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   79538篇
  免费   380篇
  国内免费   374篇
化学   25222篇
晶体学   817篇
力学   6743篇
数学   31994篇
物理学   15516篇
  2018年   10444篇
  2017年   10267篇
  2016年   6087篇
  2015年   867篇
  2014年   314篇
  2013年   384篇
  2012年   3825篇
  2011年   10547篇
  2010年   5661篇
  2009年   6077篇
  2008年   6653篇
  2007年   8815篇
  2006年   282篇
  2005年   1370篇
  2004年   1602篇
  2003年   2026篇
  2002年   1075篇
  2001年   308篇
  2000年   329篇
  1999年   173篇
  1998年   210篇
  1997年   159篇
  1996年   222篇
  1995年   126篇
  1994年   94篇
  1993年   111篇
  1992年   76篇
  1991年   90篇
  1990年   75篇
  1989年   82篇
  1988年   84篇
  1987年   81篇
  1986年   76篇
  1985年   90篇
  1984年   77篇
  1983年   64篇
  1982年   66篇
  1981年   70篇
  1980年   69篇
  1979年   82篇
  1978年   66篇
  1977年   34篇
  1976年   46篇
  1975年   34篇
  1973年   38篇
  1914年   45篇
  1913年   40篇
  1912年   40篇
  1909年   41篇
  1908年   40篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
13.
We give the form of the output function in Ginsburg’s machine in which the input and output dictionaries are abelian groups and the transition function is of a special form.  相似文献   
14.
15.
Pyrrolopyrrole aza‐BODIPY (PPAB) developed in our recent study from diketopyrrolopyrrole by titanium tetrachloride‐mediated Schiff‐base formation reaction with heteroaromatic amines is a highly potential chromophore due to its intense absorption and fluorescence in the visible region and high fluorescence quantum yield, which is greater than 0.8. To control the absorption and fluorescence of PPAB, particularly in the near‐infrared (NIR) region, further molecular design was performed using DFT calculations. This results in the postulation that the HOMO–LUMO gap of PPAB is perturbed by the heteroaromatic moieties and the aryl‐substituents. Based on this molecular design, a series of new PPAB molecules was synthesized, in which the largest redshifts of the absorption and fluorescence maxima up to 803 and 850 nm, respectively, were achieved for a PPAB consisting of benzothiazole rings and terthienyl substituents. In contrast to the sharp absorption of PPAB, a PPAB dimer, which was prepared by a cross‐coupling reaction of PPAB monomers, exhibited panchromatic absorption across the UV/Vis/NIR regions. With this series of PPAB chromophores in hand, a potential application of PPAB as an optoelectronic material was investigated. After identifying a suitable PPAB molecule for application in organic photovoltaic cells based on evaluation using time‐resolved microwave conductivity measurements, a maximized power conversion efficiency of 1.27 % was achieved.  相似文献   
16.
17.
18.
19.
The structure, chemical composition, and magnetic properties of electrochemically deposited nanocrystalline Co-Ni-Fe films were investigated using a number of techniques. A high saturation magnetic induction up to B s = 21 kG was attained. An enhancement of the saturation magnetization compared to the ideal anticipated one was revealed, which correlated with the nonlinear behavior of the structural phase composition and lattice parameters with the change of the composition. The text was submitted by the authors in English.  相似文献   
20.
A forecasting model is developed for the number of daily applications for loans at a financial services telephone call centre. The purpose of the forecasts and the associated prediction intervals is to provide effective staffing policies within the call centre. The model building process is constrained by the availability of only 2 years and 7 months of data. The distinctive feature of the data is that demand is driven in the main by advertising. The analysis given focuses on applications stimulated by press advertising. Unlike previous analyses of broadly similar data, where ARIMA models were used, a model with a dynamic level, multiplicative calendar effects and a multiplicative advertising response is developed and shown to be effective.  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