全文获取类型
收费全文 | 2567篇 |
免费 | 162篇 |
国内免费 | 1篇 |
专业分类
2730篇 |
出版年
2022年 | 16篇 |
2021年 | 24篇 |
2020年 | 15篇 |
2019年 | 25篇 |
2018年 | 23篇 |
2017年 | 15篇 |
2016年 | 34篇 |
2015年 | 39篇 |
2014年 | 53篇 |
2013年 | 291篇 |
2012年 | 129篇 |
2011年 | 92篇 |
2010年 | 71篇 |
2009年 | 83篇 |
2008年 | 95篇 |
2007年 | 106篇 |
2006年 | 84篇 |
2005年 | 78篇 |
2004年 | 100篇 |
2003年 | 98篇 |
2002年 | 91篇 |
2001年 | 86篇 |
2000年 | 109篇 |
1999年 | 108篇 |
1998年 | 29篇 |
1997年 | 24篇 |
1996年 | 22篇 |
1995年 | 21篇 |
1994年 | 16篇 |
1993年 | 25篇 |
1992年 | 67篇 |
1991年 | 61篇 |
1990年 | 55篇 |
1989年 | 38篇 |
1988年 | 55篇 |
1987年 | 32篇 |
1986年 | 41篇 |
1985年 | 30篇 |
1984年 | 39篇 |
1983年 | 29篇 |
1982年 | 29篇 |
1981年 | 30篇 |
1980年 | 17篇 |
1979年 | 18篇 |
1978年 | 19篇 |
1977年 | 19篇 |
1974年 | 18篇 |
1973年 | 16篇 |
1972年 | 19篇 |
1967年 | 18篇 |
排序方式: 共有2730条查询结果,搜索用时 0 毫秒
31.
Purification and Chemical Composition of Reticulate Bodies of the Meningopneumonitis Organisms 总被引:23,自引:13,他引:10 下载免费PDF全文
Reticulate bodies of the meningopneumonitis (MP) microorganism were purified from L cells 18 hr after infection by the combination of differential centrifugation in 30% sucrose solution and potassium tartrate density gradient centrifugation. It was ascertained by electron microscopy that purified preparations of reticulate bodies obtained were almost entirely free of host-cell components and of infectious elementary bodies of MP microorganisms. Purified reticulate bodies were easily disrupted by mechanical agitation, and it was observed in shadowed preparation that ribosome-like particles 15 mmu in diameter were scattered from broken reticulate bodies. In shadowed preparations, reticulate bodies were found to range in size from 1.0 to 1.6 mu in diameter, but in cross-section the range was 0.5 to 1.0 mu. In these preparations, the purified reticulate bodies were irregular in shape, round or oval, and were composed of rather homogenous, amorphous, or reticulate material with moderate density. Some particles exhibited a less-dense internal structure, in which a coarse fibrous reticulum was seen. Chemical fractionation of (32)P-labeled purified reticulate bodies showed that they contained three times more ribonucleic acid (RNA) than deoxyribonucleic acid, with the RNA being composed primarily of 21S, 16S, and 4S RNA. No infectivity of purified reticulate bodies could be demonstrated. 相似文献
32.
33.
34.
35.
36.
To elucidate the role of CD4 molecule in T cell activation, the effect of anti-CD4 on T cell IL-2 production was examined by using an alloreactive Th clone. The alloreactive T cell used in the present experiments produced IL-2 in response to soluble anti-CD3 epsilon-chain (anti-CD3) without accessory cell or insoluble antibody carrier. The IL-2 production was suppressed by the addition of anti-CD4 in cultures. An intracellular free Ca2+ concentration ([Ca2+]i) of the T cell clone was elevated by anti-CD3 stimulation, but the elevation was suppressed in the presence of anti-CD4. When the clone was stimulated in Ca2(+)-free medium, the elevation of [Ca2+]i was not observed. When Ca2+ influx was induced by calcium ionophore A23187 or ionomycin, the clone produced IL-2 in response to anti-CD3 in the presence of anti-CD4. When polyclonal T cell line or several other alloreactive T cell clones were examined for their anti-CD3 response, essentially the same results as mentioned above were obtained. Taken together, these results suggest that the slow and sustained elevation of [Ca2+]i is an essential signal for IL-2 production of T cells, and that anti-CD4 suppresses the IL-2 production by interfering the [Ca2+]i elevation. The significance of CD4 molecules in murine T cell activation was discussed. 相似文献
37.
