全文获取类型
收费全文 | 5913篇 |
免费 | 300篇 |
国内免费 | 8篇 |
专业分类
6221篇 |
出版年
2024年 | 19篇 |
2023年 | 92篇 |
2022年 | 216篇 |
2021年 | 312篇 |
2020年 | 146篇 |
2019年 | 166篇 |
2018年 | 180篇 |
2017年 | 153篇 |
2016年 | 270篇 |
2015年 | 294篇 |
2014年 | 310篇 |
2013年 | 467篇 |
2012年 | 424篇 |
2011年 | 460篇 |
2010年 | 263篇 |
2009年 | 236篇 |
2008年 | 318篇 |
2007年 | 287篇 |
2006年 | 260篇 |
2005年 | 216篇 |
2004年 | 200篇 |
2003年 | 169篇 |
2002年 | 168篇 |
2001年 | 47篇 |
2000年 | 41篇 |
1999年 | 39篇 |
1998年 | 30篇 |
1997年 | 32篇 |
1996年 | 18篇 |
1995年 | 27篇 |
1994年 | 28篇 |
1993年 | 22篇 |
1992年 | 18篇 |
1991年 | 16篇 |
1990年 | 15篇 |
1989年 | 17篇 |
1988年 | 17篇 |
1987年 | 18篇 |
1986年 | 7篇 |
1985年 | 23篇 |
1984年 | 21篇 |
1983年 | 15篇 |
1982年 | 25篇 |
1981年 | 13篇 |
1980年 | 16篇 |
1979年 | 9篇 |
1978年 | 13篇 |
1977年 | 10篇 |
1974年 | 6篇 |
1966年 | 7篇 |
排序方式: 共有6221条查询结果,搜索用时 15 毫秒
11.
Megasporogenesis and embryo sac development in the sexually reproducing taxa Bouteloua warnockii (2n = 22), B. media (2n = 20), B. uniflora Vasey var. uniflora (2n = 20), B. uniflora var. coahuilensis Gould and Kapadia (2n = 20), and B. curtipendula var. curlipendula (2n = 40) all were found to be of the Adoxa type, in which all 4 megaspores persist and divide once to form an 8-nucleate embryo sac. On the other hand, evidence indicated that plants of B. curtipendula var. caespitosa with high ancuploid chromosome numbers reproduce by pseudogamous fertilization of an aposporous embryo sac. In this taxon the megaspore mother cell did not go beyond the first anaphase of meiosis and the functional embryo sac developed from a nucellar cell. Although the 8-nucleate embryo sac was typical, a 3-nucleate embryo sac was observed to develop in some cases. 相似文献
12.
Kirit D. Chapatwala Mohamed S. Nawaz Juddie D. Richardson James H. Wolfram 《Journal of industrial microbiology & biotechnology》1990,5(2-3):65-69
Summary Bacteria utilizing high concentrations of acetonitrile as the sole carbon source were isolated and identified asChromobacterium sp. andPseudomonas aeruginosa. Maximum growth was attained after 96 h of incubation andP. aeruginosa grew slightly faster thanChromobacterium sp. The strains were able to grow and oxidize acetonitrile at concentrations as high as 600 mM. However, higher concentrations inhibited growth and oxygen uptake. Degradation studies with (14C)acetonitrile indicated 57% of acetonitrile was degraded byPseudomonas aeruginosa as compared to 43% byChromobacterium. The isolates utilized different nitrile compounds as carbon substrates. 相似文献
13.
Shoot regeneration from mature endosperm of Passiflora foetida 总被引:1,自引:0,他引:1
Murashige and Skoog (1962) medium supplemented with 2 M 6-benzylaminopurine (BA) induced adventitious shoots on mature endosperm explants, whilst gibberellic acid (GA3) and casein hydrolysate stimulated growth and development of these shoot primordia. Plantlets were successfully weaned in vivo. These plants were found to be triploid and flowered, although fruit set was not observed. 相似文献
14.
