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   833535篇
  免费   8730篇
  国内免费   2242篇
化学   421829篇
晶体学   11770篇
力学   41888篇
综合类   26篇
数学   118749篇
物理学   250245篇
  2021年   7023篇
  2020年   7666篇
  2019年   8579篇
  2018年   14523篇
  2017年   14694篇
  2016年   17962篇
  2015年   9866篇
  2014年   15353篇
  2013年   35858篇
  2012年   29429篇
  2011年   38564篇
  2010年   27321篇
  2009年   27167篇
  2008年   35683篇
  2007年   36979篇
  2006年   28738篇
  2005年   28041篇
  2004年   24986篇
  2003年   22729篇
  2002年   21670篇
  2001年   22747篇
  2000年   17690篇
  1999年   13700篇
  1998年   11599篇
  1997年   11295篇
  1996年   10918篇
  1995年   9849篇
  1994年   9761篇
  1993年   9421篇
  1992年   10183篇
  1991年   10545篇
  1990年   10197篇
  1989年   9875篇
  1988年   9751篇
  1987年   9581篇
  1986年   9109篇
  1985年   11766篇
  1984年   12174篇
  1983年   9994篇
  1982年   10376篇
  1981年   9961篇
  1980年   9371篇
  1979年   10076篇
  1978年   10382篇
  1977年   10198篇
  1976年   10112篇
  1975年   9592篇
  1974年   9457篇
  1973年   9665篇
  1972年   6949篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
131.
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   
132.
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   
133.
134.
135.
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   
136.
137.
138.
139.
140.
A generic strategy based on the use of CdSe/ZnS Quantum Dots (QDs) as elemental labels for protein quantification, using immunoassays with elemental mass spectrometry (ICP-MS), detection is presented. In this strategy, streptavidin modified QDs (QDs-SA) are bioconjugated to a biotinylated secondary antibody (b-Ab2). After a multi-technique characterization of the synthesized generic platform (QDs-SA-b-Ab2) it was applied to the sequential quantification of five proteins (transferrin, complement C3, apolipoprotein A1, transthyretin and apolipoprotein A4) at different concentration levels in human serum samples. It is shown how this generic strategy does only require the appropriate unlabeled primary antibody for each protein to be detected. Therefore, it introduces a way out to the need for the cumbersome and specific bioconjugation of the QDs to the corresponding specific recognition antibody for every target analyte (protein). Results obtained were validated with those obtained using UV–vis spectrophotometry and commercial ELISA Kits.  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