全文获取类型
收费全文 | 7786篇 |
免费 | 1382篇 |
国内免费 | 829篇 |
专业分类
化学 | 5814篇 |
晶体学 | 12篇 |
力学 | 902篇 |
综合类 | 52篇 |
数学 | 2144篇 |
物理学 | 1073篇 |
出版年
2024年 | 4篇 |
2023年 | 94篇 |
2022年 | 129篇 |
2021年 | 202篇 |
2020年 | 389篇 |
2019年 | 212篇 |
2018年 | 268篇 |
2017年 | 231篇 |
2016年 | 372篇 |
2015年 | 442篇 |
2014年 | 470篇 |
2013年 | 673篇 |
2012年 | 522篇 |
2011年 | 549篇 |
2010年 | 490篇 |
2009年 | 550篇 |
2008年 | 592篇 |
2007年 | 527篇 |
2006年 | 492篇 |
2005年 | 453篇 |
2004年 | 405篇 |
2003年 | 466篇 |
2002年 | 179篇 |
2001年 | 187篇 |
2000年 | 175篇 |
1999年 | 138篇 |
1998年 | 132篇 |
1997年 | 130篇 |
1996年 | 124篇 |
1995年 | 84篇 |
1994年 | 65篇 |
1993年 | 43篇 |
1992年 | 53篇 |
1991年 | 37篇 |
1990年 | 26篇 |
1989年 | 22篇 |
1988年 | 8篇 |
1987年 | 12篇 |
1986年 | 7篇 |
1985年 | 11篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1957年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有9997条查询结果,搜索用时 15 毫秒
261.
262.
263.
Pierrick Nun Violaine Pérez Monique Calmès Jean Martinez Frédéric Lamaty 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(12):3773-3779
The asymmetric alkylation of Schiff bases under basic conditions in a ball mill was performed. The starting Schiff bases of glycine were prepared beforehand by milling protected glycine hydrochloride and benzophenone imine, in the absence of solvent. The Schiff base was then reacted with a halogenated derivative in a ball mill in the presence of KOH. By adding a chiral ammonium salt derived from cinchonidine, the reaction proceeded asymmetrically under phase‐transfer catalysis conditions, giving excellent yields and enantiomeric excesses up to 75 %. Because an equimolar amount of starting material was used, purification was greatly simplified. 相似文献
264.
Rebeca Infante Dr. Javier Nieto Prof. Dr. Celia Andrés 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(14):4375-4379
A highly efficient enantioselective addition of Me2Zn to α‐ketoesters, assisted by a chiral perhydro‐1,3‐benzoxazine ligand, is described. This novel catalytic system offers homogeneous elevated enantioselectivities in the preparation of α‐hydroxyesters that bear a quaternary stereocenter, with a minor dependence on electronic and steric effects when aromatic, heteroaromatic, or aliphatic α‐ketoesters are employed. The catalyst can be recovered and reused without loss of activity. 相似文献
265.
266.
A mass conservative well‐balanced reconstruction at wet/dry interfaces for the Godunov‐type shallow water model
下载免费PDF全文
![点击此处可从《国际流体数值方法杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
This paper presents a novel mass conservative, positivity preserving wetting and drying treatment for Godunov‐type shallow water models with second‐order bed elevation discretization. The novel method allows to compute water depths equal to machine accuracy without any restrictions on the time step or any threshold that defines whether the finite volume cell is considered to be wet or dry. The resulting scheme is second‐order accurate in space and keeps the C‐property condition at fully flooded area and also at the wet/dry interface. For the time integration, a second‐order accurate Runge–Kutta method is used. The method is tested in two well‐known computational benchmarks for which an analytical solution can be derived, a C‐property benchmark and in an additional example where the experimental results are reproduced. Overall, the presented scheme shows very good agreement with the reference solutions. The method can also be used in the discontinuous Galerkin method. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
267.
Franklin A. Davis Bin Yang Jianghe Deng Yongzhong Wu Yulian Zhang Ashwin Rao 《Phosphorus, sulfur, and silicon and the related elements》2013,188(5-6):1109-1117
Abstract Sulfinimine-derived polyfunctionalized chiral building blocks, often prepared in one pot, provide efficient access, with a minimum of chemical manipulation, to enantiopure, multifunctional amine derivatives including piperidines and pyrrolidines. 相似文献
268.
A three‐dimensional Cartesian cut cell method for incompressible viscous flow with irregular domains
A three‐dimensional Cartesion cut cell method is presented for the simulations of incompressible viscous flows with irregular domains. A new model (referred to as ‘6+N’ model) is proposed to describe arbitrarily shaped cut cells and treat all the cells as polyhedrons with 6+N faces. The finite volume discretization of the Navier–Stokes equation is then implemented by using the ‘6+N’ model to separate the surface flux integrals into two parts, that is, the fluxes through the basic face of the hexahedron and those through the cutting surfaces. The previously proposed Kitta Cube algorithm and volume computer‐aided design platform (J. Comput. Aided. Des. 2005; 37(4): 1509–1520. Doi:10.1016/j.cad.2005.03.006) are adopted to generate cut cells and provide shape data and physical attributes for the numerical analysis. A modified SIMPLE‐based smoothing pressure correction scheme is applied to suppress checkerboard pressure oscillations caused by the collocated arrangement of velocities and pressure. The calculation accuracy of the numerical method expressed by L1 and L ∞ norm errors is first demonstrated by the simulation of a pipe flow. Then its feasibility, efficiency, and potential in engineering applications are verified by applying it to solve natural convections between concentric spheres and between eccentric spheres. The heat transfer patterns in eccentric spheres are also obtained by using the numerical method. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
269.
270.
The paper details the implementation of the Godunov‐type finite volume Arbitrary high order schemes using Derivatives (ADER) scheme for the case of a large source term in the continuity equation of the nonlinear shallow water equations. The particular application is the movement of a bore on a highly permeable slope. The large source term is caused by the infiltration into the initially unsaturated slope material. Infiltration is modelled as vertical downwards piston‐like flow with Forchheimer quadratic parameterisation of the resistance law. The corresponding ODE is solved using the fourth‐order Runge–Kutta method. The surface and subsurface flow models have been tested by comparison with analytical solutions. Example predictions of surface bore propagation and wetting front propagation are presented for a range of slope permeabilities. The effects of permeability on bore run‐up, water depths and velocities are illustrated. The ADER scheme is capable of handling the source term, including the extreme case when this term dominates the volume balance. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献