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   10885篇
  免费   1975篇
  国内免费   1007篇
化学   7156篇
晶体学   87篇
力学   707篇
综合类   91篇
数学   1205篇
物理学   4621篇
  2024年   43篇
  2023年   247篇
  2022年   425篇
  2021年   448篇
  2020年   444篇
  2019年   444篇
  2018年   367篇
  2017年   348篇
  2016年   540篇
  2015年   512篇
  2014年   578篇
  2013年   795篇
  2012年   944篇
  2011年   1025篇
  2010年   640篇
  2009年   670篇
  2008年   668篇
  2007年   576篇
  2006年   537篇
  2005年   440篇
  2004年   345篇
  2003年   282篇
  2002年   258篇
  2001年   207篇
  2000年   220篇
  1999年   206篇
  1998年   217篇
  1997年   193篇
  1996年   152篇
  1995年   201篇
  1994年   174篇
  1993年   135篇
  1992年   105篇
  1991年   87篇
  1990年   94篇
  1989年   68篇
  1988年   46篇
  1987年   35篇
  1986年   39篇
  1985年   21篇
  1984年   18篇
  1983年   23篇
  1982年   13篇
  1981年   6篇
  1980年   10篇
  1979年   2篇
  1978年   4篇
  1975年   3篇
  1974年   2篇
  1957年   3篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
Based on the basic theory of molecular vibration relaxation and semi-classical density matrix theory, operating parameters optimization of buffer gas in the process of miniature pulsed optically pumped submillimeter wave laser was systemically studied and the theoretical calculated result was tested by experiments. The result would do favor to develop and study high-power and wide-range tunable miniature and high-efficient pulsed optically pumped submillimeter wave laser and also had some instruction to its application.  相似文献   
32.
Sufficient conditions for asymptotic behavior of the solutions of nonlinear forced neutral delay differential equations with impulses are found. The results given in [2,4,6,7] are generalized and improved.  相似文献   
33.
We have investigated the magnetic and magneto-transport properties of a systematic sequence of five InAs/Mn digital alloys grown by a combination of molecular beam epitaxy and atomic layer epitaxy. The samples consist of 30 periods of Mn fractional monolayers (ML) (0.17–0.5 ML) separated by 14 ML thick InAs spacer layers in a superlattice configuration. Four samples show n-type electrical conduction while the fifth (0.25 ML Mn) is p-type. Squid magnetization measurements performed on these samples show remnant magnetization above room temperature, which is apparently related to a second phase.  相似文献   
34.
Retractable structures which alter their geometries according to practical requirements are widely used in roof structures of stadiums for their versatility. A retractable structure based on threefold-symmetric Bricard linkages and rotating rings of tetrahedra is proposed and developed in this paper. By replacing each link of a threefold-symmetric Bricard linkage with a tetrahedron, a retractable structure is obtained which can repeatedly open and close by rotating the tetrahedra. The geometric relationship between the retractable structure and the threefold-symmetric Bricard linkage is derived and ranges of main geometric parameters are determined to ensure a continuous and smooth movement in the deployment of the structure. Then the relative displacement of the support and the open rate of the structure, two main parameters concerned in practical applications, are investigated. Preferred ranges of main geometric parameters are proposed and a physical model is manufactured to verify them. A discussion on some possible improvements and modifications of the structure is also presented.  相似文献   
35.
Cuihua Xue  Fen-Tair Luo 《Tetrahedron》2004,60(30):6285-6294
A general and controlled bidirectional growth strategy enable a very rapid and efficient construction of oligo(phenyleneethynylene)s possessing functional groups such as methylthio and thioacetate groups at both ends. The strategy employs only one reaction type with good to moderate yields to grow the conjugated chains. The synthesis is efficient and can give 23 benzene rings and 22 carbon-carbon triple bonds in the conjugated chains. The compounds are fully characterized by 1H and 13C NMR and UV/vis and fluorescence spectroscopy.  相似文献   
36.
集合环   总被引:2,自引:1,他引:1  
本文用集环来表现模糊集,得到了表现定理的新形式,并证明了这种表现可以有限化,即用有限个经典集近似刻划模糊集并且这样的刻划是同态的。最后,证明了集对方法是集环表现的特殊情形。  相似文献   
37.
罗秀娟  马健康 《光子学报》1991,20(3):342-347
在GS-221高速摄影测量仪中,测角信息采集与处理速度的快慢是重要性能指标之一。本文讨论了如何在尽可能短的时间内对测角信息进行采集和处理的软件实现方法。  相似文献   
38.
Hydroxyapatite Ca10(PO4)6(OH)2 (HAP) is known as a bioactive and biocompatible material, HAP coatings were used to improve the biocompatible of substrate by many researcher, In this work, HAP thin films on porous silicon (PS) substrates have been prepared by aqueous precipitation method with rapid thermal annealing (RTA) processes. The HAP films had been prepared under the annealing temperature ranging from 300 to 1000 °C. By the measurement of X-ray diffraction (XRD), it was found that for the crystallinity optimization, the heat-treatment at 850–950 °C for 1 h would be favorable. Atomic force microscopy (AFM) and scanning electron microscope (SEM) measurements reveal a dense and smooth surface of the HAP film, and tightly adherence of the coating on porous silicon substrate after sintered. Thus, by this method, porous silicon could be increased its bioactivity and so that could be used in the biomedical area.  相似文献   
39.
MEASUREMENTSOFFeANDCuK-ShelIONIZATIONCROSSSECTIONSBYSLOWELECTRONIMPACTLiTaihuaAnZhuLuoZhengmingCenterforRadiationPhysics,Ins...  相似文献   
40.
In the paper, by using Ky Fan’s section theorem, we obtain an existence theorem for vector equilibrium problems. Motivated by the ideas of Kinoshita and McLennan, we introduce the concept of the essential component of the solution set for vector equilibrium problems, and we prove that there exists at least one essential component of the solution set for every vector equilibrium problem satisfying some conditions. Research was partially supported by the Natural Science Foundation of Guangdong Province, P. R. China.  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