全文获取类型
收费全文 | 1097篇 |
免费 | 169篇 |
国内免费 | 275篇 |
专业分类
化学 | 949篇 |
晶体学 | 11篇 |
力学 | 48篇 |
综合类 | 11篇 |
数学 | 151篇 |
物理学 | 371篇 |
出版年
2024年 | 6篇 |
2023年 | 16篇 |
2022年 | 40篇 |
2021年 | 30篇 |
2020年 | 45篇 |
2019年 | 51篇 |
2018年 | 37篇 |
2017年 | 37篇 |
2016年 | 60篇 |
2015年 | 33篇 |
2014年 | 47篇 |
2013年 | 92篇 |
2012年 | 79篇 |
2011年 | 105篇 |
2010年 | 71篇 |
2009年 | 63篇 |
2008年 | 86篇 |
2007年 | 64篇 |
2006年 | 68篇 |
2005年 | 68篇 |
2004年 | 45篇 |
2003年 | 54篇 |
2002年 | 70篇 |
2001年 | 71篇 |
2000年 | 38篇 |
1999年 | 38篇 |
1998年 | 19篇 |
1997年 | 22篇 |
1996年 | 18篇 |
1995年 | 17篇 |
1994年 | 10篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 9篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有1541条查询结果,搜索用时 15 毫秒
31.
32.
第一讲中子散射与散裂中子源 总被引:1,自引:0,他引:1
中子散射是研究物质微观结构和动态的理想工具之一,广泛地应用于凝聚态物质研究和应用的众多学科领域.散裂中子源能是新一代的加速器基脉冲中子源,能为中子散射提供高通量的脉冲中子.文章简明地介绍了中子散射的特点和它作为物质结构和动态探针的优越性,以及散裂中子源的基本原理、发展状况和多学科的应用优势.我国计划建设的散裂中子源CSNS中,靶站将由多片钨靶、铍/铁反射体和铁/重混凝土生物屏蔽体组成.质子束功率100kW下,脉冲中子通量约为2.4×1016n/cm2/s.第一期将设计建造高通量粉末衍射仪、高分辨粉末衍射仪、小角散射仪、多功能反射仪和直接几何非弹性散射仪等五台典型的中子散射谱仪,以覆盖大部分的中子散射研究领域. 相似文献
33.
激光空泡刚性半球面内运动 总被引:1,自引:0,他引:1
采用甚高速照相技术与建立激光空泡在刚性半球壁面内的运动模型相结合的方法,确定了激光空泡在刚性半球面壁内的运动特性与无量纲距离的关系,提出了最佳无量纲距离概念。结果表明:半球反射面的半径与激光空泡最大半径之比小于1.1时,激光空泡在第1次膨胀时就会产生严重的变形并弹出半球面,并产生空化泡和空蚀,它们均会严重影响激光声的传播。该比值在1.1~3.3时,激光空泡将在第3次收缩之前接触半球面,容易对壁面造成空蚀。在该比值大于3.3的情况下,激光空泡在第3次收缩之前不会接触半球面,对激光声的传播和反射特性影响较小。如果考虑把空泡第1次溃灭时产生的激光声的声学中心控制在击穿点时,需要把该比值控制在5以上。 相似文献
34.
35.
In order to realize a wider application for graphene materials specifically in the field of energy storage, a simple and mass-scalable method described as “the atmospheric, low-temperature, shock-heating process” is proposed in this work. During this low-temperature process, the graphite oxide without pre-treatment is completely exfoliated to form the few-layer graphene materials at atmospheric conditions. The Brunauer-Emmett-Teller (BET)-specific surface area of acquired material at 350 °C can reach 487 m2 g?1. The acquired few-layer graphene materials are also confirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM). The results demonstrate that this simple method is feasible for synthesizing the few-layer graphene materials. Besides that, the acquired graphene is also used as the cathode material in the surface-enabled lithium ion-exchanging cell. The galvanostatic charge/discharge tests show that the graphene prepared from this method is suitable for this system and displays a satisfactory electrochemical performance. The acquired graphene sample exhibits the reversible capacities of around 187, 107, 84, 58, and 45 mAh g?1 at 0.1, 2, 5, 10, and 15 A g?1, respectively. At the current density of 0.5 A g?1, the capacity retention can reach 75 % after 2000 cycles. 相似文献
36.
