全文获取类型
收费全文 | 458篇 |
免费 | 7篇 |
专业分类
化学 | 280篇 |
力学 | 13篇 |
数学 | 55篇 |
物理学 | 117篇 |
出版年
2023年 | 5篇 |
2022年 | 11篇 |
2021年 | 7篇 |
2020年 | 10篇 |
2019年 | 8篇 |
2017年 | 4篇 |
2016年 | 11篇 |
2015年 | 8篇 |
2014年 | 18篇 |
2013年 | 25篇 |
2012年 | 13篇 |
2011年 | 29篇 |
2010年 | 22篇 |
2009年 | 7篇 |
2008年 | 24篇 |
2007年 | 20篇 |
2006年 | 15篇 |
2005年 | 15篇 |
2004年 | 16篇 |
2003年 | 20篇 |
2002年 | 17篇 |
2001年 | 7篇 |
2000年 | 10篇 |
1999年 | 4篇 |
1998年 | 3篇 |
1997年 | 5篇 |
1996年 | 11篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 11篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 6篇 |
排序方式: 共有465条查询结果,搜索用时 15 毫秒
81.
FR Manby M Stella JD Goodpaster TF Miller 《Journal of chemical theory and computation》2012,8(8):2564-2568
Density functional theory (DFT) provides a formally exact framework for quantum embedding. The appearance of nonadditive kinetic energy contributions in this context poses significant challenges, but using optimized effective potential (OEP) methods, various groups have devised DFT-in-DFT methods that are equivalent to Kohn-Sham (KS) theory on the whole system. This being the case, we note that a very considerable simplification arises from doing KS theory instead. We then describe embedding schemes that enforce Pauli exclusion via a projection technique, completely avoiding numerically demanding OEP calculations. Illustrative applications are presented using DFT-in-DFT, wave-function-in-DFT, and wave-function-in-Hartree-Fock embedding, and using an embedded many-body expansion. 相似文献
82.
Mara Mirasoli Angela Buragina Luisa Stella Dolci Massimo Guardigli Patrizia Simoni Angel Montoya Elisabetta Maiolini Stefano Girotti Aldo Roda 《Analytica chimica acta》2012
Simple, rapid and highly sensitive assays, possibly allowing on-site analysis, are required in the security and forensic fields or to obtain early signs of environmental pollution. Several bioanalytical methods and biosensors based on portable devices have been developed for this purpose. Among them, Lateral Flow ImmunoAssays (LFIAs) offer the advantages of rapidity and ease of use and, thanks to the high specificity of antigen–antibody binding, allow greatly simplifying and reducing sample pre-analytical treatments. However, LFIAs usually employ colloidal gold or latex beads as labels and they rely on the formation of colored bands visible by the naked eye. With this assay format, only qualitative or semi-quantitative information can be obtained and low sensitivity is achieved. Recently, the use of enzyme-catalyzed chemiluminescence detection in LFIA has been proposed to overcome these problems. In this work, we describe the development of a quantitative CL-LFIA assay for the detection of 2,4,6-trinitrotoluene (TNT) in real samples. Thanks to the use of a portable imaging device for CL signal measurement based on a thermoelectrically cooled CCD camera, the analysis could be performed directly on-field. A limit of detection of 0.2 μg mL−1 TNT was obtained, which is five times lower than that obtained with a previously described colloidal gold-based LFIA developed employing the same immunoreagents. The dynamic range of the assay extended up to 5 μg mL−1 TNT and recoveries ranging from 97% to 111% were obtained in the analysis of real samples (post blast residues obtained from controlled explosion). 相似文献
83.
Two phase sampling techniques are developed for the analysis of the propellers wake by means of LDV. The first one (TTT)
uses the detection of Doppler signal as trigger condition; each LDV sample, tagged with the blade angular position at the
measurement time, is arranged inside angular slots. The other technique (ATT) follows an angular triggering method, with some
enhancements to reduce measurement time. The implemented techniques are complementary from the accuracy and efficiency point
of view. The TTT enables to quickly analyze the propellers wake, in view of the minimization of data acquisition time, particularly
in poor flow seeding conditions. The ATT is instead suitable for accurate investigations of space-limited and highly turbulent
flow regions.
Received: 29 July 1998/Accepted: 18 February 1999 相似文献
84.
