全文获取类型
收费全文 | 1525篇 |
免费 | 9篇 |
专业分类
系统科学 | 22篇 |
丛书文集 | 1篇 |
理论与方法论 | 10篇 |
现状及发展 | 845篇 |
研究方法 | 150篇 |
综合类 | 501篇 |
自然研究 | 5篇 |
出版年
2018年 | 23篇 |
2017年 | 15篇 |
2016年 | 21篇 |
2015年 | 11篇 |
2014年 | 21篇 |
2013年 | 19篇 |
2012年 | 56篇 |
2011年 | 72篇 |
2010年 | 36篇 |
2009年 | 14篇 |
2008年 | 87篇 |
2007年 | 73篇 |
2006年 | 82篇 |
2005年 | 68篇 |
2004年 | 60篇 |
2003年 | 65篇 |
2002年 | 54篇 |
2001年 | 35篇 |
2000年 | 50篇 |
1999年 | 22篇 |
1996年 | 12篇 |
1995年 | 11篇 |
1994年 | 19篇 |
1993年 | 10篇 |
1985年 | 12篇 |
1984年 | 14篇 |
1982年 | 14篇 |
1981年 | 13篇 |
1980年 | 27篇 |
1979年 | 16篇 |
1978年 | 17篇 |
1977年 | 16篇 |
1976年 | 20篇 |
1975年 | 21篇 |
1973年 | 23篇 |
1972年 | 23篇 |
1971年 | 31篇 |
1970年 | 24篇 |
1969年 | 22篇 |
1968年 | 24篇 |
1967年 | 25篇 |
1966年 | 22篇 |
1965年 | 19篇 |
1964年 | 15篇 |
1963年 | 15篇 |
1961年 | 13篇 |
1957年 | 9篇 |
1956年 | 12篇 |
1948年 | 11篇 |
1947年 | 12篇 |
排序方式: 共有1534条查询结果,搜索用时 250 毫秒
1.
2.
3.
4.
Hellgren M Strömberg P Gallego O Martras S Farrés J Persson B Parés X Höög JO 《Cellular and molecular life sciences : CMLS》2007,64(4):498-505
The metabolism of all-trans- and 9-cis-retinol/ retinaldehyde has been investigated with focus on the activities of human, mouse and rat alcohol dehydrogenase 2
(ADH2), an intriguing enzyme with apparently different functions in human and rodents. Kinetic constants were determined with
an HPLC method and a structural approach was implemented by in silico substrate dockings. For human ADH2, the determined Km values ranged from 0.05 to 0.3 μM and kcat values from 2.3 to 17.6 min−1, while the catalytic efficiency for 9-cis-retinol showed the highest value for any substrate. In contrast, poor activities
were detected for the rodent enzymes. A mouse ADH2 mutant (ADH2Pro47His) was studied that resembles the human ADH2 setup.
This mutation increased the retinoid activity up to 100-fold. The Km values of human ADH2 are the lowest among all known human retinol dehydrogenases, which clearly support a role in hepatic
retinol oxidation at physiological concentrations.
Received 12 October 2006; received after revision 6 December 2006; accepted 8 January 2007 相似文献
5.
6.
Lindahl E Nyman U Melles E Sigmundsson K Ståhlberg M Wahren J Obrink B Shafqat J Joseph B Jörnvall H 《Cellular and molecular life sciences : CMLS》2007,64(4):479-486
Proinsulin C-peptide is known to bind specifically to cell membranes and to exert intracellular effects, but whether it is
internalized in target cells is unknown. In this study, using confocal microscopy and immunostained or rhodamine-labeled peptide,
we show that C-peptide is internalized and localized to the cytosol of Swiss 3T3 and HEK-293 cells. In addition, transport
into nuclei was found using the labeled peptide. The internalization was followed at 37°C for up to 1 h, and was reduced at
4°C and after preincubation with pertussis toxin. Hence, it is concluded to occur via an energy-dependent, pertussis toxin-sensitive
mechanism and without detectable degradation within the experimental time course. Surface plasmon resonance measurements demonstrated
binding of HEK-293 cell extract components to C-peptide, and subsequent elution of bound material revealed the components
to be intracellular proteins. The identification of C-peptide cellular internalization, intracellular binding proteins, absence
of rapid subsequent C-peptide degradation and apparent nuclear internalization support a maintained activity similar to that
of an intracrine peptide hormone. Hence, the data suggest the possibility of one further C-peptide site of action.
Received 31 October 2006; received after revision 27 December 2006; accepted 30 December 2006 相似文献
7.
Astacin, a digestive zinc-endopeptidase from the crayfish Astacus astacus L., is the prototype for the 'astacin family', which includes mammalian metallo-endopeptidases and developmentally regulated proteins of man, fruitfly, frog and sea urchin. Here we report the X-ray crystal structure of astacin, which reveals a deep active-site cleft, with the zinc at its bottom ligated by three histidines, a water molecule and a more remote tyrosine. The third histidine (His 102) forms part of a consensus sequence, shared not only by the members of the astacin family, but also by otherwise sequentially unrelated proteinases, such as vertebrate collagenases. It may therefore represent the elusive 'third' zinc ligand in these enzymes. The amino terminus of astacin is buried forming an internal salt-bridge with Glu 103, adjacent to His 102. Astacin pro-forms extended at the N terminus, as observed for some 'latent' mammalian astacin homologues, did not exhibit this 'active' conformation, indicating an activation mechanism reminiscent of trypsin-like serine proteinases. 相似文献
8.
Crnković-Mertens I Wagener N Semzow J Gröne EF Haferkamp A Hohenfellner M Butz K Hoppe-Seyler F 《Cellular and molecular life sciences : CMLS》2007,64(9):1137-1144
Cancer cells are typically characterized by apoptosis deficiency. In order to investigate a possible role for the anti-apoptotic
livin gene in renal cell cancer (RCC), we analyzed its expression in tumor tissue samples and in RCC-derived cell lines. In addition,
we studied the contribution of livin to the apoptotic resistance of RCC cells by RNA interference (RNAi). Livin gene expression was detected in a significant portion of RCC tumor tissue specimens (13/14, 92.9%) and tumor-derived cell
lines (12/15, 80.0%). Moreover, targeted inhibition of livin by RNAi markedly sensitized RCC cells towards proapoptotic stimuli, such as UV irradiation or the chemotherapeutic drugs
etoposide, 5-fluorouracil, and vinblastine. These effects were specific for livin expressing tumor cells. We conclude that livin can contribute significantly to the apoptosis resistance of RCC cells. Targeted inhibition of livin could represent a novel therapeutic strategy to increase the sensitivity of renal cancers towards pro-apoptotic agents.
Received 30 November 2006; received after revision 22 February 2007; accepted 20 March 2007 相似文献
9.
Gösta Lindeberg 《Cellular and molecular life sciences : CMLS》1948,4(12):476-477
Zusammenfassung Es wurde die Zugkraft nasser Flachsfasern nach Behandlung mit verschiedenen Chemikalien geprüft. Es wurde gefunden, daß die Mittellamelle der Flachsfaser verschiedene miteinander verbundene Systeme enthält, nämlich Pektin, Lignin und eine im Oxalat unlös iche alkaliempfindliche Komponente. 相似文献
10.
感应电会对人体造成伤害。从电磁感应和静电感应原理入手,分析了产生感应电的过程,并就如何防止感应电的危害提出了防护对策,有一定实用价值。 相似文献