全文获取类型
收费全文 | 1079篇 |
免费 | 58篇 |
国内免费 | 1篇 |
专业分类
化学 | 762篇 |
晶体学 | 2篇 |
力学 | 52篇 |
数学 | 152篇 |
物理学 | 170篇 |
出版年
2024年 | 4篇 |
2023年 | 13篇 |
2022年 | 45篇 |
2021年 | 51篇 |
2020年 | 39篇 |
2019年 | 28篇 |
2018年 | 28篇 |
2017年 | 20篇 |
2016年 | 70篇 |
2015年 | 43篇 |
2014年 | 42篇 |
2013年 | 75篇 |
2012年 | 84篇 |
2011年 | 118篇 |
2010年 | 56篇 |
2009年 | 36篇 |
2008年 | 56篇 |
2007年 | 60篇 |
2006年 | 55篇 |
2005年 | 58篇 |
2004年 | 36篇 |
2003年 | 34篇 |
2002年 | 23篇 |
2001年 | 5篇 |
2000年 | 11篇 |
1999年 | 4篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 6篇 |
1995年 | 5篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 6篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1970年 | 1篇 |
1961年 | 1篇 |
1948年 | 1篇 |
1938年 | 1篇 |
1937年 | 1篇 |
1918年 | 1篇 |
1916年 | 1篇 |
排序方式: 共有1138条查询结果,搜索用时 15 毫秒
101.
We compare different notions of curvature on contact sub-Riemannian manifolds. In particular, we introduce canonical curvatures as the coefficients of the sub-Riemannian Jacobi equation. The main result is that all these coefficients are encoded in the asymptotic expansion of the horizontal derivatives of the sub-Riemannian distance. We explicitly compute their expressions in terms of the standard tensors of contact geometry. As an application of these results, we obtain a sub-Riemannian version of the Bonnet–Myers theorem that applies to any contact manifold. 相似文献
102.
Davide Giraudo 《Journal of Theoretical Probability》2017,30(1):196-211
We provide some sufficient mixing conditions on a strictly stationary sequence in order to guarantee the weak invariance principle in Hölder spaces. Strong mixing and \(\rho \)-mixing conditions are investigated as well as \(\tau \)-dependent sequences. The main tools are deviation inequalities for mixing sequences. 相似文献
103.
Models for the macroscopic behavior of Shape Memory Materials can be conveniently constructed within the Ziegler–Green–Naghdi
framework where all the constitutive information is encoded in two ingredients: the free energy and the dissipation function.
In a previous work, we have proposed various expressions for the basic functions suitable to model pseudoelasticity with complete
transformations cycles. In this work we consider additional effects due to Martensite reorientation and to transformation
reversal prior to transformation completion. The new constitutive model allows for the modeling of a variety of effects including:
shape memory associated with thermally induced transformation, internal pseudoelastic subloops and the determination of limit
cycles associated with repetitive stress cycling. 相似文献
104.
Some simple models for the macroscopic behavior of shape memory materials whose microstructure can be described as a mixture of two phases are derived on the basis of a free energy and a dissipation function. Keeping a common expression for the free energy, each model is based on a different expression for the dissipation function. Temperature-induced as well as isothermal, adiabatic and convective stress-induced transformations are studied. Attention is paid to closed form solutions, comparison among the models and parameter identification. 相似文献
105.
Gloria Tabacchi Ettore Fois Davide Barreca Alberto Gasparotto 《International journal of quantum chemistry》2014,114(1):1-7
First‐principles modeling can be a powerful tool for the understanding and optimization of bottom‐up processes for nanomaterials fabrication, such as chemical vapor deposition (CVD), a key technology for the development of advanced systems and devices. Molecule‐to‐material conversion by CVD involves complex chemical phenomena, which are often obscure and still largely unexplored. A proper modeling would require high level of accuracy, large sized models and should include both temperature effects and statistical sampling of reactive events. By presenting a few selected examples, this perspective surveys such problems and discusses currently available approaches for their solution. Possible strategies for future advances in the field are also highlighted. © 2013 Wiley Periodicals, Inc. 相似文献
106.
Mores D Kornatowski J Olsbye U Weckhuysen BM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(10):2874-2884
Coke formation during the methanol‐to‐olefin (MTO) conversion has been studied at the single‐particle level with in situ UV/Vis and confocal fluorescence microscopy. For this purpose, large H‐ZSM‐5 crystals differing in their Si/Al molar ratio have been investigated. During MTO, performed at 623 and 773 K, three major UV/Vis bands assigned to different carbonaceous deposits and their precursors are observed. The absorption at 420 nm, assigned to methyl‐substituted aromatic compounds, initiates the buildup of the optically active coke species. With time‐on‐stream, these carbonaceous compounds expand in size, resulting in the gradual development of a second absorption band at around 500 nm. An additional broad absorption band in the 600 nm region indicates the enhanced formation of extended carbonaceous compounds that form as the reaction temperature is raised. Overall, the rate of coke formation decreases with decreasing aluminum content. Analysis of the reaction kinetics indicates that an increased Brønsted acid site density facilitates the formation of larger coke species and enhances their formation rate. The use of multiple excitation wavelengths in confocal fluorescence microscopy enables the localization of coke compounds with different molecular dimensions in an individual H‐ZSM‐5 crystal. It demonstrates that small coke species evenly spread throughout the entire H‐ZSM‐5 crystal, whereas extended coke deposits primarily form near the crystal edges and surfaces. Polarization‐dependent UV/Vis spectroscopy measurements illustrate that extended coke species are predominantly formed in the straight channels of H‐ZSM‐5. In addition, at higher temperatures, fast deactivation leads to the formation of large aromatic compounds within channel intersections and at the external zeolite surface, where the lack of spatial restrictions allows the formation of graphite‐like coke. 相似文献
107.
