全文获取类型
收费全文 | 2386篇 |
免费 | 74篇 |
国内免费 | 16篇 |
专业分类
化学 | 1595篇 |
晶体学 | 16篇 |
力学 | 43篇 |
数学 | 466篇 |
物理学 | 356篇 |
出版年
2022年 | 24篇 |
2021年 | 28篇 |
2020年 | 26篇 |
2019年 | 36篇 |
2018年 | 23篇 |
2017年 | 25篇 |
2016年 | 37篇 |
2015年 | 31篇 |
2014年 | 42篇 |
2013年 | 107篇 |
2012年 | 83篇 |
2011年 | 131篇 |
2010年 | 79篇 |
2009年 | 64篇 |
2008年 | 115篇 |
2007年 | 92篇 |
2006年 | 110篇 |
2005年 | 106篇 |
2004年 | 118篇 |
2003年 | 102篇 |
2002年 | 87篇 |
2001年 | 20篇 |
2000年 | 33篇 |
1999年 | 23篇 |
1997年 | 20篇 |
1996年 | 52篇 |
1994年 | 29篇 |
1993年 | 21篇 |
1992年 | 25篇 |
1991年 | 22篇 |
1990年 | 28篇 |
1989年 | 21篇 |
1988年 | 20篇 |
1987年 | 18篇 |
1986年 | 21篇 |
1985年 | 43篇 |
1984年 | 34篇 |
1983年 | 28篇 |
1982年 | 32篇 |
1981年 | 32篇 |
1980年 | 31篇 |
1979年 | 27篇 |
1978年 | 35篇 |
1977年 | 32篇 |
1976年 | 22篇 |
1975年 | 29篇 |
1974年 | 34篇 |
1973年 | 30篇 |
1970年 | 20篇 |
1968年 | 19篇 |
排序方式: 共有2476条查询结果,搜索用时 15 毫秒
101.
Louis B Bushard 《Journal of Differential Equations》1976,21(2):439-443
A comparison theorem and a uniqueness corollary for positive solutions to the equation on the closure of a bounded open set are found. The important hypotheses on the nonlinear coefficients are that each pi is positive and monotone increasing in u while q is monotone decreasing in u. An application is made to equations arising in the theory of chemical reactors. 相似文献
102.
Louis Dressler Hendrik Nicolai Senda Agrebi Florian Ries Amsini Sadiki 《Entropy (Basel, Switzerland)》2022,24(5)
This contribution presents a straightforward strategy to investigate the entropy production in stratified premixed flames. The modeling approach is grounded on a chemistry tabulation strategy, large eddy simulation, and the Eulerian stochastic field method. This enables a combination of a detailed representation of the chemistry with an advanced model for the turbulence chemistry interaction, which is crucial to compute the various sources of exergy losses in combustion systems. First, using detailed reaction kinetic reference simulations in a simplified laminar stratified premixed flame, it is demonstrated that the tabulated chemistry is a suitable approach to compute the various sources of irreversibilities. Thereafter, the effects of the operating conditions on the entropy production are investigated. For this purpose, two operating conditions of the Darmstadt stratified burner with varying levels of shear have been considered. The investigations reveal that the contribution to the entropy production through mixing emerging from the chemical reaction is much larger than the one caused by the stratification. Moreover, it is shown that a stronger shear, realized through a larger Reynolds number, yields higher entropy production through heat, mixing and viscous dissipation and reduces the share by chemical reaction to the total entropy generated. 相似文献
103.
