全文获取类型
收费全文 | 449616篇 |
免费 | 28290篇 |
国内免费 | 979篇 |
专业分类
478885篇 |
出版年
2018年 | 15473篇 |
2017年 | 14203篇 |
2016年 | 12225篇 |
2015年 | 5522篇 |
2014年 | 6870篇 |
2013年 | 9745篇 |
2012年 | 15091篇 |
2011年 | 24229篇 |
2010年 | 19783篇 |
2009年 | 15130篇 |
2008年 | 19978篇 |
2007年 | 21950篇 |
2006年 | 10823篇 |
2005年 | 10340篇 |
2004年 | 11014篇 |
2003年 | 10709篇 |
2002年 | 10448篇 |
2001年 | 16066篇 |
2000年 | 15856篇 |
1999年 | 12042篇 |
1998年 | 3824篇 |
1997年 | 3795篇 |
1996年 | 3434篇 |
1995年 | 3164篇 |
1992年 | 9551篇 |
1991年 | 9763篇 |
1990年 | 9494篇 |
1989年 | 9498篇 |
1988年 | 8770篇 |
1987年 | 8256篇 |
1986年 | 7530篇 |
1985年 | 7852篇 |
1984年 | 6340篇 |
1983年 | 5334篇 |
1982年 | 3616篇 |
1981年 | 3180篇 |
1980年 | 3133篇 |
1979年 | 5962篇 |
1978年 | 4646篇 |
1977年 | 4230篇 |
1976年 | 3993篇 |
1975年 | 4808篇 |
1974年 | 5313篇 |
1973年 | 5269篇 |
1972年 | 5026篇 |
1971年 | 4745篇 |
1970年 | 3901篇 |
1969年 | 3795篇 |
1968年 | 3554篇 |
1967年 | 3201篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
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
112.
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
113.
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
114.
Introduction of valinomycin into erythrocyte incubation medium increased the cell stability to water-induced hemolysis. In these conditions the erythrocytes of spontaneously hypertensive and normotensive (control) rats release 63.2 +/- 1.5% and 80.9 +/- 1.6%, respectively, of the total hemoglobin content. Valinomycin effect is completely abolished with K+ substitution for Na+ and is independent of extracellular Ca2+ concentration. Valinomycin had no effect on human erythrocyte osmotic stability. It has been shown that valinomycin-induced kinetics of Na+ and K+ redistribution was different in human and rat erythrocytes. The distinctions are thought to be related to specific anion transport mediated by the third band protein--the main component of membrane cytoskeleton. 相似文献
115.
116.
In the experiments on the anesthesized cats sodium hydroxybutyrate and piracetam, in contrast to glyo-6, have been shown to slow down the growth rate of creatine phosphokinase activity in the blood of the coronary sinus during 60-min occlusion of the coronary artery. At the same time, in the experiments on rats with 3-day myocardial infarction GABA derivatives like glyo-6 failed to influence the final size of cardiac necrosis. It may be concluded that anti-ischemic action of some drugs may be expressed only in the reduction of the rate of ischemic lesion development in the heart, but not in the limitation of the infarction size. 相似文献
117.
Pedro J. I. Salas Dora E. Vega-Salas Enrique Rodriguez-Boulan 《The Journal of membrane biology》1987,98(3):223-236
Summary Madin-Darby canine kidney (MDCK) cells kept in suspension culture for 12–15 hr displayed high-affinity binding sites for125I-lathyritic (soluble) collagen (120,000/cell,K
D
=30nm) and preferred collagens types I and IV over laminin or fibronectin as substrates during the first hour of attachment. On the other hand, after 4 hr, attachment to all four substrates was equally efficient. Upon challenge with a collagen substrate, the high-affinity sites were rapidly recruited on it (T1/2=6 min). Their occupancy by soluble collagen triggered the exocytosis of a second large population of low-affinity collagen binding sites that included laminin and seems to be involved in a second cell-attachment mechanism. These results are compatible with a twostep model of MDCK cell attachment to the substrate: first, via high-affinity collagen binding sites, and second, via laminin of cellular origin. 相似文献
118.
119.
120.
Y Aoyagi I Tasaki J Okumura T Muramatsu 《Comparative biochemistry and physiology. A, Comparative physiology》1988,89(3):433-436
1. Effect of low ambient temperature on protein turnover in the liver and whole body was investigated in chicks together with the contribution of protein synthesis to the total heat production. 2. Both protein synthesis and degradation in the whole body were increased, the latter to a larger extent, at low ambient temperature (LT, 22 degrees C) compared with adequate temperature (AT, 30 degrees C). Liver protein synthesis was not significantly altered by the temperature treatment. 3. The total heat production of LT group was as high as 160% of the AT group. 4. The increased heat production due to enhanced whole-body protein synthesis accounted for only 1.4% of the heat increment in thermogenesis at low ambient temperature, suggesting that protein synthesis would contribute little, if any, to cold-induced thermogenesis in chicks. 相似文献