全文获取类型
收费全文 | 4103篇 |
免费 | 547篇 |
国内免费 | 434篇 |
专业分类
化学 | 3067篇 |
晶体学 | 23篇 |
力学 | 199篇 |
综合类 | 39篇 |
数学 | 359篇 |
物理学 | 1397篇 |
出版年
2024年 | 18篇 |
2023年 | 109篇 |
2022年 | 142篇 |
2021年 | 145篇 |
2020年 | 165篇 |
2019年 | 161篇 |
2018年 | 131篇 |
2017年 | 124篇 |
2016年 | 168篇 |
2015年 | 171篇 |
2014年 | 224篇 |
2013年 | 320篇 |
2012年 | 386篇 |
2011年 | 405篇 |
2010年 | 260篇 |
2009年 | 230篇 |
2008年 | 288篇 |
2007年 | 239篇 |
2006年 | 209篇 |
2005年 | 159篇 |
2004年 | 119篇 |
2003年 | 98篇 |
2002年 | 89篇 |
2001年 | 86篇 |
2000年 | 59篇 |
1999年 | 67篇 |
1998年 | 63篇 |
1997年 | 61篇 |
1996年 | 72篇 |
1995年 | 74篇 |
1994年 | 41篇 |
1993年 | 25篇 |
1992年 | 35篇 |
1991年 | 31篇 |
1990年 | 19篇 |
1989年 | 17篇 |
1988年 | 15篇 |
1987年 | 7篇 |
1986年 | 10篇 |
1985年 | 11篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 1篇 |
1979年 | 5篇 |
1974年 | 1篇 |
1940年 | 1篇 |
1902年 | 1篇 |
1898年 | 1篇 |
排序方式: 共有5084条查询结果,搜索用时 15 毫秒
71.
Hechong Chen Zehong Liang Xinyue Wang Yong Zhang Lingling Shui Dongmei Deng 《Annalen der Physik》2023,535(1):2200375
By applying a virtual source method, the exact and the paraxial solutions of the Swallowtail beams (SBs) that are governed by the inhomogeneous Helmholtz equation are introduced. The paraxial SBs generated experimentally possess both self-accelerating and self-focusing features. The parameters controlling the field distributions are discussed in theory. From the spectral representation of the Swallowtail wave, in the appropriate limit, the first four terms of the nonparaxial correction series for the (1+2)-dimensional Swallowtail waves that simplify to the SBs are obtained. 相似文献
72.
73.
74.
75.
Yinwu Li Jiahao Liu Dr. Xiao Huang Prof. Dr. Ling-Bo Qu Prof. Dr. Cunyuan Zhao Prof. Dr. Robert Langer Prof. Dr. Zhuofeng Ke 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(60):13785-13798
As a new type of bifunctional catalyst, the Lewis acid transition-metal (LA-TM) catalysts have been widely applied for hydrogen activation. This study presents a mechanistic framework to understand the LA-TM-catalyzed H2 activation through DFT studies. The mer(trans)-homolytic cleavage, the fac(cis)-homolytic cleavage, the synergetic heterolytic cleavage, and the dissociative heterolytic cleavage should be taken as general mechanisms for the field of LA-TM catalysis. Four typical LA-TM catalysts, the Z-type κ4-L3B-Rh complex tri(azaindolyl)borane-Rh, the X-type κ3-L2B-Co complex bis-phosphino-boryl (PBP)-Co, the η2-BC-type κ3-L2B-Pd complex diphosphine-borane (DPB)-Pd, and the Z-type κ2-LB-Pt complex (boryl)iminomethane (BIM)-Pt are selected as representative models to systematically illustrate their mechanistic features and explore the influencing factors on mechanistic variations. Our results indicate that the tri(azaindolyl)borane-Rh catalyst favors the synergetic heterolytic mechanism; the PBP-Co catalyst prefers the mer(trans)-homolytic mechanism; the DPB-Pd catalyst operates through the fac(cis)-homolytic mechanism, whereas the BIM-Pt catalyst tends to undergo the dissociative heterolytic mechanism. The mechanistic variations are determined by the coordination geometry, the LA-TM bonding nature, the electronic structure of the TM center, and the flexibility or steric effect of the LA ligands. The presented mechanistic framework should provide helpful guidelines for LA-TM catalyst design and reaction developments. 相似文献
76.
Experimental Mechanics - Identification of impact force is essential for various engineering applications, such as performance evaluation, design optimisation, noise suppression, and vibration... 相似文献
77.
Jie Li Prof. Dr. Shuanglin Qu Prof. Dr. Wanxiang Zhao 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(6):2380-2384
A rhodium-catalyzed remote C(sp3)−H borylation of silyl enol ethers (SEEs, E/Z mixtures) by alkene isomerization and hydroboration is reported. The reaction exhibits mild reaction conditions and excellent functional-group tolerance. This method is compatible with an array of SEEs, including linear and branched SEEs derived from aldehydes and ketones, and provides direct access to a broad range of structurally diverse 1,n-borylethers in excellent regioselectivities and good yields. These compounds are precursors to various valuable chemicals, such as 1,n-diols and aminoalcohols. 相似文献
78.
79.
We fabricate Sm-doped Ca3Co4O9+δ(CCO)bulk materials in magnetic field during both processes of chemical synthesis and cold pressing.The structure and electrical performance of the samples are investigated.With the increasing Sm concentration,the electrical conductivity 1/ρ decreases and the Seebeck coefficientαincreases.As a result,the power factor(PF=α^2/ρ)is raised slightly.After applying magnetic field,the extent of texture,grain size and density of all the bulk materials are improved obviously,thereby an enhanced electrical conductivity can be gained.Additionally,the degeneracy of Co^4+ state in the CoO2 layer of CCO is also increased as the magnetic field is used in the preparing process,which results in an enhancedα.The Ca2.85Sm0.15Co4O9+δ prepared in magnetic field shows the largest power factor(0.20 mW·m^-1·K^-2 at 1073 K). 相似文献
80.