全文获取类型
收费全文 | 41788篇 |
免费 | 3949篇 |
国内免费 | 6854篇 |
专业分类
化学 | 36584篇 |
晶体学 | 1415篇 |
力学 | 884篇 |
综合类 | 271篇 |
数学 | 2941篇 |
物理学 | 10496篇 |
出版年
2024年 | 77篇 |
2023年 | 434篇 |
2022年 | 1108篇 |
2021年 | 1032篇 |
2020年 | 1260篇 |
2019年 | 1580篇 |
2018年 | 1142篇 |
2017年 | 1705篇 |
2016年 | 1534篇 |
2015年 | 1436篇 |
2014年 | 1863篇 |
2013年 | 3347篇 |
2012年 | 2411篇 |
2011年 | 2895篇 |
2010年 | 2349篇 |
2009年 | 2736篇 |
2008年 | 2876篇 |
2007年 | 2766篇 |
2006年 | 2623篇 |
2005年 | 2395篇 |
2004年 | 2220篇 |
2003年 | 1828篇 |
2002年 | 1574篇 |
2001年 | 1296篇 |
2000年 | 1223篇 |
1999年 | 979篇 |
1998年 | 834篇 |
1997年 | 753篇 |
1996年 | 653篇 |
1995年 | 664篇 |
1994年 | 578篇 |
1993年 | 480篇 |
1992年 | 398篇 |
1991年 | 269篇 |
1990年 | 187篇 |
1989年 | 163篇 |
1988年 | 154篇 |
1987年 | 100篇 |
1986年 | 92篇 |
1985年 | 84篇 |
1984年 | 75篇 |
1983年 | 37篇 |
1982年 | 54篇 |
1981年 | 65篇 |
1980年 | 61篇 |
1979年 | 58篇 |
1978年 | 39篇 |
1977年 | 31篇 |
1976年 | 21篇 |
1973年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
981.
基于密度泛函理论和赝势平面波方法研究了立方钙钛矿RbZnF3的电子结构和光学性质;利用静水有限应变技术计算研究了RbZnF3弹性常数Cij、体积弹性模量B和剪切模量G随压力的变化关系。基态下,RbZnF3晶格常数a和体积弹性模量B0计算值与实验值以及其他理论值一致。根据能带结构、总态密度以及分波态密度分析可知:基态下立方钙钛矿结构RbZnF3为间接带隙半导体材料,带隙为3.57eV,与其他计算结果比较,本文计算结果偏低,这是由于局域密度近似(LAD)或广义梯度近似(GGA)交换关联函数的局限性所致。基态下RbZnF3的Mulliken电荷分布和集居数说明:RbZnF3属于共价键和离子键所形成的混合键化合物;RbZnF3的电荷总数主要来源于Rb 4s和4p轨道,Zn 3d轨道,以及F 2s和2p轨道。电荷主要从Rb, Zn原子向F原子转移。同时,本文还计算研究了RbZnF3的光学介电函数、吸收系数、复折射率、能量损失谱和反射系数等光学性质。 相似文献
982.
用密度泛函理论DFT方法,计算研究不对称簇合物(HFGaN3)n (n=1-6)的几何构型、稳定性、IR谱和热力学性质。结果表明,簇合物(HFGaN3)n (n=2-6)的优化构型拥有一个Ga和α−N原子交替的2n元环状结构。通过计算研究(HFGaN3)n (n=1-6)的平均结合能、二阶能量差分和能隙与团簇尺寸关系,发现后两者表现出明显的“奇-偶”振荡现象。对计算获得的IR谱进行归属,获得四个特征区。讨论了团簇尺寸和温度对(HFGaN3)n (n=1-6)热力学函数的影响。由焓变和吉布斯自由能可知,200-800 K温度范围内由单体形成稳定的多聚体(HFGaN3)n (n=2-6)在热力学上有利。 相似文献
983.
The pure Cr2O3 coated Li4Ti5O12 microspheres were prepared by a facile and cheap solutionbased method with basic chromium(III) nitrate solution (pH=11.9). And their Li-storage properties were investigated as anode materials for lithium rechargeable batteries. The pure Cr2O3 works as an adhesive interface to strengthen the connections between Li4Ti5O12 particles, providing more electric conduction channels, and reduce the inter-particle resistance. Moreover, LixCr2O3, formed by the lithiation of Cr2O3, can further stabilize Li7Ti5O12 with high electric conductivity on the surface of particles. While in the acid chromium solution (pH=3.2) modification, besides Cr2O3, Li2CrO4 and TiO2 phases were also found in the final product. Li2CrO4 is toxic and the presence of TiO2 is not welcome to improve the electrochemical performance of Li4Ti5O12 microspheres. The reversible capacity of 1% Cr2O3-coated sample with the basic chromium solution modification was 180 mAh/g at 0.1 C, and 134 mAh/g at 10 C. Moreover, it was even as high as 127 mAh/g at 5 C after 600 cycles. At-20℃, its reversible specific capacity was still as high as 118 mAh/g. 相似文献
984.
