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   307篇
  免费   4篇
  国内免费   6篇
化学   49篇
晶体学   2篇
力学   4篇
数学   171篇
物理学   91篇
  2022年   3篇
  2021年   2篇
  2019年   33篇
  2018年   46篇
  2017年   4篇
  2016年   17篇
  2015年   6篇
  2014年   4篇
  2013年   16篇
  2012年   6篇
  2011年   25篇
  2010年   10篇
  2009年   16篇
  2008年   11篇
  2007年   7篇
  2006年   12篇
  2005年   14篇
  2004年   12篇
  2003年   3篇
  2002年   9篇
  2001年   2篇
  2000年   3篇
  1999年   7篇
  1998年   1篇
  1997年   3篇
  1996年   3篇
  1995年   2篇
  1994年   3篇
  1993年   2篇
  1992年   1篇
  1991年   4篇
  1990年   2篇
  1989年   1篇
  1988年   1篇
  1987年   3篇
  1986年   2篇
  1985年   3篇
  1984年   1篇
  1982年   3篇
  1981年   2篇
  1980年   2篇
  1979年   3篇
  1978年   1篇
  1977年   3篇
  1976年   3篇
排序方式: 共有317条查询结果,搜索用时 31 毫秒
1.
In this paper, the Kinetic Flux Vector Splitting (KFVS) scheme is extended to solving the shallow water equations with source terms. To develop a well-balanced scheme between the source term and the flow convection, the source term effect is accounted in the flux evaluation across cell interfaces. This leads to a modified gas-kinetic scheme with particular application to the shallow water equations with bottom topography. Numerical experiments show better resolution of the unsteady solution than conventional finite difference method and KFVS method with little additional cost. Moreover, some positivity properties of the gas-kinetic scheme is established.  相似文献   
2.
When 64n853265325683/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-keto-ester1 a was reacted with dimethyl acetylenedicarboxylate ring expansion occurred to give substituted cyclooctadienones.Michael reactions of the title compounds1 with unsaturated ketones gave adducts, some of which underwent further cyclization reactions. A new route to 64n853265325683/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-tetralone ring system10 via cyclization of the intermediateMichael adduct9 is described.
Michael- und Ringerweiterungsreaktionen von 6-Carboethoxy-3,5-diaryl-2-cyclohexen-1-onen
Zusammenfassung Bei der Reaktion von 64n853265325683/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-Keto-ester1 a mit Dimethyl-acetylendicarboxylat wurden unter Ringerweiterung substituierte Cyclooctadienone erhalten. DieMichael-Reaktion der Titelverbindung1 mit ungesättigten Ketonen ergab Addukte, von denen einige weitere Cyclisierungsreaktionen eingingen. Es wird ein neuer Weg zum 64n853265325683/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-Tetralonsystem10 über die Cyclisierung des intermediärenMichael-Addukts9 beschrieben.
  相似文献   
3.
64/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-(2-Arylaminoethoxy)styrenes undergo cyclization in the presence of KOH to giveN-aryl-2-benzyloxazolidines inca. 90 % yield. The structures of the products were confirmed by IR and NMR spectroscopy.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 340–341, February, 1994.  相似文献   
4.
The nitrone is found to be included in the 64t061577226184/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-cyclodextrin cavity in two different stoichiometries viz., 1G : 1H and 1G : 2H – the existence of which is proved by physical methods. The 1G : 2H complex of the nitrone serves as a good potent dipolarophile in the 1,3-dipolar cycloaddition reactions with olefins resulting in rate acceleration and regioselection.  相似文献   
5.
We investigate then64/xxlarge8594.gif" alt="rarr" align="BASELINE" BORDER="0"> 64/xxlarge8734.gif" alt="infin" align="MIDDLE" BORDER="0"> limit of then-vector model single-spin and pairspin correlation functions. In this limit we show that the correlation functions become those of the corresponding spherical model.  相似文献   
6.
