全文获取类型
收费全文 | 477201篇 |
免费 | 4146篇 |
国内免费 | 1771篇 |
专业分类
化学 | 234268篇 |
晶体学 | 6996篇 |
力学 | 24051篇 |
综合类 | 7篇 |
数学 | 77215篇 |
物理学 | 140581篇 |
出版年
2021年 | 2951篇 |
2020年 | 3264篇 |
2019年 | 3756篇 |
2018年 | 14573篇 |
2017年 | 14278篇 |
2016年 | 12741篇 |
2015年 | 5276篇 |
2014年 | 7150篇 |
2013年 | 18830篇 |
2012年 | 17336篇 |
2011年 | 26672篇 |
2010年 | 16683篇 |
2009年 | 16926篇 |
2008年 | 21345篇 |
2007年 | 23498篇 |
2006年 | 14674篇 |
2005年 | 14358篇 |
2004年 | 13491篇 |
2003年 | 12520篇 |
2002年 | 11396篇 |
2001年 | 12250篇 |
2000年 | 9402篇 |
1999年 | 7293篇 |
1998年 | 6040篇 |
1997年 | 6082篇 |
1996年 | 5693篇 |
1995年 | 5255篇 |
1994年 | 4976篇 |
1993年 | 4934篇 |
1992年 | 5407篇 |
1991年 | 5450篇 |
1990年 | 5186篇 |
1989年 | 5033篇 |
1988年 | 5104篇 |
1987年 | 5002篇 |
1986年 | 4786篇 |
1985年 | 6327篇 |
1984年 | 6672篇 |
1983年 | 5511篇 |
1982年 | 5933篇 |
1981年 | 5810篇 |
1980年 | 5630篇 |
1979年 | 5699篇 |
1978年 | 6007篇 |
1977年 | 5816篇 |
1976年 | 6069篇 |
1975年 | 5523篇 |
1974年 | 5598篇 |
1973年 | 5950篇 |
1972年 | 3772篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
The products of the reaction of OClO with NO3 were investigated between 220 and 298 K using a flow reactor and infrared, visible, and ultraviolet analysis. At temperatures below 250 K new infrared and ultraviolet absorption features were observed and assigned to the novel compound chloryl nitrate (O2ClONO2). Additionally, ClO and NO2 were observed as reaction products, indicating the existence of a second reaction channel. O2ClONO2 formation predominates at temperatures below 230 K. The reaction rate constant at 220 K is estimated to be on the order of 10(-14) cm3 molecule-1 s-1 in 1-5 Torr of helium. These observations suggest that O2ClONO2 may exist in the terrestrial stratosphere. 相似文献
972.
A simple method for the determination of molybdenum and tungsten in sea and surface water is presented. Molybdenum and tungsten are concentrated on activated charcoal by adsorption as the ammonium pyrrolidine dithiocarbamate complex; the optimal pH for adsorption is 1.3. Mo and W are then determined by thermal neutron activation, forming 99Mo (T = 66.7 h) and 137W (T = 23.8 h), respectively. The 99mTc daughter of 99Mo is measured as soon as the equilibrium between 99mTc(T= 6 h) and 99Mo is established. The detection limits are 0.05 μg Mo l-1 and 0.05 μg W l-1 (or 0.001 μg W l-1 after a simple chemical separation). 相似文献
973.
A method to calculate extra-atomic relaxation energies is presented. It is based on the use of SCF hole-state calculations. The ERea (2s) and ERea (2p) values obtained for the 3d-transition metal series are in fair agreement with experimental values. 相似文献
974.
The fractional dissociation,32Γ, of 32SF6 by the output of a pulsed TEA CO2 laser has been found to depend upon Φ, the total integrated laser intensity, as 32Γ ∞ Φm for both the P(20) and P(16) laser lines, where m ≈ 3 in the range 2 < Φ < 7.2 J/cm2 and increases from 3 to ≈ 4 as Φ is reduced from 2 to 0.9 J/cm2. 相似文献
975.
Retention of strontium and promethium on hydroxides (hydrated oxides) and phosphates of iron and chromium prepared by the sol-gel method was studied. The sorption was determined under static conditions depending on the pH of the solution. The sorption isotherms and retention were investigated under dynamic conditions. 相似文献
976.
A bound on the energy obtained from the differential equation forms of Faddeev-type equations is derived. The procedure is based on the standard variation principle for the Schrödinger equation plus the observation that the ordinary Schrödinger wavefunction |ψ(i)> equals the sum of the Faddeev-type “channel wavefunctions” |ψλ(i)>. 相似文献
977.
Castiñeiras A Sicilia-Zafra AG González-Pérez JM Choquesillo-Lazarte D Niclós-Gutiérrez J 《Inorganic chemistry》2002,41(26):6956-6958
By reaction of Cu(2)CO(3)(OH)(2), 2-benzylmalonic acid (H(2)Bzmal), and 1,10-phenanthroline (phen), [Cu(Bzmal)(phen)(H(2)O)] x 3H(2)O (compound 1) has been obtained and characterized by thermal, spectral, magnetic, and X-ray diffraction methods. The molecular structure of 1 is remarkably similar to that of [Cu(Bzmal)(bipy)(H(2)O)] x 2H(2)O (compound 2, bipy = 2,2'-bipyridine). In both complexes, the aryl(Bzmal) ring produces an unexpected pi,pi-stacking interaction with the Cu(II)-(aromatic alpha,alpha'-diimine) chelate ring, at an average distance d(pi)(-)(pi) of 3.40 A, involving roughly parallel and smoothly slipped rings. This insight is discussed as new structural evidence for metalloaromaticity of Cu(II)-(aromatic alpha,alpha'-diimine) chelate rings. Interestingly, 1 recognizes itself by a weak intermolecular pi,pi-stacking interaction between aryl(Bzmal) ligands to give pairs of complex molecules. In contrast, there is an intermolecular pyridyl-pyridyl pi,pi-stacking interaction also forming pairs of complex molecules in 2. 相似文献
978.
S. P. Tripathi G. K. Chaturvedi R. C. Sharma 《Monatshefte für Chemie / Chemical Monthly》1978,109(2):283-287
Stepwise mixed ligand complex formation has been cited for the formation of 111,Ln(III)—NTA—catechol ternary complexes potentiometrically [whereLn(III)=La(III), Pr(III) or Nd(III)]. The results of titration curves indicate the formation of 11,Ln(III)—NTA complexes in beginning and the addition of catechol, takes place later on in the higher buffer region. The relative stability of these ternary complexes in terms of metal ion has been reported as La(III)< 相似文献
979.
Preparation of sulfuric acid and sodium hydroxide from solutions containing sodium sulfate was studied by the electrodialysis method in a three-chamber (?three-compartment) electrodialyzer equipped with two membranes, an anion-exchange membrane AESD-2a and a cation-exchange membrane Nafion 427. 相似文献
980.
Summary A method is described for the rapid determination of traces of copper in the ppm range in cobalt and nickel salts. The % standard deviation for the analysis is reported as 3.4 to 3.7 for aequous solutions and 4.8 to 5.0 for carbon tetrachloride sprayed directly into the flame after extraction.
Zusammenfassung Ein Verfahren zur raschen Bestimmung von Kupferspuren im ppm-Bereich in Kobalt- und Nickelsalzen wurde beschrieben. Die Standardabweichung in wäßrigen Lösungen beträgt 3,4 bis 3,7%, bei unmittelbarem Versprühen der Tetrachlorkohlenstoffextrakte in die Flamme 4,8 bis 5,0%.相似文献