全文获取类型
收费全文 | 1726篇 |
免费 | 39篇 |
国内免费 | 12篇 |
专业分类
化学 | 1070篇 |
晶体学 | 8篇 |
力学 | 77篇 |
数学 | 186篇 |
物理学 | 436篇 |
出版年
2021年 | 11篇 |
2020年 | 18篇 |
2019年 | 15篇 |
2016年 | 24篇 |
2015年 | 14篇 |
2014年 | 24篇 |
2013年 | 74篇 |
2012年 | 68篇 |
2011年 | 116篇 |
2010年 | 45篇 |
2009年 | 52篇 |
2008年 | 82篇 |
2007年 | 87篇 |
2006年 | 82篇 |
2005年 | 86篇 |
2004年 | 67篇 |
2003年 | 57篇 |
2002年 | 56篇 |
2001年 | 32篇 |
2000年 | 34篇 |
1999年 | 23篇 |
1998年 | 21篇 |
1997年 | 23篇 |
1996年 | 21篇 |
1995年 | 16篇 |
1994年 | 23篇 |
1993年 | 16篇 |
1992年 | 25篇 |
1991年 | 23篇 |
1990年 | 29篇 |
1989年 | 22篇 |
1988年 | 26篇 |
1987年 | 23篇 |
1986年 | 23篇 |
1985年 | 32篇 |
1984年 | 23篇 |
1983年 | 22篇 |
1982年 | 17篇 |
1981年 | 21篇 |
1980年 | 20篇 |
1979年 | 24篇 |
1978年 | 23篇 |
1977年 | 19篇 |
1976年 | 20篇 |
1975年 | 25篇 |
1974年 | 12篇 |
1973年 | 29篇 |
1972年 | 10篇 |
1970年 | 12篇 |
1967年 | 10篇 |
排序方式: 共有1777条查询结果,搜索用时 171 毫秒
81.
Molecular organization in MAPLE‐deposited conjugated polymer thin films and the implications for carrier transport characteristics 下载免费PDF全文
Ban Xuan Dong Anton Li Joseph Strzalka Gila E. Stein Peter F. Green 《Journal of Polymer Science.Polymer Physics》2017,55(1):39-48
The morphological structure of poly(3‐hexylthiophene) (P3HT) thin films deposited by both Matrix Assisted Pulsed Laser Evaporation (MAPLE) and solution spin‐casting methods are investigated. The MAPLE samples possessed a higher degree of disorder, with random orientations of polymer crystallites along the side‐chain stacking, π–π stacking, and conjugated backbone directions. Moreover, the average molecular orientations and relative degrees of crystallinity of MAPLE‐deposited polymer films are insensitive to the chemistries of the substrates onto which they were deposited; this is in stark contrast to the films prepared by the conventional spin‐casting technique. Despite the seemingly unfavorable molecular orientations and the highly disordered morphologies, the in‐plane charge carrier transport characteristics of the MAPLE samples are comparable to those of spin‐cast samples, exhibiting similar transport activation energies (56 vs. 54 meV) to those reported in the literature for high mobility polymers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 39–48 相似文献
82.
Jie Ju Yu Jin Li Jian Rong Gao Jian Hong Jia Liang Han Wei Jian Sheng Yi Xia Jia 《中国化学快报》2011,22(4):382-384
An aqueous solution of hydrogen peroxide and hydrogen bromide illuminated by a 60 W incandescent light bulb serves as a source of bromine radicals.Various substituted toluenes(NO2,Cl,Br,H,CH3) were high selectively brominated at the benzyl position for monobromination in CH2C12 at ice water with catalyst free.This simple but effective bromination of toluene derivatives with an aqueous H2O2-HBr system is characterized with the use of inexpensive reagents and a lower impact on the environment, which make it a good alternative to the existing bromination methods. 相似文献
83.
84.
85.
