全文获取类型
收费全文 | 371篇 |
免费 | 18篇 |
专业分类
化学 | 255篇 |
力学 | 7篇 |
数学 | 30篇 |
物理学 | 59篇 |
无线电 | 38篇 |
出版年
2024年 | 1篇 |
2023年 | 8篇 |
2022年 | 9篇 |
2021年 | 13篇 |
2020年 | 5篇 |
2019年 | 8篇 |
2018年 | 12篇 |
2017年 | 8篇 |
2016年 | 13篇 |
2015年 | 8篇 |
2014年 | 13篇 |
2013年 | 16篇 |
2012年 | 18篇 |
2011年 | 42篇 |
2010年 | 16篇 |
2009年 | 12篇 |
2008年 | 30篇 |
2007年 | 35篇 |
2006年 | 20篇 |
2005年 | 28篇 |
2004年 | 9篇 |
2003年 | 17篇 |
2002年 | 7篇 |
2001年 | 8篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1985年 | 1篇 |
1977年 | 1篇 |
1858年 | 1篇 |
排序方式: 共有389条查询结果,搜索用时 15 毫秒
21.
Gabriella Santoni Dr. Miriam Mba Dr. Marcella Bonchio Dr. William A. Nugent Cristiano Zonta Dr. Giulia Licini Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(2):645-654
The stereoselective oxidation of differently functionalised benzyl phenyl sulfides has been examined by using enantiopure TiIV trialkanolamine complexes. These complexes efficiently catalyse the sulfoxidation with good stereoselectivities. The data highlight the contribution to the stereoselectivity of steric effects and non‐covalent π–π interactions between the aromatic rings of the TiIV complex and those pertaining to the substrates. Enantiomeric excesses have been correlated with the electrostatic potential surfaces (EPS) of the reacting sulfides. The overall study leads to a mechanistic interpretation that explains the stereoselectivity of the system and dissects the role of aromatic and steric interactions in the stereoselective process. 相似文献
22.
A. Casaburi M. Ejrnaes F. Mattioli A. Gaggero R. Leoni N. Martucciello S. Pagano M. Ohkubo R. Cristiano 《Journal of nanoparticle research》2011,13(11):6121-6131
The recent progress in the nanofabrication of superconducting films opens the road toward detectors with highly improved performances.
This is the case for superconducting nano-striplines where the thickness and the width are pushed down to the extreme limits
to realize detectors with unprecedented sensitivity and ultra fast response time. In this way quantum detectors for single
photons at telecommunication wavelengths and for macromolecules such as proteins can be realized. As is often the case in
applied nanotechnology, it is a challenge to make devices with the necessary macroscopic dimensions that are needed to interface
present technologies, while maintaining the performance improvements. For nano-stripline detectors, both the fast temporal
response and the device sensitivity is generally degraded when the area is increased. Here, we present how such detectors
can be scaled up to macroscopic dimensions without losing the performance of the nano-structured active elements by using
an innovative configuration. In order to realize ultrathin superconducting film the nano-layer is growth with a careful setup
of the deposition technique which guarantees high quality and thickness uniformity at the nano-scale size. The active nano-strips
are defined with the state-of-the-art electron beam nanolithography to achieve a highly uniform linewidth. We present working
detectors based on nano-strips with thicknesses 9–40 nm and widths of 100–1000 nm which exhibit unprecedented speed and area
coverage (40 × 40 μm2 for single photon detectors and 1 × 1 mm2 for single molecule detectors) based on niobium nitride thus enabling practical use of this nanotechnology. 相似文献
23.
Cristiano Bocci Luca Chiantini Giorgio Ottaviani 《Annali di Matematica Pura ed Applicata》2014,193(6):1691-1702
We prove that the general tensor of size \(2^n\) and rank \(k\) has a unique decomposition as the sum of decomposable tensors if \(k\le 0.9997\frac{2^n}{n+1}\) (the constant 1 being the optimal value). Similarly, the general tensor of size \(3^n\) and rank \(k\) has a unique decomposition as the sum of decomposable tensors if \(k\le 0.998\frac{3^n}{2n+1}\) (the constant 1 being the optimal value). Some results of this flavor are obtained for tensors of any size, but the explicit bounds obtained are weaker. 相似文献
24.
25.
Adriana Lídia Santana Cristiano Giacomelli Paula Nunes Oliveira Alfredo Tibúrcio Nunes Pires José Roberto Bertolino Almir Spinelli 《Journal of Polymer Science.Polymer Physics》2009,47(2):215-225
The effect of poly(2‐vinyl pyridine) (P2VP) and poly(4‐vinyl pyridine) (P4VP) isomers on the growth of surface films on copper substrates was studied by electrochemical, spectroscopic, thermogravimentric, and microscopic methods. In acid environment (3% v/v acetic acid) and in the presence of KSCN, electrochemically generated copper cations reacted rapidly with SCN? and P2VP or P4VP, yielding coordination compounds, which deposited onto copper surfaces as films. The characteristics of such polymer–metal complexes (films) were markedly isomer‐dependent. Cu(I)/P2VP/SCN? complexes with monovalent cations and sulfur‐coordinated thiocyanate were obtained in the presence of P2VP, whereas the formation of Cu(II)/P4VP/SCN? complexes with divalent cations and nitrogen‐coordinated thiocyanate was observed in the presence of P4VP. Interestingly, similar physical–chemical properties (electronic structure, stoichiometry, and thermal behavior) were observed for materials synthesized by electrochemical and chemical methods. These results suggest, therefore, that control over the surface properties of copper substrates can be achieved using electrosynthesized films based on different PVP isomers. Besides acting as effective protective barriers against aggressive media and thus reducing the metal dissolution (corrosion) kinetics, these materials are potentially attractive for other applications in which surface properties are paramount, such as in catalysis. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 215–225, 2009 相似文献
26.
