全文获取类型
收费全文 | 504784篇 |
免费 | 45620篇 |
国内免费 | 250篇 |
出版年
2018年 | 6121篇 |
2017年 | 5872篇 |
2016年 | 9209篇 |
2015年 | 14552篇 |
2014年 | 15259篇 |
2013年 | 19293篇 |
2012年 | 21456篇 |
2011年 | 18890篇 |
2010年 | 12986篇 |
2009年 | 11135篇 |
2008年 | 15337篇 |
2007年 | 15650篇 |
2006年 | 14529篇 |
2005年 | 19262篇 |
2004年 | 17468篇 |
2003年 | 15314篇 |
2002年 | 12764篇 |
2001年 | 20927篇 |
2000年 | 20563篇 |
1999年 | 16872篇 |
1998年 | 5208篇 |
1997年 | 5218篇 |
1996年 | 4895篇 |
1995年 | 4661篇 |
1994年 | 4603篇 |
1993年 | 4284篇 |
1992年 | 14050篇 |
1991年 | 13655篇 |
1990年 | 13198篇 |
1989年 | 12666篇 |
1988年 | 11844篇 |
1987年 | 10984篇 |
1986年 | 10005篇 |
1985年 | 9989篇 |
1984年 | 7887篇 |
1983年 | 6787篇 |
1982年 | 4890篇 |
1981年 | 4373篇 |
1980年 | 4008篇 |
1979年 | 7524篇 |
1978年 | 5611篇 |
1977年 | 5014篇 |
1976年 | 4632篇 |
1975年 | 5456篇 |
1974年 | 5765篇 |
1973年 | 5722篇 |
1972年 | 5212篇 |
1971年 | 4630篇 |
1970年 | 4187篇 |
1969年 | 3981篇 |
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
991.
Tarun K. Dam Manju Sarkar Jharna Ghosal Amalesh Choudhury 《Molecular and cellular biochemistry》1992,117(1):1-9
Control Analysis has been carried out in the first steps of a rat liver glycolytic system. Attention has been focused on the effect of several glucose concentrations on the control, particularly regarding the role of glucokinase. From kinetic studies of the whole metabolic system we have obtained information on the flux variation under different glucose concentrations. This information together with the kinetics of glucokinase has allowed us to calculate Flux Control and Elasticity Coefficients for glucokinase and the Response Coefficient of the system with respect to glucose. The changes in of the value of Flux Control Coefficients demonstrates that in conditions of low glucose concentration, glucokinase is the main enzyme in controlling the flux through the pathway, but at high glucose concentration the control moves to phosphofructokinase. Next, we have compared our results with those obtained with the shortening and titration method, previously described (Torres, N.V., Mateo, F., Mélendez-Hevia, E. and Kacser, H., (1986) Biochem. J. 234, 169–174; Torres, N.V. and Meléndez-Hevia, E. 1991. Molec. Cell. Biochem. 101, 1–10). Furthermore, from knowledge of the enzyme kinetics of the system we have been able to build a model of the pathway that allows us computer similation of its behavior and calculation of the Flux Control Coefficient profile at different glucose concentrations. By the three methods the results correlate, supporting the use of the pathway substrate as external modulator of the metabolic system as a tool for practical application of Control Analysis. 相似文献
992.
993.
F. Šrámek 《Biologia Plantarum》1999,42(4):582-582
994.
T. R. FRASIER T. RASTOGI M. W. BROWN P. K. HAMILTON S. D. KRAUS B. N. WHITE 《Molecular ecology resources》2006,6(4):1025-1029
A North Atlantic right whale (Eubalaena glacialis) genomic library was developed and screened with a (GATA)8 probe to identify tetranucleotide microsatellite loci. Sixteen characterized loci were polymorphic in North Atlantic and/or South Atlantic (Eubalaena australis) right whales, 12 being polymorphic in E. glacialis, and 15 in E. australis. Fourteen of these were combined with 21 other previously identified loci for a suite of 35 loci which can be used to increase resolution of genetic analyses of these species. Multiplex reactions were developed for genotyping samples at these loci, providing a method that is rapid, reliable and cost‐effective. 相似文献
995.
A RAPD marker specific for the G genome of wheat was identified. The corresponding 1171-bp DNA sequence was cloned and analyzed. Screening of the database did not reveal any homologies with the known plant DNA sequences. Using the primers specific to the flanking regions of the marker sequence, PCR analysis of the polyploid wheat species and the diploid species of the section Sitopsis was carried out. In addition, using the cloned sequence as a molecular hybridization probe, RFLP analysis of the genomic DNA of these species was performed. 相似文献
996.
997.
N. A. Volkova N. A. Zinovieva L. A. Volkova L. K. Ernst 《Russian Journal of Genetics》2006,42(1):72-75
The data on the in vitro and in vivo (into embryonic disk) retroviral-mediated transfer of genetic information into chicken embryonic cells are presented. The estimated transformation frequency of the cultured target cells constituted 8 × 10?4 to 5 × 10?3. A transgenic rooster, carrying recombinant DNA in blood, heart, liver, and intestine cells, was obtained. 相似文献
998.
Acquisition of Resistance to Extended-Spectrum Cephalosporins by Salmonella enterica subsp. enterica Serovar Newport and Escherichia coli in the Turkey Poult Intestinal Tract 下载免费PDF全文
999.
K R Chintalacharuvu J F Piskurich M E Lamm C S Kaetzel 《Journal of cellular physiology》1991,148(1):35-47
The HT-29 human colon carcinoma cell line differentiates in glucose-free medium to an enterocytic phenotype. We previously isolated a series of HT-29 subclones selected for high levels of expression of secretory component (SC), the epithelial receptor for polymeric immunoglobulins. To develop a model system for studying effects of cell polarity on SC expression and release from the cell surface, the HT-29.74 subclone was induced to differentiate in glucose-free medium. Expression of SC was induced by glucose deprivation in both the parental HT-29 cell line and, to an even greater extent, in the HT-29.74 subclone. Prolonged glucose deprivation of HT-29.74 cells resulted in morphological changes consistent with enterocytic differentiation. Metabolic radiolabeling of SC in differentiated HT-29.74 cells indicated that proteolytic cleavage of membrane-bound to free SC occurred both on the cell surface and intracellularly, possibly in a vacuolar apical compartment or intrapeithelial lumen. To study effects of cell polarity on SC release, differentiated HT-29.74 cells were depolarized by culturing in low calcium medium. Within 2 hours after transfer of the cells into low calcium medium, a burst of SC release was observed concomitant with cell depolarization. Subsequently, release of SC declined significantly and remained low as long as cells were maintained in a depolarized state. The extent of cell depolarization could be controlled by varying the extracellular calcium concentration or by substituting the divalent cation Sr++, which partially prevents depolarization, for Ca++. In either case, the magnitude of the initial burst and subsequent decline in release of SC was proportional to the extent of cell depolarization. We conclude that cell polarity plays an important role in controlling the release of SC in intestinal epithelial cells, most likely by regulating the distribution of membrane-bound SC and SC protease, which are on the basolateral and apical cell surfaces, respectively, in differentiated cells. 相似文献
1000.
Genotoxicity of ptaquiloside, a bracken carcinogen, in the hepatocyte primary culture/DNA-repair test 总被引:2,自引:0,他引:2
The genotoxicity of ptaquiloside (PT), recently isolated from bracken fern and shown to be carcinogenic, was examined by means of the hepatocyte primary culture/DNA-repair test. PT elicited clear unscheduled DNA synthesis with a dose-response effect. The result indicates that PT is a genotoxic carcinogen. 相似文献