全文获取类型
收费全文 | 253376篇 |
免费 | 2712篇 |
国内免费 | 897篇 |
专业分类
化学 | 128510篇 |
晶体学 | 4123篇 |
力学 | 11398篇 |
综合类 | 10篇 |
数学 | 28671篇 |
物理学 | 84273篇 |
出版年
2021年 | 1917篇 |
2020年 | 2100篇 |
2019年 | 2309篇 |
2018年 | 3079篇 |
2017年 | 2982篇 |
2016年 | 4466篇 |
2015年 | 2834篇 |
2014年 | 4498篇 |
2013年 | 10911篇 |
2012年 | 8609篇 |
2011年 | 10565篇 |
2010年 | 7338篇 |
2009年 | 7273篇 |
2008年 | 9704篇 |
2007年 | 9700篇 |
2006年 | 9153篇 |
2005年 | 8745篇 |
2004年 | 8220篇 |
2003年 | 7010篇 |
2002年 | 6639篇 |
2001年 | 7509篇 |
2000年 | 5813篇 |
1999年 | 4499篇 |
1998年 | 3793篇 |
1997年 | 3698篇 |
1996年 | 3576篇 |
1995年 | 3259篇 |
1994年 | 3199篇 |
1993年 | 3312篇 |
1992年 | 3416篇 |
1991年 | 3551篇 |
1990年 | 3256篇 |
1989年 | 3189篇 |
1988年 | 3215篇 |
1987年 | 3102篇 |
1986年 | 2941篇 |
1985年 | 3988篇 |
1984年 | 4165篇 |
1983年 | 3349篇 |
1982年 | 3552篇 |
1981年 | 3473篇 |
1980年 | 3360篇 |
1979年 | 3456篇 |
1978年 | 3566篇 |
1977年 | 3449篇 |
1976年 | 3552篇 |
1975年 | 3235篇 |
1974年 | 3251篇 |
1973年 | 3293篇 |
1972年 | 2276篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
42.
43.
Mathieu Boiret Anna de Juan Nathalie Gorretta Yves-Michel Ginot Jean-Michel Roger 《Analytica chimica acta》2015
Raman chemical imaging provides chemical and spatial information about pharmaceutical drug product. By using resolution methods on acquired spectra, the objective is to calculate pure spectra and distribution maps of image compounds. With multivariate curve resolution-alternating least squares, constraints are used to improve the performance of the resolution and to decrease the ambiguity linked to the final solution. Non negativity and spatial local rank constraints have been identified as the most powerful constraints to be used. 相似文献
44.
45.
The Effect of the Spacer of Bis(biurea) Ligands on the Structure of A2L3‐type (A=anion) Phosphate Complexes
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)
Prof. Biao Wu Dr. Shaoguang Li Prof. Yibo Lei Prof. Huaiming Hu Dr. Nader de Sousa Amadeu Prof. Dr. Christoph Janiak Dr. Jennifer S. Mathieson Dr. De‐Liang Long Prof. Leroy Cronin Prof. Xiao‐Juan Yang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(6):2588-2593
By tuning the length and rigidity of the spacer of bis(biurea) ligands L, three structural motifs of the A2L3 complexes (A represents anion, here orthophosphate PO43?), namely helicate, mesocate, and mono‐bridged motif, have been assembled by coordination of the ligand to phosphate anion. Crystal structure analysis indicated that in the three complexes, each of the phosphate ions is coordinated by twelve hydrogen bonds from six surrounding urea groups. The anion coordination properties in solution have also been studied. The results further demonstrate the coordination behavior of phosphate ion, which shows strong tendency for coordination saturation and geometrical preference, thus allowing for the assembly of novel anion coordination‐based structures as in transition‐metal complexes. 相似文献
46.
47.
48.
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
49.
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
50.