全文获取类型
收费全文 | 2394篇 |
免费 | 221篇 |
出版年
2021年 | 23篇 |
2019年 | 18篇 |
2018年 | 18篇 |
2017年 | 18篇 |
2016年 | 34篇 |
2015年 | 54篇 |
2014年 | 81篇 |
2013年 | 103篇 |
2012年 | 90篇 |
2011年 | 108篇 |
2010年 | 82篇 |
2009年 | 62篇 |
2008年 | 90篇 |
2007年 | 123篇 |
2006年 | 91篇 |
2005年 | 83篇 |
2004年 | 105篇 |
2003年 | 76篇 |
2002年 | 70篇 |
2001年 | 71篇 |
2000年 | 87篇 |
1999年 | 69篇 |
1998年 | 31篇 |
1997年 | 23篇 |
1996年 | 28篇 |
1995年 | 19篇 |
1993年 | 24篇 |
1992年 | 36篇 |
1991年 | 56篇 |
1990年 | 54篇 |
1989年 | 40篇 |
1988年 | 35篇 |
1987年 | 46篇 |
1986年 | 37篇 |
1985年 | 36篇 |
1984年 | 34篇 |
1983年 | 32篇 |
1982年 | 27篇 |
1981年 | 22篇 |
1980年 | 17篇 |
1979年 | 31篇 |
1976年 | 35篇 |
1975年 | 41篇 |
1974年 | 26篇 |
1973年 | 31篇 |
1972年 | 21篇 |
1971年 | 20篇 |
1970年 | 20篇 |
1969年 | 24篇 |
1967年 | 18篇 |
排序方式: 共有2615条查询结果,搜索用时 46 毫秒
1.
The time course of changes in the level of uncoupling protein mRNA when cold-acclimated mice were returned to a thermoneutral environment (33 degrees C) was examined using a cDNA probe. Upon deacclimation, there was a marked loss of uncoupling protein mRNA within 24 h, which precedes the loss of uncoupling protein from mitochondria. This loss of uncoupling protein mRNA was selective, since there was no change in the relative proportion of cytochrome c oxidase subunit IV mRNA or poly(A)+ RNA in total RNA. The results suggest that the decrease in the mitochondrial content of uncoupling protein during deacclimation is likely the result of turnover of existing protein, with very little replacement due to a lower level of its mRNA. 相似文献
2.
Cultured porcine thoracic aorta endothelial cells were covalently labeled with 4-maleimido-2,2,6,6-tetramethylpiperidinooxyl. Electron paramagnetic resonance spectrometry revealed two major binding environments representing strongly and weakly immobilized species. The disorder parameter of weak/strong, determined from the respective peak amplitudes, was irreversibly elevated following incubation of endothelial cells with a superoxide-generating system, indicating increased membrane fluidity. The rate of increase in membrane disorder was dependent upon superoxide generation rates. Incorporation of the spin-label at concentrations less than 250 microM had no effect on cell viability. The cellular proteins reacting with the spin-label were predominantly membrane proteins, characterized by immunoblotting using a rabbit anti-4-maleimido-2,2,6,6-tetramethylpiperidinooxyl IgG, following sodium dodecyl sulfate-polyacrylamide gel electrophoresis and electrophorectic transfer to nitrocellulose. 相似文献
3.
A method was developed to optimize simultaneous selection for a quantitative trait with a known QTL within a male and a female line to maximize crossbred performance from a two-way cross. Strategies to maximize cumulative discounted response in crossbred performance over ten generations were derived by optimizing weights in an index of a QTL and phenotype. Strategies were compared to selection on purebred phenotype. Extra responses were limited for QTL with additive and partial dominance effects, but substantial for QTL with over-dominance, for which optimal QTL selection resulted in differential selection in male and female lines to increase the frequency of heterozygotes and polygenic responses. For over-dominant QTL, maximization of crossbred performance one generation at a time resulted in similar responses as optimization across all generations and simultaneous optimal selection in a male and female line resulted in greater response than optimal selection within a single line without crossbreeding. Results show that strategic use of information on over-dominant QTL can enhance crossbred performance without crossbred testing. 相似文献
4.
5.
6.
7.
8.
9.
10.
Dena Freeman 《The journal of the Royal Anthropological Institute》2002,8(1):23-44
This article focuses on cultural transformation in the Gamo Highlands of Ethiopia and seeks to explain the way in which certain initiation rituals have transformed over time. The article begins by considering two structural variants of the initiation ritual that exist in two neighbouring communities, Doko Gembela and Doko Masho, and argues that one is an historical transformation of the other. After comparing the contemporary form of these two variants, the article then moves to consider the macro-level forces of change that have impinged on the two communities over the past two hundred years or so. It then seeks to bring ethnography and history together by considering how the macro-level changes might have been experienced in the interpersonal relations of individuals. It explores the new types of situations that would have arisen and discusses how these new situations would have put strains on particular interpersonal relations, leading in many cases to conflict and dispute. After describing the local methods of conflict resolution, it is shown that on some occasions solutions are found which involve communal decisions to make a small change in cultural practice. In some cases these small changes have a knock-on effect leading to overall structural change. The article ends with a hypothetical reconstruction of the way in which the Doko Masho initiation rituals might have transformed. 相似文献