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121.
E-Z photoisomerizable chiral dopants are a class of materials that can be used to prepare birefringent optical components with patterned optical properties. Two new photoisomerizable chiral dopants have been synthesized and analysed. The materials were derived from nopinone and camphor. The properties of these compounds were compared with the properties of the methone derivative described in earlier publications. The E-isomers of the nopinone and camphor derivatives had helical twisting powers of 2.7 and 1.7 μm-1, respectively. This is a factor of about 10 lower than the value obtained for the menthone derivative (-19 μm-1). Due to the high absorption of the Z-isomers relative to the E-isomers of the nopinone and camphor derivatives, isomerization during 365 nm UV exposure proceeded to a much lesser extent than the isomerization of the menthone derivative. At shorter wavelengths, the absorption of the Z-isomer is much lower than that of the E-isomer and much higher degrees of conversion could be achieved. 相似文献
122.
β-Glucosidase hydrolyzes cellobiose to glucose and is an important enzyme in the consortium used for hydrolysis of cellulosic and lignocellulosic feedstocks. In the present work, β-glucosidase was covalently immobilized on non-porous magnetic particles to enable re-use of the enzyme. It was found that particles activated with cyanuric chloride and polyglutaraldehyde gave the highest bead-related immobilized enzyme activity when tested with p-nitrophenyl-β-D-glucopyranoside (104.7 and 82.2 U/g particles, respectively). Furthermore, the purified β-glucosidase preparation from Megazyme gave higher bead-related enzyme activities compared to Novozym 188 (79.0 and 9.8 U/g particles, respectively). A significant improvement in thermal stability was observed for immobilized enzyme compared to free enzyme; after 5 h (at 65 °C), 36 % of activity remained for the former, while there was no activity in the latter. The performance and recyclability of immobilized β-glucosidase on more complex substrate (pretreated spruce) was also studied. It was shown that adding immobilized β-glucosidase (16 U/g dry matter) to free cellulases (8 FPU/g dry matter) increased the hydrolysis yield of pretreated spruce from ca. 44 % to ca. 65 %. In addition, it was possible to re-use the immobilized β-glucosidase in the spruce and retain activity for at least four cycles. The immobilized enzyme thus shows promise for lignocellulose hydrolysis. 相似文献
123.
Johan R. Johansson Yubo Wang Dr. Mattias P. Eng Prof. Nina Kann Prof. Per Lincoln Dr. Johanna Andersson 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(20):6246-6256
The slow dissociation of DNA threading intercalators makes them interesting as model compounds in the search for new DNA targeting drugs, as there appears to be a correlation between slow dissociation and biological activity. Thus, it would be of great value to understand the mechanisms controlling threading intercalation, and for this purpose we have investigated how the length of the bridging ligand of binuclear ruthenium threading intercalators affects their DNA binding properties. We have synthesised a new binuclear ruthenium threading intercalator with slower dissociation kinetics from ct‐DNA than has ever been observed for any ruthenium complex with any type of DNA, a property that we attribute to the increased distance between the ruthenium centres of the new complex. By comparison with previously studied ruthenium complexes, we further conclude that elongation of the bridging ligand reduces the sensitivity of the threading interaction to DNA flexibility, resulting in a decreased AT selectivity for the new complex. We also find that the length of the bridging ligand affects the enantioselectivity with increasing preference for the ΔΔ enantiomer as the bridging ligand becomes longer. 相似文献
124.
Rianne A.G. Harmsen Nourdin Ghalit Johan Kemmink Eefjan Breukink Rob M.J. Liskamp Dirk T.S. Rijkers 《Tetrahedron》2014
The bacteria-specific membrane component lipid II is essential for bacterial cell wall synthesis. A tricyclic nisin mimic was designed and synthesized in which both thioether moieties were mimicked by an alkane-bridge, as well as the introduction of a third conformational constraint consisting of a macrocyclic lactam-bridge between the N-terminus and the B-ring. The newly designed tricyclic AB-ring mimic was found to bind lipid II since it was able to inhibit nisin-induced membrane leakage in a dose-dependent manner. These results imply that the tricyclic AB-ring mimic may form a novel class of lead structures for the development of nisin-based peptide antibiotics. 相似文献
125.
A Molecular modeling study of the changes of some steric properties of the precatalysts during the olefin metathesis reaction 下载免费PDF全文
Frans T. I. Marx Johan H. L. Jordaan Gerhard Lachmann Hermanus C. M. Vosloo 《Journal of computational chemistry》2014,35(19):1457-1463
The productive self‐metathesis of 1‐octene with a series of new phosphine ligated Grubbs‐type precatalysts was studied. The resulting structures were used to compare some steric properties of the new precatalysts with those of well‐known precatalysts. The possibility of α‐CC agnostic stabilization as well as the ability of the ligands to shield the metal was studied. A comparison of the obtained data, pointed to the unlikelihood that α‐CC agostic stabilization is a major contribution to the stabilization of the various metallacyclobutane rings. The similarity in the ability of the ligands to shield the metal also raised questions about the comparison of experimentally observed trends with those obtained theoretically. © 2014 Wiley Periodicals, Inc. 相似文献
126.
