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   784篇
  免费   9篇
  国内免费   1篇
化学   363篇
晶体学   4篇
力学   25篇
数学   39篇
物理学   363篇
  2023年   7篇
  2022年   5篇
  2021年   5篇
  2020年   12篇
  2019年   11篇
  2018年   19篇
  2017年   7篇
  2016年   18篇
  2015年   12篇
  2014年   18篇
  2013年   42篇
  2012年   22篇
  2011年   40篇
  2010年   18篇
  2009年   24篇
  2008年   47篇
  2007年   43篇
  2006年   36篇
  2005年   26篇
  2004年   12篇
  2003年   19篇
  2002年   12篇
  2001年   14篇
  2000年   18篇
  1999年   5篇
  1996年   7篇
  1995年   10篇
  1994年   26篇
  1993年   28篇
  1992年   24篇
  1991年   14篇
  1990年   8篇
  1989年   8篇
  1988年   13篇
  1987年   6篇
  1986年   11篇
  1985年   13篇
  1984年   5篇
  1983年   5篇
  1982年   13篇
  1981年   8篇
  1980年   9篇
  1979年   8篇
  1978年   7篇
  1977年   6篇
  1976年   10篇
  1975年   5篇
  1974年   8篇
  1973年   14篇
  1972年   5篇
排序方式: 共有794条查询结果,搜索用时 15 毫秒
11.
12.
Summary The mixed ligand complex, [Fe(Phen)2(N3)2] can be extracted into nitrobenzene giving a molar absorptivity of 16750 at 510 nm. This is the basis of a photometric method for iron which may be either in the trivalent or bivalent state. The new method is free from interference from a number of substances and is more sensitive than the ferroin method.
Zusammenfassung Der Eisen-Phenanthrolin-Azid-Mischkomplex [Fe(Phen)2(N3)2] ist mit Nitrobenzol extrahierbar und gibt bei 510 nm eine molare Absorption von 16750. Darauf läßt sich eine photometrische Bestimmungsmethode für zweioder dreiwertiges Eisen begründen. Diese wird von vielen Stoffen nicht gestört und ist empfindlicher als die Ferroinmethode.
  相似文献   
13.
Summary Four-coordinate nickel nitrosyl complexes of the general formula Ni(NO)X(Dppe) (Dppe=Ph2PCH2CH2PPh2) have been prepared byin situ formation of Ni(NO2)X(Dppe), (X= Cl, Br, I or SCN) followed by reduction with triphenylphosphine, or carbon monoxide, and/or DMF. Oxygenation of the nitrosyl complexes gives the corresponding nitro products and as indicated by u.v.-vis spectroscopy involves formation of an intermediate. The oxygenation rate increases markedly in the presence of light or of a catalytic amount of benzoyl peroxide and a tentative explanation is offered for these observations. Ionic adducts are formed in reactions between the nitrosyl complexes and donor molecules.Paper presented in part at the XXth ICCC Conference.  相似文献   
14.
In this paper we report a new idea for synthesizing polyaniline in an ordinary filter paper. The synthesis was carried out by a process in which aqueous acidic aniline solution and the oxidizing agent H(2)O(2) was added to the paper drop by drop and in sequence. Uniform polymerization could be obtained with the addition of reagents in either sequence. The polymer formation led to a green coloration of the paper. Formation of the emeraldine salt of polyaniline was confirmed by UV-vis and FTIR spectroscopy. Scanning electron microscopic measurements were made for surface characterization of the polymer formed in the paper. The same paper was used as a sensor for ammonia in vapor and in solution, for acid and base as well as endpoint indication, and also to filter acids and bases. We found that, using the polymer-containing paper, ammonia concentrations in a solution as low as 14 ppm could be measured.  相似文献   
15.
Depending on the pH, 1-(1-indolinyl)-3-aryltriazenes (I) or 5-arylazoindolines (II) are formed in the reaction of indoline with aryldiazonium salts. In acid media, I are rearranged to II. The dehydrogenation of I or II with chloranil gives 5-arylazoindoles.See [1] for communication LXXVI.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 648–651, May, 1972.  相似文献   
16.
A method for the construction of the essentially idempotent and Hermitian diagonal elements of the matric algebra of the permutation group Sn is proposed. For the irreducible representation [λ] = [λ1, λ2] characterising a spin state S of an n-electron system, it is found that this method generates the complete set of spin projections from the appropriate primitive spin functions. The method is applied to a 7-electron system in the spin state S = MS = 1/2 and the results are listed in the Appendix.  相似文献   
17.
A prompt gamma-ray neutron activation analysis (PGNAA) system was used to calibrate and validate a Monte Carlo model as a proof of principle for the quantification of chlorine in soil. First, the response of an n-type HPGe detector to point sources of 60Co and 152Eu was determined experimentally and used to calibrate an MCNP4a model of the detector. The refined MCNP4a detector model can predict the absolute peak detection efficiency within 12% in the energy range of 120–1400 keV. Second, a PGNAA system consisting of a light-water moderated 252Cf (1.06 g) neutron source, and the shielded and collimated HPGe detector was used to collect prompt gamma-ray spectra from Savannah River Site (SRS) soil spiked with chlorine. The spectra were used to calculate the minimum detectable concentration (MDC) of chlorine and the prompt gamma-ray detection probability. Using the 252Cf based PGNAA system, the MDC for Cl in the SRS soil is 4400 g/g for an 1800-second irradiation based on the analysis of the 6110 keV prompt gamma-ray. MCNP4a was used to predict the PGNAA detection probability, which was accomplished by modeling the neutron and gamma-ray transport components separately. In the energy range of 788 to 6110 keV, the MCNP4a predictions of the prompt gamma-ray detection probability were generally within 60% of the experimental value, thus validating the Monte Carlo model.  相似文献   
18.
19.
20.
The first use of hydroxylamine derivatives as the aminoxy equivalent of nucleophiles in palladium catalyzed addition to Baylis-Hillman acetate adducts is described. The reaction proceeds smoothly to give the substituted allyloxy amines in good yield and selectivity.  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