全文获取类型
收费全文 | 273篇 |
免费 | 8篇 |
专业分类
化学 | 192篇 |
晶体学 | 4篇 |
力学 | 8篇 |
数学 | 17篇 |
物理学 | 60篇 |
出版年
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 4篇 |
2015年 | 7篇 |
2014年 | 7篇 |
2013年 | 7篇 |
2012年 | 19篇 |
2011年 | 16篇 |
2010年 | 26篇 |
2009年 | 11篇 |
2008年 | 17篇 |
2007年 | 8篇 |
2006年 | 6篇 |
2005年 | 6篇 |
2004年 | 4篇 |
2003年 | 2篇 |
2002年 | 4篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 6篇 |
1991年 | 4篇 |
1989年 | 6篇 |
1988年 | 2篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1972年 | 6篇 |
1971年 | 2篇 |
1970年 | 3篇 |
1968年 | 2篇 |
1967年 | 6篇 |
1965年 | 2篇 |
1961年 | 2篇 |
1937年 | 2篇 |
1902年 | 2篇 |
排序方式: 共有281条查询结果,搜索用时 0 毫秒
101.
102.
The PUR-fiber-spray molding technology is a manufacturing process which produces polyurethane-based (PUR) composites by spraying the matrix together with reinforcing fibers in a tool form or on a substrate. Thereby chopped fibers are laterally (sidewise) injected in the polyurethane-air spray cone for wetting before the entire composite is spread on the substrate, where it starts curing. To investigate and compute the fiber orientation and density distribution in the final composites manufactured by this process, a new approach simplifying the multiply coupled interaction of the three phases is presented in this paper. Hereby it is presumed that the final position and orientation of a fiber on a substrate results from its dynamics and coupled interactions with air, PUR-droplets and other fibers within the spray cone. Thus, a model of the process is built, that computes the transient behavior of the air-liquid droplets mixture by the CFD code ANSYS Fluent and its influence on the dynamics of the fibers by an extra code called FIDYST. For this multiphase problem two approaches are presented for the droplet-fiber coupling using a concept called “homogenization” of the liquid phase (droplets in the continuous phase). (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
103.
In recent years Al2O3 has received tremendous interest in the photovoltaic community for the application as surface passivation layer for crystalline silicon. Especially p‐type c‐Si surfaces are very effectively passivated by Al2O3, including p‐type emitters, due to the high fixed negative charge in the Al2O3 film. In this Letter we show that Al2O3 prepared by plasma‐assisted atomic layer deposition (ALD) can actually provide a good level of surface passivation for highly doped n‐type emitters in the range of 10–100 Ω/sq with implied‐Voc values up to 680 mV. For n‐type emitters in the range of 100–200 Ω/sq the implied‐Voc drops to a value of 600 mV for a 200 Ω/sq emitter, indicating a decreased level of surface passivation. For even lighter doped n‐type surfaces the passivation quality increases again to implied‐Voc values well above 700 mV. Hence, the results presented here indicate that within a certain doping range, highly doped n‐ and p‐type surfaces can be passivated simultaneously by Al2O3. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
104.
Entanglement, one of the most important features of quantum mechanics, is at the core of the famous Einstein-Bohr philosophical
debate [1] and is the principal resource for quantum information processing [2]. We report on new experimental investigations
of the properties of entangled photon pairs with emphasis on the tension between quantum mechanics and relativity [3,4]. Entangled
photons are sent via an optical fiber network to two villages near Geneva, separated by more than 10 km where they are analyzed
by interferometers [5]. The photon pair source is set as precisely as possible in the center so that the two photons arrive
at the detectors within a time interval of less than 5 ps (corresponding to a path length difference of less than 1 mm). This
sets a lower bound on the ‘speed of quantum information’ to 107 times the speed of light. Next, one detector is set in motion [6] so that both detectors, each in its own inertial reference
frame, are first to do the measurement! The data always reproduces the quantum correlations. 相似文献
105.