Location of a synergistic factor in the capsule of a granulosis virus of the armyworm, Pseudaletia unipuncta 总被引:2,自引:0,他引:2
A synergistic factor (SyF), which enhanced the infection of nuclear polyhedrosis viruses, was purified from capsules of a Pseudaletia unipuncta granulosis virus (Hawaiian strain) by immune affinity chromatography. The isolated SyF consisted primarily of a protein with molecular mass 98 kDa. The recovery rate depended on the alkali used to dissolve the capsules: the highest rate occurred with 0.05 M Na2CO3-0.05 M NaCl, followed in turn with 0.02-0.05 M NaOH and 0.04 M NaOH-0.05 M glycine. The solubilized components from untreated capsules contained 98- and 100-kDa proteins in addition to the matrix protein (29 kDa) and its decomposed products, while those from heat-treated capsules contained only the 100-kDa protein. Virons liberated from the capsules with the glycine buffer contained three proteins (33, 98, and 100 kDa) serologically related to the SyF. Immunoelectron microscopy of infected tissue and purified virions revealed the localization of the SyF antigens on the viral envelope. 相似文献
38.
T Iida T Momose T Tamura T Matsumoto F C Chang J Goto T Nambara 《Journal of lipid research》1989,30(8):1267-1279
The complete set of the eight theoretically possible stereoisomeric 3,6,7-trihydroxy-5 beta-cholanic acids, four of which are new, related to hyocholic and muricholic acids were prepared from chenodeoxycholic acid. The principal reactions used were 1) cis-dihydroxylation of delta 6-compounds with osmium tetroxide/N-methylmorpholine N-oxide; 2) trans-dihydroxylation of 6 alpha, 7 alpha-epoxy compounds with boron trifluoride etherate in N,N-dimethyl-formamide; 3) inversion of equatorial 3 alpha-hydroxylated compounds to the corresponding 3 beta-epimers with diethyl azodicarboxylate/triphenylphosphine/formic acid; and 4) stereoselective reduction of 7-keto derivatives with zinc borohydride (or sodium borohydride) and by metallic potassium/tert-amyl alcohol. 相似文献
39.
40.
K Tamura M Kobayashi Y Ishii T Tamura K Hashimoto S Nakamura M Niwa J Zapf 《The Journal of biological chemistry》1989,264(10):5616-5621
Rat insulin-like growth factor-I (IGF-I), a serum polypeptide with growth promoting activity, was isolated from rat serum by a combination of acid/ethanol extraction, affinity chromatography, and a series of reversed phase high performance liquid chromatography, cation exchange, and reversed phase. All peptide fragments produced by chymotrypsin digestion of reduced and carboxymethylated rat IGF-I were amino acid sequenced and compared with the sequence of human IGF-I. Three out of 70 of the rat amino acid residues differed from those of human IGF-I as follows: Asp20----Pro, Ser35----Ile and Ala67----Thr. Purified rat IGF-I cross-reacted with polyclonal anti-human IGF-I antibody 75% as compared to human IGF-I, but it cross-reacted only 3% with monoclonal anti-human IGF-I antibody. Thus, it is possible to monitor the metabolic fate of human IGF-I, when injected into rats, without interference by endogenous rat IGF-I. Rat IGF-I showed 65% activity in the radioreceptor, 28.6% activity in the lipogenesis and 22.5% activity in the free fatty acid release inhibition assays as compared to human IGF-I on a protein quantity basis. 相似文献