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   697559篇
  免费   6026篇
  国内免费   1817篇
化学   348543篇
晶体学   8263篇
力学   35799篇
综合类   21篇
数学   101183篇
物理学   211593篇
  2021年   5703篇
  2020年   6337篇
  2019年   7110篇
  2018年   13566篇
  2017年   13860篇
  2016年   15450篇
  2015年   7755篇
  2014年   12310篇
  2013年   28802篇
  2012年   24188篇
  2011年   32682篇
  2010年   23036篇
  2009年   22963篇
  2008年   30335篇
  2007年   32187篇
  2006年   22989篇
  2005年   23406篇
  2004年   20330篇
  2003年   18947篇
  2002年   17803篇
  2001年   17966篇
  2000年   14223篇
  1999年   10803篇
  1998年   9363篇
  1997年   9270篇
  1996年   8796篇
  1995年   7796篇
  1994年   7779篇
  1993年   7600篇
  1992年   7859篇
  1991年   8372篇
  1990年   8024篇
  1989年   7895篇
  1988年   7745篇
  1987年   7540篇
  1986年   7255篇
  1985年   9385篇
  1984年   9838篇
  1983年   8157篇
  1982年   8642篇
  1981年   8058篇
  1980年   7655篇
  1979年   8255篇
  1978年   8676篇
  1977年   8515篇
  1976年   8465篇
  1975年   8052篇
  1974年   7914篇
  1973年   8331篇
  1972年   5937篇
排序方式: 共有10000条查询结果,搜索用时 531 毫秒
121.
122.
Journal of Sol-Gel Science and Technology - In this paper, a simple method is presented for making a conductive and hydrophobic cotton fabric using a multi-walled carbon nanotube (MWCNT). The...  相似文献   
123.
124.
We summarize the results of our recent work on Bäcklund transformations (BTs), particularly focusing on the relation between BTs and infinitesimal symmetries. We present a BT for an associated Degasperis–Procesi (aDP) equation and its superposition principle and investigate the solutions generated by applying this BT. Following our general methodology, we use the superposition principle of the BT to generate the infinitesimal symmetries of the aDP equation.  相似文献   
125.
Nanocomposites based on poly-N-vinylcaprolactam (PVC), characterized by different drying temperatures of aqueous PVC solution at 25°С (PVC25) and 40°С (PVC40), with titanium(IV) oxide nanoparticles (TONs) (η-phase (TP: TiO2 – x · mH2O) with a superstructure to the anatase structure and ordered solid solution with partial replacement of oxygen atoms in the η-phase with peroxo group O 2 2– (PP: TiO x (O2)2 – x · nH2O)) have been obtained for the first time and characterized by X-ray diffraction and IR spectroscopy. It is found that a common feature of TP/PVC and PP/PVC obtained by dry mixing and grinding is the decrease in the number of water molecules for TP and PP in the interlayer space of the structure and their attachment to the PVC amide groups; the differences are related to the specificity of PVC behavior in these systems: mechanodestruction of PVC in PP/PVC40 and different numbers of water molecules in PVC25 and PVC40.  相似文献   
126.
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   
127.
128.
The reaction mechanism for the hydrolysis of trimethyl phosphate and of the obtained phosphodiester by the di‐CoII derivative of organophosphate degrading enzyme from Agrobacterium radiobacter P230(OpdA), have been investigated at density functional level of theory in the framework of the cluster model approach. Both mechanisms proceed by a multistep sequence and each catalytic cycle begins with the nucleophilic attack by a metal‐bound hydroxide on the phosphorus atom of the substrate, leading to the cleavage of the phosphate‐ester bond. Four exchange‐correlation functionals were used to derive the potential energy profiles in protein environments. Although the enzyme is confirmed to work better as triesterase, as revealed by the barrier heights in the rate‐limiting steps of the catalytic processes, its promiscuous ability to hydrolyze also the product of the reaction has been confirmed. The important role played by water molecules and some residues in the outer coordination sphere has been elucidated, while the binuclear CoII center accomplishes both structural and catalytic functions. To correctly describe the electronic configuration of the d shell of the metal ions, high‐ and low‐spin arrangement jointly with the occurrence of antiferromagnetic coupling, have been herein considered.  相似文献   
129.
130.
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