全文获取类型
收费全文 | 226篇 |
免费 | 8篇 |
国内免费 | 1篇 |
专业分类
化学 | 129篇 |
晶体学 | 10篇 |
力学 | 21篇 |
数学 | 31篇 |
物理学 | 44篇 |
出版年
2021年 | 2篇 |
2020年 | 2篇 |
2018年 | 1篇 |
2017年 | 1篇 |
2016年 | 5篇 |
2015年 | 6篇 |
2014年 | 3篇 |
2013年 | 13篇 |
2012年 | 10篇 |
2011年 | 8篇 |
2010年 | 8篇 |
2009年 | 8篇 |
2008年 | 10篇 |
2007年 | 12篇 |
2006年 | 16篇 |
2005年 | 7篇 |
2004年 | 7篇 |
2003年 | 6篇 |
2002年 | 10篇 |
2001年 | 4篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 1篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 7篇 |
1989年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 8篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1965年 | 2篇 |
排序方式: 共有235条查询结果,搜索用时 31 毫秒
91.
It is generally accepted that mixed and penalty finite element methods can routinely solve the incompressible Navier–Stokes equations. This paper shows by means of simple examples that problems can arise even for the simpler Stokes equations. The causes of the problem fall in either of two categories: round-off and ill conditioning, or a poor choice of pressure discretization. Nonsensical solutions can be obtained. Computation of the discrete divergence of the flow field is a simple and powerful tool to diagnose such conditions. In the first part of the paper several simple techniques for minimizing the effect of round-off are reviewed. In the second part it is shown that, for coupled flow problems, care must be exercised in the choice of the pressure approximation. A unified treatment of various observations by different workers is presented. This should prove useful for general users of the finite element method. 相似文献
92.
S.William Pelletier Atanas P. Venkov Janet Finer-Moore Naresh V. Mody 《Tetrahedron letters》1980,21(9):809-812
A Michael addition of secondary amines to exocyclic α,β-unsaturated ketones has been achieved in excellent yield in the presence of alumina. In the absence of alumina, the reaction does not proceed or takes place in low yield with many side products after a long reaction time. 相似文献
93.
94.
The novel structures assigned by Yunusov et al to the C19-diterpenoid alkaloids, acomonine (), iliensine (), 14-dehydroiliensine (), and 14-bensoyliliensine () have been found to be in error. We have demonstrated that these alkaloids are identical with the well-known alkaloids, delsoline (), delcosine (), 14-dehydrodeloosine (), and 14-benzoyldelcosine (), respectively. 相似文献
95.
96.
[structure: see text]. Pure alpha-azido acids were prepared using an efficient diazo transfer method followed by buffered workup. These building blocks were used to prepare small peptides on Wang resin by two approaches. Peptides prone to diketopiperazine formation were prepared in good yields by coupling acids to resin bound iminophosphoranes during Fmoc-Wang synthesis. The iminophosphoranes can also be hydrolyzed under neutral conditions to provide unprotected amines ready for further coupling. 相似文献
97.
M. Treuil H. Jaffrezic N. Deschamps C. Derre F. Guichard J. L. Joron B. Pelletier S. Novotny C. Courtois 《Journal of Radioanalytical and Nuclear Chemistry》1973,18(1-2):55-68
Résumé Pour utiliser au mieux les possibilités de l'analyse par activation et de la spectrométrie γ à l'aide des détecteurs à semi-conducteurs,
nous proposons des schémas de séparations rapides qui permettent d'effectuer les analyses de routine des lanthanides, du scandium,
du chrome, du manganèse, du cobalt, du cuivre et du zinc, dans la plupart des minéraux et des roches avec une précision comprise
entre 3 et 10%. La méthode a été appliquée à une grande variété d'échantillons et testée sur des standards. Nous montrons
par quelques exemples tout son intérêt dans les études géochimiques systématiques des éléments de transition. 相似文献
98.
A copper triflate/t-BuOOAc-catalyzed amidation of allylic and benzylic acetates has been developed which is suitable for the coupling of a wide variety of functionalized sulfonamide nucleophiles with acetate electrophiles. The methodology allows for the amidation of benzylic substrates which are not further activated by an additional adjacent alkene or alkyne, enabling simple allylic acetates and primary benzylic acetates to be used as reaction partners. 相似文献
99.
** Corresponding author. Email: chausst{at}wmin.ac.uk A good estimate of the length of stay (LOS) of elderly peoplein institutional long-term care (ILTC) is essential to bothcare providers (care home owners) and purchasers (local authoritiesin the UK) in order to forecast their resource availabilityand future requirements. Existing methods usually rely on cohortdata, which needs to be collected on a continuous basis forseveral years and are often not available electronically. Inthis paper we develop an approach based on multi-census datato fit a Markov model in continuous-time for the LOS of elderlypeople in ILTC (residential and nursing care). We use 3 yearplacement data provided by London Borough of Merton Social Servicesto compare the estimates of the model parameters obtained usingmulti-census data with those derived from cohort data, henceto validate the multi-census approach in this context. The implicationsof the proposed multi-census approach and its advantages inthe context of long-term care planning are discussed. 相似文献
100.
Balawant S. Joshi Taikyun Rho Peter L. Rinaldi Weixia Liu Todd A. Wagler M. Gary Newton Doowon Lee S. William Pelletier 《Journal of chemical crystallography》1997,27(9):553-559
The structure of the π-molecular complex (10) was assigned on the basis of the solid state13C-nmr spectrum. The solid state13C-nmr spectrum of quinhydrone (12) has also been determined. Accurate1H and13C chemical shift assignments have been made for the compounds3,5,6,7,8, and10 on the basis of HMQC and HMBC spectral data. The π-molecular complex10 crystallizes in the space groupP21 In with cell parameters:a=4.052 (1) Å,b=6.477 (1) Å,c=19.093 (2) Å, β=90.17 (1)o,z=1,D c =1.400 g mc?32. Crystal and molecular structure of the title compound, C28H22O4, has been determined by an X-ray analysis of10 by direct methods from diffractometer data and refined by full-matrix least-squares 相似文献