M. Abu Haija Y. Romanyshyn H. Kuhlenbeck T.K. Todorova J. Döbler H.-J. Freund 《Surface science》2006,600(7):1497-1503
Well ordered V2O3(0 0 0 1) films were prepared on Au(1 1 1) and W(1 1 0) substrates. These films are terminated by a layer of vanadyl groups under typical UHV conditions. Reduction by electron bombardment may remove the oxygen atoms of the vanadyl layer, leading to a surface terminated by vanadium atoms. The interaction of oxygen with the reduced V2O3(0 0 0 1) surface has been studied in the temperature range from 80 to 610 K. Thermal desorption spectroscopy (TDS), infrared reflection absorption spectroscopy (IRAS), high resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) were used to study the adsorbed oxygen species. Low temperature adsorption of oxygen on reduced V2O3(0 0 0 1) occurs both dissociatively and molecularly. At 90 K a negatively charged molecular oxygen species is observed. Upon annealing the adsorbed oxygen species dissociates, re-oxidizing the reduced surface by the formation of vanadyl species. Density functional theory was employed to calculate the structure and the vibrational frequencies of the O2 species on the surface. Using both cluster and periodic models, the surface species could be identified as η2-peroxo () lying flat on surface, bonded to the surface vanadium atoms. Although the O-O vibrational normal mode involves motions almost parallel to the surface, it can be detected by infrared spectroscopy because it is connected with a change of the dipole moment perpendicular to the surface. 相似文献
985.
M.S. Zei 《Surface science》2006,600(9):1942-1951
The growth and structures of aluminum oxides on NiAl(1 0 0) have been investigated by RHEED (reflection high energy electron diffraction), complemented by LEED (low energy electron diffraction), AES (Auger electron spectroscopy) and STM (scanning tunneling microscopy). Crystalline θ-Al2O3 phase grows through gas-phase oxidation on the NiAl(1 0 0) substrate with its a and b-axes parallel to [0 −1 0] and [0 0 1] direction of the substrate, respectively, forming a (2 × 1) unit cell. Whilst, three-dimensional nano-sized NiAl(1 0 0) protrusions and Al2O3, NiAl(0 1 1) clusters were found to co-exit at the surface, evidenced by extraordinary transmission spots superposed to the substrate reflection rods in the RHEED patterns. Particularly, the NiAl(0 1 1) clusters develop with their (0 1 1) plane parallel to the NiAl(1 0 0) surface, and [1 0 0] axis parallel to the [0 −1 1] direction of the substrate surface. STM observation combined with information from AES and TPD (temperature programmed desorption) suggest the formation of these 3D structures is closely associated with partial decomposition of the crystalline oxides during annealing. On the other hand, smoother (2 × 1) oxide islands with thickness close to a complete monolayer of θ-Al2O3 can be formed on NiAl(1 0 0) by electro-oxidation, in contrast with the large crystalline films formed by gas-oxidation. 相似文献
986.
We have performed total-energy calculations to study theoretical scanning tunneling microscopy (STM) images of the Si(1 1 1)3 × 2 surfaces induced by the adsorption of alkaline-earth metals (AEMs). Previously, in a series of works on Ba/Si(1 1 1) system, we have found that the observed Si(1 1 1)3 × 1-Ba LEED phase indeed has a 3 × 2 periodicity with a Ba coverage of 1/6 ML and the HCC substrate structure. Based on results of the Ba case, we proposed that the HCC structure is also adopted for other AEM atoms, which was confirmed by our recent work. In this paper, we mainly report the STM simulations for different AEM systems to compare with existing experimental data. We discuss the difference in the detailed STM images for different AEM adsorbates. Especially, the difference in filled-state images between Mg and other AEM atoms is attributed to the strong Mg-Si interaction. 相似文献
987.
Jiangang Li Xiangming He Maosong Fan Rusong Zhao Changyin Jiang Chunrong Wan 《Ionics》2006,12(1):77-80
Spherical LiNi1/3Co1/3Mn1/3O2 was successfully prepared by controlled crystallization. The preparation started with the spherical coprecipitate of Ni1/3Co1/3Mn1/3CO3 from NiSO4, CoSO4, MnSO4, NH4HCO3, and NH3·H2O, followed by pyrolysis of Ni1/3Co1/3Mn1/3CO3 at 600°C for 3 h. The X-ray diffraction analysis showed that the homogeneous cubic (Ni1/3Co1/3Mn1/3)3O4 was obtained after the pyrolysis. Spherical LiNi1/3Co1/3Mn1/3O2 was obtained by sintering of the mixture of as-obtained (Ni1/3Co1/3Mn1/3)3O4 and LiOH·H2O at 900°C for 6 h in air. As-prepared spherical LiNi1/3Co1/3Mn1/3O2 presented initial discharge capacity of 162.9 mA h g−1 and capacity retention of 98% at 50th cycle. 相似文献
988.
Correlations of active galactic nuclei (AGNs) with microquasars are discussed based on the coexistence of the Blandford-Znajek (BZ) and magnetic coupling (MC) processes (CEBZMC) in black hole (BH) accretion disk.The proportions of several quantities of BH systems for both AGNs and microquasars are derived by combining the observational data with CEBZMC. It is shown that the square of the magnetic field at the BH horizon is inversely proportional to the BH mass, while the accretion rate of the disk is proportional to the BH mass. In addition, the very steep emissivity indexes from the recent XMM-Newton observations of the nearby bright Seyfert 1 galaxy MCG-6-30-15 and the microquasars XTE J1650-500 are well fitted by considering the MC effects on the disk radiation. These results suggest strongly the correlations of A GNs with microquasars. 相似文献
989.
In this paper, the entangled mapping approach (EMA) is applied to obtain variable separation solutions of (1 1)-dimensional and (3 1)-dimensional systems. By analysis, we firstly find that there also exists a common formula to describe suitable physical fields or potentials for these (1 1)-dimensional models such as coupled integrable dispersionless (CID) and shallow water wave equations. Moreover, we find that the variable separation solution of the (3 1)-dimensional Burgers system satisfies the completely same form as the universal quantity U1 in (2 1 )-dimensional systems. The only difference is that the function q is a solution of a constraint equation and p is an arbitrary function of three independent variables. 相似文献
990.