全文获取类型
收费全文 | 497839篇 |
免费 | 48710篇 |
国内免费 | 202篇 |
专业分类
546751篇 |
出版年
2018年 | 5175篇 |
2017年 | 4895篇 |
2016年 | 6418篇 |
2015年 | 7207篇 |
2014年 | 9067篇 |
2013年 | 12748篇 |
2012年 | 14812篇 |
2011年 | 15381篇 |
2010年 | 10452篇 |
2009年 | 9603篇 |
2008年 | 13745篇 |
2007年 | 14217篇 |
2006年 | 13726篇 |
2005年 | 13019篇 |
2004年 | 12961篇 |
2003年 | 12593篇 |
2002年 | 12475篇 |
2001年 | 25054篇 |
2000年 | 25092篇 |
1999年 | 19337篇 |
1998年 | 5820篇 |
1997年 | 5997篇 |
1996年 | 5562篇 |
1995年 | 5038篇 |
1994年 | 4977篇 |
1993年 | 4996篇 |
1992年 | 15226篇 |
1991年 | 15302篇 |
1990年 | 14825篇 |
1989年 | 14593篇 |
1988年 | 13609篇 |
1987年 | 12733篇 |
1986年 | 11552篇 |
1985年 | 11645篇 |
1984年 | 9214篇 |
1983年 | 7857篇 |
1982年 | 5512篇 |
1981年 | 4841篇 |
1980年 | 4665篇 |
1979年 | 8443篇 |
1978年 | 6520篇 |
1977年 | 5937篇 |
1976年 | 5513篇 |
1975年 | 6405篇 |
1974年 | 6880篇 |
1973年 | 6752篇 |
1972年 | 6022篇 |
1971年 | 5639篇 |
1970年 | 4903篇 |
1969年 | 4776篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
891.
Two kinds of water-soluble chlorophyll-protein complexes were prepared from leaves of Lepidium virginicum L., one (CP661) from the plant cultivated in a green house from seeds collected near Mono Lake, CA, and the other (CP-663) from a plant collected at Narashino, Chiba, Japan, by ammonium sulfate fractionation followed by column chromatography on DEAE-cellulose and Sephacryl S-200. The chlorophyll . proteins were further purified by crystallization. CP661 has absorption peaks at 661, 468, 439, 419, 380, 339 and 272 nm. CP663 had absorption peaks at 663, 469, 438, 419, 379, 338 and 272 nm. Estimated molecular weights were 78 000 for CP661 and 80 000 for CP663 by gel filtration chromatography and 83 000 for CP661 and 107 000 for CP663 by an equilibrium sedimentation method. 1 mol chlorophyll . protein contained 4 mol chlorophyll a and b with ratios of 1.0 in CP661 and 1.6 to 1.9 in CP663, but no carotenoids. These characters are different from those of chlorophyll-protein complexes which are prepared from the thylakoid membranes of chloroplasts with detergents. 相似文献
892.
Hormonal regulation of skeletal muscle glycogen synthase through covalent phosphorylation 总被引:3,自引:0,他引:3
Studies have been initiated to determine the hormonal regulation of glycogen synthase in rabbit skeletal muscle. It was found that glycogen synthase purified from control animals was quite highly phosphorylated (2.35 mol phosphate/mol synthase subunit) with 40% of the phosphate in the trypsin-sensitive or COOH-terminal domain, and 60% in the trypsin-insensitive or NH2-terminal domain. The phosphorylation state of synthase was elevated (3.9 mol/mol) by epinephrine injection and in the diabetic condition. With epinephrine, about 76% of the additional phosphate was incorporated in the trypsin-sensitive domain, which strongly supports the contention that this hormone acts through the cyclic AMP (cAMP)-dependent protein kinase. In the synthase purified from diabetic rabbits, 90% of the additional phosphate was in the trypsin-insensitive domain. Insulin treatment of the diabetics resulted in specific dephosphorylation of the trypsin-insensitive domain. These results indicate that in this system insulin is not acting by inhibition of the cAMP-dependent protein kinase. 相似文献
893.
