全文获取类型
收费全文 | 3409篇 |
免费 | 124篇 |
国内免费 | 146篇 |
专业分类
系统科学 | 190篇 |
丛书文集 | 74篇 |
教育与普及 | 89篇 |
理论与方法论 | 13篇 |
现状及发展 | 194篇 |
研究方法 | 73篇 |
综合类 | 3045篇 |
自然研究 | 1篇 |
出版年
2024年 | 14篇 |
2023年 | 30篇 |
2022年 | 42篇 |
2021年 | 68篇 |
2020年 | 36篇 |
2019年 | 17篇 |
2018年 | 35篇 |
2017年 | 54篇 |
2016年 | 42篇 |
2015年 | 91篇 |
2014年 | 127篇 |
2013年 | 84篇 |
2012年 | 116篇 |
2011年 | 169篇 |
2010年 | 120篇 |
2009年 | 152篇 |
2008年 | 168篇 |
2007年 | 163篇 |
2006年 | 141篇 |
2005年 | 153篇 |
2004年 | 182篇 |
2003年 | 121篇 |
2002年 | 93篇 |
2001年 | 165篇 |
2000年 | 149篇 |
1999年 | 189篇 |
1998年 | 104篇 |
1997年 | 95篇 |
1996年 | 112篇 |
1995年 | 95篇 |
1994年 | 81篇 |
1993年 | 65篇 |
1992年 | 93篇 |
1991年 | 76篇 |
1990年 | 52篇 |
1989年 | 44篇 |
1988年 | 44篇 |
1987年 | 17篇 |
1986年 | 10篇 |
1981年 | 7篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1971年 | 6篇 |
1970年 | 7篇 |
1969年 | 8篇 |
1968年 | 3篇 |
1967年 | 4篇 |
排序方式: 共有3679条查询结果,搜索用时 546 毫秒
141.
应用材料破坏分析软件MFPA2D(material failure process analysis),模拟了平面应力下双向应力比不断变化条件下脆性材料的不同破坏失稳过程,并以玻璃为例,重点研究了其在复杂应力状态下不同双向应力比对脆性材料裂纹扩展和断裂的影响. 研究结果表明,裂纹失稳扩展时的应力强度因子值随着双向应力比的升高而升高. 该结果证明双向应力确实对脆性材料的断裂韧性有影响. 理论分析得出的应变失效准则与数值模拟研究结果及试验结果的比较研究表明,应变失效准则作为脆性材料在双向应力下的断裂准则是可行的. 相似文献
142.
Antoni Camins Javier G. Pizarro Daniel Alvira Javier Gutierrez-Cuesta Aurelio Vazquez de la Torre Jaume Folch Francesc X. Sureda Ester Verdaguer Felix Junyent Joaquín Jordán Isidre Ferrer Mercè Pallàs 《Cellular and molecular life sciences : CMLS》2010,67(22):3865-3882
In the present study we demonstrated that neurotoxin MPP+-induced DNA damage is followed by ataxia telangiectasia muted (ATM) activation either in cerebellar granule cells (CGC) or in B65 cell line. In CGC, the selective ATM inhibitor KU-55933 showed neuroprotective effects against MPP+-induced neuronal cell loss and apoptosis, lending support to the key role of ATM in experimental models of Parkinson’s disease. Likewise, we showed that knockdown of ATM levels in neuroblastoma B65 cells using an ATM-specific siRNA attenuates the phosphorylation of retinoblastoma protein without affecting other cell-cycle proteins involved in the G0/G1 cell-cycle phase. Moreover, we demonstrated DNA damage, in human brain samples of PD patients. These findings support a model in which MPP+ leads to ATM activation with a subsequent DNA damage response and activation of pRb. Therefore, this study demonstrates a new link between DNA damage by MPP+ and cell-cycle re-entry through retinoblastoma protein phosphorylation. 相似文献
143.
