全文获取类型
收费全文 | 461篇 |
免费 | 21篇 |
国内免费 | 2篇 |
专业分类
化学 | 314篇 |
力学 | 2篇 |
数学 | 84篇 |
物理学 | 84篇 |
出版年
2023年 | 3篇 |
2022年 | 15篇 |
2021年 | 21篇 |
2020年 | 11篇 |
2019年 | 10篇 |
2018年 | 10篇 |
2017年 | 17篇 |
2016年 | 25篇 |
2015年 | 19篇 |
2014年 | 17篇 |
2013年 | 21篇 |
2012年 | 32篇 |
2011年 | 37篇 |
2010年 | 16篇 |
2009年 | 15篇 |
2008年 | 21篇 |
2007年 | 20篇 |
2006年 | 20篇 |
2005年 | 24篇 |
2004年 | 14篇 |
2003年 | 18篇 |
2002年 | 12篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 7篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1989年 | 3篇 |
1987年 | 2篇 |
1985年 | 3篇 |
1983年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 5篇 |
1976年 | 1篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1973年 | 6篇 |
1972年 | 3篇 |
1971年 | 1篇 |
1935年 | 1篇 |
1934年 | 2篇 |
1933年 | 1篇 |
1932年 | 1篇 |
1931年 | 1篇 |
排序方式: 共有484条查询结果,搜索用时 144 毫秒
471.
Borowski P Pasieczna-Patkowska S Barczak M Pilorz K 《The journal of physical chemistry. A》2012,116(27):7424-7435
The simple procedure of calculating the infrared spectra of polymers is presented. It is based on selecting the relevant, medium-size representative fragments of a polymer, for which the vibrational frequencies are computed within the harmonic approximation, in conjunction with the multiparameter scaling techniques. Scaling is necessary to predict the reliable fundamentals, which, along with the calculated intensities and properly chosen band widths, reproduce the observed band shapes with high accuracy. Applications to the three polymers: poly(methyl methacrylate), poly(vinyl acetate), and poly(isopropenyl acetate) are presented. The simulated spectra are in good agreement with the experiment. The assignment of bands is reported. The obtained results indicate strong delocalization of the vibrational modes within polymers, which is in accord with the most recent experimental finding [Macromolecules2008, 41, 2494-2501]. Good agreement between the observed and the calculated spectra of deuterated PMMA confirms the correctness of our approach. The preliminary results obtained for the highly irregular macromolecular compound (vinyl-functionalized silica) are also shown. 相似文献
472.
473.
Catalytic cross-metathesis of commercial divinyl sulfone allowed direct access to novel (E)-alkenylvinyl sulfones and (E,E)-dialkenyl sulfones with excellent stereoselectivity. These compounds are useful building blocks, e.g., in the synthesis of substituted thiomorpholine 1,1-dioxide derivatives. [reaction: see text] 相似文献
474.
George C. Bourantas Benjamin F. Zwick Theo Philippe Lavier Vassilios C. Loukopoulos Athanassios A. Dimas Adam Wittek Karol Miller 《国际流体数值方法杂志》2023,95(1):143-175
We present a strong form meshless solver for numerical solution of the nonstationary, incompressible, viscous Navier–Stokes equations in two (2D) and three dimensions (3D). We solve the flow equations in their stream function-vorticity (in 2D) and vector potential-vorticity (in 3D) formulation, by extending to 3D flows the boundary condition-enforced immersed boundary method, originally introduced in the literature for 2D problems. We use a Cartesian grid, uniform or locally refined, to discretize the spatial domain. We apply an explicit time integration scheme to update the transient vorticity equations, and we solve the Poisson type equation for the stream function or vector potential field using the meshless point collocation method. Spatial derivatives of the unknown field functions are computed using the discretization-corrected particle strength exchange method. We verify the accuracy of the proposed numerical scheme through commonly used benchmark and example problems. Excellent agreement with the data from the literature was achieved. The proposed method was shown to be very efficient, having relatively large critical time steps. 相似文献
475.
476.
