全文获取类型
收费全文 | 6262篇 |
免费 | 627篇 |
国内免费 | 2篇 |
出版年
2022年 | 44篇 |
2021年 | 101篇 |
2020年 | 61篇 |
2019年 | 99篇 |
2018年 | 96篇 |
2017年 | 83篇 |
2016年 | 178篇 |
2015年 | 242篇 |
2014年 | 267篇 |
2013年 | 325篇 |
2012年 | 450篇 |
2011年 | 440篇 |
2010年 | 265篇 |
2009年 | 247篇 |
2008年 | 381篇 |
2007年 | 382篇 |
2006年 | 316篇 |
2005年 | 310篇 |
2004年 | 316篇 |
2003年 | 273篇 |
2002年 | 262篇 |
2001年 | 107篇 |
2000年 | 116篇 |
1999年 | 95篇 |
1998年 | 66篇 |
1997年 | 62篇 |
1996年 | 53篇 |
1995年 | 58篇 |
1994年 | 51篇 |
1993年 | 55篇 |
1992年 | 58篇 |
1991年 | 67篇 |
1990年 | 57篇 |
1989年 | 43篇 |
1988年 | 43篇 |
1987年 | 31篇 |
1986年 | 44篇 |
1985年 | 40篇 |
1984年 | 40篇 |
1983年 | 29篇 |
1982年 | 32篇 |
1981年 | 36篇 |
1979年 | 56篇 |
1978年 | 40篇 |
1977年 | 34篇 |
1976年 | 28篇 |
1975年 | 31篇 |
1973年 | 28篇 |
1972年 | 32篇 |
1970年 | 30篇 |
排序方式: 共有6891条查询结果,搜索用时 953 毫秒
1.
2.
3.
The cost of mutualism in a fly-fungus interaction 总被引:2,自引:0,他引:2
The movement ability of individuals has become increasingly important to a variety of ecological questions. In this study,
I investigate how plant structure and changes in body size through development affect the movement ability of a predaceous
stinkbug, Podisus maculiventris, on three species of goldenrod (Solidago spp.) representing a wide range of surface complexities. I adapt existing techniques for quantifying movement in two dimensions
to the study of movement on natural plant structures in three dimensions. These experiments indicate that plant structure
and insect size are significant factors affecting the movement ability of P. maculiventris. Changes in movement ability due to factors of ontogeny and different habitat structures suggest that the scale of an individual’s
ambit or ecological sphere of influence may vary within its lifespan. Considering the influence of ontogeny and habitat structure
on movement ability may be useful to investigations of population dynamics, foraging behavior, and pest management.
Received: 14 July 1999 / Accepted: 23 March 2000 相似文献
4.
Recent evidence suggests that the nutritional state of male Mediterranean fruit flies, Ceratitis capitata (Wied.) (medfly), is an important influence on various components of their reproductive biology, including mating success. The objective of the present study was to examine experimentally the effect of temporary starvation on the mating success of wild male C. capitata. Males were maintained on protein–sugar or sugar-only diets, and for each diet we compared the mating success of continuously fed males versus males starved for 18 or 24 h immediately before testing. In trials conducted on field-caged, host trees, males starved for 24 h obtained only about half as many matings as fed males for both diets. However, when the starvation period was 18 h, starved males reared on the protein–sugar diet mated significantly less frequently than fed males, whereas starved males reared on sugar mated as often as fed males. Measurements of male pheromone calling and female attraction revealed that reduced mating success likely reflected the decreased signaling activity of starved males. 相似文献
5.
6.
7.
The cause of the pregnancy condition preeclampsia (PE) is thought to be endothelial dysfunction caused by oxidative stress. As abnormal glucose tolerance has also been associated with PE, we use a fluorinated-mimic of this metabolite to establish whether any oxidative damage to lipids and proteins in the erythrocyte membrane has increased cell membrane permeability. Data were acquired using 19F Dynamic-NMR (DNMR) to measure exchange of 3-fluoro-3-deoxyglucose (3-FDG) across the membrane of erythrocytes from 10 pregnant women (5 healthy control women, and 5 from women suffering from PE). Magnetisation transfer was measured using the 1D selective inversion and 2D EXSY pulse sequences, over a range of time delays. Integrated intensities from these experiments were used in matrix diagonalisation to estimate the values of the rate constants of exchange and membrane permeability. No significant differences were observed for the rate of exchange of 3-FDG and membrane permeability between healthy pregnant women and those suffering from PE, leading us to conclude that no oxidative damage had occurred at this carrier-protein site in the membrane. 相似文献
8.
9.
10.