全文获取类型
收费全文 | 1913篇 |
免费 | 108篇 |
国内免费 | 4篇 |
出版年
2023年 | 9篇 |
2022年 | 7篇 |
2021年 | 31篇 |
2020年 | 9篇 |
2019年 | 12篇 |
2018年 | 27篇 |
2017年 | 17篇 |
2016年 | 42篇 |
2015年 | 60篇 |
2014年 | 70篇 |
2013年 | 130篇 |
2012年 | 144篇 |
2011年 | 118篇 |
2010年 | 83篇 |
2009年 | 84篇 |
2008年 | 118篇 |
2007年 | 138篇 |
2006年 | 145篇 |
2005年 | 138篇 |
2004年 | 130篇 |
2003年 | 117篇 |
2002年 | 126篇 |
2001年 | 13篇 |
2000年 | 8篇 |
1999年 | 15篇 |
1998年 | 22篇 |
1997年 | 22篇 |
1996年 | 15篇 |
1995年 | 20篇 |
1994年 | 22篇 |
1993年 | 23篇 |
1992年 | 15篇 |
1991年 | 10篇 |
1990年 | 6篇 |
1989年 | 12篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 12篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1973年 | 3篇 |
排序方式: 共有2025条查询结果,搜索用时 15 毫秒
91.
Sashiwa H Kawasaki N Nakayama A Muraki E Yajima H Yamamori N Ichinose Y Sunamoto J Aiba S 《Carbohydrate research》2003,338(6):557-561
The Michael type reaction of chitosan with ethyl acrylate has been investigated. Although this reaction was quite slow in the case of chitosan, the reiteration of the reaction was an effective means for increasing the degree of substitution (DS) of ethyl ester. The N-carboxyethylchitosan ethyl ester as an intermediate was successfully substituted with various hydrophilic amines, although the simultaneous hydrolysis of the ester to carboxylic acid also occurred. Water-soluble chitosan derivatives were obtained by substitution with hydroxyalkylamines and diamines. 相似文献
92.
The gene encoding phosphoglucose isomerase was cloned from Thermococcus litoralis, and functionally expressed in Escherichia coli. The purified enzyme, a homodimer of 21.5 kDa subunits, was biochemically characterized. The inhibition constants for four competitive inhibitors were determined. The enzyme contained 1.25 mol Fe and 0.24 mol Zn per dimer. The activity was enhanced by the addition of Fe(2+), but inhibited by Zn(2+) and EDTA. Enzymes with mutations in conserved histidine and glutamate residues in their cupin motifs contained no metals, and showed large decreases in k(cat). The circular dichroism spectra of the mutant enzymes and the wild type enzyme were essentially the same but with slight differences. 相似文献
93.
94.
Association of a regulatory gene, slyA with a mouse virulence of Salmonella serovar Choleraesuis 总被引:1,自引:0,他引:1
Kaneko A Mita M Sekiya K Matsui H Kawahara K Danbara H 《Microbiology and immunology》2002,46(2):109-113
The influence of slyA gene, originally found in Salmonella serovar Typhimurium as a regulatory gene for the expression of virulence genes, on a mouse virulence of S. serovar Choleraesuis was investigated by using an slyA-defective mutant. The defective mutant was constructed by the insertion of a kanamycin-resistance gene (aph) into the cloned slyA gene, and the homologous recombination with the intact slyA gene on the chromosome. The mutant strain showed the LD50 value for BALB/c mouse approximately 10(5) higher than that of the parent strain. The increase of the LD50 value was the same order as that shown by the mutation of the slyA gene of S. serovar Typhimurium, although LD50 of the wild-type strain of S. serovar Choleraesuis was 40-fold higher than that of S. serovar Typhimurium. The time course of infection observed in the mice organs also proved the clear difference of the virulence between the parent and the mutant strains. These results suggested that the slyA gene product functions as a virulence-associated regulator also in S. serovar Choleraesuis. 相似文献
95.
96.
