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131.
21世纪我国老年人口规模与老年人力资源开发 总被引:9,自引:0,他引:9
21世纪上半叶将是老年人口数量及老龄化突进的时期。老年人力资源是人力资源构成的重要组成部分 ,建立市场机制 ,把老年人愿为现代化建设作贡献的主观愿望和能力 ,与社会发展对老年人力资源的客观需要 ,合理、有效地结合 ,促进人口经济协调发展 相似文献
132.
133.
J.Miller McPherson 《Social science research》1976,5(2):95-105
This paper attempts to show that the “Theory Trimming” technique makes little contribution to theory in sociology. A brief history of the technique is given, and several key assertions of its proponents are abstracted. These assertions are shown to be highly questionable. The general alternative to Theory Trimming is shown, and the relationship between Theory Trimming and more general orientations to research is discussed. 相似文献
134.
Robert M. Groves 《Social science research》1978,7(3):257-271
Concurrently administered personal and telephone surveys are compared to measure differences between the modes for identical questions. Speed of questioning is found to be greater in telephone interviews than personal interviews. The faster pace of telephone interviews is linked to shorter answers to open-ended items on the telephone. The tendency to reduce such responses is disproportionately exhibited by younger, affluent respondents who tend to provide detailed responses in personal interviews. 相似文献
135.
Research on sex differences in occupational attainment suggests that working men and working women attain essentially the same mean level of occupational attainment and do so through quite similar processes. A possible explanation for these similarities is that the sample of working women contains an overrepresentation of successful women, since women who can afford not to work will stay out of the labor force unless they find a job commensurate with their education. This we define as a censoring problem. By extending a technique developed by Heckman, we can estimate the structural parameters for all women, regardless of current employment status. This procedure allows us to assess the impact of the censoring problem on women's occupational attainment equations. 相似文献
136.
Rein Taagepera 《Social science research》1978,7(2):180-196
Area changes of about 30 best known empires and states are compiled and tabulated. Superimposed and juxtaposed graphs (size versus time) help to visualize the relative size and location in time of these empires. Size-time integral, maximum stable size, adulthood date, and duration are defined operationally and are listed for 20 empires. A criterion is given for distinctness of successive empires. The size-time integral is a direct measure of an empire's impact on history insofar as that impact depends on sheer size and duration. The integral is largest for the Chinese Hsia-Shang, Egyptian New, Old, and Middle, Assyrian New, and Hittite empires. A world-wide territorial concentration index is tabulated. It increases during the period considered from 0.08 to 1.4% of the world dry land area. 相似文献
137.
通过对有丝分裂中期及减数分裂终变期染色体数目统计,形态、行为的观察,发现莱麦草染色体呈现广泛的变异:有丝分裂中期株内染色体数目在2n=11──56内变化,含有本物种染色体数目2n=28的细胞仅占统计数的27.8%。减数分裂终变期出现36%具非整倍性的花粉母细胞,染色体数除数目变异外还有结构变异如Robertson易位等。本文对该种进行了染色体组分析,确认其为同源四倍体。同时对该物种株内产生混倍性的原因,在物种进化上的意义进行了探讨。 相似文献
138.
Teiji Sota 《Researches on Population Ecology》1998,40(2):173-174
I studied the effect of treehole (microhabitat) size distribution in local habitats on geographic difference in aquatic metazoan
community structure by comparing differences between two sites on Iriomote Island, and between Iriomote Island (subtropical)
and Tsushima Island (temperate), in southwestern Japan. In treeholes at each local site, the amount of litter, the species
richness and total biomass of metazoa were positively correlated with treehole capacity. Between the two sites on Iriomote
Island (Shirahama and Komi), the amount of litter, biomass and species number per treehole was greater at Komi where the mean
and variance of treehole size were greater, while the dependencies of these parameters on treehole capacity were common to
both sites. Total species number was larger at Komi (2 predators and 20 saprophages) than at Shirahama (1 predator and 19
saprophages). Most of the dominant taxa colonized larger treeholes with higher probabilities, although one taxa showed the
opposite trend. Treeholes on Tsushima were smaller than those on Iriomote. The metazoan fauna in treeholes consisted of 15
saprophages on Tsushima, being less richer than that on Iriomote Island which had 2 predators and 21 saprophages. However,
the dependencies of litter amount and biomass on treehole capacity did not differ significantly between the islands, although
treeholes on Iriomote harbored a greater number of species per treehole than those on Tsushima. This study indicated that
there are general correlates between community structure within individual treeholes (infracommunity structure) and treehole
capacity (microhabitat size). Therefore, microhabitat-size distribution is potentially a significant constraint of local community
structure, and its variation may contribute to the variation in local and regional species richness. 相似文献
139.
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
140.
《本草纲目》中的不少“本草”是从西方的伊斯兰诸国传入中国的,伊斯兰民族的医学典籍中的例举及其诠释足可证明这个事实。 相似文献