全文获取类型
收费全文 | 2822篇 |
免费 | 228篇 |
国内免费 | 1篇 |
出版年
2023年 | 12篇 |
2022年 | 35篇 |
2021年 | 56篇 |
2020年 | 39篇 |
2019年 | 41篇 |
2018年 | 53篇 |
2017年 | 46篇 |
2016年 | 69篇 |
2015年 | 109篇 |
2014年 | 122篇 |
2013年 | 144篇 |
2012年 | 203篇 |
2011年 | 186篇 |
2010年 | 110篇 |
2009年 | 116篇 |
2008年 | 147篇 |
2007年 | 144篇 |
2006年 | 123篇 |
2005年 | 137篇 |
2004年 | 135篇 |
2003年 | 124篇 |
2002年 | 134篇 |
2001年 | 58篇 |
2000年 | 43篇 |
1999年 | 48篇 |
1998年 | 31篇 |
1997年 | 27篇 |
1996年 | 34篇 |
1995年 | 31篇 |
1994年 | 40篇 |
1993年 | 22篇 |
1992年 | 19篇 |
1991年 | 22篇 |
1990年 | 15篇 |
1989年 | 12篇 |
1988年 | 19篇 |
1987年 | 30篇 |
1986年 | 13篇 |
1985年 | 26篇 |
1984年 | 25篇 |
1983年 | 14篇 |
1982年 | 15篇 |
1981年 | 14篇 |
1978年 | 15篇 |
1977年 | 14篇 |
1976年 | 17篇 |
1975年 | 12篇 |
1973年 | 21篇 |
1972年 | 14篇 |
1971年 | 13篇 |
排序方式: 共有3051条查询结果,搜索用时 14 毫秒
71.
N L Browse G Clemenson N T Bateman J I Gaunt D N Croft 《BMJ (Clinical research ed.)》1976,2(6047):1281-1284
The incidence of pulmonary embolism and deep vein thrombosis was measured in 50 matched pairs of patients undergoing common surgical procedures with preoperative and postoperative ventilation-perfusion lung scans and the fibrinogen uptake test. One patient in each pair was treated with intravenous dextran 70 and pneumatic leggings. The incidence of pulmonary embolism among the treated patients was significantly reduced from 24% to 8%, but the incidence of deep vein thrombosis was not significantly reduced (34% to 24%). 相似文献
72.
The microsomal fraction of Saccharomyces cerevisiae has been shown to catalyse the NADPH-dependent reduction of ergosta-5,7,22,24(28)-tetraen-3β-ol to ergosterol. This cell-free system together with whole-cell cultures of polyene-resistant mutants has been used to compare the rates of reduction of other 24-methylene sterols. The results indicate that the enzyme involved exhibits a marked specificity for ergosta-5,7,22,24(28)-tetraen-3β-ol and support the concept of a major terminal step in ergosterol biosynthesis. 相似文献
73.
Mode of formation of cholesta-5,7-dien-3β-ol from cholest-5-en-3β-ol by larvae of Calliphora erythrocephala 下载免费PDF全文
1. The conversion of cholest-5-en-3beta-ol (cholesterol) into cholesta-5,7-dien-3beta-ol by axenic Calliphora erythrocephala larvae was demonstrated. 2. The transformation is probably direct (Delta(5)-->Delta(5,7)) and does not involve a Delta(0) intermediate (Delta(5)-->Delta(0)-->Delta(7)--> Delta(5,7)). 3. Delta(7)-bond formation involves the stereospecific elimination of the 7beta hydrogen atom. 4. The relative amounts of free and esterified sterols were determined in larvae grown on cholesterol as sole sterol source and on 5alpha-cholestan-3beta-ol supplemented with minimal amounts of cholesterol. 5. The significance of the results is assessed in relation to the probable role of cholesta-5,7-dien-3beta-ol as an intermediate in the biosynthesis of ecdysones. 相似文献
74.
75.
The largest non-unit eigenvalue λ of the transition matrix for the Wright-Fisher Markov chain model of random genetic drift is found numerically with selective advantages of genotypes taken into account. Polynomials in the selection coefficients are fitted to λ in order to summarize the behaviour of λ with varying selection. Also found are the values of the selective advantages which give rise to an acceleration to the rate of fixation of alleles. These values are compared to results for the diffusion approximation to the Wright-Fisher model. 相似文献
76.
Trevor Baines 《BMJ (Clinical research ed.)》1985,291(6501):1050-1051
77.
Trevor Lukey Kuldeep Neote John F. Loman Ardythe E. Unger Fred G. Biddle Floyd F. Snyder 《Biochemical genetics》1985,23(3-4):347-356
An improved method for detecting four Np-1 (purine nucleoside phosphorylase) alleles in mouse erythrocytes by cellulose acetate electrophoresis is described. The previous linkage of Np-1 and Es-10 (esterase-10) was confirmed, with a map distance of 13.0±2.6 cM. Np-2 was detected by either specific activity assay or starch gel electrophoresis and shown to be linked to Es-10, 15.9 ± 3.1 cM, on chromosome 14. No recombinants between Np-1 and Np-2 were observed in 52 offspring, indicating either that these loci are either closely associated or that Np-2 represents simply a property of existing allelic products of the Np-1 locus.This research was supported by Medical Research Council of Canada grants to F.G.B. and F.F.S. 相似文献
78.
79.
B. A. Croft 《BioControl》1976,21(4):383-399
A summary of basic biological, ecological and toxicological characteristics of 3 phytoseiid mite predatorsTyphlodromus occidentalis
Nesbitt,Amblyseius fallacis
Garman andTyphlodromus pyri
Scheuten which have developed resistances to certain insecticides commonly used in commercial fruit orchards is presented. Methods
of culturing and mass-rearing these mites are reviewed. Also the cultural and pesticidal measures which should be maintained
to facilitate effective biological control of spider mite pest of deciduous fruit crops by these predators and to maximally
provide for their establishment in areas of the world where resistance has not developed or they do not occur naturally are
discussed.
This publication was supported in part by a NSF-EPA grant GB-34718 to the University of California. The findings, opinions and recommendations expressed herein are those of the author and not necessarily those of the University of California, NSF or EPA. Published as Journal Article N. 1559 of the Michigan State University Agricultural Experiment Station. 相似文献
Résumé L'auteur résume les caractéristiques fondamentles biologiques, écologiques et toxicologiques de 3 phytoséiides prédateurs d'acariens,Typhlodromus occidentalis Nesbitt,Amblyseius fallacis Garman etTyphlodromus pyri Scheuter, qui ont acquis une résistance à certains insecticides généralement utilisés dans les vergers de fruits commerciaux. Les méthodes d'élevage et de multiplication massive de ces acariens sont rappelées. Sont également discutées les techniques culturales et phytosanitaires qui sont à employer pour favoriser ces prédateurs comme agents de lutte biologique efficace contre les acariens nuisibles aux vergers et pour procéder à leur implantation dans les régions du monde où la résistance ne s'est pas manifestée ou bien où ces prédateurs n'existent pas naturellement.
This publication was supported in part by a NSF-EPA grant GB-34718 to the University of California. The findings, opinions and recommendations expressed herein are those of the author and not necessarily those of the University of California, NSF or EPA. Published as Journal Article N. 1559 of the Michigan State University Agricultural Experiment Station. 相似文献