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   108338篇
  免费   3079篇
  国内免费   3303篇
化学   45566篇
晶体学   1186篇
力学   7898篇
综合类   264篇
数学   36034篇
物理学   23772篇
  2023年   244篇
  2022年   594篇
  2021年   664篇
  2020年   700篇
  2019年   780篇
  2018年   10940篇
  2017年   10698篇
  2016年   6992篇
  2015年   1873篇
  2014年   1539篇
  2013年   2447篇
  2012年   5777篇
  2011年   12547篇
  2010年   7164篇
  2009年   7490篇
  2008年   8456篇
  2007年   10420篇
  2006年   1842篇
  2005年   2660篇
  2004年   2848篇
  2003年   3113篇
  2002年   2269篇
  2001年   1242篇
  2000年   1089篇
  1999年   765篇
  1998年   603篇
  1997年   591篇
  1996年   630篇
  1995年   479篇
  1994年   407篇
  1993年   457篇
  1992年   396篇
  1991年   363篇
  1990年   292篇
  1989年   282篇
  1988年   259篇
  1987年   320篇
  1986年   280篇
  1985年   310篇
  1984年   275篇
  1983年   219篇
  1982年   246篇
  1981年   252篇
  1980年   248篇
  1979年   248篇
  1978年   236篇
  1977年   205篇
  1976年   183篇
  1975年   196篇
  1973年   164篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
A method using third order moments for estimating the regression coefficients as well as the latent state scores of the reduced-rank regression model when the latent variable(s) are non-normally distributed is presented in this paper. It is shown that the factor analysis type indeterminacy of the regression coefficient matrices is eliminated. A real life example of the proposed method is presented. Differences of this solution with the reduced-rank regression eigen solution are discussed.  相似文献   
53.
Courses which teach discrete-event simulation are based on many different simulation languages. The requirements for a language to support teaching simulation are discussed. In particular, it is recommended that such languages separate into distinct modules those aspects of simulation which are taught as separate topics. Implementation of the separation is discussed. The SEESIM language, developed as a teaching aid, is described, and examples of its use are given. Straightforward use of SEESIM can be learned quickly, yet the language provides facilities for a staged introduction to advanced concepts of simulation.  相似文献   
54.
我们用最近研制成功的LMA型低频力学谱测试系统对NiTi合金马氏体相进行了在很大频率范围内(0.003~1Hz)的低频等温力学谱和温度谱的测量.我们研究的形状记忆合金NiTi(Ni50.2at%)试样长34mm,直径1mm细丝.经一定热处理,分别在333K.343K和353K做了内耗随频率的变化的测量。实验表明:频率越小,内耗越大,也就是内耗随频率减少而增大。同时我们采用阶梯升温的方法在八个温度下每个温度测量三种频率(1Hz,0.1Hz,0.01Hz)的内耗,结果清楚地表明:不同频率下,内耗峰都出现在372K(99℃)。而且频率越低,峰高越高。这是具有相变峰的特点:相变峰的峰温不随测量频率不同而变化,相变峰高度随频率减少而增大。我们还测量了在1Hz与0.5Hz频率下内耗随温度的变化。本文用马氏体相的位错理论初步讨论了上述实验结果。  相似文献   
55.
J Ashenfelter 《Pramana》2002,59(5):713-717
The ESTU began operation in 1988 and achieved the design voltage of 20 MV in 1990. Since that time, improvements to the gas handling system, negative ion injector, accelerator terminal and control system have greatly increased its capability and reliability. Today, the ESTU can efficiently produce an extensive assortment of stable ions at wide-ranging energies in support of low-energy nuclear physics.  相似文献   
56.
A pressure sensitive paint (PSP) measurement has been known as a pressure field measurement technique based on the oxygen quenching phenomenon of luminescence of specific luminophores. A PSP measurement was applied for pressure field measurement in a low-solidity circular cascade diffuser of a single-stage transonic centrifugal compressor with 5 in pressure ratio for HFC134a gas. The oxygen concentration was about 500 ppm. Ru (bath-phen) was adsorbed on a silica-gel thinlayer chromatography sheet, and the sheet was pasted onto the side-wall between the cascade vanes. A drastic change in luminescent intensity was recognized during a surge condition. Also the pressure variations based on luminescent intensity agreed well with the pressure fluctuations measured using a semiconductor pressure sensor with high-frequency-response. It was shown that a PSP measurement worked well to investigate the unsteady pressure fields in a circular cascade diffuser of a transonic centrifugal compressor. Moreover, the time response of PSP becomes clear as a problem to be overcome for the present.  相似文献   
57.
58.
Dual fractional cutting plane algorithms, in which cutting planes are used to iteratively tighten a linear relaxation of an integer program, are well-known and form the basis of the highly successful branch-and-cut method. It is rather less well-known that various primal cutting plane algorithms were developed in the 1960s, for example by Young. In a primal algorithm, the main role of the cutting planes is to enable a feasible solution to the original problem to be improved. Research on these algorithms has been almost non-existent.  In this paper we argue for a re-examination of these primal methods. We describe a new primal algorithm for pure 0-1 problems based on strong valid inequalities and give some encouraging computational results. Possible extensions to the case of general mixed-integer programs are also discussed.  相似文献   
59.
60.
The breakthrough and stoichiometric SO2 adsorption efficiencies of a biomass supported Na2CO3 system (80 wt %Na2CO3/straw) have reached 48.9% and 80.6% respectively at a desulfurization temperature of 80℃.  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