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   559113篇
  免费   5846篇
  国内免费   1425篇
化学   289191篇
晶体学   7852篇
力学   26525篇
综合类   20篇
数学   74078篇
物理学   168718篇
  2021年   5546篇
  2020年   5968篇
  2019年   6775篇
  2018年   9044篇
  2017年   9127篇
  2016年   12749篇
  2015年   7137篇
  2014年   11399篇
  2013年   25464篇
  2012年   20311篇
  2011年   23890篇
  2010年   17743篇
  2009年   17518篇
  2008年   22523篇
  2007年   22316篇
  2006年   20260篇
  2005年   18123篇
  2004年   16732篇
  2003年   14979篇
  2002年   14707篇
  2001年   15296篇
  2000年   11865篇
  1999年   9170篇
  1998年   7943篇
  1997年   7797篇
  1996年   7343篇
  1995年   6566篇
  1994年   6604篇
  1993年   6329篇
  1992年   6669篇
  1991年   7115篇
  1990年   6829篇
  1989年   6674篇
  1988年   6495篇
  1987年   6321篇
  1986年   6057篇
  1985年   7659篇
  1984年   8021篇
  1983年   6697篇
  1982年   7005篇
  1981年   6515篇
  1980年   6196篇
  1979年   6628篇
  1978年   6874篇
  1977年   6762篇
  1976年   6702篇
  1975年   6402篇
  1974年   6206篇
  1973年   6532篇
  1972年   4762篇
排序方式: 共有10000条查询结果,搜索用时 875 毫秒
191.
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   
192.
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   
193.
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   
194.
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   
195.
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   
196.
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   
197.
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   
198.
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   
199.
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   
200.
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