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   2104058篇
  免费   112942篇
  国内免费   103479篇
化学   1237571篇
晶体学   25326篇
力学   103110篇
综合类   10714篇
数学   310109篇
物理学   633649篇
  2022年   20371篇
  2021年   33445篇
  2020年   36703篇
  2019年   38990篇
  2018年   39734篇
  2017年   40978篇
  2016年   57773篇
  2015年   47520篇
  2014年   63197篇
  2013年   120958篇
  2012年   110808篇
  2011年   126027篇
  2010年   89550篇
  2009年   88331篇
  2008年   112662篇
  2007年   108546篇
  2006年   101596篇
  2005年   89715篇
  2004年   76832篇
  2003年   63146篇
  2002年   55598篇
  2001年   48678篇
  2000年   47510篇
  1999年   33191篇
  1998年   26129篇
  1997年   26380篇
  1996年   29118篇
  1995年   27780篇
  1994年   28633篇
  1993年   27864篇
  1992年   27742篇
  1991年   23267篇
  1990年   21804篇
  1989年   20973篇
  1988年   19465篇
  1987年   19202篇
  1986年   18308篇
  1985年   24236篇
  1984年   22929篇
  1983年   18484篇
  1982年   19485篇
  1981年   19113篇
  1980年   17871篇
  1979年   18483篇
  1978年   18721篇
  1977年   18259篇
  1976年   17833篇
  1975年   16856篇
  1974年   16529篇
  1973年   16710篇
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
991.
Journal of Thermal Analysis and Calorimetry - The nanofluid is a mixture of base fluid and solid nanoparticles in nanosize. The heat transfer generated by the nanofluid is more than the base fluid...  相似文献   
992.
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   
993.
994.
Journal of Thermal Analysis and Calorimetry - The present study reports numerical simulations of water-based Al2O3 nanofluid flowing in a 2D channel with a heated wall-mounted obstacle. The...  相似文献   
995.
Russian Journal of Organic Chemistry - The reaction of 6,6-dialkyl-5,6-dihydrobenzo[f]pyrrolo[2,1-a]isoquinoline-8,9-diones with hydrazine is used to prepare enaminoketohydrazides of the...  相似文献   
996.
Journal of Thermal Analysis and Calorimetry - The paper presents the effect of the tabletting pressure and time on the chemical structure and crystallinity of the CuBTC and MIL-53(Al)...  相似文献   
997.
Carbocyclic carbenes (CCCs) are a class of nucleophilic carbenes which are very similar to N-heterocyclic carbenes (NHCs) in terms of their reactivity, but they do not contain a stabilizing heteroatom in their cyclic ring system. In this study, 17 representative known CCCs and 34 newly designed CCCs are evaluated using quantum chemical methods, and the results are compared in terms of their stability, nucleophilicity, and proton affinity (PA) parameters. The results are divided on the basis of ring size of the known and reported CCCs. The stability, nucleophilicity, PA, complexation energy, and bond strength–related parameters were estimated using M06/6-311++G(d,p) method. The results indicated that the CCCs known in the literature are strong σ-electron donating species and have considerable π-accepting properties. This study led to the design and identification of a few new CCCs with dimethylamine and diaminomethynyl substituents which can be singlet stable and are substantially nucleophilic. © 2018 Wiley Periodicals, Inc.  相似文献   
998.
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   
999.
Applied Biochemistry and Biotechnology - The effects of ethanol/broth proportions and the number of steps at varying pH in the presence or absence of sodium chloride (NaCl) were studied as...  相似文献   
1000.
Transition Metal Chemistry - The present study reports the synthesis and crystal structures of Cu(II) complexes with pyridoxal S-allyldithiocarbazate (H2L1) and pyridoxal thiosemicarbazones...  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