全文获取类型
收费全文 | 7065篇 |
免费 | 150篇 |
国内免费 | 86篇 |
专业分类
化学 | 4292篇 |
晶体学 | 76篇 |
力学 | 153篇 |
数学 | 1699篇 |
物理学 | 1081篇 |
出版年
2020年 | 68篇 |
2019年 | 59篇 |
2018年 | 79篇 |
2017年 | 47篇 |
2016年 | 132篇 |
2015年 | 104篇 |
2014年 | 120篇 |
2013年 | 404篇 |
2012年 | 315篇 |
2011年 | 356篇 |
2010年 | 229篇 |
2009年 | 200篇 |
2008年 | 321篇 |
2007年 | 319篇 |
2006年 | 383篇 |
2005年 | 363篇 |
2004年 | 321篇 |
2003年 | 269篇 |
2002年 | 239篇 |
2001年 | 72篇 |
2000年 | 58篇 |
1999年 | 70篇 |
1998年 | 71篇 |
1997年 | 85篇 |
1996年 | 124篇 |
1995年 | 86篇 |
1994年 | 79篇 |
1993年 | 75篇 |
1992年 | 82篇 |
1991年 | 77篇 |
1990年 | 63篇 |
1989年 | 60篇 |
1988年 | 57篇 |
1987年 | 71篇 |
1986年 | 59篇 |
1985年 | 104篇 |
1984年 | 119篇 |
1983年 | 86篇 |
1982年 | 92篇 |
1981年 | 118篇 |
1980年 | 129篇 |
1979年 | 96篇 |
1978年 | 105篇 |
1977年 | 80篇 |
1976年 | 90篇 |
1975年 | 102篇 |
1974年 | 93篇 |
1973年 | 92篇 |
1972年 | 49篇 |
1971年 | 42篇 |
排序方式: 共有7301条查询结果,搜索用时 15 毫秒
1.
Golumbic Martin Charles Hoffman Frederick Rosen Zvi 《Journal of Algebraic Combinatorics》2022,55(1):1-3
Journal of Algebraic Combinatorics - 相似文献
2.
Structural Chemistry - Boronic acids, R–B(OH)2, play an important role in synthetic, biological, medicinal, and materials chemistry. Borinic acids, R–BH(OH), find relevance in similar... 相似文献
3.
We consider the problem of optimizing heat transport through an incompressible fluid layer. Modeling passive scalar transport by advection-diffusion, we maximize the mean rate of total transport by a divergence-free velocity field. Subject to various boundary conditions and intensity constraints, we prove that the maximal rate of transport scales linearly in the r.m.s. kinetic energy and, up to possible logarithmic corrections, as the one-third power of the mean enstrophy in the advective regime. This makes rigorous a previous prediction on the near optimality of convection rolls for energy-constrained transport. On the other hand, optimal designs for enstrophy-constrained transport are significantly more difficult to describe: we introduce a “branching” flow design with an unbounded number of degrees of freedom and prove it achieves nearly optimal transport. The main technical tool behind these results is a variational principle for evaluating the transport of candidate designs. The principle admits dual formulations for bounding transport from above and below. While the upper bound is closely related to the “background method,” the lower bound reveals a connection between the optimal design problems considered herein and other apparently related model problems from mathematical materials science. These connections serve to motivate designs. © 2019 Wiley Periodicals, Inc. 相似文献
4.
Dr. Zhao Liu Prof. Dr. Charles C. Sorrell Dr. Pramod Koshy Dr. Judy N. Hart 《Chemphyschem》2019,20(16):2074-2081
Methanol decomposition is a promising method for hydrogen production. However, the performance of current catalysts for this process is not sufficient for commercial applications. In this work, methanol adsorption on the CeO2 low-index surfaces is studied by density functional theory (DFT). The results show that methanol always dissociates spontaneously on the (100) surface, whereas dissociation on the (110) surface is site-selective; dissociation does not occur at all on the (111) surface, where only weak physisorption is found. The results confirm that surfaces with higher energies are more catalytically active. Analysis of the surface geometries shows that the dominant factors for the dissociation of methanol are the degree of undercoordination and the charges of the surface ions. The adsorption energy of each methanol molecule decreases with increasing coverage and there is a transition threshold between dissociative and associative adsorption. The present work indicates that a strategy to design catalysts with high activity is to maximize exposure of surfaces on which the ions have a high degree of undercoordination and a strong tendency to donate/accept electrons. The results demonstrate the importance of appropriately selecting and controlling exposed facets and particle morphology for optimizing catalyst performance. 相似文献
5.
6.
Transition Metal Chemistry - (η5-Dp)Ru(PPh3)2H (Dp?=?C8H9?, 1,2-dihydropentalenyl) was synthesized in 90% yield by reaction of (η5-Dp)Ru(PPh3)2Cl with sodium formate.... 相似文献
7.
Dr. Waqar Rizvi Naxhije Berisha Dr. Christopher Farley Dr. N. V. S. Dinesh K. Bhupathiraju Dr. Chrysafis Andreou Emaad Khwaja German V. Fuentes Dr. Moritz F. Kircher Dr. Ruomei Gao Dr. Charles Michael Drain 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(64):14517-14521
Distortion of nominally planar phthalocyanine macrocycles affects the excited state dynamics in that most of the excited-state energy decays through internal conversion. A click-type annulation reaction on a perfluorophthalocyanine platform appending a seven-membered ring to the β-positions on one or more of the isoindoles distorts the macrocycle and modulates solubility. The distorted derivative enables photoacoustic imaging, photothermal effects, and strong surface-enhanced resonance Raman signals. 相似文献
8.
Model reduction techniques such as Proper Generalized Decomposition (PGD) are decision-making tools that are about to revolutionize many domains. Unfortunately, their computation is still problematic for problems involving many parameters, for which one has to face the “curse of dimensionality”. An answer to this challenge is given in solid mechanics by the so-called “parameter-multiscale PGD”, which is based on Saint-Venant's principle. In this article, a model problem composed of up to a thousand parameters is presented, showing that the method is able to overcome the “curse of dimensionality”. 相似文献
9.
Rational design of methacrylate monomers containing oxadiazole moieties for single‐layer organic light emitting devices 下载免费PDF全文
Bogdan Zdyrko Yuriy Bandera Volodymyr Tsyalkovsky Christopher F. Huebner Jamie A. Shetzline Parul Rungta Ryan D. Roeder Charles Tonkin Stephen E. Creager Stephen H. Foulger 《Journal of Polymer Science.Polymer Physics》2015,53(23):1663-1673
Methacrylate derived monomers functionalized with pendant oxadiazole moieties were synthesized and copolymerized with carbazole containing monomers to form polymers with electron and hole transporting fragments in the same molecule. Substituents on the oxidazole moiety were varied with the purpose of bandgap tuning and performance optimization when employed in single‐layer organic light emitting devices (OLED). Quantum mechanical calculations of the HOMO‐LUMO levels of the oxidazole derivatives were used to down‐select promising candidates for chemical synthesis and testing in single‐layer OLEDs. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1663–1673 相似文献