全文获取类型
收费全文 | 1067篇 |
免费 | 179篇 |
国内免费 | 100篇 |
专业分类
化学 | 716篇 |
晶体学 | 5篇 |
力学 | 85篇 |
综合类 | 2篇 |
数学 | 81篇 |
物理学 | 457篇 |
出版年
2024年 | 2篇 |
2023年 | 22篇 |
2022年 | 25篇 |
2021年 | 34篇 |
2020年 | 37篇 |
2019年 | 52篇 |
2018年 | 30篇 |
2017年 | 24篇 |
2016年 | 48篇 |
2015年 | 40篇 |
2014年 | 38篇 |
2013年 | 69篇 |
2012年 | 112篇 |
2011年 | 114篇 |
2010年 | 76篇 |
2009年 | 64篇 |
2008年 | 67篇 |
2007年 | 49篇 |
2006年 | 49篇 |
2005年 | 40篇 |
2004年 | 48篇 |
2003年 | 24篇 |
2002年 | 25篇 |
2001年 | 20篇 |
2000年 | 29篇 |
1999年 | 31篇 |
1998年 | 23篇 |
1997年 | 16篇 |
1996年 | 26篇 |
1995年 | 21篇 |
1994年 | 13篇 |
1993年 | 15篇 |
1992年 | 10篇 |
1991年 | 12篇 |
1990年 | 12篇 |
1989年 | 6篇 |
1988年 | 1篇 |
1987年 | 7篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有1346条查询结果,搜索用时 0 毫秒
931.
932.
Chen J Wang M Liu B Fan Z Cui K Kuang Y 《The journal of physical chemistry. B》2006,110(24):11775-11779
Carbon nanotube (CNT) supported Pt nanoparticle catalysts have been prepared by spontaneous reduction of PtCl6(2-) ion as a result of direct redox reactions between PtCl6(2-) and oxygen-containing functional groups at defect sites of CNTs, which were introduced by chemical and electrochemical oxidation treatment of CNTs. The electrocatalytic properties of as-prepared Pt-CNT catalysts for methanol oxidation were investigated by chronopotentiometry and cyclic voltammetry. Compared with Pt catalysts prepared by hydrogen reduction and electrochemical deposition methods, Pt catalysts synthesized by functional CNT defects show excellent antipoisoning ability and long-term cycle stability. 相似文献
933.
One-pot simultaneous debrominative decarboxylation and sulfamation of anti-2,3-dibromo-3-(4-chlorosulfonylphenyl)propanoic acid in DMF (for alkyl amines) or DMF-pyridine (for aryl amines) using a diverse range of alkyl and aryl amines under microwave irradiation condition stereoselectively afforded (Z)-4-(2-bromovinyl)benzenesulfonamides in good yields. 相似文献
934.
Ni nanoparticles (Ni(1) and Ni(2)) and Ni loaded SiMCM‐41 (15Ni/SiMCM‐41) were prepared and characterized with XRD, TEM, N2 adsorption, CO chemisorption, and H2‐TPR. The Ni specific surface area followed the order of 15Ni/SiMCM‐41 > Ni(1) >> Ni(2), whereas the Ni particle size exhibited the opposite trend. These catalysts were utilized for vapour phase hydrogenation of cinnamaldehyde at 1 atm and 200 °C in a fixed‐bed, down flow reactor. The main products include hydrocinnamaldehyde, styrene, ethylbenzene, and 2‐phenyl‐1‐propanol. The catalytic activity decreased in the same order as that of Ni specific surface areas. The SiMCM‐41 support possessed very large surface area, leading to enhanced dispersion and specific surface area of Ni nanoparticles. As a result, the 15Ni/SiMCM‐41 catalyst exhibited the highest activity. Based on the investigation of reaction pathways, it is important to emphasize that both hydrogenation and hydroelimination of formaldehyde (hydrodeformylation) occur in the vapour phase reaction. 相似文献
935.
Shun-Tsung Lo Kuang Yao Chen T.L. Lin Li-Hung Lin Dong-Sheng Luo Y. Ochiai N. Aoki Yi-Ting Wang Zai Fong Peng Yiping Lin J.C. Chen Sheng-Di Lin C.F. Huang C.-T. Liang 《Solid State Communications》2010,150(39-40):1902-1905
We have performed low-temperature transport measurements on a disordered two-dimensional electron system (2DES). Features of the strong localization leading to the quantum Hall effect are observed after the 2DES undergoes a direct insulator–quantum Hall transition on increasing the perpendicular magnetic field. However, such a transition does not correspond to the onset of strong localization. The temperature dependences of the Hall resistivity and Hall conductivity reveal the importance of the electron–electron interaction effects for the observed transition in our study. 相似文献
936.
