全文获取类型
收费全文 | 1116篇 |
免费 | 11篇 |
国内免费 | 5篇 |
专业分类
化学 | 499篇 |
晶体学 | 6篇 |
力学 | 37篇 |
数学 | 187篇 |
物理学 | 403篇 |
出版年
2021年 | 7篇 |
2019年 | 9篇 |
2017年 | 10篇 |
2016年 | 23篇 |
2015年 | 7篇 |
2014年 | 23篇 |
2013年 | 58篇 |
2012年 | 37篇 |
2011年 | 48篇 |
2010年 | 31篇 |
2009年 | 29篇 |
2008年 | 37篇 |
2007年 | 42篇 |
2006年 | 49篇 |
2005年 | 40篇 |
2004年 | 39篇 |
2003年 | 41篇 |
2002年 | 33篇 |
2001年 | 38篇 |
2000年 | 26篇 |
1999年 | 15篇 |
1998年 | 17篇 |
1997年 | 15篇 |
1996年 | 23篇 |
1995年 | 16篇 |
1994年 | 19篇 |
1993年 | 19篇 |
1992年 | 24篇 |
1991年 | 11篇 |
1990年 | 13篇 |
1989年 | 14篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1985年 | 19篇 |
1984年 | 14篇 |
1983年 | 19篇 |
1982年 | 19篇 |
1981年 | 24篇 |
1980年 | 21篇 |
1979年 | 8篇 |
1978年 | 18篇 |
1977年 | 20篇 |
1976年 | 14篇 |
1975年 | 11篇 |
1974年 | 16篇 |
1973年 | 11篇 |
1972年 | 8篇 |
1971年 | 8篇 |
1967年 | 7篇 |
排序方式: 共有1132条查询结果,搜索用时 359 毫秒
961.
Alizadeh E Gschliesser D Bartl P Hager M Edtbauer A Vizcaino V Mauracher A Probst M Märk TD Ptasińska S Mason NJ Denifl S Scheier P 《The Journal of chemical physics》2011,134(5):054305
Dissociative electron attachment to dialanine and alanine anhydride has been studied in the gas phase utilizing a double focusing two sector field mass spectrometer. We show that low-energy electrons (i.e., electrons with kinetic energies from near zero up to 13 eV) attach to these molecules and subsequently dissociate to form a number of anionic fragments. Anion efficiency curves are recorded for the most abundant anions by measuring the ion yield as a function of the incident electron energy. The present experiments show that as for single amino acids (M), e.g., glycine, alanine, valine, and proline, the dehydrogenated closed shell anion (M-H)(-) is the most dominant reaction product. The interpretation of the experiments is aided by quantum chemical calculations based on density functional theory, by which the electrostatic potential and molecular orbitals are calculated and the initial electron attachment process prior to dissociation is investigated. 相似文献
962.
Nanodroplets containing mixtures of silicone oil and squalene are dispersed in a simple aqueous surfactant solution, quenched in liquid ethane, and examined using cryogenic transmission electron microscopy (CTEM). Depending on the phase of ice that forms around the nanodroplets and on the composition of the oil mixture, nanoinclusions can be observed inside oil nanodroplets, independent of surfactant type. Our observations suggest that these nanoinclusions arise from nucleation of vapor cavities as the water freezes and expands while the oil remains liquid during the quench. 相似文献
963.
SJ Harley HE Mason JG McAlpin RD Britt WH Casey 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(34):10476-10479
Beneath the sheets: (31) P?NMR data suggests that phosphates are liberated freely in the interlayer of a cobalt-hydroxide water-oxidation catalyst. The cobalt-hydroxide sheets are separated by an interlayer region with water, counterions and phosphate, which help to shuttle protons as the layer develops charge. 相似文献
964.
Mason K Chang J Prescimone A Garlatti E Carretta S Tasker PA Brechin EK 《Dalton transactions (Cambridge, England : 2003)》2012,41(29):8777-8785
Strapping two salicylaldoxime units together with aliphatic α,Ω-aminomethyl links in the 3-position gives ligands which allow the assembly of the polynuclear complexes [Fe(7)O(2)(OH)(6)(H(2)L1)(3)(py)(6)](BF(4))(5)·6H(2)O·14MeOH (1·6H(2)O·14MeOH), [Fe(6)O(OH)(7)(H(2)L2)(3)](BF(4))(3)·4H(2)O·9MeOH (2·4H(2)O·9MeOH) and [Mn(6)O(2)(OH)(2)(H(2)L1)(3)(py)(4)(MeCN)(2)](BF(4))(5)(NO(3))·3MeCN·H(2)O·5py (3·3MeCN·H(2)O·5py). In each case the metallic skeleton of the cluster is based on a trigonal prism in which two [M(III)(3)O] triangles are tethered together via three helically twisted double-headed oximes. The latter are present as H(2)L(2-) in which the oximic and phenolic O-atoms are deprotonated and the amino N-atoms protonated, with the oxime moieties bridging across the edges of the metal triangles. Both the identity of the metal ion and the length of the straps connecting the salicylaldoxime units have a major impact on the nuclearity and topology of the resultant cluster, with, perhaps counter-intuitively, the longer straps producing the "smallest" molecules. 相似文献
965.
