全文获取类型
收费全文 | 1254554篇 |
免费 | 98940篇 |
国内免费 | 1361篇 |
专业分类
1354855篇 |
出版年
2021年 | 17698篇 |
2020年 | 12599篇 |
2019年 | 16120篇 |
2018年 | 18281篇 |
2017年 | 17123篇 |
2016年 | 28311篇 |
2015年 | 42146篇 |
2014年 | 50096篇 |
2013年 | 76371篇 |
2012年 | 33617篇 |
2011年 | 22038篇 |
2010年 | 43723篇 |
2009年 | 45051篇 |
2008年 | 21143篇 |
2007年 | 18996篇 |
2006年 | 24350篇 |
2005年 | 25838篇 |
2004年 | 24865篇 |
2003年 | 22462篇 |
2002年 | 20662篇 |
2001年 | 26136篇 |
2000年 | 23267篇 |
1999年 | 25828篇 |
1998年 | 24506篇 |
1997年 | 24105篇 |
1996年 | 23812篇 |
1995年 | 21924篇 |
1994年 | 21800篇 |
1993年 | 20762篇 |
1992年 | 22802篇 |
1991年 | 21489篇 |
1990年 | 20341篇 |
1989年 | 21460篇 |
1988年 | 19678篇 |
1987年 | 18539篇 |
1986年 | 17652篇 |
1985年 | 19908篇 |
1984年 | 20346篇 |
1983年 | 17962篇 |
1982年 | 19035篇 |
1981年 | 18487篇 |
1980年 | 17293篇 |
1979年 | 16131篇 |
1978年 | 15899篇 |
1977年 | 15384篇 |
1976年 | 14806篇 |
1975年 | 14230篇 |
1974年 | 14550篇 |
1973年 | 15016篇 |
1972年 | 12489篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
221.
John L. Graner 《CMAJ》1985,133(9):855-857,880
In 1849 Thomas Addison described the clinical entity now known as pernicious anemia. In 1855 he reported several cases of adrenal insufficiency, or Addison''s disease. Considering the importance of these works, there remains a great deal of confusion about them. Contrary to what many historians have written, a review of Addison''s original publications demonstrates a firm appreciation of the distinction between pernicious anemia and adrenal insufficiency, based particularly on the discoloration of the skin in these conditions. Three major sources of possible confusion for historians who are attempting to understand Addison''s views include Addison''s early attempts to link pernicious anemia with disease of the supra-renal capsules, Addison''s redefinition of pernicious anemia in his monograph on adrenal disease, and several confusing statements made by Wilks and Daldy in the first reprint of Addison''s monograph. 相似文献
222.
C. J. Gray 《Biocatalysis and Biotransformation》1988,1(3):187-196
The polypeptide chain of an enzyme is folded so that the necessary functional groups are brought together in the active site. Conformational changes may disrupt this arrangement and cause loss of enzymic activity. The effect of soluble additives on the unfolding process is discussed. Additives may be classified as substrates and similar ligands, small uncharged organic molecules, specific and non-specific ionic species, and polymers. 相似文献
223.
224.
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
225.
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
226.
227.
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
228.
229.
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
230.
M V Sauer 《The Western journal of medicine》1994,161(2):164-165