全文获取类型
收费全文 | 5216篇 |
免费 | 361篇 |
出版年
2022年 | 21篇 |
2021年 | 51篇 |
2020年 | 24篇 |
2019年 | 44篇 |
2018年 | 60篇 |
2017年 | 57篇 |
2016年 | 74篇 |
2015年 | 137篇 |
2014年 | 146篇 |
2013年 | 411篇 |
2012年 | 231篇 |
2011年 | 217篇 |
2010年 | 123篇 |
2009年 | 142篇 |
2008年 | 237篇 |
2007年 | 286篇 |
2006年 | 298篇 |
2005年 | 290篇 |
2004年 | 290篇 |
2003年 | 292篇 |
2002年 | 278篇 |
2001年 | 151篇 |
2000年 | 164篇 |
1999年 | 129篇 |
1998年 | 77篇 |
1997年 | 81篇 |
1996年 | 62篇 |
1995年 | 67篇 |
1994年 | 48篇 |
1993年 | 43篇 |
1992年 | 100篇 |
1991年 | 92篇 |
1990年 | 78篇 |
1989年 | 89篇 |
1988年 | 82篇 |
1987年 | 64篇 |
1986年 | 48篇 |
1985年 | 50篇 |
1984年 | 46篇 |
1983年 | 36篇 |
1982年 | 26篇 |
1981年 | 21篇 |
1980年 | 27篇 |
1979年 | 33篇 |
1978年 | 22篇 |
1977年 | 18篇 |
1975年 | 22篇 |
1974年 | 29篇 |
1973年 | 22篇 |
1967年 | 19篇 |
排序方式: 共有5577条查询结果,搜索用时 31 毫秒
31.
H Murofushi A Ikai K Okuhara S Kotani H Aizawa K Kumakura H Sakai 《The Journal of biological chemistry》1988,263(25):12744-12750
Kinesin was purified from bovine adrenal medulla. The sedimentation coefficient was 8.8 S. Sedimentation equilibrium ultracentrifugation studies showed the molecular weight of kinesin to be 300,000. The calculated axial ratio was 1:16. The Stokes radius was estimated to be 8.9 nm by gel filtration. Circular dichroism showed the alpha-helix content to be about 50%. Purified kinesin preparation contained a major polypeptide with a molecular weight of 120,000 and minor ones with molecular weights of 71,000, 68,000, and 65,000. Bovine adrenal kinesin had an ATPase activity which was stimulated severalfold by microtubules to a specific activity of about 0.1 mumol/min.mg. Kinesin molecules adsorbed to a glass slide promoted the movement of microtubules on the glass surface at a rate of about 0.5 micron/s. Immunostaining of EBTr (bovine embryonic trachea fibroblast) cells and bovine adrenal chromaffin cells in interphase with an affinity-purified antibody against the major polypeptide of kinesin showed that some kinesin was located on microtubules and the rest distributed throughout the cytoplasm in a diffuse manner. EBTr cells in mitotic phase gave a staining pattern showing that kinesin was present throughout the cytoplasm with higher concentration in the region of mitotic apparatus. 相似文献
32.
Monoclonal antibodies to mouse complement receptor type 1 (CR1). Their use in a distribution study showing that mouse erythrocytes and platelets are CR1-negative 总被引:14,自引:0,他引:14
T Kinoshita J Takeda K Hong H Kozono H Sakai K Inoue 《Journal of immunology (Baltimore, Md. : 1950)》1988,140(9):3066-3072
mAb to murine C receptor type 1 (CR1) were produced and three of them were characterized. One antibody, designated as 8C12, immunoprecipitated a protein of 190,000 Mr from a detergent extract of surface-labeled spleen cells and stained spleen B but not T lymphocytes in fluorescent flow cytometry. It inhibited both CR1-mediated rosette formation and the cofactor activity of CR1 for factor I-mediated cleavage of C3b, suggesting that it recognizes the ligand-binding site of CR1. The two other antibodies, designated as 7G6 and 7E9, recognized different epitopes from that recognized by 8C12, and they cross-reacted with a protein of 150,000 Mr that is present in a spleen extract. The distribution of CR1 in murine hemopoietic cells was studied by binding experiments with radiolabeled 8C12 and fluorescent flow cytometry. When CR1 was not detected by 8C12 alone, the two other antibodies were used in combination with 8C12 to confirm the negative results. Almost all B lymphocytes from the spleen, lymph nodes, and peripheral blood were CR1 positive. Most of the Thy-1-positive lymphocytes from these tissues were CR1 negative. Thymus lymphocytes were also CR1 negative. Peritoneal macrophages and chemotactic factor stimulated but not unstimulated peripheral blood granulocytes were CR1 positive. In contrast to human E, mouse E were CR1 negative. This pattern of distribution was consistent with previous results obtained by rosette assays. Although mouse platelets cause immune adherence hemagglutination with C3b-bearing SRBC, they are CR1 negative. Three other lines of evidence also indicated that platelets are CR1 negative. First, no band of CR1 was demonstrated by immunoprecipitation with 8C12 of an extract of surface-labeled platelets. Second, 8C12, which inhibited rosette formation by lymphocytes, alone or in combination with 7G6 and 7E9, did not inhibit immune adherence between platelets and C3b-bearing SRBC. Third, polyclonal rabbit IgG prepared from anti-mouse CR1 antiserum did not inhibit immune adherence by platelets. These results strongly suggest that the C3b-binding factor(s) on mouse platelets is different from CR1 and that processing of C3b-bearing immune complexes in mouse blood may be mediated by a new and as yet unidentified C3b-binding factor(s). 相似文献
33.
