全文获取类型
收费全文 | 14960篇 |
免费 | 1375篇 |
国内免费 | 1658篇 |
出版年
2024年 | 37篇 |
2023年 | 220篇 |
2022年 | 409篇 |
2021年 | 894篇 |
2020年 | 648篇 |
2019年 | 759篇 |
2018年 | 707篇 |
2017年 | 512篇 |
2016年 | 692篇 |
2015年 | 1008篇 |
2014年 | 1138篇 |
2013年 | 1277篇 |
2012年 | 1392篇 |
2011年 | 1309篇 |
2010年 | 777篇 |
2009年 | 725篇 |
2008年 | 785篇 |
2007年 | 672篇 |
2006年 | 660篇 |
2005年 | 432篇 |
2004年 | 423篇 |
2003年 | 396篇 |
2002年 | 335篇 |
2001年 | 243篇 |
2000年 | 202篇 |
1999年 | 203篇 |
1998年 | 167篇 |
1997年 | 117篇 |
1996年 | 108篇 |
1995年 | 96篇 |
1994年 | 78篇 |
1993年 | 65篇 |
1992年 | 86篇 |
1991年 | 58篇 |
1990年 | 54篇 |
1989年 | 50篇 |
1988年 | 41篇 |
1987年 | 31篇 |
1986年 | 22篇 |
1985年 | 28篇 |
1984年 | 19篇 |
1983年 | 13篇 |
1982年 | 17篇 |
1981年 | 11篇 |
1980年 | 8篇 |
1979年 | 11篇 |
1978年 | 10篇 |
1977年 | 7篇 |
1975年 | 11篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
991.
Intein-mediated rapid purification of recombinant human pituitary adenylate cyclase activating polypeptide 总被引:3,自引:0,他引:3
In order to obtain the recombinant human PACAP efficiently by intein-mediated single column purification, a gene encoding human PACAP was synthesized and cloned into Escherichia coli expression vector pKYB. The recombinant vector pKY-PAC was transferred into E. coli ER2566 cells and the target protein was over-expressed as 相似文献
992.
Expression of a modified Cry1Ie gene in E. coli and in transgenic tobacco confers resistance to corn borer 总被引:1,自引:0,他引:1
Liu YJ Song FP He KL Yuan Y Zhang XX Gao P Wang JH Wang GY 《Acta biochimica et biophysica Sinica》2004,36(4):309-313
The wild-type Crylle gene from Bacillus thuringiensis was modified for its efficient expression in transgenic plants. Modified Crylle gene (designated as Cryllem) was cloned into prokaryotic expressionvector pET28b and its expression in E.coli was confirmed by SDS-PAGE analysis. Bioassays using crude expression products in E.coli revealed that CrylIem protein had a similar toxicity to corn borer as wild-type CrylIe. CrylIem gene was then inserted downstream of the maize ubiquitin-1 promoter in plant expression vector p3301. Transgenic tobacco plants carrying Cryllem showed insecticidal activity against corn borer. 相似文献
993.
Sara?Cheek Yuan?Qi S?Sri?Krishna Lisa?N?Kinch Nick?V?GrishinEmail author 《BMC bioinformatics》2004,5(1):197
Background
Inference of remote homology between proteins is very challenging and remains a prerogative of an expert. Thus a significant drawback to the use of evolutionary-based protein structure classifications is the difficulty in assigning new proteins to unique positions in the classification scheme with automatic methods. To address this issue, we have developed an algorithm to map protein domains to an existing structural classification scheme and have applied it to the SCOP database. 相似文献994.
995.
The inclusion complexation behavior of paclitaxel with a series of oligo(ethylenediamino) bridged bis(beta-cyclodextrin)s possessing bridge chains in different length (1-4) has been investigated in order to improve the water solubility of paclitaxel. It is found that only the long-tethered bis(beta-cyclodextrin)s 1 and 2 can form the inclusion complexes with paclitaxel, which are characterized by NMR, SEM, XRD, FT-IR, TG-DTA, DSC, and microcalorimetry technology. The results obtained show that bis(beta-cyclodextrin)s 1 and 2 are able to solubilize paclitaxel to high levels up to 2 and 0.9 mg/mL, respectively. The high complex stability of bis(beta-cyclodextrin) 1 and paclitaxel is discussed from thermodynamic viewpoint. Furthermore, the cytotoxicity of these complexes assessed using a human erythroleukemia K562 cell line indicates that the IC(50) value of 1/paclitaxel complex is 6.0 x 10(-10) mol/dm(3) (calculated as paclitaxel molar concentration), which means that the antitumor activity of 1/paclitaxel complex is better than that of parent paclitaxel (IC(50) value 9.8 x 10(-10) mol/dm(3)). This high antitumor activity, along with the satisfactory water solubility and high thermal stability of the 1/paclitaxel complex, will be potentially useful for its clinical application as a highly effective antitumor drug. 相似文献
996.
