全文获取类型
收费全文 | 1510374篇 |
免费 | 132871篇 |
国内免费 | 1946篇 |
出版年
2021年 | 18112篇 |
2019年 | 16266篇 |
2018年 | 19385篇 |
2017年 | 18167篇 |
2016年 | 29222篇 |
2015年 | 43132篇 |
2014年 | 51214篇 |
2013年 | 77519篇 |
2012年 | 43297篇 |
2011年 | 34129篇 |
2010年 | 46878篇 |
2009年 | 47337篇 |
2008年 | 31305篇 |
2007年 | 29893篇 |
2006年 | 33588篇 |
2005年 | 34740篇 |
2004年 | 33745篇 |
2003年 | 30951篇 |
2002年 | 28898篇 |
2001年 | 40179篇 |
2000年 | 37750篇 |
1999年 | 36314篇 |
1998年 | 26250篇 |
1997年 | 26033篇 |
1996年 | 25407篇 |
1995年 | 23571篇 |
1994年 | 23291篇 |
1993年 | 22401篇 |
1992年 | 31481篇 |
1991年 | 30255篇 |
1990年 | 28990篇 |
1989年 | 29578篇 |
1988年 | 27243篇 |
1987年 | 25747篇 |
1986年 | 24557篇 |
1985年 | 26370篇 |
1984年 | 25229篇 |
1983年 | 22181篇 |
1982年 | 21502篇 |
1981年 | 20540篇 |
1980年 | 19317篇 |
1979年 | 21191篇 |
1978年 | 19627篇 |
1977年 | 18563篇 |
1976年 | 17716篇 |
1975年 | 17969篇 |
1974年 | 18725篇 |
1973年 | 18991篇 |
1972年 | 16264篇 |
1971年 | 15005篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
331.
ABSTRACT. An actograph is described for recording the behaviour of small insects, by using a standing-wave radar system in an enclosed metal cabinet. Experiments show that the system produces an output frequency dependent only on the speed of movement of the subject. By filtering the signal electrically into components below and above 5 Hz, walking and flying of adult Musca domestica could be separately recorded. Each filter is followed by a level-comparator with hysteresis. Activity causing signal to cross the hysteresis-band is recorded as an event on a digital counter, and also integrated or summed to be displayed as a stepped-integral or bar-chart of total distance covered by the subject in each counting period. The energy-density of the radar can be kept very low, so that possible influence on the subject is minimal. The detector is remote from the box containing the subject, giving great flexibility in container design, so that the apparatus is ideally suited to the study of environmental factors. 相似文献
332.
Victoria V. Hargreaves Scarlet S. Shell Dan J. Mazur Martin T. Hess Richard D. Kolodner 《The Journal of biological chemistry》2010,285(12):9301-9310
Indirect evidence has suggested that the Msh2-Msh6 mispair-binding complex undergoes conformational changes upon binding of ATP and mispairs, resulting in the formation of Msh2-Msh6 sliding clamps and licensing the formation of Msh2-Msh6-Mlh1-Pms1 ternary complexes. Here, we have studied eight mutant Msh2-Msh6 complexes with defective responses to nucleotide binding and/or mispair binding and used them to study the conformational changes required for sliding clamp formation and ternary complex assembly. ATP binding to the Msh6 nucleotide-binding site results in a conformational change that allows binding of ATP to the Msh2 nucleotide-binding site, although ATP binding to the two nucleotide-binding sites appears to be uncoupled in some mutant complexes. The formation of Msh2-Msh6-Mlh1-Pms1 ternary complexes requires ATP binding to only the Msh6 nucleotide-binding site, whereas the formation of Msh2-Msh6 sliding clamps requires ATP binding to both the Msh2 and Msh6 nucleotide-binding sites. In addition, the properties of the different mutant complexes suggest that distinct conformational states mediated by communication between the Msh2 and Msh6 nucleotide-binding sites are required for the formation of ternary complexes and sliding clamps. 相似文献
333.
M V Sauer 《The Western journal of medicine》1994,161(2):164-165
334.