Heinz Günter Viehe Robert Mernyi Lucien Stella Zdenek Janousek 《Angewandte Chemie (International ed. in English)》1979,18(12):917-932
The 100 yers old Wurster's salts have long been recognized as compounds with redical cations. Their unusual stabilization derives partly form capto-dative (cd) substitution. This principle is now discussed as one factor of radical stabilization and it is applied to simple methine derivatives. cd-Substitution has synthetically useful applications: cd-substituents on a carbon atom allow its selective dehydrodimerization. Olefines with geminal and thus cross-conjugated cd-substituents are “radicophilic” and permit twofold carbon radical addition. cd-Substituted olefines are useful antioxidants, polymerization inhibitors and are promising agents in the control of biological radical reactions. Generally, many reactions of cd-substituted molecules appear to involve radicals. 相似文献
85.
In two experiments we explored the instructional value of a cross‐domain mapping between “number” and “line” in secondary school students' understanding of density. The first experiment investigated the hypothesis that density would be more accessible to students in a geometrical context (infinitely many points on a straight line segment) compared to a numerical context (infinitely many numbers in an interval). The participants were 229 seventh to eleventh graders. The results supported this hypothesis but also showed that students' conceptions of the line segment were far from that of a dense array of points. We then designed a text-based intervention that attempted to build the notion of density in a geometrical context, making explicit reference to the number-to-points correspondence and using the “rubber line” bridging analogy (the line as an imaginary unbreakable rubber band) to convey the no-successor principle. The participants were 149 eighth and tenth graders. The text intervention improved student performance in tasks regarding the infinity of numbers in an interval; the “rubber line” bridging analogy further improved performance successfully conveying the idea that these numbers can never be found one immediately next to the other. 相似文献
86.
Monica Marras Stella Vernier‐Piro Giuseppe Viglialoro 《Mathematical Methods in the Applied Sciences》2016,39(11):2787-2798
This paper deals with a parabolic–parabolic Keller–Segel‐type system in a bounded domain of , {N = 2;3}, under different boundary conditions, with time‐dependent coefficients and a positive source term. The solutions may blow up in finite time t?; and under appropriate assumptions on data, explicit lower bounds for blow‐up time are obtained when blow up occurs. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
87.
Mariano Venanzi Giuseppina Pace Lorenzo Stella Manuela Scarselli Fernando Formaggio Giovanni Marletta 《Surface science》2006,600(2):409-416
A novel hexapeptide was functionalized at the N-terminus by a lipoyl group for binding to gold substrates. Owing to the high content of α-aminoisobutyric acid residues, the peptide adopts a rigid helical conformation despite the shortness of its main chain. Binding of the peptide to gold was investigated by quartz crystal microbalance, cyclic voltammetry, X-ray photoelectron spectroscopy, and scanning tunneling microscopy under ultra-high vacuum conditions. Scanning tunneling microscopy experiments revealed that the peculiar self-assembly properties of this short helical peptide determine the complex morphology of the monolayer, showing ‘stripes’, i.e. peptide aggregates horizontally layered on the gold surface, and ‘holes’, i.e. Au vacancy islands coated by the peptide monolayer. 相似文献
88.
89.
We show that the cycloaddition of α-methylthioacrylonitrile to cyclohexadiene is faster than that of acrylonitrile. This indicates that the captodative substitution exerts an accelerating effect on the Diels-Alder reaction despite the larger steric bulk of the methylthio group compared to hydrogen. 相似文献
90.
Dakrong Pissuwan Stella M. Valenzuela Murray C. Killingsworth Xiaoda Xu Michael B. Cortie 《Journal of nanoparticle research》2007,9(6):1109-1124
Gold nanorods manifest a readily tunable longitudinal plasmon resonance with light and consequently have potential for use
in photothermal therapeutics. Recent work by others has shown how gold nanoshells and rods can be used to target cancer cells,
which can then be destroyed using relatively high power laser radiation (∼1×105 to 1×1010 W/m2). Here we extend this concept to demonstrate how gold nanorods can be modified to bind to target macrophage cells, and show
that high intensity laser radiation is not necessary, with even 5×102 W/m2 being sufficient, provided that a total fluence of ∼30 J/cm2 is delivered. We used the murine cell line RAW 264.7 and the monoclonal antibody CD11b, raised against murine macrophages,
as our model system and a 5 mW solid state diode laser as our energy source. Exposure of the cells labeled with gold nanorods
to a laser fluence of 30 J/cm2 resulted in 81% cell death compared to only 0.9% in the control, non-labeled cells. 相似文献