全文获取类型
收费全文 | 604篇 |
免费 | 19篇 |
国内免费 | 6篇 |
专业分类
化学 | 318篇 |
晶体学 | 1篇 |
力学 | 35篇 |
数学 | 111篇 |
物理学 | 164篇 |
出版年
2022年 | 3篇 |
2020年 | 9篇 |
2019年 | 8篇 |
2018年 | 10篇 |
2017年 | 6篇 |
2016年 | 13篇 |
2015年 | 5篇 |
2014年 | 18篇 |
2013年 | 22篇 |
2012年 | 32篇 |
2011年 | 38篇 |
2010年 | 21篇 |
2009年 | 16篇 |
2008年 | 36篇 |
2007年 | 22篇 |
2006年 | 37篇 |
2005年 | 34篇 |
2004年 | 21篇 |
2003年 | 23篇 |
2002年 | 19篇 |
2001年 | 11篇 |
2000年 | 8篇 |
1999年 | 14篇 |
1998年 | 15篇 |
1997年 | 11篇 |
1996年 | 11篇 |
1995年 | 9篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 8篇 |
1981年 | 15篇 |
1980年 | 8篇 |
1979年 | 12篇 |
1978年 | 8篇 |
1977年 | 10篇 |
1975年 | 7篇 |
1974年 | 8篇 |
1973年 | 6篇 |
1972年 | 3篇 |
1971年 | 5篇 |
1965年 | 4篇 |
1962年 | 2篇 |
1940年 | 2篇 |
排序方式: 共有629条查询结果,搜索用时 15 毫秒
561.
The conditions of the appearance of in-phase oscillations in the time dependences of the low-frequency internal friction and effective shear modulus G eff in Al-0.01 wt% Cu and Al-0.001 wt % Cu alloys are studied. The in-phase oscillations are shown to appear in the alloys only when their dislocation-impurity structure is disturbed from equilibrium and the impurity concentration near a dislocation is optimum. This fact suggests that the in-phase oscillations are due to a collective character of dislocation-impurity interactions, which leads to a transfer of energy of translational dislocation motion to transverse dislocation vibrations in the main slip plane. 相似文献
562.
The Bailey transform and false theta functions 总被引:1,自引:0,他引:1
An empirical exploration of five of Ramanujan's intriguing false theta function identities leads to unexpected instances of
Bailey's transform which, in turn, lead to many new identities for both false and partial theta functions.
2000 Mathematics Subject Classification Primary—33D15, 11P83
Partially supported by National Science Foundation Grant DMS 0457003.
Supported by the Australian Research Council. 相似文献
563.
Qian Huang Marc Mangnus Nicolas J. Alvarez Rudy Koopmans Ole Hassager 《Rheologica Acta》2016,55(5):343-350
The nonlinear rheology of three selected commercial low-density polyethylenes (LDPE) is measured in uniaxial extensional flow. The measurements are performed using three different devices including an extensional viscosity fixture (EVF), a homemade filament stretching rheometer (DTU-FSR) and a commercial filament stretching rheometer (VADER-1000). We show that the measurements from the EVF are limited by a maximum Hencky strain of 4, while the two filament stretching rheometers are able to probe the nonlinear behavior at larger Hencky strain values where the steady state is reached. With the capability of the filament stretching rheometers, we show that LDPEs with quite different linear viscoelastic properties can have very similar steady extensional viscosity. This points to the potential for independently controlling shear and extensional rheology in certain rate ranges. 相似文献
564.
Morten B. Schou Sverre Georg Sæther Ole Kristian Drange Karoline Krane-Gartiser Solveig K. Reitan Arne E. Vaaler Daniel Kondziella 《BMC neuroscience》2018,19(1):68
Background
The clinical significance of anti-neuronal antibodies in patients with psychiatric disorders, but without encephalitis, remains unknown. In patients admitted to acute psychiatric inpatient care we aimed to identify clinical features distinguishing anti-neuronal antibody positive patients from matched controls.Results
Patients who were serum-positive to N-methyl d-aspartate receptor (NMDAR) (n?=?21), contactin-associated protein 2 (CASPR2) (n?=?14) and/or glutamic acid decarboxylase 65 (GAD65) (n?=?9) antibodies (cases) were age and sex matched (1:2) with serum-negative patients from the same cohort (controls). The prevalence and severity of psychiatric symptoms frequently encountered in NMDAR, CASPR2 and GAD65 antibody associated disorders were compared in cases and controls. NMDAR, CASPR2 and GAD65 antibody positive patients did not differ in their clinical presentation from matched serum negative controls.Conclusion
In this cohort, patients with and without NMDAR, CASPR2 and GAD65 antibodies admitted to acute psychiatric inpatient care had similar psychiatric phenotypes. This does not exclude their clinical relevance in subgroups of patients, and studies further investigating the clinical significance of anti-neuronal antibodies in patients with psychiatric symptomatology are needed.565.
