全文获取类型
收费全文 | 56138篇 |
免费 | 6286篇 |
国内免费 | 19篇 |
出版年
2022年 | 396篇 |
2021年 | 870篇 |
2020年 | 625篇 |
2019年 | 734篇 |
2018年 | 892篇 |
2017年 | 802篇 |
2016年 | 1332篇 |
2015年 | 2187篇 |
2014年 | 2416篇 |
2013年 | 2961篇 |
2012年 | 3595篇 |
2011年 | 3588篇 |
2010年 | 2373篇 |
2009年 | 2106篇 |
2008年 | 2897篇 |
2007年 | 2869篇 |
2006年 | 2677篇 |
2005年 | 2475篇 |
2004年 | 2488篇 |
2003年 | 2228篇 |
2002年 | 2161篇 |
2001年 | 1158篇 |
2000年 | 1162篇 |
1999年 | 1079篇 |
1998年 | 634篇 |
1997年 | 560篇 |
1996年 | 530篇 |
1995年 | 542篇 |
1994年 | 502篇 |
1993年 | 483篇 |
1992年 | 798篇 |
1991年 | 738篇 |
1990年 | 724篇 |
1989年 | 699篇 |
1988年 | 684篇 |
1987年 | 627篇 |
1986年 | 517篇 |
1985年 | 568篇 |
1984年 | 529篇 |
1983年 | 481篇 |
1982年 | 424篇 |
1981年 | 396篇 |
1980年 | 362篇 |
1979年 | 447篇 |
1978年 | 379篇 |
1977年 | 365篇 |
1976年 | 360篇 |
1975年 | 375篇 |
1974年 | 333篇 |
1973年 | 352篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
91.
First appearing in 2000, and with 20,000 copies sold as it entered its sixth printing in 2004, Richard Trudgen's Why Warriors Lie down and Die is a minor publishing phenomenon. Although scholarly forums have generally ignored the book, Christian media outlets, the popular press and neo‐conservative political activists have enthusiastically received and promoted it. An examination of the merits of Why Warriors Lie down and Die suggests that its popularity is only partly explained by original observations or insights on the part of the author. The most important explanation, and implication, of the book's remarkable take‐up lies in the opportune way in which it corresponds with now ascendant neo‐conservative political perspectives on indigenous policy. 相似文献
92.
93.
94.
95.
96.
When the thyroglobulin content is subtracted, actin represents approximately 4.6% of the total protein content in the hog thyroid gland. Actin has been isolated from acetone-dehydrated slices and purified to homogeneity by gel filtration, DEAE-cellulose chromatography and two polymerization-depolymerization cycles. Purified actin (Mr = 42000) contains the beta and gamma species with a 2 to 1 stoichiometry. In the presence of 0.1 M KCl and 2 mM MgCl2 thyroid actin polymerized into 6 nm diameter filaments; under these conditions the critical concentration was 30 micrograms/ml and the intrinsic viscosity 4.7 dl/g. 相似文献
97.
98.
The conformation of Ca4-calmodulin in solution, as assessed by far-UV peptide circular dichroism, contains significantly less alpha-helix than the proposed X-ray crystal structure. We now show that Ca4-calmodulin adopts significant additional helical structure in solution in the presence of a helicogenic solvent (50%, v/v, aqueous 2,2,2-trifluoroethanol or 50%, v/v, methylpentane-5,5-diol). We suggest that the long continuous helix (residues 66-92 of the crystal structure) is not necessarily a normal feature of the calmodulin structure in solution, and may be due in part to the conditions of crystallisation. This result is supported by time-resolved tyrosine fluorescence anisotropy studies indicating that Ca4-calmodulin in solution is an essentially compact globular structure which undergoes isotropic rotational motion. We conclude that, under appropriate ionic and apolar environmental conditions, Ca4-calmodulin undergoes a substantial helical transition, which may involve residues in the central region of the molecule. Such a transition could have an important function in determining specificity and affinity in interactions of calmodulin with different target sequences of Ca2+-dependent regulatory enzymes. 相似文献
99.
Human keratinocytes have been serially cultivated in low (0.015 mM) and high (1.8 mM) calcium containing medium. The calcium concentration of the growth medium significantly influenced the cell growth period in vitro. Cells grown in low calcium medium underwent 35-40 population doublings over 16-17 passages, while cells grown in high calcium medium ceased to proliferate after 20 population doublings over 7 passages. Changing the keratinocytes from one in vitro environment to the other drastically altered the lifespan in culture of populations derived from the same primary tissue. The degree of DNA methylation of human keratinocytes was shown to decrease with age in both high and low calcium culture conditions but does not appear to be associated with differentiation. 相似文献
100.