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   317074篇
  免费   1401篇
  国内免费   387篇
化学   143886篇
晶体学   4539篇
力学   18377篇
综合类   7篇
数学   49759篇
物理学   102294篇
  2020年   2486篇
  2019年   3012篇
  2018年   11260篇
  2017年   11946篇
  2016年   8848篇
  2015年   3208篇
  2014年   4863篇
  2013年   9547篇
  2012年   11203篇
  2011年   19262篇
  2010年   13026篇
  2009年   13409篇
  2008年   17228篇
  2007年   20167篇
  2006年   7873篇
  2005年   11721篇
  2004年   8997篇
  2003年   8819篇
  2002年   7395篇
  2001年   6849篇
  2000年   5273篇
  1999年   3853篇
  1998年   3523篇
  1997年   3279篇
  1996年   3143篇
  1995年   2802篇
  1994年   2718篇
  1993年   2765篇
  1992年   2851篇
  1991年   3178篇
  1990年   3066篇
  1989年   3156篇
  1988年   2967篇
  1987年   2936篇
  1986年   2765篇
  1985年   3420篇
  1984年   3526篇
  1983年   3033篇
  1982年   3108篇
  1981年   2963篇
  1980年   2731篇
  1979年   3091篇
  1978年   3356篇
  1977年   3389篇
  1976年   3420篇
  1975年   3188篇
  1974年   3148篇
  1973年   3326篇
  1972年   2626篇
  1971年   2398篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
Lipina  T. I. 《Mathematical Notes》2020,108(5-6):721-726
Mathematical Notes - An algorithm is presented which determines in a finite number of steps whether an initial finite binary automaton is spherically transitive. Since the class of deterministic...  相似文献   
162.
163.
A zinc coordination polymer derived from pyridine-2,6-dicarboxylate (PDC), {[Zn2(PDC)2]}n, was successfully prepared via conventional, sonication and microwave-irradiation methods. The composition and characteristics of the obtained coordination polymers (CPs) were investigated by elemental analysis, TGA/DTA, X-ray diffraction and spectroscopic techniques. The so obtained CPs were heat-treated in the air at 600 °C for 2 h to produce ZnO of nanosized particles (NPs). It is of interest to note that the synthesis approach of the precursor greatly affects both the nanoparticle size and the structure of the resulting ZnO NPs. Moreover, the smallest particle size was associated with the sample derived from the ultrasonically prepared precursor. TEM analysis revealed that all samples have sphere-like morphologies. Structural analysis of the prepared ZnO samples was conducted and compared using Rietveld analysis of their PXRD patterns. Optical band gap calculations based on analysis of the UV–vis spectra of ZnO samples using Tauc's power law were achieved. The highest band gap of 3.63 eV was observed for ZnO sample obtained from the ultrasonically prepared precursor. Furthermore, the photocatalytic activity of ZnO NPs for the removal of Eosin Y color was monitored. The highest removal efficiency was recorded for ZnO originated from the ultrasonically synthesized precursor. Enhancement of removal efficiency that reached 98% was attained in only a period of 8 min. Its recycling test showed that it can be reused without structural changes over four cycling experiments.  相似文献   
164.
165.
166.
Enhancement of spontaneous emission in a resonant Bragg quantum well (QW) structure with 60 periods of triple InAs monolayers embedded in a GaAs matrix is studied experimentally and theoretically. From measurements of the time‐resolved photoluminescence, besides the QW exciton at 1.47 eV, a specific super‐radiant (SR) emission demonstrating nonlinear properties is found. The SR mode shows a near‐quadratic dependence of intensity on excitation power, while its energy position follows the Bragg condition. It is revealed that the SR mode shows a peculiar non‐monotonic dependence of intensity on direction, with a maximum observed at approximately 40°. The enhancement in the SR emission at a specific direction is correlated well with suggested theoretical consideration of the modal Purcell factor for periodic quantum well structures.  相似文献   
167.
Radiophysics and Quantum Electronics - We present the results of comparing the total electron content measurements based on GLONASS satellite signals and the EISCAT UHF incoherent scatter radar...  相似文献   
168.
Radiophysics and Quantum Electronics - We consider whether it is possible in principle to retrieve the key parameters of the mixed layer in the upper ocean (its thickness, bulk eddy viscosity and...  相似文献   
169.
Monatshefte für Chemie - Chemical Monthly - A comparative analysis is performed on the stability constants $${\upbeta }_{1yn}$$ and intramolecular redox decomposition rate constants $$k_{n\; =...  相似文献   
170.
Siberian Mathematical Journal - Under study are the right-symmetric algebras over a field  $ F $ which possess a “unital” matrix subalgebra  $...  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