全文获取类型
收费全文 | 1600篇 |
免费 | 95篇 |
国内免费 | 24篇 |
出版年
2023年 | 8篇 |
2022年 | 24篇 |
2021年 | 27篇 |
2020年 | 16篇 |
2019年 | 33篇 |
2018年 | 42篇 |
2017年 | 36篇 |
2016年 | 38篇 |
2015年 | 83篇 |
2014年 | 91篇 |
2013年 | 118篇 |
2012年 | 165篇 |
2011年 | 139篇 |
2010年 | 79篇 |
2009年 | 54篇 |
2008年 | 81篇 |
2007年 | 84篇 |
2006年 | 84篇 |
2005年 | 73篇 |
2004年 | 55篇 |
2003年 | 65篇 |
2002年 | 61篇 |
2001年 | 24篇 |
2000年 | 28篇 |
1999年 | 15篇 |
1998年 | 15篇 |
1997年 | 10篇 |
1996年 | 14篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 7篇 |
1992年 | 10篇 |
1991年 | 12篇 |
1990年 | 8篇 |
1989年 | 9篇 |
1988年 | 3篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1978年 | 9篇 |
1974年 | 3篇 |
1973年 | 5篇 |
1971年 | 6篇 |
1970年 | 3篇 |
1966年 | 4篇 |
1965年 | 3篇 |
1907年 | 2篇 |
排序方式: 共有1719条查询结果,搜索用时 15 毫秒
1.
Summary 1. Indirect and direct twitch (0.1-Hz) stimulation of the rat phrenic nerve-diaphragm disclosed that the inhibitory effect of HgCl2, 3.7 × 10–5
M, on the neuromuscular transmission and in the muscle cell, was accelerated by 10-sec periods of 50-Hz tetanic stimulation every 10 min. This activity-dependent enhancement suggested an inhibitory mechanism of HgCl2 related to the development of fatigue, like membrane depolarization or decreased excitability, decreased availability of transmitter, or interference with the factors controlling excitation-secretion coupling of the nerve terminal, i.e. (Ca2+)0 or (Ca2+)i, and excitation-contraction coupling in the muscle cell, i.e., (Ca2+)i.2. During both indirect and direct stimulation, HgCl2-induced inhibition was enhanced markedly by pretreatment with caffeine, which releases Ca2+ from endoplasmic and sarcoplasmic reticulum in the nerve terminal and muscle cell, respectively. This caffeine-induced enhancement was completely antagonized by dantrolene, which inhibits the caffeine-induced release. However, dantrolene alone did not antagonize the HgCl2-induced inhibition.3. Since caffeine depletes the intracellular Ca2+ stores of the smooth endoplasmic reticulum, HgCl2 probably inhibits by binding to SH groups of transport proteins conveying the messenger function of (Ca2+)i. In the muscle cell this leads to inhibition of contraction. In the nerve terminal, an additional enhancement of the HgCl2-induced inhibition, by inhibiting reuptake of choline by TEA and tetanic stimulation, suggested that HgCl2 inhibited a (Ca2+)i signal necessary for this limiting factor in resynthesis of acetylcholine.4. The (Ca2+)0 signal necessary for stimulus-induced release of acetylcholine was not affected by HgCl2. Hyperpolarization in K+-free solution antagonized the inhibitory effect of HgCl2 at indirect stimulation, and Ca2+-free solution enhanced the inhibitory effect at direct stimulation. K+ depolarization, membrane electric field increase with high Ca2+, membrane stabilization with lidocaine, and half-threshold stimulation, did not change the inhibitory effect of HgCl CH3HgCl, 1.85 × 10–5
M, disclosed a synergistic interaction with caffeine during direct, but not during indirect, stimulation. 相似文献
2.
Xiuling Li Songbai Yang Zhonglin Tang Kui Li Max F. Rothschild Bang Liu Bin Fan 《Animal genetics》2014,45(3):329-339
Due to the direction, intensity, duration and consistency of genetic selection, especially recent artificial selection, the production performance of domestic pigs has been greatly changed. Therefore, we reasoned that there must be footprints or selection signatures that had been left during domestication. In this study, with porcine 60K BeadChip genotyping data from both commercial Large White and local Chinese Tongcheng pigs, we calculated the extended haplotype homozygosity values of the two breeds using the long‐range haplotype method to detect selection signatures. We found 34 candidate regions, including 61 known genes, from Large White pigs and 25 regions comprising 57 known genes from Tongcheng pigs. Many selection signatures were found on SSC1, SSC4, SSC7 and SSC14 regions in both populations. According to quantitative trait loci and network pathway analyses, most of the regions and genes were linked to growth, reproduction and immune responses. In addition, the average genetic differentiation coefficient FST was 0.254, which means that there had already been a significant differentiation between the breeds. The findings from this study can contribute to further research on molecular mechanisms of pig evolution and domestication and also provide valuable references for improvement of their breeding and cultivation. 相似文献
3.
4.
The cis/trans interconversion of Glt-Ala-Ala-Pro-Phe-4-nitroanilide and Glt-Ala-Gly-Pro-Phe-4-nitroanilide was studied both enzymatically and nonenzymatically by measuring kinetic β-deuterium isotope effects. The hydrogen atom at the α-carbon atom of the Xaa residue within the Xaa-Pro moiety was substituted by deuterium. In the nonenzymatic case the transition state of rotation is reflected by kH/kD > 1. When catalysed by 17 kDa PPIase the same bond rotation is characterized by kH/kD < 1. This suggests a covalent mechanism of catalysis which involves an approximately tetravalent carbon of the prolyl imidic bond for the transition state of reaction. 相似文献
5.
