全文获取类型
收费全文 | 1489篇 |
免费 | 122篇 |
专业分类
1611篇 |
出版年
2022年 | 14篇 |
2021年 | 26篇 |
2020年 | 11篇 |
2019年 | 25篇 |
2018年 | 16篇 |
2017年 | 24篇 |
2016年 | 35篇 |
2015年 | 58篇 |
2014年 | 73篇 |
2013年 | 91篇 |
2012年 | 99篇 |
2011年 | 88篇 |
2010年 | 83篇 |
2009年 | 56篇 |
2008年 | 98篇 |
2007年 | 76篇 |
2006年 | 57篇 |
2005年 | 66篇 |
2004年 | 74篇 |
2003年 | 60篇 |
2002年 | 56篇 |
2001年 | 33篇 |
2000年 | 31篇 |
1999年 | 26篇 |
1998年 | 15篇 |
1997年 | 13篇 |
1996年 | 12篇 |
1995年 | 15篇 |
1994年 | 12篇 |
1993年 | 12篇 |
1992年 | 26篇 |
1991年 | 22篇 |
1990年 | 14篇 |
1989年 | 10篇 |
1988年 | 12篇 |
1987年 | 15篇 |
1986年 | 9篇 |
1985年 | 12篇 |
1984年 | 13篇 |
1983年 | 13篇 |
1982年 | 7篇 |
1981年 | 11篇 |
1980年 | 6篇 |
1979年 | 13篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1976年 | 11篇 |
1975年 | 10篇 |
1973年 | 6篇 |
1968年 | 5篇 |
排序方式: 共有1611条查询结果,搜索用时 0 毫秒
41.
A new method for the evaluation of 3-hydroxy-3-methylglutaryl-CoA reductase activity is described, based on the multiple-selected ion monitoring of the amount of mevalonate formed in incubations of 3-hydroxy-3-methylglutaryl-CoA with microsomal proteins. Analysis is carried out on crude extracts using deuterated mevalonic acid lactone as internal standard. The sensitivity of the technique allows the quantitative evaluation of mevalonate in microassays (100 μg microsomal protein) of the enzyme activity at the minimum value of the diurnal rhythm. 相似文献
42.
C Spagnuolo L Sautebin G Galli G Racagni C Galli S Mazzari M Finesso 《Prostaglandins》1979,18(1):53-61
The effects of ligation of both common carotid arteries in the gerbil on the levels of PGF2 alpha, TXB2, HETE and of energy metabolites in brain cortex, have been investigated. Also, in the same experimental conditions the changes of cyclic AMP in brain cortex, cerebellum, striatum and hippocampus have been monitored. ATP, glycogen, glucose and phosphocreatine decrease whereas, lactate and cyclic AMP are enhanced in the ischemic brain, as previously reported. In contrast, levels of arachidonic acid metabolites are not modified. During ischemia following decapitation, instead, PGF2 alpha, and TXB2, show considerable increase. 相似文献
43.
Probenecid in single or repeated doses does not modify levels of PGF2 alpha and TXB2 in rat brain cortex. After administration of subconvulsant dose of pentamethylene tetrazole (PMT) PGF2 alpha increases sharply and rapidly declines subsequently, whereas the elevation of TXB2 is smaller but of longer duration. After probenecid pretreatment PGF2 alpha levels do not decline up to 30 minutes after the initial peak and are still elevated after 60 minutes. Levels of TXB2 tend to be reduced after pretreatment. Differences in transport process or in biosynthetic compartments for these arachidonic acid (AA) metabolites may account for the observed data. 相似文献
44.
C. Spagnuolo A. Petroni M. Blasevich C. Galli 《Prostaglandins & other lipid mediators》1979,18(2):311-315
Probenecid in single or repeated doses does not modify levels of PGF2α and TXB2 in rat brain cortex. After administration of subconvulsant dose of pentamethylene tetrazone (PMT) PGF2α increases sharply and rapidly declines subsequently, whereas the elevation of TXB2 is smaller but of longer duration. After probenecid pretreatment PGF2α levels do not decline up to 30 minutes after the initial peak and are still elevated after 60 minutes. Levels of TXB2 tend to be reduced after pretreatment. Differences in transport process or in biosynthetic compartments for these arachidonic acid (AA) metabolites may account for the observed data. 相似文献
45.
Substrate and steric specificity of hydropyrimidine hydrase. 总被引:7,自引:0,他引:7
46.
