全文获取类型
收费全文 | 89999篇 |
免费 | 1900篇 |
国内免费 | 1320篇 |
专业分类
化学 | 32431篇 |
晶体学 | 896篇 |
力学 | 7297篇 |
综合类 | 45篇 |
数学 | 33837篇 |
物理学 | 18713篇 |
出版年
2023年 | 251篇 |
2022年 | 250篇 |
2021年 | 460篇 |
2020年 | 518篇 |
2019年 | 535篇 |
2018年 | 10756篇 |
2017年 | 10523篇 |
2016年 | 6579篇 |
2015年 | 1362篇 |
2014年 | 982篇 |
2013年 | 1248篇 |
2012年 | 4820篇 |
2011年 | 11494篇 |
2010年 | 6306篇 |
2009年 | 6670篇 |
2008年 | 7323篇 |
2007年 | 9372篇 |
2006年 | 803篇 |
2005年 | 1751篇 |
2004年 | 1898篇 |
2003年 | 2261篇 |
2002年 | 1278篇 |
2001年 | 499篇 |
2000年 | 511篇 |
1999年 | 347篇 |
1998年 | 339篇 |
1997年 | 280篇 |
1996年 | 378篇 |
1995年 | 266篇 |
1994年 | 184篇 |
1993年 | 204篇 |
1992年 | 162篇 |
1991年 | 162篇 |
1990年 | 161篇 |
1989年 | 136篇 |
1988年 | 120篇 |
1987年 | 128篇 |
1986年 | 118篇 |
1985年 | 101篇 |
1984年 | 88篇 |
1983年 | 79篇 |
1982年 | 89篇 |
1981年 | 79篇 |
1980年 | 77篇 |
1979年 | 102篇 |
1978年 | 73篇 |
1977年 | 54篇 |
1976年 | 51篇 |
1975年 | 49篇 |
1973年 | 50篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
131.
Myocardial infarction results from the rupture of an atherosclerotic plaque, which occurs in response to both mechanical stress
and inflammatory processes. In order experimentally observe flow into atherosclerotic coronary artery morphologies, a novel
technique for molding realistic compliant phantom featuring injection-molded inclusions and multiple layers has been developed.
This transparent phantom allows for particle image velocimetry (PIV) flow analysis and can supply experimental data to validate
computational fluid dynamics algorithms and hypothesis. 相似文献
132.
A new optical technique based on real time holographic interferometry in true colors has been implemented around the transonic
wind tunnel of the ONERA-Lille center to analyze 2D unsteady wake flows. Tests realized in color interferometry, real time
and double exposure, use simultaneously three wavelengths of a continuous waves laser (argon and krypton mixed) and holograms
are recorded on silver-halide single-layer panchromatic Slavich PFG03c plates. The very principle of real-time true color
holographic interferometry uses three primary wavelengths (red, green and blue) to record, under no-flow conditions, the interference
among the three measurement beams and the three reference beams simultaneously on a single reference hologram. After the holographic
plate is developed, it is placed on the test setup again in the position it occupied during exposure and the hologram is illuminated
again by the three reference beams and three measurement beams. A flat, uniform color can then be observed behind the hologram.
So a horizontal, vertical, or even circular fringe pattern can be formed and the achromatic central fringe can be made out
very clearly. The single color is used to determine the path difference zero on the interferograms. The flow studied was the
unsteady flow downstream of a cylinder placed crosswise in the test section. A sequence of hundred interferograms was recorded
on the flow around the cylinder at Mach 0.37. The vortex formation and dissipation phases can be seen very clearly, along
with the fringe beat to either side of the cylinder. 相似文献
133.
134.
Andr Luciani Christopher J. G. Plummer Tuan Nguyen Lszl Garamszegi Jan‐Anders E. Mnson 《Journal of Polymer Science.Polymer Physics》2004,42(7):1218-1225
The effects of the size (pseudo‐generation number) and nature of end groups on physical and rheological properties were investigated for a series of hyperbranched polyesters based on an ethoxylated pentaerythritol core and 2,2‐bis‐(hydroxymethyl)propionic acid repeat units. The observed linear dependence of the melt viscosity on the molar mass in the high pseudo‐generation‐number limit indicated that entanglement effects were substantially absent. Moreover, the marked influence of end capping of the end groups on the physical and rheological properties suggested that intermolecular interactions were dominated by contacts between the outer shells of the molecules, in which the end groups were assumed to be concentrated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1218–1225, 2004 相似文献
135.
Su Nee Tan Daniel Fornasiero Rossen Sedev John Ralston 《Colloids and surfaces. A, Physicochemical and engineering aspects》2004,250(1-3):307-315
The foam behaviour of low molecular weight polypropylene glycols (PPG) was investigated as a function of concentration and molecular weight (190–2000 g mol−1). For each polypropylene glycol, foam stability increases with concentration and passes through a maximum, beyond which foamability is suppressed as the solubility limit of the glycol is exceeded and droplets of glycol form. Light-scattering data as well as static and dynamic surface tension results provide the key information leading to these interpretations. A maximum in foamability was observed for the PPG molecules with increasing molecular weight (caused by a change in molecular conformation at the interface). This suppresses the Marangoni effect and leads to a decrease in foam stability. 相似文献
136.
137.
138.
We shall answer several questions concerning additive or multiplicative commutators in a division ring which are algebraic of bounded degree over its center. 相似文献
139.
Panos M. Pardalos Wanpracha Chaovalitwongse Leonidas D. Iasemidis J. Chris Sackellares Deng-Shan Shiau Paul R. Carney Oleg A. Prokopyev Vitaliy A. Yatsenko 《Mathematical Programming》2004,101(2):365-385
There is growing evidence that temporal lobe seizures are preceded by a preictal transition, characterized by a gradual dynamical change from asymptomatic interictal state to seizure. We herein report the first prospective analysis of the online automated algorithm for detecting the preictal transition in ongoing EEG signals. Such, the algorithm constitutes a seizure warning system. The algorithm estimates STLmax, a measure of the order or disorder of the signal, of EEG signals recorded from individual electrode sites. The optimization techniques were employed to select critical brain electrode sites that exhibit the preictal transition for the warning of epileptic seizures. Specifically, a quadratically constrained quadratic 0-1 programming problem is formulated to identify critical electrode sites. The automated seizure warning algorithm was tested in continuous, long-term EEG recordings obtained from 5 patients with temporal lobe epilepsy. For individual patient, we use the first half of seizures to train the parameter settings, which is evaluated by ROC (Receiver Operating Characteristic) curve analysis. With the best parameter setting, the algorithm applied to all cases predicted an average of 91.7% of seizures with an average false prediction rate of 0.196 per hour. These results indicate that it may be possible to develop automated seizure warning devices for diagnostic and therapeutic purposes.Mathematics Subject Classification (1991):20E28, 20G40, 20C20 相似文献
140.
Harish Seshadri 《Mathematische Zeitschrift》2004,247(3):487-503
We study closed Einstein 4-manifolds which admit S1 actions of a certain type, i.e., warped products. In particular, we classify them up to isometry when the fixed point of the S1 action satisfies certain natural geometric conditions. The proof uses the Bochner-Weitzenböck formula for 1-forms and the theory of minimal surfaces in 3-manifolds.in final form: 22 January 2003 相似文献