首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1194篇
  免费   126篇
  国内免费   100篇
化学   801篇
晶体学   19篇
力学   58篇
综合类   8篇
数学   237篇
物理学   297篇
  2023年   21篇
  2022年   23篇
  2021年   40篇
  2020年   51篇
  2019年   46篇
  2018年   49篇
  2017年   42篇
  2016年   69篇
  2015年   53篇
  2014年   63篇
  2013年   84篇
  2012年   72篇
  2011年   98篇
  2010年   62篇
  2009年   54篇
  2008年   61篇
  2007年   56篇
  2006年   62篇
  2005年   54篇
  2004年   35篇
  2003年   24篇
  2002年   19篇
  2001年   15篇
  2000年   22篇
  1999年   18篇
  1998年   14篇
  1997年   13篇
  1996年   18篇
  1995年   23篇
  1994年   11篇
  1993年   16篇
  1992年   16篇
  1991年   17篇
  1990年   9篇
  1989年   5篇
  1988年   4篇
  1987年   5篇
  1986年   6篇
  1985年   8篇
  1984年   5篇
  1983年   8篇
  1982年   6篇
  1981年   4篇
  1980年   5篇
  1978年   7篇
  1977年   6篇
  1976年   6篇
  1975年   2篇
  1974年   3篇
  1973年   4篇
排序方式: 共有1420条查询结果,搜索用时 15 毫秒
41.
42.
43.
Based on the grey system theory and methods, the grey-target decision-making problem is discussed, in which the attribute values are grey numbers and the maximum probability of the value of grey number is known. Firstly, the optimal effect vector is the positive bull’s-eye and positive bull’s-eye distance of each scheme is defined. Subjectively or objectively weighting method is integrated to determine the index weight and integrated optimization model of index weight is established. Finally, the critical effect vector is the negative bull’s-eye and negative bull’s-eye distance of each scheme is defined, then relative bull’s-eye distance and comprehensive the bull’s-eye distance of grey target decision-making are given. An example is also presented to illustrate the usefulness and effectiveness of the methods obtained in this paper and provides a new idea for grey target decision-making method research.  相似文献   
44.
Due to its enormously high flexibility laser forming has been gaining importance in recent years. This rapidness and flexibility demand very precise controlling strategies especially when simulating the process of large plates and challenging the limited computation power of the current workstation. A simple, robust and accurate modeling method of laser forming has been demonstrated to solve this problem. The simplified model is meshed by multi-layered shell element, simulated with a more real scanning method and fewer parameters. The intelligent meshing strategies have reduced the number of elements dramatically. Thus the simulation efficiency has been improved significantly. By comparing the simulation results under the simplified model with the results under the traditional model for laser forming, the applicability of proposed method has been proven. The method of these simplified models is also suitable to simulate complex finite element models, which take much time to simulate. It would throw some light on the thermal mechanically coupled-field simulation of large sheet.  相似文献   
45.
46.
The chemical constituents of the fungus Verticillium psalliotae were studied. Two new aromadendrane sesquiterpenes inonotin M (1) and inonotin N (2) were isolated from the EtOAc extract of the fungal culture broth. The structures of compounds were elucidated mainly by HRESIMS experiments, and 1D, 2D-NMR spectroscopy analysis.  相似文献   
47.
From an EtOAc-soluble fraction of the stem barks of Swintonia floribunda (Anacardiaceae), one new dimeric alkylresorcinol named integracin E (1), together with 4 known compounds (25) were isolated. Their chemical structures were elucidated based on the spectroscopic data interpretation. The absolute configuration of 1 was determined by the specific rotation analysis of its acid-catalyzed hydrolysis product. Compound 1 showed potent tyrosinase inhibitory activity with an IC50 value of 48.2?μM.  相似文献   
48.
熔盐堆作为第四代核反应堆备选堆型之一,运行温度高,对材料高温性能要求严格;熔盐堆空气换热器作为实验堆关键设备,工作温度高,启停机次数多,长期运行后,材料许用应力松弛下降,应力、应变可能超出允许限值,或发生蠕变疲劳失效。使用Workbench软件,对熔盐堆空气换热器进行力学分析,并对A级使用载荷要求进行结构完整性评定,结果表明:熔盐堆空气换热器满足力学性能要求,其中疲劳损伤占比重较大,高温蠕变损伤也较为显著。  相似文献   
49.
A series of novel 1,2,3-benzotriazin-4-one derivatives were designed,synthesized and their inhibitory activities against leulcotriene A_4 hydrolase aminopeptidase in vitro were evaluated.Many compounds showed moderate to good activities at the concentration of 10 μmol/L.Among them,compound Ⅳ-16 exhibited the highest inhibitory activity up to 80.6% with an IC_(50) of 1.30 ± 0.20 μmol/L The compound Ⅳ-16 was also tested the proliferation inhibitory activities in THP1 human AML cell line and its binding model with LTA_4H enzyme by molecular docking was studied.It indicated that 1,2,3-benzotriazin-4-one was a promising scaffold for further study.The relationship between structure and inhibitory activity was also preliminarily discussed.  相似文献   
50.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号