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   569篇
  免费   6篇
化学   357篇
力学   14篇
数学   25篇
物理学   179篇
  2021年   5篇
  2020年   5篇
  2019年   6篇
  2016年   7篇
  2015年   6篇
  2014年   16篇
  2013年   16篇
  2012年   21篇
  2011年   14篇
  2010年   8篇
  2009年   18篇
  2008年   20篇
  2007年   23篇
  2006年   18篇
  2005年   13篇
  2004年   17篇
  2003年   20篇
  2002年   18篇
  2001年   11篇
  2000年   17篇
  1999年   10篇
  1998年   5篇
  1996年   15篇
  1995年   12篇
  1994年   7篇
  1993年   16篇
  1992年   11篇
  1991年   9篇
  1990年   15篇
  1989年   7篇
  1988年   9篇
  1987年   6篇
  1985年   9篇
  1984年   5篇
  1982年   7篇
  1981年   4篇
  1980年   5篇
  1979年   6篇
  1978年   5篇
  1976年   8篇
  1975年   6篇
  1974年   8篇
  1973年   8篇
  1972年   5篇
  1967年   9篇
  1966年   5篇
  1940年   4篇
  1931年   4篇
  1930年   6篇
  1926年   4篇
排序方式: 共有575条查询结果,搜索用时 281 毫秒
461.
462.
Jury  A.  Balandraud  X.  Heller  L.  Šittner  P.  Karlik  M. 《Experimental Mechanics》2021,61(2):349-366
Experimental Mechanics - Shape memory alloys (SMAs) are phase transforming materials featuring strong thermomechanical couplings. Infrared thermography and heat source reconstruction (HSR) enable...  相似文献   
463.
The aim of this study was to develop a fast capillary electrophoresis method for the determination of propranolol in pharmaceutical preparations. In the method development the pH and constituents of the background electrolyte were selected using the effective mobility versus pH curves. Benzylamine was used as the internal standard. The background electrolyte was composed of 60 mmol L−1 tris(hydroxymethyl)aminomethane and 30 mmol L−1 2-hydroxyisobutyric acid, at pH 8.1. Separation was conducted in a fused-silica capillary (32 cm total length and 8.5 cm effective length, 50 μm I.D.) with a short-end injection configuration and direct UV detection at 214 nm. The run time was only 14 s. Three different strategies were studied in order to develop a fast CE method with low total analysis time for propranolol analysis: low flush time (Lflush) 35 runs/h, without flush (Wflush) 52 runs/h, and Invert (switched polarity) 45 runs/h. Since the three strategies developed are statistically equivalent, Wflush was selected due to the higher analytical frequency in comparison with the other methods. A few figures of merit of the proposed method include: good linearity (R2 > 0.9999); limit of detection of 0.5 mg L−1; inter-day precision better than 1.03% (n = 9) and recovery in the range of 95.1–104.5%.  相似文献   
464.
Microwave-enhanced reactions are very fast in comparison to thermal reactions. The determination of optimal end point often fails because conventional analytical methods are too slow. Therefore, we established a fast method using FTIR spectroscopy. The result of the reaction control analysis is obtained within less than 1 min.  相似文献   
465.
Heller et al. (J Math Phys 46:122501, 2005; Int J Theor Phys 46:2494, 2007) proposed a model unifying general relativity and quantum mechanics based on a noncommutative algebra defined on a groupoid having the frame bundle over space–time as its base space. The generalized Einstein equation is assumed in the form of the eigenvalue equation of the Einstein operator on a module of derivations of the algebra . No matter sources are assumed. The closed Friedman world model, when computed in this formalism, exhibits two interesting properties. First, generalized eigenvalues of the Einstein operator reproduce components of the perfect fluid energy-momentum tensor for the usual Friedman model together with the corresponding equation of state. One could say that, in this case, matter is produced out of pure (noncommutative) geometry. Second, owing to probabilistic properties of the model, in the noncommutative regime (on the Planck level) singularities are irrelevant. They emerge in the process of transition to the usual space–time geometry. These results are briefly discussed.  相似文献   
466.
467.
468.
Because of incresing problems due to the general non-acceptance of the application of open radioactivity in modern industrial research an investigation was made concerning the possibility of replacing radiotracers by inactive substances activated by photons after sampling. As an example, investigations in the glass-processing industry was selected. The results were confirmed by the radiotracer experiment performed in parallel. The data obtained were in good agreement.  相似文献   
469.
470.
A formalism based on macroscopic Maxwell equations is developed for the case of media with violations of the space symmetry and time reversal. It is demonstrated that the parity violation in a medium is equivalent to the manifestation of spatial dispersion and natural optical activity. The proposed formalism makes it possible to uniquely calculate the macroscopic parameters of equations in terms of the microscopic theory. The parameters of gyrotropy and dichroism of a gaseous medium are determined within a model describing an interaction of resonance radiation with transitions to states that have different parities and are mixed by a weak interaction of an electron with the nucleus of the atom. It is established that, in the range of the resonance with a magnetic dipole transition, the effect of parity violation is enhanced as a result of the considerable difference between the natural broadenings of the electric and magnetic dipole transitions. This enhancement is suppressed when the dominant Doppler broadening of the atomic transitions is taken into account. It is shown that, owing to the unitarity of the weak interaction, the effects of parity violation are alternating functions of the radiation frequency and are integrally absent in the entire spectrum.  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