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101.
Michal Nowak Wieslaw Tryniszewski Agata Sarniak Anna Wlodarczyk Piotr J. Nowak Dariusz Nowak 《Molecules (Basel, Switzerland)》2022,27(11)
Hydroxyl radical (•OH) scavenging and the regeneration of Fe2+ may inhibit or enhance peroxidative damage induced by a Fenton system, respectively. Plant polyphenols reveal the afore-mentioned activities, and their cumulative net effect may determine anti- or pro-oxidant actions. We investigated the influence of 17 phenolics on ultra-weak photon emission (UPE) from a modified Fenton system (92.6 µmol/L Fe2+, 185.2 µmol/L EGTA (ethylene glycol-bis(β-aminoethyl-ether)-N,N,N′,N,-tetraacetic acid) and 2.6 mmol/L H2O2 pH = 7.4). A total of 8 compounds inhibited (antioxidant effect), and 5 enhanced (pro-oxidant effect) UPE at all studied concentrations (5 to 50 µmol/L). A total of 4 compounds altered their activity from pro- to antioxidant (or vice versa) along with increasing concentrations. A total of 3 the most active of those (ferulic acid, chlorogenic acid and cyanidin 3-O-glucoside; mean UPE enhancement by 63%, 5% and 445% at 5 µmol/L; mean UPE inhibition by 28%, 94% and 24% at 50 µmol/L, respectively) contained catechol or methoxyphenol structures that are associated with effective •OH scavenging and Fe2+ regeneration. Most likely, these structures can determine the bidirectional, concentration-dependent activity of some phenolics under stable in vitro conditions. This is because the concentrations of the studied compounds are close to those occurring in human fluids, and this phenomenon should be considered in the case of dietary supplementation with isolated phenolics. 相似文献
102.
Jiri Kos Tomas Gonec Michal Oravec Izabela Jendrzejewska Josef Jampilek 《Molecules (Basel, Switzerland)》2021,26(14)
A set of twenty-four 3-hydroxynaphthalene-2-carboxanilides, disubstituted on the anilide ring by combinations of methoxy/methyl/fluoro/chloro/bromo and ditrifluoromethyl groups at different positions, was prepared. The compounds were tested for their ability to inhibit photosynthetic electron transport (PET) in spinach (Spinacia oleracea L.) chloroplasts. N-(3,5-Difluorophenyl)-, N-(3,5-dimethylphenyl)-, N-(2,5-difluorophenyl)- and N-(2,5-dimethylphenyl)-3-hydroxynaphthalene-2-carboxamides showed the highest PET-inhibiting activity (IC50 ~ 10 µM) within the series. These compounds were able to inhibit PET in photosystem II. It has been found that PET-inhibiting activity strongly depends on the position of the individual substituents on the anilide ring and on the lipophilicity of the compounds. The electron-withdrawing properties of the substituents contribute towards the PET activity of these compounds. 相似文献
103.
Anna Sopková Michal Šingliar Ján Skoršepa Juraj Matanin Eva Terpáková 《Journal of inclusion phenomena and macrocyclic chemistry》1985,3(3):297-313
The structure and reactivity of one unique molecule may be understood only in relation to its molecular surroundings. The non-stoichiometric forms of the tetracyano complexes M(B)
mM (CN)4·nG (B=nitrogen or oxygen containing base; G=aromatic compound or H2O,m0,n>0) are understood in this respect. Their stoichiometric or non-stoichiometric forms, with voids either completely or more often partially occupied, are responsible for their observed sorptive and resorptive abilities. The effects of the surroundings are correlated with the results of thermal analysis, magnetic measurements and their sorptive abilities.Dedicated to Professor H. M. Powell. 相似文献
104.
