全文获取类型
收费全文 | 28361篇 |
免费 | 3680篇 |
国内免费 | 2700篇 |
专业分类
化学 | 13647篇 |
晶体学 | 178篇 |
力学 | 1130篇 |
综合类 | 118篇 |
数学 | 2717篇 |
物理学 | 7449篇 |
综合类 | 9502篇 |
出版年
2024年 | 134篇 |
2023年 | 550篇 |
2022年 | 797篇 |
2021年 | 885篇 |
2020年 | 969篇 |
2019年 | 814篇 |
2018年 | 775篇 |
2017年 | 740篇 |
2016年 | 1074篇 |
2015年 | 1143篇 |
2014年 | 1397篇 |
2013年 | 1725篇 |
2012年 | 1969篇 |
2011年 | 2022篇 |
2010年 | 1515篇 |
2009年 | 1422篇 |
2008年 | 1600篇 |
2007年 | 1451篇 |
2006年 | 1270篇 |
2005年 | 1153篇 |
2004年 | 969篇 |
2003年 | 992篇 |
2002年 | 1254篇 |
2001年 | 1050篇 |
2000年 | 778篇 |
1999年 | 898篇 |
1998年 | 761篇 |
1997年 | 699篇 |
1996年 | 656篇 |
1995年 | 614篇 |
1994年 | 500篇 |
1993年 | 393篇 |
1992年 | 345篇 |
1991年 | 317篇 |
1990年 | 280篇 |
1989年 | 245篇 |
1988年 | 174篇 |
1987年 | 132篇 |
1986年 | 113篇 |
1985年 | 59篇 |
1984年 | 37篇 |
1983年 | 26篇 |
1982年 | 18篇 |
1981年 | 11篇 |
1980年 | 5篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1969年 | 1篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
In this article, we introduce two least‐squares finite element procedures for parabolic integro‐differential equations arising in the modeling of non‐Fickian flow in porous media. By selecting the least‐squares functional properly the presented procedure can be split into two independent subprocedures, one subprocedure is for the primitive unknown and the other is for the flux. The optimal order convergence analysis is established. Numerical examples are given to show the efficiency of the introduced schemes. © 2012 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2013 相似文献
992.
In this article, we disclose a method to fabricate polymer-stabilised azo-dye photo alignment layers for liquid crystal. The idea includes the introduction of polymer network in the alignment layer, in optimal concentration, followed by two-step irradiation. The stabilised photo-alignment layer has been explored for different aspects of the display-related parameters, viz. anchoring energy, stability for various display-related environments as a function of concentration of monomer and irradiation, residual DC and voltage holding ratio. The composite photo-alignment layer offers well-suited parameters for the liquid crystal alignment and therefore could find application in a variety of modern photonic and display devices. 相似文献
993.
A fluorine-containing polyacrylate emulsion was synthesized by a UV-initiated emulsion polymerization from methyl methacrylate (MMA) and hexafluorobutly methacrylate (HFMA) in the presence of 2-hydroxy-4-(2-hydroxyethoxy)-2-methyl-propiophenone (Irgacure 2959) as a hydrophilic photoinitiator at room temperature. The latex and films were characterized by Fourier transformed infrared (FT-IR) spectrometry, nuclear magnetic resonance (1H-NMR, 19F-NMR) spectrometry, transmission electron microscopy (TEM), recycling gel permeation chromatography (GPC), dynamic light scattering (DLS), and contact angle (CA) analysis, respectively. The effects of photoinitiator and emulsifier concentration on the polymerization were discussed. Compared to the corresponding thermal polymerization, UV-initiated polymerization of the MMA/HFMA emulsion could be accomplished at a much higher speed. The polymerization conversion in UV-initiated polymerization reached 95% within 10 min at an emulsifier concentration of 0.6 wt%, photoinitiator concentration of 0.4 wt%, and monomer concentration of 10 wt%. 相似文献
994.
Qian Wang Assoc. Prof. Fuhang Song Dr. Xue Xiao Pei Huang Assoc. Prof. Li Li Prof. Aaron Monte Dr. Wael M. Abdel‐Mageed Dr. Jian Wang Hui Guo Dr. Wenni He Feng Xie Dr. Huanqin Dai Miaomiao Liu Dr. Caixia Chen Hao Xu Assoc. Prof. Mei Liu Dr. Andrew M. Piggott Assoc. Prof. Xueting Liu Prof. Robert J. Capon Prof. Lixin Zhang 《Angewandte Chemie (International ed. in English)》2013,52(4):1231-1234
995.
