全文获取类型
收费全文 | 679篇 |
免费 | 26篇 |
国内免费 | 4篇 |
专业分类
化学 | 479篇 |
晶体学 | 6篇 |
力学 | 14篇 |
数学 | 70篇 |
物理学 | 140篇 |
出版年
2023年 | 3篇 |
2022年 | 11篇 |
2021年 | 13篇 |
2020年 | 9篇 |
2019年 | 12篇 |
2018年 | 8篇 |
2016年 | 25篇 |
2015年 | 24篇 |
2014年 | 22篇 |
2013年 | 47篇 |
2012年 | 43篇 |
2011年 | 51篇 |
2010年 | 31篇 |
2009年 | 26篇 |
2008年 | 31篇 |
2007年 | 32篇 |
2006年 | 31篇 |
2005年 | 27篇 |
2004年 | 28篇 |
2003年 | 14篇 |
2002年 | 21篇 |
2001年 | 8篇 |
2000年 | 12篇 |
1998年 | 11篇 |
1997年 | 11篇 |
1996年 | 6篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 8篇 |
1990年 | 7篇 |
1989年 | 9篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1977年 | 7篇 |
1976年 | 5篇 |
1975年 | 2篇 |
1974年 | 6篇 |
1973年 | 6篇 |
1972年 | 9篇 |
1971年 | 5篇 |
1969年 | 2篇 |
1961年 | 3篇 |
1911年 | 2篇 |
排序方式: 共有709条查询结果,搜索用时 0 毫秒
101.
Andre Rosowsky Marilyn K. Nadel Edward J. Modest 《Journal of heterocyclic chemistry》1972,9(3):645-650
A modified three-component reaction of arylamines, cyanoguanidine, and acetone is described, wherein formation of anomalous guanidinoquinazoline byproducts is greatly enhanced at the expense of the normal dihydro-s-triazines. Four new guanidinoquinazolines and four new dihydro-s-triazines were synthesized via this modification, starting from 2,4-, 2,5-, 3,4-, and 3,5-dimethoxyaniline. The guanidinoquinazoline to dihydro-s-triazine ratio was much higher with 3,4- and 3,5-dimethoxyaniline than with 2,4-dimethoxyaniline. 2,5-Dimethoxyaniline gave an unexpectedly low yield of guanidinoquinazoline, apparently because of steric hindrance. The modified three-component synthesis was also examined in detail with 2-naphthylamine. 相似文献
102.
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
103.
Extractive electrospray ionization for direct analysis of undiluted urine, milk and other complex mixtures without sample preparation 总被引:7,自引:0,他引:7
On-line droplet-droplet extraction occurs when a sample spray intersects a reagent electrospray; this allows continuous analysis of trace amounts of compounds directly in complex matrices including undiluted urine, milk and polluted water over extended periods of time. 相似文献
104.
105.
Lionel Cucala Christophe Demattei Paulo Lopes Andre Ribeiro 《Computational Statistics》2013,28(1):357-369
We propose a new spatial scan statistic based on graph theory as a method for detecting irregularly-shaped clusters of events over space. A graph-based method is proposed for identifying potential clusters in spatial point processes. It relies on linking the events closest than a given distance and thus defining a graph associated to the point process. The set of possible clusters is then restricted to windows including the connected components of the graph. The concentration in each of these possible clusters is measured through classical concentration indices based on likelihood ratio and also through a new concentration index which does not depend on any alternative hypothesis. These graph-based spatial scan tests seem to be very powerful against any arbitrarily-shaped cluster alternative, whatever the dimension of the data. These results have applications in various fields, such as the epidemiological study of rare diseases or the analysis of astrophysical data. 相似文献
106.
For the Ore extension R[t, S,D], where R is a prime ring, we describe prime having zero intersection with R. 相似文献
107.
Kristina O. Kvashnina Anna Yu. Romanchuk Ivan Pidchenko Lucia Amidani Evgeny Gerber Alexander Trigub Andre Rossberg Stephan Weiss Karin Popa Olaf Walter Roberto Caciuffo Andreas C. Scheinost Sergei M. Butorin Stepan N. Kalmykov 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(49):18044-18044
108.
Huebl H Hoehne F Grolik B Stegner AR Stutzmann M Brandt MS 《Physical review letters》2008,100(17):177602
The electrical detection of spin echoes via echo tomography is used to observe coherent processes associated with the electrical readout of the spin state of phosphorus donor electrons in silicon near a SiO2 interface. Using the Carr-Purcell pulse sequence, an echo decay with a time constant of 1.7+/-0.2 micros is observed and discussed in terms of decoherence and recombination times. Electrical spin echo tomography thus can be used to study the dynamics of the spin-dependent transport processes, e.g., in realistic spin qubit devices for quantum information processing. 相似文献
109.
110.