Jensen KK Larsen ON Attenborough K 《The Journal of the Acoustical Society of America》2008,123(1):507
In a study of hooded crow communication over open fields an excellent correspondence is found between the attenuation spectra predicted by a "turbulence-modified ground effect plus atmospheric absorption" model, and crow call attenuation data. Sound propagation predictions and background noise measurements are used to predict an optimal frequency range for communication ("sound communication window") from an average of crow call spectra predicted for every possible combination of the sender/receiver separations 300, 600, 900, and 1200 m and heights 3,6,9 m thereby creating a matrix assumed relevant to crow interterritorial communication. These predictions indicate an optimal frequency range for sound communication between 500 Hz and 2 kHz. Since this corresponds to the frequency range in which crow calls have their main energy and crow hearing in noise is particularly sensitive, it suggests a specific adaptation to the ground effect. Sound propagation predictions, together with background noise measurements and hearing data, are used to estimate the radius of the hooded crow active space. This is found to be roughly 1 km in moderately windy conditions. It is concluded that the propagation modeling of the sort introduced here could be used for assessing the impact of human noise on animal communication. 相似文献
566.
We report on measurements of the ion velocity distribution as a function of distance to a target immersed in a magnetized argon plasma. Two situations are investigated: (a) practically the whole plasma streams onto a large target, and (b) the size of the target is significantly smaller than the plasma diameter. The Mach number M=u/c_{s} decreases from M=1 at the target surface to values around 0.5 at a typical scale of lambda_{a}=30 mm and lambda_{b}=5 mm, respectively. In order to explain these small decay lengths, the measurements of case (a) are compared with a source-diffusion model and those of (b) to Hutchinson's model. In (a) good agreement between modeling and experiment is obtained assuming a low neutral gas temperature. The data in (b) also agree excellently with modeled profiles, although the large fitting parameter D=20 m;{2}/s indicates that other processes than diffusion contribute significantly to the transport. 相似文献
567.
Gautier R Andersen OK Gougeon P Halet JF Canadell E Martin JD 《Inorganic chemistry》2002,41(18):4689-4699
Magnetic and electrical resistivity properties of RMo(8)O(14) (R = La, Ce, Pr, Nd, Sm) compounds containing different bicapped-octahedral Mo(8) clusters are discussed. Extended Hückel (EH) molecular calculations were carried out in order to study the influence of the position of metal capping atoms on the electronic structure of different Mo(8) isomers. Different optimal metal electron counts are possible for these clusters. Periodic density functional calculations confirm the molecular character of these compounds and allow the understanding of their semiconducting and magnetic properties. 相似文献
568.
Schulte-Herbrüggen T Meissner A Papanikos A Meldal M Sørensen OW 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2002,156(2):282-294
The MBOB, broadband HMBC, and broadband XLOC NMR pulse sequences (A. Meissner and O. W. S?rensen (2000, Magn. Reson. Chem. 38, 981-984; 2001, 39, 49-52)) were introduced as a means of obtaining heteronuclear long-range correlation spectra with broadband excitation over an interval of heteronuclear long-range J coupling constants. However, it is not trivial what combination of delays to choose for a given purpose, particularly if one-bond and long-range correlation spectra are obtained simultaneously as in MBOB. This paper presents a way to determine sets of delays for MBOB, broadband HMBC, and broadband XLOC resolving the problem. The results tabulated suit various ranges of J coupling constants and transverse relaxation times. 相似文献
569.
[reaction: see text] The neuraminic acid derivative 5 is readily converted in several steps to the neuraminic acid dimer 12, linked through the hydroxyl of a 5-N-glycolyl group in an alpha-2,5 glycosidic linkage. The sequence is shown to proceed through a spirocyclic intermediate 9 by in situ NMR experiments. Similar derivatives of N-glycolylneuraminic acid (Neu5Gc), including polymers, have been identified from marine sources, including starfish and sea urchins, often as sulfated derivatives and are thought to mediate sperm-egg recognition. 相似文献
570.
A series of substituted isoxazolidinylacetophenones (II to VI) have been shown to fragment subsequent to electron-impact in a generally predictable fashion. One characteristic fragmentation of all the compounds investigated was the loss of H2O2 from their respective molecular ions. 相似文献