全文获取类型
收费全文 | 437篇 |
免费 | 7篇 |
国内免费 | 4篇 |
专业分类
化学 | 202篇 |
晶体学 | 1篇 |
力学 | 18篇 |
数学 | 131篇 |
物理学 | 96篇 |
出版年
2022年 | 4篇 |
2021年 | 7篇 |
2020年 | 4篇 |
2019年 | 4篇 |
2018年 | 4篇 |
2017年 | 4篇 |
2016年 | 11篇 |
2015年 | 8篇 |
2014年 | 23篇 |
2013年 | 26篇 |
2012年 | 22篇 |
2011年 | 25篇 |
2010年 | 18篇 |
2009年 | 19篇 |
2008年 | 28篇 |
2007年 | 25篇 |
2006年 | 25篇 |
2005年 | 22篇 |
2004年 | 20篇 |
2003年 | 8篇 |
2002年 | 14篇 |
2001年 | 3篇 |
2000年 | 14篇 |
1999年 | 6篇 |
1998年 | 5篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 8篇 |
1990年 | 2篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1970年 | 2篇 |
1965年 | 2篇 |
1963年 | 3篇 |
1935年 | 2篇 |
1933年 | 2篇 |
1907年 | 2篇 |
1893年 | 2篇 |
排序方式: 共有448条查询结果,搜索用时 15 毫秒
351.
Stan Chiriţă Alexandre Danescu 《International Journal of Solids and Structures》2008,45(17):4850-4859
The present paper studies the strong ellipticity for all crystal classes of tetragonal system in a linearly elastic material. Explicit conditions characterizing the strong ellipticity of the elasticity tensor are established for the tetragonal system with six elasticities (that is tetragonal–scalenohedral, ditetragonal–pyramidal, tetragonal–trapezohedral, ditetragonal–dipyramidal crystal classes) as well as for the tetragonal system with seven elasticities (tetragonal–disphenoidal, tetragonal–pyramidal and tetragonal–dipyramidal crystal classes). 相似文献
352.
The combination of on-line methylation using trimethylsulfonium hydroxide with large volume injection of 100 μL was evaluated for the analysis of organic acids and phenols in water. Solvent split injection was applied with complete evaporation of the solvent before analytes were transferred onto the GC column. Despite complete solvent removal, losses were very low compared to conventional splitless injection even for volatile acidic compounds such as propionic acid and phenol. This is explained by intermediate formation of low volatility trimethylsulfonium salts of the analytes which were held in the injector for long evaporation times of up to 10 min, if the evaporation temperature was as low as 10°C. Using a simple liquid/liquid extraction procedure, volatile fatty acids, dicarboxylic acids, benzoic acids and phenols could be detected in 5 mL of water at concentrations of 0.04–0.1 μmol/L with GC/MS in full scan mode. Lactic, pyruvic, and also malonic acids could only be detected at higher levels because of their limited extractability from water as well as their poorer methylation yields. The method provides an easy way to sensitively detect acidic compounds of medium to high volatility in water. It was applied for screening of organic acids and phenols in batch cultures of anaerobic bacteria of which one example is shown. 相似文献
353.
In this paper a mono–objective optimum design procedure for a six–degree of freedom parallel micro robot is outlined by using optimality criterion of workspace and numerical aspects. A mono–objective optimization problem is formulated by referring to a basic performance of parallel robots. Additional objective functions can be used to extend the proposed design procedure to more general but specific design problems. A kinematic optimization was performed to maximize the workspace of the mini parallel robot. Optimization was performed using Genetic Algorithms. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
354.
We are concerned with the existence of solutions for the singular fractional boundary value problem $^{c}\kern-1pt D^{\alpha}u = f(t,u)$ , u(0)+u(1)=0, u′(0)=0, where α∈(1,2), f∈C([0,1]×(??{0})) and lim x→0 f(t,x)=∞ for all t∈[0,1]. Here, $^{c}\kern-1pt D$ is the Caputo fractional derivative. Increasing solutions of the problem vanish at points of (0,1), that is, they “pass through” the singularity of f inside of (0,1). The results are based on combining regularization and sequential techniques with a nonlinear alternative. In limit processes, the Vitali convergence theorem is used. 相似文献
355.
通过时频分析法从海底环境噪声数据中提取界面波频散曲线,进而采用非线性贝叶斯反演方法估算海底沉积物厚度、剪切波速度、压缩波速度和密度等参数及其不确定性。参数的最大后验概率(MAP)估计值和边缘概率分布分别通过自适应单纯形模拟退火法和Metropolis-Hastings采样法在各参数先验区间内搜索获得,采用贝叶斯信息准则(BIC)从不同参数化模型中选择最优模型。界面波频散曲线反演结果表明:满足实测数据的最优海底模型结构为3层均匀分布剪切波速度剖面结构,海底深度的反演精度在800m以内,比起压缩波速度和密度,剪切波速度的不确定性更小,对界面波频散曲线更敏感。 相似文献
356.
357.
High temperature gas chromatography (HT-GC) coupled to atomic emission detection (AED) has been applied for the determination of alkyl chain distribution, mole average degree of ethoxylation and weight percent distribution of the corresponding homologues of alcohol ethoxylates without all the actual homologues being available as pure references. Based upon its constant elemental response, the HT-GC-AED system has been evaluated for its applicability to compound independent calibration within the homologous series of the alcohols and alcohol ethoxylates. Discrimination against high molecular weight components by gas chromatography requires conversion to the acetyl or trimethylsilyl derivatives. The latter includes introduction of the hetero atom silicon and thus allows monitoring of the silicon trace. Thus selectivity will be enhanced by excluding detection of compounds which do not react with the derivatization reagent. The method has been validated with the analysis of the technical product Brij 30, consisting of a mixture of alcohol ethoxylates with a vendor-specified mole average degree of ethoxylation of four. The experimental result yields a mole average degree of 4.0 ± 0.1 in the carbon, silicon and oxygen traces. 相似文献
358.
359.
The main topic refers to enhancing the machining accuracy by minimizing the path error while machining through linear, circular
or other interpolations on CNC machines for milling, boring and milling, grinding or turning. Currently the path error minimizing
process while machining on CNC machine tools is a little explored, because of the absence of the dependence relations between
the path error and the parameters of the kinematical axes taking part to the interpolation of the work piece contour. This
work establishes and analyzes the relations of dependence between the path error and the response times of the kinematical
axes that take part to the linear and circular interpolation. The theoretical results are experimentally verified by performing
several machining operations through circular interpolation, where the moving speed along the contour and the response times
of the kinematical axes are modified. The results of this research are intended for the machine tool designers and those who
use such machines. 相似文献
360.
JPC – Journal of Planar Chromatography – Modern TLC - A high-performance thin-layer chromatography (HPTLC) method has been established for the analysis of α-phellandrene and... 相似文献