全文获取类型
收费全文 | 24466篇 |
免费 | 1745篇 |
国内免费 | 154篇 |
专业分类
26365篇 |
出版年
2024年 | 31篇 |
2023年 | 82篇 |
2022年 | 317篇 |
2021年 | 501篇 |
2020年 | 350篇 |
2019年 | 424篇 |
2018年 | 653篇 |
2017年 | 484篇 |
2016年 | 837篇 |
2015年 | 1319篇 |
2014年 | 1448篇 |
2013年 | 1612篇 |
2012年 | 2095篇 |
2011年 | 1974篇 |
2010年 | 1264篇 |
2009年 | 1085篇 |
2008年 | 1553篇 |
2007年 | 1347篇 |
2006年 | 1214篇 |
2005年 | 1101篇 |
2004年 | 1059篇 |
2003年 | 851篇 |
2002年 | 854篇 |
2001年 | 660篇 |
2000年 | 667篇 |
1999年 | 450篇 |
1998年 | 179篇 |
1997年 | 146篇 |
1996年 | 135篇 |
1995年 | 98篇 |
1994年 | 96篇 |
1993年 | 80篇 |
1992年 | 168篇 |
1991年 | 138篇 |
1990年 | 98篇 |
1989年 | 118篇 |
1988年 | 79篇 |
1987年 | 75篇 |
1986年 | 71篇 |
1985年 | 56篇 |
1984年 | 53篇 |
1983年 | 40篇 |
1982年 | 30篇 |
1978年 | 33篇 |
1976年 | 37篇 |
1975年 | 33篇 |
1973年 | 40篇 |
1971年 | 29篇 |
1970年 | 28篇 |
1969年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
The material properties of bone-particle impregnated PMMA 总被引:4,自引:0,他引:4
The elastic Young's modulus and shear modulus of bone-particle impregnated polymethylmethacrylate (PMMA) has been measured experimentally at room temperature as a function of bone particle concentration. It was found that the moduli increased with increasing bone particle content. This increase was less than the stiffness increase predicted by higher-order composite theory [1, 2] under the assumption of perfect bonding between particles and matrix. It was concluded that a bond existed but that it was not a perfect bond. 相似文献
52.
Monoclonal antibody-directed immunopurification and identification of cytochromes P-450 总被引:4,自引:0,他引:4
F K Friedman R C Robinson S S Park H V Gelboin 《Biochemical and biophysical research communications》1983,116(3):859-865
A 28 amino acid peptide with diuretic and natriuretic activity has been purified from rat atrial muscle. The primary structure of this atrial peptide is H-Ser-Leu-Arg-Arg-Ser-Ser-Cys-Phe-Gly-Gly-Arg-Ile-Asp-Arg-Ile-Gly- (sequence in text) Ala-Gln-Ser-Gly-Leu-Gly-Cys-Asn-Ser-Phe-(Arg)-Tyr-OH. The biological activity of this peptide is identical to that of atrial natriuretic factor and cardionatrin I isolated from rat atria. 相似文献
53.
The metabolism of [6,7-3H]ethinylestradiol [( 3H]EE2) by rat liver microsomes was studied in vitro. After incubation of [3H]EE2 with rat liver microsomes for 20 min, 90% of the substrate was metabolised and 18% of the 3H-labelled material irreversibly bound to microsomal protein. Ascorbic acid (1 mM) decreased irreversible binding of 3H and produced an accumulation of 2-hydroxyethinylestradiol (2OH-EE2), while mixed-function oxidase inhibitors (0.5 mM) decreased binding of 3H to protein by inhibiting EE2 2-hydroxylation. Addition of thiols gave water-soluble metabolites which were characterised as 1(4)-thioether derivatives of 2OH-EE2 by co-chromatography with synthetic products. The results are consistent with the hypothesis that the chemically reactive metabolite of EE2 formed in vitro is either a quinone or o-semiquinone derived from 2OH-EE2 [1]. 相似文献
54.
55.
Production of mature sporophores ofAgaricus bisporus was achieved for the first time in amended, autoclaved soil, gamma-sterilized soil, and soil-extract agar medium. The initiation of sporophores was triggered by metabolites of soil-inhabiting bacteria, particularly nodule forming isolates. Whether a single metabolite or several metabolites of these bacteria caused formation of sporophores could not be established; however, biotin alone when added to soil extract medium produced comparable results. The potentiality of different bacteria to induce sporophore formation varied considerably within species and isolates.Amino acids favored vegetative growth ofA. bisporus, but failed to induce formation of sporophores. Organic acids supported luxuriant growth and poor sporophore formation. Among several growth-promoting substances and vitamins, biotin induced abundant formation of mature sporophores.The authors are thankful to Dr. C. Corke, Department of Soil Microbiology, University of Guelph, Ontario, for providing some bacterial cultures used in this study. 相似文献
56.
57.
58.
59.