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   111138篇
  免费   19410篇
  国内免费   12025篇
化学   76404篇
晶体学   1363篇
力学   7306篇
综合类   731篇
数学   13065篇
物理学   43704篇
  2024年   114篇
  2023年   2229篇
  2022年   2441篇
  2021年   3654篇
  2020年   4583篇
  2019年   4438篇
  2018年   3783篇
  2017年   3578篇
  2016年   5495篇
  2015年   5235篇
  2014年   6426篇
  2013年   8383篇
  2012年   10174篇
  2011年   10706篇
  2010年   7220篇
  2009年   6933篇
  2008年   7361篇
  2007年   6705篇
  2006年   6161篇
  2005年   5135篇
  2004年   3834篇
  2003年   3008篇
  2002年   2729篇
  2001年   2176篇
  2000年   1853篇
  1999年   2124篇
  1998年   1927篇
  1997年   1751篇
  1996年   1885篇
  1995年   1552篇
  1994年   1504篇
  1993年   1202篇
  1992年   1101篇
  1991年   1016篇
  1990年   820篇
  1989年   589篇
  1988年   474篇
  1987年   389篇
  1986年   384篇
  1985年   330篇
  1984年   243篇
  1983年   157篇
  1982年   141篇
  1981年   108篇
  1980年   77篇
  1979年   46篇
  1978年   34篇
  1976年   37篇
  1975年   35篇
  1974年   46篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
72.
73.
The first-principles DFT calculations together with microkinetic analysis reveal the complex catalytic mechanism of low-content NO oxidation on CrO2(110) at room temperature. It quantitatively makes clear that CrO2(110) can exhibit considerable activity with the Mars-van-Krevelen mechanism preferred, and the nitrate species serves as the key poisoning species.  相似文献   
74.
Journal of Thermal Analysis and Calorimetry - The present task is to investigate the influence of iron on the mineral composition and microstructure of the phase Q (C20A13M3S3, in the text below...  相似文献   
75.
Journal of Thermal Analysis and Calorimetry - The fire behavior of one flame-retardant PVC cable used as building wire is investigated in this work. Bench scale tests were performed using a cone...  相似文献   
76.
77.
Monoester‐diterpenoid alkaloids are the main bioactive components of Sini decoction, which is a well‐known traditional Chinese medicine formula for the treatment of myocardial infarction (MI) and heart failure in China. In this work, an ultra‐high‐performance liquid chromatography–mass spectrometry combined with microdialysis method was successfully established and applied for investigating for the first time comparative plasma pharmacokinetics of three monoester‐diterpenoid alkaloids (benzoylmesaconitine, benzoylaconitine and benzoylhypacoitine) in normal and MI rats after oral administration of Sini decoction. The statistical results of pharmacokinetic parameters demonstrated that benzoylmesaconitine, benzoylaconitine and benzoylhypacoitine showed lower peak concentration, longer half‐life, smaller area under the concentration–time curve, slower clearance, time to peak concentration and mean residence time in MI rats than in normal rats (p < 0.05), which indicated that monoester‐diterpenoid alkaloids exhibited lower systemic exposure and slower elimination in the MI rats. The results provided the experimental basis for understanding the metabolic fate and therapeutic effects of Sini decoction.  相似文献   
78.
Development of effective organocatalysts for the living ring‐opening polymerization (ROP) of lactones is highly desired for the preparation of biocompatible and biodegradable polyesters with controlled microstructures and physical properties. Herein, a new class of hydrogen‐bond donating bisurea catalysts is reported for the ROP of lactones under solvent‐free conditions. ROP of lactones mediated by the bisurea/7‐methyl‐1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (MTBD) catalyst exhibits a living/controlled manner, affording the polymers and copolymers with the well‐defined structure, predictable molecular weight, narrow molecular weight distribution, and high selectivity for monomer at low catalyst loadings at ambient temperature. The possible mechanism of bisurea/MTBD‐catalyzed ROP of lactones is proposed, in which the bisurea activates the carbonyl group of lactones while MTBD facilitates the nucleophilic attack of the initiating/propagating alcohol by hydrogen bonding. Moreover, the poly(ε‐caprolactone‐co‐δ‐valerolactone) [P(CL‐co‐VL)] random copolymers with various compositions were synthesized using the bisurea/MTBD catalyst. The measurements of thermal properties and crystalline structure demonstrate that the CL and VL units are cocrystallized in the crystalline phase of P(CL‐co‐VL) copolymers. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 90–100  相似文献   
79.
Acta Mathematicae Applicatae Sinica, English Series - This paper summarizes the parameter estimation of systems with set-valued signals, which can be classified to three catalogs: one-time...  相似文献   
80.
Chen  Shuang  Pang  Li-ping  Li  Dan  Wang  Jin-he 《应用数学学报(英文版)》2019,35(3):591-606
Acta Mathematicae Applicatae Sinica, English Series - For the variational inequality with symmetric cone constraints problem, we consider using the inexact modified Newton method to efficiently...  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