全文获取类型
收费全文 | 378篇 |
免费 | 28篇 |
专业分类
化学 | 312篇 |
力学 | 6篇 |
数学 | 35篇 |
物理学 | 53篇 |
出版年
2023年 | 7篇 |
2022年 | 10篇 |
2021年 | 12篇 |
2020年 | 32篇 |
2019年 | 14篇 |
2018年 | 14篇 |
2017年 | 7篇 |
2016年 | 19篇 |
2015年 | 22篇 |
2014年 | 16篇 |
2013年 | 17篇 |
2012年 | 41篇 |
2011年 | 36篇 |
2010年 | 16篇 |
2009年 | 20篇 |
2008年 | 22篇 |
2007年 | 18篇 |
2006年 | 14篇 |
2005年 | 15篇 |
2004年 | 14篇 |
2003年 | 12篇 |
2002年 | 7篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1997年 | 2篇 |
1993年 | 1篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1975年 | 1篇 |
1970年 | 1篇 |
1968年 | 2篇 |
1914年 | 1篇 |
排序方式: 共有406条查询结果,搜索用时 171 毫秒
351.
Mark A. Wieczorek Frederik J. Simons 《Journal of Fourier Analysis and Applications》2007,13(6):665-692
We develop a method to estimate the power spectrum of a stochastic process on the sphere from data of limited geographical
coverage. Our approach can be interpreted either as estimating the global power spectrum of a stationary process when only
a portion of the data are available for analysis, or estimating the power spectrum from local data under the assumption that
the data are locally stationary in a specified region. Restricting a global function to a spatial subdomain—whether by necessity
or by design—is a windowing operation, and an equation like a convolution in the spectral domain relates the expected value
of the windowed power spectrum to the underlying global power spectrum and the known power spectrum of the localization window.
The best windows for the purpose of localized spectral analysis have their energy concentrated in the region of interest while
possessing the smallest effective bandwidth as possible. Solving an optimization problem in the sense of Slepian (1960) yields
a family of orthogonal windows of diminishing spatiospectral localization, the best concentrated of which we propose to use
to form a weighted multitaper spectrum estimate in the sense of Thomson (1982). Such an estimate is both more representative
of the target region and reduces the estimation variance when compared to estimates formed by any single bandlimited window.
We describe how the weights applied to the individual spectral estimates in forming the multitaper estimate can be chosen
such that the variance of the estimate is minimized. 相似文献
352.
Frederik Wurm Dr. Andreas F. M. Kilbinger Dr. 《Angewandte Chemie (International ed. in English)》2009,48(45):8412-8421
Since de Gennes’ Nobel lecture in 1991, in which he coined the term “Janus grains”, research into asymmetric particles has boomed. Macroscopic, microscopic and nanoscopic particles have been prepared in which certain parts of their surface differ in chemical composition, polarity, color, or any other property. Spherical, cylindrical, disc‐like, snowman‐, hamburger‐, and raspberry‐like structures have been synthesized from organic or inorganic materials or even as hybrids of both. Synthetic strategies towards such particles vary greatly from simple polymer mixtures to the bulk self‐assembly of sophisticated terpolymers to immobilization methods of symmetric particles. Polymeric Janus particles are particularly promising, as they can often be prepared cheaply and sometimes even on larger scales. 相似文献
353.
Vermoortele F Maes M Moghadam PZ Lennox MJ Ragon F Boulhout M Biswas S Laurier KG Beurroies I Denoyel R Roeffaers M Stock N Düren T Serre C De Vos DE 《Journal of the American Chemical Society》2011,133(46):18526-18529
Para-disubstituted alkylaromatics such as p-xylene are preferentially adsorbed from an isomer mixture on three isostructural metal-organic frameworks: MIL-125(Ti) ([Ti(8)O(8)(OH)(4)(BDC)(6)]), MIL-125(Ti)-NH(2) ([Ti(8)O(8)(OH)(4)(BDC-NH(2))(6)]), and CAU-1(Al)-NH(2) ([Al(8)(OH)(4)(OCH(3))(8)(BDC-NH(2))(6)]) (BDC = 1,4-benzenedicarboxylate). Their unique structure contains octahedral cages, which can separate molecules on the basis of differences in packing and interaction with the pore walls, as well as smaller tetrahedral cages, which are capable of separating molecules by molecular sieving. These experimental data are in line with predictions by molecular simulations. Additional adsorption and microcalorimetric experiments provide insight in the complementary role of the two cage types in providing the para selectivity. 相似文献
354.
WD Malsche SD Bruyne JO Beeck S Eeltink F Detobel H Gardeniers G Desmet 《Journal of separation science》2012,35(16):NA
DOI: 10.1002/jssc.201200279 A 9 cm silicon long pillar array containing 5 μm diameter silicon pillars cladded with a meso-porous silica layer with a thickness of 300 nm was directly interfaced to a capillary LC instrument, yielding protein digest peak capacities of up to 150. 相似文献
355.
Caught in a 'S(N) Ar'e: A one-step, high-yielding, catalyst-free method is described for N-arylation of azoles and indoles from unactivated monofluorobenzenes. This S(N) Ar reaction tolerates a wide range of substituents and can also generate halogenated N-aryl products. The reaction can also be performed simultaneously with or subsequent to a copper- or palladium-catalyzed cross-coupling reaction in the same pot. 相似文献
356.
Cytometric methods for measuring bacteria in water: advantages, pitfalls and applications 总被引:1,自引:0,他引:1
Rapid detection of microbial cells is a challenge in microbiology, particularly when complex indigenous communities or subpopulations
varying in viability, activity and physiological state are investigated. Flow cytometry (FCM) has developed during the last
30 years into a multidisciplinary technique for analysing bacteria. When used correctly, FCM can provide a broad range of
information at the single-cell level, including (but not limited to) total counts, size measurements, nucleic acid content,
cell viability and activity, and detection of specific bacterial groups or species. The main advantage of FCM is that it is
fast and easy to perform. It is a robust technique, which is adaptable to different types of samples and methods, and has
much potential for automation. Hence, numerous FCM applications have emerged in industrial biotechnology, food and pharmaceutical
quality control, routine monitoring of drinking water and wastewater systems, and microbial ecological research in soils and
natural aquatic habitats. This review focuses on the information that can be gained from the analysis of bacteria in water,
highlighting some of the main advantages, pitfalls and applications. 相似文献
357.
Periodic ab initio density functional calculations on ultrathin films of AlN, BeO, GaN, SiC, ZnO, and ZnS demonstrate the stabilization of thicker films terminating with the polar {0001} surface via charge transfer and metallization of the surface layers. In contrast thinner films remove the dipole by adopting a graphiticlike structure in which the atoms are threefold coordinate. This structure is thermodynamically the most favorable for these thinner films. Implications for the crystal growth of wurtzite materials are discussed. 相似文献
358.
359.
360.
Karel Piron Sara Kenis Guido Verniest Riccardo Surmont Jan Willem Thuring Peter ten Holte Frederik Deroose Norbert De Kimpe 《Tetrahedron》2012,68(34):6941-6947
A synthetic route toward new 8,8-difluoro-1,6-naphthyridine-5,7-diones, which are of interest as new building blocks in pharmaceutical chemistry, is described. The key steps include a copper-mediated cross-coupling of ethyl bromodifluoroacetate and 2-bromo-3-cyanopyridine, followed by hydrolysis of the nitrile function and subsequent cyclization. 相似文献