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   80062篇
  免费   6500篇
  国内免费   5099篇
化学   24007篇
晶体学   1809篇
力学   3521篇
综合类   364篇
数学   18620篇
物理学   43340篇
  2022年   174篇
  2021年   349篇
  2020年   642篇
  2019年   943篇
  2018年   923篇
  2017年   620篇
  2016年   442篇
  2015年   417篇
  2014年   1065篇
  2013年   1898篇
  2012年   1155篇
  2011年   1714篇
  2010年   2295篇
  2009年   6813篇
  2008年   7891篇
  2007年   6337篇
  2006年   5807篇
  2005年   3951篇
  2004年   3774篇
  2003年   4001篇
  2002年   5236篇
  2001年   3748篇
  2000年   3519篇
  1999年   3350篇
  1998年   2759篇
  1997年   1923篇
  1996年   1723篇
  1995年   2208篇
  1994年   2137篇
  1993年   1595篇
  1992年   1098篇
  1991年   830篇
  1990年   675篇
  1989年   603篇
  1988年   562篇
  1987年   403篇
  1986年   192篇
  1985年   942篇
  1984年   616篇
  1983年   487篇
  1982年   638篇
  1981年   792篇
  1980年   719篇
  1979年   558篇
  1978年   581篇
  1977年   538篇
  1976年   540篇
  1975年   317篇
  1974年   354篇
  1973年   462篇
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
971.
Continuous mapping of an ozone episode in Paris in June 1999 has been performed using a differential absorption lidar system. The 2D ozone concentration vertical maps recorded over 33 h at the Champ de Mars are compiled in a video clip that gives access to local photochemical dynamics with unprecedented precision. The lidar data are compared over the whole period with point monitors located at 0-, 50-, and 300-m altitudes on the Eiffel Tower. Very good agreement is found when spatial resolution, acquisition time, and required concentration accuracy are optimized. Sensitivity to these parameters for successful intercomparison in urban areas is discussed. Received: 11 February 2002 / Published online: 14 March 2002  相似文献   
972.
The currents and their fluctuations in two capacitively coupled single electron transistors are determined in the limit of sequential tunnelling. Our considerations are restricted to the case when the islands (dots) of the transistors are atomic-sized, which means each of them has only one single electronic level available for the tunnelling processes. The Coulomb interactions of accumulated charges on the both single electron transistors lead to the effect of the negative differential resistance. An enhancement of the current shot-noise was also found. Spectral decomposition analysis indicated the two main contributions to the shot-noise: low- and high-frequency fluctuations. It was found that the low frequency fluctuations (polarization noise) are responsible for a strong enhancement of the current noise. Received 9 October 2001 / Received in final form 8 March 2002 Published online 9 July 2002  相似文献   
973.
Two types of extreme collective motion, large-amplitude many-phonon vibration of the ionic core and rotation of the cluster with high angular momenta, are considered. The interplay between vibration and collective motion towards fission is discussed. A new mechanism of formation and rupture of the neck is proposed which is based on the Franck-Condon principle, and accounts for the interplay between vibration and fission. Under rotation, the change of the shape of the cluster and a phase transition from axially symmetric to triaxial ellipsoid are predicted. For studying the effects, vibrational motion can be induced by laser radiation. Rotational motion may arise in collisions of clusters. Received 26 April 2001 and Received in final form 15 October 2001  相似文献   
974.
We consider the semilinear Cauchy problem for a class of pseudo-differential operators generating sub-Markovian semigroups. Solutions of such problems with negative definite nonlinearity play an important role in constructing branching measure-valued processes. We establish local existence and uniqueness of solutions in the context of the Dirichlet space associated to the problem. Comparison and global properties of solutions are also studied. Accepted 29 August 2001. Online publication 17 December 2001.  相似文献   
975.
本通过引入激励经济学的思想来探讨解决目前我国技术创新中的激励不足问题。本从分析具体的激励模型(包括简单激励模型、多代理任务模型和自我选择模型)入手,并进行模型的推广应用,通过选择性的讨论,针对技术创新的具体问题提出激励机制设计思想和政策建议。  相似文献   
976.
给出了几乎齐次函数的一个新的刻划定理,这一刻划是齐次函数欧拉定理的拓广。  相似文献   
977.
图的划分问题曾引起图论界的广泛关注,在文献[4]中讨论了k-单圈划分,本文进一步研究基于k-单圈划分的优化问题,即在一个赋权图中求一个最小权可k-单圈划分的支撑子图,以及对一个不存在k-单圈划分支撑子图的图,如何添最少的边使得它有k-单圈划分的支撑子图。  相似文献   
978.
For each compact subset K of N let (K) denote the space of functions that are harmonic on some neighbourhood of K. The space (K) is equipped with the topology of uniform convergence on K. Let Ω be an open subset of N such that 0Ω and N\Ω is connected. It is shown that there exists a series ∑Hn, where Hn is a homogeneous harmonic polynomial of degree n on N, such that (i) ∑Hn converges on some ball of centre 0 to a function that is continuous on Ω and harmonic on Ω, (ii) the partial sums of ∑Hn are dense in (K) for every compact subset K of N\Ω with connected complement. Some refinements are given and our results are compared with an analogous theorem concerning overconvergence of power series.  相似文献   
979.
介绍一种实用的可靠性增长模型杜安 (Duane)模型 ,并探讨如何运用该模型来分析、指导斯特林制冷机的可靠性增长试验 ,包括试验前的准备、试验数据的处理、曲线的绘制 ,以及如何对增长过程进行估计和监测  相似文献   
980.
反应离子镀光学薄膜的微观结构分析   总被引:2,自引:1,他引:1  
王建成  韩丽瑛 《光学学报》1993,13(10):56-959
用反应离子镀方法制备了TiO2单层膜及TiO2/SiO2多层膜,用透射电子显微镜分别观察了由反应离子镀方法及传统蒸镀法二种不同工艺制得的TiO2单层膜及TiO2/SiO2多层膜的断面结构,并对TiO2单层膜进行了喇曼分析和卢瑟福背散射分析。  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