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   1308150篇
  免费   29913篇
  国内免费   12206篇
化学   648345篇
晶体学   20519篇
力学   75393篇
综合类   420篇
数学   241080篇
物理学   364512篇
  2021年   14577篇
  2020年   16975篇
  2019年   17223篇
  2018年   12792篇
  2016年   28510篇
  2015年   21875篇
  2014年   31800篇
  2013年   76169篇
  2012年   37076篇
  2011年   31838篇
  2010年   37213篇
  2009年   40147篇
  2008年   31352篇
  2007年   26232篇
  2006年   33209篇
  2005年   25349篇
  2004年   27237篇
  2003年   26161篇
  2002年   27574篇
  2001年   24971篇
  2000年   22808篇
  1999年   21918篇
  1998年   21103篇
  1997年   20985篇
  1996年   21329篇
  1995年   19396篇
  1994年   18805篇
  1993年   18284篇
  1992年   17749篇
  1991年   18058篇
  1990年   17270篇
  1989年   17307篇
  1988年   16812篇
  1987年   16851篇
  1986年   15729篇
  1985年   22172篇
  1984年   23533篇
  1983年   19798篇
  1982年   21521篇
  1981年   20759篇
  1980年   20099篇
  1979年   20092篇
  1978年   21513篇
  1977年   21059篇
  1976年   20717篇
  1975年   19380篇
  1974年   19014篇
  1973年   19497篇
  1972年   14016篇
  1967年   12270篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Palladium and molybdenum polycrystalline layers (clusters) have been deposited in a stainless steel UHV system onto a layer of alumina (Al2O3). This layer has been prepared by high temperature oxidation of an aluminium layer. The interaction of this system with nitrogen has been investigated at room temperature by an FEM technique. Under these conditions nitrogen spillover from molybdenum to palladium has been observed.  相似文献   
52.
Open circuit voltage (OCV) measurements in H2O/air concentration cells at T<580 K using Yb-doped SrCeO3 electrolyte indicate that under these conditions, protons are transported through the electrolyte as -ve ions, possibly as hydroxyl (OH) ions. The H+ ionic transport, which is generally reported, becomes the dominant mode for H2O/air concentration cells at temperatures greater than 750 K or when H2O/air electrodes are replaced by H2/Ar, and the anomalous OCV sign disappears. The combination of low temperature and the presence of hydrogen and oxygen as provided by the H2O/air system appears to be necessary for the postulated hydroxyl ion electrode reactions to take place. In addition to OCV measurements, results from impedance spectroscopy are used to provide evidence in support of the suggested hydroxyl ion mode of protonic transport under the specified conditions. These findings are directly relevant in the development of novel humidity sensors in the temperature range 450–580K and is reported in a separate paper in this conference. Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996  相似文献   
53.
We report on a cw mode-locked non-critically phase matched KTP optical parametric oscillator synchronously pumped by a picosecond Ti:Sapphire laser. High average signal output power of up to 950 mW over a large tuning range has been achieved. For this OPO the influence of resonator-length detuning on the output power, pulse duration and spectral bandwidth has been investigated. The measured data are in good agreement with the results of a numerical simulation using a split-step Fourier method which considers the group-velocity mismatch, the group-velocity dispersion and the self-phase modulation. The numerical simulation also describes the measured strong pump depletion and its influence on the OPO output and efficiency.  相似文献   
54.
55.
56.
57.
本文研究了铁矿石、铬矿石、锰矿石中的微量磷的电感耦合等离子体发射光谱法的测定。方法简便,具有很好的精密度和准确度。标准样品的分析结果基本与标称值相吻合,回收率在95%-105%之间。  相似文献   
58.
The Weierstrass nowhere differentiable function, and functions constructed from similar infinite series, have been studied often as examples of functions whose graph is a fractal. Though there is a simple formula for the Hausdorff dimension of the graph which is widely accepted, it has not been rigorously proved to hold. We prove that if arbitrary phases are included in each term of the summation for the Weierstrass function, the Hausdorff dimension of the graph of the function has the conjectured value for almost every sequence of phases. The argument extends to a much wider class of Weierstrass-like functions.

  相似文献   

59.
NaY zeolite samples loaded with sodium metal by vapor phase deposition have been investigated using129Xe NMR spectroscopy. At low sodium concentration, the129Xe NMR spectrum showed three resonance lines which clearly indicate the existence of distinct domains in the zeolite sample. Such an observation suggests that the diffusion of the xenon atoms into each domain only occurs with respect to the NMR time scale (2.9 ms). As the sodium concentration increases, observation of a single broad line indicate a macroscopic homogenization of the system. The shift of this line is explained in part due to a paramagnetic interaction between the xenon atoms and the unpaired electrons of particles containing an odd number of sodium atoms. The linewidth is due to the distribution of the local magnetic fields partially averaged by the rapid motion of the xenon atoms and to the statistical distribution of the sodium particles in the supercage cavities. The paramagnetic interaction vanishes with the oxidation of the sample leading to a narrowing and a shift of the line to higher magnetic fields.  相似文献   
60.
The Thoms effect observed with water-soluble cationic copolymer of acrylamide was studied in relation to the concentration, molecular weight, and molecular weight polydispersity of the polymeric additive, with its composition and composition polydispersity being constant.  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