By means of radioimmunoassay a clear-cut peak of melatonin concentration was found in the pineal organ of the pigeon at the middle of the scotophase (Coisin et al. 1982a). The aim of the present study was to identify the cell type responsible for the nocturnal indole metabolism, including melatonin synthesis, in the pineal of this avian species. After a short-term incubation or organ culture in the presence of [3H]-indolic precursors, [3H]-5-hydroxytryptophan or [3H]-5-hydroxytryptamine, the relative amounts of deaminated and acetylated products occurring in the pineal organ were measured by the use of thin layer chromatography and liquid-scintillation counting. It was possible to modify the relative amounts of deaminated and acetylated indoles by the application of some inhibitors of monoamine oxidase and cyclic nucleotide phosphodiesterase. Irrespective of the experimental conditions, high-resolution autoradiography combined with the above-mentioned radiochemical experiments showed that the cells of the receptor line (modified photoreceptor cells) are responsible for indole storage and metabolism, and very probably also for melatonin biosynthesis. The other cell types of the pineal parenchyma did not display significant labeling. 相似文献
894.
The uptake of two different preparations of99mTechnetium-methylene diphosphonate in fetal rat calvaria is compared. The localization of99mTc after administration of99mTc(Sn)-MDP and99mTc-MDP showed equal distribution in autoradiography. 相似文献
895.
K H?kkinen M Alén P V Komi 《European journal of applied physiology and occupational physiology》1984,53(2):97-105
Various aspects of neuromuscular, anaerobic, and aerobic performance capacity were investigated in four powerlifters, seven bodybuilders, and three wrestlers with a history of specific training for several years. The data (means +/- SD) showed that the three subject groups possessed similar values for maximal isometric force per unit bodyweight (50.7 +/- 9.6, 49.3 +/- 4.1, and 49.3 +/- 10.9 N/kg, respectively). However, significant (P less than 0.05) differences were observed in the times for isometric force production, so that e.g., times to produce a 30% force level were shorter for the wrestlers and bodybuilders (28.3 +/- 3.1 and 26.4 +/- 6.6 ms) than that (53.3 +/- 23.7 ms) for the powerlifters. Utilization of elastic energy by the wrestlers was significantly (P less than 0.05) better than that of the other two subject groups, as judged from differences between the counter-movement and squat jumps at 0, 40, and 100 kg's loads. No differences were observed between the groups in anaerobic power in a 1-min maximal test, but the values for VO2 max were higher (P less than 0.05) among the wrestlers and bodybuilders (57.8 +/- 6.6 and 50.8 +/- 6.8 ml X kg-1 X min-1) as compared to the powerlifters (41.9 +/- 7.2 ml X kg-1 X min-1). Within the limitations of the subject sample, no differences of a statistical significancy were observed between the groups in fibre distribution, fibre areas, or the area ratio of fast (FT) and slow (ST) twitch fibres in vastus lateralis.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
896.
897.
898.
Most of the previous studies on the effects of iron deficiency on skeletal muscle respiratory capacity and work performance have been investigated in severe or moderate iron-deficiency anemia. We report here that even in mild iron deficiency where the hemoglobin concentration was 10 g/dl and the iron stores in livers and spleen were not completely depleted, a marked reduction in succinate dehydrogenase was observed in skeletal muscles but not in heart. Similarly, cytochrome oxidase activities were reduced. Although no significant change in glycerophosphate dehydrogenase was detected in the iron-deficient rats, exposure to cold in this group greatly reduced this enzyme activity. As cold acclimatization accelerates marrow erythropoiesis (20) which in turn, demands more iron, it seems that in the iron-insufficient state, this iron demand for marrow activity may persist at the expense of the tissue iron pool, resulting in a marked reduction in glycerophosphate dehydrogenase activities. Since succinate dehydrogenase plays a significant role in the impairment of mitochondrial function and early fatigue of iron-deficient muscle (11), the present study shows that even in mild iron deficiency, some loss of muscle functions could result as succinate dehydrogenase activities were greatly reduced. 相似文献
899.
Martin T. R. Kuiper Marijke Holtrop Hans de Vries 《Molecular & general genetics : MGG》1988,213(2-3):519-528
900.