全文获取类型
收费全文 | 3447篇 |
免费 | 139篇 |
国内免费 | 9篇 |
专业分类
化学 | 2726篇 |
晶体学 | 39篇 |
力学 | 57篇 |
数学 | 319篇 |
物理学 | 454篇 |
出版年
2023年 | 18篇 |
2022年 | 18篇 |
2021年 | 38篇 |
2020年 | 64篇 |
2019年 | 56篇 |
2018年 | 31篇 |
2017年 | 33篇 |
2016年 | 86篇 |
2015年 | 84篇 |
2014年 | 102篇 |
2013年 | 148篇 |
2012年 | 233篇 |
2011年 | 273篇 |
2010年 | 130篇 |
2009年 | 117篇 |
2008年 | 242篇 |
2007年 | 245篇 |
2006年 | 229篇 |
2005年 | 228篇 |
2004年 | 188篇 |
2003年 | 152篇 |
2002年 | 136篇 |
2001年 | 56篇 |
2000年 | 49篇 |
1999年 | 35篇 |
1998年 | 34篇 |
1997年 | 28篇 |
1996年 | 50篇 |
1995年 | 42篇 |
1994年 | 25篇 |
1993年 | 37篇 |
1992年 | 33篇 |
1991年 | 17篇 |
1990年 | 12篇 |
1989年 | 12篇 |
1988年 | 11篇 |
1987年 | 22篇 |
1986年 | 14篇 |
1985年 | 20篇 |
1984年 | 20篇 |
1983年 | 12篇 |
1982年 | 17篇 |
1981年 | 14篇 |
1980年 | 19篇 |
1978年 | 16篇 |
1977年 | 18篇 |
1976年 | 14篇 |
1975年 | 14篇 |
1973年 | 11篇 |
1972年 | 12篇 |
排序方式: 共有3595条查询结果,搜索用时 31 毫秒
1.
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
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
2.
3.
Ieva
Dauickait Amos S. Lawless Jennifer A. Scott Peter Jan van Leeuwen 《Numerical Linear Algebra with Applications》2020,27(5)
We consider the large sparse symmetric linear systems of equations that arise in the solution of weak constraint four‐dimensional variational data assimilation, a method of high interest for numerical weather prediction. These systems can be written as saddle point systems with a 3 × 3 block structure but block eliminations can be performed to reduce them to saddle point systems with a 2 × 2 block structure, or further to symmetric positive definite systems. In this article, we analyse how sensitive the spectra of these matrices are to the number of observations of the underlying dynamical system. We also obtain bounds on the eigenvalues of the matrices. Numerical experiments are used to confirm the theoretical analysis and bounds. 相似文献
4.
5.
A free-piston driver that employs entropy-raising shock processes with diaphragm rupture has been constructed, which promises
significant theoretical advantages over isentropic compression. Results from a range of conditions with helium and argon driver
gases are reported. Significant performance gains were achieved in some test cases. Heat losses are shown to have a strong
effect on driver processes. Measurements compare well with predictions from a quasi-one-dimensional numerical code.
Received 7 September 1996 / Accepted 5 October 1996 相似文献
6.
Christos Kravvaritis Marilena Mitrouli Jennifer Seberry 《Linear and Multilinear Algebra》2007,55(5):471-490
In the present article we concentrate our study on the growth problem for the weighing matrix W(12,11) and show that the unique W(12,11) has three pivot structures. An improved algorithm for extending a k × k (0,+,-) matrix to a W(n,n-1), if possible, has been developed to simplify the proof. For the implementation of the algorithm special emphasis is given to the notions of data structures and parallel processing. 相似文献
7.
8.
Ian R. Butler Alfonso G. Callabero Jennifer R. Amey Dafydd A. Thomas Thomas Gelbrich 《Tetrahedron letters》2004,45(3):467-472
The synthesis of a range of ferrocene-substituted ethynylanthracenes and 1,1′-(bis-(2-ethenylanthraquinoyl)ferrocene has been achieved. The synthesis relies on the production of ferrocenylanthraquinones as key precursors. The products were obtained in the reactions of ferrocenylanthraquinones with phenylethynyllithium or trimethylsilylethynyllithium followed by reduction with tin chloride. The key products such as 1- and 2-ferrocenyl(9,10-bis-phenylethynyl)anthracenes have been characterised by X-ray single crystal diffraction. 相似文献
9.
10.
E. Possenriede P. Jacobs H. Kröse O. F. Schirmer 《Applied Physics A: Materials Science & Processing》1992,55(1):73-81
On the basis of a previous identification of paramagnetic defects in nominally undoped as grown BaTiO3 single crystals, we have investigated the changes of the concentrations of these centers and their optical absorptions under illumination with light of varying wavelengths. The most pronounced charge transfers occur by hole ionization of Fe4+ and — to a lesser extent — of Cr5+ and Cr4+. At low temperatures the created holes are trapped in the form of O–-ions next to Al3+ or unknown acceptor defects. Corresponding Fe4+ and O– absorptions have been identified. 相似文献