Karol Wtorek Piotr F. J. Lipiski Anna Adamska-Bartomiejczyk Justyna Piekielna-Ciesielska Jarosaw Sukiennik Alicja Kluczyk Anna Janecka 《Molecules (Basel, Switzerland)》2022,27(1)
Our formerly described pentapeptide opioid analog Tyr-c[D-Lys-Phe-Phe-Asp]NH2 (designated RP-170), showing high affinity for the mu (MOR) and kappa (KOR) opioid receptors, was much more stable than endomorphine-2 (EM-2) in the rat brain homogenate and displayed remarkable antinociceptive activity after central (intracerebroventricular) and peripheral (intravenous ) administration. In this report, we describe the further modification of this analog, which includes the incorporation of a β3-amino acid, (R)- and (S)-β3-Lys, instead of D-Lys in position 2. The influence of such replacement on the biological properties of the obtained analogs, Tyr-c[(R)-β3-Lys-Phe-Phe-Asp]NH2 (RP-171) and Tyr-c[(S)-β3-Lys-Phe-Phe-Asp]NH2, (RP-172), was investigated in vitro. Receptor radiolabeled displacement and functional calcium mobilization assays were performed to measure binding affinity and receptor activation of the new analogs. The obtained data revealed that only one of the diastereoisomeric peptides, RP-171, was able to selectively bind and activate MOR. Molecular modeling (docking and molecular dynamics (MD) simulations) suggests that both compounds should be accommodated in the MOR binding site. However, in the case of the inactive isomer RP-172, fewer hydrogen bonds, as well as instability of the canonical ionic interaction to Asp147, could explain its very low MOR affinity. 相似文献
477.
Frederick J. Karol 《Macromolecular Symposia》1995,89(1):563-575
Developments in the UNIPOL® process for polyethylene, FLEXOMERS®, EPR/EPDM, and polypropylene continue to demonstrate the broad versatility and scope of the process. The potential of catalyst technology to provide dramatic new opportunities in the gas phase remains high. Selection of the appropriate catalyst with control of ligand environment at the active site will provide the basis for improved process operations and unique product opportunities. 相似文献
478.
479.
ukasz Pakowski Maciej Karolak Andrzej Skrzypczak Marta Wojcieszak Filip Walkiewicz Jonasz Podemski Karol Jaroch Barbara Bojko Katarzyna Materna Jerzy Krysiski 《Molecules (Basel, Switzerland)》2022,27(6)
In this study, a series of 10 novel 1-methyl-3-octyloxymethylimidazolium derivatives carrying various anionic moieties (4-hydroxybenzenesulfonate, benzenesulfonate, carvacroloxyacetate, chloride, formate, propionate, thymoloxyacetate, vanillinoxyacetate, eugenoloxyacetate and trimethylacetate) were synthesized. Compounds were tested for their antimicrobial activity against six microbe strains (Staph-ylococcus aureus, Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, Enterococcus faecalis, and Candida albicans), cytotoxic activity against the mouse melanoma cell line (B16 F10), and surface active properties. All synthesized compounds exhibited antimicrobial activity (expressed as minimum inhibitory concentration; in range of 0.10–27.82 mM/L), especially against Gram-positive bacteria and fungi. In addition, all compounds demonstrated cytotoxicity on B16 F10 cells (IC50 values 0.0101–0.0197 mM/L). Surface properties defined as CMC values, ranged from 0.72 to 32.35 mmol L-1. The obtained results provide an insight into the promising activity of a novel group of quaternary imidazolium derivatives having ionic liquid properties. The most potent compounds, containing a thymoloxyacetate and eugenoloxyacetate moiety, could be candidates for new antimicrobial agents or surfactants. 相似文献
480.
Karol Wrblewski Magorzata Szultka-Myska Daria Janiszewska Anna Petruczynik Bogusaw Buszewski 《Molecules (Basel, Switzerland)》2022,27(6)
Vortioxetine (VOR) is a new antidepressant drug used to treat major depressive disorder. In this work, a novel, simple, rapid, accurate, precise, selective, stability-indicating, and fully validated high-performance liquid chromatography method with diode array detection (HPLC-DAD) was developed to determine VOR in bulk and pharmaceutical formulations. A Polar-RP column was used, with a mobile phase consisting of acetonitrile (ACN), methanol (MeOH), acetate buffer pH 3.5, and addition of diethylamine (DEA) in the isocratic elution mode. Assessing the stability of the VOR is fundamental to guarantee the efficacy, safety, and quality of drug products. In this study, the VOR active pharmaceutical ingredient (API) and tablets were subjected to a detailed study of forced degradation, using several degrading agents (acid, alkaline, water, heat, light, and oxidation agents). The developed HPLC-DAD method allows the collection of all the essential data to determine degradation kinetics. It was found that the decomposition of vortioxetine is fragile towards oxidative conditions and photolysis, yielding the first-order and second-order kinetic reaction in the above stress conditions, respectively. The degradation products (DPs) were identified by the high-resolution liquid chromatography coupled with electrospray ionization-quadrupole-time of flight-mass spectrometry (LC-ESI-QTOF-MS) method. The HPLC-DAD method was successfully applied for the quantification of VOR in tablets. Additionally, in silico toxicity prediction of the DPs was performed. 相似文献