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   6647篇
  免费   939篇
  国内免费   452篇
化学   1729篇
晶体学   85篇
力学   1252篇
综合类   4篇
数学   1135篇
物理学   3833篇
  2025年   27篇
  2024年   87篇
  2023年   166篇
  2022年   161篇
  2021年   208篇
  2020年   272篇
  2019年   206篇
  2018年   148篇
  2017年   248篇
  2016年   234篇
  2015年   281篇
  2014年   351篇
  2013年   416篇
  2012年   558篇
  2011年   561篇
  2010年   491篇
  2009年   507篇
  2008年   392篇
  2007年   418篇
  2006年   376篇
  2005年   240篇
  2004年   165篇
  2003年   175篇
  2002年   156篇
  2001年   138篇
  2000年   91篇
  1999年   112篇
  1998年   73篇
  1997年   68篇
  1996年   50篇
  1995年   45篇
  1994年   18篇
  1993年   15篇
  1989年   11篇
  1988年   45篇
  1987年   101篇
  1986年   85篇
  1981年   10篇
  1974年   11篇
  1972年   14篇
  1971年   37篇
  1970年   15篇
  1968年   26篇
  1967年   43篇
  1966年   16篇
  1965年   20篇
  1964年   13篇
  1963年   12篇
  1962年   9篇
  1961年   10篇
排序方式: 共有8038条查询结果,搜索用时 0 毫秒
1.
《Fluid Phase Equilibria》2006,244(1):86-98
Bubble point temperatures near ambient pressure, for the binary mixtures, formed by o-cresol or p-cresol with – methanol, ethanol, n- and iso-propanols and n-, iso-, sec- and tert-butanols – covering the whole composition range, are measured using a Swietoslawski-type ebulliometer. The liquid phase composition–bubble point temperature measurements are found to be well represented by the Wilson model. Values of the optimum Wilson parameters as well as the computed values of vapor phase mole fractions and activity coefficients are tabulated. The results are discussed in terms of isomerization with reference to the selected set of compounds, constituting the mixtures and the stearic effects in the cresols.  相似文献   
2.
A series of novel N-dichloroacetyl oxazolidine herbicide safeners was synthesized and characterized by IR, 1H NMR, 13C NMR, elemental analysis and X-ray diffraction. The preliminary biological test shows that the compounds could protect maize against injury caused by chlorsulfuron to a certain extent.  相似文献   
3.
Jia-Sheng Ye  Shu-Tian Liu 《Optik》2006,117(5):225-230
The finite-thickness model (FTM) is applied to the design of cylindrical microlenses based on the wave-front interference principle, rather than the existing zero-thickness model (ZTM). This design method is very simple in physics and highly efficient in computations. For cylindrical lenses with different f-numbers (from f/1.5 to f/0.6), the detailed designs by using both the FTM and the ZTM are carried out. To show the superiority of the FTM to the ZTM, we investigate the focal performance of all the designed lenses based on rigorous electromagnetic theory and the boundary element method. Numerical results reveal that the constructed cylindrical lenses by the FTM are witnessed to exhibit much better focusing performance than those by the ZTM, especially for the small f-numbers.  相似文献   
4.
A new way to enhance the directional stability of laser beams with alternating intensity by fast feedback control of both linear and angular drifts has been proposed for alignment of laser beams at higher accuracy. Both linear and angular drifts of laser beams, processed through light intensity modulation and primary alignment using single-mode optical fiber (SMOF), are separated using light path arrangement and detected using phase-lock technique, and are controlled using fast feedback control mechanisms according to their detected magnitudes, so that both linear and angular drifts are suppressed to enhance the directional stability of the emitting laser beams. Theoretical analyses and preliminary experimental results indicate that the approach proposed can be used to achieve an alignment accuracy of more than 10−8 rad.  相似文献   
5.
