全文获取类型
收费全文 | 618347篇 |
免费 | 58276篇 |
国内免费 | 452篇 |
出版年
2016年 | 8129篇 |
2015年 | 12537篇 |
2014年 | 13825篇 |
2013年 | 17435篇 |
2012年 | 18301篇 |
2011年 | 16428篇 |
2010年 | 11771篇 |
2009年 | 11034篇 |
2008年 | 13698篇 |
2007年 | 14387篇 |
2006年 | 13671篇 |
2005年 | 18825篇 |
2004年 | 17666篇 |
2003年 | 15540篇 |
2002年 | 13265篇 |
2001年 | 25533篇 |
2000年 | 25784篇 |
1999年 | 20832篇 |
1998年 | 6781篇 |
1997年 | 6950篇 |
1996年 | 6347篇 |
1995年 | 6118篇 |
1994年 | 5963篇 |
1993年 | 6004篇 |
1992年 | 17554篇 |
1991年 | 17421篇 |
1990年 | 16989篇 |
1989年 | 16592篇 |
1988年 | 15625篇 |
1987年 | 14874篇 |
1986年 | 13854篇 |
1985年 | 14118篇 |
1984年 | 11480篇 |
1983年 | 9783篇 |
1982年 | 7298篇 |
1981年 | 6706篇 |
1980年 | 6248篇 |
1979年 | 11104篇 |
1978年 | 8914篇 |
1977年 | 8040篇 |
1976年 | 7610篇 |
1975年 | 8802篇 |
1974年 | 9832篇 |
1973年 | 9766篇 |
1972年 | 9110篇 |
1971年 | 8252篇 |
1970年 | 7198篇 |
1969年 | 7108篇 |
1968年 | 6505篇 |
1967年 | 5699篇 |
排序方式: 共有10000条查询结果,搜索用时 562 毫秒
991.
992.
M A Danilovski? A V Tokarev B I Klement'ev G A Vartanian 《Biulleten' eksperimental'no? biologii i meditsiny》1985,100(8):132-135
The peptide nature of the posture asymmetry factor (PAF) produced in the brain after unilateral removal of the motor region of the neocortex was established. The inactivation of PAF activity in the brain toward the end of the third week after the removal is due to PAF inactivation by the endogenous factor absent from the intact brain. The molecular weight of the inactivation factor exceeds 5.0 kD that makes it possible to separate it from the PAF by gel filtration on Sephadex G-25. The correlation was marked between the increasing activity of the PAF inactivation factor and the recovery of the initial symmetric functioning of the spinal centers during three weeks after unilateral damage to the CNS. 相似文献
993.
Thirteen model alpha-ketocarboxylic acids and alpha-dicarbonyl compounds have been observed to be reduced by titanium(III) chloride. The products of these reactions were shown by melting (boiling) points, mixed melting points, derivatives, refractive indices, infrared, and NMR comparisons with authentic compounds or literature information to be the corresponding alpha-hydroxycarboxylic acids or alpha-hydroxyketones. 相似文献
994.
U H Lewinski G M Mavligit P M Epstein E M Hersh R A Ortez W J Thompson 《Biomedicine / [publiée pour l'A.A.I.C.I.G.]》1980,33(7):217-219
Endogenous cyclic adenosine and guanosine monophosphate (cAMP, cGMP) levels were studied in human peripheral blood lymphocytes during mixed leukocyte reactions (MLR). cAMP level was consistently elevated in one-way MLR, with good correlation to 3H-thymidine uptake in these reactions. In contrast, cGMP level was practically unchanged. Irradiation of reacting cell populations resulted in inhibition of cyclic nucleotide phosphodiesterase (PDE) activity. These results suggest that metabolic alterations in cAMP may be associated with immune reactions of cellular recognition. 相似文献
995.
996.
A comparison of the respiratory chain in particles from Paracoccus denitrificans and bovine heart mitochondria by EPR spectroscopy 总被引:6,自引:0,他引:6
S P Albracht H W van Verseveld W R Hagen M L Kalkman 《Biochimica et biophysica acta》1980,593(2):173-186
A study is presented on the EPR characteristics of the paramagnetic groups in the respiratory chain present in membrane particles of Paracoccus denitrificans, the respiratory system of which is very similar to that in submitochondrial particles from beef heart. All paramagnetic prosthetic groups of the mitochondrial system are also found in the bacterial plasma membrane. Their properties suggest that the respiratory groups are embedded in very similar protein environments in the two systems. 相似文献
997.
I. V. Korovnikov 《Paleontological Journal》2014,48(5):465-470
A collection of trilobites of the genus Plicatolina Shaw, 1951 from the upper Ogon’or Formation, Cambrian Section, Chekurovka Anticline (northeastern Siberian Platform, Kharaulakh Mountains), is studied. It is shown that all specimens of this collection belong to the same species, Plicatolina lucida Lazarenko, 1966, but represent different age stages. It is also shown that species of the genus Plicatolina (P. quadrata Pokrovskaya, 1966 and P. yakutica Pokrovskaya, 1966) described from the Upper Cambrian of the Siberian Platform are probably synonyms of P. lucida. 相似文献
998.
999.
A serum- and glucocorticoid-regulated 4-kilobase mRNA encodes a cyclooxygenase-related protein. 总被引:21,自引:0,他引:21
M K O'Banion H B Sadowski V Winn D A Young 《The Journal of biological chemistry》1991,266(34):23261-23267
1000.
Matthias Schlichting Pamela Menegazzi Charlotte Helfrich-F?rster 《Proceedings. Biological sciences / The Royal Society》2015,282(1815)
Circadian clocks are thought to be essential for timing the daily activity of animals, and consequently increase fitness. This view was recently challenged for clock-less fruit flies and mice that exhibited astonishingly normal activity rhythms under outdoor conditions. Compensatory mechanisms appear to enable even clock mutants to live a normal life in nature. Here, we show that gradual daily increases/decreases of light in the laboratory suffice to provoke normally timed sharp morning (M) and evening (E) activity peaks in clock-less flies. We also show that the compound eyes, but not Cryptochrome (CRY), mediate the precise timing of M and E peaks under natural-like conditions, as CRY-less flies do and eyeless flies do not show these sharp peaks independently of a functional clock. Nevertheless, the circadian clock appears critical for anticipating dusk, as well as for inhibiting sharp activity peaks during midnight. Clock-less flies only increase E activity after dusk and not before the beginning of dusk, and respond strongly to twilight exposure in the middle of the night. Furthermore, the circadian clock responds to natural-like light cycles, by slightly broadening Timeless (TIM) abundance in the clock neurons, and this effect is mediated by CRY. 相似文献