全文获取类型
收费全文 | 4701篇 |
免费 | 432篇 |
国内免费 | 98篇 |
专业分类
5231篇 |
出版年
2024年 | 17篇 |
2023年 | 109篇 |
2022年 | 89篇 |
2021年 | 159篇 |
2020年 | 196篇 |
2019年 | 222篇 |
2018年 | 202篇 |
2017年 | 206篇 |
2016年 | 243篇 |
2015年 | 310篇 |
2014年 | 315篇 |
2013年 | 460篇 |
2012年 | 193篇 |
2011年 | 239篇 |
2010年 | 197篇 |
2009年 | 238篇 |
2008年 | 248篇 |
2007年 | 230篇 |
2006年 | 144篇 |
2005年 | 131篇 |
2004年 | 124篇 |
2003年 | 107篇 |
2002年 | 103篇 |
2001年 | 75篇 |
2000年 | 57篇 |
1999年 | 64篇 |
1998年 | 57篇 |
1997年 | 56篇 |
1996年 | 61篇 |
1995年 | 34篇 |
1994年 | 46篇 |
1993年 | 39篇 |
1992年 | 28篇 |
1991年 | 30篇 |
1990年 | 24篇 |
1989年 | 24篇 |
1988年 | 23篇 |
1987年 | 12篇 |
1986年 | 19篇 |
1985年 | 22篇 |
1984年 | 9篇 |
1983年 | 12篇 |
1982年 | 16篇 |
1981年 | 7篇 |
1980年 | 9篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
排序方式: 共有5231条查询结果,搜索用时 0 毫秒
1.
《Ethnic and racial studies》2012,35(8):1427-1446
Abstract The national census is often seen as a site of struggle for minorities seeking recognition and equality. Much less is known about the conditions under which ethnic majorities are galvanized to stake identity claims in the census. This article examines recent trends in New Zealand where an increasing number of people from the dominant New Zealand European group are redefining themselves as ethnic New Zealanders. Drawing from the literature on ethnic boundaries, we theorize the factors underlying the surge in New Zealander identification, and present census data to demonstrate its selective appeal. We also review patterns of national naming in North America and Australia to show that the New Zealander phenomenon reflects a broader shift by settler state majorities to reimagine their identities. The implications for ethnic counting in other contexts are briefly considered. 相似文献
2.
H. Ronald Pulliam 《Human ecology: an interdisciplinary journal》1982,10(3):353-363
Patterns of conflict and cooperation both within and between societies may be related to the degree of cultural similarity within and between the same societies. A simple model of social learning is used to predict patterns of conflict and cooperation in hypothetical societies that differ in the roles of relatives and nonrelatives in the enculturation of children. The model is illustrated by comparing its predictions to known differences in the patterns of conflict between males inpatrilocal and matrilocal societies. 相似文献
3.
Reginald B. Cocroft 《Journal of Insect Behavior》2003,16(1):79-95
Many membracid treehoppers are attended by honeydew-harvesting ants. Ant mutualism often favors group living, which will in turn influence social interactios and communication. I investigated aspects of life history that underlie the social behavior of an aggregating, ant-attended treehopper. The number of adults, and their patterns of distribution, changes dramatically over the course of a season. Despite the relatively low vagility and high persistence in the same clump of host plants, individuals encounter a wide range of social environments. This aggregating species differs from solitary species in the clumped distribution of females, and possibly in the intensity of acoustic competition among males, but both aggregating and solitary species exhibit large temporal changes in density. A high degree of temporal and spatial variation in the social environment is probably characteristic of many insects and may be an important source of selection on insect communication. 相似文献
4.
《Journal of biological education》2012,46(3):158-161
Ecology and evolution Agricultural education Evolution and education Education division elections ISII in Europe Tree project Science teaching scholarship Biology of terrestrial arthropods A microscopied museum 相似文献
5.
6.
Dominant males of nonseasonally breeding species should have more opportunity than seasonal breeders to monopolize access to estrous females and thus enhance their reproductive success. They may also use other strategies for maximizing reproductive success such as producing offspring by relatively high ranking females. To test these hypotheses, the paternity of 35 (80%) of 44 Macaca fascicularis offspring, born over a 28-month period, was established using electrophoretically and serologically defined genetic markers. The social ranks of each of the seven potential fathers and 26 potential mothers were determined by recording outcomes of dyadio agonistic interactions. No evidence could be found to support either hypothesis. Further, in view of previously reported significant, positive correlations between male social rank and sexual activity rates in this study group, sexual activity rates do not appear to predict the number of offspring a male sires in this species. 相似文献
7.
A.S. Purewal 《FEMS microbiology letters》1991,82(2):229-232
The nucleotide sequence of the gene specifying the ethidium efflux system of Escherichia coli has been determined. The translated open reading frame has identified a membrane-bound polypeptide of 110 amino acids (11,960 Da) which shares 42% identity with a staphylococcal protein specifying resistance to ethidium. 相似文献
8.
Richard G. Condon 《Human ecology: an interdisciplinary journal》1991,19(3):287-321
Birth seasonally at high latitudes is a complex phenomenon which is undoubtedly affected by a subtle interaction between environmental rhythmicity (most notably in photoperiod and temperature) and cultural adaption. There is intriguing evidence that human gonadotrophic activity (and hence fertility) may be affected by seasonal fluctuations in light intensity and duration. Nevertheless, cultural factors are important insofar as they mediate between environmental rhythmicity and human fertility/birth patterns. This article examines the distribution of births over several decades in an Inuit community located 300 miles north of the Arctic Circle. Several shifts in birth seasonality are noted, the most significant of which is a dramatic shift from pronounced seasonality in the 1970s to non-seasonality in the 1980s. Longitudinal ethnographic fieldwork has allowed an examination of social and economic changes accounting for the rather sudden disappearance of birth seasonality. These include increasing reliance upon wage employment and social assistance, decreased dependence upon subsistence hunting and trapping, changing attitudes on the part of young people entering their prime reproductive years, and the introduction of television, radio, and southern-style recreational activities. 相似文献
9.
1. Larval success was compared when one, two, or three egg clutches were laid in kumquat fruits (≈ 10 ml in volume) either successively on the same day or at the rate of one clutch per day. 2. Increased clutch density was associated with a significant decrease in larval survival rate and non‐significant decreases in larval growth rate and pupal mass. 3. Larval and pupal parameters showed significantly larger variance when clutches were laid on successive days than on the same day, suggesting a competitive advantage for older larvae over younger larvae. 4. The results suggest that, in small fruit, reduced fitness due to larval competition may act against possible fitness benefits due to social facilitation among adult females, hence reducing the likelihood of non‐linear population dynamics caused by processes such as the Allee effect. 相似文献
10.