全文获取类型
收费全文 | 3570篇 |
免费 | 274篇 |
出版年
2023年 | 20篇 |
2022年 | 40篇 |
2021年 | 86篇 |
2020年 | 65篇 |
2019年 | 75篇 |
2018年 | 103篇 |
2017年 | 100篇 |
2016年 | 135篇 |
2015年 | 178篇 |
2014年 | 201篇 |
2013年 | 252篇 |
2012年 | 266篇 |
2011年 | 272篇 |
2010年 | 145篇 |
2009年 | 139篇 |
2008年 | 170篇 |
2007年 | 165篇 |
2006年 | 163篇 |
2005年 | 141篇 |
2004年 | 130篇 |
2003年 | 125篇 |
2002年 | 107篇 |
2001年 | 86篇 |
2000年 | 102篇 |
1999年 | 70篇 |
1998年 | 33篇 |
1997年 | 26篇 |
1996年 | 23篇 |
1995年 | 26篇 |
1994年 | 21篇 |
1993年 | 17篇 |
1992年 | 27篇 |
1991年 | 29篇 |
1990年 | 22篇 |
1989年 | 27篇 |
1988年 | 21篇 |
1987年 | 23篇 |
1986年 | 17篇 |
1985年 | 15篇 |
1984年 | 24篇 |
1983年 | 11篇 |
1982年 | 13篇 |
1981年 | 15篇 |
1979年 | 11篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1974年 | 13篇 |
1973年 | 19篇 |
1972年 | 7篇 |
1970年 | 8篇 |
排序方式: 共有3844条查询结果,搜索用时 15 毫秒
1.
2.
Margarida A. Ferreira M.Aurea Cruz Costa A.Correia Alves M.Helena Lopes 《Phytochemistry》1973,12(2):433-435
7-MethyljugIone, 8,8′-dihydroxy-4,4′-dimethoxy-6,6′-dimethyl-2,2′-binaphthyl-1,1′-quinone, 2-methylnaphthazarin, mamegakinone and euclein have been isolated from Euclea pseudebenus. Euclein is the 3,6′-dimer of 7-methyljuglone. 相似文献
3.
4.
5.
Natural antibodies to interferon-gamma 总被引:3,自引:0,他引:3
Natural antibodies to interferon (IFN)-γ were detected in the serum of virus-infected patients and also, at a low titre, in
the serum of healthy subjects. The increased titre of antibodies to IFN-γ in the sera of virus-infected patients, and its
decrease with clinical resolution, indicate that these antibodies are related to viral infection and probably reflect IFN-γ
production as a result of antigenic stimulationin vivo. Natural antibodies to IFN-γ were affinity purified and studied for their capability to interferein vitro with the multiple activities of the lymphokine. Data obtained show that these human anti-IFN-γ antibodies have no inhibitory
effect on the antiviral and antiproliferative activity of IFN-γ and do not interfere with the binding of the lymphokine to
its specific cell receptor. Instead, they can inhibit the expression of HLA-DR antigens induced by IFN-γ on U937 cells and
interfere, in mixed lymphocyte culture, with the proliferation of lymphocytes and the generation of cytotoxic lymphocytes.
Experiments in animal models suggest that natural antibodies to IFN-γ may have a role in the immunoregulatory process limiting
the intensity and/or duration of immune response. As they can interfere only with the immunomodulating activities of IFN-γ,
these antibodies might open up new therapeutic approaches to diseases with evidence of activated cell-mediated immunity. 相似文献
6.
7.
Levans produced by four Zymomonas mobilis strains showed antitumour activity against sarcoma 180 and Ehrlich carcinoma in Swiss albino mice. Levans from two strains (ZAP and CP4) had the highest effects. NMR analysis showed that the polymers were composed only of fructose units. The results suggested that the antineoplasic effect is associated to the polysaccharide molecular weight and that a particular molecular weight range may be responsible for this effect. 相似文献
8.
Ethanol Administration in the Rat Decreases Prostacyclin Production by Isolated Brain Microvessels 总被引:1,自引:0,他引:1
The effects of short- and long-term ethanol administration to rats on basal levels and formation of prostacyclin (PGI2) measured as 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha), and on lipid class content and fatty acid composition of isolated brain microvessels (BMV) were studied. After acute treatment (2 h, at the peak of plasma ethanol concentration) basal 6-keto-PGF1 alpha levels in BMV and release on incubation were reduced to 50% of control values. After chronic administration (15 days), PGI2 release was reduced to about 40% of control values, without changes in basal levels. Total lipid, phospholipid, and cholesterol levels in BMV, measured after prolonged administration of alcohol, were not modified. Also, only minor changes in the fatty acid composition of individual phospholipid classes were detected. The observed reduction of PGI2 synthesis in BMV thus could not be related to changes of the fatty acid precursor pool in the preparation. Precursor release and/or the biosynthetic pathways may be affected by ethanol administration. 相似文献
9.
The potential association between integration or deletion of mouse mammary tumor virus (MMTV) retroviral sequences and the appearance of non-H-2 histocompatibility (H) antigen mutations was investigated. Genomic blots from inbred strains carrying 22 loss, gain-loss, and gain mutations on the BALB/c and C57BL/6 backgrounds were hybridized with probes homologous to the long terminal repeat (LTR) and envelope (env) regions of MMTV. Twenty-one mutants were identical in restriction patterns to the respective background strains with all tested restriction enzymes and both probes. However, genomic blots of one gain mutant, B6.C-KH-84, exhibited restriction fragments which were not exhibited by either of the parental strains, C57BL/6 or BALB/c. An additional 5.5 kb Eco RI fragment was observed with the env probe and additional 9.2 kb and 5.5 kb fragments were observed with the LTR probe. These observations were substantiated by hybridization of these two probes with genomic blots generated with additional restriction enzymes. Assuming that the new provirus contains a single, internal Eco RI site as has been observed for other MMTV proviral sequences, it is presumed that the new provirus includes both 5 and 3 LTRs in addition to the env region. Based on the unique sizes of the observed restriction fragments relative to other identified MMTV proviral sequences, this provirus has been designated Mtv-22. The potential role of Mtv-22 in the genesis of the gained histocompatibility antigen in B6.C-KH-84 is discussed.On leave of absence from Istituto Nazionale per to Studio e la Cura dei Tumori, Milano, Italy 相似文献
10.
Addition of 200 mm of a polyol to anthocyanin containing carrot (Daucus carota L.) cells in suspension culture decreased turgor pressure to zero and induced hyperpolarization of the membrane potential and acidification of the medium due to H+ extrusion. These changes were shown to be slightly affected by vanadate. In parallel, a decrease in intracellular ATP and total adenylate concentrations were observed. However, when the osmoticum was NaCl acidification of the medium occurred in the absence of considerable changes in intracellular ATP concentration. These results are interpreted as indicating that a drop of turgor, by addition of a polyol, triggers a proton extrusion activity which is only slightly inhibited by vanadate but apparently ATP utilizing. The observed decrease in ATP level occurs without a change in respiration rate and is accompanied by a drop in total adenylate pool. However when NaCl is the osmoticum it is assumed that ΔμH+ is enhanced through a Na+/H+ antiporter. The difference between the two types of osmotica as related to their ability to penetrate through the cellular membrane is discussed. 相似文献