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991.
Sinha AE Johnson KJ Prazen BJ Lucas SV Fraga CG Synovec RE 《Journal of chromatography. A》2003,983(1-2):195-204
A high-temperature configuration for a diaphragm valve-based gas chromatography (GCXGC) instrument is demonstrated. GCxGC is a powerful instrumental tool often used to analyze complex mixtures. Previously, the temperature limitations of valve-based GCxGC instruments were set by the maximum operating temperature of the valve, typically 175 degrees C. Thus, valve-based GCxGC was constrained to the analysis of mainly volatile components; however, many complex mixtures contain semi-volatile components as well. A new configuration is described that extends the working temperature range of diaphragm valve-based GCxGC instruments to significantly higher temperatures, so both volatile and semi-volatile compounds can be readily separated. In the current investigation, separations at temperatures up to 250 degrees C are demonstrated. This new design features both chromatographic columns in the same oven with the valve interfacing the two columns mounted in the side of the oven wall so the valve is both partially inside as well as outside the oven. The diaphragm and the sample ports in the valve are located inside the oven while the temperature-restrictive portion of the valve (containing the O-rings) is outside the oven. Temperature measurements on the surface of the valve indicate that even after a sustained oven temperature of 240 degrees C, the portions of the valve directly involved with the sampling from the first column to the second column track the oven temperature to within 1.2% while the portions of the valve that are temperature-restrictive remain well below the maximum temperature of 175 degrees C. A 26-component mixture of alkanes, ketones, and alcohols whose boiling points range from 65 degrees C (n-hexane) to 270 degrees C (n-pentadecane) is used to test the new design. Peak shapes along the first column axis suggest that sample condensation or carry-over in the valve is not a problem. Chemometric data analysis is performed to demonstrate that the resulting data have a bilinear structure. After over 6 months of use and temperature conditions up to 265 degrees C, no deterioration of the valve or its performance has been observed. 相似文献
992.
Bryan Ringstrand Jacob Vroman Dell Jensen Adam Januszko Piotr Kaszynski Jerzy Dziaduszek Witold Drzewinski 《Liquid crystals》2005,32(8):1061-1070
Twelve esters were prepared from pentyl-substituted p-carborane, bicyclo[2.2.2]octane, cyclohexane, and benzene carboxylic acids and three substituted phenols. The mesogenic properties of the series of esters were examined using thermal analysis and optical microscopy. The relationships between structure and mesogenic properties were analysed by comparison of the series of homostructural esters. Thus, the effects of variation of the carboxylic acid structure, introduction of fluorine into the phenol part, and replacement of the central phenyl ring with the -CH2CH2- group on the stability of mesophases and their widths were investigated. In general, carborane derivatives exhibit broad nematic phases and narrow SmA phases, while other derivatives demonstrate rich smectic and soft crystal polymorphism. 相似文献
993.
994.
995.
Spectroelectrochemistry of EuCl3 in Four Molten Salt Eutectics; 3 LiCl−NaCl, 3 LiCl−2 KCl,LiCl−RbCl,and 3 LiCl−2 CsCl; at 873 K 下载免费PDF全文
Cynthia A. Schroll Sayandev Chatterjee Tatiana Levitskaia William R. Heineman Samuel A. Bryan 《Electroanalysis》2016,28(9):2158-2165
Key electrochemical properties affecting pyroprocessing of nuclear fuel were examined in four eutectic melts using Eu3+/2+ as a representative probe. We report the electrochemical and spectroelectrochemical behavior of EuCl3 in four molten salt eutectics (3 LiCl?NaCl, 3 LiCl?2 KCl, LiCl?RbCl and 3 LiCl?2 CsCl) at 873 K. Cyclic voltammetry was used to determine the reduction potential for Eu3+/2+ and the applied potentials for spectroelectrochemistry. Single step chronoabsorptometry and thin‐layer spectroelectrochemistry were used to obtain the number of electrons transferred, reduction potentials and diffusion coefficients for Eu3+ in each eutectic melt. The reduction potentials determined by thin‐layer spectroelectrochemistry were essentially the same as those obtained using cyclic voltammetry. The diffusion coefficient for Eu3+ was the largest in the 3 LiCl?NaCl melt, showed a negative shift in the 3 LiCl?2 KCl melt, and was the smallest in the LiCl?RbCl and 3 LiCl?2 CsCl eutectic melts. The basic one‐electron reversible electron transfer for Eu3+/2+ was not affected by melt composition. 相似文献
996.