Queen WL Bloch ED Brown CM Hudson MR Mason JA Murray LJ Ramirez-Cuesta AJ Peterson VK Long JR 《Dalton transactions (Cambridge, England : 2003)》2012,41(14):4180-4187
The hydrogen storage properties of Fe(2)(dobdc) (dobdc(4-) = 2,5-dioxido-1,4-benzenedicarboxylate) and an oxidized analog, Fe(2)(O(2))(dobdc), have been examined using several complementary techniques, including low-pressure gas adsorption, neutron powder diffraction, and inelastic neutron scattering. These two metal-organic frameworks, which possess one-dimensional hexagonal channels decorated with unsaturated iron coordination sites, exhibit high initial isosteric heats of adsorption of -9.7(1) and -10.0(1) kJ mol(-1), respectively. Neutron powder diffraction has allowed the identification of three D(2) binding sites within the two frameworks, with the closest contacts corresponding to Fe-D(2) separations of 2.47(3) and 2.53(5) ?, respectively. Inelastic neutron scattering spectra, obtained from p-H(2) (para-H(2)) and D(2)-p-H(2) mixtures adsorbed in Fe(2)(dobdc), reveal weak interactions between two neighboring adsorption sites, a finding that is in opposition to a previous report of possible 'pairing' between neighboring H(2) molecules. 相似文献
966.
David M. Mason 《Journal of Theoretical Probability》2013,26(2):589-593
We correct and clarify some ambiguous statements in D. M. Mason (2005): The asymptotic distribution of self-normalized triangular arrays. J. Theoret. Probab., 18, 853–870. 相似文献
967.
Group invariant solution for a pre-existing fracture driven by a power-law fluid in impermeable rock
A.G. Fareo D.P. Mason 《Communications in Nonlinear Science & Numerical Simulation》2013,18(12):3298-3316
The effect of power-law rheology on hydraulic fracturing is investigated. The evolution of a two-dimensional fracture with non-zero initial length and driven by a power-law fluid is analyzed. Only fluid injection into the fracture is considered. The surrounding rock mass is impermeable. With the aid of lubrication theory and the PKN approximation a partial differential equation for the fracture half-width is derived. Using a linear combination of the Lie-point symmetry generators of the partial differential equation, the group invariant solution is obtained and the problem is reduced to a boundary value problem for an ordinary differential equation. Exact analytical solutions are derived for hydraulic fractures with constant volume and with constant propagation speed. The asymptotic solution near the fracture tip is found. The numerical solution for general working conditions is obtained by transforming the boundary value problem to a pair of initial value problems. Throughout the paper, hydraulic fracturing with shear thinning, Newtonian and shear thickening fluids are compared. 相似文献
968.
Representative organic vapors have been introduced into the flowing afterglow of a low power (<5 W) dc-glow discharge, coupled to a quadrupole mass spectrometer. When a positive bias was applied to the ion sampling orifice, the very surprising result was that molecular mass spectra were obtained with a high sensitivity. When a negative bias was applied to the ion sampling orifice, fragmentation of the analyte was observed with an increase in the extent of ion dissociation as the voltage was increased. The breakdown pattern is compound-specific and would be useful in confirming the identity of an unknown sample. When combined with chromatographic separation, the FFGD-MS technique could be used for chemical speciation studies at the sub-picogram level. 相似文献
969.
We study the folding instability of a viscous thread surrounded by a less viscous miscible liquid flowing from a square to a diverging microchannel. Because of the change in the flow introduced by the diverging channel, the viscous thread minimizes viscous dissipation by oscillating to form bends rather than by simply dilating. The folding frequency and the thread diameter can be related to the volume flow rates and thus to the characteristic shear rate. Diffusive mixing at the boundary of the thread can significantly modify the folding flow morphologies. This microfluidic system enables us to control the bending of the thread and to enhance mixing between liquids having significantly different viscosities. 相似文献
970.
Mason RJ 《Physical review letters》2006,96(3):035001
The fast ignitor is a modern approach to laser fusion that uses a short-pulse laser to initiate thermonuclear burn. In its simplest form the laser launches relativistic electrons that carry its energy to a precompressed fusion target. Cones have been used to give the light access to the dense target core through the low-density ablative cloud surrounding it. Here the ANTHEM implicit hybrid simulation model shows that the peak ion temperatures measured in recent cone target experiments arose chiefly from return current joule heating, mildly supplemented by relativistic electron drag. Magnetic fields augment this heating only slightly, but capture hot electrons near the cone surface and force the hot electron stream into filaments. 相似文献