全文获取类型
收费全文 | 1410篇 |
免费 | 310篇 |
国内免费 | 70篇 |
专业分类
化学 | 729篇 |
晶体学 | 60篇 |
力学 | 32篇 |
综合类 | 21篇 |
数学 | 21篇 |
物理学 | 927篇 |
出版年
2023年 | 15篇 |
2022年 | 18篇 |
2021年 | 31篇 |
2020年 | 40篇 |
2019年 | 45篇 |
2018年 | 26篇 |
2017年 | 44篇 |
2016年 | 62篇 |
2015年 | 69篇 |
2014年 | 88篇 |
2013年 | 150篇 |
2012年 | 75篇 |
2011年 | 111篇 |
2010年 | 75篇 |
2009年 | 100篇 |
2008年 | 105篇 |
2007年 | 110篇 |
2006年 | 100篇 |
2005年 | 76篇 |
2004年 | 73篇 |
2003年 | 74篇 |
2002年 | 62篇 |
2001年 | 54篇 |
2000年 | 28篇 |
1999年 | 25篇 |
1998年 | 20篇 |
1997年 | 29篇 |
1996年 | 16篇 |
1995年 | 19篇 |
1994年 | 13篇 |
1993年 | 7篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 7篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有1790条查询结果,搜索用时 15 毫秒
141.
J.-F. Colomer L. Henrard Ph. Lambin G. Van Tendeloo 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(1):111-118
The atomic structure of single-wall carbon nanotube bundles produced by three different techniques (laser ablation, electric
arc discharge and catalytic chemical vapor deposition (CCVD)) has been characterized by electron diffraction and microscopy.
Information on the helicity and the lattice packing has been obtained. Concerning the helicity, small bundles produced by
CCVD exhibit only one or two tube helicities within a single bundle. The diffraction patterns of laser-ablation produced bundles
also present well-defined but more diversified chiralities within a single bundle. By contrast the data acquired on bundles
formed by arc discharge show a more diffuse pattern, characteristic of a random chirality dispersion within a single bundle.
Concerning the lattice packing, informations are obtained via a detailed study of the equatorial line of the diffraction pattern for bundles produced by the three techniques. This electron
diffraction study is completed by high-resolution electron microscopy.
Received 8 August 2001 and Received in final form 14 March 2002 相似文献
142.
Adriana Boschetti‐de‐Fierro Daniel Fierro Julio Albuerne Sérgio S. Funari Volker Abetz 《Journal of Polymer Science.Polymer Physics》2007,45(23):3197-3206
The bulk morphology of poly(1,4‐butadiene)–block–polystyrene–block–poly (ethylene oxide) (PB‐b‐PS‐b‐PEO) and polyethylene–block–polystyrene–block–poly (ethylene oxide) (PE‐b‐PS‐b‐PEO) triblock terpolymers is analyzed under a thermal protocol. This allows the investigation of the morphology during the occurrence of thermal transitions, such as crystallization and melting, which is a neat way of studying the competition between microphase separation and crystallization for the morphology formation. Only one of the studied systems presented a morphological transition upon melting of the PEO and the PE blocks, attributed to the crystallization of the PE block in finite interconnected domains. All the other systems presented no morphological transitions during the thermal scan. The results prove that the crystallization only disrupt the microphases generated in the molten state under very specific circumstances for these block copolymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3197–3206, 2007 相似文献
143.
Chunheng Liu Yueguang Lu Chunlei Du Xiangang Luo 《International Journal of Infrared and Millimeter Waves》2007,28(12):1115-1122
A aperture-coupled patch antenna is designed with parasitic elements connecting to the rectangle ring on the bottom of antenna
substrate through metal vias, which lead the current induced by patch radiator to the top surface of antenna substrate. Therefore,
the effective radiation is enhanced and higher gain is achieved. The bandwidth is broadened simultaneously due to the structure
of aperture-coupled patch antenna with parasitic elements. Compared to the conventional aperture-coupled patch antenna, the
antenna gain increases averagely 2 dB due to the novel structure. Compared to patch antenna of electromagnetic band-gap, the
dimensions of novel patch antenna greatly decreases, which can be used as element in the array antenna. Two kinds manufactured
antenna are both measured in an anechoic chamber. The good agreements between numerical simulation and experimental prototype
have been obtained. 相似文献
144.