Kanno T Fujita H Muranaka S Yano H Utsumi T Yoshioka T Inoue M Utsumi K 《Physiological chemistry and physics and medical NMR》2002,34(2):91-102
The opening of mitochondrial membrane permeability transition (MPT) pores, which results in a cyclosporin A (CsA)-sensitive and Ca(2+)-dependent dissipation of the membrane potential (delta psi) and swelling (classical MPT), has been postulated to play an important role in the release of cytochrome c (Cyt.c) and also in apoptotic cell death. Recently, it has been reported that CsA-insensitive or Ca(2+)-independent MPT can be classified as non-classic MPT. Therefore, we studied the effects of apoptosis-inducing agents on mitochondrial functions with respect to their CsA-sensitivity and Ca(2+)-dependency. CsA-sensitive mitochondrial swelling, depolarization, and the release of Ca2+ and Cyt.c were induced by low concentrations of arachidonic acid, triiodothyronine (T3), or 6-hydroxdopamine but not by valinomycin and high concentrations of the fatty acid or T3. Fe2+/ADP and 2,2,-azobis-(2-amidinopropane) dihydrochloride (AAPH) induced swelling of mitochondria and the release of Ca2+ and Cyt.c were not coupled with depolarization or CsA-sensitivity while dibucaine-induced swelling occurred without depolarization, Cyt.c-release or by a CsA-sensitive mechanism. A protonophoric FCCP and SF-6847 induced depolarization and Ca(2+)-release occurred in a CsA-insensitive manner and failed to stimulate the release of Cyt.c. These results indicate that ambient conditions of mitochondria can greatly influence the state of membrane stability and that Cyt.c release may occur not only via a CsA-sensitive MPT but also by way of a CsA-insensitive membrane deterioration. 相似文献
97.
98.
Ishiyama T Iimura S Ohsuki S Uoto K Terasawa H Soga T 《Bioorganic & medicinal chemistry letters》2002,12(7):1083-1086
To synthesize new highly active taxoids, we designed and synthesized 9 beta-dihydro-9,10-acetal taxoids. In vitro study of these analogues clearly showed them to be more potent than docetaxel. 相似文献
99.
Regeneration of hippocampal pyramidal neurons after ischemic brain injury by recruitment of endogenous neural progenitors 总被引:129,自引:0,他引:129
Nakatomi H Kuriu T Okabe S Yamamoto S Hatano O Kawahara N Tamura A Kirino T Nakafuku M 《Cell》2002,110(4):429-441
The adult brain is extremely vulnerable to various insults. The recent discovery of neural progenitors in adult mammals, however, raises the possibility of repairing damaged tissue by recruiting their latent regenerative potential. Here we show that activation of endogenous progenitors leads to massive regeneration of hippocampal pyramidal neurons after ischemic brain injury. Endogenous progenitors proliferate in response to ischemia and subsequently migrate into the hippocampus to regenerate new neurons. Intraventricular infusion of growth factors markedly augments these responses, thereby increasing the number of newborn neurons. Our studies suggest that regenerated neurons are integrated into the existing brain circuitry and contribute to ameliorating neurological deficits. These results expand the possibility of novel neuronal cell regeneration therapies for stroke and other neurological diseases. 相似文献
100.
A novel experimental technique, based on atomic force microscopy (AFM), is proposed to visualize the lateral organization of membrane systems in the nanometer range. The technique involves the use of a ligand-receptor pair, biotin-avidin, which introduces a height variation on a solid-supported lipid bilayer membrane. This leads to a height amplification of the lateral membrane organization that is large enough to be clearly imaged by scanning AFM. The power of the technique is demonstrated for a binary dipalmitoylphosphocholine-diarachidoylphosphocholine lipid mixture which is shown to exhibit a distinct lateral lipid domain formation. The new and simple ligand-receptor-based AFM approach opens up new ways to investigate lipid membrane microstructure in the nanometer range as well as the lateral distribution of ligand-lipid and receptor-protein complexes in supported membrane systems. 相似文献