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   78426篇
  免费   348篇
  国内免费   385篇
化学   24448篇
晶体学   790篇
力学   6748篇
数学   32009篇
物理学   15164篇
  2018年   10436篇
  2017年   10262篇
  2016年   6068篇
  2015年   852篇
  2014年   306篇
  2013年   331篇
  2012年   3808篇
  2011年   10538篇
  2010年   5643篇
  2009年   6060篇
  2008年   6616篇
  2007年   8761篇
  2006年   244篇
  2005年   1327篇
  2004年   1549篇
  2003年   1981篇
  2002年   1022篇
  2001年   260篇
  2000年   318篇
  1999年   168篇
  1998年   197篇
  1997年   148篇
  1996年   202篇
  1995年   122篇
  1994年   78篇
  1993年   104篇
  1992年   61篇
  1991年   70篇
  1990年   56篇
  1989年   61篇
  1988年   65篇
  1987年   60篇
  1986年   61篇
  1985年   52篇
  1984年   49篇
  1983年   38篇
  1982年   45篇
  1981年   42篇
  1980年   49篇
  1979年   49篇
  1978年   40篇
  1973年   26篇
  1914年   45篇
  1913年   40篇
  1912年   40篇
  1910年   24篇
  1909年   41篇
  1908年   40篇
  1907年   32篇
  1904年   28篇
排序方式: 共有10000条查询结果,搜索用时 93 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.
3.
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   
4.
5.
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   
6.
This study describes the development of a simple, enzyme-free, label-free, sensitive, and selective system for detecting adenosine based on the use of Tween 20-stabilized gold nanoparticles (Tween 20-AuNPs) as an efficient fluorescence quencher for boron dipyrromethene-conjugated adenosine 5′-triphosphate (BODIPY-ATP) and as a recognition element for adenosine. BODIPY-ATP can interact with Tween 20-AuNPs through the coordination between the adenine group of BODIPY-ATP and Au atoms on the NP surface, thereby causing the fluorescence quenching of BODIPY-ATP through the nanometal surface energy transfer (NSET) effect. When adenosine attaches to the NP surface, the attached adenosine exhibits additional electrostatic attraction to BODIPY-ATP. As a result, the presence of adenosine enhances the efficiency of AuNPs in fluorescence quenching of BODIPY-ATP. The AuNP-induced fluorescence quenching of BODIPY-ATP progressively increased with an increase in the concentration of adenosine; the detection limit at a signal-to-noise ratio of 3 for adenosine was determined to be 60 nM. The selectivity of the proposed system was more than 1000-fold for adenosine over any adenosine analogs and other nucleotides. The proposed system combined with a phenylboronic acid-containing column was successfully applied to the determination of adenosine in urine.  相似文献   
7.
8.
9.
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