全文获取类型
收费全文 | 2938篇 |
免费 | 230篇 |
国内免费 | 2篇 |
出版年
2023年 | 18篇 |
2022年 | 13篇 |
2021年 | 69篇 |
2020年 | 51篇 |
2019年 | 54篇 |
2018年 | 58篇 |
2017年 | 44篇 |
2016年 | 73篇 |
2015年 | 143篇 |
2014年 | 165篇 |
2013年 | 178篇 |
2012年 | 276篇 |
2011年 | 231篇 |
2010年 | 153篇 |
2009年 | 128篇 |
2008年 | 201篇 |
2007年 | 176篇 |
2006年 | 152篇 |
2005年 | 137篇 |
2004年 | 117篇 |
2003年 | 105篇 |
2002年 | 99篇 |
2001年 | 41篇 |
2000年 | 23篇 |
1999年 | 23篇 |
1998年 | 20篇 |
1997年 | 9篇 |
1996年 | 9篇 |
1995年 | 17篇 |
1994年 | 10篇 |
1993年 | 11篇 |
1991年 | 18篇 |
1990年 | 13篇 |
1989年 | 9篇 |
1988年 | 9篇 |
1987年 | 13篇 |
1985年 | 14篇 |
1984年 | 17篇 |
1983年 | 17篇 |
1982年 | 15篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 21篇 |
1978年 | 14篇 |
1977年 | 8篇 |
1976年 | 11篇 |
1975年 | 10篇 |
1974年 | 13篇 |
1973年 | 15篇 |
1968年 | 10篇 |
排序方式: 共有3170条查询结果,搜索用时 179 毫秒
71.
72.
73.
Seymour Philps 《BMJ (Clinical research ed.)》1941,2(4212):459-460
74.
75.
In the preceding paper are described the isolation and physical characterization of seven narrowly disperse fractions of calf thymus DNA in the molecular weight range 0.3 to 1.3 × 106 daltons. Herein, we have determined by light scattering the molecular weights and root mean square radii of these fractions in a solvent comprising 0.2 M NaCl, 2 mM EDTA, 2m MNa-PO4, pH 7. Measurements were made in a modified Wippler—Scheibling photometer to a 20° lower limit of scattering angle on solutions rendered virtually dust-free by procedures described. The optical aniso tropics of the DNA fractions were measured permitting the experimental molecular weights and root mean square radii to be corrected to their true values. From these values, with appropriate polydispersity corrections, we calculate a Kratky—Porod persistence length, a, of 54.0 ± 5.6 nm which is invariant over the molecular weight range examined. From the sedimentation coefficients (preceding paper) and the theory of Yamakawa and Fujii, we calculate a to be 66 nm, a value found to apply equally well to several DNA samples of various origins whose sedimentation rates are known in the molecular weight range from about 4 × 104 to 108 daltons. Similarly, from the intrinsic viscosities and the theory of Yamakawa and Fujii, we calculate a to be 59 nm, which again adequately applies to a number of DNA samples whose viscosities have been measured by other workers in the molecular weight range 3 × 105 to 108 daltons. The Flory—Mandelkern parameter, β, was found to vary with molecular weight in the manner predicted by the theory of Yamakawa and Fujii. The average value of a from the three sets of measurements is 60 ± 6 nm, which we believe applies to double-stranded DNA molecules, independent of chain length, over the whole range of molecular weights for which reliable data exist. 相似文献
76.
77.
78.
79.
80.