全文获取类型
收费全文 | 26627篇 |
免费 | 2526篇 |
国内免费 | 2720篇 |
出版年
2024年 | 60篇 |
2023年 | 410篇 |
2022年 | 901篇 |
2021年 | 1447篇 |
2020年 | 1004篇 |
2019年 | 1273篇 |
2018年 | 1162篇 |
2017年 | 867篇 |
2016年 | 1185篇 |
2015年 | 1716篇 |
2014年 | 1974篇 |
2013年 | 2124篇 |
2012年 | 2509篇 |
2011年 | 2266篇 |
2010年 | 1440篇 |
2009年 | 1265篇 |
2008年 | 1421篇 |
2007年 | 1280篇 |
2006年 | 1152篇 |
2005年 | 996篇 |
2004年 | 877篇 |
2003年 | 815篇 |
2002年 | 692篇 |
2001年 | 500篇 |
2000年 | 417篇 |
1999年 | 362篇 |
1998年 | 223篇 |
1997年 | 227篇 |
1996年 | 195篇 |
1995年 | 147篇 |
1994年 | 186篇 |
1993年 | 101篇 |
1992年 | 127篇 |
1991年 | 94篇 |
1990年 | 84篇 |
1989年 | 79篇 |
1988年 | 68篇 |
1987年 | 49篇 |
1986年 | 37篇 |
1985年 | 54篇 |
1984年 | 25篇 |
1983年 | 24篇 |
1982年 | 17篇 |
1981年 | 5篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1973年 | 2篇 |
1971年 | 2篇 |
1961年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
大豆下胚轴线粒体产生超氧物自由基的效率 总被引:4,自引:0,他引:4
大豆下胚轴线粒体在呼吸基质存在下,显著地增加了肾上腺素氧化速率,这种氧化速率能为外源SOD抑制,表明线粒体呼吸时产生分子氧的单电子还原成O_2(?)。亚线粒体颗粒产生O_2(?)的效率略高于线粒体。大豆下胚轴线粒体吸链内O_2(?)的产生为NADH所支持并与交替途径无关。表明分子氧单电子还原的部位可能是NADH-黄素蛋白和UbQ-Cyt.B。 相似文献
52.
A highly conserved clonotype has been identified within the repertoire of B cells specific for the negatively charged hapten phthalate. The prototype of this phthalate-specific clonotype is a primary-response hybridoma (2E9) that produces a mu,kappa anti-phthalate antibody. The 2E9 monoclonal antibody was found to share idiotypic determinants with several other independently-derived mu,kappa and gamma 1,kappa anti-phthalate monoclonal antibodies and with a significant proportion of conventional anti-phthalate antibodies derived from all of the BALB/c mice immunized with phthalate-keyhole limpet hemocyanin. Competitive RIA analysis of the 2E9 idiotypic relatedness between primary and secondary response antibodies was consistent with the hypothesis that the primary response mu,kappa antibodies represent a conserved germ-line product, whereas the secondary response to gamma 1,kappa antibodies reflect somatic variants of the 2E9 clonotype. Further analysis with a site-specific anti-idiotype reagent suggests that the idiotypic differences between mu,kappa and gamma 1,kappa monoclonal antibodies occur at positions outside of the combining site. Fine specificity analysis of the monoclonal antibodies expressing the 2E9 cross-reactive idiotype (CRI) also supports this hypothesis. Seven to 35% of the anti-phthalate antibodies after a single immunization with phthalate-KLH and 1 to 10% of the antibodies after a second immunization express the 2E9 CRI. The 2E9 CRI was also found in several other strains of mice, and its expression was associated exclusively with anti-phthalate antibodies. 相似文献
53.
The isolation, structure determination and synthesis of ergosta-5, 24(28), 25-trien-3 beta-ol, as well as the synthesis of its 28-14C analog--a possible biosynthetic precursor of several marine sterols--is described. 相似文献
54.
55.
56.
青海贵德、共和两盆地晚新生代哺乳动物 总被引:22,自引:3,他引:19
本文记述了青海省贵德及共和两盆地的几个含晚新生代哺乳动物化石地点的地层剖面及采自18个地点的26种(代表20个属)哺乳动物化石.对其中的 Myospalax arvicolinus, Microtus, Anancus, Leptobos crassus gonghenensis subsp. nov., L. vallisarni, Bison (Superbison) crassicornis, Boopsis breviceps作了较详细的描述和讨论.通过对动物群的分析初步确定了盆地主要堆积物的时代——贵德盆地:上新世—早更新世;共和盆地:早—中更新世,并简略探讨了两盆地的发育历史. 相似文献
57.
58.
59.
Serum beta 2 microglobulin levels, measured by radioimmunoassay (Phadebas test), were found increased in acute myeloid leukemias at diagnosis. Serum beta 2 microglobulin levels were significantly higher in patients with monocytic leukemias (13 patients, M4-M5 FAB classification) than in those with other cytological types (18 patients). Beta 2 microglobulin levels at diagnosis were correlated with serum lysozyme levels, but they were not correlated with blood blast counts, serum LDH and ferritin levels. 195 serum beta 2 microglobulin measurements were made serially in 30 patients with acute myeloid leukemias in first remission. Compared to values at diagnosis, beta 2 microglobulin levels in remission were significantly decreased. Out of 30 patients in remission 12 had increased serum beta 2 microglobulin levels (greater than 3 mg/l). Serial measurements were not predictive for relapses. 相似文献
60.
E Arnold J W Erickson G S Fout E A Frankenberger H J Hecht M Luo M G Rossman R R Rueckert 《Journal of molecular biology》1984,177(3):417-430
A new cubic crystal form (a = 445.1 A) of space group P23 is reported for human rhinovirus R14. There are four particles per unit cell, each situated on a crystallographic 3-fold axis. The orientation of these particles has been determined with a rotation function and their approximate positions have been derived from a Patterson map. The crystals diffract to at least 2.8 A resolution. Limitations to the possible surface features of the virus are set by a comparison of the cubic and orthorhombic crystal forms. 相似文献