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   1271篇
  免费   69篇
  国内免费   5篇
化学   922篇
晶体学   11篇
力学   14篇
数学   41篇
物理学   357篇
  2023年   6篇
  2022年   9篇
  2021年   13篇
  2020年   24篇
  2019年   27篇
  2018年   18篇
  2017年   18篇
  2016年   36篇
  2015年   29篇
  2014年   26篇
  2013年   47篇
  2012年   81篇
  2011年   72篇
  2010年   47篇
  2009年   41篇
  2008年   59篇
  2007年   68篇
  2006年   69篇
  2005年   73篇
  2004年   60篇
  2003年   42篇
  2002年   28篇
  2001年   30篇
  2000年   25篇
  1999年   21篇
  1998年   19篇
  1997年   20篇
  1996年   18篇
  1995年   6篇
  1994年   15篇
  1993年   11篇
  1992年   25篇
  1991年   12篇
  1990年   7篇
  1989年   14篇
  1988年   11篇
  1987年   11篇
  1986年   10篇
  1985年   9篇
  1984年   22篇
  1983年   10篇
  1982年   12篇
  1981年   8篇
  1980年   17篇
  1979年   14篇
  1978年   17篇
  1977年   17篇
  1976年   14篇
  1975年   11篇
  1974年   10篇
排序方式: 共有1345条查询结果,搜索用时 46 毫秒
91.
On slow cooling, a precursor phenomenon in supercooled benzene was probed by longitudinal absorption. On quenching, in-situ observation of ultrasonic measurements was carried out at the fixed temperature. Sequence of the transmitted waves was multiple scattered in quenched benzene. The dynamic ultrasound scattering is sensitive to the local strain and dynamic inhomogeneous fluctuations. The quenched benzene shows the maximum value of longitudinal absorption at incubation time, tinc. Crystal domain growth/coarsening is promoted by the ultrasonic irradiation at tinc < t. In addition, tinc depends on the quenching temperature. Ultrasonic irradiation and quenching effects dominate the extraordinal nucleation and growth process of benzene in spite of simple and non-polar molecular liquid.  相似文献   
92.
93.
News     
  相似文献   
94.
95.
News     
  相似文献   
96.
Water-soluble C60-porphyrin hybrid molecules were first synthesized toward their pharmaceutical applications.  相似文献   
97.
The structure of Ge(105)-(1 x 2) grown on Si(105) is examined by scanning tunneling microscopy (STM) and first-principles calculations. The morphology evolution with an increasing amount of Ge deposited documents the existence of a tensile surface strain in Si(105) and its relaxation with increasing coverage of Ge. A detailed analysis of high-resolution STM images and first-principles calculations produce a new stable model for the Ge(105)-(1 x 2) structure formed on the Si(105) surface that includes the existence of surface strain. It corrects the model developed from early observations of the facets of "hut" clusters grown on Si(001).  相似文献   
98.
Kubo K  Sakaguchi S  Sakurai T 《Talanta》1999,49(4):735-744
Armed crown ethers (1-4) bonding through an amine, amide, ether, or ester linkage to naphthyl group were found to display unique photophysical properties in the presence of guest salts. Complexation of PET fluoroionophores (1a and 1b) with Zn(2+) increased the fluorescence intensities of the host by a factor of 2.4 and 2.7, respectively. (1)H and (13)C NMR analyses of this complexation behavior of 1a revealed that Zn(2+) strongly coordinates with the armed crown nitrogen to cause a dramatic decrease in an intramolecular charge-transfer character. The armed crowns (2 and 3), bonding through an ether or ester linkage to a naphthalene, gave fluorescence quenching with guest thiocyanates. While the amide derivative (4) exhibited high Ba(2+) fluorescence selectivity and in the presence of this cation the host fluorescence intensity was by a factor of 3.69.  相似文献   
99.
We report experimental and theoretical results for two-phase convection in a thin horizontal layer of a fluid with a first-order phase change and heated from below. A top layer of the nematic phase of a liquid crystal is located above the bottom layer of the isotropic phase of the same substance. A horizontal field of 1000 G is applied in order to align the director of the nematic phase. Over some ranges of the thickness of the isotropic phase, and in sufficiently large thermal gradients, the more dense nematic phase can be stably stratified above the less dense isotropic one, with a stable interface between them. Based on the equations of motion derived for this problem by Busse and Schubert [J. Fluid Mech. 46, 801 (1971)], we evaluate the bifurcation lines between the quiescent and convecting states and the corresponding critical wave vectors as a function of the interface position. We report experimental measurements based on Nusselt-number determinations for the locations of the bifurcation lines. They are in good agreement with the theoretical results. We also report approximate determinations of the critical wave numbers which are semiquantitatively consistent with the theory. A great diversity of patterns is observed in the convecting states, including normal and parallel rolls, rolls with defects and disorder, target patterns and spirals, and cellular flow with upflow or downflow at the cell center. These patterns are discussed in terms of the breaking of the mirror symmetry at the horizontal midplane by the interface, and in terms of the orienting effects of the magnetic field.  相似文献   
100.
The luminescence and conduction currents of a doubly-insulated thin-film electroluminescent device were studied under various excitation conditions. The conduction current waveform was calculated numerically from the luminescence waveform. It was composed of two components: a fast transient component jfc, which rises and decays rapidly when a pulse is applied, and a dc-like component jdc, which maintains a constant level during the duration of pulse. The ratio of these components varied considerably with applied voltage. Both the slow response of luminescence to voltage change and the change in jfc when the excitation conditions were changed from repetitive pulses to a single pulse suggest an accumulation of charges inside the electroluminescence layer. This accumulation causes a space charge effect which explains the dominance of jfc in the high-brightness region. The fact that luminescence intensity in this region is not related to the amplitude of individual pulses, but rather to the average amplitude of the pulse train also indicates that the space-charge-induced internal electric field is the main factor in accelerating the carriers which excite the luminescence centers. It was found that the two conduction current components showed similar characteristics in singly-insulated devices.  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