全文获取类型
收费全文 | 2118篇 |
免费 | 413篇 |
国内免费 | 131篇 |
专业分类
化学 | 572篇 |
晶体学 | 21篇 |
力学 | 302篇 |
综合类 | 33篇 |
数学 | 1351篇 |
物理学 | 383篇 |
出版年
2024年 | 1篇 |
2023年 | 8篇 |
2022年 | 33篇 |
2021年 | 47篇 |
2020年 | 44篇 |
2019年 | 99篇 |
2018年 | 77篇 |
2017年 | 118篇 |
2016年 | 130篇 |
2015年 | 137篇 |
2014年 | 118篇 |
2013年 | 235篇 |
2012年 | 112篇 |
2011年 | 125篇 |
2010年 | 122篇 |
2009年 | 121篇 |
2008年 | 118篇 |
2007年 | 128篇 |
2006年 | 114篇 |
2005年 | 115篇 |
2004年 | 92篇 |
2003年 | 101篇 |
2002年 | 81篇 |
2001年 | 81篇 |
2000年 | 75篇 |
1999年 | 89篇 |
1998年 | 41篇 |
1997年 | 35篇 |
1996年 | 15篇 |
1995年 | 5篇 |
1994年 | 8篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 5篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 7篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有2662条查询结果,搜索用时 15 毫秒
121.
The effect of wavelength and relative velocity on the disturbed interface of two‐phase stratified regime is modeled and discussed. To analyze the stability, a small perturbation is imposed on the interface. Growth or decline of the disturbed wave, relative velocity, and surface tension with respect to time will be discussed numerically. Newly developed scheme applied to a two‐dimensional flow field and the governing Navier–Stokes equations in laminar regime are solved. Finite volume method together with non‐staggered curvilinear grid is a very effective approach to capture interface shape with time. Because of the interface shape, for any time advancement, a new grid is performed separately on each stratified field, liquid, and gas regime. The results are compared with the analytical characteristics method and one‐dimensional modeling. This comparison shows that solving the momentum equation including viscosity term leads to physically more realistic results. In addition, the newly developed method is capable of predicting two‐phase stratified flow behavior more precisely than one‐dimensional modeling. It was perceived that the surface tension has an inevitable role in dissipation of interface instability and convergence of the two‐phase flow model. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
122.
Synthesis of poly(isopropenylphenoxy propylene carbonate) and its facile side‐chain functionalization into hydroxy‐polyurethanes
下载免费PDF全文
![点击此处可从《Journal of polymer science. Part A, Polymer chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Chun Chieh Huang Ching Hsuan Lin Shenghong A. Dai 《Journal of polymer science. Part A, Polymer chemistry》2016,54(6):802-808
4‐Isopropenyl phenol ( 4‐IPP ) is a versatile dual functional intermediate that can be prepared readily from bisphenol‐A ( BPA ). Through etherification with epichlorohydrin to the phenolic group of 4‐IPP , it can be converted into 4‐isopropenyl phenyl glycidyl ether ( IPGE ). On further reaction with carbon dioxide in the presence of tetra‐n‐butyl ammonium bromide ( TBAB ) as the catalyst, IPGE was transformed into 4‐isopropenylphenoxy propylene carbonate ( IPPC ) in 90% yield. Cationic polymerization of IPPC with strong acid such as trifluoromethanesulfonic acid or boron trifluoride diethyl etherate as the catalyst at ?40 °C gave a linear poly(isopropenylphenoxy propylene carbonate), poly( IPPC ), with multicyclic carbonate groups substituted uniformly at the side‐chains of the polymer. The cyclic carbonate groups of poly( IPPC ) were further reacted with different aliphatic amines and diamines resulting in formation of polymers with hydroxy‐polyurethane on side‐chains. Syntheses, characterizations of poly( IPPC ) and its conversion into hydroxy‐polyurethane crosslinked polymers were presented. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 802–808 相似文献
123.
124.
Pilot-Wave Theory and Financial Option Pricing 总被引:1,自引:0,他引:1
This paper tries to argue why pilot-wave theory could be of use in financial economics. We introduce the notion of information
wave. We consider a stochastic guidance equation and part of the drift term of that equation makes reference to the phase
of the wave. In order to embed information in financial option pricing we could use such a drift. We also briefly argue how
we could embed information in the pricing kernel of the option price.
