全文获取类型
收费全文 | 44792篇 |
免费 | 4174篇 |
国内免费 | 33篇 |
专业分类
48999篇 |
出版年
2022年 | 274篇 |
2021年 | 608篇 |
2020年 | 338篇 |
2019年 | 412篇 |
2018年 | 559篇 |
2017年 | 514篇 |
2016年 | 930篇 |
2015年 | 1597篇 |
2014年 | 1746篇 |
2013年 | 2214篇 |
2012年 | 2779篇 |
2011年 | 2845篇 |
2010年 | 1867篇 |
2009年 | 1804篇 |
2008年 | 2620篇 |
2007年 | 2631篇 |
2006年 | 2574篇 |
2005年 | 2530篇 |
2004年 | 2470篇 |
2003年 | 2432篇 |
2002年 | 2379篇 |
2001年 | 516篇 |
2000年 | 394篇 |
1999年 | 573篇 |
1998年 | 682篇 |
1997年 | 483篇 |
1996年 | 438篇 |
1995年 | 419篇 |
1994年 | 406篇 |
1993年 | 410篇 |
1992年 | 351篇 |
1991年 | 332篇 |
1990年 | 343篇 |
1989年 | 260篇 |
1988年 | 303篇 |
1987年 | 283篇 |
1986年 | 279篇 |
1985年 | 347篇 |
1984年 | 390篇 |
1983年 | 345篇 |
1982年 | 447篇 |
1981年 | 438篇 |
1980年 | 420篇 |
1979年 | 287篇 |
1978年 | 308篇 |
1977年 | 273篇 |
1976年 | 280篇 |
1975年 | 216篇 |
1974年 | 291篇 |
1973年 | 261篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Victoria V. Hargreaves Scarlet S. Shell Dan J. Mazur Martin T. Hess Richard D. Kolodner 《The Journal of biological chemistry》2010,285(12):9301-9310
Indirect evidence has suggested that the Msh2-Msh6 mispair-binding complex undergoes conformational changes upon binding of ATP and mispairs, resulting in the formation of Msh2-Msh6 sliding clamps and licensing the formation of Msh2-Msh6-Mlh1-Pms1 ternary complexes. Here, we have studied eight mutant Msh2-Msh6 complexes with defective responses to nucleotide binding and/or mispair binding and used them to study the conformational changes required for sliding clamp formation and ternary complex assembly. ATP binding to the Msh6 nucleotide-binding site results in a conformational change that allows binding of ATP to the Msh2 nucleotide-binding site, although ATP binding to the two nucleotide-binding sites appears to be uncoupled in some mutant complexes. The formation of Msh2-Msh6-Mlh1-Pms1 ternary complexes requires ATP binding to only the Msh6 nucleotide-binding site, whereas the formation of Msh2-Msh6 sliding clamps requires ATP binding to both the Msh2 and Msh6 nucleotide-binding sites. In addition, the properties of the different mutant complexes suggest that distinct conformational states mediated by communication between the Msh2 and Msh6 nucleotide-binding sites are required for the formation of ternary complexes and sliding clamps. 相似文献
3.
Cynthia L. Deitrick Richard E. Katholi David J. Huddleston Kathy Hardiek Lucienne Burrus 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2001,751(2)
Vitamin B6, measured as pyridoxal 5′-phosphate (PLP), is a co-enzyme in the transsulfuration pathway of homocysteine metabolism. Since depletion of PLP has been suggested as an independent risk factor for coronary artery disease, PLP is frequently measured to guide patient care. By a change and utilization of an Aquasil C18 column and the addition of an acetonitrile clean-up gradient to the potassium phosphate, with sodium perchlorate and bisulfite buffer between samples we report the modification of a previously described method for analysis of PLP. The result is a more practical, efficient, reliable and robust method for daily clinical use. We also determined and report that it is critical to protect freshly prepared standard PLP samples from light exposure during assay preparation. 相似文献
4.
Richard D. Gregory 《Ecography》1998,21(1):92-96
5.
The oxidative half-reaction of phenol hydroxylase has been studied by stopped-flow spectrophotometry. Three flavin-oxygen intermediates can be detected when the substrate is thiophenol, or m-NH2, m-OH, m-CH3, m-Cl, or p-OH phenol. Intermediate I, the flavin C(4a)-hydroperoxide, has an absorbance maximum at 380-390 nm and an extinction coefficient approximately 10,000 M-1 cm-1. Intermediate III, the flavin C(4a)-hydroxide, has an absorbance maximum at 365-375 nm and an extinction coefficient approximately 10,000 M-1 cm-1. Intermediate II has absorbance maxima of 350-390 nm and extinction coefficients of 10,000-16,000 M-1 cm-1 depending on the substrate. A Hammett plot of the logarithm of the rates of the oxygen transfer step, the conversion of intermediate I to intermediate II, gives a straight line with a slope -0.5. Fluoride ion is a product of the enzymatic reaction when 2,3,5,6-tetrafluorophenol is the substrate. These results are consistent with an electrophilic substitution mechanism for oxygen transfer. The conversions of I to II and II to III are acid-catalyzed. A kinetic isotope effect of 8 was measured for the conversion of II to III using deuterated resorcinol as substrate. The conversion of III to oxidized enzyme is base-catalyzed, suggesting that the reaction depends on the removal of the flavin N(5) proton. Product release occurs at the same time as the formation of intermediate III, or rapidly thereafter. The results are interpreted according to the ring-opened model of Entsch et al. (Entsch, B., Ballou, D. P., and Massey, V. (1976) J. Biol. Chem. 251, 2550-2563). 相似文献
6.
Concentration factor and biological half-life of 54Mn were determined in three species representing an ecologically and economically important food chain. Green algae (Chlorella spp.), Daphnia magna and yellow perch (Perca flavescens) were exposed to 54Mn in water and assayed for 54Mn uptake. Steady state concentration factors computed from the laboratory data for algae, Daphnia and perch were 4230, 17 000 and 11, respectively. Respective biological half-lives were 1.6, 1.2 and 8.3 days. 相似文献
7.
David M. Anderson Richard H. Scheller James W. Posakony Linda B. McAllister Steven G. Trabert Clifford Beall Roy J. Britten Eric H. Davidson 《Journal of molecular biology》1981,145(1):5-28
Three repetitive sequence families from the sea urchin genome were studied, each defined by homology with a specific cloned probe one to a few hundred nucleotides long. Recombinant λ-sea urchin DNA libraries were screened with these probes, and individual recombinants were selected that include genomic members of these families. Restriction mapping, gel blot, and kinetic analyses were carried out to determine the organization of each repeat family. Sequence elements belonging to the first of the three repeat families were found to be embedded in longer repeat sequences. These repeat sequences frequently occur in small clusters. Members of the second repeat family are also found in a long repetitive sequence environment, but these repeats usually occur singly in any given region of the DNA. The sequences of the third repeat are only 200 to 300 nucleotides long, and are generally terminated by single copy DNA, though a few examples were found associated with other repeats. These three repeat sequence families constitute sets of homologous sequence elements that relate distant regions of the DNA. 相似文献
8.
9.
10.
Richard L. Hughson 《CMAJ》1980,122(10):1115-1119