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   175728篇
  免费   1686篇
  国内免费   523篇
化学   91811篇
晶体学   3059篇
力学   7208篇
综合类   3篇
数学   20000篇
物理学   55856篇
  2021年   1400篇
  2020年   1517篇
  2019年   1698篇
  2018年   2094篇
  2017年   2162篇
  2016年   3348篇
  2015年   2050篇
  2014年   3251篇
  2013年   7964篇
  2012年   6080篇
  2011年   7216篇
  2010年   5244篇
  2009年   5174篇
  2008年   6805篇
  2007年   6721篇
  2006年   6323篇
  2005年   5715篇
  2004年   5275篇
  2003年   4745篇
  2002年   4571篇
  2001年   5263篇
  2000年   3909篇
  1999年   3006篇
  1998年   2526篇
  1997年   2411篇
  1996年   2271篇
  1995年   2130篇
  1994年   2112篇
  1993年   2018篇
  1992年   2322篇
  1991年   2257篇
  1990年   2202篇
  1989年   2125篇
  1988年   2127篇
  1987年   2130篇
  1986年   2020篇
  1985年   2635篇
  1984年   2696篇
  1983年   2386篇
  1982年   2496篇
  1981年   2313篇
  1980年   2288篇
  1979年   2431篇
  1978年   2468篇
  1977年   2391篇
  1976年   2441篇
  1975年   2362篇
  1974年   2327篇
  1973年   2504篇
  1972年   1624篇
排序方式: 共有10000条查询结果,搜索用时 19 毫秒
81.
We discuss the inviscid limits for the randomly forced 2D Navier-Stokes equation (NSE) and the damped/driven KdV equation. The former describes the space-periodic 2D turbulence in terms of a special class of solutions for the free Euler equation, and we view the latter as its model. We review and revise recent results on the inviscid limit for the perturbed KdV and use them to suggest a setup which could be used to make a next step in the study of the inviscid limit of 2D NSE. The proposed approach is based on an ergodic hypothesis for the flow of the 2D Euler equation on iso-integral surfaces. It invokes a Whitham equation for the 2D Navier-Stokes equation, written in terms of the ergodic measures. Dedicated to Vladimir Igorevich Arnold on his 70th birthday  相似文献   
82.
For two types of qutrits specified by the dynamical symmetry SU(3) and SU(2), we consider the difference in entanglement caused by the lack of quantum observables in the latter case. In particular, we show that the SU(2) qutrits can have specific separable entanglement caused by quantum correlations of intrinsic degrees of freedom in a single party without interparty correlations.  相似文献   
83.
Nowadays much attention is being paid to the determination of trace amounts of noble metals in geological, industrial, biological and environmental samples. The most promising techniques, such as inductively coupled plasma atomic emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS) and electrothermal atomic absorption spectrometry (ETAAS) are characterized by high sensitivity. However, the accurate determination of trace noble metals has been limited by numerous interferences generated from the presence of matrix elements. To decrease, or eliminate, these interferences, the sorption preconcentration of noble metals is often used prior to their instrumental detection. A great number of hyphenated methods of noble metal determination using sorption preconcentration have been developed. This review describes the basic types of available sorbents, preconcentration procedures and preparations of the sorbent to the subsequent determination of noble metals. The specific features of instrumental techniques and examples of ETAAS, FAAS, ICP-AES, ICP-MS determinations after the sorption preconcentration of noble metals are considered. The references cited here were selected mostly from the period 1996 - 2006.  相似文献   
84.
The adsorption of nonionic surfactant Triton X-100 on quartz sand and methylated quartz sand from water and toluene was investigated by means of spectrophotometry, the radiotracer technique, and wetting angle measurements.  相似文献   
85.
For the NO molecule, modelled as a Morse oscillator, time-dependent (TD) nuclear Schr?dinger equation has been numerically solved for the multiphoton vibrational dynamics of the molecule under a far-infrared laser of wavelength 10503 nm, and four different intensities,I = 1 × 108, 1 × 1013, 5 × 1016, and 5 × 1018 W cm−2 respectively. Starting from the vibrational ground state at zero time, various TD quantities such as the norm, dissociation probability, potential energy curve and dipole moment are examined. Rich high-harmonics generation (HHG) spectra and above-threshold dissociation (ATD) spectra, due to the multiphoton interaction of vibrational motions with the laser field, and consequent elevation to the vibrational continuum, have been obtained and analysed. Dedicated to Professor C N R Rao on his 70th birthday An erratum to this article is available at .  相似文献   
86.
87.
The behavior of the intensity of anomalous and galactic cosmic rays in the outer heliosphere is compared. The previous hypothesis, according to which the lowest energy galactic cosmic rays affected by large-scale electric fields far beyond the termination shock wave of the solar wind may contribute to the behavior of the anomalous component intensity, is analyzed.  相似文献   
88.
89.
90.
Electron spin resonance (ESR) spectra of poly(acrylic acid) (PAA) γ-irradiated in air at room temperature and recorded at room temperature and at liquid-nitrogen temperature have been studied to identify the radiation products. The ESR spectra are composed of eight lines with hyperfine splittings of 23 ± 1 G and 11 ± 1 G. The method of least-squares total curve fitting, employing the Lorentzian line shape function, to the observed spectra enabled the assignment of the spectra. Computed spectra obtained by the superposition of a singlet and the spectra due to chain radicals are considered to give the best fits to the observed ESR spectra. The singlet is assigned to the radicals COOH, and the component 10-line spectra are assigned to the chain radicals CH3? CH? CH2 ~ and/or ~ CH2? CH? CH2 ~. The observed change in line shape with temperature of the ESR spectra is attributed to the hindered oscillations of the methyl groups about the Cα? Cβ bond axis of the chain radicals. The existence of the methyl groups is confirmed by the measurement of infrared absorption.  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