全文获取类型
收费全文 | 457412篇 |
免费 | 56157篇 |
国内免费 | 279篇 |
出版年
2018年 | 3920篇 |
2017年 | 3627篇 |
2016年 | 5616篇 |
2015年 | 8378篇 |
2014年 | 9449篇 |
2013年 | 13488篇 |
2012年 | 15349篇 |
2011年 | 15440篇 |
2010年 | 10212篇 |
2009年 | 9453篇 |
2008年 | 13542篇 |
2007年 | 14023篇 |
2006年 | 12684篇 |
2005年 | 12499篇 |
2004年 | 12285篇 |
2003年 | 11730篇 |
2002年 | 11176篇 |
2001年 | 22018篇 |
2000年 | 22145篇 |
1999年 | 17578篇 |
1998年 | 6172篇 |
1997年 | 6406篇 |
1996年 | 6163篇 |
1995年 | 5802篇 |
1994年 | 5856篇 |
1993年 | 5657篇 |
1992年 | 13883篇 |
1991年 | 13165篇 |
1990年 | 12850篇 |
1989年 | 12691篇 |
1988年 | 11362篇 |
1987年 | 10939篇 |
1986年 | 10039篇 |
1985年 | 9789篇 |
1984年 | 8286篇 |
1983年 | 7185篇 |
1982年 | 5627篇 |
1981年 | 5066篇 |
1980年 | 4715篇 |
1979年 | 7793篇 |
1978年 | 5978篇 |
1977年 | 5492篇 |
1976年 | 5099篇 |
1975年 | 5412篇 |
1974年 | 5842篇 |
1973年 | 5710篇 |
1972年 | 5145篇 |
1971年 | 4763篇 |
1970年 | 3967篇 |
1969年 | 3883篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
Two human retinoblastoma cell lines (Y79 and McA) were evaluated for the presence of binding sites for human beta-endorphin (beta h-EP). Using tritiated beta h-EP (3H-beta h-EP) and synthetic beta-EP analogues, it was possible to demonstrate binding sites for 3H-beta h-EP with an ED50 of 3.5 nM in Y79 cells and 8 nM in McA cells respectively. The non-opioid segment [beta h-EP-(6-31)] retained about 20% relative potency in Y79 and 40% in McA in displacing the tritiated hormone when compared with beta h-EP. Camel beta-EP had a relative potency of less than 1% and beta h-EP-(1-27) was inactive in both cells in doses as high as 4 microM. Taken together with previous reports on similar binding sites in human neuroblastoma and glioblastoma cell lines, it appears that cell lines of neural origin have binding sites for the COOH-terminal of human beta-EP. 相似文献
992.
Abstract Cell contents of Clostridium sphenoides , labeled with [32 P]orthophosphate under strict anaerobic conditions, were analyzed by two-dimensional gel electrophoresis. Autoradiography of these gels demonstrated the presence of at least 15 32 P-labeled protein species, of which M r and iso-electric point were determined. Treatment of the radioactively labeled cell contents with alkaline phosphatase and acid phosphatase showed that all these proteins were modified by phosphorylation. These findings demonstrate for the first time the presence of phosphorproteins in a strictly anaerobic bacterium. 相似文献
993.
Summary A new method for the distillation of glutaradlehyde to obtain the monomeric form is presented. The monomer is obtained after only one distillation and it has a purification index (Pi) smaller than 0.20. 相似文献
994.
Storage of Hg in the ileum of Blatella germanica: biochemical characterization of metallothionein 总被引:1,自引:0,他引:1
J M Bouquegneau C Ballan-Dufrancais A Y Jeantet 《Comp. Biochem. Physiol. C, Comp. Pharmacol. Toxicol.》1985,80(1):95-98
Cockroach ileum has a high capability to concentrate mercury compared with other tissues. Part of the mercury contained in the soluble phase of this organ is bound to metallothionein. It is suggested that mercury of the insoluble phase is stored in lysosomes under a polymerized metallothionein form. 相似文献
995.
996.
The salicylic acid derivative acetylsalicylic acid (ASA) was found to promote colony formation from protoplasts isolated from embryogenic suspension cultures of an elite maize inbred line. The drug was most effective at concentrations of 30–100 mg/l, and increases of more than 20-fold in the number of colonies recovered from protoplasts were obtained. The rate of growth of protoplast-derived cell colonies was not affected.Abbreviations 2,4-D
2,4-dichlorophenoxyacetic acid
- DMSO
dimethylsulfoxide
- KM
Kao and Michayluk medium (1975)
- MES
2[N-morpholino]ethanesulfonic acid
- ASA
acetylsalicylic acid 相似文献
997.
The technique of limited necropsy by histological examination of needle tissue cores obtained percutaneously is indicated when a full necropsy is not justified owing to the risk of infection or when tissue for special investigations is needed soon after death without recourse to full necropsy facilities. The method is ideal for detecting conditions producing diffuse changes in an organ. Because the cadaver is preserved essentially intact relatives who refuse permission for a standard necropsy might consent to a needle necropsy if this option is offered to them. 相似文献
998.
The neurotensin receptor protein, solubilized with digitonin/asolectin from bovine cerebral cortex membranes, was purified to apparent homogeneity by affinity chromatography using immobilized neurotensin. The product exhibits saturable and specific binding of [3,11-tyrosyl-3,5-3H]neurotensin with an apparent affinity (Kd = 5.5 nM) comparable to that measured in intact membranes and crude soluble extracts. The affinity-purified material, after reduction with 100 mM dithiothreitol, in denaturing gel electrophoresis showed a single polypeptide of Mr 72,000. Under nonreducing conditions the apparent Mr, however, was 50,000, suggesting the presence of intramolecular disulfide bonds. The purified neurotensin receptor was judged to be homogeneous, in that (i) only a single polypeptide was detectable; and (ii) the overall purification was 30,000-50,000-fold, giving a specific neurotensin-binding activity close to the theoretical maximum. 相似文献
999.
Joint Report of the First International Comparison Test on Swine Lymphocyte Alloantigens (SLA) 总被引:5,自引:0,他引:5
CH. RENARD B. KRISTENSEN C. GAUTSCHI V. HRUBAN M. FREDHOLM M. VAIMAN 《Animal genetics》1988,19(1):63-72
The first international comparison test on swine lymphocyte alloantigens (SLA) was held in Helsinki, Finland in July 1986. The results reported were based on a comparison of 157 alloantisera originating from six laboratories. The antisera were tested against a selected panel of 264 lymphocyte samples belonging to four laboratories. The most common breeds in Europe were chosen for this first comparison test (Landrace and Large White). Eighteen of the 31 previously known specificities were confirmed and a new nomenclature was established. 相似文献
1000.
The duration of the lag phase of Salmonella typhimurium injured by heating, freezing, acidification or drying was measured using the 'Malthus' conductance meter. Results confirmed those previously obtained by viable counting and additionally, revealed the very wide variation in lag between and within populations and the extreme length of lag that can occur in some severely injured cells. In an extreme example, the measured lag times of low numbers of bacteria taken from the same heat-injured population ranged from 16 h to 70 h. The implications for the detection of injured micro-organisms in food are discussed. 相似文献