Robert Lassfolk Manuel Pedrón Prof. Tomás Tejero Prof. Pedro Merino Johan Wärnå Prof. Reko Leino 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(34):e202200499
Acyl group migration affects the synthesis, isolation, manipulation and purification of all acylated organic compounds containing free hydroxyl groups, in particular carbohydrates. While several isolated studies on the migration phenomenon in different buffers have been reported, comprehensive insights into the overall migration process in different monosaccharides under similar conditions have been lacking. Here, we have studied the acyl migration in different monosaccharides using five different acyl groups by a combination of experimental, kinetic and theoretical tools. The results show that the anomeric configuration in the monosaccharide has a major influence on the migration rate, together with the relative configurations of the other hydroxyl groups and the nature of the migrating acyl group. Full mechanistic model, based on computations, demonstrates that the acyl migration proceeds through an anionic stepwise mechanism with linear dependence on the [OH−] and the pKa of the hydroxyl group toward which the acyl group is migrating. 相似文献
127.
Dr. Yanhui Wang Dr. Maroua Bouchneb Rimeh Mighri Dr. Johan G. Alauzun Dr. P. Hubert Mutin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(8):2670-2682
Several non-hydrolytic sol–gel syntheses involving different precursors, oxygen donors, and conditions have been screened aiming to selectively produce mesoporous t-ZrO2 or m-ZrO2 with significant specific surface areas. The in situ water formation was systematically investigated by Karl Fisher titration of the syneresis liquids. XRD and nitrogen physisorption were employed to characterize the structure and texture of the ZrO2 samples. Significant amounts of water were found in several cases, notably in the reactions of Zr(OnPr)4 with ketones (acetone, 2-pentanone, acetophenone), and of ZrCl4 with alcohols (benzyl alcohol, ethanol) or acetone. Conversely, the reactions of Zr(OnPr)4 with acetic anhydride or benzyl alcohol at moderate temperature (200 °C) and of ZrCl4 with diisopropyl ether appear strictly non-hydrolytic. Although reaction time and reaction temperature were also important parameters, the presence of water played a crucial role on the structure of the final zirconia: t-ZrO2 is favored in strictly non-hydrolytic routes, while m-ZrO2 is favored in the presence of significant amounts of water. 1H and 13C NMR analysis of the syneresis liquids allowed us to identify the main reactions responsible for the formation of water and of the oxide network. The morphology of the most interesting ZrO2 samples was further investigated by electron microscopy (SEM, TEM). 相似文献
128.
129.
Taye B. Demissie Nataliya Kostenko Stanislav Komorovsky Michal Repisky Johan Isaksson Annette Bayer Kenneth Ruud 《Journal of Physical Organic Chemistry》2015,28(12):723-731
We present a theoretical and experimental study of the structure and nuclear magnetic resonance (NMR) parameters of the pentacarbonyltungsten complexes of η1‐2‐(trimethylstannyl)‐4,5‐dimethylphosphinine, η2‐norbornene, and imidazolidine‐2‐thione. The three complexes have a pseudo‐octahedral molecular structure with the six ligands bonded to the tungsten atom. The η1‐2‐(trimethylstannyl)‐4,5‐dimethylphosphinine‐pentacarbonyl tungsten complex was synthesized for the first time. For all compounds, we present four‐component relativistic calculations of the NMR parameters at the Dirac–Kohn–Sham density functional level of theory using hybrid functionals. These large‐scale relativistic calculations of NMR chemical shifts and spin–spin coupling constants were compared with available experimental data, either taken from the literature or measured in this work. The inclusion of solvent effects modeled using a conductor‐like screening model was found to improve agreement between the calculated and experimental NMR parameters, and our best estimates for the NMR parameters are generally in good agreement with available experimental results. The present work demonstrates that four‐component relativistic theory has reached a level of maturity that makes it a convenient and accurate tool for modeling and understanding chemical shifts and indirect spin–spin coupling constants of organometallic compounds containing heavy elements, for which conventional non‐relativistic theory breaks down. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
130.
Dr. Christina I. Schroeder Dr. Lachlan D. Rash Xavier Vila‐Farrés Dr. K. Johan Rosengren Dr. Mehdi Mobli Prof. Glenn F. King Prof. Paul F. Alewood Prof. David J. Craik Dr. Thomas Durek 《Angewandte Chemie (International ed. in English)》2014,53(4):1017-1020
Mambalgins are a novel class of snake venom components that exert potent analgesic effects mediated through the inhibition of acid‐sensing ion channels (ASICs). The 57‐residue polypeptide mambalgin‐2 (Ma‐2) was synthesized by using a combination of solid‐phase peptide synthesis and native chemical ligation. The structure of the synthetic toxin, determined using homonuclear NMR, revealed an unusual three‐finger toxin fold reminiscent of functionally unrelated snake toxins. Electrophysiological analysis of Ma‐2 on wild‐type and mutant ASIC1a receptors allowed us to identify α‐helix 5, which borders on the functionally critical acidic pocket of the channel, as a major part of the Ma‐2 binding site. This region is also crucial for the interaction of ASIC1a with the spider toxin PcTx1, thus suggesting that the binding sites for these toxins substantially overlap. This work lays the foundation for structure–activity relationship (SAR) studies and further development of this promising analgesic peptide. 相似文献