全文获取类型
收费全文 | 2977篇 |
免费 | 249篇 |
国内免费 | 2篇 |
专业分类
3228篇 |
出版年
2023年 | 9篇 |
2022年 | 11篇 |
2021年 | 19篇 |
2020年 | 14篇 |
2019年 | 34篇 |
2018年 | 45篇 |
2017年 | 30篇 |
2016年 | 49篇 |
2015年 | 89篇 |
2014年 | 91篇 |
2013年 | 140篇 |
2012年 | 207篇 |
2011年 | 181篇 |
2010年 | 138篇 |
2009年 | 128篇 |
2008年 | 163篇 |
2007年 | 190篇 |
2006年 | 195篇 |
2005年 | 193篇 |
2004年 | 182篇 |
2003年 | 174篇 |
2002年 | 151篇 |
2001年 | 41篇 |
2000年 | 24篇 |
1999年 | 31篇 |
1998年 | 51篇 |
1997年 | 33篇 |
1996年 | 34篇 |
1995年 | 47篇 |
1994年 | 33篇 |
1993年 | 42篇 |
1992年 | 40篇 |
1991年 | 22篇 |
1990年 | 27篇 |
1989年 | 34篇 |
1988年 | 20篇 |
1987年 | 13篇 |
1986年 | 17篇 |
1985年 | 20篇 |
1984年 | 26篇 |
1983年 | 25篇 |
1982年 | 26篇 |
1981年 | 19篇 |
1980年 | 23篇 |
1979年 | 11篇 |
1978年 | 25篇 |
1977年 | 16篇 |
1976年 | 13篇 |
1974年 | 12篇 |
1973年 | 7篇 |
排序方式: 共有3228条查询结果,搜索用时 0 毫秒
951.
Summary The baso-lateral cell-membrane area in kidney tubules appears to be associated with the capacity for electrolyte transport; in the rabbit, it decreases from the distal convoluted tubule (DCT-cells) over the connecting tubule (CNT-cells) to the cortical collecting duct (principal cells).Adaptation to low Na-, high K-intake changes this pattern: CNT-cells at the beginning of the connecting tubule have the highest membrane area, which decreases along the segment, but remains two-fold higher than in controls. Principal cells have a four-fold higher membrane area than in controls. Simultaneous treatment with the antimineralocorticoid canrenoate-K inhibits the structural changes in CNT-cells only in end-portions of the connecting tubule and in principal cells.After prolonged high Na-, low K-intake DCT-cells display a two-fold higher membrane area than controls, while CNT-cells and principal cells are not affected. Simultaneous treatment with DOCA does not affect the DCT-cells but provokes a moderate increase in membrane area in CNT-cells, and a 5.5-fold increase in principal cells.The data provide evidence that DCT-, CNT- and principal cells are functionally different cell types. The baso-lateral cell-membrane area, associated with electrolyte-transport capacity, appears to be influenced in DCT-cells mainly by Na-intake, in CNT-cells mainly by K-intake and in part also by mineralocorticoids, and in principal cells mainly by mineralocorticoids.Supported by SFB90, CARVAS, Heidelberg and Swiss National Science Foundation, Grant No. 3.900-0.79 相似文献
952.
953.
Brigitte M. Frey Felix J. Frey 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1982,229(2)
We describe the first method for routine measurement of prednisone, prednisolone and 6β-hydroxyprednisolone concomitantly in urine. Urine (3 ml) is extracted with ethyl acetate, washed with base and separated by high-performance liquid chromatography on a silica column with a solvent system of hexane—diethyl ether—ethanol—tetrahydrofuran—glacial acetic acid (59.9:31:2.3:6.5:0.3, v/v). The steroids are detected at 254 nm. Because no conventional internal standard was found, 6β-[3H]hydroxycortisol and [3H]prednisolone are added to urine prior to extraction; 3H is monitored by a radioactivity detector coupled with the chromatograph. The assay exhibits linearity from 200 to 7500 ng and an inter-day variability of < 11.4% (C.V.). 相似文献
954.
Abstract: Primary cultures prepared from newborn rat brain were grown for 16 or 17 days in culture. Addition of brain extract from newborn rats to the medium stimulated the maturation of astrocytes and the development of oligodendrocytes. Both cell types were characterized by morphology and by immunohistochemistry. The phospholipid composition of these cells was estimated. Incubations were performed with l-[3 H]alkyl- sn -glycerophosphoethanolamine in varying concentrations for 3 h. About one-third of the substrate supplied was internalized by the cells. Several enzymic reactions were observed. The acylating enzyme system was the most active one—a K m was determined with 5 nmol intracellular 1-alkyl- sn -glycerophosphoethanolamine/mg cell protein. Plasmalogen formation was rather low. 1-Alkyl- sn -glycerol, a hydrolysis product, was found in small amounts. Some radioactivity was also incorporated into the phosphatidylcholine fraction. 相似文献
955.