Rats were taught to lift up a lever to train the plantar flexors. After 2 wk of adaptation the rats were trained for 36 wk. The mass of weights on the lever rose by 85% over the 36-wk period (P less than 0.05) The estimated force that the plantar flexors had to develop to lift the lever rose by 32% (P less than 0.05), just as the work per lift rose by 28% (P less than 0.05). For the trained group of rats the soleus muscles of the right and the left limb were 34% (P less than 0.05) and 31% (P less than 0.05) heavier, respectively, after the training period than those of the control group. Similarly, the plantaris muscles of both the right and the left limb were 24% heavier (P less than 0.05). For the trained group the maximum twitch and tetanus tensions of the soleus were 63% (P less than 0.05) and 65% (P less than 0.05) higher, respectively. Relative to the plantaris these measures were 79% (P less than 0.05) and 37% (P less than 0.05), respectively. The described model, therefore, seems appropriate for the study of the skeletal muscles' adaptation to usage. 相似文献
6.
Streptomycetes possess peptidyl-prolyl cis-trans isomerases that strongly resemble cyclophilins from eukaryotic organisms 总被引:2,自引:0,他引:2
Andreas Pahl Monika Ühlein Holger Bang Wilhelm Schlumbohm Ullrich Keller 《Molecular microbiology》1992,6(23):3551-3558
A functionally active 17.5 kDa peptidyl-prolyl cis-trans isomerase was purified to homogeneity from Streptomyces chrysomallus, a Gram-positive filamentous bacterium. Characterization of the enzyme revealed inhibition and binding characteristics, against the immunsuppressive drug cyclosporin A, which were similar to cyclophilins from eukaryotes such as mammals, plants, fungi and yeasts, but different from those of cyclophilins from enterobacteria such as Escherichia coli. The amino acid sequence of the S. chrysomallus cyclophilin, as deduced from the gene sequence, revealed a striking degree of amino acid sequence identity with the corresponding 17 kDa proteins of humans (66%), Neurospora (70%) and yeast (69%). Comparison with cyclophilin sequences from the Gram-negative enterobacteria revealed much less homology (25% identity with E. coli b, 23% identity with E. coli a). Cyclophilin was detected in each of the four other Streptomyces species tested. The cyclophilins from the various streptomycetes differed in size, varying between 17 and 20.5 kDa. The cyclophilins were abundant in the Streptomyces cells, and present throughout growth. 相似文献
7.
Data on the permanent dentition of 63 coastal and 33 inland Alaskan Eskimos are presented. The number of cusps and groove pattern of the mandibular molars were recorded. Agenesis of the mandibular third molars was classified and the mesiodistal and buccolingual crown diameter was measured on the first and the second mandibular molars. The predominant pattern of the lower first molars was Y5, while for the second molar the dominating patterns were +5 and +4. In the lower third molar, +5 was found in the majority of cases. For M1 and M2, men showed a stronger tendency toward a conservative pattern than did women. In the case of M2, the inland population exhibited a more conservative trait than did the coastal population. No connection was seen between the groove pattern and agenesis of M3, however, a reduction in the mesiodistal crown diameter for the second molars was seen when the number of cusps is reduced from 5 to 4. 相似文献
8.
Ultrastructural analysis of ineffective alfalfa nodules formed by nif::Tn5 mutants of Rhizobium meliloti. 总被引:24,自引:12,他引:12
Ineffective alfalfa nodules formed by Rhizobium meliloti nif::Tn5 mutants were examined by light and electron microscopy. R. meliloti nifH::Tn5 mutants formed nodules that were similar in structure to wild-type nodules except that nifH- bacteroids accumulated a compact, electron-dense body. In contrast to nodules induced by wild type and nifH mutants, nifDK- R. meliloti mutants induced nodules which contained numerous starch grains and prematurely senescent bacteroids. In addition, meristematic activity in nifDK- nodules ceased significantly earlier than in nifH- nodules. All mutant nodules exhibited elevated levels of rough endoplasmic reticulum and Golgi membranes compared to wild-type nodule cells. These elevated levels may reflect either a response to nitrogen starvation in the ineffective nodules or an abnormal synthesis and export of nodule-specific proteins during later developmental stages. 相似文献
9.
Continuous production of L-tryptophan from indole and L-serine by immobilized Escherichia coli cells 总被引:1,自引:0,他引:1
Escherichia coli B 10, which has high activity of tryptophan synthetase, was grown in a 50-L batch culture in order to determine in which growth phase the cells have the highest specific tryptophan productivity. Accordingly, whole cells of the stationary phase were used for immobilization in polyacrylamide beads. After immobilization, these immobilized cells had 56% activity of tryptophan synthetase compared with that of free cells. First, the properties of immobilized cells were investigated. Next, discontinuous productions of L-tryptophan were carried out by using immobilized cells. In discontinuous production of L-tryptophan by the batch, the activity remaining of immobilized cells was 76-79% after 30 times batchwise use. In continuous production of L-tryptophan with a continuous stirred tank reactor (CSTR), the activity remaining of the immobilized cells was 80% after continuous use for 50 days. The maximum productivity of L-tryptophan in this CSTR system was 0.12 g tryptophan L(-1) h(-1). 相似文献
10.
ELECTRON MICROSCOPY OF VIRUS-INFECTED YEAST CELLS 总被引:1,自引:0,他引:1