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   30614篇
  免费   123篇
  国内免费   272篇
化学   11669篇
晶体学   271篇
力学   1411篇
综合类   12篇
数学   9243篇
物理学   8403篇
  2022年   63篇
  2021年   61篇
  2020年   54篇
  2019年   43篇
  2018年   1214篇
  2017年   1477篇
  2016年   736篇
  2015年   569篇
  2014年   495篇
  2013年   747篇
  2012年   3228篇
  2011年   2387篇
  2010年   1847篇
  2009年   1603篇
  2008年   672篇
  2007年   697篇
  2006年   681篇
  2005年   4495篇
  2004年   3971篇
  2003年   2333篇
  2002年   526篇
  2001年   309篇
  2000年   113篇
  1999年   183篇
  1998年   116篇
  1997年   86篇
  1996年   70篇
  1995年   60篇
  1994年   68篇
  1992年   193篇
  1991年   169篇
  1990年   153篇
  1989年   129篇
  1988年   123篇
  1987年   78篇
  1986年   50篇
  1985年   68篇
  1984年   64篇
  1983年   48篇
  1982年   61篇
  1981年   47篇
  1979年   49篇
  1978年   53篇
  1976年   100篇
  1975年   43篇
  1974年   55篇
  1973年   78篇
  1972年   52篇
  1970年   39篇
  1969年   40篇
排序方式: 共有10000条查询结果,搜索用时 22 毫秒
91.
92.
93.
A pulsed field gradient version of the sensitivity-enhanced 2D TOCSY experiment is proposed which yields high-quality spectra with improved sensitivity and a minimum of two scans pert1increment. For rapid acquisition of 1D TOCSY spectra, the 1D DPFGSE–TOCSY experiment was modified to include phase-encoded multiple-selective excitation followed by a simple spectral editing. Combination of these two building blocks is used in a sensitivity-enhanced 2D analog of the 3D TOCSY–TOCSY experiment which provides an efficient tool for resolving severely overlapped signals of oligomers in short experimental time.  相似文献   
94.
超重元素(新核素)合成研究进展情况分析和展望   总被引:2,自引:0,他引:2  
刘建业 《物理学进展》2002,22(3):272-282
本文在介绍和分析国际、国内在超重元素(新核素)合成实验研究与理论研究进展情况的基础上对我国今后如何从理论与实验的结合上开展超重元素(核)合成研究工作提出一些看法和建议,提供讨论。  相似文献   
95.
96.
Gold ultra-microelectrode arrays are used to explore the electrochemical oxidation of hydroxide ions and are shown to be analytical useful. Two types of ultra-microelectrode arrays are used; the first consist of 256 individual electrodes of 5 microm in radius, 170 of which are electrochemically active in a cubic arrangement which are separated from their nearest neighbour by a distance of 100 microm. The second array compromises 2597 electrodes of 2.5 microm in radius and of which 1550 of which are electrochemically active in a hexagonal arrangement separated by the nearest neighbour by 55 microm. Well defined voltammetric waves are found with peak currents proportional to the concentration of hydroxide ions in the range 50 microM to 1 mM. Detection limits of 20 microM using the 170 ultra-microelectrode and 10 microM with the 1550 ultra-microelectrode array are shown to be possible but with a higher sensitivity of 4 mA M(-1) observed using the 1550 ultra-microelectrode array compared to 1.2 mA M(-1) with the 170 ultra-microelectrode array.  相似文献   
97.
In a recent work it was demonstrated that in linear hexagonal chains the distribution of π-electrons into rings (as computed by means of the Randić–Balaban method) is uniform, irrespective of the nature of the terminal fragments. We now establish that an analogous, yet somewhat more complex, uniformity in the π-electron distribution exists also in double linear hexagonal chains, as well as in some other benzenoid systems.  相似文献   
98.
In this note, we examine the algorithm of Drezner and Wesolowsky for locating a facility with maximin rectilinear distance to a given set of demand points. The concept of the closest-point constraint is introduced as a technique for increasing the efficiency of the algorithm. This potential increase in efficiency is demonstrated by an example.  相似文献   
99.
Thin films of silicon oxynitride have largely replaced pure silicon oxide films as gate and tunnel oxide films in modern technology due to their superior properties in terms of efficiency as boron barrier, resistance to electrical stress and high dielectric strength. A single chamber system for plasma enhanced chemical vapor deposition was employed to deposit different films of SiOxNyHz with 0.85 < x < 1.91. All films were previously characterized by Rutherford back-scattering and infrared spectroscopy to determine the stoichiometry and the presence of various bonding configurations of constituent atoms. We used X-ray reflectivity to determine the electron density profile across the depth, and we showed that the top layer is densified. Moreover, grazing incidence small-angle X-ray scattering was used to study inhomogeneities (clustering) in the films, and it is shown that plate-like inhomogeneities exist in the top and sphere-like particles at the bottom part of the film. Their shape and size depend on the stoichiometry of the films.  相似文献   
100.
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