全文获取类型
收费全文 | 15926篇 |
免费 | 796篇 |
国内免费 | 21篇 |
专业分类
16743篇 |
出版年
2023年 | 111篇 |
2022年 | 273篇 |
2021年 | 421篇 |
2020年 | 252篇 |
2019年 | 256篇 |
2018年 | 398篇 |
2017年 | 430篇 |
2016年 | 495篇 |
2015年 | 672篇 |
2014年 | 742篇 |
2013年 | 1037篇 |
2012年 | 1141篇 |
2011年 | 1039篇 |
2010年 | 625篇 |
2009年 | 571篇 |
2008年 | 656篇 |
2007年 | 648篇 |
2006年 | 563篇 |
2005年 | 475篇 |
2004年 | 448篇 |
2003年 | 378篇 |
2002年 | 345篇 |
2001年 | 334篇 |
2000年 | 305篇 |
1999年 | 244篇 |
1998年 | 125篇 |
1997年 | 106篇 |
1996年 | 96篇 |
1995年 | 112篇 |
1994年 | 101篇 |
1993年 | 95篇 |
1992年 | 221篇 |
1991年 | 206篇 |
1990年 | 200篇 |
1989年 | 193篇 |
1988年 | 168篇 |
1987年 | 164篇 |
1986年 | 148篇 |
1985年 | 174篇 |
1984年 | 167篇 |
1983年 | 115篇 |
1982年 | 112篇 |
1981年 | 99篇 |
1980年 | 92篇 |
1979年 | 147篇 |
1978年 | 109篇 |
1977年 | 95篇 |
1974年 | 118篇 |
1973年 | 91篇 |
1972年 | 100篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
161.
162.
Axonal guidance signals are transduced through growth cone surface receptors to the interior leading to changes of actin dynamics
and actin binding proteins, which are critical in determining the outcome of actin cytoskeleton reorganization. We report
here the characterization of the Drosophila actin binding protein abLIM/Unc-115 homolog Dunc-115 and its role in the nervous system. Three Dunc-115 isoforms are identified
as Dunc-115L, M and S, respectively. While Dunc-115L is a canonical homolog of Unc-115 with four LIM domains and one villin
headpiece domain, Dunc-115M and S are novel isoforms without counterparts in other species. Our molecular modeling shows Dunc-115L
is likely to bind to actin. Mutant analysis reveals that Dunc-115 is involved in axonal projection in both the visual and
central nervous system. 相似文献
163.
164.
A Puri R Sethi B Singh SK Dwivedi VS Narain RK Saran VK Puri 《Indian pacing and electrophysiology journal》2009,9(3):186-189
A 25-year-old previously asymptomatic pregnant woman at 36 weeks'' gestation was noticed to have repetitive monomorphic ventricular tachycardia. A dilated left ventricle with moderately reduced systolic function was found on echocardiographic examination. This is a very rare presentation of peripartum cardiomyopathy (PPCMP) presenting with repetitive monomorphic ventricular tachycardia. 相似文献
165.
Chang KH Multani PS Sun KH Vincent F de Pablo Y Ghosh S Gupta R Lee HP Lee HG Smith MA Shah K 《Molecular biology of the cell》2011,22(9):1452-1462
Nuclear fragmentation is a common feature in many neurodegenerative diseases, including Alzheimer's disease (AD). In this study, we show that nuclear lamina dispersion is an early and irreversible trigger for cell death initiated by deregulated Cdk5, rather than a consequence of apoptosis. Cyclin-dependent kinase 5 (Cdk5) activity is significantly increased in AD and contributes to all three hallmarks: neurotoxic amyloid-β (Aβ), neurofibrillary tangles (NFT), and extensive cell death. Using Aβ and glutamate as the neurotoxic stimuli, we show that deregulated Cdk5 induces nuclear lamina dispersion by direct phosphorylation of lamin A and lamin B1 in neuronal cells and primary cortical neurons. Phosphorylation-resistant mutants of lamins confer resistance to nuclear dispersion and cell death on neurotoxic stimulation, highlighting this as a major mechanism for neuronal death. Rapid alteration of lamin localization pattern and nuclear membrane change are further supported by in vivo data using an AD mouse model. After p25 induction, the pattern of lamin localization was significantly altered, preceding neuronal death, suggesting that it is an early pathological event in p25-inducible transgenic mice. Importantly, lamin dispersion is coupled with Cdk5 nuclear localization, which is highly neurotoxic. Inhibition of nuclear dispersion rescues neuronal cells from cell death, underscoring the significance of this event to Cdk5-mediated neurotoxicity. 相似文献
166.
