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   165842篇
  免费   17483篇
  国内免费   9966篇
化学   85274篇
晶体学   1658篇
力学   12110篇
综合类   541篇
数学   41431篇
物理学   52277篇
  2024年   357篇
  2023年   2090篇
  2022年   3397篇
  2021年   3557篇
  2020年   4032篇
  2019年   3628篇
  2018年   12971篇
  2017年   12486篇
  2016年   10305篇
  2015年   5292篇
  2014年   5746篇
  2013年   7239篇
  2012年   11990篇
  2011年   18502篇
  2010年   11017篇
  2009年   11213篇
  2008年   12170篇
  2007年   13581篇
  2006年   5101篇
  2005年   5194篇
  2004年   4470篇
  2003年   4237篇
  2002年   3144篇
  2001年   2096篇
  2000年   1931篇
  1999年   2040篇
  1998年   1808篇
  1997年   1759篇
  1996年   1805篇
  1995年   1490篇
  1994年   1261篇
  1993年   1122篇
  1992年   926篇
  1991年   871篇
  1990年   704篇
  1989年   572篇
  1988年   437篇
  1987年   368篇
  1986年   385篇
  1985年   310篇
  1984年   194篇
  1983年   154篇
  1982年   142篇
  1981年   95篇
  1980年   89篇
  1979年   59篇
  1914年   45篇
  1912年   40篇
  1909年   41篇
  1908年   40篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
121.
In this paper, we extend a classical result of Hua to arithmetic progressions with large moduli. The result implies the Linnik Theorem on the least prime in an arithmetic progression.  相似文献   
122.
In this paper the quantum-statistical properties of light beams propagating in a directional nonlinear coupler are investigated. This device is composed of a pair of linearly coupled nonlinear waveguides operating by means of degenerate parametric downconversion. The possibility of generation of nonclassical states of light in single and compound modes, using the short-length approximation, is discussed. Influence of linear and nonlinear mismatches for generation of nonclassical light is taken into account. This work was supported by Project LN00A015, Research Project No. CEZ: J14/98 and the COST project OC P11.003 of the Czech Ministry of Education.  相似文献   
123.
A low cost, coolerless 980nm diode pumped, gain flattened L band EDFA with fast transient control, high pump efficiency and gain clamping effect was realized by using FBGs as C band seed generators.  相似文献   
124.
In this paper, we describe an aircraft loading problem submitted by the French military agency (DGA) as part of a more general military airlift planning problem. It can be viewed as a kind of bi-dimensional bin-packing problem, with heterogeneous bins and several additional constraints. We introduce two-phase methods for solving this NP-hard problem. The first phase consists in building good initial solutions, thanks to two fast algorithms: a list-based heuristic and a loading pattern generation method. Both algorithms call a constraint-based subroutine, able to determine quickly if the items already loaded can be reshuffled to accommodate a new object. The second phase improves these preliminary solutions using local search techniques. Results obtained on real data sets are presented.  相似文献   
125.
This paper gives the weighted Lp convergence rate estimations of the Gruenwald interpolatory polynomials based on the zeros of Chebyshev polymomials of the first kind,and proves that the order of the estimations is optimal for p≥1.  相似文献   
126.
非完整约束奇异广义力学系统的Poincaré-Cartan积分   总被引:1,自引:0,他引:1       下载免费PDF全文
李爱民  张莹  李子平 《物理学报》2004,53(9):2816-2820
对受高阶微商非完整约束并用奇异Lagrange量描述的广义力学系 统,基于广义Apell-Четаев约束条件,并考虑到系统的内在约束,导出了该非完整 约 束奇异广义力学系统的广义Poincaré-Cartan积分不变量. 并证明了该不变量与非完整约束 奇异广义力学系统的广义正则方程等价.  相似文献   
127.
Nicholas Nathan tries to resist the current version of the causal argument for sense-data in two ways. First he suggests that, on what he considers to be the correct re-construction of the argument, it equivocates on the sense of proximate cause. Second he defends a form of disjunctivism, by claiming that there might be an extra mechanism involved in producing veridical hallucination, that is not present in perception. I argue that Nathan’s reconstruction of the argument is not the appropriate one, and that, properly interpreted, the argument does not equivocate on proximate cause. Furthermore, I claim that his postulation of a modified mechanism for hallucinations is implausibly ad hoc.  相似文献   
128.
129.
A method for fabricating well-dispersed nanowire suspension has been demonstrated in the paper. Thin gold nanowires were prepared by template synthesis, and then functionalized with sulphonate group-terminated thiols before suspended in different solvents. The degree of aggregation of the obtained suspension was evaluated with transmission electron microscopy (TEM) and UV-vis spectroscopy. It was found that the degree of aggregation was predominated by the solvents, and the best degree of dispersion was obtained when isopropyl alcohol (IPA) was used as the solvent. The gold nanowires from the suspension can be selectively assembled onto chemically patterned substrates. This well-dispersed nanowire suspension is potentially useful for fabricating novel nanodevices.  相似文献   
130.
A novel and simple two-frequency Brillouin fiber laser is presented. It is based on a fiber Fabry-Perot cavity with fiber Bragg gratings as reflectors. The model of stimulated Brillouin scattering in fiber grating-based Fabry-Perot resonator is investigated. The laser allows conversion efficiency of close to 100% and suppresses the higher-order Stokes waves. The theoretical prediction is presented and the experimental demonstration is realized.  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