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   5347篇
  免费   346篇
  国内免费   424篇
化学   1371篇
晶体学   12篇
力学   495篇
综合类   40篇
数学   3075篇
物理学   1124篇
  2023年   55篇
  2022年   85篇
  2021年   103篇
  2020年   150篇
  2019年   129篇
  2018年   103篇
  2017年   160篇
  2016年   141篇
  2015年   122篇
  2014年   225篇
  2013年   445篇
  2012年   190篇
  2011年   296篇
  2010年   233篇
  2009年   375篇
  2008年   401篇
  2007年   433篇
  2006年   346篇
  2005年   265篇
  2004年   232篇
  2003年   189篇
  2002年   175篇
  2001年   123篇
  2000年   100篇
  1999年   115篇
  1998年   101篇
  1997年   107篇
  1996年   68篇
  1995年   57篇
  1994年   60篇
  1993年   38篇
  1992年   28篇
  1991年   21篇
  1990年   31篇
  1989年   18篇
  1988年   26篇
  1987年   16篇
  1986年   25篇
  1985年   26篇
  1984年   21篇
  1982年   14篇
  1981年   21篇
  1980年   37篇
  1979年   37篇
  1978年   36篇
  1977年   28篇
  1976年   31篇
  1974年   14篇
  1973年   24篇
  1972年   15篇
排序方式: 共有6117条查询结果,搜索用时 0 毫秒
101.
This paper presents results of studies on dc electrical conductivity and transference number measurements on potassium bromate (KBrO3) complexed polyvinyl chloride (PVC) films prepared by solution cast technique. Temperature dependence of dc electrical conductivity and transference number data indicated the dominance of ion type charge transport in these specimens. The magnitude of conductivity increased with increase in concentration of the salt and temperature. Using this (PVC + KBrO3) electrolyte, solid-state electrochemical cells were fabricated, and their discharge profiles were studied under a constant load of 100 kΩ. Several cell profiles such as open circuit voltage, short circuit current, power density, and energy density associated with these cells were evaluated and were reported. The features of complexation of the electrolytes were studied by X-ray diffraction and Fourier transform infrared spectroscopy. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006  相似文献   
102.
LI Biao  CHEN Yong   《理论物理通讯》2007,48(9):391-398
In the paper, a generalized sub-equation method is presented to construct some exact analytical solutions of nonlinear partial differential equations. Making use of the method, we present rich exact analytical solutions of the onedimensional nonlinear Schr(o)dinger equation which describes the dynamics of solitons in Bose-Einstein condensates with time-dependent atomic scattering length in an expulsive parabolic potential. The solutions obtained include not only non-traveling wave and coefficient function's soliton solutions, but also Jacobi elliptic function solutions and Weierstrass elliptic function solutions. Some plots are given to demonstrate the properties of some exact solutions under the Feshbachmanaged nonlinear coefficient and the hyperbolic secant function coefficient.  相似文献   
103.
全气相化学激光体系的直流放电研究   总被引:1,自引:2,他引:1       下载免费PDF全文
为了提高化学激光体系(AGIL)中F原子的产率,采用直流放电引发方式,对棒式电极的放电特性进行了研究。在对NF3/He混合气体进行解离时,通过选择不同平衡电阻,得到了3 kW左右的放电注入功率。用光谱分析仪对F原子产率进行了测量。通过拟合计算可得:一个NF3分子能够解离出1.3~1.5个F原子。  相似文献   
104.
ABSTRACT

Five ortho and para bands of the ν2 umbrella mode of the NH3–Ar van der Waals complex have been recorded at high resolution using jet-cooled infrared laser spectroscopy. A rovibrational analysis provides accurate band centres and upper state rotational constants for the Πs(j?=?1,k?=?0)?←?Σa(j,k?=?0) and Σs(j?=?1,k?=?0)?←?Σa(j,k?=?0) ortho bands. The puzzling para bands observed in the region of the lower and upper components of the inversion splitting doublet have been assigned by comparison with rovibrational and tunnelling levels and transitions calculated ab initio. The latter calculations are based on the four-dimensional potential energy surface reported by Loreau et al. [J. Chem. Phys. 141, 224303 (2014)], which takes explicitly into account the umbrella motion of the ammonia molecule. The very good agreement found between Πs/a,lower(j?=?1,k?=?1)?←?Σa(j?=?1,k?=?1) and Πs/a,upper(j?=?1,k?=?1)?←?Σs(j?=?1,k?=?1) experimental and calculated transitions has been exploited to determine precisely two different inversion splittings in the ν2 state (32.003(1) and 36.008(1)?cm?1) from extrapolated Q(0) line frequencies and to obtain a qualitative picture of Coriolis couplings present in both the ν2?=?0 and ν2?=?1 states.  相似文献   
105.
106.
We study a G/GI/1 single-server queuing model with i.i.d. service times that are independent of a stationary process of inter-arrival times. We show that the distribution of the waiting time converges to a stationary law as time tends to infinity provided that inter-arrival times satisfy a Gärtner-Ellis type condition. A convergence rate is given and a law of large numbers established. These results provide tools for the statistical analysis of such systems, transcending the standard case with independent inter-arrival times.  相似文献   
107.
In most of the earlier research for multiple zeros, in order to obtain a new iteration function from the existing scheme, the usual practice is to make no change at the first substep. In this paper, we explore the idea that what are the advantages if the flexibility of choice is also given at the first substep. Therefore, we present a new two-point sixth-order scheme for multiple roots (m>1). The main advantages of our scheme over the existing schemes are flexibility at both substeps, simple body structure, smaller residual error, smaller error difference between two consecutive iterations, and smaller asymptotic error constant. The development of the scheme is based on midpoint formula and weight functions of two variables. We compare our methods with the existing methods of the same order with real-life applications as well as standard test problems. From the numerical results, we find that our methods can be considered as better alternates for the existing methods of the same order. Finally, dynamical study of the proposed schemes is presented that confirms the theoretical results.  相似文献   
108.
对快速数值差分递推公式进行了改进,使之能够求解带有脉冲自陡峭项和脉冲内喇曼散射项的非线性薛定谔方程.通过与传统孤子解析结果及分步傅里叶方法数值结果的对比分析表明,快速数值差分递推改进算法是一种快速而准确的数值计算方法,它不仅能够同步考虑光学媒质中的群速色散作用和非线性克尔作用,而且将所有高阶非线性项对光脉冲传输的影响也...  相似文献   
109.
花巍  刘学深 《物理学报》2011,60(11):57-62
采用辛算法数值求解了一维立方五次方非线性Schrdinger方程,研究了不同非线性参数下非线性Schrdinger方程的动力学性质.数值结果表明,随着立方非线性参数的增加,系统经历了拟周期状态、混沌状态和周期状态,且在五次方项的调制下,呼吸子解可以退化为单孤子解.  相似文献   
110.
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