全文获取类型
收费全文 | 1220127篇 |
免费 | 101491篇 |
国内免费 | 4027篇 |
专业分类
1325645篇 |
出版年
2021年 | 19263篇 |
2020年 | 13633篇 |
2019年 | 17377篇 |
2018年 | 18085篇 |
2017年 | 16507篇 |
2016年 | 28697篇 |
2015年 | 43867篇 |
2014年 | 52229篇 |
2013年 | 78626篇 |
2012年 | 34067篇 |
2011年 | 20832篇 |
2010年 | 42848篇 |
2009年 | 44795篇 |
2008年 | 19526篇 |
2007年 | 16549篇 |
2006年 | 22839篇 |
2005年 | 23735篇 |
2004年 | 22848篇 |
2003年 | 20604篇 |
2002年 | 18636篇 |
2001年 | 28585篇 |
2000年 | 25349篇 |
1999年 | 27061篇 |
1998年 | 24781篇 |
1997年 | 24628篇 |
1996年 | 24241篇 |
1995年 | 22320篇 |
1994年 | 22221篇 |
1993年 | 21103篇 |
1992年 | 22835篇 |
1991年 | 21009篇 |
1990年 | 19316篇 |
1989年 | 20469篇 |
1988年 | 18628篇 |
1987年 | 17269篇 |
1986年 | 16461篇 |
1985年 | 18462篇 |
1984年 | 19200篇 |
1983年 | 17096篇 |
1982年 | 18787篇 |
1981年 | 18161篇 |
1980年 | 16913篇 |
1979年 | 14937篇 |
1978年 | 15042篇 |
1977年 | 14613篇 |
1976年 | 13850篇 |
1975年 | 12879篇 |
1974年 | 12920篇 |
1973年 | 13433篇 |
1972年 | 11085篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
201.
Binomial parameters of transmitter secretion were calculated on the basis of analysis of synaptic potentials in the frog sartorius muscle. Negative values of the parameter p were found in some synapses. This happened most often in low Ca2+ concentrations and with low amplitude of miniature end-plate potentials. The results were interpreted in terms of a model assuming spatial heterogeneity of probability of transmitter quantum release at different release points. Simulation of transmitter secretion by computer showed that the appearance of negative values of the parameter p and incorrect estimates of n experimentally are connected with the form of distribution of probability of transmitter quantum release in the synapse and with the amplitude of miniature potentials.S. V. Kurashov Kazan' Medical Institute, Ministry of Health of the RSFSR. Translated from Neirofiziologiya, Vol. 16, No. 2, pp. 182–189, March–April, 1984. 相似文献
202.
M. J. Rice 《Australian Journal of Entomology》1985,24(4):300-300
Insect Pests of Trees and Timber in Tasmania: H. J. Elliott and D. W. deLittle. Forestry Commission, Tasmania, 1985. Pp. X + 90. $7.50. 相似文献
203.
204.
Abstract. 1. We tested a prediction from contemporary foraging theory that animals should decrease their allocation of energy to the searching of individual patches when interpatch travel costs decrease.
2. We used individual Rhagoletis pomonella Walsh (Diptera: Tephritidae) females foraging for oviposition sites (= Crataegus fruit) in a host tree which was surrounded by four other trees at varying distances.
3. We found that flies generally invested less search, measured as time spent searching a tree or number of leaves visited on a tree, when neighbouring trees were nearby than when farther away.
4. Under our test conditions, flies appeared to have difficulty locating neighbouring trees at a distance of more than 1.6 m.
5. Our study calls into question the interpretation of search effort by insects within resource patches in the absence of information on interpatch distances. 相似文献
2. We used individual Rhagoletis pomonella Walsh (Diptera: Tephritidae) females foraging for oviposition sites (= Crataegus fruit) in a host tree which was surrounded by four other trees at varying distances.
3. We found that flies generally invested less search, measured as time spent searching a tree or number of leaves visited on a tree, when neighbouring trees were nearby than when farther away.
4. Under our test conditions, flies appeared to have difficulty locating neighbouring trees at a distance of more than 1.6 m.
5. Our study calls into question the interpretation of search effort by insects within resource patches in the absence of information on interpatch distances. 相似文献
205.
206.
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
207.
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
208.
209.
L-myo-Inositol-1-phosphate synthase has been found to have at least a 5-fold preference for the beta-anomer of its natural substrate D-Glc-6-P. The alpha-anomer appears to be an inhibitor of the reaction and may be converted to product as well. As well as showing an enzymatic preference for the equatorial C-1 hydroxyl of D-Glc-6-P, our results suggest that it is the pyranose form of D-Glc-6-P that binds to the enzyme and that ring-opening is an enzymatic step. We have also found D-2-dGlc-6-P, D-2-F-2-dGlc-6-P, and D-Man-6-P each to be both competitive inhibitors and substrates that are converted to inositol phosphates by the synthase. D-Allose-6-P is a weak inhibitor of the enzyme, but not a substrate. D-Gal-6-P is neither substrate nor inhibitor. Thus the specificity of the synthase with respect to single position epimers of D-Glc-6-P increases in the order C1 less than C2 much less than C3 less than C4. 相似文献
210.
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