全文获取类型
收费全文 | 531篇 |
免费 | 9篇 |
国内免费 | 1篇 |
专业分类
化学 | 383篇 |
晶体学 | 1篇 |
力学 | 3篇 |
数学 | 65篇 |
物理学 | 89篇 |
出版年
2022年 | 3篇 |
2021年 | 8篇 |
2020年 | 7篇 |
2019年 | 7篇 |
2018年 | 3篇 |
2017年 | 4篇 |
2016年 | 7篇 |
2015年 | 4篇 |
2014年 | 17篇 |
2013年 | 22篇 |
2012年 | 30篇 |
2011年 | 28篇 |
2010年 | 26篇 |
2009年 | 10篇 |
2008年 | 30篇 |
2007年 | 33篇 |
2006年 | 29篇 |
2005年 | 22篇 |
2004年 | 15篇 |
2003年 | 17篇 |
2002年 | 13篇 |
2001年 | 10篇 |
2000年 | 16篇 |
1999年 | 4篇 |
1996年 | 7篇 |
1995年 | 7篇 |
1994年 | 4篇 |
1992年 | 10篇 |
1991年 | 3篇 |
1990年 | 7篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1986年 | 8篇 |
1985年 | 6篇 |
1984年 | 11篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1978年 | 9篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1975年 | 8篇 |
1974年 | 7篇 |
1973年 | 8篇 |
1972年 | 5篇 |
1969年 | 4篇 |
1899年 | 4篇 |
1882年 | 2篇 |
排序方式: 共有541条查询结果,搜索用时 15 毫秒
91.
Kohler A Bertrand D Martens H Hannesson K Kirschner C Ofstad R 《Analytical and bioanalytical chemistry》2007,389(4):1143-1153
In this paper we present an algorithm for analysing sets of FTIR microscopic images of tissue sections. The proposed approach
allows one to investigate sets of many FTIR tissue images both with respect to sample information (variation from image to
image) and spatial variations of tissues (variation within the image). The algorithm is applied to FTIR microscopy images
of beef loin muscles containing myofibre and connective tissue regions. The FTIR microscopy images are taken of sub-samples
from five different beef loin muscles that were aged for four different lengths of time. The images were investigated regarding
variation due to the ageing length and due to the homogeneity of the connective tissue regions. The presented algorithm consists
of the following main elements: (1) pre-processing of the spectra to overcome large quality differences in FTIR spectra and
differences due to scatter effects, (2) identification of connective tissue regions in every image, (3) labelling of every
connective tissue spectrum with respect to its location in the connective tissue region, and (4) analysis of variations in
the FTIR microscopic images in regard to ageing time and pixel position of the spectra in the connective tissue region. Important
spectral parameters characterising collagen and proteoglycan structure were determined.
Figure Effective optical path length estimated by EMSC 相似文献
92.
We describe an independent trajectory implementation of semiclassical Liouville method for simulating quantum processes using classical trajectories. In this approach, a single ensemble of trajectories describes all semiclassical density matrix elements of a coupled electronic state problem, with the ensemble evolving classically under a single reference Hamiltonian chosen on the basis of physical grounds. In this paper, we introduce an additional uncoupled trajectory approximation, allowing the members of the ensemble to evolve independently of one another and eliminating the major computational costs of our previous coupled trajectory implementation. The accuracy of the method is demonstrated for model one-dimensional problems. In addition, the approach is applied to the chemical reaction dynamics of a collinear triatomic system, yielding excellent agreement with exact calculations. This method allows molecular dynamics involving coupled electronic surfaces to be modeled with essentially the same effort as classical molecular dynamics and ensemble averaging. 相似文献
93.
Piperidine was stereoselectively alpha-alkynylated in a four-step sequence made up of transformation to a chiral nonracemic N-sulfinylpiperidine, anodic oxidation to N-sulfinyliminium ion equivalent, alkynylation through addition of a mixed organoaluminum derivative, and final acidic deprotection of the sulfoxide. Overall yields are around 50%, and the diastereoselectivity of the nucleophilc addition was between 92 and 99% de, allowing isolation of the final product with 99% enantiomeric purity. 相似文献
94.
Eslava S Baklanov MR Kirschhock CE Iacopi F Aldea S Maex K Martens JA 《Langmuir : the ACS journal of surfaces and colloids》2007,23(26):12811-12816
Ellipsometric porosimetry was used to determine the adsorption isotherms of toluene, methanol, and water on b-oriented Silicalite-1 coatings with a thickness of less than ca. 250 nm and to obtain adsorption kinetics. The adsorption isotherms are of sufficient quality to reveal several aspects of the pore structure such as the adsorbate capacity and the adsorbate/framework affinity. The use of a combination of different molecular probes in ellipsometric porosimetry to elucidate the molecular accessibility of Silicalite-1 pores is demonstrated. It is shown that ellipsometric porosimetry is an appropriate technique for probing the influence of aging of the Silicalite-1 coating and of planarization polishing on the porosity, pore accessibility, and adsorbate/framework affinity. 相似文献
95.