We use photoluminescence (PL) measurements by a silicon charge‐coupled device camera to generate high‐resolution lifetime images of multicrystalline silicon wafers. Absolute values of the excess carrier density are determined by calibrating the PL image by means of contactless photoconductance measurements. The photoconductance setup is integrated in the camera‐based PL setup and therefore identical measurement conditions are realised. We demonstrate the validity of this method by comparison with microwave‐detected photoconductance decay measurements. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
106.
Sonja Hermann Nils-Peter Harder Rolf Brendel Dirk Herzog Heinz Haferkamp 《Applied Physics A: Materials Science & Processing》2010,99(1):151-158
In this work, we report on laser ablation of thermally grown SiO2 layers from silicon wafer substrates, employing an 8–9 ps laser, at 1064 (IR), 532 (VIS) and 355 nm (UV) wavelengths. High-intensity
short-pulse laser radiation allows direct absorption in materials with bandgaps higher than the photon energy. However, our
experiments show that in the intensity range of our laser pulses (peak intensities of <2×1012 W/cm2) the removal of the SiO2 layer from silicon wafers does not occur by direct absorption in the SiO2 layer. Instead, we find that the layer is removed by a “lift off” mechanism, actuated by the melting and vaporisation of
the absorbing silicon substrate. Furthermore, we find that exceeding the Si melting threshold is not sufficient to remove
the SiO2 layer. A second threshold exists for breaking of the layer caused by sufficient vapour pressure. For SiO2 layer ablation, we determine layer thickness dependent minimum fluences of 0.7–1.2 J/cm2 for IR, 0.1–0.35 J/cm2 for VIS and 0.2–0.4 J/cm2 for UV wavelength. After correcting the fluences by the reflected laser power, we show that, in contrast to the melting threshold,
the threshold for breaking the layer depends on the SiO2 thickness. 相似文献
107.
In this study, magnetic cores made of amorphous rectangular tape layers are investigated. The quality factor Q of the tape material decreases rapidly, however, when stacking at least two tape layers. The hysteresis loop becomes non-linear, and the coercivity increases. These effects are principally independent of the frequency and occur whether tape layers are insulated or not. The Kerr-microscopy was used to monitor local hysteresis loops by varying the distance of two tape layers. The magnetization direction of each magnetic domain is influenced by the anisotropy axis, the external magnetic field and the stray field of magnetic domains of the neighboring tape layers. We found that crossed easy axes (as the extreme case for inclined axes) of congruent domains retain the remagnetization and induce a plateau of the local loop. Summarizing local loops leads to the observed increase of coercivity and non-linearity of the inductively measured loop. A high Q-factor can be preserved if the easy axes of stacked tape layers are identical within the interaction range in the order of mm. 相似文献
108.
Nicola Mingirulli Jan Haschke Ralf Gogolin Rafel Ferré Tim F. Schulze J. Düsterhöft Nils‐Peter Harder Lars Korte Rolf Brendel Bernd Rech 《固体物理学:研究快报》2011,5(4):159-161
We present back‐contacted amorphous/crystalline silicon heterojunction solar cells (IBC‐SHJ) on n‐type substrates with fill factors exceeding 78% and high current densities, the latter enabled by a SiNx /SiO2 passivated phosphorus‐diffused front surface field. Voc calculations based on carrier lifetime data of reference samples indicate that for the IBC architecture and the given amorphous silicon layer qualities an emitter buffer layer is crucial to reach a high Voc, as known for both‐side contacted silicon heterojunction solar cells. A back surface field buffer layer has a minor influence. We observe a boost in solar cell Voc of 40 mV and a simultaneous fill factor reduction introducing the buffer layer. The aperture‐area efficiency increases from 19.8 ± 0.4% to 20.2 ± 0.4%. Both, efficiencies and fill factors constitute a significant improvement over previously reported values. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
109.
110.