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   78833篇
  免费   386篇
  国内免费   391篇
化学   24769篇
晶体学   794篇
力学   6785篇
数学   32105篇
物理学   15157篇
  2021年   68篇
  2020年   46篇
  2019年   62篇
  2018年   10476篇
  2017年   10284篇
  2016年   6102篇
  2015年   883篇
  2014年   361篇
  2013年   440篇
  2012年   3846篇
  2011年   10553篇
  2010年   5674篇
  2009年   6078篇
  2008年   6621篇
  2007年   8780篇
  2006年   249篇
  2005年   1325篇
  2004年   1532篇
  2003年   1973篇
  2002年   1012篇
  2001年   249篇
  2000年   302篇
  1999年   157篇
  1998年   192篇
  1997年   149篇
  1996年   197篇
  1995年   118篇
  1994年   76篇
  1993年   96篇
  1992年   55篇
  1991年   68篇
  1990年   52篇
  1989年   63篇
  1988年   62篇
  1987年   65篇
  1986年   59篇
  1985年   55篇
  1984年   49篇
  1983年   45篇
  1982年   45篇
  1981年   44篇
  1980年   48篇
  1979年   44篇
  1978年   37篇
  1914年   45篇
  1913年   40篇
  1912年   40篇
  1909年   41篇
  1908年   40篇
  1907年   32篇
排序方式: 共有10000条查询结果,搜索用时 340 毫秒
1.
In the paper, the authors establish several integral representations for the generating functions of the large and little Schröder numbers and for the large and little Schröder numbers.  相似文献   
2.
Mesoscopic modeling at the pore scale offers great promise in exploring the underlying structure transport performance of flow through porous media. The present work studies the fluid flow subjected to capillarity-induced resonance in porous media characterized by different porous structure and wettability. The effects of porosity and wettability on the displacement behavior of the fluid flow through porous media are discussed. The results are presented in the form of temporal evolution of percentage saturation and displacement of the fluid front through porous media. The present study reveals that the vibration in the form of acoustic excitation could be significant in the mobilization of fluid through the porous media. The dependence of displacement of the fluid on physicochemical parameters like wettability of the surface, frequency along with the porosity is analyzed. It was observed that the mean displacement of the fluid is more in the case of invading fluid with wetting phase where the driving force strength is not so dominant.  相似文献   
3.
4.
We prove that the group of diffeomorphisms of the interval [0, 1] contains surface groups whose action on (0, 1) has no global fix point and such that only countably many points of the interval (0, 1) have non-trivial stabiliser.  相似文献   
5.
Journal of Thermal Analysis and Calorimetry - Nanofluids are attractive alternatives for the current heat transfer fluids due to their remarkably higher thermal conductivity which leads to the...  相似文献   
6.
7.
8.
9.
In this study, multiwalled carbon nanotube (MWCNT) was modified by the pyridine group using a silane agent and characterized by infrared spectroscopy (IR), thermal analysis (TG/DTA), and elemental analysis (CHN) and scanning electron microscopy (SEM). The application of this sorbent was investigated in determination of lead ions in aqueous samples, using flame atomic absorption spectrometry (FAAS). Through this study, different parameters such as pH and sample flow rate on adsorption process and eluent concentration, volume and flow rate were optimized. The limit of detection (LOD), the relative standard deviation and the recovery of the method were 2 ng mL?1, 1.3% and 99.7%, respectively. Two standard reference materials (NIST 1571 and NIST 1572) were used to verify accuracy of this method. Finally, the sorbent was successfully applied for extraction and determination of low levels of Pb(II) ions in aqueous samples.  相似文献   
10.
The structure and properties of 12Cr1MoV steel irradiated with a zirconium ion beam were studied by optical microscopy, scanning electron microscopy, and micro- and nanoindentation. It is shown that the modification covers the entire cross-section of the irradiated specimens to a depth of 1 mm. The data on irradiation-induced structural changes are used to interpret the changes in mechanical properties of the irradiated specimens under static and cyclic loading. Particular attention is given to analysis of strain estimation by the digital image correlation method.  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