全文获取类型
收费全文 | 858篇 |
免费 | 62篇 |
专业分类
920篇 |
出版年
2023年 | 6篇 |
2022年 | 5篇 |
2021年 | 19篇 |
2020年 | 7篇 |
2019年 | 16篇 |
2018年 | 20篇 |
2017年 | 14篇 |
2016年 | 24篇 |
2015年 | 40篇 |
2014年 | 47篇 |
2013年 | 52篇 |
2012年 | 64篇 |
2011年 | 61篇 |
2010年 | 41篇 |
2009年 | 37篇 |
2008年 | 54篇 |
2007年 | 63篇 |
2006年 | 46篇 |
2005年 | 42篇 |
2004年 | 37篇 |
2003年 | 45篇 |
2002年 | 33篇 |
2001年 | 3篇 |
2000年 | 6篇 |
1999年 | 8篇 |
1998年 | 9篇 |
1997年 | 12篇 |
1996年 | 8篇 |
1995年 | 7篇 |
1994年 | 11篇 |
1993年 | 9篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1976年 | 5篇 |
1974年 | 2篇 |
1967年 | 1篇 |
1966年 | 1篇 |
1964年 | 2篇 |
1960年 | 1篇 |
排序方式: 共有920条查询结果,搜索用时 15 毫秒
11.
The purpose of this work was to test whether induction of massive -carotene synthesis in the alga Dunaliella bardawil is triggered by oxygen radicals. The following results were obtained: (i) The induction of -carotene synthesis is preceded by a lag period of about 4 h during which the cells swell and photosynthesis is partially inhibited, (ii) Addition of promoters of oxygen radicals or of azide (an inhibitor of catalase and superoxide dismutase) during the induction period, under conditions which are suboptimal for massive -carotene accumulation, greatly enhances -carotene synthesis, photodegradation of chlorophyll and inhibition of photosynthesis, (iii) High irradiance, which induces massive -carotene accumulation, also induces a high catalase activity. It is suggested that photosynthetically produced oxygen radicals are involved in triggering massive -carotene accumulation in D. bardawil. 相似文献
12.
13.
Ingmar Sethson Ulf Edlund Tadeusz A. Holak Alfred Ross Bengt-Harald Jonsson 《Journal of biomolecular NMR》1996,8(4):417-428
Summary The backbone NMR resonances of human carbonic anhydase I (HCA I) have been assigned. This protein is one of the largest monomeric proteins assigned so far. The assignment was enabled by a combination of 3D triple-resonance experiments and extensive use of amino acid-specific 15N-labeling. The obtained resonance assignment has been used to evaluate the secondary structure elements present in solution. The solution structure appears to be very similar to the crystal structure, although some differences can be observed. Proton-deuteron exchange experiments have shown that the assignments provide probes that can be used in future folding studies of HCA I.The chemical shift data have been deposited in the BioMagResBank in Madison, WI, U.S.A. 相似文献
14.
The isoelectrofocusing patterns of l-amino acid oxidase (LAO) from venom gland homogenates and of the secreted venom of Vipera palaestinae have been compared. The LAO isozyme profile of actively synthesizing gland spans over a wider range of pIs (4.8–6.0) and includes more variants as compared with the profile of the secreted venom. A basic shift of the isoelectrofocusing pattern of LAO obtained by treatment of the gland homogenate or the venom with neuraminidase indicates that sialic acid residues are responsible for the changes in the electronegativity of the isozymes. Analyses of subcellular fractions show that the microsomal fraction of the venom gland homogenate exhibits the highest multiplicity of molecular forms of LAO, whereas the fraction including the secretory granules has an isozyme profile similar to the venom. Double labelling experiments show that the newly synthesized LAO include isozymes which span over a wide range of pIs, whereas later on labelling of the more acidic isozymes is prominent. The results obtained may suggest that the sialic acid residues which are attached to LAO during its transport serve as “markers” for secretion. 相似文献
15.
Sequential degradation of a chondroitin sulphate trisaccharide by lysosomal enzymes from embryonic-chick epiphysial cartilage. 总被引:1,自引:1,他引:0 下载免费PDF全文
The disulphated trisaccharide D-N-acetylgalactosamine sulphate-beta-D-glucuronic acid-beta-D-N-acetylgalactosamine sulphate prepared from 35S- or 14C-labelled chondroitin sulphate was incubated with a preparation of lysosomal enzymes from embryonic-chick epiphysial cartilage. Degradation was demonstrated by analysis of the reaction products. By use of the appropriate intermediate products as substrates, in conjunction with specific enzyme inhibitors, it was shown that the degradation proceeded sequentially from the non-reducing end. It was initiated by sulphatase (preferentially hydrolysing sulphate ester groups at the 6-position), followed by beta-N-acetylgalactosaminidase and beta-glucuronidase, converting the substrate into monosaccharides and inorganic sulphate. The latter enzyme preferentially attacked disaccharides carrying their sulphate ester group at C-4 of the hexosamine residue. Generation of chondroitin sulphate oligosaccharides may occur by the action of an endoglycosidase, previously demonstrated in embryonic-chick cartilage. Endo- and exo-enzymes may thus form a functional unit in lysosomal degradation of chondroitin sulphate. 相似文献
16.
Karin Dahlgren Caldwell Rolf Axn Margareta Bergwall Ingmar Olsson Jerker Porath 《Biotechnology and bioengineering》1976,18(11):1605-1614
Hexyl-groups have been introduced into crosslinked Sepharose 6B, yielding gels with degrees of substitution which range from 0.02 to 0.70 mol hexyl-side chain per mole galactose residue. The gels were exposed to β-amylase in solution, and the resulting adsorbates indicated a monotonic increase in adsorption capacity with an increasing hexyl-content. Adsorbate activity, by contrast, displayed a maximum for a carrier gel with a hexyl–galactose ratio of 0.51. Adsorbates based on gels with different hexyl-content were used in column reactors for continuous maltose production from a soluble starch substrate. 相似文献
17.
Studying the brain circuits that control behavior is challenging, since in addition to their structural complexity there are continuous feedback interactions between actions and sensed inputs from the environment. It is therefore important to identify mathematical principles that can be used to develop testable hypotheses. In this study, we use ideas and concepts from systems biology to study the dopamine system, which controls learning, motivation, and movement. Using data from neuronal recordings in behavioral experiments, we developed a mathematical model for dopamine responses and the effect of dopamine on movement. We show that the dopamine system shares core functional analogies with bacterial chemotaxis. Just as chemotaxis robustly climbs chemical attractant gradients, the dopamine circuit performs ‘reward-taxis’ where the attractant is the expected value of reward. The reward-taxis mechanism provides a simple explanation for scale-invariant dopaminergic responses and for matching in free operant settings, and makes testable quantitative predictions. We propose that reward-taxis is a simple and robust navigation strategy that complements other, more goal-directed navigation mechanisms. 相似文献
18.
19.
20.