全文获取类型
收费全文 | 30930篇 |
免费 | 5702篇 |
国内免费 | 3268篇 |
专业分类
化学 | 21963篇 |
晶体学 | 349篇 |
力学 | 1804篇 |
综合类 | 136篇 |
数学 | 2991篇 |
物理学 | 12657篇 |
出版年
2024年 | 136篇 |
2023年 | 692篇 |
2022年 | 1204篇 |
2021年 | 1328篇 |
2020年 | 1392篇 |
2019年 | 1374篇 |
2018年 | 1165篇 |
2017年 | 1048篇 |
2016年 | 1597篇 |
2015年 | 1514篇 |
2014年 | 1947篇 |
2013年 | 2392篇 |
2012年 | 2859篇 |
2011年 | 2868篇 |
2010年 | 1871篇 |
2009年 | 1783篇 |
2008年 | 1993篇 |
2007年 | 1739篇 |
2006年 | 1624篇 |
2005年 | 1280篇 |
2004年 | 976篇 |
2003年 | 764篇 |
2002年 | 757篇 |
2001年 | 588篇 |
2000年 | 467篇 |
1999年 | 594篇 |
1998年 | 517篇 |
1997年 | 501篇 |
1996年 | 495篇 |
1995年 | 431篇 |
1994年 | 344篇 |
1993年 | 283篇 |
1992年 | 282篇 |
1991年 | 229篇 |
1990年 | 211篇 |
1989年 | 151篇 |
1988年 | 94篇 |
1987年 | 80篇 |
1986年 | 105篇 |
1985年 | 75篇 |
1984年 | 38篇 |
1983年 | 44篇 |
1982年 | 28篇 |
1981年 | 22篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1957年 | 4篇 |
1923年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
952.
A robust and fast line detection method based on Hough transform (HT) is proposed in this paper. Edge pixels are extracted based on the summation and ratio of principal curvatures. Probabilistic sampling on the edge pixels is applied to reduce the count of voting. Then a one-to-one voting strategy is applied by taking advantages of the information of principal direction. The principal direction is also conducive for the successive accurate line segment extraction. The experiments demonstrate that the proposed method shows better locating accuracy and computation efficiency compared with several significant variations of HT. 相似文献
953.
954.
955.
956.
Yue Zhang Xianxian Shi Yifeng Yu Shuchun Zhao Haiwen Song Aibing Chen 《International Journal of Polymer Analysis and Characterization》2014,19(1):83-93
A vanillin cross-linked chitosan microsphere delivery system was established for stabilization and controlled release of pterostilbene. The prepared microspheres were characterized by SEM images, FT-IR spectra, thermogravimetry, and X-ray diffraction. FT-IR spectra results indicated that chitosan was cross-linked by vanillin successfully. Thermal analysis showed that pterostilbene had been totally incorporated into the microspheres and the encapsulation of pterostilbene decreases the rate of degradation and increases the stability. XRD analysis was conducted to confirm the results of DSC analysis. The release rate of pterostilbene from microspheres in pH 3.6 buffer solution could be up to 58.1 % within 48 h. 相似文献
957.
Bin Cai Jun-Wei Zhao Bai-Feng Yang Huan He Guo-Yu Yang 《Journal of Cluster Science》2014,25(4):1047-1059
Hydrothermal reactions of trilacunary precursor A-α-AsW9O34 9? polyoxoanions and nickel ions in the presence of ethylenediamine (en = ethylenediamine) led to two new hexa-Ni-substituted Keggin-type tungstoarsenates [Ni6(μ 3-OH)3(en)3(H2O)6(B-α-AsW9O34)]·6H2O (1) and [Ni6(μ 3-OH)3(en)3(H2O)6(B-α-AsW9O34)]·10H2O (2), which have been characterized by elemental analyses, IR spectra, powder X-ray diffraction, thermogravimetric analyses and single-crystal X-ray diffraction. Crystal data for 1: hexagonal, R3c, a = b = 20.4379(5) Å, c = 21.5062(6) Å, β = 120º, V = 7779.8 (3) Å3 and Z = 6; for 2: momoclinic, P21/c, a = 13.4200(3) Å, b = 19.1428(5) Å, c = 22.8845(9) Å, β = 112.403(3)º, V = 5435.2(3) Å3 and Z = 4. Structural analyses reveal that the [Ni6(μ 3-OH)3(B-α-AsW9O34)] clusters in 1 and 2 are covalently functionalized by neutral en ligands, in which two similar {Ni6(μ 3-OH)3(en)3(H2O)6}9+ cores have been observed by our lab. Notably, 1 and 2 represent the highest number of substituted transition metal ions in all known lacunary Keggin-type polyoxotungstoarsenate monomers. 相似文献
958.