A method for the evaluation of PGF-2alpha and PGE-2 biosynthesis in rat cerebral cortex is described. Tissue slices were incubated without any added precursor for different lengths of time. The analytical procedure involves prostaglandin extraction, purification and quantitative determination by mass fragmentography. Significant amounts of both prostaglandins were synthesized. The biosynthesis reached a plateau after 30 minutes and the ratio of PGF-2alpha to PGE-2 was approximately 3. 相似文献
47.
A method for the evaluation of PGF2α and PGE2 biosynthesis in rat cerebral cortex is described. Tissue slices were incubated without any added precursor for different lengths of time. The analytical procedure involves prostaglandin extraction, purification and quantitative determination by mass fragmentography. Significant amounts of both prostaglandins were synthesized. The biosynthesis reached a plateau after 30 minutes and the ratio of PGF2α to PGE2 was approximately 3. 相似文献
48.
Chloramphenicol (Cm) and its fluorinated derivative florfenicol (Ff) represent highly potent inhibitors of bacterial protein biosynthesis. As a consequence of the use of Cm in human and veterinary medicine, bacterial pathogens of various species and genera have developed and/or acquired Cm resistance. Ff is solely used in veterinary medicine and has been introduced into clinical use in the mid-1990s. Of the Cm resistance genes known to date, only a small number also mediates resistance to Ff. In this review, we present an overview of the different mechanisms responsible for resistance to Cm and Ff with particular focus on the two different types of chloramphenicol acetyltransferases (CATs), specific exporters and multidrug transporters. Phylogenetic trees of the different CAT proteins and exporter proteins were constructed on the basis of a multisequence alignment. Moreover, information is provided on the mobile genetic elements carrying Cm or Cm/Ff resistance genes to provide a basis for the understanding of the distribution and the spread of Cm resistance--even in the absence of a selective pressure imposed by the use of Cm or Ff. 相似文献
49.
M Columbo E M Horowitz L M Botana D W MacGlashan B S Bochner S Gillis K M Zsebo S J Galli L M Lichtenstein 《Journal of immunology (Baltimore, Md. : 1950)》1992,149(2):599-608
The gene product of the steel locus of the mouse represents a growth factor for murine mast cells and a ligand for the c-kit proto-oncogene receptor, a member of the tyrosine kinase receptor class of oncogenes (for review, see O. N. Witte. 1990. Cell 63:5). We have studied the effect of the human recombinant c-kit receptor ligand stem cell factor (rhSCF) on the release of inflammatory mediators from human skin mast cells and peripheral blood basophils and compared its activity to that of rhIL-3, rhSCF (1 ng/ml to 1 microgram/ml) activated the release of histamine and PGD2 from mast cells isolated from human skin. Analysis by digital video microscopy indicated that purified human skin mast cells (84 +/- 5% pure) responded to rhSCF (0.1 to 1 microgram/ml) challenge with a rapid, sustained rise in intracellular Ca2+ levels that was accompanied by secretion of histamine. A brief preincubation (10 min) of mast cells with rhSCF (0.1 pg/ml to 1 ng/ml) significantly enhanced (100 +/- 35%) the release of histamine induced by anti-IgE (3 micrograms/ml), but was much less effective on IgE-mediated release of PGD2. In contrast, a short term incubation with rhSCF did not potentiate the secretion of histamine activated by substance P (5 microM). A 24-h incubation of mast cells with rhSCF did not affect the release of mediators induced by anti-IgE (3 micrograms/ml), probably due to receptor desensitization, rhSCF (1 ng/ml to 3 micrograms/ml) neither caused release of histamine or leukotriene C4 (LTC4) release from leukocytes of 14 donors, nor induced a rise in intracellular Ca2+ levels in purified (greater than 70%) basophils. Brief preincubation (10 min) of leukocytes with rhSCF (1 ng/ml to 3 micrograms/ml) caused an enhancement (69 +/- 11%) of anti-IgE-induced release of histamine that was significant at concentrations as low as 3 ng/ml (p less than 0.05), whereas it appeared less effective in potentiating IgE-mediated LTC4 release. In contrast, a prolonged incubation (24 h) with rhSCF (0.1 pg/ml to 100 ng/ml) did not enhance the release of histamine or LTC4 induced by anti-IgE (0.1 microgram/ml), whereas rhIL-3 (3 ng/ml) significantly potentiated the release of both mediators.(ABSTRACT TRUNCATED AT 400 WORDS) 相似文献
50.