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   4046篇
  免费   128篇
  国内免费   19篇
化学   2651篇
晶体学   42篇
力学   110篇
数学   281篇
物理学   772篇
无线电   337篇
  2023年   36篇
  2022年   74篇
  2021年   86篇
  2020年   94篇
  2019年   93篇
  2018年   95篇
  2017年   91篇
  2016年   147篇
  2015年   118篇
  2014年   187篇
  2013年   309篇
  2012年   288篇
  2011年   317篇
  2010年   196篇
  2009年   164篇
  2008年   237篇
  2007年   230篇
  2006年   197篇
  2005年   194篇
  2004年   117篇
  2003年   103篇
  2002年   92篇
  2001年   45篇
  2000年   47篇
  1999年   42篇
  1998年   39篇
  1997年   26篇
  1996年   32篇
  1995年   27篇
  1994年   31篇
  1993年   21篇
  1992年   31篇
  1991年   27篇
  1990年   17篇
  1989年   20篇
  1988年   17篇
  1987年   27篇
  1985年   29篇
  1984年   27篇
  1983年   16篇
  1982年   26篇
  1981年   20篇
  1980年   23篇
  1979年   14篇
  1978年   18篇
  1977年   8篇
  1976年   13篇
  1975年   12篇
  1974年   8篇
  1973年   8篇
排序方式: 共有4193条查询结果,搜索用时 0 毫秒
1.
Pal  Abhijit 《Geometriae Dedicata》2021,213(1):121-135
Geometriae Dedicata - Given a finite graph of relatively hyperbolic groups with its fundamental group relatively hyperbolic and edge groups quasi-isometrically embedded and relatively quasiconvex...  相似文献   
2.
Structural Chemistry - The hydrogen bond interactions between methyl-imidazolium cation (MIM+) and fatty acid anions (CmHnCOO–, where m?=?1–6; n-3–13) of ionic liquids...  相似文献   
3.
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   
4.
5.
Wireless Personal Communications - The orthogonal frequency division multiplexing (OFDM) is the most encouraging multi-carrier modulation system chosen for the high data rates but the objective is...  相似文献   
6.
7.
Palladium nanoparticle‐incorporated metal–organic framework MIL‐101 (Pd/MIL‐101) was successfully synthesized and characterized using X‐ray diffraction, nitrogen physisorption, X‐ray photoelectron, UV–visible and infrared spectroscopies, and transmission electron microscopy. The characterization techniques confirmed high porosity and high surface area of MIL‐101 and high stability of nano‐size palladium particles. Pd/MIL‐101 nanocomposite was investigated for the Sonogashira cross‐coupling reaction of aryl and heteroaryl bromides with various alkynes under copper‐free conditions. The reusability of the catalyst was tested for up to four cycles without any significant loss in catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
8.
The stereoselective intramolecular cyclizations of bis(cinnamyl)tosylamides and dimethyl bis(cinnamyl)malonates mediated by cerium(IV) ammonium nitrate leading to the synthesis of 3,4-trans-disubstituted pyrrolidines and cyclopentanes are described.  相似文献   
9.
Reduction of 2-aryl-oxazolines with NiCl2/NaBH4 followed by hydrolysis gives the corresponding aldehydes in good yields.  相似文献   
10.
We characterize all equivariant odd spectral triples for the quantum SU(2) group acting on its L 2-space and having a nontrivial Chern character. It is shown that the dimension of an equivariant spectral triple is at least three, and given any element of the K-homology group of SUq(2), there is an equivariant odd spectral triple of dimension 3 inducing that element. The method employed to get equivariant spectral triples in the quantum case is then used for classical SU(2), and we prove that for p < 4, there does not exist any equivariant spectral triple with nontrivial K-homology class and dimension p acting on the L 2-space.The first author would like to acknowledge support from the National Board of Higher Mathematics, India.  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