The Effect of Alcohol and Carbonyl Functional Groups on the Competition between Unimolecular Decomposition and Isomerization in C4 and C5 Alkoxy Radicals 下载免费PDF全文
Presented here are computed rates for the thermal unimolecular decomposition of a variety of alkoxy radicals with four‐ and five‐carbon length backbones. Three classes of molecules are examined: alkoxy radicals with saturated hydrocarbon backbones, those with alcohol functional groups, and those with carbonyl functional groups. The chosen species represent many of those found during the combustion of fossil fuels as well as bio‐derived alternatives. Density functional theory calculations were benchmarked against higher level coupled cluster calculations and used to explore the potential energy surfaces of these systems. Transition state theory was used to calculate high‐pressure limit rate coefficients of all radical intermediates in the regimes relevant to atmospheric chemistry and combustion. We show that the assumption that alkoxy radicals quickly decompose via β‐scission to aldehydes and other radicals is not valid for some of the alkoxy radicals investigated in this work. We further illustrate how intra‐H migrations in larger alkoxy radicals with carbonyl and alcohol functional groups can dominate unimolecular decomposition under combustion and atmospheric relevant conditions. Finally, we discuss why carbonyl groups can increase or decrease intra‐H migration barriers depending on their location relative to the transferring H‐atom. 相似文献
86.
Andrew Gomm Dr. William Lewis Dr. Anthony P. Green Dr. Elaine O'Reilly 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(36):12692-12695
The application of ω‐transaminase biocatalysts for the synthesis of optically pure chiral amines presents a number of challenges, including difficulties associated with displacing the challenging reaction equilibria. Herein, we report a highly effective approach using low equivalents of the new diamine donor, cadaverine, which enables high conversions of challenging substrates to the corresponding chiral amines in excellent ee. This approach paves the way for the design of self‐sufficient fermentation processes combining transaminase biotransformations with existing strategies for cadaverine production by decarboxylation of endogenous lysine. 相似文献
87.
R.M. Green 《Journal of Algebraic Combinatorics》2002,15(3):241-252
We introduce the notion of 321-avoiding permutations in the affine Weyl group W of type A
n – 1 by considering the group as a George group (in the sense of Eriksson and Eriksson). This enables us to generalize a result of Billey, Jockusch and Stanley to show that the 321-avoiding permutations in W coincide with the set of fully commutative elements; in other words, any two reduced expressions for a 321-avoiding element of W (considered as a Coxeter group) may be obtained from each other by repeated applications of short braid relations.Using Shi's characterization of the Kazhdan–Lusztig cells in the group W, we use our main result to show that the fully commutative elements of W form a union of Kazhdan–Lusztig cells. This phenomenon has been studied by the author and J. Losonczy for finite Coxeter groups, and is interesting partly because it allows certain structure constants for the Kazhdan–Lusztig basis of the associated Hecke algebra to be computed combinatorially.We also show how some of our results can be generalized to a larger group of permutations, the extended affine Weyl group associated to GL
n
() 相似文献
88.
89.
The substrate is shown to induce substantial ordering in diblock copolymer thin films above the bulk order-disorder transition
(ODT) where, thermodynamically, a phase mixed state is favored. Initially, uniform films reorganize to form a hierarchy of
transient surface patterns and stable film thicknesses that depend on the initial film thickness and on the substrate. Self-consistent
field calculations of the free energy of the system for different situations, depending on the relative tendency for the different
block components to be attracted to the substrate and/or free surface, provide an explanation of the formation of the stable
film thicknesses. A continuum picture proposed earlier by Brochard et al.rovides an explanation of the wetting characteristics of this system. In some cases the ordering destabilizes the film so
that dewetting occurs (wetting autophobicity), whereas in other cases the surface ordering results in a kinetic stabilization
of a film that would otherwise dewet.
Received 3 August 2001 and Received in final form 1 November 2001 相似文献
90.
Düffels A Green LG Ley SV Miller AD 《Chemistry (Weinheim an der Bergstrasse, Germany)》2000,6(8):1416-1430
The concise synthesis of five biantennary oligomannose neoglycolipids is presented. Employing a strategy based on the principles of reactivity tuning and orthogonal activation, the oligomannose moieties, isolated from the glycoprotein 63 of the parasite Leishmania mexicana amazonensis, were rapidly assembled taking advantage of common structural motifs found in these N-glycans. Deprotection of all structures was achieved in high yield by hydrogenolysis. The deprotected glycoconjugates were subsequently coupled to a cholesteroldiamine derivative using diethylsquarate as a linker. The resulting neoglycolipids will be used as additives to cationic liposome formulations in the active targeting of liposomes to macrophages. 相似文献