全文获取类型
收费全文 | 298093篇 |
免费 | 7438篇 |
国内免费 | 5233篇 |
专业分类
化学 | 165594篇 |
晶体学 | 4299篇 |
力学 | 13565篇 |
综合类 | 328篇 |
数学 | 34334篇 |
物理学 | 92644篇 |
出版年
2022年 | 2776篇 |
2021年 | 3536篇 |
2020年 | 3995篇 |
2019年 | 4432篇 |
2018年 | 5546篇 |
2017年 | 5348篇 |
2016年 | 7134篇 |
2015年 | 4525篇 |
2014年 | 6843篇 |
2013年 | 13485篇 |
2012年 | 11332篇 |
2011年 | 13010篇 |
2010年 | 9662篇 |
2009年 | 9558篇 |
2008年 | 11975篇 |
2007年 | 11676篇 |
2006年 | 10874篇 |
2005年 | 9809篇 |
2004年 | 8711篇 |
2003年 | 7893篇 |
2002年 | 7879篇 |
2001年 | 8073篇 |
2000年 | 6379篇 |
1999年 | 4902篇 |
1998年 | 4356篇 |
1997年 | 4170篇 |
1996年 | 3946篇 |
1995年 | 3277篇 |
1994年 | 3440篇 |
1993年 | 3412篇 |
1992年 | 3518篇 |
1991年 | 3623篇 |
1990年 | 3517篇 |
1989年 | 3431篇 |
1988年 | 3256篇 |
1987年 | 3187篇 |
1986年 | 3109篇 |
1985年 | 3807篇 |
1984年 | 3990篇 |
1983年 | 3252篇 |
1982年 | 3494篇 |
1981年 | 3278篇 |
1980年 | 3052篇 |
1979年 | 3359篇 |
1978年 | 3517篇 |
1977年 | 3530篇 |
1976年 | 3583篇 |
1975年 | 3371篇 |
1974年 | 3369篇 |
1973年 | 3511篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
M. Kroon E. Andreasson E. Persson Jutemar V. Petersson L. Persson M. Dorn P.A.T. Olsson 《Experimental Mechanics》2018,58(1):75-86
Injection-moulding is one of the most common manufacturing processes used for polymers. In many applications, the mechanical properties of the product is of great importance. Injection-moulding of thin-walled polymer products tends to leave the polymer structure in a state where the mechanical properties are anisotropic, due to alignment of polymer chains along the melt flow direction. The anisotropic elastic-viscoplastic properties of low-density polyethylene, that has undergone an injection-moulding process, are therefore examined in the present work. Test specimens were punched out from injection-moulded plates and tested in uniaxial tension. Three in-plane material directions were investigated. Because of the small thickness of the plates, only the in-plane properties could be determined. Tensile tests with both monotonic and cyclic loading were performed, and the local strains on the surface of the test specimens were measured using image analysis. True stress vs. true strain diagrams were constructed, and the material response was evaluated using an elastic-viscoplasticity law. The components of the anisotropic compliance matrix were determined together with the direction-specific plastic hardening parameters. 相似文献
62.
Erosion and sediments transport processes have a great impact on industrial structures and on water quality. Despite its limitations, the Saint‐Venant‐Exner system is still (and for sure for some years) widely used in industrial codes to model the bedload sediment transport. In practice, its numerical resolution is mostly handled by a splitting technique that allows a weak coupling between hydraulic and morphodynamic distinct softwares but may suffer from important stability issues. In recent works, many authors proposed alternative methods based on a strong coupling that cure this problem but are not so trivial to implement in an industrial context. In this work, we then pursue 2 objectives. First, we propose a very simple scheme based on an approximate Riemann solver, respecting the strong coupling framework, and we demonstrate its stability and accuracy through a number of numerical test cases. However, second, we reinterpret our scheme as a splitting technique and we extend the purpose to propose what should be the minimal coupling that ensures the stability of the global numerical process in industrial codes, at least, when dealing with collocated finite volume method. The resulting splitting method is, up to our knowledge, the only one for which stability properties are fully demonstrated. 相似文献
63.
64.
Inside Cover: Photoinduced Formation of an Azobenzene‐Based CD‐Active Supramolecular Cyclic Dimer (Chem. Eur. J. 18/2015)
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
65.
66.
67.
Polypyrrole Shell@3D‐Ni Metal Core Structured Electrodes for High‐Performance Supercapacitors
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Gao‐Feng Chen Yu‐Zhi Su Pan‐Yong Kuang Zhao‐Qing Liu Dao‐Yi Chen Xu Wu Nan Li Prof. Shi‐Zhang Qiao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(12):4614-4621
Three‐dimensional (3D) nanometal films serving as current collectors have attracted much interest recently owing to their promising application in high‐performance supercapacitors. In the process of the electrochemical reaction, the 3D structure can provide a short diffusion path for fast ion transport, and the highly conductive nanometal may serve as a backbone for facile electron transfer. In this work, a novel polypyrrole (PPy) shell@3D‐Ni‐core composite is developed to enhance the electrochemical performance of conventional PPy. With the introduction of a Ni metal core, the as‐prepared material exhibits a high specific capacitance (726 F g?1 at a charge/discharge rate of 1 A g?1), good rate capability (a decay of 33 % in Csp with charge/discharge rates increasing from 1 to 20 A g?1), and high cycle stability (only a small decrease of 4.2 % in Csp after 1000 cycles at a scan rate of 100 mV s?1). Furthermore, an aqueous symmetric supercapacitor device is fabricated by using the as‐prepared composite as electrodes; the device demonstrates a high energy density (≈21.2 Wh kg?1) and superior long‐term cycle ability (only 4.4 % and 18.6 % loss in Csp after 2000 and 5000 cycles, respectively). 相似文献
68.
69.
70.
Jing Yu Jingwei Han Chuanzhong Li 《Mathematical Methods in the Applied Sciences》2020,43(6):3076-3085
For the orthosymplectic Lie superalgebra , we choose a set of basis matrices. A linear combination of those basis matrices presents a spatial spectral matrix. The compatible condition of the spatial part and the corresponding temporal parts of the spectral problem leads to a generalized super AKNS (GSAKNS) hierarchy. By making use of the supertrace identity, the obtained GSAKNS hierarchy can be written as the super bi-Hamiltonian structures. 相似文献