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   564048篇
  免费   13962篇
  国内免费   6979篇
化学   297545篇
晶体学   7746篇
力学   26926篇
综合类   341篇
数学   77002篇
物理学   175429篇
  2021年   4382篇
  2020年   5078篇
  2019年   4982篇
  2018年   13223篇
  2017年   13973篇
  2016年   12058篇
  2015年   7753篇
  2014年   9358篇
  2013年   22706篇
  2012年   22759篇
  2011年   33501篇
  2010年   21193篇
  2009年   20950篇
  2008年   29087篇
  2007年   32005篇
  2006年   18680篇
  2005年   23292篇
  2004年   17936篇
  2003年   15963篇
  2002年   13911篇
  2001年   13912篇
  2000年   11011篇
  1999年   8865篇
  1998年   7321篇
  1997年   7095篇
  1996年   7107篇
  1995年   6498篇
  1994年   6096篇
  1993年   5739篇
  1992年   6305篇
  1991年   6183篇
  1990年   5804篇
  1989年   5527篇
  1988年   5717篇
  1987年   5289篇
  1986年   5123篇
  1985年   7085篇
  1984年   7210篇
  1983年   5923篇
  1982年   6340篇
  1981年   6319篇
  1980年   6035篇
  1979年   6310篇
  1978年   6410篇
  1977年   6259篇
  1976年   6250篇
  1975年   6095篇
  1974年   5994篇
  1973年   6178篇
  1972年   3656篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
31.
Jin  Zhuochen  Cao  Nan  Shi  Yang  Wu  Wenchao  Wu  Yingcai 《显形杂志》2021,24(2):349-364
Journal of Visualization - The increasing availability of spatiotemporal data provides unprecedented opportunities for understanding the structure of an urban area in terms of people’s...  相似文献   
32.
Zhan  Yang  Dang  Chuangyin 《Mathematical Programming》2021,190(1-2):585-613
Mathematical Programming - In the general equilibrium with incomplete asset markets (GEI) model, the excess demand functions are typically not continuous at the prices for which the assets have...  相似文献   
33.
Ukrainian Mathematical Journal - We establish new criteria of compatibility for a linear system of equations (equivalent to the Kronecker–Capelli theorem) or inequalities (equivalent to the...  相似文献   
34.
International Journal of Theoretical Physics - The Majorana representation, which provides an intuitive way to represent the quantum state by stars on the Bloch sphere, has drawn considerable...  相似文献   
35.
Chen  R. J.  Chen  W.  Kong  F. L. 《Analysis Mathematica》2022,48(1):19-28

Restricted testing conditions were considered recently. For the maximal operator, Hytönen, Li and Sawyer [8] first obtained parental testing condition. Later, they [9] showed that it suffices to restrict testing to doubling cubes. Chen and Lacey [3] gave a similar restricted testing condition. In our paper, we discuss a version of the latter in the multilinear setting.

  相似文献   
36.
Acridone as a new kind of visible light photocatalyst has been developed to catalyze metal free atom transfer radical polymerization (ATRP). The photocatalyst possess low excited state potential as can undergo an oxidative quenching pathway to initiate ATRP of vinyl monomers. Kinetic study and light on/off reaction demonstrate the “living”/controlled nature of the polymerization by light. Block copolymers can be achieved by using PMMA as macroinitiator to reinitiate polymerization of other vinyl monomers, which shows highly preserved Br chain-end functionality in the synthesized polymers. Moreover, the polymerization can be conducted under air atmosphere as most photocatalysts need anaerobic condition, which may give inspiration of further application of this kind of photocatalyst.  相似文献   
37.
在砂土地层中,串囊式充气锚杆的研究还比较少,其承载特性及受力机理尚不明确。本文基于莫尔-库仑模型和Vesic圆孔扩张理论法,分别对圆柱体、球体、组合体、椭球体假设下的串囊式充气锚杆的扩大段进行计算分析。并将计算结果与试验得到的实测值进行对比。结果表明:四种形状假设中椭球体的形状假设理论值与实测值的误差最小,仅为8.35%。通过拟合试验数据,并引入与端阻力和侧摩阻力有关的两个系数对承载力公式进行修正,得到了抗拔承载力的经验公式。  相似文献   
38.
A facile biosynthesis route was followed to prepare zinc oxide nanoparticles (ZnO NPs) using Euphorbia milii (E. milii) leaf constituents. The SEM images exhibited presence of spherical ZnO NPs and the corresponding TEM images disclosed monodisperse nature of the ZnO NPs with diameter ranges between 12 and 20 nm. The Brunauer–Emmett–Teller (BET) analysis revealed that the ZnO NPs have specific surface area of 20.46 m2/g with pore diameter of 2 nm–10 nm and pore volume of 0.908 cm3/g. The EDAX spectrum exemplified the existence of Zn and O elements and non-appearance of impurities that confirmed pristine nature of the ZnO NPs. The XRD pattern indicated crystalline peaks corresponding to hexagonal wurtzite structured ZnO with an average crystallite size of 16.11 nm. The FTIR spectrum displayed strong absorption bands at 512 and 534 cm?1 related to ZnO. The photocatalytic action of ZnO NPs exhibited noteworthy degradation of methylene blue dye under natural sunlight illumination. The maximum degradation efficiency achieved was 98.17% at an illumination period of 50 min. The reusability study proved considerable photostability of the ZnO NPs during photocatalytic experiments. These findings suggest that the E. milii leaf constituents can be utilized as suitable biological source to synthesis ZnO NPs for photocatalytic applications.  相似文献   
39.
40.
Incorporating nanoscale Si into a carbon matrix with high dispersity is desirable for the preparation of lithium-ion batteries (LIBs) but remains challenging. A space-confined catalytic strategy is proposed for direct superassembly of Si nanodots within a carbon (Si NDs⊂C) framework by copyrolysis of triphenyltin hydride (TPT) and diphenylsilane (DPS), where Sn atomic clusters created from TPT pyrolysis serve as the catalyst for DPS pyrolysis and Si catalytic growth. The use of Sn atomic cluster catalysts alters the reaction pathway to avoid SiC generation and enable formation of Si NDs with reduced dimensions. A typical Si NDs⊂C framework demonstrates a remarkable comprehensive performance comparable to other Si-based high-performance half LIBs, and higher energy densities compared to commercial full LIBs, as a consequence of the high dispersity of Si NDs with low lithiation stress. Supported by mechanic simulations, this study paves the way for construction of Si/C composites suitable for applications in future energy technologies.  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