956.
Simian Immunodeficiency Virus (SIV) from Sun-Tailed Monkeys (Cercopithecus solatus): Evidence for Host-Dependent Evolution of SIV within the C. lhoesti Superspecies 下载免费PDF全文
Brigitte E. Beer Elizabeth Bailes Robert Goeken George Dapolito Cheik Coulibaly Stephen G. Norley Reinhard Kurth Jean-Pierre Gautier Annie Gautier-Hion Dominique Vallet Paul M. Sharp Vanessa M. Hirsch 《Journal of virology》1999,73(9):7734-7744
Recently we reported the characterization of simian immunodeficiency virus (SIVlhoest) from a central African l'hoest monkey (Cercopithecus lhoesti lhoesti) that revealed a distant relationship to SIV isolated from a mandrill (SIVmnd). The present report describes a novel SIV (SIVsun) isolated from a healthy, wild-caught sun-tailed monkey (Cercopithecus lhoesti solatus), another member of the l'hoest superspecies. SIVsun replicated in a variety of human T-cell lines and in peripheral blood mononuclear cells of macaques (Macaca spp.) and patas monkeys (Erythrocebus patas). A full-length infectious clone of SIVsun was derived, and genetic analysis revealed that SIVsun was most closely related to SIVlhoest, with an amino acid identity of 71% in Gag, 73% in Pol, and 67% in Env. This degree of similarity is reminiscent of that observed between SIVagm isolates from vervet, grivet, and tantalus species of African green monkeys. The close relationship between SIVsun and SIVlhoest, despite their geographically distinct habitats, is consistent with evolution from a common ancestor, providing further evidence for the ancient nature of the primate lentivirus family. In addition, this observation leads us to suggest that the SIVmnd lineage should be designated the SIVlhoest lineage. 相似文献
957.
David Dauvillée Christophe Colleoni Eudean Shaw Gregory Mouille Christophe D''Hulst Matthew Morell Michael S. Samuel Brigitte Bouchet Daniel J. Gallant Anthony Sinskey Steven Ball 《Plant physiology》1999,119(1):321-330
We isolated two muskmelon (Cucumis melo) cDNA homologs of the Arabidopsis ethylene receptor genes ETR1 and ERS1 and designated them Cm-ETR1 (C. melo ETR1; accession no. AF054806) and Cm-ERS1 (C. melo ERS1; accession no. AF037368), respectively. Northern analysis revealed that the level of Cm-ERS1 mRNA in the pericarp increased in parallel with the increase in fruit size and then markedly decreased at the end of enlargement. In fully enlarged fruit the level of Cm-ERS1 mRNA was low in all tissues, whereas that of Cm-ETR1 mRNA was very high in the seeds and placenta. During ripening Cm-ERS1 mRNA increased slightly in the pericarp of fruit before the marked increase of Cm-ETR1 mRNA paralleled climacteric ethylene production. These results indicate that both Cm-ETR1 and Cm-ERS1 play specific roles not only in ripening but also in the early development of melon fruit and that they have distinct roles in particular fruit tissues at particular developmental stages. 相似文献
958.
Jonathan L. Heeney Gerrit Koopman Brigitte Rosenwirth Willy Bogers Jeanette van Dijk Ivonne Nieuwenhuis Henk Niphuis Peter ten Haaft Thomas Hanke Gary Rhodes Peter Berglund Arsene Burny Francoise Bex Gerd Sutter & Peter Liljeström 《Journal of medical primatology》1999,29(3-4):268-273
A large number of recombinant of viral and bacterial systems have been engineered as vectors to express foreign genes for vaccination and/or gene therapy. A common problem is the immune response to the vector itself. The presence of anti-vector immune responses may preclude sufficient 'priming' or immunogenicity if pre-existing immune responses are present, or they may impair optimal 'boosting' upon repeated immunization or delivery with the same vector. To circumvent this problem we developed a strategy using different chimeric vectors which share only the expression of common specific antigens desired for immunization. This approach not only has the advantage of avoiding increased anti-vector responses, but allows the use of combinations of vectors which could subsequently present the same or related antigen differently to the immune system as well as at alternative sites to induce the optimal type of immunity against the pathogen of interest. 相似文献
959.
960.