全文获取类型
收费全文 | 679983篇 |
免费 | 74030篇 |
国内免费 | 304篇 |
出版年
2016年 | 7644篇 |
2015年 | 10263篇 |
2014年 | 12145篇 |
2013年 | 17990篇 |
2012年 | 19617篇 |
2011年 | 20229篇 |
2010年 | 13728篇 |
2009年 | 12464篇 |
2008年 | 17922篇 |
2007年 | 18898篇 |
2006年 | 17728篇 |
2005年 | 17017篇 |
2004年 | 17135篇 |
2003年 | 16687篇 |
2002年 | 16365篇 |
2001年 | 28369篇 |
2000年 | 28389篇 |
1999年 | 22756篇 |
1998年 | 8022篇 |
1997年 | 8331篇 |
1996年 | 7885篇 |
1995年 | 7851篇 |
1994年 | 7697篇 |
1993年 | 7594篇 |
1992年 | 19987篇 |
1991年 | 19428篇 |
1990年 | 19379篇 |
1989年 | 18924篇 |
1988年 | 17807篇 |
1987年 | 16856篇 |
1986年 | 15607篇 |
1985年 | 16093篇 |
1984年 | 13300篇 |
1983年 | 11606篇 |
1982年 | 9015篇 |
1981年 | 8044篇 |
1980年 | 7612篇 |
1979年 | 13071篇 |
1978年 | 10058篇 |
1977年 | 9451篇 |
1976年 | 8915篇 |
1975年 | 9683篇 |
1974年 | 10584篇 |
1973年 | 10530篇 |
1972年 | 9717篇 |
1971年 | 8976篇 |
1970年 | 7661篇 |
1969年 | 7607篇 |
1968年 | 6949篇 |
1967年 | 6005篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
62.
63.
T. Friedel F. G. Barth 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,180(3):223-233
Spiders can use air particle movements to localize moving prey. We studied the responses of 32 wind-sensitive interneurones
in the hunting spider Cupiennius salei to prey stimuli.
Stimulation with a tethered flying fly or with artificial air pulses activated plurisegmental interneurones that responded
to changes in air movement velocity and were thus well suited to represent the highly fluctuating air stream typical of prey
stimuli. In most interneurones (n = 18) the responses to the stimulation of different legs were not significantly different from each other.
Different interneurones had different response characteristics and their latencies largely overlapped suggesting that there
is parallel processing of the signals by populations of interneurones with different response characteristics.
In two interneurones the number of spikes and the spiking pattern elicited by stimulation of each of the eight legs markedly
differed depending on the leg stimulated. These neurones may play an important role in directional information processing.
Stimulation of the adjacent legs from front to back or from back to front revealed two interneurones sensitive to the direction
of successive stimulation of the legs. These neurones may be able to detect the motion of an air movement source in a preferred
direction and thus act as nearfield motion detectors to localize a moving prey item.
Accepted: 28 September 1996 相似文献
64.
Liu Yewei; Kranias Evangelia G.; Schneider Martin F. 《American journal of physiology. Cell physiology》1997,273(6):C1915
The effects ofphosphorylation status on Ca2+release and Ca2+ removal werestudied in fast-twitch flexor digitorum brevis and slow-twitch soleusskeletal muscle fibers enzymatically isolated from wild-type andphospholamban knockout (PLBko) mice. In all fibers the adenosine3',5'-cyclic monophosphate-dependent protein kinase (PKA)inhibitor H-89 decreased the peak amplitude of the intracellularCa2+ concentration([Ca2+]) transient fora single action potential, and the PKA activator dibutyryl adenosine3',5'-cyclic monophosphate (DBcAMP) reversed this effect,indicating modulation of Ca2+release by phosphorylation status in all fibers. H-89 decreased thedecay rate constant of the[Ca2+] transient andDBcAMP reversed this effect only in phospholamban-expressing fibers(wild-type soleus), indicating modulation ofCa2+ removal only in the presenceof phospholamban. A high basal level of PKA phosphorylation in soleusfibers maintained under our control conditions was indicated bythe lack of effect of direct application of DBcAMP onCa2+ release orCa2+ removal in wild-type or PLBkosoleus fibers and was confirmed by analysis of phospholamban fromwild-type soleus fibers. 相似文献
65.
