全文获取类型
收费全文 | 236篇 |
免费 | 5篇 |
国内免费 | 2篇 |
专业分类
化学 | 119篇 |
晶体学 | 2篇 |
力学 | 1篇 |
数学 | 44篇 |
物理学 | 77篇 |
出版年
2023年 | 2篇 |
2021年 | 2篇 |
2019年 | 3篇 |
2018年 | 1篇 |
2017年 | 3篇 |
2016年 | 4篇 |
2015年 | 7篇 |
2014年 | 6篇 |
2013年 | 9篇 |
2012年 | 11篇 |
2011年 | 11篇 |
2010年 | 9篇 |
2009年 | 8篇 |
2008年 | 20篇 |
2007年 | 12篇 |
2006年 | 21篇 |
2005年 | 16篇 |
2004年 | 15篇 |
2003年 | 10篇 |
2002年 | 8篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 4篇 |
1993年 | 1篇 |
1991年 | 6篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 5篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 5篇 |
1970年 | 2篇 |
1966年 | 1篇 |
排序方式: 共有243条查询结果,搜索用时 15 毫秒
71.
A simple synthetic route to prepare carbon-coated copper or nickel nanoparticles is developed in an ionic liquid under microwave heating. The obtained products are characterized by XRD, UV-spectroscopy, and Raman spectroscopy. The morphologies are studied with the help of TEM, HRSEM, and HRTEM. A bulk transport property for carbon coated nickel is reported in this letter. 相似文献
72.
We present a simple and facile synthesis of MnO octahedral nanocrystals and MnO@C core-shell composite nanoparticles. The synthesis is accomplished by a single-step direct pyrolysis of cetyltrimethylammonium permanganate in specially made Let-lock union cells. The products are characterized by HRSEM, HRTEM, Raman spectroscopy, and cyclic voltammetry (CV). The product consists mainly of octahedral MnO nanocrystals and MnO coated with carbon (MnO@C). The core-shell particles are observed only when the core size is smaller than 150 nm. The shape of the nanocrystals can be controlled by varying parameters such as reaction temperature and duration. As the temperature increases from 600 to 800 degrees C, the octahedral MnO crystals observed are without any carbon shell. The effect of time and temperature on the octahedral MnO nanocrystal formation is described. The electrocatalytic activities of the products are studied for oxygen reduction reaction in aqueous basic medium and are compared with bulk MnO. The MnO nanocrystals and core-shell composites exhibit higher activity than that of bulk MnO. 相似文献
73.
David S. Jacob Avner Rothschild Harry L. Tuller Aharon Gedanken 《Ultrasonics sonochemistry》2010,17(4):726-729
An efficient one-step process for forming uniform solid-like layers of ionic liquid (IL) entrapped in colloidal silica network on interdigitated electrodes (IDE) using ultrasonic deposition is described in this communication. The electrical response of such layers deposited on insulating substrates fitted with interdigitated electrodes was measured upon exposure to different gases (H2, NO2, CO, and CH4) in air demonstrating reversible and sensitive response at 100 °C. 相似文献
74.
We prove that for almost allσ ∈G ℚ the field
has the following property: For each absolutely irreducible affine varietyV of dimensionr and each dominating separable rational mapϕ:V→
there exists a point a ∈
such thatϕ(a) ∈ ℤr. We then say that
is PAC over ℤ. This is a stronger property then being PAC. Indeed we show that beside the fields
other fields which are algebraic over ℤ and are known in the literature to be PAC are not PAC over ℤ. 相似文献
75.
The MCD spectrum of gas phase cyclopropane and the CD spectrum of trans 1,2-dimethyl cyclopropane were measured in the spectral region 210–140 nm. The absorption spectra are also reported. Comparison of CD and absorption spectra of dimethyl cyclopropane and consideration of the anisotropy factors g = Δε/ε as a guide to the assignment of magnetic dipole allowed transitions led to the ordering of the states of the first excited configuration as A′1, A′2, E′ in order of increasing energy. The magnetic moments of the two observed allowed excited states of cyclopropane were determined from the MCD spectrum. LCAO MO level calculations of the MCD parameters 1/0 for the lowest three excited E′ states were carried out and the results were used to discuss the assignment of the allowed transitions. It is concluded that configuration interaction is of considerable importance in the low energy excited states of cyclopropane. 相似文献
76.
Chalcogenide glasses of the composition 0.7Ga2S3·0.27La2S3·0.03Nd2S3 doped by 3 mol% of Nd3+ were prepared. The absorption and emission spectra of these glasses were compared to those of commercial ED-2 3.1 wt.% Nd-doped silicate glass. The absorption intensities of Nd3+ in chalcogenide glass are higher than in silicate glass due to the increasing covalency of Nd3+ in these glasses. Because of the low phonon frequency of the chalcogenide glasses nonradiative relaxations from the 4F, 2H to the 4F are lower than in other oxide glasses and so fluorescence from this state is observed. 相似文献
77.
