全文获取类型
收费全文 | 303篇 |
免费 | 0篇 |
专业分类
系统科学 | 4篇 |
教育与普及 | 1篇 |
理论与方法论 | 1篇 |
现状及发展 | 89篇 |
研究方法 | 14篇 |
综合类 | 194篇 |
出版年
2014年 | 4篇 |
2013年 | 2篇 |
2012年 | 6篇 |
2011年 | 2篇 |
2010年 | 2篇 |
2008年 | 9篇 |
2007年 | 3篇 |
2006年 | 7篇 |
2005年 | 8篇 |
2004年 | 5篇 |
2003年 | 7篇 |
2002年 | 7篇 |
2001年 | 12篇 |
2000年 | 10篇 |
1999年 | 7篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 8篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 12篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 2篇 |
1979年 | 17篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1974年 | 10篇 |
1973年 | 15篇 |
1972年 | 10篇 |
1971年 | 8篇 |
1970年 | 12篇 |
1969年 | 8篇 |
1968年 | 10篇 |
1967年 | 10篇 |
1966年 | 3篇 |
1965年 | 1篇 |
1964年 | 2篇 |
1958年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有303条查询结果,搜索用时 15 毫秒
31.
32.
Specific inhibition of herpesvirus ribonucleotide reductase by a nonapeptide derived from the carboxy terminus of subunit 2 总被引:15,自引:0,他引:15
Ribonucleotide reductase, an essential enzyme for the synthesis of deoxyribonucleotides, is formed by the association of two nonidentical subunits in almost all prokaryotic and eukaryotic cells. The same model probably holds for the herpes simplex virus (HSV)-encoded ribonucleotide reductase; two polypeptides of relative molecular mass 136,000 (136K; H1) and 40K (H2) (referred to elsewhere as RR1 and RR2; see for example, Dutia et al.) have been associated with the viral enzyme by both genetic and immunological studies. Furthermore, DNA sequence analyses have shown significant stretches of amino-acid homology between these viral polypeptides and those of, respectively, subunit 1 (ref. 12) and subunit 2 (ref. 13) of the Escherichia coli and mammalian enzymes. To assess the involvement of the 40K polypeptide in reductase activity, we synthesized a nonapeptide corresponding to the sequence of its carboxy terminus with the intention of raising neutralizing antibodies specific for the viral activity (E.A.C. et al., in preparation). We report here the unexpected finding that the nonapeptide itself specifically inhibits the HSV ribonucleotide reductase activity in a reversible, non-competitive manner, and we suggest that it does this by impairment of the correct association of the two subunits. This phenomenon emphasizes the potential usefulness of synthetic peptides in probing critical sites involved in macromolecular interactions. 相似文献
33.
34.
W. G. Christen H. I. Cohen T. W. Robertson R. W. Winters 《Cellular and molecular life sciences : CMLS》1979,35(8):1073-1074
Summary The surround response mechanism in on-center X-cells in cat retina was found to be bimodally distributed and weak or nonexistent in the receptive field middle. An on-inhibition measure was used to assess surround mechanism gain.Acknowledgments. This research is supported by Public Health Service grant No. EY 00701. 相似文献
35.
A point mutation in the last intron responsible for increased expression and transforming activity of the c-Ha-ras oncogene 总被引:19,自引:0,他引:19
The T24/EJ allele of the Ha-ras proto-oncogene owes its powerful oncogenic activity not merely to the well documented mutation that perturbs the structure of the encoded polypeptide, but in addition to a second single nucleotide alteration in an intron that causes a tenfold increase in expression. This effect on expression is maintained upon transfer of the surrounding DNA to a heterologous gene, and as such defines a novel regulatory element. 相似文献
36.
Time course measurements of the action of muscarinic antagonists were performed in the spontaneously beating carp atrium. Several high affinity drugs, which embody the quinuclidine structure were examined. The structural flexibility of these molecules was reflected in the dissociation of the drugs from the muscarinic receptor. The dissociation of rigid drugs was very much prolonged as compared to flexible drugs of the same affinity. 相似文献
37.
38.
Cloning of the mycobacterial epitope recognized by T lymphocytes in adjuvant arthritis 总被引:112,自引:0,他引:112
W van Eden J E Thole R van der Zee A Noordzij J D van Embden E J Hensen I R Cohen 《Nature》1988,331(6152):171-173
Adjuvant arthritis (AA) is a chronic disease inducible in rats by immunization with an antigen of Mycobacterium tuberculosis. After the isolation of arthritogenic T-cell lines and clones, it became possible to demonstrate that the critical M. tuberculosis antigen contained an epitope cross-reactive with a self-antigen in joint cartilage. Like AA rats, patients suffering from rheumatoid arthritis demonstrated specific T-lymphocyte reactivity to the M. tuberculosis fraction containing the cross-reactive epitope. To characterize the critical M. tuberculosis epitope we used AA T-cell clones to screen mycobacterial antigens expressed in Escherichia coli and genetically engineered truncated proteins and synthetic peptides. The AA T-cell clones recognized an epitope formed by the amino acids at positions 180-188 in the sequence of a Mycobacterium bovis BCG antigen. Administration of this antigen to rats induced resistance to subsequent attempts to produce AA. 相似文献
39.
Endogenous mammary tumour virus DNA varies among wild mice and segregates during inbreeding. 总被引:44,自引:0,他引:44
Proviruses of the mouse mammary tumour virus (MMTV) endogenous to normal mice can be identified by molecular hybridisation and distinguished using restriction endonucleases. Feral mice display marked heterogeneity with respect to the number of copies and the sites of insertion of endogenous MMTV-specific DNA, with occasional mice apparently free of MMTV DNA. Several different MMTV proviruses present in laboratory mice have segregated like stable, independent genetic elements during the inbreeding which followed a cross between Bagg albino and DBA mice 60 years ago. The results favour the hypothesis that endogenous proviruses have been established by multiple, independent infections of germ cells rather than by somatic mutation of ancestral proviruses or of cellular genes. 相似文献
40.