全文获取类型
收费全文 | 24091篇 |
免费 | 4719篇 |
国内免费 | 3533篇 |
专业分类
化学 | 18011篇 |
晶体学 | 348篇 |
力学 | 1404篇 |
综合类 | 267篇 |
数学 | 2918篇 |
物理学 | 9395篇 |
出版年
2024年 | 54篇 |
2023年 | 565篇 |
2022年 | 727篇 |
2021年 | 1018篇 |
2020年 | 1177篇 |
2019年 | 1212篇 |
2018年 | 954篇 |
2017年 | 894篇 |
2016年 | 1238篇 |
2015年 | 1398篇 |
2014年 | 1589篇 |
2013年 | 1926篇 |
2012年 | 2302篇 |
2011年 | 2333篇 |
2010年 | 1621篇 |
2009年 | 1679篇 |
2008年 | 1737篇 |
2007年 | 1448篇 |
2006年 | 1326篇 |
2005年 | 1065篇 |
2004年 | 860篇 |
2003年 | 653篇 |
2002年 | 719篇 |
2001年 | 540篇 |
2000年 | 465篇 |
1999年 | 442篇 |
1998年 | 352篇 |
1997年 | 296篇 |
1996年 | 272篇 |
1995年 | 224篇 |
1994年 | 188篇 |
1993年 | 197篇 |
1992年 | 134篇 |
1991年 | 117篇 |
1990年 | 103篇 |
1989年 | 99篇 |
1988年 | 84篇 |
1987年 | 55篇 |
1986年 | 56篇 |
1985年 | 61篇 |
1984年 | 38篇 |
1983年 | 21篇 |
1982年 | 26篇 |
1981年 | 13篇 |
1980年 | 5篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1972年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
891.
892.
This paper reports numerical convergence study for simulations of steady shock‐induced combustion problems with high‐resolution shock‐capturing schemes. Five typical schemes are used: the Roe flux‐based monotone upstream‐centered scheme for conservation laws (MUSCL) and weighted essentially non‐oscillatory (WENO) schemes, the Lax–Friedrichs splitting‐based non‐oscillatory no‐free parameter dissipative (NND) and WENO schemes, and the Harten–Yee upwind total variation diminishing (TVD) scheme. These schemes are implemented with the finite volume discretization on structured quadrilateral meshes in dimension‐by‐dimension way and the lower–upper symmetric Gauss–Seidel (LU–SGS) relaxation method for solving the axisymmetric multispecies reactive Navier–Stokes equations. Comparison of iterative convergence between different schemes has been made using supersonic combustion flows around a spherical projectile with Mach numbers M = 3.55 and 6.46 and a ram accelerator with M = 6.7. These test cases were regarded as steady combustion problems in literature. Calculations on gradually refined meshes show that the second‐order NND, MUSCL, and TVD schemes can converge well to steady states from coarse through fine meshes for M = 3.55 case in which shock and combustion fronts are separate, whereas the (nominally) fifth‐order WENO schemes can only converge to some residual level. More interestingly, the numerical results show that all the schemes do not converge to steady‐state solutions for M = 6.46 in the spherical projectile and M = 6.7 in the ram accelerator cases on fine meshes although they all converge on coarser meshes or on fine meshes without chemical reactions. The result is based on the particular preconditioner of LU–SGS scheme. Possible reasons for the nonconvergence in reactive flow simulation are discussed.Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
893.
The Horner-Wadsworth-Emmons olefination of diethyl-(1-benzotri-azolmethyl)phosphonate by means of aldehydes was found to be a convenient method for the stereoselective preparation of (E)-1-(1-Alkenyl)benzotriazoles. 相似文献
894.
In this paper, we give discreteness criteria of subgroups of the special linear group on Qp or Cp in two and higher dimensions. J rgensen's inequality gives a necessary condition for a nonelementary group of Mbius transformations to be discrete. We give a version of Jфrgensen's inequality for SL(m, Cp). 相似文献
895.
Chromatographia - A novel method for the rapid simultaneous determination of multiple fungicide residues in tobacco was established using ultra-performance liquid chromatography–tandem mass... 相似文献
896.
S. S. Krishnan J. M. Abshire P. B. Sunderland Z.-G. Yuan J. P. Gore 《Combustion Theory and Modelling》2013,17(4):605-620
Flame shape is an important observed characteristic of flames that can be used to scale flame properties such as heat release rates and radiation. Flame shape is affected by fuel type, oxygen levels in the oxidiser, inverse burning and gravity. The objective of this study is to understand the effect of high oxygen concentrations, inverse burning, and gravity on the predictions of flame shapes. Flame shapes are obtained from recent analytical models and compared with experimental data for a number of inverse and normal ethane flame configurations with varying oxygen concentrations in the oxidiser and under earth gravity and microgravity conditions. The Roper flame shape model was extended to predict the complete flame shapes of laminar gas jet normal and inverse diffusion flames on round burners. The Spalding model was extended to inverse diffusion flames. The results show that the extended Roper model results in reasonable predictions for all microgravity and earth gravity flames except for enhanced oxygen normal diffusion flames under earth gravity conditions. The results also show trends towards cooler flames in microgravity that are in line with past experimental observations. Some key characteristics of the predicted flame shapes and parameters needed to describe the flame shape using the extended Roper model are discussed. 相似文献
897.
Jiawei Zhang Yiliu Liu Bin Yuan Prof. Zhiqiang Wang Prof. Monika Schönhoff Prof. Xi Zhang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(47):14968-14973
Stable multilayer films with cucurbit[8]uril have been fabricated on the basis of the alternating layer‐by‐layer assembly of a novel side‐chain pseudopolyrotaxane and a photoreactive polyanion. The as‐prepared multilayer films exhibit good properties as surface‐imprinted multilayers, because cucurbit[8]uril molecules that are locked inside the multilayers can act as nanocontainers with specific binding to certain guest molecules, and the loading and release of the guest is redox‐controllable and reversible. 相似文献
898.
Long Yuan Mohammed Jemal Anne‐Francoise Aubry 《Rapid communications in mass spectrometry : RCM》2012,26(12):1465-1474
899.
900.
Yong-Dong Li Hao Zhao Nan Zhang 《International Journal of Solids and Structures》2013,50(22-23):3610-3617
The purpose of the present work is to study the mixed mode fracture of a piezoelectric–piezomagnetic composite with two un-coaxial cracks parallel to the interface and each in a layer. Methods of generalized dislocation simulation, Green’s function, Cauchy singular integral equation and Lobatto–Chebyshev collocation are combined together to get the numerical results of mechanical strain energy release rate (MSERR). Three kinds of effects are revealed by parametric studies, i.e., the free-surface effect, the shielding effect and the interference effect, and they are used to interpret the characteristics of COD and MSERR curves. In addition, the effects of shear loading, magnetic loading and electric loading on MSERR are also disclosed, respectively, by varying the corresponding loading factor. 相似文献