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   21197篇
  免费   3716篇
  国内免费   2531篇
化学   15324篇
晶体学   263篇
力学   1367篇
综合类   204篇
数学   2291篇
物理学   7995篇
  2024年   22篇
  2023年   480篇
  2022年   468篇
  2021年   685篇
  2020年   880篇
  2019年   863篇
  2018年   686篇
  2017年   650篇
  2016年   1022篇
  2015年   1024篇
  2014年   1157篇
  2013年   1501篇
  2012年   1931篇
  2011年   2001篇
  2010年   1353篇
  2009年   1216篇
  2008年   1415篇
  2007年   1391篇
  2006年   1217篇
  2005年   1086篇
  2004年   789篇
  2003年   666篇
  2002年   553篇
  2001年   450篇
  2000年   435篇
  1999年   487篇
  1998年   358篇
  1997年   368篇
  1996年   291篇
  1995年   300篇
  1994年   303篇
  1993年   254篇
  1992年   195篇
  1991年   207篇
  1990年   187篇
  1989年   122篇
  1988年   89篇
  1987年   92篇
  1986年   64篇
  1985年   50篇
  1984年   41篇
  1983年   25篇
  1982年   26篇
  1981年   20篇
  1980年   13篇
  1977年   1篇
  1975年   3篇
  1971年   1篇
  1957年   4篇
  1936年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Liu  Qingsheng  Liu  Youqiong  Jiang  Chuntao  Zheng  Supei 《Rheologica Acta》2020,59(2):109-121
Rheologica Acta - Weld lines are one of the typical quality issues of injection molded parts. They are unavoidable even for moderate complex products. To explore the formation of weld lines in...  相似文献   
42.
Distance weighted discrimination (DWD) is an appealing classification method that is capable of overcoming data piling problems in high-dimensional settings. Especially when various sparsity structures are assumed in these settings, variable selection in multicategory classification poses great challenges. In this paper, we propose a multicategory generalized DWD (MgDWD) method that maintains intrinsic variable group structures during selection using a sparse group lasso penalty. Theoretically, we derive minimizer uniqueness for the penalized MgDWD loss function and consistency properties for the proposed classifier. We further develop an efficient algorithm based on the proximal operator to solve the optimization problem. The performance of MgDWD is evaluated using finite sample simulations and miRNA data from an HIV study.  相似文献   
43.
Wang  Xiaojing  Han  Wenxiu  Yan  Xin  Zhang  Jun  Yang  Mengqi  Jiang  Pei 《Molecular diversity》2020,24(2):407-412
Molecular Diversity - Methods of three-dimensional molecular alignment generally treat all pharmacophore features equally when superimposing. However, some pharmacophore features can be more...  相似文献   
44.
Based on the surface passivation of n-type silicon in a silicon drift detector(SDD), we propose a new passivation structure of SiO2/Al2O3/SiO2 passivation stacks. Since the SiO2 formed by the nitric-acid-oxidation-of-silicon(NAOS)method has good compactness and simple process, the first layer film is formed by the NAOS method. The Al2O3 film is also introduced into the passivation stacks owing to exceptional advantages such as good interface characteristic and simple process. In addition, for requirements of thickness and deposition temperature, the third layer of the SiO2 film is deposited by plasma enhanced chemical vapor deposition(PECVD). The deposition of the SiO2 film by PECVD is a low-temperature process and has a high deposition rate, which causes little damage to the device and makes the SiO2 film very suitable for serving as the third passivation layer. The passivation approach of stacks can saturate dangling bonds at the interface between stacks and the silicon substrate, and provide positive charge to optimize the field passivation of the n-type substrate.The passivation method ultimately achieves a good combination of chemical and field passivations. Experimental results show that with the passivation structure of SiO2/Al2O3/SiO2, the final minority carrier lifetime reaches 5223 μs at injection of 5×1015 cm-3. When it is applied to the passivation of SDD, the leakage current is reduced to the order of nA.  相似文献   
45.
Jiang  Sen  Ji  Hua  Feng  Donglin  Li  Qian  Wu  Sunke  Chen  Zhi 《Meccanica》2020,55(6):1379-1391
Meccanica - This paper introduces an analytical approach to optimize the textured bearing with cavitation to improve the load support. For this purpose, a grooved parallel slider bearing is...  相似文献   
46.
Quantum coherence captures the essential nature of a quantum system[1]and can serve as a resource for quantum information processing[2].Recent studies also provide evidence that long-lived quantum coherence is crucial for overcoming the classical limits of measurement accuracy in quantum metrology[3-5].However,in practice,the unavoidable interaction of a principal system with its surroundings results in decoherence in most situations.Consequently,the advantage of quantum coherence in empowering the performance of quantum tasks will disappear in a very short time interval,which remains one of the major obstacles in its potential application.  相似文献   
47.
为数值求解描述不同物质间相位分离现象的高阶非线性Cahn-Hilliard(C-H)方程,发展了一种基于局部加密纯无网格有限点集法(local refinement finite pointset method,LR-FPM).其构造过程为:1)将C-H方程中四阶导数降阶为两个二阶导数,连续应用基于Taylor展开和加权最小二乘法的FPM离散空间导数;2)对区域进行局部加密和采用五次样条核函数以提高数值精度;3)局部线性方程组求解中准确施加含高阶导数Neumann边值条件.随后,运用LR-FPM求解有解析解的一维/二维C-H方程,分析粒子均匀分布/非均匀分布以及局部粒子加密情况的误差和收敛阶,展示了LR-FPM较网格类算法在非均匀布点情况下的优点.最后,采用LR-FPM对无解析解的一维/二维C-H方程进行了数值预测,并与有限差分结果相比较.数值结果表明,LR-FPM方法具有较高的数值精度和收敛阶,比有限差分法更易数值实现,能够准确展现不同类型材料间相位分离非线性扩散现象随时间的演化过程.  相似文献   
48.
49.
This study is concerned with a new,explicit approach by means of which forms of the large strain elastic potential for multiaxial rubberlike elasticity may be obtained based on data for a single deformation mode.As a departure from usual studies,here for the first time errors may be estimated and rendered minimal for all possible deformation modes and,furthermore,failure behavior may be incorporated.Numerical examples presented are in accurate agreement with Treloar's well-known data.  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