Wang Z Yang F Zhang G Bo Y Liu S Xie S Xu Y Zong N Li F Liu B Xu J Peng Q Zhang J Cui D Wu Y Xu Z 《Optics letters》2012,37(12):2403-2405
We demonstrate a high-power UV 278 nm laser by fourth-harmonic generation (FHG) of a 1112 nm Nd:YAG laser in a nonlinear optical (NLO) crystal CsB3O5 (CBO) for the first time, to our best knowledge. A 30 W level diode-pumped Q-switched Nd:YAG laser at 1112 nm with beam quality factor M2=1.2 was used as the fundamental light source at a pulse width of 500 ns. With an LiB3O5 crystal, the 1112 nm laser was first frequency-doubled to 556 nm with an average output power of 13.5 W. It was then frequency doubled again in a CBO crystal to obtain the FHG output at 278 nm. The maximum average output power of the 278 nm laser is up to 1.5 W. The results demonstrated that CBO crystal is a promising NLO material for UV high-power lasers below 300 nm. 相似文献
37.
Yong-Li Li Qiang Zhang Jian-Jun Wu Li-Jun Xue Li-Ming Chen Jun-Mian Tian Zhuo-Ni Xu Ying Chen Xian-Wen Yang Xiao-Jiang Hao Jie Li 《Tetrahedron letters》2019,60(10):751-753
From Abies nukiangensis, two novel 13,14-seco-abietane diterpenes, nukiangendines A (1) and B (2) were isolated. Their relative structures were determined by extensive NMR and HRMS spectroscopic analysis. The absolute configuration of 1 was established by ECD calculations. Compound 1 showed significant anti-hepatitis C virus (HCV) effects. 相似文献
38.
Liu R Zong W Jin K Lu X Zhu J Zhang L Gao C 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2008,70(1):198-200
By using the techniques of resonance light scattering (RLS) and absorption spectra, we studied the toxicosis and detoxifcation mechanism of anionic surfactant SDBS and cationic surfactant CTMAB targeted to bovine serum albumin (BSA). Small quantity of CTMAB combines with SDBS-BSA complex to form SDBS-BSA-CTMAB complex and the IRLS of system enhanced greatly. With the cumulation of quantity, CTMAB captures SDBS from SDBS-BSA complex by electrostatic attraction and CTMAB-SDBS complex forms, meanwhile BSA automatically frees, which is corresponding to the toxicosis and detoxifcation process. Absorption experiment validates that SDBS induces the denaturalization of BSA and CTMAB facilitates the refolding of this protein. 相似文献
39.
Wei Zong Wang A. B. Murphy J. D. Yan Ming Zhe Rong J. W. Spencer M. T. C. Fang 《Plasma Chemistry and Plasma Processing》2012,32(1):75-96
This paper is devoted to the calculation of the chemical equilibrium composition and thermodynamic properties of reacting
mixtures of carbon and water at high temperature. Equilibrium particle concentrations and thermodynamic properties including
mass density, molar weight, entropy, enthalpy and specific heat at constant pressure, sonic velocity, and heat capacity ratio
are determined by the method of Gibbs free energy minimization, using species data from standard thermodynamic tables. The
calculations, which assume local thermodynamic equilibrium, are performed in the temperature range from 400 to 30,000 K for
pressures of 0.10, 1.0, 3.0, 5.0 and 10.0 atm. The properties of the reacting mixture are affected by the possible occurrence
of solid carbon formation at low temperature, and therefore attention is paid to the influence of the carbon phase transition
by comparing the results obtained with and without considering solid carbon formation. The results presented here clarify
some basic chemical process and are reliable reference data for use in the simulation of plasmas in reacting carbon and water
mixtures together with the need of transport coefficients computation. 相似文献
40.
Jin Hong Park Dae Hyun Yoon Soo-Hyoung Lee Kyukwan Zong 《European Polymer Journal》2010,46(8):1790-3271
New thieno[3,4-b]thiophene derivatives were prepared via a short and versatile synthetic route. Electrochemical studies of 2-heptenylthieno[3,4-b]thiophene, 2-styrylthieno[3,4-b]thiophene, and 2-phenyl-3-(thieno[3,4-b]thiophene-2-yl)acrylonitrile and the corresponding polymers revealed that raising the HOMO and lowering the LUMO can be attained by functionalizing thieno[3,4-b]thiophene with aromatic resonance-enhancing and electron-withdrawing groups. The bandgap of resulting polymers varied from 0.78 to 1.0 eV, indicating that poly(2-phenyl-3-(thieno[3,4-b]thiophene-2-yl)acrylonitrile) is one of the lowest bandgap polymers ever reported. 相似文献