全文获取类型
收费全文 | 22764篇 |
免费 | 3488篇 |
国内免费 | 2447篇 |
专业分类
化学 | 16090篇 |
晶体学 | 276篇 |
力学 | 1355篇 |
综合类 | 187篇 |
数学 | 2315篇 |
物理学 | 8476篇 |
出版年
2024年 | 68篇 |
2023年 | 426篇 |
2022年 | 740篇 |
2021年 | 811篇 |
2020年 | 850篇 |
2019年 | 841篇 |
2018年 | 713篇 |
2017年 | 744篇 |
2016年 | 1017篇 |
2015年 | 1039篇 |
2014年 | 1172篇 |
2013年 | 1609篇 |
2012年 | 1868篇 |
2011年 | 1990篇 |
2010年 | 1299篇 |
2009年 | 1266篇 |
2008年 | 1464篇 |
2007年 | 1351篇 |
2006年 | 1217篇 |
2005年 | 970篇 |
2004年 | 774篇 |
2003年 | 658篇 |
2002年 | 632篇 |
2001年 | 461篇 |
2000年 | 454篇 |
1999年 | 481篇 |
1998年 | 422篇 |
1997年 | 423篇 |
1996年 | 463篇 |
1995年 | 365篇 |
1994年 | 381篇 |
1993年 | 272篇 |
1992年 | 254篇 |
1991年 | 233篇 |
1990年 | 165篇 |
1989年 | 129篇 |
1988年 | 117篇 |
1987年 | 97篇 |
1986年 | 95篇 |
1985年 | 86篇 |
1984年 | 58篇 |
1983年 | 49篇 |
1982年 | 38篇 |
1981年 | 28篇 |
1980年 | 31篇 |
1979年 | 18篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1975年 | 7篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Ingrid Daubechies Jianfeng Lu Hau-Tieng Wu 《Applied and Computational Harmonic Analysis》2011,30(2):243-261
The EMD algorithm is a technique that aims to decompose into their building blocks functions that are the superposition of a (reasonably) small number of components, well separated in the time–frequency plane, each of which can be viewed as approximately harmonic locally, with slowly varying amplitudes and frequencies. The EMD has already shown its usefulness in a wide range of applications including meteorology, structural stability analysis, medical studies. On the other hand, the EMD algorithm contains heuristic and ad hoc elements that make it hard to analyze mathematically.In this paper we describe a method that captures the flavor and philosophy of the EMD approach, albeit using a different approach in constructing the components. The proposed method is a combination of wavelet analysis and reallocation method. We introduce a precise mathematical definition for a class of functions that can be viewed as a superposition of a reasonably small number of approximately harmonic components, and we prove that our method does indeed succeed in decomposing arbitrary functions in this class. We provide several examples, for simulated as well as real data. 相似文献
992.
Isovalent cation substitution into rocksalt oxides, MO, has been investigated using atomistic simulation. A strain related parameter, ε, is established that relates the size of a substitutional cation to the host lattice ion for which it has been substituted. This has allowed us to identify relationships between solution energy, defect volume and a strain parameter, which are general for any rocksalt oxide host lattice and as such are predictive for any combination of a divalent cation and rocksalt host lattice. 相似文献
993.
994.
Li Dong Guo Enyan Lu Qifang Ji Xueyang Wei Mingzhi 《Journal of Solid State Electrochemistry》2017,21(8):2313-2320
Journal of Solid State Electrochemistry - The one-dimensional graphene/TiO2 composite nanofibers with the unique microstructures have been successfully synthesized via an efficient method and... 相似文献
995.
Tian Jin Lu Zhao Maolin Huang Yan Yue Zhe-Bin Zheng Won-Hun Ham 《Tetrahedron: Asymmetry》2017,28(5):725-729
Concise stereoselective syntheses of (?)-clavaminol A and deacetyl (+)-clavaminol H have been achieved from simple starting materials. Highlights of the synthesis for (?)-clavaminol A include a highly diastereoselective chelation-controlled hydride reduction of an amino ketone to give the anti amino alcohol directly, and NaBH4-mediated dehalogenation. The main synthetic approach for deacetyl (+)-clavaminol H features a highly diastereoselective chelation-controlled hydride reduction of the amino ketone to construct the anti amino alcohol and a palladium catalyzed hydrogenation reaction at the final step. 相似文献
996.
997.
Lingling Lu Pan Zhou Biao Hu Xiang Li Rong Huang Fuchao Yu 《Tetrahedron letters》2017,58(37):3658-3661
We report herein an improved Pfitzinger reaction for the synthesis of highly functionalized quinaldines from 1,3-dicarbonyl compounds, isatins and alcohols mediated by TMSCl. This synthesis involves cyclization and esterification in one-step cascade process for the formation of a carboxylate (CO2R) at the 4-position of quinaldine ring. Moreover, this procedure shows highly efficient, good functional group tolerance, operational simplicity, environment-friendly and feasibility of scale up. 相似文献
998.
Solution properties,unperturbed dimensions,and chain flexibility of poly(1‐adamantyl acrylate) 下载免费PDF全文
Wei Lu Panchao Yin Masashi Osa Weiyu Wang Nam‐Goo Kang Kunlun Hong Jimmy W. Mays 《Journal of Polymer Science.Polymer Physics》2017,55(20):1526-1531
Poly(1‐adamantyl acrylate) (PAdA) exhibits much higher glass transition and degradation temperatures than other polyacrylates. However, the quantitative evaluation of the stiffness of this polymer chain has not been reported previously. In this study, the dilute solution properties and conformational characteristics of PAdA were evaluated using viscometry and scattering techniques. The unperturbed dimensions of this polymer were evaluated using the Burchard–Stockmayer–Fixman extrapolation and the touched‐bead wormlike chain model. The PAdA chain has a comparable persistence length, diameter per bead and characteristic ratio to poly(methyl methacrylate) and polystyrene. All these results indicate that PAdA is less flexible than common polyacrylates. In addition, the second virial coefficients (A2) of PAdA in different solvents obtained by static light scattering were compared. Among the solvents investigated, tetrahydrofuran is a moderate solvent. Radius of gyration of a polymer sample in the various solvents ranged from 16.8 to 30.3 nm. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1526–1531 相似文献
999.
1000.
Let k, m, and r be three integers such that 2≤k≤m≤r. Let G be a 2r-regular, 2m-edge-connected graph of odd order. We obtain some sufficient conditions for G-v to contain a k-factor for all v∈V(G). 相似文献