全文获取类型
收费全文 | 275篇 |
免费 | 12篇 |
国内免费 | 2篇 |
专业分类
化学 | 247篇 |
晶体学 | 1篇 |
数学 | 16篇 |
物理学 | 25篇 |
出版年
2023年 | 1篇 |
2022年 | 6篇 |
2021年 | 8篇 |
2020年 | 6篇 |
2019年 | 2篇 |
2018年 | 3篇 |
2017年 | 4篇 |
2016年 | 9篇 |
2015年 | 6篇 |
2014年 | 9篇 |
2013年 | 12篇 |
2012年 | 23篇 |
2011年 | 17篇 |
2010年 | 10篇 |
2009年 | 10篇 |
2008年 | 23篇 |
2007年 | 26篇 |
2006年 | 20篇 |
2005年 | 22篇 |
2004年 | 14篇 |
2003年 | 10篇 |
2002年 | 11篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1974年 | 3篇 |
排序方式: 共有289条查询结果,搜索用时 31 毫秒
141.
Giovanni M Ambrosi A Pumera M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(6):1806-1810
Bioavailable residual metallic impurities within carbon nanotubes (CNTs) are responsible for the toxicity of CNTs. Herein we present a method for fast, sensitive determination of bioavailable molybdenum residual catalyst impurities within CNTs by using electrochemical oxidation in neutral pH buffers at low potentials. This method is unique because no other method can rapidly distinguish between bioavailable/mobilizable impurities from defects in CNTs and between the total amounts of impurities. This method will be indispensable for future toxicological studies of CNTs. 相似文献
142.
143.
Szabolcs L. Fancsali Peter Sziklai Marcella Takáts 《Journal of Algebraic Combinatorics》2013,37(1):27-37
In this article we prove a theorem about the number of directions determined by less then q affine points, similar to the result of Blokhuis et al. (in J. Comb. Theory Ser. A 86(1), 187–196, 1999) on the number of directions determined by q affine points. 相似文献
144.
145.
146.
Temporão G Tanzilli S Zbinden H Gisin N Aellen T Giovannini M Faist J 《Optics letters》2006,31(8):1094-1096
We report a procedure to detect mid-infrared single photons at 4.65 microm by means of a two-stage scheme based on sum-frequency generation, by using a periodically poled lithium niobate nonlinear crystal and a silicon avalanche photodiode. An experimental investigation shows that, in addition to a high timing resolution, this technique yields a detection sensitivity of 1.24 pW with 63 mW of net pump power. 相似文献
147.
In this work, m‐phenylenediamine (MPD) is used to prepare cross‐linked polyetherimide (PEI)‐based nanofiltration (NF) membrane for treatment of dye containing wastewater. The effects of dope solution composition, cross‐linking time, and dye concentration on membrane performance are investigated. Results indicate that the rejection of dye is increased with the increase of acetone concentration in the dope solution, cross‐linking time, and dye concentration. Meanwhile, membrane flux showed the opposite trend. With the aid of SEM and FTIR analysis, the cross‐linking between MPD and PEI is confirmed. The cross‐linked membrane has thicker and dense selective layer compared to the unmodified membrane. The cross‐linked NF membrane (PEI: 15 wt%; acetone: 20 wt%; cross‐linking time: 10 minutes) showed good performance in filtration of synthetic dye wastewater (Reactive Red 120, 1500 ppm) with 98% dye rejection and 0.013 L m?2 hour?1 of flux at relatively low operating pressure (60 psi). 相似文献
148.
Bartoli G Bosco M Dalpozzo R Giuliani A Marcantoni E Mecozzi T Sambri L Torregiani E 《The Journal of organic chemistry》2002,67(25):9111-9114
2-Alkylidenecycloalkanones are powerful synthons used as the key intermediates in many important syntheses. Because of their potential, a general method of preparation from readily available starting materials, under very mild conditions, was considered to be worthwhile. Cerium(III) chloride heptahydrate in combination with sodium iodide in refluxing acetonitrile promotes a regio- and stereoselective beta-elimination reaction to (E)-2-alkylidenecycloalkanones in 2-(1-hydroxyalkyl)cycloalkanones. The synthetic value of the present procedure is demonstrated by the synthesis of monoterpene (S)-(-)-pulegone (8) in its optically active form. 相似文献
149.
The first example of an iridium biscyclometalated complex with a C wedge N wedge C 2,6-diphenylpyridine (dppy)-type ligand, [(4'-(4-bromophenyl)-2:2',6':2' '-terpyridine)Ir(2,6-diphenyl-4-(4-tolyl)pyridine)](NO(3)) (1), has been synthesized and characterized by various techniques such as X-ray crystallography, mass spectrometry, (1)H and (13)C NMR, cyclic voltammetry, and both steady-state and time-resolved emission and absorption studies. Preliminary density functional theory calculations have also been conducted. 1 crystallizes in the monoclinic space group P2(1)/n. The crystallographic data are as follows: C(45)H(31)BrN(4)IrO(3).2H(2)O, a = 17.4308(4) A, b = 9.0312(2) A, c = 26.7601(7) A, beta = 104.496(1) degrees, V = 4078.5(2) A(3), Z = 4. The relatively long Ir-C distances (2.122 and 2.094 A) reflect the strong mutual trans effect of the cyclometalating carbons. The complex exhibits strong visible absorption and long-lived (1.7 micros) emission (lambda(max), 690 nm) in room temperature solution. The inherent asymmetry of the coordination environment offers a unique directional character to the emitting excited state, which is predominantly ligand-to-ligand charge transfer (dppy --> 2,2':6',2' '-terpyridine) in nature. 相似文献
150.
Mauro Francaviglia Marcella Palese Raffaele Vitolo 《Czechoslovak Mathematical Journal》2002,52(1):197-213
We refer to Krupka's variational sequence, i.e. the quotient of the de Rham sequence on a finite order jet space with respect to a variationally trivial subsequence. Among the morphisms of the variational sequence there are the Euler-Lagrange operator and the Helmholtz operator.In this note we show that the Lie derivative operator passes to the quotient in the variational sequence. Then we define the variational Lie derivative as an operator on the sheaves of the variational sequence. Explicit representations of this operator give us some abstract versions of Noether's theorems, which can be interpreted in terms of conserved currents for Lagrangians and Euler-Lagrange morphisms. 相似文献