全文获取类型
收费全文 | 12016篇 |
免费 | 641篇 |
国内免费 | 7篇 |
专业分类
12664篇 |
出版年
2022年 | 65篇 |
2021年 | 128篇 |
2020年 | 65篇 |
2019年 | 96篇 |
2018年 | 136篇 |
2017年 | 133篇 |
2016年 | 192篇 |
2015年 | 286篇 |
2014年 | 343篇 |
2013年 | 699篇 |
2012年 | 604篇 |
2011年 | 583篇 |
2010年 | 372篇 |
2009年 | 389篇 |
2008年 | 609篇 |
2007年 | 561篇 |
2006年 | 567篇 |
2005年 | 538篇 |
2004年 | 523篇 |
2003年 | 561篇 |
2002年 | 523篇 |
2001年 | 441篇 |
2000年 | 431篇 |
1999年 | 353篇 |
1998年 | 161篇 |
1997年 | 128篇 |
1996年 | 111篇 |
1995年 | 101篇 |
1994年 | 94篇 |
1993年 | 94篇 |
1992年 | 254篇 |
1991年 | 252篇 |
1990年 | 207篇 |
1989年 | 189篇 |
1988年 | 193篇 |
1987年 | 161篇 |
1986年 | 151篇 |
1985年 | 151篇 |
1984年 | 131篇 |
1983年 | 112篇 |
1982年 | 92篇 |
1981年 | 60篇 |
1980年 | 61篇 |
1979年 | 91篇 |
1978年 | 87篇 |
1977年 | 62篇 |
1976年 | 58篇 |
1975年 | 51篇 |
1973年 | 60篇 |
1970年 | 49篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Escherichia coli disruptants defective in the yaeM gene, which is located at 4.2 min on the chromosome map, were constructed and characterized. The disruptants showed auxotrophy for 2-C-methylerythritol, a free alcohol of 2-C-methyl-D-erythritol 4-phosphate that is a biosynthetic precursor in the nonmevalonate pathway. This result clearly shows that the yaeM gene is indeed involved in this pathway in E. coli. 相似文献
3.
T Kaidoh S Natsuume-Sakai M Takahashi 《Journal of immunology (Baltimore, Md. : 1950)》1981,126(2):463-467
A simple, 3-step method was described for purification of murine C4 binding protein (C4-bp), a recently recognized serum protein that functions as one of the regulatory proteins of the complement system. The method consists of 1) affinity chromatography using TNBS-BGG-conjugated Sepharose beads, 2) gel filtration on a Sepharose 6B column, and 3) heparin-Sepharose chromatography. By this method, milligram quantities of C4-bp can be easily purified by more than 500-fold from EDTA-serum of various mouse strains, and the whole purification process can be completed within 1 wk. The overall yield of C4-bp is about 15%. The C4-bp thus prepared is homogeneous as judged by SDS-polyacrylamide gel electrophoresis and immunelectrophoresis. The purified mouse C4-bp showed physicochemical properties very similar to those described for human C4-bp. Like human C4-bp, mouse C4-bp is composed of several apparently identical subunits of the m.w. of 80,000. However unlike the human counterpart, the subunits of mouse C4-bp are not linked by disulfide bonds but are connected by non-covalent forces that can be disrupted by SDS. The purified mouse C4-bp retained binding affinity for C4 and showed unaltered antigenicity. Immunization of rabbits with the purified mouse C4-bp resulted in the production of potent and monospecific antisera. 相似文献
4.
5.
Shigeki Takeura Hiizu Aoki Tatsuya Tsurumi Yukihiro Nishiyama Hisashi Fujioka Saiji Yoshii Koichiro Maeno 《Microbiology and immunology》1984,28(4):427-437
Host-dependent restriction of influenza B virus replication in L cells was analysed in comparison with productive infection in MDCK or 1–5C-4 cells. The synthesis and intracellular distribution of virus-specific proteins and the production of cytoplasmic ribonucleoproteins in nonpermissive L cells were similar to those in permissive MDCK cells. However, an electron microscopic study of infected L cells showed neither extracellular virions nor budding virus particles on the cell surface, in contrast to MDCK cells which produced numerous virus particles. PAGE analysis of the plasma membrane isolated from the cells demonstrated no significant difference in the composition of viral polypeptides between permissive 1-5C-4 and nonpermissive L cells. It was noted that the abortiveness of influenza B virus infection in L cells may be due to a defect in host cell function involved in the initiation of virus budding. 相似文献
6.
7.
8.
9.
N Nakagata K Matsumoto M Anzai A Takahashi Y Takahashi Y Matsuzaki K Miyata 《Jikken dobutsu》1992,41(4):537-540
Spermatozoa of a homozygous transgenic mouse, in which the firefly luciferase gene was expressed under the control of beta-actin promoter, were frozen at -196 degrees C. One fourth of the frozen sperm was later thawed and used for in vitro fertilization. Thirty-six of 65 oocytes (55.4%) developed to the 2-cell stage. All the 2-cell embryos were transferred to the oviducts of pseudopregnant recipients and 23 young (63.9%, 23/36) were born. All of young analyzed carried the transgene and showed the luciferase gene expression. 相似文献
10.
Expression of the fragile X site fra(X)(q27.3) was studied in thymidine-prototrophic and auxotrophic human-mouse somatic cell hybrids. In these cells, low thymidylate stress, achieved by 5-fluoro-2'-deoxyuridine (FdU) treatment and by limiting the exogenous supply of thymidine (dT), induced fragile X expression. High thymidylate stress, produced by supplying excess amounts of dT, was also effective in inducing fragile X expression, even in a hybrid clone that retained a fragile X chromosome as the only human chromosome; addition of deoxycytidine (dC) completely abolished this effect. In contrast, 5-bromo-2'-deoxyuridine (BrdU) did not induce fragile X expression. Cell-cycle analysis of BrdU-deprived thymidine-auxotrophic hybrid cells indicated that one round of DNA replication under thymidylate stress conditions is sufficient for fragile X expression. Our results suggest that the expression is an intrinsic property of the fragile site itself, which is believed to be composed of replicon clusters with pyrimidine-rich DNA sequence(s). 相似文献