Ming-Wei Hong Li Song Yi Zhao Lai-Shun Qin Cong-Yong Wang Hong-Sheng Shi Jia-Yu Guo Xiao-Dong Tao Kang-Ying Shu Wen-Xiang Chai 《Journal of Cluster Science》2014,25(6):1627-1640
A series of strongly phosphorescent copper(I) halide complexes, namely [Cu(μ-X)POP]2 (X = Cl (1), Br (2), I (3), Br0.5Cl0.5 (4), POP = bis[2-(diphenylphosphino)phenyl]ether), have been synthesized by reacting CuX with the diphosphine ligand in 1:1 molar ratio. All complexes were characterized by spectroscopic analysis (IR, UV–Vis), elemental analysis, and photoluminescence study. Single-crystal X-ray diffraction revealed that complex 2 is a dinuclear structure which is constructed by two μ-X bridges and two POP ligands as μ2 bridges. Other complexes were determined as isologues of complex 2 by powder X-ray diffraction and elemental analysis. All complexes exhibit intense blue-green phosphorescence with a lifetime of ~1 μs in the solid state. The halogen-mixed complex presents a lightly change in the luminescence comparing to that of parent complexes. The excited states of all complexes have been assigned as halide-to-ligand charge transfer state mixed metal-to-ligand charge transfer character based on the time-dependent density functional theory calculations. All complexes are thermally stable according to thermogravimetric analysis so that they are suitable for applying in luminescent devices. 相似文献
959.
Miao Zhao Yakai Feng Guang Li Yuan Li Yalong Wang Ying Han Xujun Sun Xiaohua Tan 《先进技术聚合物》2014,25(9):927-933
Addition‐cure silicone resin is considered as a good choice for light emitting diodes (LEDs); however, it has very poor adhesion to the substrate, which limits its practical application. A novel polysiloxane with self‐adhesion ability and higher refractive index for the encapsulating of high‐power LEDs is prepared and characterized. This polysiloxane containing vinyl groups, phenyl groups, and epoxy groups was synthesized by a sol‐gel condensation process from methacryloxy propyl trimethoxyl silane, γ‐(2,3‐epoxypropoxy)propytrimethoxysilane, and diphenylsilanediol under the catalysis of an anion exchange resin. Then, the resin‐type encapsulation material was prepared by hydrosilylation of methylphenyl hydrogen‐containing silicone resin and the newly synthesized polysiloxane material. The novel polysiloxane was characterized by 1H‐NMR and Fourier transform infrared spectroscopy. On the basis of higher refractive index, higher transparency, excellent thermal stability, and appropriate hardness, as well as good adhesive strength between the encapsulating material and the LED lead frame (polyphthalamide), the curable silicone resin‐type encapsulation material can be used as an encapsulant for LEDs. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
960.
D. Zhao T. Shi C. Chen Z. Si Q. Duan L. Shi 《Russian Journal of Coordination Chemistry》2014,40(4):224-231
Three Mn(II) complexes of [MnL(Bipy)(H2O)] n (I), [Mn3(Phen)2(HL)2(L)2]n (II), and [Mn(Phen)2(HL)(OH)] (III), where L = 4,4′-(2-acetylpropane-1,3-diyl)dibenzoic acid, Bipy = 2,2′-bipyridine, and Phen = 1,10-phenanthroline, were hydrothermally synthesized and characterized by single crystal X-ray diffractions, infrared spectroscopy, thermogravimetric analyses, and magnetic analyses. Complexes I and II are one dimensional (1D) coordination polymers which can form the supramolecules with the help of the intermolecular hydrogen bond interactions. Finally, the landé factors are simulated by magentochemical analysis to be 2.15 and 1.80 for I and II with S = 5/2, respectively. 相似文献