The purpose of this study was to investigate the stabilizing action of polyols against various protein degradation mechanisms
(eg, aggregation, deamidation, oxidation), using a model protein lysozyme. Differential scanning calorimeter (DSC) was used
to measure the thermodynamic parameters, mid point transition temperature and calorimetric enthalpy, in order to evaluate
conformational stability. Enzyme activity assay was used to corroborate the DSC results. Mannitol, sucrose, lactose, glycerol,
and propylene glycol were used as polyols to stabilize lysozyme against aggregation, deamidation, and oxidation. Mannitol
was found to stabilize lysozyme against aggregation, sucrose against deamidation both at neutral pH and at acidic pH, and
lactose against oxidation. Stabilizers that provided greater conformational stability of lysozyme against various degradation
mechanisms also protected specific enzyme activity to a greater extent. It was concluded that DSC and bioassay could be valuable
tools for screening stabilizers in protein formulations. 相似文献
167.
Early effects of gibberellic acid on barley aleurone layers 总被引:4,自引:0,他引:4
168.
Parekkat Ramachandran Ragesh Tenzin Nyibum Bhutia Satish Ganta Ashok Kumar Singh 《Archives Of Phytopathology And Plant Protection》2016,49(1-4):19-30
Repellent, antifeedant and toxic effect of crude hexane extract of Ageratum conyzoides were investigated against Helicoverpa armigera. In orientation bioassay, the extract exhibited dose-dependent repellency against neonates. Extract significantly increased the mortality and decreased growth of different larval stages when administrated orally in artificial diet. EC50 value was at 0.11% for larval growth inhibition. Toxicity of the extract was manifested by high mortality of first instar larvae after 7 days of feeding on diet containing 0.05–0.4% of extract with LC50 of 0.17%. Under choice bioassay, extract showed strong antifeedant activity against fifth instar larvae with DI50 of 0.21%. In nutritional bioassay, extract significantly reduced RCR, RGR, ECI and ECD of fifth instar larvae with increased AD. When RGR were plotted against RCR, the growth efficiency of larvae fed on treated diet was significantly lower than the control fed larvae suggesting the antifeedant and toxic effect of extract. 相似文献
169.
Isolation and functional characterization of hydrocarbon emulsifying and solubilizing factors produced by a Pseudomonas species 总被引:1,自引:0,他引:1
Reddy PG Singh HD Pathak MG Bhagat SD Baruah JN 《Biotechnology and bioengineering》1983,25(2):387-401
Pseudomonas PG-1 cultivated on pristane produced in good amount a heat-stable polymeric substance which showed strong hydrocarbon emulsifying and solubilizing properties. The substance was isolated in crude form and was found to contain 34% protein, 16% carbohydrate, and 40% lipid. The hydrocarbon solubilizing activity of the isolate was strongly inhibited by EDTA but the chelating agent had no effect on the hydrocarbon emulsifying activity. Both activities of the isolate were strongly inhibited by chymotrypsin treatment indicating the importance of the protein moiety for its activity. Hydrocarbon solubilization by the isolate showed a certain degree of specificity to pristane in modest agitation generally used in microbial cultivation, but this specificity was lost by vigorous agitation in a Waring blender. It was proposed that in the first case, solubilization was effected by a solubilizing factor specific to pristane, whereas in the latter case, nonspecific solubilization occurred due to the action of the emulsifying factor. The rate of pristane solubilization by heat-treated culture broth under the conditions of agitation used in cultivation (rotary shaker, 120 rpm) was found to be ca. 750 mg L(-1) h(-1) which was much larger than the maximal pristane uptake rate of 170 mg L(-1) h(-1) observed during microbial growth on the substrate. It was concluded that hydrocarbon solubilization could satisfactorily account for the substrate uptake and growth. 相似文献
170.
D. Brady P. Nigam R. Marchant D. Singh A. P. McHale 《Bioprocess and biosystems engineering》1997,17(1):31-34
The thermotolerant, ethanol producing yeast strain, K. marxianus IMB3 was immobilized in calcium alginate containing magnetically responsive Fe3O4 particles. In these studies the β-galactosidase derived from K. marxianus IMB3 was immobilized onto the Fe3O4 particles prior to inclusion into the alginate matrix. Ethanol production by the immobilized microorganism in the presence of Fe3O4 reached a maximum of 16?g/L on 40?g/L lactose whereas prior immobilization of the enzyme to the particles and inclusion into the alginate matrix increased ethanol production to a maximum concentration of 18 g/L. When Mn2+ was incorporated into fermentations containing the immobilized enzyme in the alginate matrix, ethanol production increased further to a maximum concentration of 20?g/L. In addition, the behaviour of the magnetically responsive biocatalyst containing the co-immobilized enzyme was examined in a batch-fed system in the presence and absence of Mn2+. 相似文献