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   579193篇
  免费   17908篇
  国内免费   8474篇
化学   305489篇
晶体学   8170篇
力学   28753篇
综合类   323篇
数学   78434篇
物理学   184406篇
  2022年   4260篇
  2021年   6263篇
  2020年   7171篇
  2019年   7301篇
  2018年   14756篇
  2017年   15099篇
  2016年   15270篇
  2015年   9439篇
  2014年   12538篇
  2013年   25363篇
  2012年   25248篇
  2011年   35010篇
  2010年   23396篇
  2009年   23093篇
  2008年   30255篇
  2007年   32256篇
  2006年   20000篇
  2005年   22776篇
  2004年   18500篇
  2003年   16425篇
  2002年   14544篇
  2001年   14947篇
  2000年   11626篇
  1999年   9462篇
  1998年   7915篇
  1997年   7630篇
  1996年   7538篇
  1995年   6608篇
  1994年   6391篇
  1993年   6037篇
  1992年   6563篇
  1991年   6577篇
  1990年   6223篇
  1989年   5922篇
  1988年   5904篇
  1987年   5733篇
  1986年   5414篇
  1985年   6844篇
  1984年   6944篇
  1983年   5487篇
  1982年   5555篇
  1981年   5520篇
  1980年   5115篇
  1979年   5484篇
  1978年   5629篇
  1977年   5457篇
  1976年   5424篇
  1975年   4991篇
  1974年   4954篇
  1973年   4998篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
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   
93.
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   
94.
95.
96.
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   
97.
98.
99.
100.
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