PACS: 03, 89.65.Gh. 相似文献
125.
To Fu Ma 《Mathematical Methods in the Applied Sciences》2001,24(8):583-594
In this paper, we study the equation under non‐linear boundary conditions which model the vibrations of a beam clamped at x=0 and supported by a non‐linear bearing at x=L. By adding only one damping mechanism at x=L, we prove the existence of a global solution and exponential decay of the energy. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
126.
Let a open subset of
n
, n3, and
an open. Existence and unicity are proved for the Dirichlet problem
It is assumed that the linear part of satisfy the conditions of Hervé, (·,u,u): ××
n
satisfy Carathéodory's condition and structure conditions (H1), (H2) and (H3) below. Let H denote the sheaf of L-solutions, we prove that (,H) is a nonlinear Bauer harmonic space. 相似文献
127.
高亮度白光LED用外延片的新进展 总被引:5,自引:0,他引:5
文章首先介绍了发光二极管(LED)的内量子效率、外量子效率的基本概念和提高量子效率的基本方法,接着对LED外延的结构和方法做了简要介绍.文章的第三和第四部分则着重介绍了提高内、外量子效率的外延方法,这些方法包括外延结构的优化,侧向外延生长,SiC和GaN衬底的生长,AIInGaN四元系有源区生长,非极性面、半极性面的外延,表面粗化结构生长,图形化二次外延结构.图形化蓝宝石衬底上的外延,提高载流子注入效率的结构和组分设计.文章的第五部分则介绍了基于可靠性和成本考虑的其他新型外延结构,第六部分介绍了提高LED可靠性的外延方法.最后得出结论:采用非极性面的GaN衬底,生长优化的LED结构,并结合光子晶体技术,可望取得突破性进展. 相似文献
128.
Based on the careful analysis of the definition of arbitrage portfolio and its return, the author presents a mean–variance analysis of the return of arbitrage portfolios, which implies that Korkie and Turtle's results ( B. Korkie, H.J. Turtle, A mean–variance analysis of self-financing portfolios, Manage. Sci. 48 (2002) 427–443) are misleading. A practical example is given to show the difference between the arbitrage portfolio frontier and the usual portfolio frontier. 相似文献
129.
This paper presents a local domain‐free discretization (DFD) method for the simulation of unsteady flows over moving bodies governed by the incompressible Navier–Stokes equations. The discretization strategy of DFD is that the discrete form of partial differential equations at an interior point may involve some points outside the solution domain. All the mesh points are classified as interior points, exterior dependent points and exterior independent points. The functional values at the exterior dependent points are updated at each time step by the approximate form of solution near the boundary. When the body is moving, only the status of points is changed and the mesh can stay fixed. The issue of ‘freshly cleared nodes/cells’ encountered in usual sharp interface methods does not pose any particular difficulty in the presented method. The Galerkin finite‐element approximation is used for spatial discretization, and the discrete equations are integrated in time via a dual‐time‐stepping scheme based on artificial compressibility. In order to validate the present method for moving‐boundary flow problems, two groups of flow phenomena have been simulated: (1) flows over a fixed circular cylinder, a harmonic in‐line oscillating cylinder in fluid at rest and a transversely oscillating cylinder in uniform flow; (2) flows over a pure pitching airfoil, a heaving–pitching airfoil and a deforming airfoil. The predictions show good agreement with the published numerical results or experimental data. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
130.
Polyethylene terephthalates (PETs) with well‐defined chemical structures were prepared by molecular design, and the effect of the chemical structure on the physical properties of PET was investigated. Hydroxyl‐group end‐capped PETs with ηinh = 0.4–0.6 dL/g exhibited a viscosity behavior similar to Bingham fluids, although other PETs with similar molecular weights (MWs) showed Newtonian flow behavior. This rheological feature was more noticeable for hydroxyl‐group end‐capped branched PETs. In addition, hydroxyl‐group end‐capped branched PETs became solidlike from 80 rad/s as the frequency was increased. On the other hand, hydroxyl end‐capped linear PETs showed a noticeable viscoelastic transition peak around 20 rad/s. High MW linear and branched PETs with ηinh ≥ 0.9 prepared by multistep synthesis showed non‐Newtonian fluid behavior. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 1027–1035, 2001 相似文献