Monitoring and Understanding the Paraelectric–Ferroelectric Phase Transition in the Metal–Organic Framework [NH4][M(HCOO)3] by Solid‐State NMR Spectroscopy 下载免费PDF全文
Dr. Jun Xu Dr. Bryan E. G. Lucier Regina Sinelnikov Dr. Victor V. Terskikh Prof. Viktor N. Staroverov Prof. Yining Huang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(41):14348-14361
The paraelectric–ferroelectric phase transition in two isostructural metal–organic frameworks (MOFs) [NH4][M(HCOO)3] (M=Mg, Zn) was investigated by in situ variable‐temperature 25Mg, 67Zn, 14N, and 13C solid‐state NMR (SSNMR) spectroscopy. With decreasing temperature, a disorder–order transition of NH4+ cations causes a change in dielectric properties. It is thought that [NH4][Mg(HCOO)3] exhibits a higher transition temperature than [NH4][Zn(HCOO)3] due to stronger hydrogen‐bonding interactions between NH4+ ions and framework oxygen atoms. 25Mg and 67Zn NMR parameters are very sensitive to temperature‐induced changes in structure, dynamics, and dielectric behavior; stark spectral differences across the paraelectric–ferroelectric phase transition are intimately related to subtle changes in the local environment of the metal center. Although 25Mg and 67Zn are challenging nuclei for SSNMR experiments, the highly spherically symmetric metal‐atom environments in [NH4][M(HCOO)3] give rise to relatively narrow spectra that can be acquired in 30–60 min at a low magnetic field of 9.4 T. Complementary 14N and 13C SSNMR experiments were performed to probe the role of NH4+–framework hydrogen bonding in the paraelectric–ferroelectric phase transition. This multinuclear SSNMR approach yields new physical insights into the [NH4][M(HCOO)3] system and shows great potential for molecular‐level studies on electric phenomena in a wide variety of MOFs. 相似文献
997.
Matthew Dion Andrew B. Larson Bryan D. Vogt 《Journal of Polymer Science.Polymer Physics》2010,48(22):2366-2370
Commercial polydisperse atactic poly(methyl methacrylate) (PMMA) exhibits a decreased glass transition temperature (Tg) when the film thickness is less than ~60 nm, whereas more model atactic PMMA shows an increased Tg in thin films supported on clean silicon wafers. NMR indicates no difference in tacticity, so the divergent thin film behavior appears related to the relative distribution of molecular mass. Extraction of some low molecular weight PMMA components from the commercial sample results in a significant modification of the thin film Tg compared with the initial PMMA fraction. The extracted sample exhibits initially a slight decrease in Tg as the film thickness is reduced below ~60 nm, but then Tg appears to increase for films thinner than 20 nm. These results illustrate the sensitivity of polymer thin film properties to low‐molecular mass components and could explain some of the contradictory reports on the Tg of polymer thin films that exist in the literature. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010 相似文献
998.
999.
Bryan B. Sauer R. Scott McLean Reinoud J. Gaymans Meike C. J. E. Niesten 《Journal of Polymer Science.Polymer Physics》2004,42(9):1783-1792
The crystal morphological properties of segmented poly(ether ester aramide) elastomers with aromatic hard‐segment amide units of uniform length were studied. Four samples with hard‐segment fractions ranging from 3.4 to 9 wt % were studied by tapping atomic force microscopy (AFM). For one sample, both solution and melt‐processed surfaces were examined, and similar crystal morphologies were found. The semicrystalline morphologies of these polymers had some similarities to other low‐hard‐segment segmented elastomers. The very thin needlelike or ribbonlike crystallites at the surface had a high aspect ratio for all the samples. The main difference observed for the different compositions was a decrease in the surface area density of ribbons with a decrease in the hard‐segment fraction. One sample was chosen for in situ AFM studies during film extension. The details of the crystallite orientation and breakup were studied in increments up to 700% elongation (8× stretch ratio) and after relaxation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1783–1792, 2004 相似文献
1000.
Zachary M. Hudson Yi Sun Bryan Ross Rui‐Yao Wang Suning Wang 《Acta Crystallographica. Section C, Structural Chemistry》2009,65(8):m328-m330
The trimetallic compound catena‐poly[dipotassium(I) [bis(2,2′‐bipyridine)di‐μ3‐trifluoroacetato‐dodeca‐μ2‐trifluoroacetato‐diplatinum(II)octasilver(I)]], K2[Pt2Ag8(C2F3O2)14(C10H8N2)2], forms an extended structure in the solid state. Electrostatic interactions involving the K+ ions play a key role in the formation of the extended structure in three dimensions. The AgI ions form one‐dimensional coordination polymers, with alternating Ag2 and Ag6 units linked by CF3CO2− ligands. Pt...Pt interactions perpendicular to the one‐dimensional polymerization axis provide another element of long‐range order, and electrostatic interactions with K+ ions provide connectivity between adjacent polymeric structures. 相似文献