全文获取类型
收费全文 | 4443篇 |
免费 | 330篇 |
国内免费 | 1篇 |
专业分类
4774篇 |
出版年
2023年 | 24篇 |
2022年 | 46篇 |
2021年 | 103篇 |
2020年 | 82篇 |
2019年 | 81篇 |
2018年 | 120篇 |
2017年 | 62篇 |
2016年 | 146篇 |
2015年 | 230篇 |
2014年 | 265篇 |
2013年 | 315篇 |
2012年 | 428篇 |
2011年 | 331篇 |
2010年 | 220篇 |
2009年 | 227篇 |
2008年 | 250篇 |
2007年 | 224篇 |
2006年 | 251篇 |
2005年 | 217篇 |
2004年 | 218篇 |
2003年 | 194篇 |
2002年 | 192篇 |
2001年 | 61篇 |
2000年 | 47篇 |
1999年 | 39篇 |
1998年 | 56篇 |
1997年 | 48篇 |
1996年 | 42篇 |
1995年 | 37篇 |
1994年 | 25篇 |
1993年 | 25篇 |
1992年 | 26篇 |
1991年 | 27篇 |
1990年 | 11篇 |
1989年 | 8篇 |
1988年 | 11篇 |
1987年 | 12篇 |
1986年 | 7篇 |
1985年 | 4篇 |
1984年 | 8篇 |
1982年 | 8篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1973年 | 2篇 |
1972年 | 4篇 |
1971年 | 4篇 |
1970年 | 2篇 |
排序方式: 共有4774条查询结果,搜索用时 9 毫秒
991.
Jouannic S Argout X Lechauve F Fizames C Borgel A Morcillo F Aberlenc-Bertossi F Duval Y Tregear J 《FEBS letters》2005,579(12):2709-2714
This is the first report of a systematic study of genes expressed by means of expressed sequence tag (EST) analysis in oil palm, a species of the Arecales order, a phylogenetically key clade of monocotyledons that is not widely represented in the sequence databases. Five different cDNA libraries were generated from male and female inflorescences, shoot apices and zygotic embryos and unidirectional systematic sequencing was performed. A total of 2411 valid EST sequences were thus obtained. Cluster analysis enabled the identification of 209 groups of related sequences and 1874 singletons. Putative functions were assigned to 1252 of the set of 2083 non-redundant ESTs obtained. The EST database described here is a first step towards gene discovery and cDNA array-based expression analysis in oil palm. 相似文献
992.
993.
994.
995.
Nickel Resistance Determinants in Bradyrhizobium Strains from Nodules of the Endemic New Caledonia Legume Serianthes calycina 下载免费PDF全文
Clmence Chaintreuil Frdric Rigault Lionel Moulin Tanguy Jaffr Joël Fardoux Eric Giraud Bernard Dreyfus Xavier Bailly 《Applied microbiology》2007,73(24):8018-8022
Bradyrhizobium strains, isolated in New Caledonia from nodules of the endemic legume Serianthes calycina growing in nickel-rich soils, were able to grow in the presence of 15 mM NiCl2. The genomes of these strains harbored two Ni resistance determinants, the cnr and nre operons. By constructing a cnrA mutant, we demonstrated that the cnr operon determines the high nickel resistance in Bradyrhizobium strains. 相似文献
996.
Putrescine accumulation confers drought tolerance in transgenic Arabidopsis plants over-expressing the homologous Arginine decarboxylase 2 gene 总被引:1,自引:0,他引:1
997.
998.
Olga Otero Aurélie Pinton Henri Cappetta Sylvain Adnet Xavier Valentin Mustapha Salem Jean-Jacques Jaeger 《PloS one》2015,10(12)
In the early nineteen sixties, Arambourg and Magnier found some freshwater fish (i.e., Polypterus sp., Siluriformes indet. and Lates sp.) mixed with marine members in an Eocene vertebrate assemblage at Gebel Coquin, in the southern Libyan Desert. This locality, aged ca 37–39Ma and now known under the name of Dur At-Talah, has been recently excavated. A new fish assemblage, mostly composed of teeth, was collected by the Mission Paléontologique Franco-Libyenne. In this paper, we describe freshwater fish members including a dipnoan (Protopterus sp.), and several actinopterygians: bichir (Polypterus sp.), aba fish (Gymnarchus sp.), several catfishes (Chrysichthys sp. and a mochokid indet.), several characiforms (including the tiger fish Hydrocynus sp., and one or two alestin-like fish), and perciforms (including the snake-head fish Parachanna sp. and at least one cichlid). Together with the fossiliferous outcrops at Birket Qarun in Egypt, the Libyan site at Dur At-Talah reduces a 10-Ma chronological gap in the fossil record of African freshwater fish. Their fish assemblages overlap in their composition and thus constitute a rather homogenous, original and significant amount of new elements regarding the Paleogene African ichthyofauna. This supports the establishment of the modern African freshwater fish fauna during this time period because these sites mostly contain the earliest members known in modern genera. 相似文献
999.
Impacts of climate warming on lake fish community structure and potential effects on ecosystem function 总被引:5,自引:0,他引:5
Erik Jeppesen Mariana Meerhoff Kerstin Holmgren Ivan González-Bergonzoni Franco Teixeira-de Mello Steven A. J. Declerck Luc De Meester Martin Søndergaard Torben L. Lauridsen Rikke Bjerring José Maria Conde-Porcuna Néstor Mazzeo Carlos Iglesias Maja Reizenstein Hilmar J. Malmquist Zhengwen Liu David Balayla Xavier Lazzaro 《Hydrobiologia》2010,646(1):73-90
Fish play a key role in the trophic dynamics of lakes, not least in shallow systems. With climate warming, complex changes in fish community structure may be expected owing to the direct and indirect effects of temperature, and indirect effects of eutrophication, water-level changes and salinisation on fish metabolism, biotic interactions and geographical distribution. We review published and new data supporting the hypotheses that, with a warming climate, there will be changes in: fish community structure (e.g. higher or lower richness depending on local conditions); life history traits (e.g. smaller body size, shorter life span, earlier and less synchronised reproduction); feeding mode (i.e. increased omnivory and herbivory); behaviour (i.e. stronger association with littoral areas and a greater proportion of benthivores); and winter survival. All these changes imply higher predation on zooplankton and macroinvertebrates with increasing temperatures, suggesting that the changes in the fish communities partly resemble, and may intensify, the effects triggered by eutrophication. Modulating factors identified in cold and temperate systems, such as the presence of submerged plants and winter ice cover, seem to be weaker or non-existent in warm(ing) lakes. Consequently, in the future lower nutrient thresholds may be needed to obtain clear-water conditions and good ecological status in the future in currently cold or temperate lakes. Although examples are still scarce and more research is needed, we foresee biomanipulation to be a less successful restoration tool in warm(ing) lakes without a strong reduction of the nutrient load. 相似文献
1000.