全文获取类型
收费全文 | 13005篇 |
免费 | 38篇 |
国内免费 | 39篇 |
专业分类
系统科学 | 92篇 |
丛书文集 | 207篇 |
教育与普及 | 39篇 |
理论与方法论 | 72篇 |
现状及发展 | 6370篇 |
研究方法 | 565篇 |
综合类 | 5535篇 |
自然研究 | 202篇 |
出版年
2013年 | 124篇 |
2012年 | 220篇 |
2011年 | 380篇 |
2010年 | 96篇 |
2008年 | 232篇 |
2007年 | 249篇 |
2006年 | 256篇 |
2005年 | 298篇 |
2004年 | 241篇 |
2003年 | 248篇 |
2002年 | 249篇 |
2001年 | 318篇 |
2000年 | 319篇 |
1999年 | 210篇 |
1992年 | 196篇 |
1991年 | 170篇 |
1990年 | 171篇 |
1989年 | 165篇 |
1988年 | 172篇 |
1987年 | 171篇 |
1986年 | 179篇 |
1985年 | 248篇 |
1984年 | 168篇 |
1983年 | 156篇 |
1982年 | 116篇 |
1981年 | 138篇 |
1980年 | 165篇 |
1979年 | 407篇 |
1978年 | 310篇 |
1977年 | 347篇 |
1976年 | 249篇 |
1975年 | 247篇 |
1974年 | 372篇 |
1973年 | 322篇 |
1972年 | 343篇 |
1971年 | 353篇 |
1970年 | 480篇 |
1969年 | 420篇 |
1968年 | 440篇 |
1967年 | 400篇 |
1966年 | 342篇 |
1965年 | 254篇 |
1964年 | 112篇 |
1959年 | 130篇 |
1958年 | 221篇 |
1957年 | 181篇 |
1956年 | 170篇 |
1955年 | 139篇 |
1954年 | 136篇 |
1948年 | 112篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
The role of peroxisomes in aging 总被引:2,自引:0,他引:2
993.
Immunological activity of covalently linked T-cell epitopes. 总被引:6,自引:0,他引:6
Immune responses to proteins necessarily involve the recognition by T lymphocytes of a peptide or peptides derived from a protein complexed with a major histocompatibility antigen. The T-cell response of BALB/c mice to the bacteriophage lambda cI repressor protein (residues 1-102) is directed predominantly towards the epitope contained within a single peptide encompassing residues 12-26. Similar phenomena of immunodominance of a particular peptide have also been observed in other protein systems. The mechanisms that have been suggested to account for the focusing of the T-cell response are partial deletion in the T-cell repertoire, biased antigen processing, and competition for binding to the presenting molecule, the major histocompatibility complex encoded class II transplantation antigen. In a model system with a polypeptide containing two synthetically linked immunologically active epitopes, we now demonstrate the existence of a hierarchy between these epitopes, so that the immune response elicited is directed mainly towards the more immunogenic epitope, whereas the less immunogenic epitope elicits little or no T-cell reactivity. In addition, the same hierarchy of dominance is also apparent when the polypeptide is used to induce tolerance in the periphery in adult mice. The chimaeric peptide can induce tolerance only towards the more immunogenic epitope. These experiments indicate that the rules governing antigen processing and presentation that result in T-cell activation are apparently the same as the rules that govern the processes resulting in the induction of tolerance. 相似文献
994.
T. Aoyagi T. Wada M. Nagai F. Kojima S. Harada T. Takeuchi H. Takahashi K. Hirokawa T. Tsumita 《Cellular and molecular life sciences : CMLS》1990,46(1):94-97
Summary We examined the changes in the intracerebral activities, at the time of postmortem autopsy, in patients with Alzheimer's disease. When compared with the control group, the activity of kallikrein-like enzyme was significantly decreased, while prolyl endopeptidase activity increased, in the patients group. Aprotinin inhibited 50% of the activity of the former enzyme at 2×10–7M. Taken together with the results of a multivariate study, the above findings may indicate that intracerebral kallikrein deficiency plays an important role in the pathogenesis of Alzheimer's disease. 相似文献
995.
996.
The ability of dog renal cortex slices to accumulate beta-methyl-glucoside or glycine is enhanced by the flavonoid (+)-catechin at a concentration of 3.5 mM. This stimulatory effect is apparently due to a decreased rate of efflux of either substrate. On the other hand, the uptake of p-amino-hippuric acid and N1-methyl-nicotinamide is inhibited by (+)-catechin. The drug at the same concentration is without action on amino-acid transport by guinea-pig intestine in vitro. 相似文献
997.
Binding of 2-p-toluidinylnaphthalene-6-sulfonate (TNS) to adenylylated (E--11) glutamine synthetase is cooperative and time-dependent, with 3 dye sites per subunit. In fluorescence polarization experiments TNS and pyrene butyrate give normalized Perrin plots that indicate a symmetrical arrangement of dye excited state dipoles, relative to the rotational axis of the oblate ellipsoid of the dodecameric native enzyme. 相似文献
998.
999.
1000.