全文获取类型
收费全文 | 402篇 |
免费 | 6篇 |
国内免费 | 1篇 |
专业分类
化学 | 230篇 |
晶体学 | 5篇 |
力学 | 7篇 |
数学 | 26篇 |
物理学 | 141篇 |
出版年
2020年 | 4篇 |
2019年 | 6篇 |
2018年 | 3篇 |
2015年 | 5篇 |
2014年 | 5篇 |
2013年 | 12篇 |
2012年 | 11篇 |
2011年 | 24篇 |
2010年 | 16篇 |
2009年 | 11篇 |
2008年 | 22篇 |
2007年 | 15篇 |
2006年 | 13篇 |
2005年 | 22篇 |
2004年 | 16篇 |
2003年 | 21篇 |
2002年 | 16篇 |
2001年 | 13篇 |
2000年 | 12篇 |
1999年 | 8篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 10篇 |
1994年 | 4篇 |
1993年 | 11篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 3篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1974年 | 3篇 |
1973年 | 5篇 |
1972年 | 2篇 |
1944年 | 2篇 |
1943年 | 2篇 |
1942年 | 2篇 |
1941年 | 2篇 |
1934年 | 2篇 |
1919年 | 2篇 |
1908年 | 2篇 |
1905年 | 3篇 |
1903年 | 2篇 |
1888年 | 2篇 |
排序方式: 共有409条查询结果,搜索用时 250 毫秒
71.
Sawicki M Siaugue JM Jacopin C Moulin C Bailly T Burgada R Meunier S Baret P Pierre JL Taran F 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(12):3689-3697
New tripodal gem-(bis-phosphonates) uranophiles were discovered by a screening method that allowed for the selection of ligands with strong uranyl-binding properties in a convenient microtiter-plate format. The method is based on competitive uranium binding by using Sulfochlorophenol S as chromogenic chelate. This dye compound was found to present high uranyl complexation properties and allowed to highlight ligands presenting association constants for UO(2+)(2) up to 10(18) at pH 7.4 and 10(20) at pH 9. A collection of 40 known ligands including polycarboxylate, hydroxamate, catecholate, hydroxypyridonate and hydroxyquinoline derivatives was tested. Also screened was a combinatorial library prepared from seven amine scaffolds and eight acrylates bearing diverse chelating moieties. Among these 96 tested candidates, a tripod derivative bearing gem-bis-phosphonates moieties was found to present the highest complexation properties over a wide range of pH and was further studied. 相似文献
72.
A numerical method, using the Ritz-Galerkin approach has been applied to the problem of determining the propagation characteristics of inhomogeneous planar optical waveguides. It is shown that very accurate results are obtained for mode spectra and field distributions when compared with the predictions of other exact or approximate methods. 相似文献
73.
We present a detailed study of scaling violations for non-singlet, singlet and glue distribution functions in the framework of several approximation schemes of QCD. Our formalism consists of direct resolution of the Altarelli-Parisi type equations and leads to a simple exponential form for the function q(x, Q2). This form is very suitable for the analysis of experimental data and for the exploration of different evolution schemes. In particular, we examine the implications on the QCD scaling parameter Λ and the gluon parameter nG. 相似文献
74.
Summary Three optimized small-scale methods for amino acid separation are described and compared. Two dimensional separations are
based on paper or cellulose thin-layer ionophoresis and chromatography with simple and inexpensive apparatus. The influence
of experimental conditions on resolution and amount required for amino acids possessing almost identical mobilities, is studied.
The quickest procedure based on the coupling of 200×200×0.25 mm thin-layer, low-voltage electrophoresis (20 V/cm) with chromatography,
and the system: cellulose −1.04 mol dm−3 formic acid — tertbutanol/methanol/pyridine/formic acid/water (33∶43∶9.6∶0.4∶20), provides very reproducible results with
high separating power for small samples (2–10 nmoles). 相似文献
75.
Preliminary results on the transition metal catalyzed expoxidation of styrene and cyclohexene with sodium hypochlorite solution and phase-transfer reagent are described. 相似文献
76.