Pan Li Guoying Zheng Yan Yang Chunguang Zhang Ping Xiong Yong Xu Min Fang Zheng Tan Fang Zheng Feili Gong 《Cellular and molecular life sciences : CMLS》2010,67(18):3197-3208
When they recognize a target cell, natural killer (NK) cells mount an attack to kill the target by exerting their cytotoxicity
via the exocytosis of cytotoxic granules. Although the details of this process (which includes the movement of cytotoxic granules
in the immune synapse and their fusion with the plasma membrane, releasing granzymes and perforin into the synaptic cleft)
are relatively better understood, the post-exocytosis regulation of the process is still largely unknown. Here we show that
a clathrin-dependent endocytosis stimulated by target cell occurs in NK92 cell line, which is closely correlated with granzyme
B recovery. Inhibition of the endocytosis significantly attenuates the cytotoxicity of NK92 cells. The NK cell recovery of
its released effector molecules, in turn, suggests that endocytosis may well play a key role in the post exocytosis regulation
of immune cells. 相似文献
144.
Hu Z Xia Y Guo X Dai J Li H Hu H Jiang Y Lu F Wu Y Yang X Li H Yao B Lu C Xiong C Li Z Gui Y Liu J Zhou Z Shen H Wang X Sha J 《Nature genetics》2012,44(2):183-186
Non-obstructive azoospermia (NOA) is one of the most severe forms of male infertility. Its pathophysiology is largely unknown, and few genetic influences have been defined. To identify common variants contributing to NOA in Han Chinese men, we performed a three-stage genome-wide association study of 2,927 individuals with NOA and 5,734 controls. The combined analyses identified significant (P < 5.0 × 10(-8)) associations between NOA risk and common variants near PRMT6 (rs12097821 at 1p13.3: odds ratio (OR) = 1.25, P = 5.7 × 10(-10)), PEX10 (rs2477686 at 1p36.32: OR = 1.39, P = 5.7 × 10(-12)) and SOX5 (rs10842262 at 12p12.1: OR = 1.23, P = 2.3 × 10(-9)). These findings implicate genetic variants at 1p13.3, 1p36.32 and 12p12.1 in the etiology of NOA in Han Chinese men. 相似文献
145.
Extensive and coordinated transcription of noncoding RNAs within cell-cycle promoters 总被引:5,自引:0,他引:5
146.
F.A.Zhang L.Chen J.Q.Ma X.Yang 《复旦学报(自然科学版)》2007,46(5)
1 Results Nanocomposite has attracted more and more interest all over the world.Polystyrene (PS) is a commercialized and mass-productive polymer,continuous research efforts have been devoted to the development of polystyrene/montmorillonite (PS/MMT) nanocomposites[1-2].But the polarity of styrene (St) is too small to intercalate the space between the clay layers.The polarity of hydrophilic monomer is so strong that it can intercalate the MMT easily,the intercalated smectic clays maybe exfoliated by usin... 相似文献
147.
148.
熊冬春 《广西师范学院学报(自然科学版)》2009,(1):119-123
在物理课堂中利用计算机仿真演示实验进行辅助教学一直受到许多关注与研究.已有各种技术被应用到进行物理仿真演示的多媒体教学软件的开发中.本文论述了如何利用3dsMax中的Reactor动力学系统这一新技术进行物理力学现象的仿真演示,这种技术具有不需编程、创作快捷、形象直观且容易学习、实现交互性好等特点. 相似文献
149.
<正>To detect the deformation of the tunnel structure based on image sensor networks is the advanced study and application of spatial sensor technology.For the vertical settlement of metro tunnel caused by internal and external stress after its long period operation,the overall scheme and measuring principle of tunnel deformation detection system is introduced. The image data acquisition and processing of detection target are achieved by the cooperative work of image sensor,ARM embedded system.RS485 communication achieves the data transmission between ARM memory and host computer.The database system in station platform analyses the detection data and obtains the deformation state of tunnel inner wall,which makes it possible to early-warn the tunnel deformation and take preventive measures in time. 相似文献
150.