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   2273篇
  免费   350篇
  国内免费   217篇
化学   1704篇
晶体学   16篇
力学   150篇
综合类   29篇
数学   184篇
物理学   757篇
  2024年   9篇
  2023年   53篇
  2022年   66篇
  2021年   91篇
  2020年   102篇
  2019年   94篇
  2018年   78篇
  2017年   55篇
  2016年   109篇
  2015年   114篇
  2014年   106篇
  2013年   148篇
  2012年   190篇
  2011年   204篇
  2010年   122篇
  2009年   112篇
  2008年   156篇
  2007年   137篇
  2006年   121篇
  2005年   127篇
  2004年   73篇
  2003年   56篇
  2002年   59篇
  2001年   51篇
  2000年   51篇
  1999年   47篇
  1998年   38篇
  1997年   35篇
  1996年   30篇
  1995年   29篇
  1994年   31篇
  1993年   22篇
  1992年   18篇
  1991年   28篇
  1990年   18篇
  1989年   8篇
  1988年   9篇
  1987年   9篇
  1985年   5篇
  1984年   3篇
  1983年   8篇
  1982年   2篇
  1981年   2篇
  1980年   5篇
  1978年   1篇
  1976年   2篇
  1974年   1篇
  1959年   1篇
  1947年   1篇
  1946年   1篇
排序方式: 共有2840条查询结果,搜索用时 46 毫秒
71.
Middle-phase microemulsions of green surfactant alkyl polyglucosides   总被引:1,自引:0,他引:1  
Microemulsions are important organized molecular assembles in surfactant solutions and are used in various fields such as tertiary oil recovery, pharmaceutics, cosmetics, nanoparticle synthe-sis and chemical engineering. The more commonly used nonionic surfactants to produce micro- emulsions are the ethylene oxide-based compounds (CiEj). In recent years alkyl polyglucosides have been received considerable attention in producing microemulsions[17]. Alkyl polyglucosides (APG), which are widely…  相似文献   
72.
本文用X射线衍射及差热分析等方法, 研究了BaO-B_2O_3-GeO_2(BaO≤50 mol%)三元系的室温截面相图。发现了一个新的三元化合物Ba_3B_6Ge_2O_(16)(3BaO·3B_2O_3·2GeO_2)。并且研究了BaB_2O_4-Ba_3B_6Ge_2O_(16), BaGeO_3-Ba_3B_6Ge_2O_(16), BaB_2O_4-BaGeO_3三个二元系相图。它们都是共晶体系, 共晶温度分别为937±3 ℃、879±3 ℃875±3 ℃; 共晶组分分别为(BaO)_(0.42)(B_2O_3)_(0.42)(GeO_2)_(0.16), (BaO)_(0.42)(B_2O_3)_(0.24)(GeO_2)_(0.34), (BaO)_(0.50)(B_2O_3)_(0.27)(GeO_2)_(0.23)。这三个二元系组成一个三元共晶体系, 其三元共晶温度为870±3 ℃, 共晶组分为(BaO)_(0.46)(B_2O_3)_(0.27)(GeO_2)_(0.27)。  相似文献   
73.
74.
Chen  J.-J.  Huang  P.-Y.  Yang  Z.-S.  Cai  X.-Z.  Shi  Y.  Hu  W.-Y.  Zhang  X.-H.  Chai  H.-F.  Huang  Z.-Y. 《Journal of Structural Chemistry》2021,62(10):1543-1550
Journal of Structural Chemistry - N-(2-methoxy-5-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)pyridin-3-yl)cyclopropanesulfonamide is an organic intermediate with borate and sulfonamide groups,...  相似文献   
75.
A worldwide challenge in the near future will be to find a way of producing radioisotopes in sufficient quantity without relying on research reactors. The motivation for this innovative work on targets lies in the accelerator-based production of radioisotopes using a neutron converter target as in the transmutation by adiabatic resonance crossing concept. Thermal analysis of a multi-channel helium cooled device is performed with the computational fluid dynamics code CFX. Different boundary conditions are taken into account in the simulation process and many important parameters such as maximum allowable solid target temperature as well as uniform inlet velocity and outlet pressure changes in the channels are investigated. The results confirm that the cooling configuration works well; hence such a solid target could be operated safely and may be considered for a prototype target.  相似文献   
76.
Russian Journal of Physical Chemistry A - A new mesoporous carbon containing nitrogen and copper was prepared by carbonizing a polymer obtained by blending p-phenylenediamine, copper(II) sulfate,...  相似文献   
77.
The aim of this paper is to study the exact controllability of the Petrovsky equation. Under some checkable geometric assumptions, we establish the observability inequality via the multiplier method for the Dirichlet control problem.  相似文献   
78.
Although the reaction chemistry of transition metallacyclopropenes has been well-established in the last decades, the reactivity of rare-earth metallacyclopropenes remains elusive. Herein, we report the reaction of lutetacyclopropene 1 toward a series of unsaturated molecules. The reaction of 1 with one equiv. of PhCOMe, Ar1CHO (Ar1=2,6-Me2C6H3), W(CO)6, and PhCH=NPh provided oxalutetacyclopentenes, metallacyclic lutetoxycarbene, and azalutetacyclopentene via 1,2-insertion of C=O, C≡O, or C=N bonds into Lu−Csp2 bond, respectively. However, the reaction between 1 and Ar2N=C=NAr2 (Ar2=4-MeC6H4) gave an acyclic lutetium complex with a diamidinate ligand by the coupling of one molecule of 1 with two carbodiimides, irrespective of the amount of carbodiimide employed. More interestingly, when 1 was treated with two equiv. of Ar1CHO, the reductive coupling of two C=O bonds was discovered to give a lutetium pinacolate complex along with the release of tolan. Remarkably, the reactivity of 1 is significantly different from that of scandacyclopropenes; these metallacycles derived from 1 all represent the first cases in rare-earth organometallic chemistry.  相似文献   
79.
Deferoxamine grafted alginate (SA‐DFA) was successfully synthesized via amidation of sodium alginate with deferoxamine mesylate as determined by H‐NMR and elemental analysis. SA‐DFA with different graft yield was obtained by adjusting the ratio of sodium alginate and deferoxamine mesylate. It was found that aqueous solution of SA‐DFA could form hydrogel spontaneously due to hydrogen bonding interactions, which also endowed the SA‐DFA hydrogel with self‐healing capability. The healing efficiency of SA‐DFA hydrogels ranged from 53.64 to 90.16%. In addition, surface morphologies of SA‐DFA hydrogels before/after self‐healing process were demonstrated by SEM images. We anticipated that such self‐healable alginate hydrogel would be applied in the field of wound healing. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 856–865  相似文献   
80.
A practical eight-step synthesis of lignanamide cannabisin F starting from vanillin is reported for the first time. This synthetic strategy applies the aldol reaction followed by the Wittig reaction to afford the key 8-O-4′-neolignan intermediate diacid. The diacid was condensed with N,O-protected tyramine giving, after deprotection, cannabisin F.  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