全文获取类型
收费全文 | 642篇 |
免费 | 13篇 |
国内免费 | 4篇 |
专业分类
化学 | 393篇 |
晶体学 | 6篇 |
力学 | 10篇 |
数学 | 79篇 |
物理学 | 171篇 |
出版年
2023年 | 5篇 |
2022年 | 3篇 |
2021年 | 5篇 |
2020年 | 6篇 |
2019年 | 16篇 |
2018年 | 8篇 |
2017年 | 5篇 |
2016年 | 13篇 |
2015年 | 18篇 |
2014年 | 16篇 |
2013年 | 33篇 |
2012年 | 32篇 |
2011年 | 37篇 |
2010年 | 27篇 |
2009年 | 18篇 |
2008年 | 35篇 |
2007年 | 25篇 |
2006年 | 32篇 |
2005年 | 37篇 |
2004年 | 22篇 |
2003年 | 25篇 |
2002年 | 23篇 |
2001年 | 10篇 |
2000年 | 13篇 |
1999年 | 4篇 |
1998年 | 12篇 |
1997年 | 10篇 |
1996年 | 14篇 |
1995年 | 14篇 |
1994年 | 12篇 |
1993年 | 11篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1973年 | 3篇 |
1972年 | 3篇 |
1968年 | 4篇 |
1943年 | 6篇 |
1931年 | 3篇 |
1922年 | 2篇 |
1880年 | 2篇 |
排序方式: 共有659条查询结果,搜索用时 109 毫秒
81.
We calculated highly excited states of the HFCO molecule, comparing results from two methods. In the first method, Van Vleck perturbation theory is used to transform away all off-diagonal couplings except those between nearly degenerate states. This perturbative transformation leads to a matrix representation where eigenvalues are obtained with relatively small matrices. In the second method, variational eigenvalues are obtained by combining the Jacobi-Wilson approach with the block-Davidson scheme. The key ingredient here is a prediagonalized-perturbative scheme applied to a subspace of a curvilinear normal-mode basis set. Comparisons of the two methods provide a critical test of the less time-consuming perturbation theory. Two different coordinate sets are used to test the sensitivity of the results to coordinate choice. Perturbation theory also requires a polynomial fit to the potential. The implications of this restriction are investigated. 相似文献
82.
This article reviews recent advances in mesoscopic physics, namely experimental and theoretical investigations of persistent (equilibrium) currents in normal metal rings. While theory and experiment are consistent in the ballistic regime, theoretical studies so far have not been able to account for the unexpectedly huge currents observed experimentally in disordered (diffusive) samples, in which the elastic mean free path is much less than the circumference of the rings. 相似文献
83.
Emil Daniel Schwab 《代数通讯》2013,41(5):1779-1789
We study the incidence algebra of the reduced standard division category of a combinatorial bisimple inverse monoid [with (E(S), ≤) locally finite], and we describe semigroups of poset type (i.e., a combinatorial inverse semigroup for which the corresponding Möbius category is a poset) as being combinatorial strict inverse semigroups. Up to isomorphism, the only Möbius-division categories are the reduced standard division categories of combinatorial inverse monoids. 相似文献
84.
85.
Multicomponent Self‐Assembly with a Shape‐Persistent N‐Heterotriangulene Macrocycle on Au(111)
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Kang Cui Dr. Florian Schlütter Dr. Oleksandr Ivasenko Dr. Milan Kivala Dr. Matthias G. Schwab Dr. Shern‐Long Lee Dr. Stijn F. L. Mertens Dr. Kazukuni Tahara Prof. Yoshito Tobe Prof. Klaus Müllen Dr. Kunal S. Mali Prof. Steven De Feyter 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(4):1652-1659
Multicomponent network formation by using a shape‐persistent macrocycle ( MC6 ) at the interface between an organic liquid and Au(111) surface is demonstrated. MC6 serves as a versatile building block that can be coadsorbed with a variety of organic molecules based on different types of noncovalent interactions at the liquid–solid interface. Scanning tunneling microscopy (STM) reveals the formation of crystalline bicomponent networks upon codeposition of MC6 with aromatic molecules, such as fullerene (C60) and coronene. Tetracyanoquinodimethane, on the other hand, was found to induce disorder into the MC6 networks by adsorbing on the rim of the macrocycle. Immobilization of MC6 itself was studied in two different noncovalently assembled host networks. MC6 assumed a rather passive role as a guest and simply occupied the host cavities in one network, whereas it induced a structural transition in the other. Finally, the central cavity of MC6 was used to capture C60 in a complex three‐component system. Precise immobilization of organic molecules at discrete locations within multicomponent networks, as demonstrated here, constitutes an important step towards bottom‐up fabrication of functional surface‐based nanostructures. 相似文献
86.