Abstract: cis -Methyldioxolane (CD) is a muscarinic receptor agonist. [3 H] CD has been used to label a subpopulation of muscarinic receptors described as exhibiting high agonist affinity. Pharmacological evidence suggests that the population of receptors labeled by [3 H] CD consists of m2 and/or m4 subtypes; however, no studies have directly addressed the subtype selectivity of [3 H] CD. The present study characterizes binding of this ligand to individual human receptor subtypes expressed in transfected Chinese hamster ovary cells. Results indicate that [3 H] CD binds with high affinity only to Hm2 receptors but not to all Hm2 receptors. Twenty-eight percent of Hm2 receptors bound [3 H] CD with a K D of 3.5 ± 0.5 nM. Binding was eliminated in the presence of guanosine 5'- O -(3-thiotriphosphate), indicating that the Hm2 receptors labeled by [3 H] CD are those that are associated with GDP-bound G protein. Binding of [3 H] CD by only a subpopulation of Hm2 receptors is in agreement with data generated from studies of [3 H] CD binding in mammalian brain. Because muscarinic receptors have been implicated to play a role in the pathogenesis of both Alzheimer's and Parkinson's disease, as well as the neurotoxicity of organophosphorus compounds, knowledge of the binding specificity of the muscarinic agonist [3 H] CD should aid research in these areas. 相似文献
15.
Mohamed Mandour 《BMJ (Clinical research ed.)》1994,308(6925):412-413
16.
Christine L. Lanning Kenneth R. Wilmarth Mohamed B. Abou-Donia 《Neurochemical research》1994,19(9):1165-1173
2,5-Hexanedione (2,5-HD) induces central-peripheral axonpathy characterized by the accumulation of 10-nm neurofilaments proximal to the nodes of Ranvier and a Wallerian-type degeneration. It has been postulated that neurofilament crosslinking may be involved in the production of this axonopathy. A potential initiating event in this neurotoxic process may be the direct binding of 2,5-HD to neurofilament and microtubule proteins. In this study, the in vitro binding of [14C]2,5-HD to neurofilament and microtubule proteins was examined. Neurofilament proteins isolated from rat spinal cord or microtubule proteins isolated from rat brain were incubated in the presence of 2,5-HD at concentrations ranging 25 to 500 mM. Quantitative analysis of sodium dodecyl sulfate (SDS) polyacrylamide gels revealed a dose- and time-dependent binding of 2,5-HD to both neurofilament proteins and microtubule proteins. Expressed as pmol 2,5-HD bound per g protein, the observed relative binding was MAP2>NF160>NF200>NF68>tubulin. These data demonstrate the direct binding of 2,5-HD to cytoskeletal proteins including both neurofilaments and microtubules. 相似文献
17.
18.
19.
Mohamed S. Dehlawi Amira T. Eldefrawi Mohyee E. Eldefrawi Nabil A. Anis James J. Valdes 《Journal of biochemical and molecular toxicology》1994,9(5):261-268
A light addressable potentiometric sensor was used to measure acetylcholinesterase (AChE) activity in order to evaluate the protective effects of quaternary compounds and NaF against enzyme phosphorylation and aging by two organophosphates. The use of the immobilized AChE made possible the quick removal of reagents (i.e., organophosphate, 2-pralidoxime, and protectant), thereby permitting accurate determination of AChE activity before and after phosphorylation and aging. Paraoxon was 15-fold more potent in inhibiting AChE than DFP, while the percent aging following phosphorylation by diiso-propylfluorophosphate (DFP) was much higher. Sodium fluoride (NaF), the most effective protectant against phosphorylation and aging, and the quaternary ammonium compounds reduced significantly AChE inhibition by DFP and paraoxon, to similar degrees. Even though the percent AChE activity that was lost to aging was reduced by these agents, aging as a percent of phosphorylated AChE was not reduced. Thus, their major effect was in reducing the percent AChE phosphorylation, which consequently resulted in reduction of total aged AChE. The finding that quaternary ammonium compounds protect against phosphorylation is consonant with the proposed presence of the active site of AChE in an aromatic gorge. 相似文献
20.
Sally Badawi Feda E. Mohamed Divya Saro Varghese Bassam R. Ali 《Traffic (Copenhagen, Denmark)》2023,24(8):312-333
Endoplasmic reticulum-associated protein degradation (ERAD) is a stringent quality control mechanism through which misfolded, unassembled and some native proteins are targeted for degradation to maintain appropriate cellular and organelle homeostasis. Several in vitro and in vivo ERAD-related studies have provided mechanistic insights into ERAD pathway activation and its consequent events; however, a majority of these have investigated the effect of ERAD substrates and their consequent diseases affecting the degradation process. In this review, we present all reported human single-gene disorders caused by genetic variation in genes that encode ERAD components rather than their substrates. Additionally, after extensive literature survey, we present various genetically manipulated higher cellular and mammalian animal models that lack specific components involved in various stages of the ERAD pathway. 相似文献