Robert A. Skutnik Louis Lehmann Sergej Püschel-Schlotthauer George Jackson Martin Schoen 《Molecular physics》2019,117(20):2830-2845
ABSTRACTMonte Carlo simulations in the isothermal-isobaric ensemble are used to investigate the formation of an ordered, biaxial nematic phase in a binary mixture of thermotropic liquid crystals. The orientational dependence of the interaction between molecules of each pure component is the same as in the well-known Maier-Saupe model; each pure component of the mixture is therefore capable of forming a uniaxial nematic phase. For the interaction between molecules of different components, we use the same Maier-Saupe model but change the sign of the coupling constant. As a consequence a T-shaped arrangement of these molecules is energetically favoured. The formation of the biaxial phase occurs in two steps. At higher temperatures T, one of the components forms a uniaxial nematic phase whereas the other is in a quasi two-dimensional restricted isotropic liquid state. We develop a simple theoretical model to understand the high degree of (ostensible) nematic order in the latter. At lower T, the second component becomes nematic and then the entire mixture of the two compounds has biaxial symmetry. The biaxial nematic phase does not demix into domains rich in molecules of one or the other species. 相似文献
104.
105.
Maxime Guitet Pinglu Zhang Filipa Marcelo Coralie Tugny Jesús Jimnez‐Barbero Olivier Buriez Christian Amatore Virginie Mouris‐Mansuy Jean‐Philippe Goddard Louis Fensterbank Yongmin Zhang Sylvain Roland Mickaël Mnand Matthieu Sollogoub 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2013,125(28):7354-7359
106.
Back Cover: Rhodium‐Catalyzed Ketone Methylation Using Methanol Under Mild Conditions: Formation of α‐Branched Products (Angew. Chem. Int. Ed. 3/2014)
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
107.
Two efficient syntheses of 3-chloro-7-[(chlorocarbonyl)methoxy]-4-methylcoumarin are described, one utilizing traditional chemistry starting from 3-chloro-7-hydroxy-4-methylcoumarin, while the other uses a novel reagent, sulfuryl chloride/thionyl chloride, in a one-pot reaction starting from 7-(carboxymethoxy)-4-methylcoumarin. 相似文献
108.
Stuart Lipsitz Garrett Fitzmaurice Debajyoti Sinha Nathanael Hevelone Jim Hu Louis L. Nguyen 《Journal of computational and graphical statistics》2017,26(3):734-737
Medical studies increasingly involve a large sample of independent clusters, where the cluster sizes are also large. Our motivating example from the 2010 Nationwide Inpatient Sample (NIS) has 8,001,068 patients and 1049 clusters, with average cluster size of 7627. Consistent parameter estimates can be obtained naively assuming independence, which are inefficient when the intra-cluster correlation (ICC) is high. Efficient generalized estimating equations (GEE) incorporate the ICC and sum all pairs of observations within a cluster when estimating the ICC. For the 2010 NIS, there are 92.6 billion pairs of observations, making summation of pairs computationally prohibitive. We propose a one-step GEE estimator that (1) matches the asymptotic efficiency of the fully iterated GEE; (2) uses a simpler formula to estimate the ICC that avoids summing over all pairs; and (3) completely avoids matrix multiplications and inversions. These three features make the proposed estimator much less computationally intensive, especially with large cluster sizes. A unique contribution of this article is that it expresses the GEE estimating equations incorporating the ICC as a simple sum of vectors and scalars. 相似文献
109.
110.
Dr. Aron J. Huckaba Dr. Aswani Yella Dr. Louis E. McNamara April E. Steen J. Scott Murphy Casey A. Carpenter George D. Puneky Prof. Nathan I. Hammer Prof. Mohammad Khaja Nazeeruddin Prof. Michael Grätzel Prof. Jared H. Delcamp 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(43):15536-15542
Desirable components for dye‐sensitzed solar cell (DSC) sensitizers and fluorescent imaging dyes include strong donating building blocks coupled with well‐balanced acceptor functionalities for absorption beyond the visible range. We have evaluated the effects of increasing acceptor strengths and incorporation of dye morphology controlling groups on molar absorptivity and absorption breadth with indolizine donor‐based dyes. Indolizine‐based D –A and D –π–A sensitizers incorporating bis‐rhodanine, tricyanofuran (TCF), and cyanoacrylic acid functionalities were analyzed for performance in DSC devices. The TCF derivatives were also evaluated as near‐infrared (NIR)‐emissive materials with the AH25 emissions extending past 1000 nm. 相似文献