The cytokinetic effects of carboplatin(CBDCA) on a human ovarian cancer cell line(KF-1) were examined by means of cell survival rate and flow cytometry in comparison with cisplatin(CDDP). CBDCA and CDDP exhibited dose dependent cytotoxicity on KF-1, and CBDCA showed compatible cell growth inhibition to that of 15 times concentration of CDDP in comparison with IC50 of 72 hrs after drug addition. From the analysis of cell cycle, CBDCA and CDDP inhibited cell cycle progression at G2 + M phase. CBDCA exhibited G2 + M phase block to that of 15 to 20 times the concentration of CDDP. We suggested that CBDCA had potential therapeutic activity against ovarian cancer, but should be evaluated carefully in the clinical use. 相似文献
34.
35.
Structural and functional features of cis-acting sequences in the basic replicon of plasmid ColIb-P9.
下载免费PDF全文
![点击此处可从《Nucleic acids research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
K Tanaka H Sakai Y Honda T Nakamura A Higashi T Komano 《Nucleic acids research》1992,20(11):2705-2710
We have structurally and functionally analyzed the cis-elements essential for ColIb-P9 plasmid DNA replication. The putative oriV region encompassed a region of 172 base pairs (bp) located 152 bp downstream of the repZ gene. A typical dnaA box found in this region proved nonessential for the DNA replication of ColIb-P9. The ssi signal of ColIb-P9 is a homologue of the G-sites of R1 and R100 plasmids. Deletion of the G-site led to 1.5-fold reduction of the copy number, suggesting that although this G-site is not essential, it is important for efficient ColIb-P9 DNA replication. In addition, the ColIb-P9 replicon is highly and extensively homologous with the P307 (RepFIC) replicon, and highly homologous with the R100 (RepFIIA) replicon around the G-site region. These facts imply a common ancestry from which the plasmids have evolved. 相似文献
36.
Summary A transient increase in rosmarinic acid (RA) content in cultured cells of Lithospermum erythrorhizon was observed after addition of yeast extract (YE) to the suspension cultures, reaching a maximum at 24 hr. The highest increase of the RA content (2.5-fold) was obtained when 6-day-old cells in the exponential growth phase were treated with YE. Preceding the induced RA accumulation, phenylalanine ammonia-lyase (PAL) activity increased rapidly, whereas tyrosine aminotransferase (TAT) activity was largely unaffected by the treatment. The incorporation of both 14C-phenylalanine and 14C-tyrosine into RA was enhanced in the YE-treated cells, consistent with increased synthesis of the ester.Abbreviations 2,4-D
2,4 dichlorophenoxyacetic acid
- PAL
phenylalanine ammonia-lyase
- TAT
tyrosine aminotransferase
- RA
rosmarinic acid
- YE
yeast extract 相似文献
37.
