全文获取类型
收费全文 | 13964篇 |
免费 | 2245篇 |
国内免费 | 1048篇 |
专业分类
化学 | 2083篇 |
晶体学 | 169篇 |
力学 | 2701篇 |
综合类 | 242篇 |
数学 | 6452篇 |
物理学 | 5610篇 |
出版年
2024年 | 36篇 |
2023年 | 126篇 |
2022年 | 254篇 |
2021年 | 263篇 |
2020年 | 345篇 |
2019年 | 309篇 |
2018年 | 285篇 |
2017年 | 457篇 |
2016年 | 477篇 |
2015年 | 382篇 |
2014年 | 670篇 |
2013年 | 993篇 |
2012年 | 742篇 |
2011年 | 741篇 |
2010年 | 663篇 |
2009年 | 775篇 |
2008年 | 829篇 |
2007年 | 943篇 |
2006年 | 830篇 |
2005年 | 836篇 |
2004年 | 710篇 |
2003年 | 739篇 |
2002年 | 657篇 |
2001年 | 560篇 |
2000年 | 521篇 |
1999年 | 495篇 |
1998年 | 383篇 |
1997年 | 369篇 |
1996年 | 261篇 |
1995年 | 218篇 |
1994年 | 167篇 |
1993年 | 167篇 |
1992年 | 139篇 |
1991年 | 114篇 |
1990年 | 99篇 |
1989年 | 52篇 |
1988年 | 75篇 |
1987年 | 60篇 |
1986年 | 55篇 |
1985年 | 71篇 |
1984年 | 62篇 |
1983年 | 30篇 |
1982年 | 41篇 |
1981年 | 53篇 |
1980年 | 27篇 |
1979年 | 38篇 |
1978年 | 43篇 |
1977年 | 33篇 |
1976年 | 21篇 |
1971年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
倒数示波计时电位滴定新技术 总被引:2,自引:1,他引:2
倒数交流示波极谱具有抑制充电电流、突出电解电流的优点,利用(dE/dt)~(-1)-E曲线上去极剂峰的突然消失或出现指示滴定终点的方法称作倒数示波计时电位滴定法.由运算放大器组装的模拟电子线路可以对(dE/dt)~(-1)-E曲线进行反馈、反对数及微分处理,从而获得各种类型的倒数示波计时电位曲线(图1),以进一步提高滴定的灵敏度。 相似文献
132.
Kazuhiro Matsuo 《Journal of statistical physics》1978,18(6):535-555
A projection operator method is presented, which provides the most efficient way for calculating the stationary behavior of nonlinear Brownian motion. A continued-fraction expansion of the Fourier-Laplace transform of the displacement correlation function or the spectral density is used. This method utilizes a successive optimization procedure on the nonlinear terms and includes the method of statistical linearization as the lowest order approximation. A systematic way to calculate the continued fraction numerically up to sufficient order for convergence is developed, which enables us to obtain the spectral density of a system previously uncomputable.Numerical computations of the spectral density of a nonlinear oscillator with a double-well potential are presented and compared with the results obtained by statistical linearization.This work was supported in part by the National Science Foundation under Grant CHE 75-20624. 相似文献
133.
Summary A computer procedure TFIT, which uses a molecular superposition force field to flexibly match test compounds to a 3D pharmacophore, was evaluated to find out whether it could reliably predict the bioactive conformations of flexible ligands. The program superposition force field optimizes the overlap of those atoms of the test ligand and template that are of similar chemical type, by applying an attractive force between atoms of the test ligand and template which are close together and of similar type (hydrogen bonding, charge, hydrophobicity). A procedure involving Monte Carlo torsion perturbations, followed by torsional energy minimization, is used to find conformations of the test ligand which cominimize the internal energy of the ligand and the superposition energy of ligand and template. The procedure was tested by applying it to a series of flexible ligands for which the bioactive conformation was known experimentally. The 15 molecules tested were inhibitors of thermolysin, HIV-1 protease or endothiapepsin for which X-ray structures of the bioactive conformation were available. For each enzyme, one of the molecules served as a template and the others, after being conformationally randomized, were fitted. The fitted conformation was then compared to the known binding geometry. The matching procedure was successful in predicting the bioactive conformations of many of the structures tested. Significant deviation from experimental results was found only for parts of molecules where it was readily apparent that the template did not contain sufficient information to accurately determine the bioactive conformation. 相似文献
134.
Takahito Itoh Hiroki Saitoh Shouji Iwatsuki 《Journal of polymer science. Part A, Polymer chemistry》1995,33(10):1589-1596
1,1′-Dialkylferrocene-3,3′-dicarbaldehydes ( 1a–c ) with long alkyl chains such as ethyl, hexyl, and dodecyl groups were prepared in 13–25% yield via three-step reactions. The titanium-induced dicarbonyl-coupling reaction of 1a–c gave poly(1,1′-dialkyl-3,3′-ferrocenylenevi-nylene)s ( 2a–c ) in quantitative yields, which were the molecular weights of 3000–10,000 and highly soluble in chloroform, benzene, and hexane. The electrical conductivity and the third-order nonlinear optical susceptibility for poly(1,1′-dihexyl-3,3′-ferrocenylenevinylene) ( 2b ) were estimated to be 1 × 10?2 S/cm on doping with iodine and 1–4 × 10?12 esu at a wavelength of 1–2.4 μm, respectively. © 1995 John Wiley & Sons, Inc. 相似文献
135.
