全文获取类型
收费全文 | 1517篇 |
免费 | 189篇 |
国内免费 | 1篇 |
出版年
2021年 | 18篇 |
2020年 | 11篇 |
2018年 | 17篇 |
2017年 | 21篇 |
2016年 | 37篇 |
2015年 | 47篇 |
2014年 | 61篇 |
2013年 | 83篇 |
2012年 | 71篇 |
2011年 | 85篇 |
2010年 | 69篇 |
2009年 | 59篇 |
2008年 | 65篇 |
2007年 | 59篇 |
2006年 | 82篇 |
2005年 | 67篇 |
2004年 | 63篇 |
2003年 | 55篇 |
2002年 | 48篇 |
2001年 | 46篇 |
2000年 | 47篇 |
1999年 | 33篇 |
1998年 | 12篇 |
1997年 | 24篇 |
1996年 | 14篇 |
1995年 | 12篇 |
1994年 | 15篇 |
1993年 | 10篇 |
1992年 | 24篇 |
1991年 | 34篇 |
1990年 | 25篇 |
1989年 | 21篇 |
1988年 | 31篇 |
1987年 | 22篇 |
1986年 | 16篇 |
1985年 | 20篇 |
1984年 | 16篇 |
1983年 | 26篇 |
1981年 | 11篇 |
1980年 | 13篇 |
1978年 | 10篇 |
1977年 | 18篇 |
1976年 | 13篇 |
1975年 | 11篇 |
1974年 | 9篇 |
1973年 | 19篇 |
1972年 | 11篇 |
1971年 | 14篇 |
1970年 | 15篇 |
1969年 | 18篇 |
排序方式: 共有1707条查询结果,搜索用时 15 毫秒
51.
52.
Robert E. Ferrell Donald C. Morizot Jacqueline Horn Curtis J. Carley 《Biochemical genetics》1980,18(1-2):39-49
The red wolf (Canis rufus), native to much of the southeastern United States, is endangered by man's activities and by hybridization with other species of the genus Canis. The absence of diagnostic morphological markers to distinguish the red wolf from its hybrids has led to the application of the methods of biochemical genetics to this problem. The finding of a unique electrophoretically determined allele with a distribution congruent with the geographical distribution of the remaining red wolf population is reported.This research was supported by NIH Public Health Service Grants GM 19513 and CA 19311 and by the State of Texas. 相似文献
53.
W E Bollenbacher A F Faux M N Galbraith L I Gilbert D H Horn J S Wilkie 《Steroids》1979,34(5):509-526
3 beta, 14 alpha-Dihydroxy-5 alpha-7-en-6-one (5 alpha-ketodiol) (1) is metabolized by the prothoracic glands to 2,22-dideoxy-5 alpha-ecdysone (4) and 2-deoxy-5 alpha-ecdysone (3) but not to ecdysone (5) or any other 5 beta-metabolites. Similarly, 3 beta,5 alpha,14 alpha-trihydroxy-cholest-7-en-6-one (5 alpha-ketotriol) (8) is hydroxylated at C-22 and C-25 (9,10) of the side chain. However, 3 beta,14 alhpa-dihydroxy-cholesta-4,7-diene-6-one (ketodienediol) (11) is not metabolized. The absence of 2 beta-hydroxymetabolites for substrates (1) and (8) implies that hydroxylation at C-2 can occur only when the A-B rings are cis fused (5 beta-configuration). By contrast, the enzyme complexes that introduce hydroxyls at C-22 and C-25 do not exhibit a preference for cis over trans fusion and appraently cannot recognize the planar A-B ring configuration. 相似文献
54.
55.
56.
A method is described for preparation of 1,2-3H-21-deoxycortisol by incubation of 1,2-3H-17-hydroxyprogesterone with rat adrenal mitoochondria. The radiochemical purity of the product was established by two subsequent chromatographies, reversed isotopic dilution and oxidation to 21-deoxycortisone. The final yield of 1,2-3H-21-deoxycortisol was approximately 15%. 相似文献
57.
The distribution of concanavalin A (con A) receptor sites on the membranes of chromaffin granules has been investigated by binding studies using 125I-labelled con A and by electron-microscope studies using ferritin-labelled con A. In both experiments con A was observed to bind to chromaffin granule membranes but not to intact granules. The ferritin-con A particles bind to only one of the two possible surfaces of the chromaffin granule membranes. These results are in agreement with previous observations concerning the asymmetric distribution of saccharide residues on the surfaces of a number of different plasma membranes. They suggest that for the intracellular membrane of the chromaffin granule the saccharide sites, like those in plasma membranes, are not exposed to the cell cytoplasm. Further work is necessary to establish whether these sites are on the inner surface of the membrane or whether they are unmasked during the conversion of granules to membrane ghosts. 相似文献
58.
Isolation and identification of the conidial germination factor of Neurospora crassa. 总被引:9,自引:5,他引:4 下载免费PDF全文
The germination-essential substance (germination factor [GF]) that is lost from conidia of Neurospora crassa on exposure to solutions of low water activity has been isolated and identified as a group of iron-transport compounds, or siderochromes. The principal siderochrome of conidia is ferricrocin, a cyclic hexapeptide. A closely related substance, ferrichrome C, is tentatively identified as a minor constituent. The same substances are also present in extracts of mycelium along with small amounts of a third siderochrome, which has not been identified. The GF activity of culture filtrates is due to coprogen, the only siderochrome previously identified with N. crassa. 相似文献
59.
A list of microlepidoptera belonging to the superfamily Gelechioidea was produced from June trap samples from sites within the Wayne National Forest (Lawrence County), an Appalachian forest in Southern Ohio that was once a greatly disturbed area and has since re-established over a period of nearly 100 years. The composition and diversity of Lawrence county is compared to lists of gelechioid moths generated by other surveys in the eastern United States: the Great Smoky Mountains National Park, an Ohio study (Summerville and Crist 2003), and unpublished data from Connecticut (Wagner). From comparison with these studies, we address two questions: (1) How well do passive surveys of Gelechioidea compare to more labor intensive surveys? (2) How does the regenerated Wayne National Forest compare to other well documented areas with respect to gelechioid diversity? Our sample of diversity, though more narrow in time and area, compares favorably to more exhaustive sampling and demonstrates that it may be more efficient to focus on target groups in focal localities when time and resources are limited rather than conduct extensive sampling programs. 相似文献
60.