全文获取类型
收费全文 | 37475篇 |
免费 | 6080篇 |
国内免费 | 5529篇 |
专业分类
化学 | 27920篇 |
晶体学 | 604篇 |
力学 | 2000篇 |
综合类 | 447篇 |
数学 | 4383篇 |
物理学 | 13730篇 |
出版年
2024年 | 127篇 |
2023年 | 680篇 |
2022年 | 1267篇 |
2021年 | 1344篇 |
2020年 | 1524篇 |
2019年 | 1552篇 |
2018年 | 1345篇 |
2017年 | 1361篇 |
2016年 | 1781篇 |
2015年 | 1953篇 |
2014年 | 2317篇 |
2013年 | 2949篇 |
2012年 | 3504篇 |
2011年 | 3542篇 |
2010年 | 2745篇 |
2009年 | 2597篇 |
2008年 | 2790篇 |
2007年 | 2497篇 |
2006年 | 2292篇 |
2005年 | 1883篇 |
2004年 | 1370篇 |
2003年 | 1094篇 |
2002年 | 1044篇 |
2001年 | 856篇 |
2000年 | 784篇 |
1999年 | 626篇 |
1998年 | 434篇 |
1997年 | 396篇 |
1996年 | 337篇 |
1995年 | 332篇 |
1994年 | 285篇 |
1993年 | 228篇 |
1992年 | 183篇 |
1991年 | 172篇 |
1990年 | 154篇 |
1989年 | 111篇 |
1988年 | 112篇 |
1987年 | 63篇 |
1986年 | 80篇 |
1985年 | 62篇 |
1984年 | 30篇 |
1983年 | 32篇 |
1982年 | 33篇 |
1981年 | 14篇 |
1980年 | 22篇 |
1979年 | 23篇 |
1978年 | 23篇 |
1977年 | 10篇 |
1973年 | 10篇 |
1971年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Chongyi Wan Shiming Liu Rongqing Tan Jin Wu Jinwen Zhou Yan Lv Yanning Yu Hua Yang 《Optics & Laser Technology》2004,36(8):2389-649
A high average power, high-repetition-rate TEA CO2 laser employing printed-circuit-board preionizer is described. The power scaling of this preionization configuration has been demonstrated. The average output power reaches 3.6 kW at pulse repetition rate of 180 pps. Furthermore, the scaling-up ability of the rotating spark gap as high-voltage switch for high-average-power gas laser has been validated. 相似文献
82.
83.
Wenping Deng Gang Xu Lei Wan Anwen Liu Bo Gao Junhe Du Shuiming Hu Yang Chen 《Acta Physico》2008,24(8):1329-1334
Apparatus integrating a Fourier transform-infrared (FT-IR) spectrometer and a mid-infrared difference frequency generation (DFG) laser spectrometer was built for the study of the matrix isolation spectrum in solid molecular hydrogen. A 3-cm-long molecular hydrogen crystal was grown in a liquid-helium Dewar, and its infrared absorption spectrum in the 1-5 μm region was recorded to test the system. The W0(0) (ν=0←0, J=6←0) line around 2410 cm−1 of solid hydrogen was investigated with the DFG laser spectroscopy. High-resolution matrix isolation spectrum of CO2 co-deposited with hydrogen on a BaF2 cold plate at liquid-helium temperature was studied. 相似文献
84.
85.
86.
87.
The purpose of this paper is to present general approaches for bounding some multi-stage stochastic programs from above. The results are based on restricting the solution set, such that the remaining multi-stage stochastic program is easy to solve. An example where the methods can be applied is presented.Supported in part by NATO Collaborative Research Grant No. 0785/87. 相似文献
88.
Fa‐Yan Meng Xu‐Qing Liu Seik Weng Ng 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(7):m341-m342
The terephthalate dianion and the bis(imidazolyl)benzene ligand of the title compound, {[Zn(C8H4O4)(C20H14N4)]·C2H6O}n, each bridges two adjacent zinc centers, resulting in a layer‐type coordination polymer; the zinc center shows tetrahedral coordination. The disordered ethanol solvent molecules occupy the spaces between the layers and are hydrogen bonded to the layers. The two symmetry‐independent dianions lie on different inversion sites. 相似文献
89.
Ab initio energetic calculations based on the density functional theory (DFT) and projector augmented wave (PAW) pseudo-potentials method were performanced to determine the crystal structural parameters and phase transition data of the polymorphic rare-earth sesquioxides Ln2O3 (where Ln=La-Lu, Y, and Sc) with A-type (hexagonal) and B-type (monoclinic) configurations at ground state. The calculated results agree well with the limited experimental data and the critically assessed results. A set of systematic and self-consistent crystal structural parameters, energies and pressures of the phase transition were established for the whole series of the A- and B-type rare-earth sesquioxides Ln2O3. With the increase of the atomic number, the ionic radii of rare-earth elements Ln and the volumes of the sesquioxides Ln2O3 reflect the so-called “lanthanide contraction”. With the increase of the Ln3+-cation radius, the bulk modulus of Ln2O3 decreases and the polymorphic structures show a degenerative tendency. 相似文献
90.
Kan‐Yi Pu Yi Chen Xiao‐Ying Qi Chun‐Yang Qin Qing‐Quan Chen Hong‐Yu Wang Yun Deng Qu‐Li Fan Yan‐Qin Huang Shu‐Juan Liu Wei Wei Bo Peng Wei Huang 《Journal of polymer science. Part A, Polymer chemistry》2007,45(16):3776-3787
In this contribution, we demonstrate a new effective methodology for constructing highly efficient and durable poly(p‐phenyleneethynylene) (PPE) containing emissive material with nonaggregating and hole‐facilitating properties through the introduction of hole‐transporting blocks into the PPE system as the grafting coils as well as building the energy donor–acceptor architecture between the grafting coils and the PPE backbone. Poly(2‐(carbazol‐9‐yl)ethyl methacrylate) (PCzEMA), herein, is chosen as the hole‐transporting blocks, and incorporated into the PPE system as the grafting coils via atom transfer radical polymerization. The chemical structure of the resultant copolymer, PPE‐g‐PCzEMA, was characterized by NMR and gel permeation chromatography, showing that the desirable copolymer was obtained with the narrow polydispersity. The increased thermal stability of PPE‐g‐PCzEMA was confirmed by thermogravimetric analysis and differential scanning calorimetry along with its macroinitiator. The optoelectronic properties of this copolymer were studied in detail by ultraviolet‐visible absorption, photoluminescence emission and excitation spectra, and cyclic voltammogram (CV). The results indicate that PPE‐g‐PCzEMA exhibits the solid‐state luminescent property dominated by individual lumophores, and also the energy transfer process from the PCzEMA blocks to the PPE backbone with a relatively higher energy transfer efficiency in the solid‐state compared to that of the solution state. Additionally, the hole‐injection property is greatly facilitated due to the presence of PCzEMA, as confirmed by CV profiles. All these data indicate that PPE‐g‐PCzEMA is a good candidate for use in optoelectronic devices. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3776–3787, 2007 相似文献