全文获取类型
收费全文 | 216篇 |
免费 | 3篇 |
国内免费 | 2篇 |
专业分类
化学 | 116篇 |
力学 | 5篇 |
数学 | 44篇 |
物理学 | 56篇 |
出版年
2022年 | 2篇 |
2021年 | 8篇 |
2020年 | 3篇 |
2019年 | 3篇 |
2018年 | 7篇 |
2017年 | 5篇 |
2016年 | 13篇 |
2015年 | 2篇 |
2014年 | 3篇 |
2013年 | 14篇 |
2012年 | 17篇 |
2011年 | 8篇 |
2010年 | 8篇 |
2009年 | 14篇 |
2008年 | 12篇 |
2007年 | 14篇 |
2006年 | 8篇 |
2005年 | 6篇 |
2004年 | 11篇 |
2003年 | 5篇 |
2002年 | 5篇 |
2001年 | 9篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 4篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1987年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 4篇 |
1972年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有221条查询结果,搜索用时 732 毫秒
31.
32.
We construct three new infinite families of hypohamiltonian graphs having respectively 3k+1 vertices (k?3), 3k vertices (k?5) and 5k vertices (k?4); in particular, we exhibit a hypohamiltonian graph of order 19 and a cubic hypohamiltonian graph of order 20, the existence of which was still in doubt. Using these families, we get a lower bound for the number of non-isomorphic hypohamiltonian graphs of order 3k and 5k. We also give an example of an infinite graph G having no two-way infinite hamiltonian path, but in which every vertex-deleted subgraph G - x has such a path. 相似文献
33.
Turbulent deposition of particles from two-phase flow onto the smooth wall of a tube has been studied theoretically and experimentally. A model is proposed for the deposition motion of large particles based on turbulent diffusion in the core followed by a free flight towards the wall. The theory shows that within the Stokes regime, the dimensionless deposition velocity * depends on Re and only, where u* is the friction velocity, Re is the tube Reynolds number and is the dimensionless particle relaxation time. Deposition data are obtained for air-water droplet flow through a 12.7-mm i.d. acrylic tubing at and 94,600. The proposed theory satisfactorily describes the existing deposition data as well as present measurements, covering a wide range of Re and . 相似文献
34.
DMSO affects the alkaline hydrolysis of acyl-activated anilides through a rate decrease of direct decomposition of the tetrahedral intermediate, a rate increase or decrease, according to basicity of the leaving group, of hydroxide catalysed decomposition of the tetrahedral intermediate, and a preferential orientation toward this step. 相似文献
35.
Viviane Ribeiro Tomaz da Silva 《代数通讯》2013,41(9):3342-3359
Let E be the infinite-dimensional Grassmann algebra over a field F of characteristic zero, and consider L the F-vector space spanned by all generators of E. Let ? l be any fixed automorphism of E of order 2 such that L is an homogeneous subspace. Our goal is to finish the computation of the sequences of ? l -codimensions, by finding its exact value for the unique open case, that is, when the subspace of L corresponding to the eigenvalue 1 is finite-dimensional. As a consequence we get the ?-codimensions for a large amount of arbitrary automorphisms ? of E of order 2. 相似文献
36.
Viviane Pilla Leandro P. Alves Marcos T.T. Pacheco Egberto Munin 《Optics Communications》2008,281(23):5925-5928
Thermo-optical parameters of CdSe/ZnS core-shell nanoparticles suspended in toluene were measured using a thermal lens (TL) technique. TL transient measurements were performed using the mode-mismatched dual-beam (excitation and probe) configuration. A He-Ne laser at λp = 632.8 nm was used as the probe beam and an Ar+ laser (at λe = 514.5 nm) was used as the excitation beam for studies as a function of both core size and concentration of CdSe/ZnS nanocrystals. The fraction thermal load (φ) and radiative quantum efficiencies (η) of the CdSe/ZnS were determined. Dependence on core size (∼2-5 nm) and concentration (∼0.01-0.62 mg/ml) was observed for both φ and η parameters. 相似文献
37.
38.
A vacuum membrane distillation (VMD) model has been developed and validated with experimental data. The model consists of an extended transport model for the VMD process and is able to predict the effects of concentration and temperature polarization on the overall process performance. To validate the model, first it was tested with few experimental case studies from literature [S. Bandini, G.G. Sarti, Heat and mass transport resistances in vacuum membrane distillation per drop, AIChE J. 45 (7) (1999) 1422–1433; K.W. Lawson, D.R. Lloyd, Membrane distillation. I. Module design and performance evaluation using vacuum membrane distillation, J. Membr. Sci. 120 (1996) 111–121; A.M. Urtiaga, G. Ruiz, I. Ortiz, Kinetic analysis of the vacuum membrane distillation of chloroform from aqueous solutions, J. Membr. Sci. 165 (2000) 99–110]. Then the VMD model has been validated with experimental data collected from the recovery of aroma compounds from black currant [R.B. Jørgensen, A.S. Meyer, C. Varming, G. Jonsson, Recovery of volatile aroma compounds from black currant juice by vacuum membrane distillation, J. Food Eng. 64 (2004) 23–31]. In this work, recovery of 12 characteristic volatile aroma compounds from black currant juice has been studied. The simulated results from the VMD model, in terms of aroma concentration in the permeate have been compared with those obtained from laboratory experiments. The validated model has been used to study the effects of various process and membrane parameters on the concentration factor. The physical properties of various aroma compounds have been predicted using group contribution method as a function of temperature. 相似文献
39.
Efthymios I. Ioannidis Terry Z. H. Gani Heather J. Kulik 《Journal of computational chemistry》2016,37(22):2106-2117
We present an automated, open source toolkit for the first‐principles screening and discovery of new inorganic molecules and intermolecular complexes. Challenges remain in the automatic generation of candidate inorganic molecule structures due to the high variability in coordination and bonding, which we overcome through a divide‐and‐conquer tactic that flexibly combines force‐field preoptimization of organic fragments with alignment to first‐principles‐trained metal‐ligand distances. Exploration of chemical space is enabled through random generation of ligands and intermolecular complexes from large chemical databases. We validate the generated structures with the root mean squared (RMS) gradients evaluated from density functional theory (DFT), which are around 0.02 Ha/au across a large 150 molecule test set. Comparison of molSimplify results to full optimization with the universal force field reveals that RMS DFT gradients are improved by 40%. Seamless generation of input files, preparation and execution of electronic structure calculations, and post‐processing for each generated structure aids interpretation of underlying chemical and energetic trends. © 2016 Wiley Periodicals, Inc. 相似文献
40.
Viviane A.S. Falcomer Sebastião S. Lemos Guilherme B.C. Martins Gleison A. Casagrande Robert A. Burrow Ernesto S. Lang 《Polyhedron》2007
Complexes of general formula [CuL4][BF4] (L = benzonitrile – PhCN 2 or phenylacetonitrile – BzCN 3) have been prepared and structurally characterized by NMR spectroscopy and X-ray crystallography. Their structure and reactivity have been compared to the well known [Cu(MeCN)4][BF4] (1). The 63Cu line width and the 63Cu chemical shift have been evaluated by varying the temperature and the concentration of the complex 2 in benzonitrile solutions. The phenylacetonitrile solutions of the complex 3 give extremely broad signals which are beyond detection. Accordingly, compound 3 has been studied by 63Cu MAS NMR spectroscopy. The solution NMR data are consistent to the prevalence of dynamic equilibrium between tetra- and low-coordinated species in both complexes. The X-ray structure of 3 revealed that the copper(I) atom sits in a slightly distorted tetrahedral geometry, surrounded by four BzCN ligands. 相似文献