全文获取类型
收费全文 | 11333篇 |
免费 | 910篇 |
国内免费 | 760篇 |
专业分类
13003篇 |
出版年
2024年 | 20篇 |
2023年 | 212篇 |
2022年 | 395篇 |
2021年 | 629篇 |
2020年 | 395篇 |
2019年 | 512篇 |
2018年 | 535篇 |
2017年 | 341篇 |
2016年 | 508篇 |
2015年 | 710篇 |
2014年 | 791篇 |
2013年 | 914篇 |
2012年 | 1067篇 |
2011年 | 928篇 |
2010年 | 571篇 |
2009年 | 495篇 |
2008年 | 533篇 |
2007年 | 492篇 |
2006年 | 427篇 |
2005年 | 361篇 |
2004年 | 302篇 |
2003年 | 225篇 |
2002年 | 187篇 |
2001年 | 202篇 |
2000年 | 170篇 |
1999年 | 174篇 |
1998年 | 101篇 |
1997年 | 123篇 |
1996年 | 105篇 |
1995年 | 87篇 |
1994年 | 91篇 |
1993年 | 48篇 |
1992年 | 74篇 |
1991年 | 55篇 |
1990年 | 44篇 |
1989年 | 46篇 |
1988年 | 38篇 |
1987年 | 27篇 |
1986年 | 19篇 |
1985年 | 22篇 |
1984年 | 12篇 |
1983年 | 9篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
MicroRNAs Involved in Skeletal Muscle Differentiation 总被引:1,自引:0,他引:1
MicroRNAs (miRNAs) negatively regulate gene expression by promoting degradation of target mRNAs or inhibiting their translation. Previous studies have expanded our understanding that miRNAs play an important role in myogenesis and have a big impact on muscle mass, muscle fiber type and muscle-related diseases. The muscle-specific miRNAs, miR-206, miR-1 and miR-133, are among the most studied and best characterized miRNAs in skeletal muscle differentiation. They have a profound influence on multiple muscle differ-entiation processes, such as alternative splicing, DNA synthesis, and cell apoptosis. Many non-muscle-specific miRNAs are also required for the differentiation of muscle through interaction with myogenic factors. Studying the regulatory mechanisms of these miRNAs in muscle differentiation will extend our knowledge of miRNAs in muscle biology and will improve our understanding of the myogenesis regulation. 相似文献
92.
Activation of Raf-1 is a complex process in which phosphorylation of Ser(338)-Tyr(341) is a critical step. Previous studies have shown that Pak1/2 is implicated in both Ras-dependent and -independent activation of Raf-1 by phosphorylating Raf Ser(338). The present study explores the structural basis of Raf-1 phosphorylation by Pak1. We found that Pak directly associates with Raf-1 under both physiological and overexpressed conditions. The association is greatly stimulated by 4beta-12-O-tetradecanoylphorbol-13-acetate and nocodazole and by expression of the active mutants of Rac and Ras. The active forms of Pak generated by mutation of Thr(423) to Glu or truncation of the amino-terminal moiety exhibit a greater binding to Raf than the wild type, whereas the kinase-dead mutant Pak barely binds Raf. The extent of binding to Raf-1 is correlated with the ability of Pak to phosphorylate Raf and induce mitogen-activated protein kinase activation. Furthermore, the Raf-1 binding site is defined to the carboxyl terminus of the Pak catalytic domain. In addition, our results suggest that the amino-terminal regulatory region of Raf inhibits the interaction. Taken together, the results indicate that the interaction depends on the active conformations of Pak and Raf. They also argue that Pak1 is a physiological candidate for phosphorylation of Raf Ser(338) during the course of Raf activation. 相似文献
93.
Shijia Luo Yanhong He Guogui Ning Jiaqi Zhang Guangying Ma Manzhu Bao 《Trees - Structure and Function》2011,25(6):1063-1071
Dove tree (Davidia involucrate) is a Tertiary relic species endemic to China and is reputed to be a ‘living fossil’ in the plant kingdom. Genetic diversity
and genetic structure of this species were analyzed for its conservation and management, using inter-simple sequence repeat
(ISSR) data obtained from eight populations distributed throughout seven provinces of China. A relatively high level of genetic
diversity, at both population and species levels, was detected using the POPGENE software. Analysis of molecular variance
(AMOVA) revealed a moderate level of among-population variation (i.e., 33.21%). The genetic structure of dove tree was closely
consistent with their isolated topographical distribution region based on the results of the STRUCTURE, POPGENE-UPGMA and
PCA analysis. It is postulated that the relatively high level of genetic diversity has been maintained because of: (a) the
original wild geographical distribution, (b) propagation through outcrossing seeds or root suckers, (c) the longevity of individuals
and (d) the relatively little human disturbance. Genetic drift and restricted gene are important factors affecting genetic
differentiation. There was no significant correlation between geographical distances and a pairwise comparison with genetic
distances, as analyzed by the Mantel test, but the clustering result of genetic diversity was consistent with their isolated
topographical distribution regions. Thus, maintaining the stable special habitats associated with this species is recommended
for the in situ conservation. Furthermore, it is important to develop an effective seed germination system for the maintenance
of an ex situ conservation pool of the germplasm resources. 相似文献
94.
