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   2732篇
  免费   408篇
  国内免费   294篇
化学   2196篇
晶体学   20篇
力学   155篇
综合类   42篇
数学   192篇
物理学   829篇
  2024年   13篇
  2023年   55篇
  2022年   101篇
  2021年   112篇
  2020年   108篇
  2019年   118篇
  2018年   81篇
  2017年   70篇
  2016年   98篇
  2015年   118篇
  2014年   153篇
  2013年   185篇
  2012年   224篇
  2011年   228篇
  2010年   173篇
  2009年   160篇
  2008年   169篇
  2007年   172篇
  2006年   130篇
  2005年   112篇
  2004年   98篇
  2003年   83篇
  2002年   77篇
  2001年   79篇
  2000年   84篇
  1999年   57篇
  1998年   62篇
  1997年   48篇
  1996年   49篇
  1995年   34篇
  1994年   20篇
  1993年   30篇
  1992年   16篇
  1991年   18篇
  1990年   14篇
  1989年   10篇
  1988年   11篇
  1987年   11篇
  1986年   8篇
  1985年   4篇
  1984年   2篇
  1983年   6篇
  1978年   4篇
  1977年   3篇
  1976年   2篇
  1974年   2篇
  1971年   2篇
  1966年   2篇
  1959年   4篇
  1884年   1篇
排序方式: 共有3434条查询结果,搜索用时 31 毫秒
991.
Digital radiography (DR) and whole-body fluorescent optical imaging (WFOI) have been widely applied in the field of molecular imaging, with the advantages in tissues and functional imaging. The integration of them contributes to the development and discovery of medicine. We introduce an equipment, performance of which is better than that of another molecular imaging system manufactured by Kodak Corp. It can take real-time small animal imaging in vivo, with lower cost and shorter development cycle on the LabVIEW platform. At last, a paradigm experiment on a nude mouse with green fluorescent protein (GFP) transgenic tumor is given to present a real-time DR-WFOI fusion simultaneous image.  相似文献   
992.
聚并苯导电高分子材料的ESR研究   总被引:4,自引:0,他引:4  
本文对由热固性酚醛树脂通过高温裂解制备的聚并苯导电高分子本征材料的ESR进行了研究。结果表明在各种裂解温度下制备的样品由于其结构不同,表现在ESR线宽、自旋浓度、线型的峰高比等差异很大,并给予了解释。  相似文献   
993.
An intracavity frequency-doubled vertical external cavity surface emitting laser (VECSEL) with green light is demonstrated. The fundamental frequency laser cavity consists of a distributed Bragg reflector (DBR) of the gain chip and an external mirror. A 12-mW frequency-doubled output has been reached at 540 nm with a nonlinear crystal LBO when the fundamental frequency output is 44 mW at 1080 nm. The frequency doubling efficiency is about 30%.  相似文献   
994.
汽轮机调节阀内流动特性的试验研究   总被引:13,自引:0,他引:13  
介绍了最常用的G-I型调节阀内的动态压力测量方法及其各关键部位的流动特性,尤其是引起不稳定流动的主要因素即气流的压力脉动特性。测试结果表明,调节阀处于不稳定工作状态即阀杆振动工况取决于脉动压力与阀杆固频率是否同频,并非其脉动压力值大小;调整阀杆固有频率是消除调节阀振动最简便和有效的方法。  相似文献   
995.
[structure: see text] A solid-phase fluorenylmethyloxycarbonyl (Fmoc)-based synthesis strategy is described for "mixed" aza-beta3-peptides as well as a convenient general approach for their required building blocks, the aza-beta3-amino acid residues (aza-beta3-aa). These monomers allow the synthesis of relatively large quantities of pure mixed aza-beta3-peptides. The required Fmoc-substituted aza-beta3-amino acids are accessible by convenient synthesis, and a number of monomers including those containing side chains with functional groups have been synthesized. The method was applied toward the solid-phase synthesis of aza-beta3-peptide mimetics of a biologically active histone H4 sequence.  相似文献   
996.
997.
The ruthenium(II)-supported heteropolyanions [HXW7O28Ru(dmso)3]6-(X=P, 1; As, 2) are composed of a Ru(dmso)3 group attached to an unprecedented heptatungstate fragment via two Ru-O-W bonds and one Ru-O-X bond, which represents a fundamentally novel mode of Ru-coordination to a polyoxoanion framework. Multinuclear 183W, 31P, 13C, and 1H NMR studies indicate high stability of 1 and 2 in solution.  相似文献   
998.
A novel catalyst for the Fenton reaction was prepared by immobilizing Fe(III) onto collagen fiber and its high activity as a catalyst for degradation of dyes under irradiation of UVC was proved.  相似文献   
999.
Single-crystalline wurtzite ZnS nanobelts are synthesized by the vapor phase transport (VPT) process. When oxidized, a single-crystalline ZnS nanobelt turns into a ZnO nanotwin belt containing two twinning parts with a sharp and clear edge, which is a (0001) twinning plane parallel to and running through the length direction. The two twinning parts in a ZnO nanotwin belt have the same crystalline direction, [0001], along their width, and the and crystalline directions along the length direction. On some ZnO nanobelts, nanovoids appear along the twinning planes and when those nanovoids connect with each other, one original ZnS nanobelt can divide into two single-crystalline ZnO nanobelts with quite clear edges.  相似文献   
1000.
We propose a phenomenological form of the charged lepton mass matrix which extends the idea of a ”lopsided” mass matrix found in the literature. The features of the form are that both the 2-3 and 1-3 elements of the charged lepton mass matrix are of order 1 and that the small elements have a new structure. This form leads to the interesting result that both large atmospheric and solar neutrino mixing can be accounted for by the matrix. Another interesting result of this mass matrix is that it leads to very small 1-3 mixing in the lepton sector and can suppress the branching ratio of under the present experimental limit in the supersymmetric see-saw case. Received: 3 October 2002 / Revised version: 10 November 2002 / Published online: 24 January 2003 RID="a" ID="a" e-mail: bixj@mail.tsinghua.edu.cn RID="b" ID="b" e-mail: dyb@itp.ac.cn  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