145.
Xiu Yin Zhang Sheng Li Xie Bin Jie Hu 《International Journal of Infrared and Millimeter Waves》2007,28(3):223-227
A suspended planar antenna with a novel feeding structure is proposed for bandwidth enhancement. This feeding structure can
provide extra degrees of freedom to tune the antenna for compensating for the large inductance induced by the long feeding
probe. An impedance bandwidth of 56% for VSWR<2 is obtained. Simulated and measured results are compared and good agreements
are observed. 相似文献
146.
Aqueous aggregates of zinc 31-hydroxy- and 31-methoxy-131-oxo-chlorins possessing a hydrophilic tetraoxyethylene chain were prepared. Zinc 31-methoxy-chlorin formed a well-ordered aggregate without intermolecular hydrogen bonding which has been widely accepted in most structural models for BChl-c, d, e aggregates in a major light-harvesting antenna of green photosynthetic bacteria, chlorosome. 相似文献
147.
J.D. Song W.J. Choi J.I. Lee J.Y. Lee 《Physica E: Low-dimensional Systems and Nanostructures》2006,32(1-2):115
We report structural and optical properties of In0.5Ga0.5As/GaAs quantum dots (QDs) in a 100 Å-thick In0.1Ga0.9As well grown by repeated depositions of InAs/GaAs short-period superlattices with atomic force microscope, transmission electron microscope (TEM) and photoluminescence (PL) measurement. The QDs in an InGaAs well grown at 510 °C were studied as a function of n repeated deposition of 1 monolayer thick InAs and 1 monolayer thick GaAs for n=5–10. The heights, widths and densities of dots are in the range of 6–22.0 nm, 40–85 nm, and 1.6–1.1×1010/cm2, respectively, as n changes from 5 to 10 with strong alignment along [1 −1 0] direction. Flat and pan-cake-like shape of the QDs in a well is found in TEM images. The bottoms of the QDs are located lower than the center of the InGaAs well. This reveals that there was intermixing—interdiffusion—of group III materials between the InGaAs QD and the InGaAs well during growth. All reported dots show strong 300 K-PL spectrum, and 1.276 μm (FWHM: 32.3 meV) of 300 K-PL peak was obtained in case of 7 periods of the QDs in a well, which is useful for the application to optical communications. 相似文献
148.
A new technique for generating a continuous range of true time delay values is introduced. Heating optical fiber in order to change the effective index of the guided mode produces time delays. A 45-m section of single-mode silica fiber is demonstrated to produce a continuous range of time delay values from 0 to 211 ps over a temperature tuning range of 50°C (30–80°C). A thermal time delay factor is introduced and found to be 0.096 ps/m°C for Corning LEAF fiber. A 7.66-m section of multimode Lucina polymer fiber is demonstrated to produce a range of time delay values from 0 to 32 ps over a temperature tuning range of 30°C (30–60°C). The thermal time delay factor for this fiber is −0.1427 ps/m°C. 相似文献
149.
本文报道用X-射线衍射(XRD),TEM和FTIR光谱考察了在不同的制备条件下BSA-SDS-Ag的SDS-Ag聚合物纳米微粒的结构,形貌以及表面性质,随制备条件的不同,微粒的表面形貌有很大的差异。体系在微也液状态下,用甲醛作还原剂,可把银离子还原为单质,进而聚集成包裹型的团状微粒,微粒粒径32-60nm;微粒表面结构复杂,表明Ag^+先后与蛋白质中的某些氨基酸残基产生化学键合,再还原为Ag粒,进而聚合成网状结构的聚合物。 相似文献
150.