全文获取类型
收费全文 | 7380篇 |
免费 | 1031篇 |
国内免费 | 1138篇 |
专业分类
化学 | 5901篇 |
晶体学 | 131篇 |
力学 | 364篇 |
综合类 | 135篇 |
数学 | 861篇 |
物理学 | 2157篇 |
出版年
2024年 | 7篇 |
2023年 | 102篇 |
2022年 | 224篇 |
2021年 | 197篇 |
2020年 | 273篇 |
2019年 | 260篇 |
2018年 | 210篇 |
2017年 | 197篇 |
2016年 | 350篇 |
2015年 | 335篇 |
2014年 | 425篇 |
2013年 | 537篇 |
2012年 | 602篇 |
2011年 | 669篇 |
2010年 | 553篇 |
2009年 | 480篇 |
2008年 | 550篇 |
2007年 | 551篇 |
2006年 | 516篇 |
2005年 | 371篇 |
2004年 | 367篇 |
2003年 | 272篇 |
2002年 | 295篇 |
2001年 | 226篇 |
2000年 | 158篇 |
1999年 | 135篇 |
1998年 | 104篇 |
1997年 | 90篇 |
1996年 | 80篇 |
1995年 | 51篇 |
1994年 | 46篇 |
1993年 | 50篇 |
1992年 | 41篇 |
1991年 | 32篇 |
1990年 | 36篇 |
1989年 | 20篇 |
1988年 | 15篇 |
1987年 | 15篇 |
1986年 | 14篇 |
1985年 | 14篇 |
1984年 | 7篇 |
1983年 | 13篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1978年 | 6篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1969年 | 3篇 |
1928年 | 3篇 |
排序方式: 共有9549条查询结果,搜索用时 15 毫秒
71.
72.
73.
Preparation and characterization of nitrogen-doped TiO2 photocatalyst in different acid environments
Ye Cong Ling Xiao Jinlong Zhang Feng Chen Masakazu Anpo 《Research on Chemical Intermediates》2006,32(8):717-724
Nitrogen-doped TiO2 powders were successfully prepared by a wet method, i.e., a micro-emulsion-hydrothermal method, in different acid environments.
Several characterization techniques, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV-visible diffuse
reflectance spectra, were combined to determine the crystal phase, concentration and chemical states of the nitrogen doped
in TiO2. The high photocatalytic activity of the nitrogen-doped TiO2 was evaluated through the decomposition of rhodanmine B under visible light irradiation. It was suggested that the doped
nitrogen formed oxynitride (NO) and produced impurity states at higher above the valence band of TiO2. Therefore, the nitrogen doping could enhance the response of photocatalyst to the visible light and improve the photocatalytic
activity because of the narrowing of band gap of TiO2. 相似文献
74.
YiJianCHEN GuiYingXU ShiLingYUAN HaiYingSUN 《中国化学快报》2005,16(5):688-690
Molecular dynamics (MD) simulation are used to study the properties of gemini surfactant of ethyl-α,ω-bis(dodecyldimethylammonium bromide) (C12C2C12) and dodecyl-trimethylammonium bromide (DTAB) at the air/water interface, respectively. In the two systems,t he surfactant concentrations are both 28 wt.%, and other conditions are also the same. After reaching the thermodynamic equilibrium, the concentration profiles, the radial distributions functions (RDF) and the mean squared displacement (MSD) are investigated. The results reveal that the surface activity of C12C2C12 surfactant is higher than DTAB surfactant. 相似文献
75.
设计合成了两种新型的以聚类吡唑硼酸盐为配体的钒氧配合物VO(acac)[HB(pz)3](1)和VO(acac)[HB(3,5-Me2pz)3]·CH3CN(2). 运用元素分析、 红外光谱和紫外光谱对所合成的配合物进行了表征, 并用X射线衍射测定了它们的晶体结构. 同时, 采用量子化学的Hartree Fock方法和自然轨道分析方法(NBO), 使用3-21G*(6d, 7f)基组计算得到了两个分子体系的分子轨道、原子电荷以及键级, 并对其结构进行了分析. 相似文献
76.
