全文获取类型
收费全文 | 51213篇 |
免费 | 17298篇 |
国内免费 | 2315篇 |
专业分类
70826篇 |
出版年
2024年 | 45篇 |
2023年 | 233篇 |
2022年 | 557篇 |
2021年 | 1163篇 |
2020年 | 2696篇 |
2019年 | 4301篇 |
2018年 | 4403篇 |
2017年 | 4601篇 |
2016年 | 4809篇 |
2015年 | 5250篇 |
2014年 | 5126篇 |
2013年 | 5825篇 |
2012年 | 4044篇 |
2011年 | 3421篇 |
2010年 | 4342篇 |
2009年 | 2995篇 |
2008年 | 2285篇 |
2007年 | 1744篇 |
2006年 | 1650篇 |
2005年 | 1593篇 |
2004年 | 1470篇 |
2003年 | 1353篇 |
2002年 | 1182篇 |
2001年 | 914篇 |
2000年 | 780篇 |
1999年 | 653篇 |
1998年 | 340篇 |
1997年 | 252篇 |
1996年 | 230篇 |
1995年 | 205篇 |
1994年 | 194篇 |
1993年 | 150篇 |
1992年 | 209篇 |
1991年 | 177篇 |
1990年 | 199篇 |
1989年 | 184篇 |
1988年 | 135篇 |
1987年 | 127篇 |
1986年 | 100篇 |
1985年 | 76篇 |
1984年 | 57篇 |
1983年 | 68篇 |
1982年 | 52篇 |
1981年 | 51篇 |
1979年 | 56篇 |
1978年 | 43篇 |
1977年 | 34篇 |
1976年 | 34篇 |
1975年 | 45篇 |
1973年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
Absence of a direct role for RNase HI in initiation of DNA replication at the oriC site on the Escherichia coli chromosome. 总被引:1,自引:0,他引:1 下载免费PDF全文
On the basis of the experiments carried out with rnhA224 mutants, we previously concluded that RNase HI is not essential for initiation of Escherichia coli chromosome replication at oriC (T. Kogoma, N.L. Subia, and K. von Meyenburg, Mol. Gen. Genet. 200:103-109, 1985). In light of the recent finding that rnhA224 is a UGA nonsense mutation which can be leaky in certain genetic backgrounds, we reexamined this conclusion with the use of rnhA339 (Null)::cat mutants. The possibility that recB+ is required for initiation at the alternative origins (oriKs) of replication in rnhA mutants was also tested. The results clearly indicated that RNase HI is not essential for oriC initiation and that recB+ is not required for initiation at oriK sites. 相似文献
52.
Neuza Domingues André R. A. Marques Rita Diogo Almeida Calado Inês S. Ferreira Cristiano Ramos José Ramalho Maria I. L. Soares Telmo Pereira Luís Oliveira José R. Vicente Louise H. Wong Inês C. M. Simões Teresa M. V. D. Pinho e Melo Andrew Peden Cláudia Guimas Almeida Clare E. Futter Rosa Puertollano Winchil L. C. Vaz Otília V. Vieira 《Traffic (Copenhagen, Denmark)》2023,24(7):284-307
53.
54.
An absorbable catheter for use in regional anticoagulation in microvascular and peripheral vascular surgery was studied in 20 sites in 10 adult beagle dogs to answer three questions: (1) Could the polyglycolic acid and trimethylene carbonate catheter withstand intraarterial pressures of infusion and completely absorb over a predictable time interval? (2) Could the catheter be filled with heparin and maintain patency for reuse after a 24-hour interval? (3) Could the catheter be placed in a side branch of a major artery and, after catheter dissolution, maintain long-term patency of the primary feeding artery? The catheters were completely absorbed from 24 to 34 weeks following implantation. The catheters were able to withstand intraarterial pressures, and no evidence of significant thrombosis of the primary feeding artery was seen in any animal studied. No complications of catheter leak, hematoma formation within the catheter placement sites, or sepsis were noted in any of the 20 catheter sites studied. 相似文献
55.
黄精凝集素Ⅱ分子稳定性与生物学活性研究鲍锦库,曾仲奎,周红(四川大学生物系,成都,610064)本文在黄精凝集素Ⅱ纯化及性质研究的基础上,应用多种变性条件,研究其分子特性,同时对分子的巯基和色氨酸进行修饰,研究该凝集素分子保持其生物学活性与这些基团的... 相似文献
56.
Abstract The present paper deals with a new species Habrophlebiodes zijinensis sp. nov. collected in Nanjing, Jiangsu Povince, China. 相似文献
57.
B A Pirola F Mayer I A Borthwick G Srivastava B K May W H Elliott 《European journal of biochemistry》1984,144(3):577-579
The structure of chick embryo liver 5-aminolaevulinate synthase has been examined by electron microscopic studies using negative staining. From the different projections of the enzyme particles observed in electron micrographs, a model for the enzyme molecule has been proposed. In this model, an enzyme molecule consists of two curved and identical subunits associated in opposite polarities. From the dimensions of an enzyme molecule subunit measured from electron micrographs, the relative molecular mass of each subunit is estimated to be 70 000. 相似文献
58.
Suspensions of rat pancreatic microsomal fraction release alpha-amylase and ribonuclease on incubation at 37 degrees C, but not at 2 degrees C. The release is abolished by proteolytic enzymes. Ribonuclease associated with the microsomal fraction is protected from subtilisin BPN' attack, but is sensitive after release. 相似文献
59.
60.
A Neville J B Palmer J Gaddie C S May K N Palmer L E Murchison 《BMJ (Clinical research ed.)》1977,1(6058):413-414
The effects of intravenous salbutamol (4 mug/kg) were compared with those of aerosol salbutamol (200 mug) in 10 asthmatic patients in a double-blind placebo-controlled study. Both methods of administration produced equal bronchodilatation. Intravenous salbutamol caused significant increases in plasma insulin and glucose levels and a fall in serum potassium concentration in addition to tachycardia and tremor, whereas aerosol salbutamol produced only a small transient increase in the plasma glucose level. The initially raised non-esterified fatty acid levels decreased significantly after aerosol and placebo but not after intravenous salbutamol. 相似文献