全文获取类型
收费全文 | 665篇 |
免费 | 29篇 |
国内免费 | 4篇 |
专业分类
化学 | 455篇 |
晶体学 | 4篇 |
力学 | 23篇 |
数学 | 127篇 |
物理学 | 89篇 |
出版年
2023年 | 4篇 |
2022年 | 9篇 |
2021年 | 7篇 |
2020年 | 9篇 |
2019年 | 15篇 |
2018年 | 10篇 |
2017年 | 8篇 |
2016年 | 19篇 |
2015年 | 23篇 |
2014年 | 27篇 |
2013年 | 43篇 |
2012年 | 53篇 |
2011年 | 65篇 |
2010年 | 38篇 |
2009年 | 38篇 |
2008年 | 39篇 |
2007年 | 38篇 |
2006年 | 40篇 |
2005年 | 36篇 |
2004年 | 33篇 |
2003年 | 21篇 |
2002年 | 25篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1998年 | 4篇 |
1997年 | 5篇 |
1994年 | 7篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 5篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1969年 | 2篇 |
1968年 | 2篇 |
1967年 | 2篇 |
1966年 | 2篇 |
排序方式: 共有698条查询结果,搜索用时 156 毫秒
171.
Trapping cations in specific positions in tuneable "artificial cell" channels: new nanochemistry perspectives 总被引:1,自引:0,他引:1
172.
173.
Cationic triarylmethane dyes containing one, two or three naphthalene moieties have been prepared. Their synthesis and preliminary spectral, nonlinear optical and theoretical characterization are reported here. The major electronic and steric hindrance effects of the 1,4-linked naphthalene have been examined by comparison of the UV-vis absorption of the 1,4-linked and 2,6-linked series. 相似文献
174.
Two quanta of the aldehyde H-wag vibrational mode are observed with relatively constant activity in the vibrational structure of 3A″ (nπ*) → 1A′ phosphorescence spectra of benzaldehyde, deuterated benzaldehydes, pyridine aldehydes, p-methylbenzaldehyde, p-fluorobenzaldehyde, and p-chlorobenzaldehyde at 4.2°K in a methylcyclohexane polycrystalline environment. The fundamental is either missing or very weak. Contrasted to the aldehyde H-wag mode, higher quanta of the CHO torsional mode are observed in the phosphorescence of the same molecules with variable intensity and progression length. These results are interpreted in terms of a static (i.e., valence) distortion of the 3nπ potential surface along the aldehyde H-wagging coordinate, and pseudo-Jahn-Teller distortion along the CHO torsional coordinate. The valence distortion is analogous to a distortion found for the 3nπ* state in propynal and its origin probably lies in excess electron density at the carbonyl carbon in the excited state. The dynamical Jahn-Teller distortion is ascribed to vibronic interaction between 3A″ (nπ) and the nearest 3A′(nπ*) states. 相似文献
175.
Jérôme Lamontagne Lionel Desgranges Christophe Valot Jean Noirot Thierry Blay Ingrid Roure Bertrand Pasquet 《Mikrochimica acta》2006,155(1-2):183-187
The behaviour of gases produced by fission is of great importance for nuclear fuel operation. Within this context, an experimental
method for the characterisation of the fission gas including gas bubbles in an irradiated UO2 nuclear fuel was developed in our laboratory using SIMS, EPMA and SEM results. SIMS and EPMA have been used to measure the
radial distribution of xenon and SEM gives information on bubble formation across the fuel pellet radius. Using SIMS, xenon
concentration can be determined in the matrix and in the bubbles. A quantification method, allowing the determination of the
total inventory of xenon, is proposed and qualified with EPMA results. It is concluded that the complementary micro-analytical
techniques SIMS, EPMA and SEM are very powerful tools for the characterisation of the fission gas bubbles in irradiated nuclear
fuel. 相似文献
176.
