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   13552篇
  免费   2245篇
  国内免费   1501篇
化学   9373篇
晶体学   126篇
力学   910篇
综合类   91篇
数学   1676篇
物理学   5122篇
  2024年   46篇
  2023年   290篇
  2022年   494篇
  2021年   533篇
  2020年   546篇
  2019年   487篇
  2018年   470篇
  2017年   413篇
  2016年   584篇
  2015年   654篇
  2014年   751篇
  2013年   1002篇
  2012年   1143篇
  2011年   1163篇
  2010年   810篇
  2009年   758篇
  2008年   838篇
  2007年   775篇
  2006年   698篇
  2005年   580篇
  2004年   426篇
  2003年   356篇
  2002年   342篇
  2001年   297篇
  2000年   245篇
  1999年   293篇
  1998年   271篇
  1997年   201篇
  1996年   223篇
  1995年   221篇
  1994年   191篇
  1993年   166篇
  1992年   135篇
  1991年   152篇
  1990年   151篇
  1989年   110篇
  1988年   92篇
  1987年   79篇
  1986年   59篇
  1985年   64篇
  1984年   28篇
  1983年   33篇
  1982年   26篇
  1981年   20篇
  1980年   13篇
  1979年   10篇
  1978年   8篇
  1977年   10篇
  1974年   6篇
  1973年   9篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
郭玉彬  李加 《光学学报》1995,15(3):13-319
描述了用高功率脉冲激光打靶产生的等离子体作为软X射线源而进行的接近式软X射线光刻研究,采用负性辐射线光刻胶聚氯甲基苯乙烯,得到了一些新的实验结果。  相似文献   
972.
 使用X射线衍射、差热分析、透射电镜及X射线能谱分析,研究了Pd82Si18合金在高压下的凝固特点及所形成的相的结构和稳定性。在5.5 GPa压力下以100 K/s的冷却速率淬火,得到了面心立方结构钯硅固溶体(MS-Ⅰ),其点阵常数为a=0.388 3 nm。与钯硅固溶体共存的还有另一未知结构亚稳相(MS-Ⅱ)。在700 K时上述亚稳相转变成平衡相Pd+Pd3Si。  相似文献   
973.
本文讨论机敏结构的制作方法、集成光纤传感器存在的问题、现有解决方法和今后的研究方向。  相似文献   
974.
In this paper, we propose and investigate a new general model of fuzzy stochastic discrete-time complex networks (SDCNs) described by Takagi–Sugeno (T–S) fuzzy model with discrete and distributed time-varying delays. The proposed model takes some well-studied models as special cases. By employing a new Lyapunov functional candidate, we utilize some stochastic analysis techniques and Kronecker product to deduce delay-dependent synchronization criteria that ensure the mean-square synchronization of the proposed T–S fuzzy SDCNs with mixed time-varying delays. These sufficient conditions are computationally efficient as it can be solved numerically by the LMI toolbox in Matlab. A numerical simulation example is provided to verify the effectiveness and the applicability of the proposed approach.  相似文献   
975.
By using the bifurcation theory of dynamical systems to the generalized Kadomtsov-Petviashvili-Benjamin-Bona-Mahony equation, the existence of solitary wave solutions, compactons solution, non-smooth periodic cusp wave solutions and uncountably infinite many smooth periodic wave solutions is obtained. Under different parametric conditions, various sufficient conditions to guarantee the existence of the above solutions are given. Some exact explicit parametric representations of the above waves are determined.  相似文献   
976.
In this paper, a class of delayed predator-prey model of prey dispersal in two-patch environments is considered. By analyzing the associated characteristic transcendental equation, its linear stability is investigated and Hopf bifurcation is demonstrated. Some explicit formulae determining the stability and the direction of the Hopf bifurcation periodic solutions bifurcating from Hopf bifurcations are obtained by using the normal form theory and center manifold theory. Some numerical simulation for justifying the theoretical analysis are also provided. Finally, biological explanations and main conclusions are given.  相似文献   
977.
 用金刚石压砧高压X光衍射技术研究了Ⅱ-Ⅵ族化合物CdTe的室温状态方程和室温高压相变。实验的最高压力达39.2 GPa。实验中发现CdTe从(3.3±0.1)GPa开始从闪锌矿结构相相NaCl结构相转变,相变时体积收缩15.8%;从(10.3±0.2)GPa开始从NaCl相向β-Sn结构相转变,相变时无体积突变;在(12.2±0.2)GPa由β-Sn相向正交结构相转变,相变时也无体积突变。CdTe的压缩数据用最小二乘法以Bridgman状态方程和Murnaghan状态方程拟合,得到其零压时合相变压力时各个相的体弹模量及体弹模量的压力微商,并与其它的实验合理论结果进行比较。  相似文献   
978.
In this paper, an ultra-wideband Janus metastructure (MS) utilizing anapole mode for detector in the terahertz (THz) range by graphene is proposed. Specifically, when Fermi level (Ef) is set to 0.9 eV, the MS demonstrates ultra-broadband absorption exceeding 0.9 from 0.754 to 5 THz in the −z-direction with a relative bandwidth of 147.6 %, in which perfect absorption of over 98% develops from 3.24 to 5 THz. In the case of the +z-direction, the absorptivity maintains around 0.6 within the 0.745 ∼ 5 THz range. As Ef equals 0 eV, the difference in absorption between the −z-direction and +z-direction exceeds 0.9 from 4.49 to 4.76 THz. The study also explores the MS for refractive index sensing near 3.71 THz by a unique difference detection, measuring two refractive index ranges: 1.2 ∼ 2.6 and 4.5 ∼ 4.7, with corresponding sensitivities of 0.0450 and 0.0304, respectively. Owing to its highly symmetrical structure, the MS is insensitive to the polarization state of the electromagnetic (EM) waves, performing remarkable angular stability as the incident angle varies from 0 to 60 degrees in the −z-direction. These splendid properties make the design a good candidate for biomedical sensing, EM cloaking, and full-space EM wave control.  相似文献   
979.
叶青  唐坤发  胡嘉桢 《物理学报》1987,36(8):1019-1026
本文运用作者所发展的严格docimation- 平均场近似方法对Potts 模型的临界指数作了计算.所得结果与严格解符合得很好, 而与计算工作量相当的重正化群方法相比, 精确度大为提高。 关键词:  相似文献   
980.
In the recent literature, the boundary element method (BEM) is extensively used to solve time-dependent partial differential equations. However, most of these formulations yield algorithms where one has to include all interior points in the computation process if finite difference procedures are used to approximate the temporal derivative. This obviously restricts the advantages of the BEM, which is mainly considered to be a boundary only algorithm for time-independent problems. A new algorithm is demonstrated here, which extends the boundary only nature of the method to time-dependent partial differential equations. Using this procedure, one can reduce the finite difference time integration algorithm, generated in a standard manner, to a boundary only process. The proposed method is demonstrated with considerable success for diffusion problems. Results obtained in these applications are presented comparatively with analytical and other boundary element time integration procedures. The algorithm proposed may utilize several coordinate functions in the secondary reduction phase of the formulation. A summary of such functions is described here and performances of these functions are tested and compared in three applications. It is shown that some coordinate functions perform better than others under certain conditions. Using these results, we propose a general coordinate function, which may be used with satisfactory results in all parabolic partial differential equation applications.  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