全文获取类型
收费全文 | 1803篇 |
免费 | 220篇 |
国内免费 | 136篇 |
专业分类
化学 | 255篇 |
晶体学 | 18篇 |
力学 | 123篇 |
综合类 | 24篇 |
数学 | 1045篇 |
物理学 | 694篇 |
出版年
2023年 | 21篇 |
2022年 | 29篇 |
2021年 | 31篇 |
2020年 | 39篇 |
2019年 | 48篇 |
2018年 | 39篇 |
2017年 | 47篇 |
2016年 | 58篇 |
2015年 | 35篇 |
2014年 | 94篇 |
2013年 | 122篇 |
2012年 | 90篇 |
2011年 | 96篇 |
2010年 | 90篇 |
2009年 | 143篇 |
2008年 | 122篇 |
2007年 | 125篇 |
2006年 | 118篇 |
2005年 | 95篇 |
2004年 | 73篇 |
2003年 | 71篇 |
2002年 | 64篇 |
2001年 | 53篇 |
2000年 | 58篇 |
1999年 | 53篇 |
1998年 | 46篇 |
1997年 | 46篇 |
1996年 | 36篇 |
1995年 | 35篇 |
1994年 | 23篇 |
1993年 | 20篇 |
1992年 | 11篇 |
1991年 | 13篇 |
1990年 | 13篇 |
1989年 | 8篇 |
1988年 | 13篇 |
1987年 | 9篇 |
1986年 | 4篇 |
1985年 | 18篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1971年 | 2篇 |
排序方式: 共有2159条查询结果,搜索用时 31 毫秒
61.
《Operations Research Letters》2022,50(5):541-547
We consider two-stage recourse models with integer restrictions in the second stage. These models are typically non-convex and hence, hard to solve. There exist convex approximations of these models with accompanying error bounds. However, it is unclear how these error bounds depend on the distributions of the second-stage cost vector q. In this paper, we derive parametric error bounds whose dependence on the distribution of q is explicit: they scale linearly in the expected value of the -norm of q. 相似文献
62.
Prof. Dr. René T. Boeré Christoph Bolli Prof. Dr. Maik Finze Dr. Alexander Himmelspach Prof. Dr. Carsten Knapp Dr. Tracey L. Roemmele 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(5):1784-1795
The range of electrochemical stability of a series of weakly coordinating halogenated (Hal=F, Cl, Br, I) 1‐carba‐closo‐dodecaborate anions, [1‐R‐CB11X5Y6]? (R=H, Me; X=H, Hal, Me; Y=Hal), has been established by using quantum chemical calculations and electrochemical methods. The structures of the neutral and dianionic radicals, as well as the anions, have been optimized by using DFT calculations at the PBE0/def2‐TZVPP level. The calculated structures are in good agreement with existing experimental data and with previous calculations. Their gas‐phase ionization energies and electron affinities were calculated based on their optimized structures and were compared with experimental (cyclic and square‐wave) voltammetry data. Electrochemical oxidation was performed in MeCN at room temperature and in liquid sulfur dioxide at lower temperatures. All of the anions show a very high resistance to the onset of oxidation (2.15–2.85 V versus Fc0/+), with only a minor dependence of the oxidation potential on the different halogen substituents. In contrast, the reduction potentials in MeCN are strongly substituent dependent (?1.93 to ?3.32 V versus Fc0/+). The calculated ionization energies and electron affinities correlate well with the experimental redox potentials, which provide important verification of the thermodynamic validity of the mostly irreversible redox processes that are observed for this series. The large electrochemical windows that are afforded by these anions indicate their suitability for electrochemical applications, for example, as supporting electrolytes. 相似文献
63.
64.
We use different determinantal Hartree-Fock (HF) wave functions to calculate true variational upper bounds for the ground
state energy of N spin-half fermions in volume V
0, with mass m, electric charge zero, and magnetic moment μ, interacting through magnetic dipole-dipole interaction. We find that at high
densities when the average interparticle distance r
0 becomes small compared to the magnetic length r
m ≡ 2mμ2/ħ2, a ferromagnetic state with spheroidal occupation function n
↑(), involving quadrupolar deformation, gives a lower upper bound compared to the variational energy for the uniform paramagnetic
state or for the state with dipolar deformation. This system is unstable towards infinite density collapse, but we show explicitly
that a suitable short-range repulsive (hard core) interaction of strength U
0 and range a can stop this collapse. The existence of a stable equilibrium high density ferromagnetic state with spheroidal occupation
function is possible as long as the ratio of coupling constants Γcm ≡ (U
0
a
3/μ2) is not very small compared to 1.
相似文献
65.
