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   220200篇
  免费   34383篇
  国内免费   24271篇
化学   148589篇
晶体学   2474篇
力学   14345篇
综合类   1632篇
数学   29389篇
物理学   82425篇
  2024年   445篇
  2023年   3758篇
  2022年   5863篇
  2021年   7108篇
  2020年   7979篇
  2019年   7745篇
  2018年   6993篇
  2017年   6546篇
  2016年   9880篇
  2015年   9495篇
  2014年   11868篇
  2013年   15889篇
  2012年   19002篇
  2011年   20123篇
  2010年   13866篇
  2009年   13535篇
  2008年   14397篇
  2007年   13071篇
  2006年   12218篇
  2005年   10319篇
  2004年   8085篇
  2003年   6430篇
  2002年   6071篇
  2001年   5000篇
  2000年   4440篇
  1999年   4758篇
  1998年   4089篇
  1997年   3725篇
  1996年   3952篇
  1995年   3314篇
  1994年   3074篇
  1993年   2549篇
  1992年   2295篇
  1991年   2019篇
  1990年   1661篇
  1989年   1274篇
  1988年   1037篇
  1987年   880篇
  1986年   808篇
  1985年   692篇
  1984年   530篇
  1983年   402篇
  1982年   331篇
  1981年   237篇
  1980年   179篇
  1979年   102篇
  1978年   93篇
  1976年   88篇
  1975年   87篇
  1974年   78篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
On congruence lattices of regular semigroups with Q-inverse transversals   总被引:5,自引:0,他引:5  
Communicated by F. Pastijn  相似文献   
992.
湿度对绝缘体表面电导和气体电导有一定的影响,但通常在湿度传感器的研究中忽略了气体电导的贡献。本文通过特殊设计装置来区分表面电导和气体电导,并分别从实验和理论上进行了定性的研究。  相似文献   
993.
To satisfy the volatile nature of today’s markets, businesses require a significant reduction in product development lead times. Consequently, the ability to develop precise product sales forecasts is of fundamental importance to decision-makers. Over the years, many forecasting techniques of varying capabilities have been introduced. The precise extent of their influences, and the interactions between them, has never been fully clarified, although various forecasting factors have been explored in previous studies. Accordingly, this study adopts the Taguchi method to calibrate the controllable factors of a forecasting model. An L9(34) inner orthogonal array is constructed for the controllable factors of data period, horizon length, and number of observations required. An experimental design is then performed to establish the appropriate levels for each factor. At the same time, an L4(23) outer orthogonal array is used to consider the inherited parameters of forecasting method as the noise factors of Taguchi method simultaneously. An illustrated example, employing data from a power company, serves to demonstrate the thesis. The results show that the proposed model permits the construction of a highly efficient forecasting model through the suggested data collection method.  相似文献   
994.
本文在经典风险模型的基础上,将索赔到达过程推广为更新过程,索赔可以批量到达,且带有常数利息力和Brown运动干扰项,得到一个新的风险模型,运用Markov骨架过程的方法,得出盈余过程的瞬时分布和生存概率.  相似文献   
995.
Molecular dynamics (MD) method is used to investigate the behavior of the pressure-volume-temperature (P-V-T) relationship, lattice constant and thermal expansivity for ZnO with rock-salt structure at high pressures and temperatures. The interionic potential is taken to be the sum of pair-wise additive Coulomb, van der Waals attraction, and repulsive interactions. The isothermal and isobaric properties are discussed from the corresponding P-V-T relationship, and it is shown that the MD simulation is successful in reproducing the measured volumes of ZnO over a wide range of temperature and pressure. Meanwhile, the equations of state parameters including lattice constant, linear thermal expansion coefficient, and isothermal bulk modulus are calculated and compared with the available experimental data and the latest theoretical results. At an extended pressure and temperature range, P-V-T relationship, lattice constant, and linear thermal expansion coefficient have been predicted. The structural and thermodynamic properties of ZnO with rock-salt structure are summarized in the pressure 0-100 GPa ranges and the temperature up to 3100 K.  相似文献   
996.
The ultra-short laser metal ablation is a very complex process, the complete simulation of which requires applications of complicated hydrodynamics or molecular dynamics models, which, however, are often time-consuming and difficult to apply. For many practical applications, where the laser ablation depth is the main concern, a simplified model that is easy to apply but at the same time can also provide reasonably accurate predictions of ablation depth is very desirable. Such a model has been developed and presented in this paper, which has been found to be applicable for laser pulse duration up to 10 ps based on comparisons of model predictions with experimental measurements.  相似文献   
997.
A novel heath monitoring system of the rocket based on fiber optic Bragg gratings is brought forward, its component units and working principle are also described.  相似文献   
998.
给出目标信息系统学习的多准则决策方法,建立多准则决策的规则学习模型,讨论该模型的性质。该模型优于Z.Pawlak方法,将规则提取与信息融合为一体。也优于AHP等模型,具有简洁性.通过实例计算,取得了满意结果。  相似文献   
999.
Ag-Bi高温超导线材转变温度的测量   总被引:2,自引:0,他引:2  
介绍了 Bi系银包套高温超导线材的电阻温度特性 ,用测电阻和电磁感应两种方法分别测量了材料的超导转变温度 ,电磁感应法测量曲线上台阶的出现表明材料中 Bi(2 2 2 3)和 Bi(2 2 12 )两相的存在。  相似文献   
1000.
Single-crystalline layered lithium manganese oxide nanorods were prepared via a low-temperature molten salt synthesis method. The material was investigated by a variety of techniques, including X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectrum (XPS).  相似文献   
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