全文获取类型
收费全文 | 11222篇 |
免费 | 873篇 |
国内免费 | 831篇 |
出版年
2024年 | 20篇 |
2023年 | 143篇 |
2022年 | 345篇 |
2021年 | 613篇 |
2020年 | 403篇 |
2019年 | 475篇 |
2018年 | 511篇 |
2017年 | 396篇 |
2016年 | 472篇 |
2015年 | 701篇 |
2014年 | 768篇 |
2013年 | 852篇 |
2012年 | 1083篇 |
2011年 | 937篇 |
2010年 | 546篇 |
2009年 | 460篇 |
2008年 | 620篇 |
2007年 | 526篇 |
2006年 | 455篇 |
2005年 | 380篇 |
2004年 | 298篇 |
2003年 | 278篇 |
2002年 | 206篇 |
2001年 | 180篇 |
2000年 | 152篇 |
1999年 | 162篇 |
1998年 | 100篇 |
1997年 | 98篇 |
1996年 | 104篇 |
1995年 | 86篇 |
1994年 | 88篇 |
1993年 | 72篇 |
1992年 | 60篇 |
1991年 | 76篇 |
1990年 | 61篇 |
1989年 | 44篇 |
1988年 | 32篇 |
1987年 | 17篇 |
1986年 | 23篇 |
1985年 | 18篇 |
1984年 | 17篇 |
1983年 | 20篇 |
1982年 | 8篇 |
1980年 | 3篇 |
1978年 | 2篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1971年 | 3篇 |
1968年 | 2篇 |
1966年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
121.
Genetic exchange of transposon and integrative plasmid markers in Mycoplasma pulmonis. 总被引:1,自引:1,他引:0
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Matings of genetically marked derivatives of Mycoplasma pulmonis resulted in the exchange of chromosomal DNA and the appearance of doubly marked transconjugants. Transposons Tn916 and Tn4001, and a series of integrative plasmids derived from their cloned antibiotic resistance genes, were used to construct antibiotic-resistant mycoplasmal derivatives to examine this phenomenon at the molecular level. Genetic exchange occurred on agar surfaces at frequencies ranging from 3.3 X 10(-4) to 6.4 X 10(-8) transconjugants per CFU. Examination of chromosomal DNA from transconjugants by hybridization revealed that the transposons or integrated plasmids were in the same chromosomal locations as in the parental strains, indicating that exchange involved the transfer of chromosomal DNA and homologous recombination. Transfer was not affected by DNase, polyethylene glycol, EDTA, or calcium chloride but was affected by treatment of either parent with trypsin. Mixing of mating strains before plating had no effect on mating frequencies, but mating did occur in liquid media. The ability to exchange chromosomal markers was limited to selected strains of M. pulmonis; mating did not occur with Acholeplasma laidlawii or M. gallisepticum. Heat and UV inactivation studies revealed that nonviable cells could act as donors in matings. The evidence presented supports a conjugationlike mechanism involving specific trypsin-sensitive membrane components. 相似文献
122.
Threonine 1336 of the human insulin receptor is a major target for phosphorylation by protein kinase C 总被引:6,自引:0,他引:6
The ability of tumor-promoting phorbol diesters to inhibit both insulin receptor tyrosine kinase activity and its intracellular signaling correlates with the phosphorylation of the insulin receptor beta subunit on serine and threonine residues. In the present studies, mouse 3T3 fibroblasts transfected with a human insulin receptor cDNA and expressing greater than one million of these receptors per cell were labeled with [32P]phosphate and treated with or without 100 nM 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA). Phosphorylated insulin receptors were immunoprecipitated and digested with trypsin. Alternatively, insulin receptors affinity purified from human term placenta were phosphorylated by protein kinase C prior to trypsin digestion of the 32P-labeled beta subunit. Analysis of the tryptic phosphopeptides from both the in vivo and in vitro labeled receptors by reversed-phase HPLC and two-dimensional thin-layer separation revealed that PMA and protein kinase C enhanced the phosphorylation of a peptide with identical chromatographic properties. Partial hydrolysis and radiosequence analysis of the phosphopeptide derived from insulin receptor phosphorylated by protein kinase C indicated that the phosphorylation of this tryptic peptide occurred specifically on a threonine, three amino acids from the amino terminus of the tryptic fragment. Comparison of these data with the known, deduced receptor sequence suggested that the receptor-derived tryptic phosphopeptide might be Ile-Leu-Thr(P)-Leu-Pro-Arg. Comigration of a phosphorylated synthetic peptide containing this sequence with the receptor-derived phosphopeptide confirmed the identity of the tryptic fragment. The phosphorylation site corresponds to threonine 1336 in the human insulin receptor beta subunit.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
123.
