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   298470篇
  免费   57544篇
  国内免费   51624篇
化学   144711篇
晶体学   4347篇
力学   13641篇
综合类   2763篇
数学   29011篇
物理学   105802篇
无线电   107363篇
  2024年   1234篇
  2023年   5279篇
  2022年   7880篇
  2021年   8951篇
  2020年   8913篇
  2019年   9023篇
  2018年   8602篇
  2017年   10170篇
  2016年   11370篇
  2015年   13795篇
  2014年   15829篇
  2013年   20334篇
  2012年   23249篇
  2011年   24555篇
  2010年   24974篇
  2009年   25070篇
  2008年   19872篇
  2007年   18353篇
  2006年   17443篇
  2005年   15314篇
  2004年   12995篇
  2003年   10111篇
  2002年   9318篇
  2001年   8955篇
  2000年   8132篇
  1999年   6714篇
  1998年   5181篇
  1997年   4552篇
  1996年   4832篇
  1995年   4899篇
  1994年   4705篇
  1993年   4547篇
  1992年   3981篇
  1991年   3395篇
  1990年   2823篇
  1989年   2728篇
  1988年   2451篇
  1987年   1627篇
  1986年   1665篇
  1985年   1214篇
  1984年   1266篇
  1983年   629篇
  1982年   1101篇
  1981年   873篇
  1980年   881篇
  1979年   606篇
  1978年   581篇
  1977年   664篇
  1976年   1076篇
  1972年   548篇
排序方式: 共有10000条查询结果,搜索用时 797 毫秒
121.
Journal of Thermal Analysis and Calorimetry - Artificial neural network/kriging interpolation method optimization method which is evaluated concerned the hybrid nanofluid composed of iron oxide...  相似文献   
122.
Three‐dimensional (3D) nanometal films serving as current collectors have attracted much interest recently owing to their promising application in high‐performance supercapacitors. In the process of the electrochemical reaction, the 3D structure can provide a short diffusion path for fast ion transport, and the highly conductive nanometal may serve as a backbone for facile electron transfer. In this work, a novel polypyrrole (PPy) shell@3D‐Ni‐core composite is developed to enhance the electrochemical performance of conventional PPy. With the introduction of a Ni metal core, the as‐prepared material exhibits a high specific capacitance (726 F g?1 at a charge/discharge rate of 1 A g?1), good rate capability (a decay of 33 % in Csp with charge/discharge rates increasing from 1 to 20 A g?1), and high cycle stability (only a small decrease of 4.2 % in Csp after 1000 cycles at a scan rate of 100 mV s?1). Furthermore, an aqueous symmetric supercapacitor device is fabricated by using the as‐prepared composite as electrodes; the device demonstrates a high energy density (≈21.2 Wh kg?1) and superior long‐term cycle ability (only 4.4 % and 18.6 % loss in Csp after 2000 and 5000 cycles, respectively).  相似文献   
123.
A new spectral problem is proposed, and nonlinear differential equations of the corresponding hierarchy are obtained. With the help of the nonlinearization appr...  相似文献   
124.
For the orthosymplectic Lie superalgebra ◂⋅▸OSP(2,2), we choose a set of basis matrices. A linear combination of those basis matrices presents a spatial spectral matrix. The compatible condition of the spatial part and the corresponding temporal parts of the spectral problem leads to a generalized super AKNS (GSAKNS) hierarchy. By making use of the supertrace identity, the obtained GSAKNS hierarchy can be written as the super bi-Hamiltonian structures.  相似文献   
125.
Photoactivated chemotherapy (PACT) has appealing merits over traditional chemotherapy as well as photodynamic therapy (PDT) by virtue of its spatial and temporal control on drug activity and oxygen-independent mechanisms of action. However, the short photoactivation wavelengths, e.g., visible light–activated Ru(II)-based PACT agents, limit the clinical application severely. In this work, a facile construction of supramolecular nanoparticles from a poly(ethylene glycol) (PEG)-modified [Ru(dip)2(py-SO3)]+ (abbreviated as Ru-PEG, dip = 4,7-diphenyl-1,10-phenanthroline, py-SO3 = pyridine-2-sulfonate) and 1,3-phenylenebis(pyren-1-ylmethanone) (BP) is shown. While Ru-PEG may undergo photoinduced ligand dissociation and release anticancer species of [Ru(dip)2(H2O)2]2+, BP has extremely large two-photon absorption cross sections (δ2) in the NIR region and intense fluorescence over the wavelengths where Ru-PEG has strong absorption. Thus, two-photon excitation of BP followed by an efficient Förster resonance energy transfer (FRET) from BP to Ru-PEG may lead to a potent inactivation against cisplatin-resistant cancer cells and 3D multicellular tumor spheroids (MCTSs). The residue fluorescence of BP also allows the cellular uptake of the particles to be visualized. This work provides a universal and convenient strategy to realize theranostic PACT in the ideal phototherapeutic window of 650–900 nm.  相似文献   
126.
通过热重法研究了松木与聚氯乙烯复合材料的催化热解特性,结果表明聚氯乙烯脱氯阶段与松木的纤维素、半纤维素热分解阶段温度区间重合,二者共热解时存在协同效应,并且HCl的释放对纤维素的脱水反应能够产生催化作用,HCl释放也对木质素的热分解及碳化反应有着明显的催化作用,导致二者共热解制备的碳化物产率提高,约为29.61%。并且利用元素分析仪、扫描电镜和能谱仪对成碳材料进行表征分析,结果表明成碳材料表面粗糙呈现多孔结构,其碳元素含量较高达到74.67%。  相似文献   
127.
128.
A new approach has been developed to improve SO2 sorption by cyano‐containing ionic liquids (ILs) through tuning the basicity of ILs and cyano–sulfur interaction. Several kinds of cyano‐containing ILs with different basicity were designed, prepared, and used for SO2 capture. The interaction between these cyano‐containing ILs and SO2 was investigated by FTIR and NMR methods. Spectroscopic investigations and quantum chemical calculations showed that dramatic effects on SO2 capacity originate from the basicity of the ILs and enhanced cyano–sulfur interaction. Furthermore, the captured SO2 was easy to release by heating or bubbling N2 through the ILs. This efficient and reversible process, achieved by tuning the basicity of ILs, is an excellent alternative to current technologies for SO2 capture.  相似文献   
129.
130.
A series of tetraimidazolium salts with different anions was prepared and applied in the isomerization of β-pinene oxide. After examining the activity of different catalysts, a remarkable enhancement of the selectivity of perillyl alcohol (47 %) was obtained over [PEimi][HNO3]4 under mild reaction conditions and using DMSO as the solvent. Furthermore, noncovalent interactions between solvent molecules and the catalyst were found by FT-IR spectroscopy and confirmed by computational chemistry. The homogeneous catalyst showed excellent stability and was reused up to six times without significant loss.  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