Using the periodic unfolding method of Cioranescu, Damlamian and Griso, we study the homogenization for equations of the formin a perforated domain with holes of size \({\varepsilon \delta }\) periodically distributed in the domain, where \({A_\varepsilon }\) is a function whose values are maximal monotone graphs (on R N ). Two different unfolding operators are involved in such a geometric situation. Under appropriate growth and coercivity assumptions, if the corresponding two sequences of unfolded maximal monotone graphs converge in the graph sense to the maximal monotone graphs A(x, y) and A 0(x, z) for almost every \({(x,y,z)\in \Omega \times Y \times {\rm {\bf R}}^N}\), as \({\varepsilon \to 0}\), then every cluster point (u 0, d 0) of the sequence \({(u_{\varepsilon , \delta }, d_{\varepsilon , \delta } )}\) for the weak topology in the naturally associated Sobolev space is a solution of the homogenized problem which is expressed in terms of u 0 alone. This result applies to the case where \({A_{\varepsilon}(x)}\) is of the form \({B(x/\varepsilon)}\) where B(y) is periodic and continuous at y = 0, and, in particular, to the oscillating p-Laplacian.
相似文献
$-{\rm div}\,\,d_\varepsilon=f,\,\,{\rm with}\,\,\left(\nabla u_{\varepsilon , \delta }(x),d_{\varepsilon , \delta }(x)\right) \in A_\varepsilon(x)$
77.
Comparison of loudspeakers is a major concern during design or product selection. There are several standards for the measurement of loudspeaker characteristics, but none of them provides hints for a rigorous comparison between devices. In this study, different ways of evaluating acoustical dissimilarity between loudspeakers were compared. Several methods of signal analysis were used, and for each method a metric evaluating the dissimilarity between two signals was defined. The correlation between the different dissimilarity evaluations over a significant panel of loudspeakers led to identified classes of measurements. A specific aspect of this work is that measurements were performed in a standard listening environment, rather than in an anechoic or reverberant one. It allowed the use of the recorded signals for a simple listening test, providing a perceptual metric which was compared to the acoustical ones. It also allowed the introduction of auditory models in the computation of some acoustical metrics, so defining a new class of measurements which gave results close to the perceptual ones. 相似文献
78.
Dr. Carlos Sánchez-Sánchez Dr. Thomas Dienel Dr. Adrien Nicolaï Dr. Neerav Kharche Dr. Liangbo Liang Colin Daniels Prof. Vincent Meunier Dr. Junzhi Liu Prof. Xinliang Feng Prof. Klaus Müllen Dr. Juan Ramón Sánchez-Valencia Dr. Oliver Gröning Dr. Pascal Ruffieux Prof. Roman Fasel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(52):12074-12082
A bottom up method for the synthesis of unique tetracene-based nanoribbons, which incorporate cyclobutadiene moieties as linkers between the acene segments, is reported. These structures were achieved through the formal [2+2] cycloaddition reaction of ortho-functionalized tetracene precursor monomers. The formation mechanism and the electronic and magnetic properties of these nanoribbons were comprehensively studied by means of a multitechnique approach. Ultra-high vacuum scanning tunneling microscopy showed the occurrence of metal-coordinated nanostructures at room temperature and their evolution into nanoribbons through formal [2+2] cycloaddition at 475 K. Frequency-shift non-contact atomic force microscopy images clearly proved the presence of bridging cyclobutadiene moieties upon covalent coupling of activated tetracene molecules. Insight into the electronic and vibrational properties of the so-formed ribbons was obtained by scanning tunneling microscopy, Raman spectroscopy, and theoretical calculations. Magnetic properties were addressed from a computational point of view, allowing us to propose promising candidates to magnetic acene-based ribbons incorporating four-membered rings. The reported findings will increase the understanding and availability of new graphene-based nanoribbons with high potential in future spintronics. 相似文献
79.
80.
Jean-Cyrille Hierso David Evrard Dominique Lucas Philippe Richard Hélène Cattey Bernard Hanquet Philippe Meunier 《Journal of organometallic chemistry》2008,693(3):574-578
From the analysis of several nickel and palladium halide complexes of a constrained ferrocenyl tetraphosphine, the existence in solution phase of unique 31P-31P “through-space” nuclear spin-spin coupling constants (JPP) had been previously evidenced. Due to the blocked conformation of the species in solution, and based on the NMR spectra obtained for the complexes and their corresponding solid state X-ray structures, these JPP constants had been shown to clearly depend on the mutual spatial position of the corresponding phosphorus atoms. Herein, the quantitative correlation disclosed at that time (P?P distance dependence of coupling constants) is remarkably confirmed, and mathematically refined owing to the study of a new palladium dibromide tetraphosphine complex, for which the synthesis and the solution NMR and solid state X-ray characterizations are reported. 相似文献