Li H Wang R Hong Q Chen L Zhong Z Koltypin Y Calderon-Moreno J Gedanken A 《Langmuir : the ACS journal of surfaces and colloids》2004,20(19):8352-8356
Metallic Ru nanoparticles have been successfully produced and incorporated into the pores of SBA-15 in situ employing a simple ultrasound-assisted polyol method. The product has been confirmed by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy, where ultrasound provides both the energy for the reduction of the Ru(III) ion and the driving force for the loading of the Ru(0) nanoparticles into the SBA-15 pores. An ultrasound-assisted insertion mechanism has been proposed based on the microjets and shake-wave effect of the collapsed bubbles. The catalytic properties of the SBA-15-supported Ru nanoparticles have been tested by the partial oxidization of methane and show very high activity and high CO selectivity. 相似文献
78.
I. Perelshtein N. Perkas Sh. Magdassi T. Zioni M. Royz Z. Maor A. Gedanken 《Journal of nanoparticle research》2008,10(1):191-195
A new method of dispersing the aggregated strontium hexaferrite (SrFe12O19) magnetic nanoparticles in organic solvents such as propylene glycol monomethyl ether acetate (PGMEA), propylene glycol (PG),
and glycerol, by an ultrasonic bath is reported herein. The particles size of SrFe12O19 after treatment with the PGMEA is in the range 70–100 nm. The structure of dispersed SrFe12O19 was characterized using transmission electron microscopy (TEM), high resolution scanning electron microscopy (HR SEM) and
thermo gravimetric analysis (TGA). This dispersed material was used for the preparation of a topical magnetic cosmetic product
as follows: The dispersion of SrFe12O19 in PG was mixed with “Dermud-Ahava Body Cream”, an ‘oil in water’ emulsion of a Dead Sea mineral cosmetic, “AHAVA”, and the
magnetic properties of the created composite were determined. The ferrimagnetic behavior of the composite has been demonstrated
as being very similar to the behavior of strontium hexaferrite itself. 相似文献
79.
From discrete particles to spherical aggregates: a simple approach to the self-assembly of Au colloids 总被引:1,自引:0,他引:1
Zhong Z Subramanian AS Highfield J Carpenter K Gedanken A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(5):1473-1478
Here we demonstrate a simple, template-free approach to the formation of spherical gold aggregates through the reduction of HAuCl4 by NaBH4, in the presence of cysteine (Cys) as a capping agent. The resulting aggregates are quite stable in solution. The pH of the solution and the molar ratio of Au:Cys are two key empirical factors in the formation of such highly ordered aggregates. At slightly alkaline pH (7-10) and with Au:Cys ratios ranging from 1:0.5 to 1:2, spherical Au aggregates of 30-80 nm are formed. At lower Cys ratios (Au:Cys> or =1:0.5) very loosely linked aggregates are formed; however, at very high Cys ratios (Au:Cys< or =1:3), highly dispersed Au particles of 2-4 nm are obtained, which are virtually indistinguishable from the original colloidal form. Aggregate size is influenced markedly by component concentration; a 3-fold increase in standard levels resulted in Au spherical aggregates of a larger size, 200-500 nm. In addition, we used a combination of Cys and lysine (Lys) as a capping agent/cross-linker and found that the morphology of the Au colloid aggregates can be easily manipulated from a linear to a spherical form by adjusting the proportions of Cys and Lys in the capping agent/cross-linker mixture. The introduction of mercapto (SH)-containing organic acids reduced the cross-linking ability of Cys, especially in the case of long-chain acids. Complete disruption of the spherical aggregates highlights the importance of Cys per se. An explanation of this ordered self-assembly process is proposed, in the context of the known surface chemistry of Au colloids. 相似文献
80.
Preparation of stable porous nickel and cobalt oxides using simple inorganic precursor, instead of alkoxides, by a sonochemical technique 总被引:3,自引:0,他引:3
Srivastava DN Pol VG Palchik O Zhang L Yu JC Gedanken A 《Ultrasonics sonochemistry》2005,12(3):205-212
Porous nickel and cobalt oxides were prepared using NiSO4.6H2O and anhydrous Co(CH3COO)2, a precursor other than alkoxides and cetyltrimethylammonium bromide as organic surfactant. The sonication method has been used for such synthesis. The surfactants were removed by calcination, as well as by solvent extraction and it is extent was examined by IR spectroscopy. The trend of removal of surfactant was followed by TGA studies and the change in phases by DSC. The products were identified by XRD. Peak in low angle XRD indicates the porous nature of the oxides. The morphology of the pores was studied by transmission electron microscopy. The pores were found less ordered, having an average size of 4-6 nm. The Brunauer-Emmet-Teller surface areas of the as-prepared, as well as the treated samples are reported having H2 and H4 type hysteresis for Ni and Co, respectively. 相似文献