Forty-two white-rot fungi isolated in South America were incubated with long fibre sugar cane bagasse (LFB). The residual composition of LFB was determined after white-rot decay at 30 and 60 days. The ratio of residual lignin to residual lignin to residual cellulose (RL/RC) of untreated material (LFB) was 0.48. After white-rot-decay, the residual material with lower RL/RC ratios indicated that mainly lignin was degraded. In only 30 days, Phlebia sp. MVHC 5535, Athelia sp. MVHC 5509 and Spongipellis pachyodon MVHC 5019 caused a decrease in the RL/RC ratio to 0.36, 0.37 and 0.38, respectively, while it took 60 days for Ganoderma applanatum MVHC 5347, Hyphodontia sp. MVHC 5544, Panus tigrinus MVHC 5400, Stereum sp. MVHC 5113, Phellinus punctatus MVHC 5346 and MVHC 6388 to reach a ratio lower than 0.40. No correlation was found between the amount of some ligninolytic enzymes secreted and the residual composition of bagasse after white-rot fungi fermentation. Most of the fungal strains caused an increase in the relative amount of residual cellulose, indicating that hemicellulose was the preferred energy source. 相似文献
335.
336.
The distribution of grooming and touching behaviours was recorded in a group of captive ring-tailed lemurs. Grooming was found
to be performed chiefly by older, higher ranking animals; touching (i.e., “reach out and touch” behaviour) was directed primarily
by younger, low ranking animals to older, high ranking individuals. It is suggested that such touching is a submissive gesture
in this species. 相似文献
337.
L S Katkova 《Biulleten' eksperimental'no? biologii i meditsiny》1985,99(4):413-415
Extensibility, contractile function and resistance to excess calcium of the right atrium myocardium were studied in normotensive Wistar-Kyoto and August rats and in spontaneously hypertensive rats (SHR). It was shown that long-term stress results in a decrease in the measured parameters in normotensive animals. SHR do not show any stress-induced disturbances. It was discovered that in intact SHR rats, the myocardium has a greater resistance to excess calcium, indirect evidence for higher efficiency of the Ca-pump of the sarcoplasmic reticulum in cardiomyocytes of SHR animals, which is apparently a constituent part of the mechanism of such animals' heart increased resistance to stress-induced damage. 相似文献
338.
THE TIMING OF DIVISION IN CHLAMYDOMONAS 总被引:3,自引:2,他引:1
339.
A L Nevmiatullin O N Vorob'eva A N Maianski? 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1985,(7):67-71
The neutrophil-stimulating properties of 38 S. aureus strains and 32 S. epidermidis strains were studied in the reaction of luminol-mediated chemiluminescence. All S. aureus strains and 29 S. epidermidis strains were found to possess neutrophil-stimulating activity, the mean activity index for S. aureus being significantly higher. The stimulating activity of the strains varied within a wide range (the variation coefficient was 120.0 +/- 21.9%) and did not correlate with the content of protein A in bacterial cells and the degree of their hydrophoby. The opsonization of staphylococci with normal human serum enhanced the neutrophil reaction 1.5- to 100-fold and simultaneously leveled out the chemiluminescence indices in experiments with different strains (the variation coefficient was 8.0 +/- 1.5%). The nature of the neutrophil-stimulating effect of staphylococci and its relationship to the exploratory reactions of phagocytes are discussed. 相似文献
340.
R. J. Rowbury 《Letters in applied microbiology》1986,2(1):17-19
Introduction of the ColV,I-K94 plasmid into any of four strains of Escherichia coli gave derivatives which grew less well than the parent at alkaline pH. The alkali sensitivity of the 1829 derivative resulted from the presence of the plasmid rather than from its introduction into a less alkali tolerant variant. Of two other ColV plasmids tested, one (ColV-K30) conferred substantial alkali sensitivity whereas the other (ColV-41) had little effect. Of several other plasmids examined, R124-F2 (which confers derepressed transfer properties) resembled ColV,I-K94 in its effect on alkali sensitivity and ColV-K98 produced a marked effect. The other plasmids (F lac , R124 itself, R1 and R483ColIa) had only a small effect. For ColV plasmids, it appears to be the presence of transfer and colicin components together which leads to the reduced tolerance to alkaline pHs. 相似文献