Aramburo LR Karwacki L Cubillas P Asahina S de Winter DA Drury MR Buurmans IL Stavitski E Mores D Daturi M Bazin P Dumas P Thibault-Starzyk F Post JA Anderson MW Terasaki O Weckhuysen BM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(49):13773-13781
A combination of atomic force microscopy (AFM), high‐resolution scanning electron microscopy (HR‐SEM), focused‐ion‐beam scanning electron microscopy (FIB‐SEM), X‐ray photoelectron spectroscopy (XPS), confocal fluorescence microscopy (CFM), and UV/Vis and synchrotron‐based IR microspectroscopy was used to investigate the dealumination processes of zeolite ZSM‐5 at the individual crystal level. It was shown that steaming has a significant impact on the porosity, acidity, and reactivity of the zeolite materials. The catalytic performance, tested by the styrene oligomerization and methanol‐to‐olefin reactions, led to the conclusion that mild steaming conditions resulted in greatly enhanced acidity and reactivity of dealuminated zeolite ZSM‐5. Interestingly, only residual surface mesoporosity was generated in the mildly steamed ZSM‐5 zeolite, leading to rapid crystal coloration and coking upon catalytic testing and indicating an enhanced deactivation of the zeolites. In contrast, harsh steaming conditions generated 5–50 nm mesopores, extensively improving the accessibility of the zeolites. However, severe dealumination decreased the strength of the Brønsted acid sites, causing a depletion of the overall acidity, which resulted in a major drop in catalytic activity. 相似文献
108.
Llanes-Pallas A Yoosaf K Traboulsi H Mohanraj J Seldrum T Dumont J Minoia A Lazzaroni R Armaroli N Bonifazi D 《Journal of the American Chemical Society》2011,133(39):15412-15424
A H-bond-driven, noncovalent, reversible solubilization/functionalization of multiwalled carbon nanotubes (MWCNTs) in apolar organic solvents (CHCl(3), CH(2)Cl(2), and toluene) has been accomplished through a dynamic combination of self-assembly and self-organization processes leading to the formation of supramolecular polymers, which enfold around the outer wall of the MWCNTs. To this end, a library of phenylacetylene molecular scaffolds with complementary recognition sites at their extremities has been synthesized. They exhibit triple parallel H-bonds between the NH-N-NH (DAD) functions of 2,6-di(acetylamino)pyridine and the CO-NH-CO (ADA) imidic groups of uracil derivatives. These residues are placed at 180° relative to each other (linear systems) or at 60°/120° (angular modules), in order to tune their ability of wrapping around MWCNTs. Molecular Dynamics (MD) simulations showed that the formation of the hybrid assembly MWCNT?[X?Y](n) (where X = 1a or 1b -DAD- and Y = 2, 3, or 4 -ADA-) is attributed to π-π and CH-π interactions between the graphitic walls of the carbon materials and the oligophenyleneethynylene polymer backbones along with its alkyl groups, respectively. Addition of polar or protic solvents, such as DMSO or MeOH, causes the disruption of the H-bonds with partial detachment of the polymer from the CNTs, followed by precipitation. Taking advantage of the chromophoric and luminescence properties of the molecular subunits, the solubilization/precipitation processes have been monitored by UV-vis absorption and luminescence spectroscopies. All hybrid MWCNTs-polymer materials have been also structurally characterized via thermogravimetric analysis (TGA), transmission electron microscopy (TEM), atomic force microscopy (AFM), scanning tunneling microscopy (STM), and X-ray photoelectron spectroscopy (XPS). 相似文献
109.
Maffeo D Velkov Z Misiakos K Mergia K Paulidou A Zavali M Mavridis IM Yannakopoulou K 《Journal of colloid and interface science》2011,358(2):369-375
The monitoring of the antibacterial agent triclosan binding at nanomolar concentration from an aqueous solution by employing a well-packed monolayer with a predetermined single orientation made of specifically synthesized 2,3-dimethyl-6-(undec-10-enamide)-6-deoxy-β-cyclodextrin (DMBUA) on a silicon wafer (Si/SiO(2)) coated with a novolac resin is reported. A white light reflectance spectroscopy (WLRS) setup was used for the real-time monitoring of the DMBUA deposition and triclosan binding processes. Film thicknesses obtained by WLRS were in very good agreement with the ones measured by X-ray reflectivity (XRR) experiments. Triclosan binds strongly to the DMBUA monolayer (logK(assoc)=6.68). NMR studies in aqueous solution indicated that the chlorophenolyl ring rather than the dichlorophenyl ring is preferentially inserted into DMBUA cups. The current detecting system that requires no tedious surface chemistry, no thiolated cyclodextrins, no gold surfaces, and no expensive equipment may be useful in capturing small molecules and may permit various applications, e.g., preparation of antimicrobial surfaces. 相似文献
110.
Recently, a simple scaling argument was introduced that allows us to map, with some precautions, Brownian and Monte Carlo dynamics for spherical particles. Here, we extend the scaling to study systems that have orientational degrees of freedom and carefully asses its validity over a wide region of temperature and density. Our work allows us to devise a Brownian Monte Carlo algorithm that produces, to a good approximation, physically meaningful trajectories with a minimum programming effort, although at the expense of some sampling efficiency. 相似文献