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   1416篇
  免费   42篇
  国内免费   9篇
化学   602篇
晶体学   36篇
力学   62篇
数学   401篇
物理学   366篇
  2023年   10篇
  2022年   19篇
  2021年   41篇
  2020年   20篇
  2019年   19篇
  2018年   27篇
  2017年   40篇
  2016年   38篇
  2015年   27篇
  2014年   42篇
  2013年   113篇
  2012年   69篇
  2011年   89篇
  2010年   69篇
  2009年   57篇
  2008年   79篇
  2007年   71篇
  2006年   50篇
  2005年   43篇
  2004年   44篇
  2003年   41篇
  2002年   25篇
  2001年   17篇
  2000年   21篇
  1999年   18篇
  1998年   12篇
  1996年   18篇
  1995年   10篇
  1994年   11篇
  1993年   16篇
  1992年   14篇
  1991年   14篇
  1990年   10篇
  1988年   8篇
  1987年   11篇
  1986年   7篇
  1985年   21篇
  1984年   13篇
  1983年   15篇
  1982年   21篇
  1981年   11篇
  1980年   19篇
  1979年   18篇
  1978年   11篇
  1977年   11篇
  1976年   13篇
  1975年   12篇
  1974年   7篇
  1973年   12篇
  1972年   8篇
排序方式: 共有1467条查询结果,搜索用时 671 毫秒
41.
42.
The occurance of the urinary stones varies according to the geographical regions. The presence of stones in the urinary system causes pain and discomfort. These generate colics and hence are sometimes life threatening. In the present study, infrared measurements have been made on several stone samples. It has been found that calcium oxalate, calcium phosphate, magnesiunm ammonium phosphate, calcium carbonate, uric acid, -cystine and xanthin are present, as expected. Also, silicon dioxide is found to be present in some of the stones but in small quantity, in addition to the above constituents. This constituent is responsible to exhibit piezoelectricity in the urinary calculi.  相似文献   
43.
44.
The excess volume of mixing of some electron-donating aromatic hydrocarbons like benzene, toluene,p-xylene, and mesitylene with an electronaccepting liquid 1,2,4-trichlorobenzene have been measured at 30°C. The results indicate that the interaction between the components increases as the electron-donating power of the hydrocarbons increases. The V m e values are related to the ionization potentials of the hydrocarbons.  相似文献   
45.
Sulfated zirconia has been employed as an efficient recyclable catalyst for the preparation of various β-acetamidoketones or esters at room temperature. The process involves the one-pot multicomponent reactions of aromatic aldehydes, enolizable ketones or β-ketoesters and acetonitrile in the presence of acetyl chloride.  相似文献   
46.
In this paper we establish some new dynamic inequalities on time scales which contain in particular generalizations of integral and discrete inequalities due to Hardy, Littlewood, P′olya, D'Apuzzo, Sbordone and Popoli. We also apply these inequalities to prove a higher integrability theorem for decreasing functions on time scales.  相似文献   
47.
By establishing a comparison result and using the monotone iterative technique combined with the method of upper and lower solutions, we investigate the existence of solutions for systems of nonlinear fractional differential equations.  相似文献   
48.
Parallel rods / tubes flame support layers were used to study variations in geometry and materials on radiant burner performance. An increased density of rods increased the efficiency, as more surface area was provided to extract the heat of combustion. This effect was attenuated far fraction closed areas above 0·33 because of increased interference of direct base-to-load radiation. Thinner rods (with fraction closed area constant), having a lower thermal conduction resistance, fostered higher efficiency. Greater distances between the base and rods decreased efficiency due to air entrainment. This functioned to cool the base, increasing the range of combustion intensities where a portion of combustion lifted from the burner base. Isolation of radiating materials from conducting to the burner housing resulted in a ~ 5% upward shift in efficiency. Low to high efficiency was measured for alumina, mullite, and oxidized stainless steel rods, respectively; this was related directly to the emittances of the materials used. SiC and MoSi2 coatings on alumina rods resulted in burners which were as efficient as one with stainless steel rods. A burner designed as a restricted band spectral emitter was not as efficient in its high-emission range as a more graybody emitter under the same combustion intensity; the higher-temperature spectral emitter discouraged extraction of sensible heat from the combustion product stream.  相似文献   
49.
Structural Chemistry - This work reports hydrogen uptake capacity and equilibrium isotope effect (EIE) for the Be, Li, and Ti-doped closoborate (B6H6) complexes using first-principles calculations...  相似文献   
50.
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