本文以第五次、六次人口普查数据为基础,将人均受教育年限作为切入点,在GIS软件支持下,采用标准差、变异系数、空间自相关分析法等,从地理学视角系统地分析了四川省人口文化素质的空间分布特征,得出3点结论,最后,有针对性地提出了相关建议。 相似文献
996.
Shangjiang Guo 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2013,64(2):201-222
In this paper, we consider a neural network model consisting of three neurons with delayed self- and nearest-neighbor connections. We provide multiple bifurcations of the zero solution of the system near zero eigenvalue singularity. Taking the coupling coefficients as the bifurcation parameters, four kinds of zero singularities are demonstrated through center manifold reduction and normal form calculation. 相似文献
997.
Kejing Xu Yanqing Guo Qingwen Sun Shuhua Dong Zhiguang Li 《Research on Chemical Intermediates》2013,39(3):1417-1428
Composite catalyst honeycombs without sintering were prepared via kneading, mulling, extrusion molding, and solidifying at room temperature with the magnesite oxychloride gels modified by nano-rice husk ash (RHA) as a solidifying agent. The effects of nano-RHA and composite water-resistant agents on the water resistance of magnesite materials were studied. The solidification of the modified magnesite gels on TiO2 catalyst honeycombs was analyzed. The experiments show that the proportional addition of nano-RHA markedly increases the water resistance of magnesite materials without reducing the bending strength, and the softening coefficient increases from 0.29 to 0.78. With further addiition of the complex water-resistant agents, the softening coefficient increases from 0.78 to 0.97. The optimal mass ratio of MgO in the solidifying agent to TiO2 is 4:1, and the bending strength of unsintered catalyst honeycombs is 11.46 MPa. The desulfurization rate and denitration rate of this composite catalyst honeycomb on simulation smoke was 97 and 65 %, respectively, in 3 h. 相似文献
998.
Lie Shen Du Xu Yukun Jian Wenlian Qiu Qipeng Guo 《Journal of Macromolecular Science: Physics》2017,56(4):254-261
The mutual diffusion process and interphase development taking place at the interface between disks of polystyrene (PS) and carbon black filled polystyrene (CB-PS) in the molten state were investigated by a small-amplitude, oscillatory shear, rheological technique. The rheological method was employed to probe the thermorheological complexity of these polymer disks. It was found that the dynamic complex shear modulus, G*(t), increased with the time of contact in two time regimes at a fixed frequency. The time of transition between the two regimes was observed to be close to the time needed for the transition from the Rouse mode to the reptation mode. The results showed that the content of the carbon black and the temperature affected the slope of the G*(t) – t curve. Scanning electron microscopy revealed the interface disappeared when the diffusion process was complete. 相似文献
999.
The traditional surfactant sodium dodecyl sulfate (SDS) and ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim][BF4]) have been combined to create a novel efficient medium for chromogenic catalysis of 3,3',5,5'-tetramethylbenzidine with horseradish peroxidase in presence of H2O2. The results have shown the [Emim][BF4] in the mediums can promote the rate of formation of the blue chromogen, the SDS is responsible for the stabilization of the blue chromogen due to the electrostatic attraction between positively charged blue chromogen and the negatively charged surfactant. The SDS/[Emim][BF4] combination not only enhance catalytic activity of HRP remarkably but also stabilize the blue chromogen formed in the HRP oxidation of the substrate TMB compared to the conventional medium. Based on the superior combination of SDS and [Emim][BF4], the colorimetric assay for detecting HRP activity and H2O2 concentration was established. This work demonstrates a novel efficient medium for chromogenic catalysis with potential applications in biosensors and clinical diagnosis. 相似文献
1000.
XiaoDan Fu XingQun Guo XingWei Li LiDong He YuShe Yang YouXi Chen 《Tetrahedron: Asymmetry》2013,24(13-14):827-832
An asymmetric synthesis of the melatonin receptor agonist Ramelteon 1 has been achieved, which involved a tandem C–H activation–alkylation/Heck reaction and subsequent highly diastereoselective asymmetric Michael addition to generate the corresponding chiral intermediate, which was readily converted into Ramelteon 1 in 19% overall yield in 15 linear steps. 相似文献