全文获取类型
收费全文 | 487668篇 |
免费 | 47454篇 |
国内免费 | 199篇 |
专业分类
535321篇 |
出版年
2018年 | 5055篇 |
2017年 | 4781篇 |
2016年 | 6223篇 |
2015年 | 6905篇 |
2014年 | 8757篇 |
2013年 | 12338篇 |
2012年 | 14311篇 |
2011年 | 14918篇 |
2010年 | 10144篇 |
2009年 | 9305篇 |
2008年 | 13356篇 |
2007年 | 13853篇 |
2006年 | 13353篇 |
2005年 | 12658篇 |
2004年 | 12626篇 |
2003年 | 12253篇 |
2002年 | 12153篇 |
2001年 | 24769篇 |
2000年 | 24821篇 |
1999年 | 19093篇 |
1998年 | 5680篇 |
1997年 | 5855篇 |
1996年 | 5414篇 |
1995年 | 4931篇 |
1994年 | 4870篇 |
1993年 | 4884篇 |
1992年 | 15031篇 |
1991年 | 15105篇 |
1990年 | 14630篇 |
1989年 | 14421篇 |
1988年 | 13427篇 |
1987年 | 12559篇 |
1986年 | 11413篇 |
1985年 | 11451篇 |
1984年 | 9060篇 |
1983年 | 7730篇 |
1982年 | 5383篇 |
1981年 | 4713篇 |
1980年 | 4564篇 |
1979年 | 8299篇 |
1978年 | 6407篇 |
1977年 | 5834篇 |
1976年 | 5408篇 |
1975年 | 6309篇 |
1974年 | 6763篇 |
1973年 | 6634篇 |
1972年 | 5928篇 |
1971年 | 5538篇 |
1970年 | 4826篇 |
1969年 | 4686篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
152.
153.
154.
155.
156.
M. T. van Wijk§¶ M. Williams L. Gough† S. E. Hobbie‡ G. R. Shaver§ 《Journal of Ecology》2003,91(4):664-676
157.
The ultrastructure of the interstitial cells of Cajal (ICC) in the oesophagus of the monkey resembled that described in the oesophagus of other mammalian species but differed in their paucity and almost lack of smooth endoplasmic reticulum, caveolae and filaments. The plasmalemma of the ICC was in close contact (20- to 30-nm gaps) with that of smooth muscle cells. This may occasionally take the form of a desmosome, but gap junctions have not been observed. Vesiculated axon profiles, containing large granular or agranular vesicles were in close contact (20- to 30-nm gaps) with the plasmalemma of ICC. In a few vesiculated profiles a presynaptic density could be recognized. The intercalation of the ICC between the vesiculated axon profiles and the smooth muscle cells suggest a role in oesophageal motility. Between 3 and 21 days following bilateral vagotomy some ICC showed regressive changes such as increased electron density and shrinkage of the cytoplasm, crowding of the organelles and dissolution of the nuclear chromatin material. Axon profiles in the vicinity of the affected ICC contained glycogen granules suggesting injury. In late stages, the number of ICC and smooth muscle contacts was reduced. The results suggest that the vagus nerves exert a trophic influence on the ICC and that the intercellular relationships between ICC and smooth muscle cells possess a degree of plasticity. It is tentatively suggested that these vagal effects may be mediated via the oesophageal myenteric ganglia. 相似文献
158.
The fully enclosed Taiaro lagoon is hypersaline (42.5 psu) and non-tidal; constant salinity and water level result from strong
evaporation balanced by low percolation through the lagoon floor. Seawater can flow over the atoll rim during exceptionally
high seas and may then replenish lagoonal communities with propagules of oceanic origin. The distinctive water chemistry of
the lagoon suggests a possible way of identifying these immigrants. We established this potential by analysing stable isotopes
of carbon and oxygen in the recent growth layers of otoliths of two adult reef fishes, Chaetodon ulietensis and Acanthurus triostegus, collected from both sides of the atoll rim. Fish from the two locations were discriminated by their isotopic signatures,
suggesting that analysis of the microchemical signatures deposited during the larval development could be used in future work
to determine which individuals and species complete their life-cycles in this unusual lagoon.
Accepted: 28 August 1997 相似文献
159.
Application of 1% methol, which, along with cold, activates specific thermosensitive ionic channels, changes the number of functioning cold receptors on the skin of the forearm similarly to the cold exposure test; however, it does not affect the number of heat receptors and does not significantly change the threshold of cold sensation. Group variants of responses to menthol that indicate individual differences in the sensitivity of skin receptors to the effects of methol and cold have been found. The results obtained give grounds to suggest that, from the variant of response to menthol (a decrease, increase, or absence of changes in the number of functioning cold receptors 5 min after menthol application), it is possible to predict specific features of response to cold. 相似文献
160.
Maria V. Sergeeva Vadim V. Mozhaev Joseph O. Rich Yuri L. Khmelnitsky 《Biotechnology letters》2000,22(17):1419-1422
A novel biocatalytic reaction of transamidation of non-activated amides with amines is reported. Among 45 different lipolytic and proteolytic enzymes tested, only the lipase from Candida antarcticawas able to catalyze this reaction. The reaction proceeded with up to ca. 80% conversion in anhydrous methyl tert-butyl ether and worked with both N-substituted and unsubstituted amides. The biocatalytic transamidation is an equilibrium process and, therefore, higher conversions to the desired amide were achieved by using increased concentrations of the amine nucleophile. 相似文献