Maria PC Gal JF Massi L Burk P Tammiku-Taul J Tamp S 《Rapid communications in mass spectrometry : RCM》2005,19(4):568-573
A concerted theoretical (density-functional theory) and experimental electrospray mass spectrometry study was conducted on the formation of cesium cation adducts with small molecules taken as models of specific interactions sites in humic substances. Electrospray experiments with phenol, benzoic acid, salicylic acid, and phthalic acid, in methanolic solution containing cesium nitrate, were performed using a quadrupole ion trap. The formation of positively charged mixed clusters, [Cs(CsNO3)(n)(CsA1)(m)(Cs2A2)(p)]+ (A1 = benzoate, salicylate, and hydrogenophthalate, A2 = phthalate), was observed. Calculations of structures and bonding energetics of Cs+ in simple adducts formed with NO3-, CsNO3, A-, AH, and CsA are reported. The observation of variable cluster stoichiometry (n, m and p values) was interpreted in terms of more or less favorable interaction energies between Cs+ and the neutral species constituting the clusters. Phenol did not form clusters in significant abundances, despite a strong calculated interaction between Cs+ and cesium phenolate. This was attributed to its weak acid dissociation in the electrospray solution. 相似文献
177.
Daughter, parent and constant neutral loss spectra, and multiple reaction ion monitoring data were all evaluated for the detection and confirmation of phosphate esters during capillary column GC-MS-MS analysis with a hybrid tandem mass spectrometer. Constant neutral loss and parent modes involve scanning of the sector, thus reducing the benefits of higher sector resolution, while daughter and multiple reaction ion monitoring data may be acquired with higher sector resolution. The benefit of higher sector resolution was demonstrated for the detection and confirmation of phosphate esters in the presence of diesel exhaust extract components at levels several orders of magnitude above that of the phosphate esters. Detection limits for daughter operation were approximately the same as those obtained during capillary column GC-MS analysis of standards under electron impact ionization, and S/N ratios in excess of 100:1 were observed during multiple reaction ion monitoring of the diesel exhaust extract spiked at the 200 pg level with phosphate esters. 相似文献
178.
Lionel Moisan Thierry Le Borgne Pierre Thury Michel Ephritikhine 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(2):m98-m101
In bis[1,1′,2,2′,3,3′,4,4′‐octamethyl‐5‐(2‐pyridinio)‐5′‐(2‐pyridyl)ferrocene] di‐μ3‐chloro‐hexadeca‐μ2‐chloro‐hexachlorodi‐μ4‐oxo‐di‐μ3‐oxo‐bis[(η5,κN)‐1,2,3,4‐tetramethyl‐5‐(2‐pyridyl)cyclopentadienyl]octauranium(IV) dichloromethane tetrasolvate, [Fe(C14H17N)(C14H16N)]2[U8Cl24O4(C14H16N)2]·4CH2Cl2, (I), two protonated Fe(cp*py)2 units [cp*py is tetramethyl‐5‐(2‐pyridyl)cyclopentadiene] form an ion pair with the dianionic centrosymmetric cluster U8Cl24O4(cp*py)2. The latter is the highest nuclearity assemblage in the chemistry of uranium (non‐uranyl) compounds reported to date. 相似文献
179.
Mijno V Catalan LJ Martin F Bollinger JC 《Journal of colloid and interface science》2004,280(2):617-477
Cement-based stabilization/solidification (s/s) is a widely used treatment process for hazardous wastes containing toxic metals. The treated waste consists of a complex mixture of several solid phases produced by cement hydration reactions. Understanding and predicting the effects of leaching on these individual phases is essential for assessing the long-term immobilization of metal contaminants in s/s waste exposed to rain and groundwater. In this paper, particles of crushed Portland cement doped with copper, lead, and zinc nitrates were leached with nitric acid solutions maintained at constant pH in the range pH 4-7. Changes in solid composition at the microscopic scale were measured by scanning electron microscopy and energy dispersive X-ray spectrometry (SEM/EDX). The geochemical equilibrium model SOLTEQ-B, which accounts for the incongruent solubility behavior of calcium silicate hydrate, was used to simulate the compositional changes in the hydration gel for increasing extents of leaching. Measured concentrations of calcium, silicon, and sulfur were successfully predicted at all extents of leaching. Aluminum, lead, and zinc concentrations were also in good agreement with model predictions, except in the remineralization zones that form when metals solubilized in the outer regions of the s/s waste particles diffuse toward the interior and reprecipitate at higher pH. Copper was less accurately modeled at high extents of leaching. Accounting for the incorporation of contaminant metals into the cement hydration gel (in opposition to assuming the presence of individual metal hydroxides) is crucial for successfully predicting contaminant metal concentrations in the hydration gel at low and intermediate extents of leaching. 相似文献
180.
A review is given on the use of the bend elastic chain model for the calculation of physical properties of polymers. 相似文献