Generation of a chimeric human and simian immunodeficiency virus infectious to monkey peripheral blood mononuclear cells. 总被引:17,自引:13,他引:4
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We constructed five chimeric clones between human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIVMAC) and four SIVMAC mutants by recombinant DNA techniques. Three chimeric clones and all mutants with an alteration in either the vif, vpx, vpr, or nef gene were infectious to human CD4-positive cell lines. The susceptibility of macaque monkey peripheral blood mononuclear cells (PBMC) to infection by these mutants and chimeras was examined in vitro. Macaque PBMC supported the replication of wild-type and vpx, vpr, and nef mutant SIVMAC strains. A chimera carrying the long terminal repeats (LTRs), gag, pol, vif, and vpx of SIVMAC and tat, rev, vpu, and env of HIV-1 was also replication competent in PBMC. In contrast, HIV-1, the vif mutant of SIVMAC, a chimera containing rev and env of SIVMAC, and a chimera containing vpx, vpr, tat, rev, and env of SIVMAC did not grow in PBMC. Western immunoblotting analysis of the replicating chimera in PBMC confirmed the hybrid nature of the virus. These data strongly suggested that the sequence important for macaque cell tropism lies within the LTR, gag, pol, and/or vif sequences of the SIVMAC genome. 相似文献
38.
Two molecularly cloned coisolates of human immunodeficiency virus type 1 (HIV-1) have been found to exhibit different phenotypes of viral expression, either rapid and cytopathic (N1T-A virus) or delayed and noncytopathic (N1T-E virus [X. Ma, K. Sakai, F. Sinangil, E. Golub, and D. J. Volsky, Virology 176:184-194, 1990]). To identify the viral genetic elements responsible for these phenotypes, we prepared reciprocal recombinants in different regions of N1T-A and N1T-E viral genomes. Infectivity experiments with the recombinant viruses revealed that the rapid/cytopathic (N1T-A-like) phenotype assorted cleanly with the V1f-coding region and Vif expression. The smallest HIV-1 DNA region that conferred the complete phenotypic switch was a 284-bp NdeI-StuI fragment within the vif open reading frame. Nucleotide sequence analysis revealed a 35-bp deletion starting at nucleotide 218 in the N1T-E vif gene. A 23-kDa Vif protein was detected by immunoblotting using Vif-specific antiserum in extracts of cells infected with N1T-A but not N1T-E virus. No detectable vif protein was found in association with sedimented particles of either virus. Cotransfection of a eucaryotic vif expression plasmid with N1T-E DNA complemented the N1T-E defect; rapid/cytopathic infection similar to that in N1T-A-transfected cells was observed. We conclude that Vif controls the rate, and consequently the cytopathic outcome, of HIV-1 infection. 相似文献
39.
N Sakai J Tamaoki K Kobayashi T Kanemura K Isono K Takeyama S Takeuchi T Takizawa 《Regulatory peptides》1991,34(1):33-41
We studied the effect of vasoactive intestinal peptide (VIP) on ciliary activity in rabbit cultured tracheal epithelium by a photoelectric method in vitro. Administration of VIP (10(-7) M) elicited an increase in ciliary beat frequency (CBF) from the baseline values of 970 +/- 52 to 1139 +/- 75 beats/min (mean +/- S.E., P less than 0.01). This ciliostimulatory effect was dose-dependent, with the maximal increase and EC50 value being 17.4 +/- 1.0% (P less than 0.05) and 6.10(-11) M, respectively. The VIP-induced increase in CBF was abolished by pretreatment of cells with [4-Cl-D-Phe6, Leu17]-VIP, a VIP receptor antagonist. The neutral endopeptidase inhibitor phosphoramidon (10(-5) M) potentiated the effect of VIP, so that the CBF dose-response curve for VIP was shifted to lower concentrations by 0.5 log U. The administration of VIP increased cyclic AMP levels in epithelial cells, an effect that was also potentiated by phosphoramidon. These results suggest that VIP may interact with its specific receptors and stimulate airway ciliary activity probably through the activation of adenylate cyclase, and that neutral endopeptidase may play a role in modulating this effect of VIP. 相似文献
40.
Terhi Siimes Mikio Nakajima Hideo Yada Hajime Asama Teruyuki Nagamune Pekka Linko Isao Endo 《Biotechnology Techniques》1992,6(5):385-390
Summary A knowledge based system has been shown to be a powerful tool for diagnosing microbial activities during a fermentation process.
Knowledge about lactic acid fermentation was collected by an experimental study ofLactobacillus casei. The effects of the inoculum properties and sterilization time on the cultivation were expressed in a form of a fuzzy rule-based
knowledge network. The system was able to detect abnormal inoculum or sterilization conditions which caused malfunctions in
the cultivations. 相似文献