全文获取类型
收费全文 | 386篇 |
免费 | 9篇 |
国内免费 | 1篇 |
专业分类
化学 | 178篇 |
晶体学 | 8篇 |
力学 | 16篇 |
数学 | 66篇 |
物理学 | 128篇 |
出版年
2022年 | 4篇 |
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 5篇 |
2018年 | 11篇 |
2017年 | 11篇 |
2016年 | 14篇 |
2015年 | 8篇 |
2014年 | 18篇 |
2013年 | 39篇 |
2012年 | 20篇 |
2011年 | 21篇 |
2010年 | 14篇 |
2009年 | 17篇 |
2008年 | 18篇 |
2007年 | 17篇 |
2006年 | 18篇 |
2005年 | 9篇 |
2004年 | 18篇 |
2003年 | 11篇 |
2002年 | 6篇 |
2001年 | 6篇 |
2000年 | 8篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 6篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 8篇 |
1991年 | 3篇 |
1990年 | 17篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 7篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1922年 | 1篇 |
排序方式: 共有396条查询结果,搜索用时 0 毫秒
381.
382.
We present the results of molecular-dynamics simulations of repeated interactions of a realistically-shaped cutting edge with a model, infinitely hard grain. The model edge is composed of several hundred thousand atoms of an fcc metal treated with the Sutton–Chen potential, moving with a constant speed of 20 m s?1. Plastic deformations appearing upon contact with the rigid obstacle are observed and described by means of temperature fields and the atomic slip vector. Preferred slip planes are identified and the normal force experienced by the tool is investigated. The effect of periodic boundary conditions along the z (in-plane) direction is assessed by comparing the results of two simulations, differing only by the simulation box’s length along the z-axis. 相似文献
383.
XMCD studies of magnetic polarization at Mo atoms in CoMo alloy and magnetically coupled Co/Mo multilayers 下载免费PDF全文
Andrzej Wawro Ewelina Milińska Zbigniew Kurant Aleksiej Pietruczik Jarosław Kanak Katharina Ollefs Fabrice Wilhelm Andrei Rogalev Andrzej Maziewski 《Journal of synchrotron radiation》2018,25(5):1400-1407
Magnetic polarization of Mo atoms in Co96Mo4 alloy film and Co/Mo multilayered structures has been studied by X‐ray magnetic circular dichroism. Samples with Mo spacers of two different thicknesses (0.9 nm and 1.8 nm) were investigated. Mo atoms receive a magnetic moment of ?0.21μB in the alloy. In the multilayer with the thinner Mo spacer (dMo = 0.9 nm) the magnetic moment is much smaller (?0.03μB). In both cases the measured induced moment at the Mo site is oriented antiparallel to the moment at the Co atoms. The presence of the induced moment in the Mo spacer coincides with antiferromagnetic coupling between the Co component slabs. In contrast, neither measurable induced moment at the Mo site nor interlayer coupling between the Co layers has been found for the multilayer with the thicker Mo spacer. Possible mechanisms of the coupling associated with the induced moment are discussed in detail. 相似文献
384.
Let E be a non empty set, let P : = E × E,
:= {x × E|x ∈ E},
:= {E × x|x ∈ E}, and
:= {C ∈ 2
P
|∀X ∈
: |C ∩ X| = 1} and let
. Then the quadruple
resp.
is called chain structure resp. maximal chain structure. We consider the maximal chain structure
as an envelope of the chain structure
. Particular chain structures are webs, 2-structures, (coordinatized) affine planes, hyperbola structures or Minkowski planes.
Here we study in detail the groups of automorphisms
,
,
,
related to a maximal chain structure
. The set
of all chains can be turned in a group
such that the subgroup
of
generated by
the left-, by
the right-translations and by ι the inverse map of
is isomorphic to
(cf. (2.14)). 相似文献
385.
Jarosław Błaszczyk Michał W. Wieczorek Andrzej Okruszek Agnieszka Sierzchała Anna Kobylańska Wojciech J. Stec 《Journal of chemical crystallography》1996,26(1):33-42
Two thiophospholane derivatives of cholesterol: 2-cholesteryl-2-thio-1,3,2-oxathiaphospholane (1) and 2-cholesteryl-2-thio-1,3,2-dithiaphospholane (2) were synthesized as new reagents for introducing a cholesteryl moiety at the 5-end of oligonucleotidesvia the phosphorothioate or phosphorodithioate bond. Compounds1 and2 were subjected to structural studies by X-ray methods. Both compounds crystallized in the orthorhombic system, space group P212121,1 witha=6.283(1) Å,b=12.067(1) Å,c=38.983(3) Å,2 witha=6.371(1) Å,b=11.971(1) Å andc=39.502(3) Å. The five-membered heterocyclic rings of both compounds attain a half-chair conformation in the solid state. In structures of1 and2 a disorder of some atoms is observed. The absolute configuration at the phosphorus atom in1 of the components of diastereoisomeric mixture has been established. 相似文献
386.