Pascal Röthlisberger Fabienne Levi-Acobas Ivo Sarac Rémy Ricoux Jean-Pierre Mahy Piet Herdewijn Philippe Marlière Marcel Hollenstein 《Tetrahedron letters》2018,59(48):4241-4244
Abasic sites are amongst the most frequent DNA lesions and result from spontaneous hydrolysis of the glycosidic bond or from the removal of damaged nucleobases. These depurination events can also occur on free deoxyribonucleoside triphosphates present in cells and lead to the formation of an abasic site triphosphate of which very little is known. Herein, we report the synthesis and biochemical characterization of the minimal triphosphate dФTP. Unexpectedly, dФTP is tolerated by various DNA polymerases and the incorporation efficiency obeys the A-rule. Single incorporation of dФMP units were also observed opposite abasic sites and the addition of prosthetic molecules mimicking base-pairs do not seem to favor the process. 相似文献
87.
Zeitschrift für Physik A Hadrons and nuclei - Auf der früher gewonnenen Basis wird eine Reihe bisher abseits stehender Beobachtungen — betreffend die Ausbreitung einer Explosion im... 相似文献
88.
Fire retardancy of polymer clay nanocomposites: Is there an influence of the nanomorphology? 总被引:1,自引:0,他引:1
Fabienne Samyn Charafeddine Jama Séverine Bellayer 《Polymer Degradation and Stability》2008,93(11):2019-2024
The obvious aspect of nanodispersion and its role when investigating fire retardancy is not often clearly commented upon in the literature. Polymer clay nanocomposites can exhibit different morphologies and these might have consequences for their fire behaviour. Using solid state NMR to quantify the nanodispersion of organoclay in polyamide-6 (PA-6), we have prepared by melt blending PA-6/clay nanocomposite exhibiting different nanomorphologies. NMR results are consistent with transmission electron microscopy (TEM) images but the advantage of NMR is that it is representative of the whole sample and provides a precise quantification. PA-6 nanocomposites exhibit significant reduction of PHRR but the nanomorphology (exfoliation, intercalation and presence of tactoids) does not play any significant role. In other words, we have clearly shown that if nanodispersion is achieved, polymer/clay nanocomposite should exhibit fire retardant properties. 相似文献
89.
The modeling of reactivity in an ionic liquid is examined with DFT and DFT/MM calculations on the S(N)2 intramolecular rearrangement of the Z-phenylhydrazone of 3-benzoyl-5-phenyl-1,2,4-oxadiazole into 4-benzoylamino-2,5-diphenyl-1,2,3-triazole induced by amines. Experimental research has shown that the reaction occurs in 1-butyl-3-methylimidazolium tetrafluoroborate, and in conventional organic solvents such as acetonitrile with comparable rates. The structure for the reactants, transition states and products for the rate-determining step are optimized, and the energy barrier is computed in three different environments: gas phase, water solvent, and ionic liquid. The results are encouraging in describing the energy barrier in the ionic liquid. A simple model is formulated to explain the effect of the solvent in this particular process, and a procedure to study theoretically the reactivity in an ionic liquid is proposed. 相似文献
90.
The diisopropylphosphanyl-substituted anthracenes i-Pr2P(C14H9) (1a), i-Pr2P(C14H8)Br (2a), and (i-Pr2P)2(C14H8) (3a) and some of their oxidation products were prepared from 9-bromoanthracene and 9,10-dibromoanthracene, respectively. Low-temperature (1)H NMR spectra of the 9-monophosphanyl-substituted anthracenes 1a and 2a are in accordance with a staggered conformer, while above room temperature dynamic processes occur. The low-temperature NMR spectrum of the 9,10-diphosphanylanthracene 3a indicates the presence of two different rotational isomers. The rotational barrier for 1a was determined from variable-temperature (1)H NMR spectra to be 56 kJ mol(-1) (DeltaG(298K)). The crystal structure determinations show the solid-state conformers to be consistent with the prevailing conformer at low temperature. 相似文献