The cell cycle related apoptotic susceptibility to arsenic trioxide is associated with the level of reactive oxygen species 总被引:18,自引:1,他引:17
Double staining flow cytometry was performed using 7-amino actinomycin D and 6-carboxy-2‘,7‘-dichlorodihydrofluorescein diacetate, to detect the level fluctuation of reactive oxygen species (ROS) during the cell cycle of normal NB4 cells. Our results showed that NB4 cells possessed higher level of ROS in G2/M phase than in G1 and S phases. Double staining flow cytometry, with TdT mediated dUTP nick end labeling (Tunel) and propidium iodide(PI), indicated that As2O3 (2μM) could induce apoptosis in NB4 cells prevailingly from G2/M phase, and this efficacy was enhanced upon co-administration of 2, 3-dimethoxy-1, 4-naphthoquinone (DMNQ) (2.5μM) which could produce the endogenous ROS. These results suggested that different ROS level in different cell cycle phases of NB4 cells might determin the selective induction of G2/M apoptosis and the cells‘ susceptibility to apoptosis by As2O3. 相似文献
997.
998.
Yi?Sun Fei?Ma Bing?Xiao Junjie?Zheng Xiaodong?Yuan Minqian?Tang Li?Wang Yefei?Yu Qingwei?LiEmail author 《中国科学C辑(英文版)》2004,47(6):510-520
999.
A green mutant was obtained among the chemically induced mutants of Rhodobacter sphaeroides 601 (RS601) and named GM309. A blue shift of 20 nm of the carotenoid absorption spectrum was found in the light-harvesting
complex II (LH2) of GM309. Different from LH2 of RS601, it was found that the carotenoids in GM309-LH2 changed to be neurosporene
by mutation. Neurosporene lacks a conjugate double bond, compared with the spheroidene in RS601-LH2 which has ten conjugate
double bonds. As shown by absorption and circular dichroism spectroscopy, the overall structure of GM309-LH2 is little affected
by this change. From fluorescence emission spectra, it is found that GM309-LH2 can transfer energy from carotenoids to Bchl-B850
without any change in efficiency. But the efficiency of energy transfer from B800 to B850 in GM309-LH2 is decreased to be
42% of that of the native. This work would provide a novel method to investigate the mechanism of excitation energy transfer
in LH2. 相似文献
1000.
Remillard CV Yuan JX 《American journal of physiology. Lung cellular and molecular physiology》2004,286(1):L49-L67
Cell apoptosis and proliferation are two counterparts in sharing the responsibility for maintaining normal tissue homeostasis. In recent years, the process of the programmed cell death has gained much interest because of its influence on malignant cell growth and other pathological states. Apoptosis is characterized by a distinct series of morphological and biochemical changes that result in cell shrinkage, DNA breakdown, and, ultimately, phagocytic death. Diverse external and internal stimuli trigger apoptosis, and enhanced K+ efflux has been shown to be an essential mediator of not only early apoptotic cell shrinkage, but also of downstream caspase activation and DNA fragmentation. The goal of this review is to discuss the role(s) played by K+ transport or flux across the plasma membrane in the regulation of the apoptotic volume decrease and apoptosis. Attention has also been paid to the role of inner mitochondrial membrane ion transport in the regulation of mitochondrial permeability and apoptosis. We provide specific examples of how deregulation of the apoptotic process contributes to pulmonary arterial medial hypertrophy, a major pathological feature in patients with pulmonary arterial hypertension. Finally, we discuss the targeting of K+ channels as a potential therapeutic tool in modulating apoptosis to maintain the balance between cell proliferation and cell death that is essential to the normal development and function of an organism. 相似文献