Within a microscopic approach we show that in the case of an ideal quantum gas enclosed in a slit the Casimir force can be simply expressed in terms of the bulk one-particle density matrix. The corresponding formula, which holds both for bosons and fermions, allows to relate the range of the Casimir force to the bulk correlation length. The low-temperature behavior of the Casimir forces is derived. 相似文献
387.
We show that every symmetric 2-structure ${(P,\mathfrak G_1,\mathfrak G_2,\mathfrak K)}$ of the class (III) [cf. Karzel H et?al. (Result. Math., submitted)] is point symmetric, i.e. any two orthogonal chains ${A,B \in \mathfrak K}$ intersect in exactly one point and that any two points ${a,b \in P}$ have exactly one midpoint m :?=?a * b (with ${\widetilde m(a) = b}$ where ${\widetilde m}$ is the unique symmetry in the point m). ${ \widetilde{P} := \{\widetilde p \ | \ p \in P \}}$ is invariant, i.e. ${\forall a,b \in P : \widetilde a\circ \widetilde b\circ \widetilde a \in \widetilde P}$ . Therefore the pair ${(P,\widetilde{P})}$ is an invariant regular involution set and the loop derivation in a point ${o \in P}$ gives a K-loop (P,?+) uniquely 2-divisible. 相似文献
388.
On-going efforts to improve protein structure prediction stimulate the development of scoring functions and methods for model quality assessment (MQA) that can be used to rank and select the best protein models for further refinement. In this work, sequence-based prediction of relative solvent accessibility (RSA) is employed as a basis for a simple MQA method for soluble proteins, and subsequently extended to the much less explored case of (alpha-helical) membrane proteins. In analogy to soluble proteins, the level of exposure to the lipid of amino acid residues in transmembrane (TM) domains is captured in terms of the relative lipid accessibility (RLA), which is predicted from sequence using low-complexity Support Vector Regression models. On an independent set of 23 TM proteins, the new SVR-based predictor yields correlation coefficient (CC) of 0.56 between the predicted and observed RLA profiles, as opposed to CC of 0.13 for a baseline predictor that utilizes TMLIP2H empirical lipophilicity scale (with standard deviations of about 0.15). A simple MQA approach is then defined by ranking models of membrane proteins in terms of consistency between predicted and observed RLA profiles, as a measure of similarity to the native structure. The new method does not require a set of decoy models to optimize parameters, circumventing current limitations in this regard. Several different sets of models, including those generated by fragment based folding simulations, and decoys obtained by swapping TM helices to mimic errors in template based assignment, are used to assess the new approach. Predicted RLA profiles can be used to successfully discriminate near native models from non-native decoys in most cases, significantly improving the separation of correct and incorrectly folded models compared to a simple baseline approach that utilizes TMLIP2H. As suggested by the robust performance of a simple MQA method for soluble proteins that utilizes more accurate RSA predictions, further significant improvements are likely to be achieved. The steady growth in the number of resolved membrane protein structures is expected to yield enhanced RLA predictions, facilitating further efforts to improve de novo and template based prediction of membrane protein structure. 相似文献
389.
Dr. Jarosław J. Panek Dr. Aneta Jezierska‐Mazzarello Prof. Aleksander Koll Prof. Galina Dovbeshko Dr. Olena Fesenko 《Chemphyschem》2011,12(13):2485-2495
Adsorption of guest molecules on host surfaces can lead to dramatic changes in the spectral properties of the guest. One such effect is surface‐enhanced infrared absorption (SEIRA), observed when the guest is adsorbed on, for example, thin films, metal surfaces, or nanotubes. p‐Nitrobenzoic acid (p‐NBA) exhibits a SEIRA effect when adsorbed on Ag and Au. Herein, the IR spectra of p‐NBA adsorbed on a homemade rough Au surface, recorded in reflection mode with an angle of incidence of 16.5°, are reported. This SEIRA experiment reveals more bands than found by previous SEIRA studies. The intensities of both symmetric and asymmetric COO? and NO2 stretching, in‐plane CH, and C?C ring stretching modes are enhanced. Theoretical models constructed on the basis of density functional theory reveal the binding mode of p‐NBA to gold “particles”. The p‐NBA anion binds to gold much more strongly than the neutral form, and interaction via the carboxylic oxygen atoms is preferred over the nitro group–gold contact. A significant charge transfer during chemisorption is found, which is considered to be crucial in leading to a high SEIRA enhancement factor. 相似文献
390.
Jarosław Spychała 《合成通讯》2013,43(23):2985-2992
Treatment of hexakis(bromomethyl)benzene with a cyclic amine {morpholine, 1‐methylpiperazine, 1‐(2‐hydroxyethyl)piperazine, isonipecotamide, 4‐hydroxypiperidine, 4‐[3‐(4‐piperidyl)propyl]‐1‐piperidineethanol} gave a range of di‐ and trispirocyclic ammonium salts in satisfactory yields (22–62%). Presumably, the electrostatic and repulsion forces play an important role in their formation. The structure in solution and the protonation site have been investigated by NMR and IR spectroscopy. 相似文献