全文获取类型
收费全文 | 416380篇 |
免费 | 53193篇 |
国内免费 | 194篇 |
专业分类
469767篇 |
出版年
2018年 | 3556篇 |
2016年 | 4626篇 |
2015年 | 6598篇 |
2014年 | 7616篇 |
2013年 | 11022篇 |
2012年 | 12231篇 |
2011年 | 12579篇 |
2010年 | 8450篇 |
2009年 | 7876篇 |
2008年 | 11104篇 |
2007年 | 11468篇 |
2006年 | 10662篇 |
2005年 | 10283篇 |
2004年 | 9932篇 |
2003年 | 9910篇 |
2002年 | 9529篇 |
2001年 | 19725篇 |
2000年 | 19935篇 |
1999年 | 15734篇 |
1998年 | 5477篇 |
1997年 | 6037篇 |
1996年 | 5741篇 |
1995年 | 5361篇 |
1994年 | 5255篇 |
1993年 | 5383篇 |
1992年 | 13353篇 |
1991年 | 13181篇 |
1990年 | 12564篇 |
1989年 | 12366篇 |
1988年 | 11279篇 |
1987年 | 10925篇 |
1986年 | 10209篇 |
1985年 | 10159篇 |
1984年 | 8502篇 |
1983年 | 7339篇 |
1982年 | 5642篇 |
1981年 | 5023篇 |
1980年 | 4845篇 |
1979年 | 7997篇 |
1978年 | 6397篇 |
1977年 | 5822篇 |
1976年 | 5488篇 |
1975年 | 6028篇 |
1974年 | 6220篇 |
1973年 | 6150篇 |
1972年 | 5551篇 |
1971年 | 5106篇 |
1970年 | 4258篇 |
1969年 | 4101篇 |
1968年 | 3674篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
871.
872.
873.
D Brinkley 《BMJ (Clinical research ed.)》1985,291(6497):685-686
874.
875.
In order to verify the applicability of biochemical methods for species identification of Trypanosomatidae, 13 species of monoxenic trypanosomatids plus the heteroxenous Trypanosoma cruzi were comparatively analyzed by three different biochemical methods. Insect trypanosomatids examined were: Crithidia acanthocephali, C. fasciculata (three varieties), C. luciliae luciliae, C. luciliae thermophila, C. deanei, C. oncopelti, Herpetomonas muscarum muscarum, H. megaseliae, H. samuelpessoai, H. mariadeanei, Leptomonas seymouri, L. collosoma, L. samueli, and Blastocrithidia culicis. Also included in the survey were aposymbiotic strains of C. deanei and C. oncopelti. Methods used were: electrophoretic profiling of endonuclease-generated fragments of k-DNA, esterase isoenzymes profiling, and polyacrylamide-gel electrophoresis (SDS-PAGE) of radioiodinated cell surface proteins. Interspecific but not intraspecific differences were detected by all three methods among the 13 monoxenic species examined. Thus, it is concluded that these methods can be successfully used, in addition to classical criteria, for species identification of insect trypanosomatids. 相似文献
876.
The solution conformation of short ragweed allergen Ra5, a protein of 45 amino acid residues cross-linked with four disulfide bridges, has been investigated by 1H NMR spectroscopy at 500 MHz. The aromatic region, which contains resonances from three tyrosines and two tryptophans, has been partially assigned. Two tyrosines titrate with a pK of 10.2; a third tyrosine is buried under the tryptophan resonances, and its pK could not be determined. The two tryptophans reside in different microenvironments; the resonances of one are very similar to those found in random coil structures while the other has dramatically shifted peaks. Nuclear Overhauser effect (NOE) difference spectroscopy is used to define two distinct spin-diffusion systems for the aromatic residues and to further identify several methyl-containing amino acids involved in these systems. Assignments in the methyl region are based on selective decoupling, chemical shifts, NOE difference spectra, and 2-D J-resolved and 2-D J-correlated spectroscopy (COSY) methodology. A unique ring-current-shifted methyl doublet in the Ra5 spectrum titrates into the bulk methyl region with a pK of 10.2. Examination of the COSY map suggests that this resonance belongs to either leucine-1 or isoleucine-38. Chemical removal of the N-terminal leucine did not affect the ring-current-shifted methyl. Therefore, this unique resonance has been assigned to the methyl of isoleucine-38.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
877.
D. R. Anderson K. P. Burnham B. R. Crain 《Biometrical journal. Biometrische Zeitschrift》1985,27(7):723-731
ANDERSON and POSPAHALA (1970) investigated the estimation of wildlife population size using the belt or line transect sampling method and devised a correction for bias, thus leading to a class of estimators with desirable characteristics. This work was given a basic and rigorous mathematica framework by BURNHAM and ANDERSON (1976). In the present article we use this mathematical framework to develop an estimator of population size and density using weighted least squares. The approach is a two-stage Method. 相似文献
878.
Purification of transcription factor IIIB from HeLa cells 总被引:17,自引:0,他引:17
879.
A Santagostino G Giagnoni P Fumagalli D Pavesi E Torretta 《Biochemical and biophysical research communications》1982,104(2):577-582
The isoelectric point of the camel and the human β-endorphin, of the α-endorphin and the enkephalins were determined by analytical isoelectric focusing on 1 mm thin polyacrylamide gel slab. The difficulty of staining peptides as short as β-endorphin or smaller was overcomed using a modification of Bibring and Baxandall's or Faupel and Von Arx's staining method. The camel β-endorphin gives two bands having isoelectric point of 10.3 and 10.4, the human β-endorphin focus at pH 9.9, while α-endorphin, leu and met-enkephalin at pH 5.9, 5.5 and 5.45 respectively. The staining method described coupled with the isoelectric focusing seems to be fit for discriminating β-endorphin in a crude rat pituitary extract. 相似文献
880.
N.m.r. studies of metabolism in perfused organs 总被引:1,自引:0,他引:1
J J Ackerman P J Bore D G Gadian T H Grove G K Radda 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》1980,289(1037):425-436
Several metabolites and intracellular pH in intact organs can be studied in a non-destructive manner by phorphorus nuclear magnetic resonance (31P n.m.r.). This possibility was demonstrated by us nearly five years ago. Since then we have developed the appropriate physiological techniques and improved the n.m.r. method for the study of animal hearts and kidneys. Here we described measurements aimed at clarifying three problesm. (1) Having measured the enzyme-catalysed fluxes between phosphocreatine and ATP by the method of saturation transfer n.m.r., we examine the relations between energy supply and heart rate in the isolated perfused rat heart. (2) We describe experiments to establish the validity of the perfusion model. For the first time, we report 31P n.m.r. measurements of an in vivo rat heart and compare the results with those obtained for the perfused rat heart. (3) Ischaemia and metabolism in rabbit kidneys is investigated to establish the relation between functional and metabolic recovery after a renal transplant operation. 相似文献