J.-Y. Roh H.-W. Park Y.-H. Je D.-W. Lee B.-R. Jin H.-W. Oh S. S. Gill & S.-K. Kang 《Letters in applied microbiology》1997,24(6):451-454
Bacillus thuringiensis NTB-1 isolated from soil samples in Korea produces ovoidal parasporal inclusions with proteins of approximately 24–40 kDa in size. Although serological study indicated that the isolate has a flagella (H) antigen identical with subsp. israelensis , it seemed to be non-insecticidal against Lepidoptera and Coleoptera as well as Diptera. To investigate the activity of non-insecticidal B. thuringiensis transformed with insecticidal crystal protein genes, cryIVD and cytA genes of B. thuringiensis subsp. morrisoni PG-14, highly toxic to mosquito larvae, were introduced into the isolate NTB-1. The expression of mosquitocidal crystal protein genes in NTB-1 was characterized by SDS–PAGE analysis and electron microscopy. The results showed that crystalline inclusions of host, CryIVD and CytA were stably expressed in the transformant. However, the mosquitocidal activity of transformant was similar to that of B. thuringiensis subsp. kurstaki Cry− B harbouring cryIVD and cytA genes, demonstrating that a synergistic effect by an interaction of both introduced insecticidal and resident non-insecticidal crystal proteins was not observed. 相似文献
66.
A. Ugolini B. Tiribilli C. Castellini 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,182(1):43-50
Experiments on compass orientation under artificial light were conducted with adult individuals of Talitrus saltator. The aim was to reproduce in the laboratory an orientation based on the sun compass corresponding to that recorded in conditions
of the true sun and sky. This was obtained by the creation within an opaque Plexiglas dome of a scenario that permitted variation
of the brightness of the artificial sky and sun. The results show that it is possible to obtain sun compass orientation corresponding
to the natural situation even in an artificial environment. It can be concluded that sandhoppers identify an artificial light
source as the sun if the artificial sky is also illuminated and if the intensities of the artificial sun and sky exceed certain
threshold values (1.13 and 10 μW cm−2, respectively). The results of other experiments under the natural blue sky with an artificial sun and with the real sun
attenuated are discussed.
Accepted: 23 May 1997 相似文献
67.
Cassava mesocarp carbohydrate and its modified form were used as fillers in low density polyethylene to give plastic films that were biodegradable. It was found that the tensile strength of the films decreased with an increase in the amount of the filler incorporated. The water absorption results of the films showed that modification of the cassava mesocarp carbohydrate made it hydrophobic and therefore more compatible with the polyethylene. 相似文献
68.
Isolation and characterization of a glycosylated form of human insulin-like growth factor I produced in Saccharomyces cerevisiae 总被引:3,自引:0,他引:3
P Gellerfors K Axelsson A Helander S Johansson L Kenne S Lindqvist B Pavlu A Skottner L Fryklund 《The Journal of biological chemistry》1989,264(19):11444-11449
Expression and secretion of human insulin-like growth factor-I (IGF-I) in Saccharomyces cerevisiae was achieved by linking an actin (ACT) promoter to an MF alpha 1 prepro leader peptide/IGF-I gene fusion. Purified human IGF-I from yeast culture media was found to contain, in addition to the native form, also a glycosylated variant. Structural studies showed that both IGF-I forms were processed identically, resulting in 70-amino-acid long polypeptides, with intact N-terminal and C-terminal residues of glycine and alanine, respectively. The glycosylation site was determined to threonine-29 (Thr29), by 1H NMR spectroscopy and protein sequence analysis of an isolated tryptic peptide(22-36). No other glycosylation sites were found. Only mannose was detected in the sugar analysis, with an estimated content of 4.5% w/w corresponding to 2 mannose residues per molecule of IGF-I. The carbohydrate structure, determined by 1H and 13C NMR spectroscopy, was found to be alpha-D-Manp(1----2)alpha-D-Manp(1----3)Thr corresponding to an O-linked glycoprotein structure. No other post-translational modifications could be identified in the glycosylated IGF-I form. Furthermore, this form was highly active, comparable to native IGF-I, exhibiting a specific activity of 20,500 units/mg, as determined by a radio-receptor assay. 相似文献
69.
70.