Three new compounds, 1 – 3 , and 20 known compounds were isolated from the AcOEt and BuOH extract of edible Opuntia Milpa Alta. The petroleum ether extract was examined by GC and MS. A total of 26 compounds were identified, representing 95.6% of the total extract, phytosterol (36.03%) being the most abundant component, and polyunsaturated fatty acids (18.57%) represented the second largest group, followed by phytol (12.28%), palmitic acid, palmitate (13.54%), vitamin E (4.51%), and other compounds (7.47%). The effects of various extracts from edible Opuntia Milpa Alta (petroleum ether extract, AcOEt extract, BuOH extract, aqueous extract, H2O parts) and the positive control (received dimethylbiguanide) were tested on streptozotocin (STZ)‐induced diabetic mice. The results indicated that all the treatment groups could significantly decrease blood glucose levels in STZ‐induced diabetic mice compared to the model control group (P<0.01), except the aqueous extract group (P<0.05). Especially, the petroleum ether extract group and the positive control group showed remarkable decrease of blood glucose levels. Taken together, the results indicate that the petroleum ether extract is the major hypoglycemic part in edible Opuntia Milpa Alta, which may be developed to a potential natural hypoglycemic functional ingredient. 相似文献
95.
96.
表达SLTEC保护性抗原的重组猪霍乱沙门氏菌C500株的构建及生物学特性 总被引:1,自引:0,他引:1
摘要:【目的】 利用平衡致死系统构建表达产类志贺氏毒素大肠杆菌(Shiga-like toxin Escherichia coli , SLTEC)保护性抗原的减毒猪霍乱沙门氏菌。【方法】 构建表达SLT-IIeB-FedF的重组质粒 ,再将其电转入终宿主菌减毒猪霍乱沙门氏菌ΔasdC500株中构建成口服活疫苗株 ,经聚丙烯酰胺凝胶电泳检测SLT-IIeB-FedF融合蛋白的表达情况,并观察重组菌体外培养的稳定性。【结果】 利用宿主-载体平衡致死系统构建了表达SLTEC保护性抗原的重组减毒猪霍乱沙门氏菌 相似文献
97.
98.
99.
目的总结分析成人降主动脉置换术中各种体外循环灌注的技术特点和管理方法。方法 2006年1月至2009年12月,共有60例患者行降主动脉置换手术。按体外循环灌注技术类型分为3组:左心转流组4例,股动静脉转流组37例,上下半身分别灌注组19例。三组预充均采用勃脉力A和胶体,常规加入白蛋白和激素,监测混合静脉氧饱和度和血细胞压积,积极应用超滤技术和自体血液回收技术。结果术中转流平稳,血流动力学稳定,监测指标均在正常范围,仅出现9例并发症(截瘫、偏瘫、谵妄、苏醒延迟、低氧血症)。结论成人降主动脉置换术中根据不同的手术方式,正确选择和熟练应用相应的灌注技术是决定手术成功的重要因素。 相似文献
100.
An in vitro comparative study on the reactivation of nerve agent-inhibited guinea pig and human acetylcholinesterases by oximes 总被引:1,自引:0,他引:1
The reactivation of nerve agent-inhibited acetylcholinesterase (AChE) by oxime is the most important step in the treatment of nerve agent poisoning. Since the evaluation of nerve agent antidotes cannot be conducted in humans, results from animal experiments are extrapolated to humans. Guinea pig is one of the animal models that is frequently used for conducting nerve agent antidote evaluations. Several investigations have demonstrated that the efficacy of an oxime primarily depends on its ability to reactivate nerve agent-inhibited AChE. If the in vitro oxime reactivation of nerve agent-inhibited animal AChE is similar to that of human AChE, it is likely that the results of an in vivo animal study will reliably extrapolate to humans. Therefore, the goal of this study was to compare the reactivation of guinea pig and human AChEs inhibited by six different G and V type nerve agents. Reactivation kinetic studies with five mono- and bis-pyridinium oximes showed that oxime reactivation of nerve agent-inhibited human AChE in most cases was faster than guinea pig AChE. The most significant enhancement was observed in the reactivation of human AChE inhibited by nerve agents containing bulky side chains GF, GD, and VR, by H-series oximes HLo-7, HI-6, and ICD-585. In these cases, species-related differences observed between the two AChEs, based on the second-order reactivation rate constants, were 90- to over 400-fold. On the other hand, less than 3-fold differences were observed in the rates of aging of nerve agent-inhibited guinea pig and human AChEs. These results suggest that the remarkable species-related differences observed in the reactivation of nerve agent-inhibited guinea pig and human AChEs were not due to differences in the rates of aging. These results also suggest that guinea pig may not be an appropriate animal model for the in vivo evaluation of oxime therapy. 相似文献