial characteristics of the forest canopy at each site. We found predictable patterns in species diversity (Shannon index), spatial heterogeneity in species composition (mean percent dissimilarity), and all measures of patch fragmentation (canopy cover and patch number and size). There were clear differences in tree density and total basal area between forested sites and developed sites, but there was little resolution among developed sites. Species richness and average DBH showed no clear pattern, suggesting that landscaping preference largely determined these values. We present a modified version of an intermediate heterogeneity model that can be used to predict diversity patterns in urban areas. We discuss probable mechanisms that led to these patterns and the potential implications for animal communities in urban environments. 相似文献
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297.
It is quite common to observe heteroskedasticity in real data, in particular, cross-sectional or micro data. Previous studies concentrate on improving the finite-sample properties of tests under heteroskedasticity of unknown forms in linear models. The advantage of a heteroskedasticity consistent covariance matrix estimator (HCCME)-type small-sample improvement for linear models does not carry over to the nonlinear model specifications since there is no obvious counterpart for the diagonal element of the projection matrix in linear models, which is crucial for implementing the finite-sample refinement. Within the framework of nonlinear models, we develop a straightforward approach by extending the applicability of HCCME-type corrections to the two-step GMM method. The Monte Carlo experiments show that the proposed method not only refines the testing procedure in terms of the error of rejection probability, but also improves the coefficient estimation based on the mean squared error (MSE) and the mean absolute error (MAE). The estimation of a constant elasticity of substitution (CES)-type production function is also provided to illustrate how to implement the proposed method empirically. 相似文献
298.
Eric Rosseel 《Social indicators research》1991,25(1):51-61
Images of the future and orientations to work of university graduates were investigated in a sample of university graduates before and after finishing their studies. The results indicate that university students of the eigthties generally tend to attitudes of individualistic and conventional careerism in contrast to the New Work Ethic of the seventies. Differences between people-oriented and technology-oriented students tend to vanish. Positive images of the future are linked to careerism, while negative images are linked to New Work Ethic attitudes. Differences between employed and non-employed graduates were already present before the end of studies: the students most adhering to carreeristic attitudes have the least difficulties in finding work. 相似文献
299.
Michael Eric Bronner 《Population and environment》1997,18(5):489-507
Since the turn of the century, the pace of U.S. society has become synchronized with the rate at which we consume fossil fuels, which has anchored the automobile as a focal point in daily life. The automobile allows most of us to live where we live, work where we work, enjoy ourselves where and when we enjoy ourselves, and to connect the many different, distant dimensions of our daily lives. However, the invention which was once synonymous with boundless opportunity is already engaged in a cycle of limitation. With this cycle we are equally synchronized, as our society becomes increasingly dependent on the automobile. Of this process most Americans have, at best, a fragmented understanding. In refusing to recognize the malignant effects of our automobile dependence, which requires a straightforward acceptance and direct treatment, we allow its ill-effects to grow beyond control. Each day that our automobile dependence grows, our capacity to affect the character of this change slips a notch. The objective of this paper is to characterize the true cost of automobile dependence on our society, not in a dollar estimate, but in human terms. 相似文献
300.
The spatial separation of the poor in Canadian cities 总被引:1,自引:0,他引:1
We used the 1991 Canadian census to examine the extent of spatial separation of the poor in Canadian cities. Although there were no extensive areas of blight, decay, or housing abandonment, we found high spatial separation of poor visible minorities in the selected cities. The index of dissimilarity indicates high segregation of poor blacks and moderate separation of poor Asians from the nonpoor population. We tested the effects of three major structural factors--racial and ethnic segregation, income segregation, and urban redevelopment--and found that racial and ethnic residential patterns are related strongly to the spatial separation of poor persons. The relationship between income segregation and spatial separation of the poor is not significant, however. We also found that the relationship between urban redevelopment and spatial separation of the poor pertains only to blacks. These findings suggest that blacks are vulnerable in the process of urban redevelopment. 相似文献