全文获取类型
收费全文 | 1902篇 |
免费 | 216篇 |
出版年
2021年 | 18篇 |
2020年 | 22篇 |
2019年 | 19篇 |
2018年 | 20篇 |
2017年 | 22篇 |
2016年 | 36篇 |
2015年 | 52篇 |
2014年 | 61篇 |
2013年 | 68篇 |
2012年 | 72篇 |
2011年 | 76篇 |
2010年 | 61篇 |
2009年 | 63篇 |
2008年 | 58篇 |
2007年 | 73篇 |
2006年 | 66篇 |
2005年 | 86篇 |
2004年 | 76篇 |
2003年 | 68篇 |
2002年 | 58篇 |
2001年 | 47篇 |
2000年 | 58篇 |
1999年 | 33篇 |
1998年 | 32篇 |
1997年 | 25篇 |
1996年 | 21篇 |
1995年 | 29篇 |
1994年 | 30篇 |
1993年 | 19篇 |
1992年 | 46篇 |
1991年 | 47篇 |
1990年 | 48篇 |
1989年 | 35篇 |
1988年 | 33篇 |
1987年 | 27篇 |
1986年 | 31篇 |
1985年 | 34篇 |
1984年 | 35篇 |
1983年 | 25篇 |
1982年 | 21篇 |
1981年 | 22篇 |
1979年 | 33篇 |
1977年 | 21篇 |
1976年 | 20篇 |
1975年 | 23篇 |
1974年 | 21篇 |
1973年 | 19篇 |
1972年 | 16篇 |
1971年 | 20篇 |
1968年 | 21篇 |
排序方式: 共有2118条查询结果,搜索用时 31 毫秒
991.
Ghitarina Hasbi Rocky de Nys Kathryn Burns Steve Whalan Walter C. Dunlap 《Biology letters》2011,7(1):123-126
In this communication, we introduce a novel biomarker of aquatic contamination based on the xenobiotic-induced response of the hepatic coenzyme Q (CoQ) redox balance of fishes to polycyclic aromatic hydrocarbons (PAHs). The method is demonstrated by comparing changes in the liver CoQ redox balance with that measured using the CYP1A-based, 7-ethoxyresofurin-O-deethylase activity assay, on administration of benzo[a]pyrene (BaP) and β-naphthoflavone (BNF) to Barramundi (Lates calcarifer). Both assays showed comparable dose-dependent effects in fish treated with BaP or BNF. Perturbation in the constitutive hepatic CoQ redox balance of fishes may thus provide a simple biomarker of aquatic PAH contamination. 相似文献
992.
993.
Thomas M. Burns Carlos L. Spears S.S. Kerwar 《Archives of biochemistry and biophysics》1973,159(2):880-884
Free and membrane bound polysomes were prepared from 8-day-old chick embryos. Both polysome preparations were equally active in protein synthesis but procollagen-collagen synthesis was carried out exclusively by the membrane bound polysomes. The collagenous product was analyzed by DEAE-cellulose chromatography and after hydroxylation with peptidyl proline hydroxylase had a hydroxyproline/proline ratio of 0.77. This suggests that the collagenous product synthesized by the membrane bound polysomes is procollagen. 相似文献
994.
995.
T. H. S. Burns 《BMJ (Clinical research ed.)》1951,2(4735):852-853
996.
Habitat Use by Weddell Seals and Emperor Penguins Foraging in the Ross Sea, Antarctica 总被引:2,自引:0,他引:2
The only apex predators that live year-round at high latitudesof the Ross Sea are the Weddell seal and emperor penguin. Theseasonal distribution, foraging depths, and diet of these twospecies appear to overlap. What makes it possible for emperorpenguins and Weddell seals to co-exist at high latitude throughoutthe winter when other marine tetrapods apparently cannot? Bothspecies have similar adaptations for exploitation of the deep-waterhabitat, forage on the same species, and routinely make longand deep dives. Yet, despite these similarities, there is probablylittle trophic overlap between the adults of both species dueto geographical and seasonal differences in habitat use. Forexample, during the winter months while female emperor penguinsare ranging widely in the pack ice, adult seals are foragingand fattening for the upcoming summer fast, literally beneaththe feet of the male penguins. However, there is more extensiveoverlap between juvenile seals and adult penguins, and shiftsin prey abundance and/or distribution would likely affect thesetwo groups similarly. In contrast, juvenile penguins appearto avoid inter- and intra- specific competition by leaving theRoss Sea once they molt. 相似文献
997.
998.
999.
E.G. Alvarez Almora G.B. Huntington J.C. Burns 《Animal Feed Science and Technology》2012,171(2-4):136-145
The objective of two experiments was to evaluate non-protein N supplementation with protected urea sources in terms of rumen fermentation products, nutrient digestibility, and N balance in ruminally fistulated beef steers (initial bodyweight 239 ± 18 kg) fed switchgrass hay. Experiment 1 compared urea with Optigen II®, and Experiment 2 compared urea with RumaPro®. In both experiments, supplements (400 g/kg of daily dietary dry matter) were fed once daily or every 2 h in a balanced design. Supplements contained soybean hulls, corn grain, vitamins, and minerals as well as non-protein N sources. Non-protein N provided 0.18 g/g of dietary N. Switchgrass hay was fed once daily, at the same time as the supplement in the once-daily treatments. Dry matter intake (4.1 kg/d in Experiment 1, 4.5 kg/d in Experiment 2), dry matter digestibility (P<0.25, 0.58 ± 0.014 g/g in Experiment 1, 0.58 ± 0.010 g/g in Experiment 2), N balance (P<0.83, 11.3 ± 1.9 g/d in Experiment 1, 11.8 ± 3.6 g/d in Experiment 2), ruminal ammonia concentrations (P<0.29, 15.2 ± 1.4 mM in Experiment 1, 11.8 ± 0.6 mM in Experiment 2), and ruminal short-chain fatty acid concentrations (P<0.13, 77.7 ± 3.0 mM in Experiment 1, 75.4 ± 3.0 mM in Experiment 2) were not affected by feeding protected urea sources. Providing a steady supply of ruminally degradable N by feeding supplement every 2 h vs once daily decreased ruminal ammonia concentrations by approximately one-half by 4 h after feeding hay (P<0.01 in both experiments) and increased (P<0.02 in Experiment 1, P<0.08) in Experiment 2) apparent digestibility of dry matter (0.58–0.62 in Experiment 1, 0.56–0.61 in Experiment 2) and dietary fiber components. 相似文献
1000.
Absence of a single repeat from the coding region of the human involucrin gene leading to RFLP. 总被引:5,自引:2,他引:3 下载免费PDF全文
M Simon M Phillips H Green H Stroh K Glatt G Burns S A Latt 《American journal of human genetics》1989,45(6):910-916
The human involucrin gene has been mapped to the region q21-q22 of chromosome 1. Three of six Utah families examined were polymorphic for a PstI fragment of the involucrin gene. In one individual, the variant PstI fragment was found by DNA sequencing to be missing one of the 39 repeats that make up two-thirds of the coding region. 相似文献