A kind of biodegradable material, poly(ɛ-caprolactone-co-lactic acid) [P(CL-co-LA)] was synthesized via the direct melting polycondensation of lactic acid (LA) and ɛ-caprolactone (CL). The influences
of the polycondensation time, and the catalyst type on the intrinsic viscosity of P(CL-co-LA) were also investigated. The results indicate that P(CL-co-dl-LA), with an intrinsic viscosity of 0.4733 dL/g, can be prepared by direct melting polycondensation with the molar ratio
LA/CL = 3:7 at 180°C and 70 Pa for 12 h, using 0.5% (mass fraction) of SnCl2 as the catalyst. Compared with lactide ring-opening polycondensation (ROP), the direct melting polycondensation of LA and
CL is more practicable and simple.
Translated from Journal of South China University of Technology, 2006, 34(7): 7–11 (in Chinese) 相似文献
77.
Piezoelectric diffuse reflectance spectroelectrochemistry (PDRSEC), a new technique of diffuse reflectance spectroelectrochemistry (DRSEC) in combination with electrochemical quartz crystal microbalance (EQCM), was developed to study the electrochemical copolymerization of aniline and o-anthranilic acid in 1.0 mol l(-1) HClO4 and the properties of these copolymers. The DRSEC using an integral sphere was proven to possess a higher optical sensitivity at the unpolished piezoelectric quartz crystal electrodes used than the mirror reflectance spectroelectrochemistry mode. The copolymers grown from the copolymerization bath of different molar fractions of o-anthranilic acid (F1, relative to the total amount of the two monomers) showed intermediate properties between those of the homopolymers, which varied gradually with F1. The swelling/dissolution behavior of the copolymers vs solution pH was traced via the EQCM frequency and resistance signals, and its large dependence on F1 was found and discussed. In a HAc-NaAc buffer solution at pH 5.6, the amount of adsorbed lysozyme was found to be positively correlated with F1, via an EQCM impedance investigation, demonstrating the feasibility of using poly(aniline-co-o-anthranilic acid) as a load-adjustable immobilization matrix for cationic proteins. The novel PDRSEC method proposed is highly recommended for surface electrochemistry studies at relatively rough electrodes. 相似文献
78.
The hydrosilylation reaction of octa(hydrido)silsesquioxane with ω‐halo‐1‐alkenes and other unsaturated substrates allows attachment of 8 long‐chain functionalized alkyls on the cubic Si8O12 skeleton. Pt/C and H2PtCl6 have been adopted as the catalysts, the yields being 74–98% for compounds 2–9 . For terminal alkenes, the hydrosilylation follows the anti‐Markonikov's rule. The morphological state of 2–9 ranges from viscous liquid to crystalline materials. The pyrolysis results indicate that 7 , a material of hard spherical core and soft flexible shell, may likely act as nanometer‐size ball bearings up to more than 400 °C. The X‐ray structure of 9 reveals that the molecule is required to possess a center of symmetry crystallographically. The linear arms on 9 , except for two of them, are virtually all‐trans in conformation, not counting the ω‐C‐Cl bond. 相似文献
79.
A New Asterosaponin from the Starfish Culcita novaeguineae 总被引:1,自引:0,他引:1
HaiFengTANG YangHuaYI LingLI PengSUN DaZhengZHOU BaoShuLIU 《中国化学快报》2005,16(5):619-622
A new asterosaponin named novaeguinoside A, along with a known saponin, asteronyl pentaglycoside sulfate, was isolated from the starfish Culcita novaeguineae. The new compound was identitied to be sodium 6α-O-{β-D-fucopyranosyl-(1→2)-β-D-fucopyranosyl-(1→4)-[β-D-quinovopyranosyl-(1→2)]-β-D-xylopyranosyl-(1→3)-[β-D-quinovopyranosyl}-5α-pregn-9(11)-en-20-one-3β-yl-sulfate by extensive spectral analysis and chemical evidence. 相似文献
80.
The compound has tetragonal symmetry, space group I4 m2 with: a=b=6.315(2) and c = 15.000(2) Å and contains 6 formula units. Diffraction data with 0 < 2θ < 50° (MoKα radiation) were collected on a Nonius CAD-4 automatic diffractometer within the octant hkl. The structure was solved by Patterson synthesis and refined by full-matrix least squares to a final R(F) of 4.9% for 159 independent reflections with I > 3σ(I). The structure consists of a stacking of gallium triangular-faced dodecahedra linked to each others through direct and bifurcated Ga? Ga bonds in a non-compact netting leaving room for a sublattice of rubidium atoms with shortened Rb? Rb distances. 相似文献