全文获取类型
收费全文 | 398篇 |
免费 | 0篇 |
国内免费 | 3篇 |
专业分类
化学 | 204篇 |
晶体学 | 1篇 |
力学 | 15篇 |
数学 | 98篇 |
物理学 | 83篇 |
出版年
2024年 | 1篇 |
2022年 | 5篇 |
2021年 | 8篇 |
2020年 | 3篇 |
2019年 | 3篇 |
2018年 | 9篇 |
2017年 | 5篇 |
2016年 | 7篇 |
2015年 | 13篇 |
2014年 | 12篇 |
2013年 | 14篇 |
2012年 | 24篇 |
2011年 | 40篇 |
2010年 | 24篇 |
2009年 | 23篇 |
2008年 | 24篇 |
2007年 | 22篇 |
2006年 | 35篇 |
2005年 | 28篇 |
2004年 | 27篇 |
2003年 | 20篇 |
2002年 | 6篇 |
2001年 | 1篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 8篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1993年 | 1篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1980年 | 3篇 |
1974年 | 1篇 |
排序方式: 共有401条查询结果,搜索用时 9 毫秒
51.
Jean-Philippe Rocher Mohammed Ahmar Joelle Paris 《Journal of heterocyclic chemistry》1988,25(2):599-601
Condensation of dimethyl 3-methylglutaconate with ketones provides a one pot route for the preparation of 5-methoxycarbonyl-4-methyldihydropyran-2-ones. The experimental conditions to give selectively pyran-2-ones isomers are discussed. The structure of the different products was established on the basis of 1H and 13C nmr spectral data. 相似文献
52.
We show that pointlike defect model of glasses cannot explain the thermodynamic properties of glass formers, as for example, the excess specific heat close to the glass transition, contrary to the claim of Garrahan and Chandler [Proc. Natl. Acad. Sci. U.S.A. 100, 9710 (2003)]. More general models and approaches in terms of extended defects are also discussed. 相似文献
53.
54.
Tessonnier JP Louis B Walspurger S Sommer J Ledoux MJ Pham-Huu C 《The journal of physical chemistry. B》2006,110(21):10390-10395
On the basis of our previous H/D exchange studies devoted to the quantification of the number of Br?nsted acid sites in solid acids, we report here an innovative approach to determine both the amount and the localization of Mo atoms inside the Mo/ZSM-5 catalyst, commonly used for the methane dehydroaromatization reaction. The influence of Mo introduction in the MFI framework was studied by means of BET, X-ray diffraction, 27Al magic angle spinning NMR, NH3 temperature-programmed desorption, and H/D isotopic exchange techniques. A dependence was found between the decrease of acidic OH groups and the Mo content. Depending on the Si/Al ratio of the zeolite, i.e., the proximity of two Br?nsted acid sites, the Mo atoms substitute a different number of OH groups. Consequently, a chemical structure was proposed to describe the geometry of the Mo complex in the channels of the ZSM-5 zeolite. 相似文献
55.
Mahé P Ralaivola L Stoven V Vert JP 《Journal of chemical information and modeling》2006,46(5):2003-2014
We introduce a family of positive definite kernels specifically optimized for the manipulation of 3D structures of molecules with kernel methods. The kernels are based on the comparison of the three-point pharmacophores present in the 3D structures of molecules, a set of molecular features known to be particularly relevant for virtual screening applications. We present a computationally demanding exact implementation of these kernels, as well as fast approximations related to the classical fingerprint-based approaches. Experimental results suggest that this new approach is competitive with state-of-the-art algorithms based on the 2D structure of molecules for the detection of inhibitors of several drug targets. 相似文献
56.
Antignac JP Marchand P Gade C Matayron G Qannari el M Le Bizec B Andre F 《Analytical and bioanalytical chemistry》2006,384(1):271-279
Polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) are widely recognized by the scientific community as persistent organic
pollutants due to their toxicity and adverse effects on wildlife and human health. The actual regulation dedicated to the
monitoring of dioxins in food is based on the measurement of 17 congener concentrations. The final result is reported as a
toxic equivalent value that takes into account the relative toxicity of each congener. This procedure can minimize the qualitative
information available from the abundances of each PCDD/PCDF congener: the characteristic contamination profile of the sample.
Multivariate statistical techniques, such as principal component analysis (PCA) or linear discriminant analysis (LDA), represent
an interesting way to investigate this qualitative information. Nevertheless, they have only been applied to the analysis
of contamination data from food products and biological matrices infrequently. The objective of the present study was to analyze
a large data set from dioxin analyses performed on various food products of animal origin. The results demonstrate the existence
of differences in congener-specific patterns between the analyzed samples. Variability was first demonstrated in terms of
the food type (fish, meat, milk, fatty products). Then a variability was observed that was related to the specific animal
species for meat and milk samples (bovine, ovine, porcine, caprine and poultry). Some practical applications of these results
are discussed. The origin(s) of the observed differences, as well as their significance, now remain to be investigated, both
in terms of environmental factors and transfer through living organisms. A better knowledge of the relation between a contamination
profile and its specific source and/or food product should be of great interest to scientists working in the fields of contaminant
analysis, toxicology and metabolism, as well as to regulatory bodies and risk assessors in charge of final decisions regarding
the eventual hazards associated with theses substances. 相似文献
57.
58.
N. Biziere E. Murè J.-Ph. Ansermet 《Journal of magnetism and magnetic materials》2010,322(9-12):1357-1359
We investigate the ferromagnetic resonance of Co/Cu/Co trilayers by use of AC-spin-transfer torque excitations. Magnetic structures are grown in a 6-μm-thick commercial nanoporous polycarbonate membranes by use of electrodeposition in a cobalt/copper single bath. We show that microwave magnetic excitations corresponding to the uniform mode of the two cobalt layers are electrically detected as a change of the DC voltage of the system. 相似文献
59.
One-dimensional infinite group problems have been extensively studied and have yielded strong cutting planes for mixed integer
programs. Although numerical and theoretical studies suggest that group cuts can be significantly improved by considering
higher-dimensional groups, there are no known facets for infinite group problems whose dimension is larger than two. In this
paper, we introduce an operation that we call sequential-merge. We prove that the sequential-merge operator creates a very large family of facet-defining inequalities for high-dimensional
infinite group problems using facet-defining inequalities of lower-dimensional group problems. Further, they exhibit two properties
that reflect the benefits of using facets of high-dimensional group problems: they have continuous variables’ coefficients
that are not dominated by those of the constituent low-dimensional cuts and they can produce cutting planes that do not belong
to the first split closure of MIPs. Further, we introduce a general scheme for generating valid inequalities for lower-dimensional
group problems using valid inequalities of higher-dimensional group problems. We present conditions under which this construction
generates facet-defining inequalities when applied to sequential-merge inequalities. We show that this procedure yields some
two-step MIR inequalities of Dash and Günlük. 相似文献
60.
We consider the control of a production-inventory system with impatient customers. We show that the optimal policy can be described using two thresholds: a production base-stock level that determines when production takes place and an admission threshold that determines when orders should be accepted. We describe an algorithm for computing the performance of the system for any choice of base-stock level and admission threshold. In a numerical study, we compare the performance of the optimal policy against several other policies. 相似文献