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   594933篇
  免费   6922篇
  国内免费   1528篇
化学   310290篇
晶体学   7981篇
力学   27213篇
综合类   23篇
数学   81729篇
物理学   176147篇
  2021年   6041篇
  2020年   6474篇
  2019年   7279篇
  2018年   10048篇
  2017年   9956篇
  2016年   13948篇
  2015年   8121篇
  2014年   12408篇
  2013年   27670篇
  2012年   22340篇
  2011年   25968篇
  2010年   19138篇
  2009年   18713篇
  2008年   24290篇
  2007年   24019篇
  2006年   21777篇
  2005年   19548篇
  2004年   17922篇
  2003年   16029篇
  2002年   15597篇
  2001年   15888篇
  2000年   12527篇
  1999年   9636篇
  1998年   8274篇
  1997年   8104篇
  1996年   7777篇
  1995年   6853篇
  1994年   6944篇
  1993年   6687篇
  1992年   7033篇
  1991年   7369篇
  1990年   7146篇
  1989年   6944篇
  1988年   6743篇
  1987年   6544篇
  1986年   6274篇
  1985年   7957篇
  1984年   8279篇
  1983年   6924篇
  1982年   7235篇
  1981年   6729篇
  1980年   6371篇
  1979年   6850篇
  1978年   7087篇
  1977年   6945篇
  1976年   6923篇
  1975年   6594篇
  1974年   6398篇
  1973年   6719篇
  1972年   4877篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
Shinkorenko  A. S. 《JETP Letters》2022,116(10):759-759
JETP Letters - An Erratum to this paper has been published: https://doi.org/10.1134/S0021364022400028  相似文献   
172.
Molecular Diversity - Hypertension is a medical condition that affects millions of people worldwide. Despite the high efficacy of the current antihypertensive drugs, they are associated with...  相似文献   
173.
NOx mitigation is a central focus of combustion technologies with increasingly stringent emission regulations. NOx can also enhance the autoignition of hydrocarbon fuels and can promote soot oxidation. The reaction between allyl radical (C3H5) and NOx plays an important role in the oxidation kinetics of propene. In this work, we measured the absolute rate coefficients for the redox reaction between C3H5 and NOx over the temperature range of 1000–1252 K and pressure range of 1.5–5.0 bar using a shock tube and UV laser absorption technique. We produced C3H5 by shock heating of C3H5I behind reflected shock waves. Using a Ti:Sapphire laser system with frequency quadrupling, we monitored the kinetics of C3H5 at 220 nm. Unlike low-temperature chemistry, the two target reactions, C3H5 + NO → products (R1) and C3H5 + NO2 → products (R2), exhibited a strong positive temperature dependence for this radical-radical type reaction. However, these reactions did not show any pressure dependence over the pressure range of 1.5–5.0 bar, indicating that the measured rate coefficients are close to the high-pressure limit. The measured values of the rate coefficients resulted in the following Arrhenius expressions (in unit of cm3/molecule/s):k1(C3H5+NO)=1.49×10?10exp(?6083.6KT)(1017?1252K)k2(C3H5+NO2)=1.71×10?10exp(?3675.7KT)(1062?1250K)To our knowledge, these are the first high-temperature measurements of allyl + NOx reactions. The reported data will be highly useful in understanding the interaction of NOx with resonantly stabilized radicals as well as the mutual sensitization effect of NOx on hydrocarbon fuels.  相似文献   
174.
Algebras and Representation Theory - We introduce and study the category of twisted modules over a triangular differential graded bocs. We show that in this category idempotents split, that it...  相似文献   
175.
Journal of Solid State Electrochemistry - Due to their distinctive chemical, electronic, and environmental properties, polypyrrole is used as a blocking barrier for methanol leakage in direct...  相似文献   
176.
Popel  S. I.  Golub’  A. P. 《JETP Letters》2022,115(10):596-601
JETP Letters - One of the main features of the dusty plasma compared to the conventional plasma (without charged dust particles is anomalous dissipation that is caused by the charging of dust...  相似文献   
177.
Russian Journal of General Chemistry - Highly dispersed CaO has been synthesized by heating an aqueous solution of calcium nitrate and D-glucose up to 800°C. Calcium oxide is formed with an...  相似文献   
178.
Differential Equations - We consider an initial–boundary value problem for the heat equation in which the heat conduction coefficient and one of the functions occurring in the source depend...  相似文献   
179.
Russian Journal of Organic Chemistry - Methyl (Z)-3-[(2R,3R,4S,5S)-5-(2-methoxy-2-oxoethyl)-3,4-(isopropylidenedioxy)tetrahydrofuran-2-yl]-prop-2-enoate was synthesized, and its intramolecular...  相似文献   
180.
Tetrahydrotetrazoles are five‐membered‐ring heterocycles containing four contiguous saturated nitrogen atoms. Very few examples of such compounds have been reported in the literature. Our previous attempt at the synthesis of a member of this class of compound suggested that the N—N bonds may be more labile than expected. This finding raised the question as to whether the structures of any of the previously reported tetrahydrotetrazoles had been properly assigned. We have reproduced the synthesis of a reported tetrahydrotetrazole, namely 1,2‐di‐tert‐butyl 3‐phenyl‐1H,2H,3H,10bH‐[1,2,3,4]tetrazolo[5,1‐a]isoquinoline‐1,2‐dicarboxylate, C25H30N4O4, and have now confidently confirmed its structure via X‐ray crystallography. However, while sufficiently stable in the crystal phase, we discovered that it remains very labile in solution (having a half‐life of only 15 min at 20 °C in CDCl3). A tentative reaction pathway for its dissociation based on 1H NMR spectral evidence is provided.  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