全文获取类型
收费全文 | 93160篇 |
免费 | 269篇 |
国内免费 | 812篇 |
专业分类
94241篇 |
出版年
2022年 | 2篇 |
2021年 | 2篇 |
2018年 | 11837篇 |
2017年 | 10670篇 |
2016年 | 7447篇 |
2015年 | 585篇 |
2014年 | 275篇 |
2013年 | 299篇 |
2012年 | 4204篇 |
2011年 | 12804篇 |
2010年 | 11996篇 |
2009年 | 8221篇 |
2008年 | 9774篇 |
2007年 | 11356篇 |
2006年 | 250篇 |
2005年 | 500篇 |
2004年 | 960篇 |
2003年 | 1014篇 |
2002年 | 777篇 |
2001年 | 259篇 |
2000年 | 164篇 |
1999年 | 28篇 |
1998年 | 10篇 |
1997年 | 22篇 |
1996年 | 13篇 |
1995年 | 1篇 |
1994年 | 7篇 |
1993年 | 31篇 |
1992年 | 21篇 |
1991年 | 37篇 |
1990年 | 10篇 |
1989年 | 8篇 |
1988年 | 18篇 |
1987年 | 13篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 7篇 |
1983年 | 17篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1975年 | 5篇 |
1972年 | 246篇 |
1971年 | 274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 8 毫秒
231.
RAFIQ WAZIRI 《Nature: New biology》1971,231(26):286-288
IN the abdominal ganglion of Aplysia californica, there are two types of inhibitory post-synaptic potentials (IPSPs). There are unitary short-lasting IPSPs which occur as the result of conductance changes during the movement of Cl? across the synaptic membrane—IPSPs which have definite equilibrium potentials and characteristics similar to those described for other neuronal systems1—and there are IPSPs which last much longer and may be much more effective in regulating the activity of the neurone, which Taue has called “inhibitions of long duration” (ILD)2,3. In Aplysia some of these long lasting inhibitory potentials are produced by conductance changes and have definite equilibrium potentials4. Long lasting inhibitions or “slow inhibitory potentials” as well as short lasting IPSPs have also been described in vertebrate sympathetic ganglia5, but in these, long lasting IPSPs are not accompanied by changes in membrane conductance. Some of the long lasting inhibitions (LLI) have been explained on the basis of an ATP-dependent electrogenic Na+ pump6. Presumably this ATP-dependent pump hyperpolarizes the membrane by causing an outflux of Na+ from the cell which is more rapid than the corresponding “active” influx of K+7. There is evidence now for the existence of such an electrogenic Na+ pump in some of the identified neurones of the abdominal ganglion of Aplysia californica8. Pinsker and Kandel9 have found some evidence that in these neurones the electrogenic Na+ pump is activated by the synaptic action of an identified cholinergic inhibitory interneurone, L10, producing the long lasting “late IPSP”. But Kehoe and Ascher10, although agreeing that the same interneurone (L10) produces both types of IPSPs in the follower neurones, have shown that the “late IPSP”9 is due to an increase in the K+ conductance and that it has an equilibrium potential around ?90 mV. I have found that in this abdominal ganglion there is another specific interneurone which is electrotonically coupled to L10 and which, when activated, produces a long lasting inhibition (LLI) in a number of follower neurones. Thus L10 produces the LLI or “late IPSP” in some follower neurones not directly, but through the mediation of another interneurone. 相似文献
232.
Kimball and Wilson1 reported that the arabinose analogue of cytidine (ara-C) inhibited DNA polymerase in a crude extract prepared from Ehrlich ascites cells. Furth and Cohen2 observed cytosine arabinoside triphosphate (ara-CTP) inhibited DNA polymerase in extracts from either calf thymus or bovine lymphosarcoma tissue, although these investigators3 had already found no effect of ara-CTP on DNA polymerase from Escherichia coli. The inhibition in both of these cases could be substantially reversed by dCTP; but incorporation of the arabinose nucleotide (ara-CMP) into DNA could not be unequivocally demonstrated. Graham and Whitmore4 reported the incorporation of ara-C into DNA in vivo and the inhibition of a DNA polymerase from L cells by ara-CTP. They found that ara-CMP was initially incorporated into small DNA strands but subsequently appeared in long strands. Momparler5 has presented evidence that, in vitro, ara-C incorporation was limited to the 3′-hydroxyl end of DNA chains. Such incorporation might be expected to block further chain elongation but this expectation was not supported by the evidence presented by Graham and Whitmore. 相似文献
233.
ALINA TAYLOR 《Nature: New biology》1971,234(48):144-145
JACOB and Fuerst1,2 demonstrated the presence of a bacteriolytic enzyme (λ-endolysin) in the induced cultures of lysogenic Escherichia coli K12 (λ). The enzyme was later identified as the product of gene R; of phage λ3 which is involved in bacterial lysis at the end of a latent period. The enzyme is apt to form spheroplast-like structures in E. coli2 and one would therefore expect its substrate to be murein. 相似文献
234.
WHEN chromosomes pair at meiosis the bivalents so formed do not normally interlock. Heat-treatments can, however, induce bivalent interlocking in the locust Locusta migratoria. Only the longest bivalents interlock and usually only two are found per cell; two “rod” bivalents, with single chiasmata, two “ring” bivalents, each with two or three chiasmata, or one “rod” and one “ring” bivalent (Fig. 1a, b and c). The nature of this interlocking and the metaphase orientational and congressional properties of interlocked bivalents are analysed in detail elsewhere1. 相似文献
235.
236.
237.
M-Enterococcus medium, used for the detection and enumeration of fecal streptococci from different types of water, demonstrated a very low specificity. We propose the transfer of membrane filters to bile-esculin medium as a confirmation technique. It has proved to be more reliable, faster to perform, and more effective than the random selection of colonies, which is recommended for confirmation in Standard Methods for the Examination of Water and Wastewater (A.E. Greenberg, L.S. Clesceri, and A.D. Eaton, ed., 1992). 相似文献
238.
The effect of algae on the production of musty-smelling compounds by actinomycetes was studied. Streptomyces spp., causing intensive musty odor, were isolated from hypertrophic Lake Kasumigaura and cultured in association with algae from the same lake. Isolate E and I effectively utilized the cyanobacteria, Microcystis aeruginosa and Anabaena spiroides, and the diatom, Synedra acus, as a carbon source and produced a musty-smelling 2-methylisoborneol in the shaken sediment cultures. High populations of algae and actinomycetes, and aerobic condition in the sediment seem responsible for the occurrence of musty odor in Lake Kasumigaura. 相似文献
239.
240.
Maxim K. Elias 《Pal?ontologische Zeitschrift》1962,36(1):29-37
The type specimen ofGonioloboceras goniolobum (Meek), rediscovered by Spath in the British Museum, is the foundation for a more accurate comparative study of this and other species ofGonioloboceras.Gonioloboceras described asG. goniolobum byElias in 1938 is differentiated asGonioloboceras schmidti, new species. Suture sets (new term) for several growth stages inG. goniolobum (Meek),G. welleriSmith,G. schmidtiElias, G.eliasiMiller &Owen, andG. asiaticumLibrovitch are assembled and used for differentiation of the species.The Kazakhstan goniatite faunule containingG. asiaticum is considered of very late Pennsylvanian age. 相似文献