全文获取类型
收费全文 | 93502篇 |
免费 | 296篇 |
国内免费 | 812篇 |
专业分类
94610篇 |
出版年
2018年 | 11840篇 |
2017年 | 10672篇 |
2016年 | 7450篇 |
2015年 | 592篇 |
2014年 | 284篇 |
2013年 | 305篇 |
2012年 | 4220篇 |
2011年 | 12829篇 |
2010年 | 12007篇 |
2009年 | 8234篇 |
2008年 | 9795篇 |
2007年 | 11375篇 |
2006年 | 283篇 |
2005年 | 515篇 |
2004年 | 981篇 |
2003年 | 1043篇 |
2002年 | 797篇 |
2001年 | 262篇 |
2000年 | 170篇 |
1999年 | 32篇 |
1998年 | 23篇 |
1997年 | 27篇 |
1996年 | 13篇 |
1995年 | 6篇 |
1994年 | 10篇 |
1993年 | 38篇 |
1992年 | 25篇 |
1991年 | 37篇 |
1990年 | 13篇 |
1989年 | 10篇 |
1988年 | 20篇 |
1987年 | 15篇 |
1985年 | 4篇 |
1984年 | 11篇 |
1983年 | 20篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 11篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1975年 | 9篇 |
1974年 | 4篇 |
1972年 | 248篇 |
1971年 | 275篇 |
1970年 | 5篇 |
1965年 | 13篇 |
1962年 | 24篇 |
1956年 | 5篇 |
1944年 | 12篇 |
1940年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
932.
933.
On the basis of theoretical predictions, pollination networks seem to be resilient to random node elimination but sensitive to targeted exclusion. However, such predictions have a very weak empirical basis. In order to test the robustness of the pollination network to short-term disturbances, we removed inflorescences of the most connected species occurring in a lowland meadow network using the before–after approach and compared the result with that obtained by network modelling. The manipulated network showed no significant differences for the most commonly used metrics, but was more generalized than control networks, owing to a change in the preferences of pollinators. Furthermore, no secondary extinctions (emigrations) were found, owing to the considerable natural variation found among insect species assemblages. Following elimination of the most linked plant species, a new hub was detected in the experimental meadow, the hub node being a plant species with a similar inflorescence to that removed, and formerly playing the role of a peripheral node. We conclude that exclusion of the main food source forced insects to change their specialized preferences to other plant species that were available. Mostly, these had inflorescences similar to those that were removed. 相似文献
934.
Emily K. Mohl Emmanuel Santa-Martinez George E. Heimpel 《Arthropod-Plant Interactions》2016,10(3):249-261
Trophic cascades occur when predators benefit plants by consuming herbivores, but the overall strength of a trophic cascade depends upon the way species interactions propagate through a system. For example, plant resistance to, or tolerance of, herbivores reduces the potential magnitude of a trophic cascade. At the same time, plants can also affect predator foraging or consumption in ways that either increase or decrease the strength of trophic cascades. In this study, we investigated the effects of plant variation on cascade strength by manipulating predator access to aphid populations on two species of milkweed: the slower-growing, putatively more-defended Asclepias syriaca and the faster-growing, putatively less-defended Asclepias incarnata. Predatory insects increased plant growth and survival for both species, but the strength of these trophic cascades was greater on A. incarnata, which supported more aphid growth early in the season than did A. syriaca. More predators were observed per aphid on A. incarnata, and cage treatments generated significant patterns consistent with predator aggregation on A. incarnata, but not A. syriaca. Although predators strongly affected aphids, this effect did not differ consistently between milkweed species. Plant tolerance to herbivory may therefore be the primary driver of the difference in trophic cascade strength observed. Importantly, we observed that the timing of predator exclusion affected plant growth and survival differently, indicating that measures of “cascade strength” may change with phenology and plant physiological responses. Together, our results suggest a mechanism by which differences in resource allocation patterns could explain differences in growth, phenology, and cascade strength between species. 相似文献
935.
936.
937.
938.
Cullin-RING ubiquitin ligases are the largest Ubiquitin ligase family in eukaryotes and are multi-protein complexes. In these complexes, the Cullin protein serves as a scaffold to connect two functional modules of the ligases, the catalytic subunit and substrate-binding subunit. KLHL20 is a substrate-binding subunit of Cullin3 (Cul3) ubiquitin ligase. Recent studies have identified a number of substrates of KLHL20-based ubiquitin ligase. Through ubiquitination of these substrates, KLHL20 elicits diverse cellular functions, some of which are associated with human diseases. Furthermore, the functions, subcellular localizations, and expression of KLHL20 are regulated by several physiological and stressed signals, which allow KLHL20 to preferentially act on certain substrates to response to these signals. Here, we provide a summary of the functions and regulations of KLHL20 in several physiological processes and stress responses and its disease implications. 相似文献
939.
Research on the involvement of C1D and its yeast homologues Rrp47 (S. cerevisiae) and Cti1 (S. pombe) in DNA damage repair and RNA processing has remained mutually exclusive, with most studies predominantly concentrating on Rrp47. This review will look to reconcile the functions of these proteins in their involvement with the RNA exosome, in the regulation of chromatin architecture, and in the repair of DNA double-strand breaks, focusing on non-homologous end joining and homologous recombination. We propose that C1D is situated in a central position to maintain genomic stability at highly transcribed gene loci by coordinating these processes through the timely recruitment of relevant regulatory factors. In the event that the damage is beyond repair, C1D induces apoptosis in a p53-dependent manner. 相似文献
940.
Prabina Kumar Meher Tanmaya Kumar Sahu A. R. Rao S. D. Wahi 《Algorithms for molecular biology : AMB》2016,11(1):16