N.M. Liao W. Li Y.D. Jiang Y.J. Kuang K.C. Qi Z.M. Wu S.B. Li 《Applied Physics A: Materials Science & Processing》2008,91(2):349-352
The ordering evolution of the amorphous network of a-Si:H thin films with increasing initial silane-gas temperatures was investigated
by Raman spectroscopy. The results show that there exists a gradual ordering of the amorphous network, both in the near surface
and interior region on increasing the silane-gas temperature. In addition, the increase in the gas temperature leads to an
improved ordering of amorphous network on the short and intermediate scales towards the surface of a-Si:H thin films. Post-annealing
at 250 °C for 3 h mainly leads to a short and intermediate range improvement in the interior region of the films. Our present
results suggest that a-Si:H thin films with better quality could be deposited at higher silane-gas temperature.
PACS 63.50.+x; 61.43.-j; 75.40.-s 相似文献
937.
Lei Zhou Jin‐Feng Liao Zeng‐Guang Huang Jun‐Hua Wei Xu‐Dong Wang Hong‐Yan Chen Dai‐Bin Kuang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(43):15581-15586
Low‐dimensional lead halide perovskite materials recently have drawn much attention owing to the intriguing broadband emissions; however, the toxicity of lead will hinder their future development. Now, a lead‐free (C4H14N2)2In2Br10 single crystal with a unique zero‐dimensional (0D) structure constituted by [InBr6]3? octahedral and [InBr4]? tetrahedral units is described. The single crystal exhibits broadband photoluminescence (PL) that spans almost the whole visible spectrum with a lifetime of 3.2 μs. Computational and experimental studies unveil that an excited‐state structural distortion in [InBr6]3? octahedral units enables the formation of intrinsic self‐trapped excitons (STEs) and thus contributing the broad emission. Furthermore, femtosecond transient absorption (fs‐TA) measurement reveals that the ultrafast STEs formation together with an efficient intersystem crossing has made a significant contribution to the long‐lived and broad STE‐based emission behavior. 相似文献
938.
Jiarong Cai Wei Ma Liguang Xu Changlong Hao Maozhong Sun Xiaoling Wu Felippe Mariano Colombari Andr Farias de Moura Mariana Cristina Silva Evaldo Batista Carneiro‐Neto Ernesto Chaves Pereira Hua Kuang Chuanlai Xu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(48):17579-17585
The deposition of a monolayer nanoarray on the surface of a micrometer‐thick substrate is demonstrated, producing rectification characteristics at the nanoscale. The experimental results show that the heterogeneity of the structure and the charge density are the two key factors affecting rectification, which was confirmed with molecular dynamic (MD) and finite element simulations. Moreover, by altering the asymmetric electrolyte environment, the fabricated heterogeneous membrane can be used in energy conversion. This study provides insights into the mechanism underlying the generation of rectification and related factors, providing a theoretical basis for the characteristics of rectification. 相似文献
939.
Completely positive (CP) tensors, which correspond to a generalization of CP matrices, allow to reformulate or approximate a general polynomial optimization problem (POP) with a conic optimization problem over the cone of CP tensors. Similarly, completely positive semidefinite (CPSD) tensors, which correspond to a generalization of positive semidefinite (PSD) matrices, can be used to approximate general POPs with a conic optimization problem over the cone of CPSD tensors. In this paper, we study CP and CPSD tensor relaxations for general POPs and compare them with the bounds obtained via a Lagrangian relaxation of the POPs. This shows that existing results in this direction for quadratic POPs extend to general POPs. Also, we provide some tractable approximation strategies for CP and CPSD tensor relaxations. These approximation strategies show that, with a similar computational effort, bounds obtained from them for general POPs can be tighter than bounds for these problems obtained by reformulating the POP as a quadratic POP, which subsequently can be approximated using CP and PSD matrices. To illustrate our results, we numerically compare the bounds obtained from these relaxation approaches on small scale fourth-order degree POPs. 相似文献
940.
采用多组态参考相互作用方法和AV5Z-DK基组对CN~+离子的两个解离极限C~+(~2P_u)+N(~2D_u)和C~+(~2P_u)+N(~4S_u)下的X~1Σ~+、a~3Π、~1Δ和A~1四个电子态的势能曲线、永久偶极矩和振动能级进行了计算.为保证计算结果的精确性,在计算中考虑了Davidson修正.基于求得的势能曲线,数值求解一维径向薛定谔方程得到了各个电子态的光谱数据,并与实验值和已有的理论值吻合较好.除此之外,对A~1Π→X~1Σ~+和1~1Δ?A1~Π的跃迁性质进行了研究,同时通过跃迁的弗兰克-康登因子及辐射寿命,对CN~+离子激光冷却的可行性进行了分析. 相似文献