In this work the millimeter-wave (MMW) and far infrared (FIR) absorption spectrum for the asymmetrically deuterated Methanol (CH2DOH) species measured recently at a temperature of −60 °C with better accuracy and signal/noise (S/N) ratio than known before has been assigned for transitions originating at the lowest lying trans- to gauche-states. The entire spectrum for 50–1200 cm−1 has been re-recorded recently using the Synchrotron Radiation Source coupled with the Bruker Fourier Transform Infrared (FTIR) spectrometer with a resolution of about 0.001 cm−1 or better. Complete spectrum has not been exploited a great deal but it helped to entangle overlapping lines in the present work. This also fills the gap remaining in the usual FTIR in the range 400–500 cm−1. Hence it is expected to help the interacting partner for the Coriolis interaction encountered earlier. The assigned transitions mostly for the axial rotational angular momentum quantum number K + 1  K, both for R- and Q-sub bands for wide range of rotational angular momentum quantum number. The MMW spectrum has been recalibrated and assigned for a number of Q-branches. The assignments are confirmed rigorously using closed loop residual technique. The assigned rR and rQ lines have been analyzed in terms of polynomial expansion parameters. The new assignments are presented for about 750 transitions and a grand atlas of more than 1000 lines has been prepared which will be made available through the open source server at “research gate”. The present work should be useful in the area of astrophysical detection and further understanding of the energy relaxation pathways in the molecule.  相似文献   
6.
The quantum dynamics of carriers bound to helical tube surfaces is investigated in a thin-layer quantization scheme. By numerically solving the open-boundary Schrödinger equation in curvilinear coordinates, geometric effect on the coherent transmission spectra is analysed in the case of single propagating mode as well as multimode. It is shown that, the coiling endows the helical nanotube with different transport properties from a bent cylindrical surface. Fano resonance appears as a purely geometric effect in the conductance, the corresponding energy of quasibound state is obviously influenced by the torsion and length of the nanotube. We also find new plateaus in the conductance. The transport of double-degenerate mode in this geometry is reminiscent of the Zeeman coupling between the magnetic field and spin angular momentum in quasi-one-dimensional structure.  相似文献   
7.
We theoretically investigate the dynamics of dark solitons as well as their interaction in nonlocal media. Approximate equations describing the evolution of the beams are obtained via suitable trial functions of amplitude u and refractive index n in an averaged Lagrangian. Our results reveal that out-of-phase dark solitons can evolve into stable bound states in nonlocal materials. Moreover, it is found that the separations in the bound state monotonically increase with the degree of nonlocality in nonlocal limit. These results are in excellent agreement with the numerical simulations.  相似文献   
8.
Deyun Wei  Qiwen Ran  Yuanmin Li 《Optik》2012,123(2):137-139
Fractional Fourier transform (FRFT) plays an important role in many fields of optics and signal processing. This paper considers the problem of reconstructing a fractional bandlimited signal with FRFT. We propose a novel reconstruction method for fractional bandlimited signals using the fractional Fourier series (FRFS). The advantage is that the sampling expansion can be deduced directly not based on the Shannon theorem. By utilizing the generalized form of Parseval’s relation for complex FRFS, we obtain the sampling expansion for fractional bandlimited signals with FRFT. We show that the sampling expansion for fractional bandlimited signals with FRFT is a special case of Parseval’s relation for complex FRFS.  相似文献   
9.
10.
提出了一种基于单负Metamaterials对的带通滤波器的设计原理,给出了这种带通滤波器的谐振频率的表达式,对其谐振频率及带宽与其决定因素之间的关系进行了计算,对计算结果进行了讨论,为设计单负Metamaterial对带通滤波器的理论与方法提供了依据。研究结果表明:利用单负Metamaterials对的确可以实现带通滤波器;ENG板的磁导率μ1、MNG板的介电常数ε2、电等离子体频率ωep、磁等离子体频率ωmp、两个层的厚度比值a这五个因素决定了这种滤波器的中心频率;两个层的厚度及二者之间的比值决定这种滤波器的带宽。  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