96.
Harald Brand Dr. Jörn Martens Peter Mayer Dr. Axel Schulz Prof. Dr. Markus Seibald Thomas Soller 《化学:亚洲杂志》2009,4(10):1588-1603
The synthesis, structure, and bonding of alkali salts of resonance stabilized amides, such as diformylamide (dfa), formylcyanoamide (fca), nitrocyanoamide (nca), and for comparision, the well‐known dicyanoamide (dca), are discussed on the basis of experimental and theoretical data. The first structural reports of K(18‐crown‐6)+dfa?, K(18‐crown‐6)+fca?, Na+nca?, and Li(TMEDA)+dca? are presented. Examination of the X‐ray data reveals almost planar anions with strong cation–anion interactions resulting in network‐like structures in the solid state. For comparison, the X‐ray structures of covalently bound phenyldicyanoamide and diformamide are also discussed. The thermal behavior of the alkali salts of these amides is studied by thermoanalytical experiments. Moreover, several novel ionic liquids based on resonance stabilized amides have been prepared and were fully characterized, namely the dfa, fca, and nca salts of EMIM (1‐ethyl‐3‐methyl‐imidazolium), BMIM (1‐butyl‐3‐methyl‐imidazolium), and HMIM (1‐hexyl‐3‐methyl‐imidazolium). Most of them are liquid at room temperature, except BMIM+fca? that melts at 32 °C. These ionic liquids are neither heat nor shock sensitive, are thermally stable up to over 200 °C, and can be prepared easily in large quantities. 相似文献
97.
We solve quantum dynamical equations of simple systems by propagating ensembles of interacting trajectories. A scheme is proposed which uses adaptive kernel density estimation for representing probability distribution functions and their derivatives. The formulation is carried on in the Husimi representation to ensure the positiveness of the distribution functions. By comparing to previous work, the effect of changing representations is studied as well as the advantage of using adaptive kernels for the estimation of probability distributions. We found significant improvement in the accuracy of the results. 相似文献
98.
In this paper, we present simulations of the decay of quantum coherence between vibrational states of I(2) in its ground (X) electronic state embedded in a cryogenic Kr matrix. We employ a numerical method based on the semiclassical limit of the quantum Liouville equation, which allows the simulation of the evolution and decay of quantum vibrational coherence using classical trajectories and ensemble averaging. The vibrational level-dependent interaction of the I(2)(X) oscillator with the rare-gas environment is modeled using a recently developed method for constructing state-dependent many-body potentials for quantum vibrations in a many-body classical environment [J. M. Riga, E. Fredj, and C. C. Martens, J. Chem. Phys. 122, 174107 (2005)]. The vibrational dephasing rates gamma(0n) for coherences prepared between the ground vibrational state mid R:0 and excited vibrational state mid R:n are calculated as a function of n and lattice temperature T. Excellent agreement with recent experiments performed by Karavitis et al. [Phys. Chem. Chem. Phys. 7, 791 (2005)] is obtained. 相似文献
99.
Wiebke Germer Timo Stalling Uwe Kramer Wolfgang Saak Jürgen Martens 《Heteroatom Chemistry》2014,25(1):20-27
Starting with thiazolines, an important class of heterocyclic imines, a novel rearrangement reaction of corresponding N‐acyliminium ions is described. Furthermore, a new class of heterobicyclic compounds arylated at a single bridgehead atom is obtained diastereospecifically. 相似文献
100.
Comparative Plasma Chemical Reaction Studies of CH4/Ar and C2Hm/Ar (m = 2,4,6) Gas Mixtures in a Dielectric Barrier Discharge 下载免费PDF全文
Plasma chemical reactions in CH4/Ar and C2Hm/Ar (m = 2, 4, 6) gas mixtures in a dielectric barrier discharge at medium pressure (300 mbar) have been investigated. From mass spectrometry the production of H2 and formation of larger hydrocarbons such as CnHm with up to n = 12 is inferred. Hydrogen release is most pronounced for CH4 and C2H6 gas mixtures. Fourier Transform InfraRed (FTIR) spectroscopy reveals the formation of substituted alkane (sp3), alkene (sp2), and alkyne (sp) groups from the individual gases which are used in this work. Abundant formation of acetylene occurs from C2H4 and to a lesser extent from C2H6 and CH4 precursor gases. The main reaction pathway of acetylene leads to the formation of large molecules via C4H2 and, eventually, to nano‐size particles. The experimental results are in reasonable agreement with simulations which predict a pronounced electron temperature and gas pressure dependency. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献