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   30432篇
  免费   188篇
  国内免费   286篇
化学   11206篇
晶体学   283篇
力学   1448篇
综合类   15篇
数学   9312篇
物理学   8642篇
  2022年   49篇
  2021年   56篇
  2020年   67篇
  2019年   79篇
  2018年   1240篇
  2017年   1491篇
  2016年   792篇
  2015年   600篇
  2014年   533篇
  2013年   828篇
  2012年   3188篇
  2011年   2403篇
  2010年   1911篇
  2009年   1618篇
  2008年   654篇
  2007年   689篇
  2006年   643篇
  2005年   4479篇
  2004年   3974篇
  2003年   2370篇
  2002年   516篇
  2001年   335篇
  2000年   127篇
  1999年   184篇
  1998年   128篇
  1997年   74篇
  1996年   62篇
  1995年   48篇
  1994年   50篇
  1992年   173篇
  1991年   157篇
  1990年   143篇
  1989年   112篇
  1988年   107篇
  1987年   59篇
  1986年   48篇
  1985年   44篇
  1984年   47篇
  1983年   31篇
  1979年   35篇
  1976年   81篇
  1975年   41篇
  1974年   47篇
  1973年   55篇
  1972年   40篇
  1970年   36篇
  1969年   37篇
  1968年   36篇
  1967年   30篇
  1966年   37篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
We study a class of shape optimization problems for semi-linear elliptic equations with Dirichlet boundary conditions in smooth domains in ℝ2. A part of the boundary of the domain is variable as the graph of a smooth function. The problem is equivalently reformulated on a fixed domain. Continuity of the solution to the state equation with respect to domain variations is shown. This is used to obtain differentiability in the general case, and moreover a useful formula for the gradient of the cost functional in the case where the principal part of the differential operator is the Laplacian. Online publication 23 January 2004.  相似文献   
32.
33.
Abnormalities in the cochlear function usually cause broadening of the auditory filters which reduces the speech intelligibility. An attempt to apply a spectral enhancement algorithm has been undertaken to improve the identification of Polish vowels by subjects with cochlear-based hearing-impairment. The identification scores of natural (unprocessed) vowels and spectrally enhanced (processed) vowels has been measured for hearing-impaired subjects. It has been found that spectral enhancement improves vowel scores by about 10% for those subjects, however, a wide variation in individual performance among subjects has been observed. The overall vowels identification scores obtained were 85% for natural vowels and 96% for spectrally enhanced vowels.  相似文献   
34.
In continuation of previous work some novel 3,5-diacetyl-1,4-dihydropyridine derivatives were synthesized and their photochemical behavior was studied under oxygen and argon atmosphere. Oxidation of the dihydropyridine ring and formation of pyridine derivatives was the result of the reaction. The presence of oxygen affects not only on the rate of oxidation, but also the formation of some unidentified by-products was observed on irradiation under this atmosphere.  相似文献   
35.
PV型HgCdTe光电探测器中的混沌及其诊断   总被引:4,自引:3,他引:1       下载免费PDF全文
 对激光辐照半导体光电探测器的实验研究,发现当一束不太强的稳定连续波激光照射在PV型HgCdTe光电探测器上时,可以引起探测器出现混沌行为。利用光电探测器的光电压信号随时间变化的实验数据,通过求功率谱、计算Lyapunov指数对混沌进行了诊断。  相似文献   
36.
We extend the previously found accelerated Kerr-Schild metrics for Einstein-Maxwell-null dust and Einstein-Born-Infeld-null dust equations to the cases including the cosmological constant. This way we obtain the generalization of the charged de Sitter metrics in static space-times. We also give a generalization of the zero acceleration limit of our previous Einstein-Maxwell and Einstein-Born-Infeld solutions.  相似文献   
37.
The Kα to Lα and Kβ to Lβ intensity ratios of seven elements have been measured following photoionization at 59.5 keV by using a Si (Li) detector (FWHM=155 eV at 5.96 keV). The intensity ratios were determined by measuring K and L x-rays emitted from a standard target of a given element. The theoretical values of the Kα to Lα and Kβ to Lβ intensity ratios were calculated using theoretically tabulated values of shell/subshell photoionization cross sections, fluorescence yields, Coster-Kronig transition probabilities, and radiative decay rates for ηKLi≠ and ηKLi=0. The measured values are in good agreement with theoretical results. From Optika i Spektroskopiya, Vol. 97, No. 2, 2004, pp. 186–189. Original English Text Copyright ? 2004 by A. Kü?ük?nder, S?ğüt, E. Kü?ük?nder, Büyükkasap. This article was submitted by the authors in English.  相似文献   
38.
The reaction of a new fluorinated unsymmetrical allenylazine with dimethyl acetylenedicarboxylate and phenylacetylene affords the combined intra-intermolecular criss-cross cycloaddition products, 2,3-disubstituted-1,10-diazatricyclo[5.2.1.04,10]deca-2,6-diene derivatives. The products contain three fused five-membered rings with two nitrogen atoms within an unsaturated heterocyclic system. The structures were assigned using 2D NMR correlations and in the case of the phenylacetylene adduct by X-ray structure analysis.  相似文献   
39.
 通过数值求解一维瞬态受激布里渊散射(SBS)声光耦合波方程,从理论上分析了泵浦激光参数及光学材料参数对SBS过程发生阈值的影响。以SBS过程中建立起来的应力场抗拉(压)强度和散射场的反射率为判据,分析了激光脉宽及作用区域长度对激光超声破坏材料效果的影响,探讨了短脉冲激光(约ns)引起的激光超声对材料的破坏机理;讨论了通过参数配置有效遏制SBS过程激光超声对光学材料的破坏问题。  相似文献   
40.
We solve completely the problem of classification of germs of complex planar vector fields with nilpotent singularity with respect to formal orbital equivalence.  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