全文获取类型
收费全文 | 699篇 |
免费 | 18篇 |
国内免费 | 2篇 |
专业分类
化学 | 403篇 |
晶体学 | 13篇 |
力学 | 24篇 |
数学 | 142篇 |
物理学 | 137篇 |
出版年
2023年 | 6篇 |
2022年 | 10篇 |
2021年 | 14篇 |
2020年 | 22篇 |
2019年 | 28篇 |
2018年 | 24篇 |
2017年 | 17篇 |
2016年 | 46篇 |
2015年 | 20篇 |
2014年 | 30篇 |
2013年 | 113篇 |
2012年 | 48篇 |
2011年 | 63篇 |
2010年 | 55篇 |
2009年 | 39篇 |
2008年 | 37篇 |
2007年 | 37篇 |
2006年 | 21篇 |
2005年 | 13篇 |
2004年 | 13篇 |
2003年 | 10篇 |
2002年 | 18篇 |
2001年 | 7篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 4篇 |
1997年 | 5篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有719条查询结果,搜索用时 15 毫秒
1.
2.
3.
Activated carbon production from almond shells using phosphoric acid activation agent was achieved by applying both conventional heating and microwave heating in succession. The morphology and surface properties of activated carbon were studied using thermogravimetric and differential gravimetric analysis, Fourier-transform infrared spectroscopy, scanning electron microscopy, and Brunauer–Emmett–Teller analysis. A surface area of 1128 m2/g was achieved by optimizing the microwave power (500?W), microwave application time (15?minutes), conventional heating time (45?minutes), conventional heating temperature (500?°C), and the phosphoric acid:sample ratio (0.7:1). An adsorption capacity of methylene blue of 148?mg/g and an iodine value of 791?mg/g was obtained for the prepared activated carbon. 相似文献
4.
Robert L. Jerrard Halil Mete Soner 《Calculus of Variations and Partial Differential Equations》2002,14(2):151-191
We study the Ginzburg-Landau functional
for , where U is a bounded, open subset of . We show that if a sequence of functions satisfies , then their Jacobians are precompact in the dual of for every . Moreover, any limiting measure is a sum of point masses. We also characterize the -limit of the functionals , in terms of the function space B2V introduced by the authors in [16,17]: we show that I(u) is finite if and only if , and for is equal to the total variation of the Jacobian measure Ju. When the domain U has dimension greater than two, we prove if then the Jacobians are again precompact in for all , and moreover we show that any limiting measure must be integer multiplicity rectifiable. We also show that the total variation
of the Jacobian measure is a lower bound for the limit of the Ginzburg-Landau functional.
Received: 15 December 2000 / Accepted: 23 January 2001 / Published online: 25 June 2001 相似文献
5.
In this paper, by using fixed point theorems in cones, we study the existence of at least one, two and three positive solutions of a nonlinear second-order three-point boundary value problem for dynamic equations on time scales. As an application, we also give some examples to demonstrate our results. 相似文献
6.
7.
Turan K. Yazicilar Omer Andac Yunus Bekdemir Halil Kutuk Veysel T. Yilmaz William T. A. Harrison 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(1):m21-m22
The title compound, alternatively named sodium 6‐nitro‐3H‐1,2,3‐benzoxathiazole 2,2‐dioxide monohydrate, Na+·C6H3N2O5S?·H2O, consists of chains of NaO7 units, with the seven donor‐O atoms coming from two water molecules and five p‐nitrobenzoxasulfamate anions. The seven‐coordinate geometry around the Na+ ion is described as monocapped trigonal prismatic, but with a large distortion from ideal geometry. Each triangular face is defined by one O atom each from a water molecule, a nitro group and a sulfonyl group. An O atom from a sulfonyl group caps one of the square faces of the trigonal prism in an unsymmetrical fashion. The water molecules and one sulfonyl O atom are involved in bridging adjacent units, as is the nitro group of the anion. The sulfamate ions adopt an antiparallel alignment between the NaO7 units and are connected to each other by C—H?O and π–π interactions. The three‐dimensional crystal structure is stabilized by a network of strong O—H?N hydrogen bonds. 相似文献
8.
Saxena C Wang H Kavakli IH Sancar A Zhong D 《Journal of the American Chemical Society》2005,127(22):7984-7985
In this communication, we report the ultrafast dynamics of resonance energy transfer in a blue-light photoreceptor, Vibrio cholerae cryptochrome. The transfer was observed to occur in 60 ps. We also studied the local rigidity and solvation around the binding site of the photoantenna molecule. The results for the first time show energy transfer in cryptochrome suggesting some mechanistic similarities between photolyase that repairs damaged DNA and cryptochrome that mediates blue-light signaling. 相似文献
9.
Ibrahim Isildak Murat Yolcu Omer Isildak Nadir Demirel Giray Topal Halil Hosgoren 《Mikrochimica acta》2004,144(1-3):177-181
Two diaza-crown ether compounds were synthesized and evaluated as Ag+-selective carriers in polyvinylchloride (PVC) membrane electrodes of solid-state type. The all-solid-state PVC membrane electrode based on N,N-Dibenzyl-dibenzo-diaza-18-crown-6 exhibited a super-Nernstian response (75±10mV per decade) over the concentration range of 1×10–1 to 7×10–6M of Ag+ ion and a detection limit of 3×10–6M, at a wide range of pH (pH 4–7). The response time of the electrode was fast (less than 10s), and it can be used for three months without any significant deviation in potential. The proposed all-solid-state PVC membrane electrodes revealed high selectivity toward Ag+ ion with respect to alkali, alkaline earth, heavy and transition metal ions. A flow-through cell of all-solid-state PVC membrane Ag+-selective electrode based on N,N-Dibenzyl-dibenzo-diaza-18-crown-6 has also been prepared and applied for flow-injection analysis of Ag+ ion in solution. 相似文献
10.
Two novel bidentate Schiff base ligands, 2-(2-hydroxy-3,5-dichloro/diboromo) benzaldehyde-[4-(3-methyl-3-mesitylcyclobutyl)-1,3-thiazol-2-yl]hydrazone,
L1H, L2H and their transition metal complexes are reported. The new ligands and their complexes have been characterized by elemental
analyses, ΛM, infrared, u.v.–vis, 1H- and 13C-n.m.r. spectroscopy, and magnetic susceptibility measurements. The thermal properties of all complexes have been investigated
by TG technique. The complexes contain two monoanionic, bidentate NO ligands. It was found that all the complexes are mononuclear.
Antimicrobial activities of the ligands and their complexes have been tested against five different microorganisms, and some
of the complexes were found to be active against some of the microorganisms studied. 相似文献