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   239540篇
  免费   6285篇
  国内免费   3578篇
化学   136636篇
晶体学   3444篇
力学   10061篇
综合类   247篇
数学   26387篇
物理学   72628篇
  2021年   2124篇
  2020年   2542篇
  2019年   2653篇
  2018年   3091篇
  2017年   3113篇
  2016年   4556篇
  2015年   3318篇
  2014年   4568篇
  2013年   10197篇
  2012年   9418篇
  2011年   11206篇
  2010年   7863篇
  2009年   7521篇
  2008年   10026篇
  2007年   10106篇
  2006年   9458篇
  2005年   8659篇
  2004年   7563篇
  2003年   6653篇
  2002年   6519篇
  2001年   7096篇
  2000年   5449篇
  1999年   4122篇
  1998年   3378篇
  1997年   3363篇
  1996年   3317篇
  1995年   2908篇
  1994年   3014篇
  1993年   2824篇
  1992年   3019篇
  1991年   3088篇
  1990年   2873篇
  1989年   2724篇
  1988年   2639篇
  1987年   2582篇
  1986年   2580篇
  1985年   3343篇
  1984年   3401篇
  1983年   2827篇
  1982年   3071篇
  1981年   2828篇
  1980年   2619篇
  1979年   2788篇
  1978年   2996篇
  1977年   3032篇
  1976年   3059篇
  1975年   2795篇
  1974年   2906篇
  1973年   2952篇
  1972年   2301篇
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
1.
Kinetics and Catalysis - The catalytic properties of a nickel phosphide catalyst supported on silica gel in the reductive amination of carbonyl compounds were studied in a flow reactor using...  相似文献   
2.
Yang  T. L.  Kao  C. L.  Kuo  C. E.  Yeh  H. C.  Li  W. J.  Li  H. T.  Chen  C. Y. 《Chemistry of Natural Compounds》2022,58(5):825-827
Chemistry of Natural Compounds - A novel bibenzyl derivative, hydrangchinenin (1), was isolated from the stems of Hydrangea chinensis Maxim. (Hydrangeaceae). Its structure was determined on the...  相似文献   
3.
The coordination chemistry of f-block elements (lanthanide and actinide) in molten salts has become a resounding topic in view of its great importance to the research and development (R&D) of molten salt reactors and pyroprocessing. In this Review article, a general overview of the coordination chemistry of f-block elements in molten salts is provided including past achievements and recent advances. Particular emphases are placed on the oxidation state, speciation, and solution structure of f-block metal ions in molten salts, as well as their relationships with the salt composition. Furthermore, this review briefly discusses the spectroscopic and theoretical methods that complement each other in revealing the coordination properties.  相似文献   
4.
At present, the reactivity of cyclic alkanes is estimated by comparison with acyclic hydrocarbons. Due to the difference in the structure of cycloalkanes and acycloalkanes, the thermodynamic data obtained by analogy are not applicable. In this study, a molecular beam sampling vacuum ultraviolet photoionization time-of-flight mass spectrometer (MB-VUV-PI-TOFMS) was applied to study the low-temperature oxidation of cyclopentane (CPT) at a total pressure range from 1–3 atm and low-temperature range between 500 and 800 K. Low-temperature reaction products including cyclic olefins, cyclic ethers, and highly oxygenated intermediates (e. g., ketohydroperoxide KHP, keto-dihydroperoxide KDHP, olefinic hydroperoxides OHP and ketone structure products) were observed. Further investigation of the oxidation of CPT – electronic structure calculations – were carried out at the UCCSD(T)-F12a/aug-cc-pVDZ//B3LYP/6-31+ G(d,p) level to explore the reactivity of O2 molecules adding sequentially to cyclopentyl radicals. Experimental and theoretical observations showed that the dominant product channel in the reaction of CPT radicals with O2 is HO2 elimination yielding cyclopentene. The pathways of second and third O2 addition – the dissociation of hydroperoxide – were further confirmed. The results of this study will develop the low-temperature oxidation mechanism of CPT, which can be used for future research on accurately simulating the combustion process of CPT.  相似文献   
5.
Tian  Xiu-Zhi  Yang  Rui  Ma  Jia-Jia  Ni  Yong-Hao  Deng  Hai-Bo  Dai  Lei  Tan  Jiao-Jun  Zhang  Mei-Yun  Jiang  Xue 《高分子科学》2022,40(7):789-798
Chinese Journal of Polymer Science - Antistatic and strength properties are of vital importance for polyurethane rubber used in moving parts of many industrial instruments. Herein, polyurethane was...  相似文献   
6.
Xu  Feixiang  Luo  Jiangchen  Jiang  Liqun  Zhao  Zengli 《Cellulose (London, England)》2022,29(3):1463-1472
Cellulose - In this research, the production of levoglucosan (LG) and levoglucosenone (LGO) was improved from acid-impregnated cellulose via fast pyrolysis. Thermogravimetric and kinetic analysis...  相似文献   
7.
Russian Journal of General Chemistry - The review article traces the main trends of the synthetic approach to the solution of the problem of overcoming the resistance of pathogenic bacterial...  相似文献   
8.
Physics of Atomic Nuclei - In this paper, the analysis of the relation between the multiplication factor of neutrons of the multiplying system measured in critical experiments and the system...  相似文献   
9.
Set-Valued and Variational Analysis - In a Hilbert framework ℌ, we study the convergence properties of a Newton-like inertial dynamical system governed by a general maximally monotone...  相似文献   
10.
Crystallography Reports - The crystal and molecular structures of Cl–C6H4–O–C16H33 (I) have been studied, and its differential scanning calorimetry (DSC) study is performed....  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