Shuichi Ebisawa Takuro Tsutsumi Tetsuya Taketsugu 《Journal of computational chemistry》2021,42(1):27-39
A mathematical aspect of the anharmonic downward distortion following (ADDF) path is discussed. The ADDF method is utilized as an automated reaction path search method, which can explore transition state geometries on a potential energy surface from a potential minimum. We show that the maximum number of the ADD stationary paths intersecting the potential minimum is 2f + 1 ? 2 , where f denotes the degree of freedom of the system. We also show that the bifurcation of the ADD stationary path is essential to detect all the transition states connected from a given minimum. The ADDF computation is demonstrated for a H2O molecule in which pitchfork bifurcation is observed. 相似文献
66.
Dr. Philip Junker Alicia Rey Planells Prof. Dr. Arturo Espinosa Ferao Prof. Dr. Rainer Streubel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(36):9350-9359
Several phosphaquinodimethanes and their M(CO)5 complexes (M=Cr, Mo, W) and model derivatives have been theoretically investigated regarding the quest of non-innocence. Computed structural and electronic properties of the P-Me/NH2 substituted phosphaquinodimethanes and tungsten complexes revealed an interesting non-innocent ligand behaviour for the radical anion complexes with distonic ion character and a strong rearomatization of the middle phenyl ring. The latter was further probed taking also geometric aromaticity (HOMA) and quinoid distortion parameters (HOMQc) into account, as well as NICS(1). Furthermore, the effect of the P-substitution was investigated for real (or plausible) complexes and their free ligands focusing on the resulting aromaticity at the middle phenyl ring and vertical one-electron redox processes. The best picture of ligand engagement in redox changes was provided by representing NICS(1) values versus HOMA and the new geometric distortion parameter HOMQc8. 相似文献
67.
将遥感技术应用到测绘当中是现代地质测绘技术的发展趋势,随着光学载荷分辨率的不断提高,遥感测绘已经成为社会发展和国民经济发展的重要保障。光学载荷决定了测绘空间遥感器的分辨率、测绘精度、卫星平台体积与重量,是遥感器的核心部分。本文对高成像质量透射光学系统、同轴三反光学系统、离轴三反系统等常用的空间遥感测绘光学系统的结构形式和光学性能分别进行了介绍,并对处于研发阶段的新型空间反射光学系统的结构形式和光学性能进行了展望。分析认为,根据不同的应用环境和技术指标,合理选用不同种类的遥感测绘光学系统,可以最大程度利用平台资源,满足遥感测绘需求。 相似文献
68.
Adam Jaffe Stephanie A. Mack Yu Lin Wendy L. Mao Jeffrey B. Neaton Hemamala I. Karunadasa 《Angewandte Chemie (International ed. in English)》2020,59(10):4017-4022
We show that the onset pressure for appreciable conductivity in layered copper‐halide perovskites can decrease by ca. 50 GPa upon replacement of Cl with Br. Layered Cu–Cl perovskites require pressures >50 GPa to show a conductivity of 10?4 S cm?1, whereas here a Cu–Br congener, (EA)2CuBr4 (EA=ethylammonium), exhibits conductivity as high as 2×10?3 S cm?1 at only 2.6 GPa, and 0.17 S cm?1 at 59 GPa. Substitution of higher‐energy Br 4p for Cl 3p orbitals lowers the charge‐transfer band gap of the perovskite by 0.9 eV. This 1.7 eV band gap decreases to 0.3 eV at 65 GPa. High‐pressure X‐ray diffraction, optical absorption, and transport measurements, and density functional theory calculations allow us to track compression‐induced structural and electronic changes. The notable enhancement of the Br perovskite's electronic response to pressure may be attributed to more diffuse Br valence orbitals relative to Cl orbitals. This work brings the compression‐induced conductivity of Cu‐halide perovskites to more technologically accessible pressures. 相似文献
69.
70.
Consider K ≥ 2 independent copies of the random walk on the symmetric group SN starting from the identity and generated by the products of either independent uniform transpositions or independent uniform neighbor transpositions. At any time $n\in \mathbb{N}$, let Gn be the subgroup of SN generated by the K positions of the chains. In the uniform transposition model, we prove that there is a cut‐off phenomenon at time N ln(N)/(2K) for the non‐existence of fixed point of Gn and for the transitivity of Gn, thus showing that these properties occur before the chains have reached equilibrium. In the uniform neighbor transposition model, a transition for the non‐existence of a fixed point of Gn appears at time of order $N^{1+\frac{2}{K}}$ (at least for K ≥ 3), but there is no cut‐off phenomenon. In the latter model, we recover a cut‐off phenomenon for the non‐existence of a fixed point at a time proportional to N by allowing the number K to be proportional to ln(N). The main tools of the proofs are spectral analysis and coupling techniques. © 2011 Wiley Periodicals, Inc. Random Struct. Alg., 2012 相似文献