Cristiano Araujo Millena Gomes Edna Barros Sandro Rigo Rodolfo Azevedo Guido Araujo 《Design Automation for Embedded Systems》2005,10(4):253-283
This paper[3.5pc] presents the Platform Designer (PD) framework, a set of SystemC based tools that provide support for modeling,
simulation and analysis of multiprocessor SoC platforms (MPSoC), at different abstraction levels. PD provides mechanisms for
interconnection specification, process synchronization and communication, thus allowing the modeling of a complete platform,
in a unified environment. To do that it uses an extension of the ArchC ADL and acsys, a tool that enables the automatic generation
of a SystemC simulator of the platform. The main advantages of this approach are twofold. First, designers have more flexibility
since they can integrate and configure different processors to the platform, using a single environment. Second, it enables
a faster design space exploration, given that it automatically generates SystemC simulators of whole platforms at distinct
abstraction levels. A number of platform variations can be tried out with minor design changes, thus reducing design time.
Experimental results show the suitability of the platform simulator for design space exploration. Real applications (with
medium complexity) run in the platform in few minutes. Combined with the facility to generate platforms with minor changes,
this feature allows an improvement of the design space exploration. 相似文献
27.
28.
This paper considers the inversion of experimental field data collected with light receiving systems designed to meet operational requirements. Such operational requirements include system deployment in free drifting configurations and a limited number of acoustic receivers. A well-known consequence of a reduced spatial coverage is a poor sampling of the vertical structure of the acoustic field, leading to a severe ill-conditioning of the inverse problem and data to model cost function with a massive sidelobe structure having many local extrema. This causes difficulties to meta-heuristic global search methods, such as genetic algorithms, to converge to the true model parameters. In order to cope with this difficulty, broadband high-resolution processors are proposed for their ability to significantly attenuate sidelobes, as a contribution for improving convergence. A comparative study on simulated data shows that high-resolution methods did not outperform the conventional Bartlett processor for pinpointing the true environmental parameter when using exhaustive search. However, when a meta-heuristic technique is applied for exploring a large multidimensional search space, high-resolution methods clearly improved convergence, therefore reducing the inherent uncertainty on the final estimate. These findings are supported by the results obtained on experimental field data obtained during the Maritime Rapid Environmental Assessment 2003 sea trial. 相似文献
29.
Bruna Tischer Raquel G. Vendruscolo Roger Wagner Cristiano R. Menezes Cláudia S. Barin Sandro R. Giacomelli Jane M. Budel Juliano S. Barin 《Chemical Papers》2017,71(4):753-761
Grinding methods were evaluated aiming to determine yield and composition of essential oils (EOs) from Baccharis articulata (Lam) Pers., called as carqueja, a native plant from South Brazil. Cryogenic, knife (with and without cooling) and ball mills were used. The major constituents found in EOs were β-pinene, caryophyllene, spathulenol and caryophyllene oxide, but differences in 21 compounds were observed. All grinding processes reduced monoterpenes and oxygenated sesquiterpenes with concentration of hydrocarbon sesquiterpenes. The sesquiterpenes (hydrocarbons and oxygenated) were found from 63.55 to 86.02% while the monoterpene hydrocarbons’ concentration ranged from 13.98 to 36.45%. Plants milled with knife mill provided EOs with profile similar to those not grinded. Despite the lower working temperature, cryogenic milling resulted in smaller EO yield (0.40 ± 0.03%) in comparison to other grinding methods (yields from 0.50 ± 0.02 to 0.56 ± 0.03%) and different chromatographic profile. Microscopic analysis showed the smaller particle size provided by cryogenic grinding, which leads to glandular trichome rupture and consequently to loss of EOs. This study showed that grinding should be carefully evaluated to provide reproducible results in essential oil analysis. 相似文献
30.
La Ferla B Airoldi C Zona C Orsato A Cardona F Merlo S Sironi E D'Orazio G Nicotra F 《Natural product reports》2011,28(3):630-648
Cancer is one of the major causes of death worldwide. As a consequence, many different therapeutic approaches, including the use of glycosides as anticancer agents, have been developed. Various glycosylated natural products exhibit high activity against a variety of microbes and human tumors. In this review we classify glycosides according to the nature of their aglycone (non-saccharidic) part. Among them, we describe anthracyclines, aureolic acids, enediyne antibiotics, macrolide and glycopeptides presenting different strengths and mechanisms of action against human cancers. In some cases, the glycosidic residue is crucial for their activity, such as in anthracycline, aureolic acid and enediyne antibiotics; in other cases, Nature has exploited glycosylation to improve solubility or pharmacokinetic properties, as in the glycopeptides. In this review we focus our attention on natural glycoconjugates with anticancer properties. The structure of several of the carbohydrate moieties found in these conjugates and their role are described. The structure–activity relationship of some of these compounds, together with the structural features of their interaction with the biological targets, are also reported. Taken together, all this information is useful for the design of new potential anti-tumor drugs. 相似文献