A cDNA encoding the nucleic acid-binding domain of the hnRNP C-type protein has been cloned by DNA-affinity screening of pituitary-derived expression libraries. An analysis revealed sequence identity with the human C-type cDNA and demonstrated the presence of a peptide sequence contained within the single-stranded DNA-binding protein, UP2, which was absent from the human cDNA. Structural analysis of the protein encoded by the rat cDNA demonstrated a net charge of +15 with 14.56% and 6.33% lysines and arginines, respectively, and an amino acid sequence that is consistent with an extensive helix-loop-helix-turn-helix structure. 相似文献
124.
This paper makes an analysis and study on altogether 8 palyniferous samples from the volcano-sedimentary rock series in the Half Three Point area of the Fildes Peninsula, King George Island, Antarctica, the rock series being grey tuffaceous siltstone in lithological characters, about 5m in thickness. Only after making a number of analyses, could we find the relatively abundant sporopollen fossils from 4 samples (Nos. GWP 4—7). But the fossils are poorly preserved, and most of them can hardly be identifi... 相似文献
125.
Summary A case of D ring chromosome identified with trypsin banding as a 13 with loss of the bands p12 and q34 is reported. The clinical features characteristically associated with the loss of these specific segments were present. 相似文献
126.
127.
128.
A Ajima S G Cao K Takahashi A Matsushima Y Saito Y Inada 《Biotechnology and applied biochemistry》1987,9(1):53-57
Hemin, having two carboxyl groups, was coupled with alpha-(3-aminopropyl)-omega-methoxypoly(oxyethylene) through the acid-amide bond formed with carbodiimide. The modified hemin catalyzed the peroxidase reaction in 1,1,1-trichloroethane using benzoyl peroxide or peroxides in unsaturated fatty acids as the hydrogen acceptor and leuco crystal violet as the hydrogen donor. A basic study on quantitative microanalysis of the lipid peroxides was attempted. 相似文献
129.
130.
Yajun Chen Wenjiao Cao Lihua Wang Tianying Zhong 《Journal of cellular and molecular medicine》2020,24(13):7652-7659
AMPH1, an abundant protein in nerve terminals, plays a critical role in the recruitment of dynamin to sites of clathrin‐mediated endocytosis. Recently, it is reported to be involved in breast cancer and lung cancer. However, the impact of AMPH1 on ovarian cancer is unclear. In this study, we used gain‐of‐function and loss‐of‐function methods to explore the role of AMPH1 in ovarian cancer cells. AMPH1 inhibited ovarian cancer cell growth and cell migration, and promoted caspase‐3 activity, resulting in the increase of cell apoptosis. In xenograft mice model, AMPH1 prevented tumour progression. The anti‐oncogene effects of AMPH1 on ovarian cancer might be partially due to the inhibition of PI3K/AKT signalling pathway after overexpression of AMPH1. Immunohistochemistry analysis showed that the staining of AMPH1 was remarkably reduced in ovarian cancer tissues compared with normal ovarian tissues. In conclusion, our study identifies AMPH1 as a tumour suppressor in ovarian cancer in vitro and in vivo. This is the first evidence that AMPH1 inhibited cell growth and migration, and induced apoptosis via the inactivation of PI3K/AKT signalling pathway on ovarian cancer, which may be used as an effective strategy. 相似文献