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   266091篇
  免费   893篇
  国内免费   286篇
化学   117082篇
晶体学   3516篇
力学   16039篇
综合类   8篇
数学   44056篇
物理学   86569篇
  2019年   2323篇
  2018年   10887篇
  2017年   11638篇
  2016年   7768篇
  2015年   2571篇
  2014年   3748篇
  2013年   7212篇
  2012年   9408篇
  2011年   17692篇
  2010年   11700篇
  2009年   12046篇
  2008年   15739篇
  2007年   18958篇
  2006年   5852篇
  2005年   10456篇
  2004年   7605篇
  2003年   7482篇
  2002年   5878篇
  2001年   5181篇
  2000年   4031篇
  1999年   2897篇
  1998年   2668篇
  1997年   2497篇
  1996年   2456篇
  1995年   2172篇
  1994年   2122篇
  1993年   2144篇
  1992年   2167篇
  1991年   2473篇
  1990年   2406篇
  1989年   2495篇
  1988年   2382篇
  1987年   2404篇
  1986年   2231篇
  1985年   2734篇
  1984年   2763篇
  1983年   2406篇
  1982年   2455篇
  1981年   2359篇
  1980年   2162篇
  1979年   2501篇
  1978年   2663篇
  1977年   2673篇
  1976年   2797篇
  1975年   2592篇
  1974年   2518篇
  1973年   2739篇
  1972年   2194篇
  1971年   2001篇
  1970年   1885篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
41.
42.
43.
44.
45.
46.
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   
47.
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   
48.
49.
The aim of this work was to determine the parameters that have decisive roles in microwave-assisted reactions and to develop a model, using computational chemistry, to predict a priori the type of reactions that can be improved under microwaves. For this purpose, a computational study was carried out on a variety of reactions, which have been reported to be improved under microwave irradiation. This comprises six types of reactions. The outcomes obtained in this study indicate that the most influential parameters are activation energy, enthalpy, and the polarity of all the species that participate. In addition to this, in most cases, slower reacting systems observe a much greater improvement under microwave irradiation. Furthermore, for these reactions, the presence of a polar component in the reaction (solvent, reagent, susceptor, etc.) is necessary for strong coupling with the electromagnetic radiation. We also quantified that an activation energy of 20–30 kcal mol−1 and a polarity (μ) between 7–20 D of the species involved in the process is required to obtain significant improvements under microwave irradiation.  相似文献   
50.
This study was aimed at the development of a conductometric biosensor based on acetylcholinesterase considering the feasibility of its application for the inhibitory analysis of various toxicants. In this paper, the optimum conditions for enzyme immobilization on the transducer surface are selected as well as the optimum concentration of substrate for inhibitory analysis. Sensitivity of the developed biosensor to different classes of toxic compounds (organophosphorus pesticides, heavy metal ions, surfactants, aflatoxin, glycoalkaloids) was tested. It is shown that the developed biosensor can be successfully used for the analysis of pesticides and mycotoxins, as well as for determination of total toxicity of the samples. A new method of biosensor analysis of toxic substances of different classes in complex multicomponent aqueous samples is proposed.  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