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   1147篇
  免费   38篇
  国内免费   9篇
化学   655篇
晶体学   7篇
力学   36篇
数学   87篇
物理学   409篇
  2022年   7篇
  2021年   11篇
  2020年   22篇
  2019年   21篇
  2018年   25篇
  2017年   24篇
  2016年   28篇
  2015年   30篇
  2014年   38篇
  2013年   63篇
  2012年   35篇
  2011年   51篇
  2010年   37篇
  2009年   33篇
  2008年   43篇
  2007年   49篇
  2006年   45篇
  2005年   58篇
  2004年   45篇
  2003年   39篇
  2002年   46篇
  2001年   46篇
  2000年   28篇
  1999年   34篇
  1998年   22篇
  1997年   20篇
  1996年   9篇
  1995年   7篇
  1994年   12篇
  1993年   14篇
  1992年   15篇
  1991年   16篇
  1990年   10篇
  1989年   17篇
  1988年   11篇
  1987年   14篇
  1986年   9篇
  1984年   8篇
  1983年   10篇
  1982年   7篇
  1981年   8篇
  1979年   9篇
  1976年   7篇
  1974年   9篇
  1973年   11篇
  1972年   7篇
  1971年   14篇
  1970年   12篇
  1968年   6篇
  1967年   7篇
排序方式: 共有1194条查询结果,搜索用时 15 毫秒
11.
We describe equipment and a method for performing an experiment on a short meteor radio line of length 85 km. The feature of the experiment is monitoring of meteor-matter deposition to the atmosphere using a radar located at one point of the radio line with the simultaneous determination of the main radio-line characteristics.  相似文献   
12.
13.
The molecular structures of phenylphosphine and its analogs, aniline and phenylarsine, were studied by gas-phase electron diffraction and quantum-chemical methods. The geometry and force constants were calculated at the HF/6-31G and B3LYP/6-31G* levels of theory. Phenylphosphine and phenylarsine possess a bisector conformation with asymmetric phenyl rings. The main geometric parameters are as follows (r a): P-C 1.833(6), C-Cav 1.397(1)Å. The structures of molecules like X2YPh (X = H, F, Cl; Y = N, P, As) were discussed.  相似文献   
14.
This paper discusses recent trends in the field of reverse engineering, particularly those highlighted at the Second Working Conference on Reverse Engineering, held in July 1995. The trends observed include increased orientation toward tasks, grounding in complex real-world applications, guidance from empirical study, analysis of non-code sources, and increased formalization. The paper also summarizes open research issues and provides pointers to future events and sources of information in this area.  相似文献   
15.
The novel vanadium thiobromide, V4S9Br4, with a square-planar metal cluster core was synthesized and characterized by single-crystal X-ray diffraction, measurements of magnetic properties and the heat capacity, and DFT calculations of the electronic structure. At the room temperature, the compound displays paramagnetic properties with an independent spin on each V atom and with a weak exchange constant (J approximately 10 cm(-1)). The paramagnetic state is transformed into a low-spin state (AF-type ordering) at low temperatures. This change is accompanied by a heat-capacity anomaly. The observed magnetic and heat-capacity anomalies can be explained by the thermal excitation of electrons on the closely spaced molecular energy levels in the presence of the Jahn-Teller effect.  相似文献   
16.
Aspartame adduct of copper(II) chloride Cu(Asp)2Cl2·2H2O (Asp=aspartame) is synthesized and characterized by elemental analysis, FT IR, UV/vis, ESR spectroscopies, TG, DTG, DTA measurements and molecular mechanics calculations. Aqueous solution of the green solid absorbs strongly at 774 and 367 nm. According to the FT IR spectra, the aspartame moiety coordinates to the copper(II) ion via its carboxylate ends, whereas the ammonium terminal groups give rise to hydrogen bonding network with the water, the chloride ions or neighboring carboxylate groups. The results suggest tetragonally distorted octahedral environment of the copper ions.  相似文献   
17.
Benzopyran derivatives were synthesized in good yields by the reactions of tris[2-(chloromethyl)phenyl]bismuth diacetate and 2-(halomethyl)aryllead triacetates with phenols and naturally occurring 4-hydroxycoumarins in the presence of bases according to a three-step one-pot procedure. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2520–2529, November, 2005.  相似文献   
18.
Conclusions When the hydrogenation of dehydrolinalool to linalool is run on a Pd alloy containing 6 wt.% of Ru, which is lean in the -hydrogen phase, the selectivity is much greater than when the amount of the -hydrogen phase is greater. A high selectivity of the hydrogenation is achieved by reducing to a definite limit the amount of hydrogen in the membrane catalyst without using inhibitors of the side reactions, which can contaminate the hydrogenation products.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 926–928, April, 1984.  相似文献   
19.
Organic and Physical Chemistry Institute, Kola Scientific Center, Russian Academy of Sciences. Translated from Zhurnal Strukturnoi Khimii, Vol. 33, No. 2, pp. 133–137, March–April 1992.  相似文献   
20.
A. E. Arbuzov Institute of Organic and Physical Chemistry, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 34, No. 5, pp. 185–188, September–October, 1993.  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