Single crystals of [Ni(Phen)(i64h8/xxlarge8208.gif" alt="dash" align="MIDDLE" BORDER="0">Bu2PS2)2] (I) and [Ni(Phen)3](i64h8/xxlarge8208.gif" alt="dash" align="MIDDLE" BORDER="0">Bu2PS2)2 (III) compounds were grown, and their structures were determined by X64h8/xxlarge8208.gif" alt="dash" align="MIDDLE" BORDER="0">ray diffraction analysis (CAD64h8/xxlarge8208.gif" alt="dash" align="MIDDLE" BORDER="0">4 diffractometer, MoK 64h8/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0"> radiation, 3336 F hkl , R = 0.0373 for I and 2575 F hkl for III). The crystals of complex I have a triclinic unit cell with the following parameters: a = 11.097(1) 64h8/xxlarge8491.gif" alt="angst" align="MIDDLE" BORDER="0">, b = 14.903(2) 64h8/xxlarge8491.gif" alt="angst" align="MIDDLE" BORDER="0">, c = 22.650(3)64h8/xxlarge8491.gif" alt="angst" align="MIDDLE" BORDER="0">; 64h8/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0"> = 75.18(1)°, 64h8/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0"> = 80.50(1)°, 64h8/xxlarge947.gif" alt="gamma" align="MIDDLE" BORDER="0"> = 75.07(1)°, V = 3479.2(7)64h8/xxlarge8491.gif" alt="angst" align="MIDDLE" BORDER="0">3, Z = 4, 64h8/xxlarge961.gif" alt="rgr" align="MIDDLE" BORDER="0">calc = 1.255 g/cm3, and space group 64h8/10947_2004_Article_474369_TeX2GIFIE1.gif" alt=" $$\bar P$$ " align="middle" border="0"> 1; the crystals of III have a monoclinic unit cell with the following parameters: a = 19.010(3)64h8/xxlarge8491.gif" alt="angst" align="MIDDLE" BORDER="0">, b = 15.481(1) 64h8/xxlarge8491.gif" alt="angst" align="MIDDLE" BORDER="0">, c = 17.940(3)64h8/xxlarge8491.gif" alt="angst" align="MIDDLE" BORDER="0">; 64h8/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0"> = 97.58(1)°, V = 5233.5(12)64h8/xxlarge8491.gif" alt="angst" align="MIDDLE" BORDER="0">3, Z = 4, 64h8/xxlarge961.gif" alt="rgr" align="MIDDLE" BORDER="0">calc = 1.292 g/cm3, and space group C2/c. The structure of complex I is built from mononuclear molecules, and the structure of III, from [Ni(Phen)3]2+ complex cations and i64h8/xxlarge8208.gif" alt="dash" align="MIDDLE" BORDER="0"> Bu2PS2 - outer64h8/xxlarge8208.gif" alt="dash" align="MIDDLE" BORDER="0">sphere anions. The NiN2S4 coordination polyhedra in the structure of I and NiN6 in the structure of III are distorted octahedra. Based on structural data, the interaction between the coordinated Phen molecules of complexes I, [Ni(Phen)2(i64h8/xxlarge8208.gif" alt="dash" align="MIDDLE" BORDER="0">Bu2PS2)](i64h8/xxlarge8208.gif" alt="dash" align="MIDDLE" BORDER="0">Bu2PS2) (II), and III is considered, as well as the packing modes of these complexes.  相似文献   
7.
Synthesis of 4,464x432/xxlarge8242.gif" alt="prime" align="BASELINE" BORDER="0">-bis(4-aminophenoxy)benzophenone was performed starting from chloral. Various polyimides were obtained by reactions of 4,4 64x432/xxlarge8242.gif" alt="prime" align="BASELINE" BORDER="0">-bis(4-aminophenoxy)benzophenone with aromatic tetracarboxylic acid dianhydrides. Some of the polyimides obtained are crystalline compounds.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 673–676, March, 1996.  相似文献   
8.
LetK be a ring with an identity 1 0 andM, L two unitaryK-modules. Then, for any additive mappingf:M L, the setH f :={ K f(x)=f(x) for allx M} forms a subring ofK, the homogeneity ring off. It is shown that, forM {0},L {0} and any subringS ofK for whichM is a freeS-module, there exists an additive mappingf:ML such thatH f =S. This result is applied to the four Cauchy functional equations, and it leads also to an answer to the question as to whether it is possible to introduce onM a multiplication ·:M × M M makingM into a ring but not into aK-algebra.  相似文献   
9.
One of the most difficult operations for control and identification in copper ore concentration process is grain classification in hydrocyclone batteries. In the paper radiotracer investigations of the classification process immediately give values of hydrocyclones parameters with higher accuracy than obtained from conventional methods. Presented paper includes the results of the investigation which was carried out in “Lubin” Copper Mine in Poland.  相似文献   
10.
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