S. Kumagai 《Journal of Optimization Theory and Applications》1980,31(2):285-288
In Ref. 1, Jittorntrum proposed an implicit function theorem for a continuous mappingF:R
n ×R
m R
n, withF(x
0,y
0)=0, that requires neither differentiability ofF nor nonsingularity of
x
F(x
0,y
0). In the proof, the local one-to-one condition forF(·,y):A R
n R
n for ally B is consciously or unconsciously treated as implying thatF(·,y) mapsA one-to-one ontoF(A, y) for ally B, and the proof is not perfect. A proof can be given directly, and the theorem is shown to be the strongest, in the sense that the condition is truly if and only if. 相似文献
136.
S. N. Shkerin Yu. V. Sokolova S. M. Beresnev 《Russian Journal of Electrochemistry》2005,41(8):849-857
The polarization dependences of a porous gold electrode in contact with a solid electrolyte of the composition La0.88Sr0.12Ga0.82Mg0.18O2.85 are studied at 600–800°C and oxygen pressures of 2 × 10−2-1 atm. It is shown that the rate of cathodic reduction of oxygen out of the gas phase depends on the preliminary treatment of the sample. The activation energy is equal to 110–135 kJ mol−1 at a low polarization. After increasing the polarization, the activation energy for the cathodic reduction of oxygen equals 75–85 kJ mol−1 and depends on the oxygen pressure as a power function with a power index of 1/4. The rate of the anodic evolution of oxygen is dependent neither on the preliminary treatment of the sample nor on the oxygen pressure in the gas phase and the polarization curve has a characteristic segment, which corresponds to a limiting overvoltage.__________Translated from Elektrokhimiya, Vol. 41, No. 8, 2005, pp. 954–962.Original Russian Text Copyright © 2005 by Shkerin, Sokolova, Beresnev. 相似文献
137.
V. V. Simakov 《Russian Journal of Electrochemistry》2005,41(6):653-654
Current-voltage curves for sensor structures based on thin tin oxide films are examined in various gases. Conditions favoring symmetrical nonlinear curves in the voltage range −30 to 30 V are found.__________Translated from Elektrokhimiya, Vol. 41, No. 6, 2005, pp. 735–737.Original Russian Text Copyright © 2005 by Simakov.Published on the basis of a report delivered at the VII Meeting on Fundamental Problems in Solid-State Ionics (Chernogolovka-2004). 相似文献
138.
从自模式曲线分辨到渐进类因子分析法 总被引:1,自引:1,他引:1
本文对自模式曲线分辨法的发展作了简要回顾,其中特别对近来来迅速发展的一类用于色谱波谱联用仪产生的二维分析数据的渐进类分析法作了详尽的讨论。这些新化学计量学方法的涌现,对复杂的未知分析体系的定性定量分析,将带来深刻的变化。 相似文献
139.
To investigate the pharmacokinetic mechanism of hepatobiliary excretion and brain distribution of caffeine, this study uses a method based on microdialysis technique and liquid chromatography that allows continuous and concurrent in vivo monitoring of extracellular caffeine in the blood, brain and bile of anesthetized rats following the administration of caffeine (3 or 10 mg/kg, i.v.) through the femoral vein. Dialysates of the blood, brain and bile were directly injected onto the liquid chromatographic system and no further clean-up procedures were required. The study design consisted of two groups of six rats in parallel: the rats of the control group received caffeine (3 or 10 mg/kg, i.v.) alone and those of the cyclosporine treated-group were injected cyclosporine (10 mg/kg, i.v.) 10 min prior to caffeine administration (3 or 10 mg/kg, i.v.). The decline of caffeine in the blood, brain striatum and bile suggested that caffeine had rapid exchange and equilibration between the peripheral compartment and the central nervous system. In addition, the results indicated that caffeine underwent hepatobiliary excretion and was distributed into brain. When cyclosporine was co-administered, the pharmacokinetic parameters were not significantly altered. The results of this study reveal that the pharmacokinetic mechanism of hepatobiliary excretion and brain distribution of caffeine might not relate to P-glycoprotein. 相似文献
140.
The acid-catalysed esterification of myristic acid with isopropanol was studied by using near-infrared spectroscopy (NIR) in combination with soft-modeling curve resolution (MCR) methodology with a view to establishing the effect of experimental variables on the reaction kinetics. The reaction was conducted at temperatures above the boiling point of the alcohol, with continuous addition of an isopropanol/water mixture to the reactor. Spectral and concentration profiles were determined by applying soft-modeling curve resolution methodology to a column-wise augmented data matrix containing the spectra for the pure components. MCR profiles were compared with reference values and found to depart from then by less than 3% as %RSE for concentrations and to exhibit correlation above 0.999 for spectra.The reaction kinetics as estimated from the concentration profiles was found to be pseudo-first-order. Also, the pseudo-first-order rate constant was found to depend on the flow-rate of the isopropanol/water mixture and its water content; although the constant decreased with increase in the proportion of water, a content of ca. 15% could be used without important retarding effects on the kinetics. The proposed NIR-MCR method allows the rate constant and the influence of the initial water content to be determined with a view to minimizing consumption of the raw materials and optimizing the experimental conditions. 相似文献