Stanislav Standara Petr Kulhánek Radek Marek Michal Straka 《Journal of computational chemistry》2013,34(22):1890-1898
The isotropic 129Xe nuclear magnetic resonance (NMR) chemical shift (CS) in Xe@C60 dissolved in liquid benzene was calculated by piecewise approximation to faithfully simulate the experimental conditions and to evaluate the role of different physical factors influencing the 129Xe NMR CS. The 129Xe shielding constant was obtained by averaging the 129Xe nuclear magnetic shieldings calculated for snapshots obtained from the molecular dynamics trajectory of the Xe@C60 system embedded in a periodic box of benzene molecules. Relativistic corrections were added at the Breit–Pauli perturbation theory (BPPT) level, included the solvent, and were dynamically averaged. It is demonstrated that the contribution of internal dynamics of the Xe@C60 system represents about 8% of the total nonrelativistic NMR CS, whereas the effects of dynamical solvent add another 8%. The dynamically averaged relativistic effects contribute by 9% to the total calculated 129Xe NMR CS. The final theoretical value of 172.7 ppm corresponds well to the experimental 129Xe CS of 179.2 ppm and lies within the estimated errors of the model. The presented computational protocol serves as a prototype for calculations of 129Xe NMR parameters in different Xe atom guest–host systems. © 2013 Wiley Periodicals, Inc. 相似文献
105.
Jana Kocbov Frantiek Vavrek tpnka Novkov Lachmanov Jakub ebera Michal Valek Magdalna Hromadov 《Molecules (Basel, Switzerland)》2022,27(23)
Self-assembled monolayers (SAMs) of terpyridine-based transition metal (ruthenium and osmium) complexes, anchored to gold substrate via tripodal anchoring groups, have been investigated as possible redox switching elements for molecular electronics. An electrochemical study was complemented by atomic force microscopy (AFM) and scanning tunneling microscopy (STM) methods. STM was used for determination of the SAM conductance values, and computation of the attenuation factor β from tunneling current–distance curves. We have shown that SAMs of Os-tripod molecules contain larger adlayer structures compared with SAMs of Ru-tripod molecules, which are characterized by a large number of almost evenly distributed small islands. Furthermore, upon cyclic voltammetric experimentation, Os-tripod films rearrange to form a smaller number of even larger islands, reminiscent of the Ostwald ripening process. Os-tripod SAMs displayed a higher surface concentration of molecules and lower conductance compared with Ru-tripod SAMs. The attenuation factor of Os-tripod films changed dramatically, upon electrochemical cycling, to a higher value. These observations are in accordance with previously reported electron transfer kinetics studies. 相似文献
106.
107.
Peng Yang JinRong Wang Michal Fe
kan 《Mathematical Methods in the Applied Sciences》2019,42(10):3700-3720
In this paper, we study a new class of periodic nonautonomous differential equations with periodic noninstantaneous impulsive effects. A concept of noninstantaneous impulsive Cauchy matrix is introduced, and some basic properties are considered. We give the representation of solutions to the homogeneous problem and nonhomogeneous problem by using noninstantaneous impulsive Cauchy matrix, and the variation of constants method, adjoint systems, and periodicity of solutions is verified under standard periodicity conditions. Further, we show the existence and uniqueness of solutions of semilinear problem and establish existence result for periodic solutions via Brouwer fixed point theorem and uniqueness and global asymptotic stability via Banach fixed point theorem. 相似文献
108.
Kobayashi M Skarba M Galletto P Cakara D Borkovec M 《Journal of colloid and interface science》2005,292(1):139-147
Measuring and modeling the surface charge of clays, and more especially smectites, has become an important issue in the use of bentonites as a waste confinement material aimed at retarding migration of water and solutes. Therefore, many studies of the acid-base properties of montmorillonite have appeared recently in the literature, following older studies principally devoted to cation exchange. It is striking that beyond the consensus about the complex nature of the surface charge of clays, there are many discrepancies, especially concerning the dissociable charge, that prevents intercomparison among the published data. However, a general trend is observed regarding the absence of common intersection point on raw titration curves at different ionic strengths. Analysis of the literature shows that these discrepancies originate from the experimental procedures for the preparation of the clays and for the quantification of their surface charge. The present work is an attempt to understand how these procedures can impact the final results. Three critical operations can be identified as having significant effects on the surface properties of the studied clays. The first one is the preparation of purified clay from the raw material: the use of acid or chelation treatments, and the repeated washings in deionized water result in partial dissolution of the clays. Then storage of the purified clay in dry or wet conditions strongly influences the equilibria in the subsequent experiments respectively by precipitation or enhanced dissolution. The third critical operation is the quantification of the surface charge by potentiometric titration, which requires the use of strong acids and bases. As a consequence, besides dissociation of surface sites, many secondary titrant consuming reactions were described in the literature, such as cation exchange, dissolution, hydrolysis, or precipitation. The cumulated effects make it difficult to derive proper dissociation constants, and to build adequate models. The inadequation of the classical surface complexation models to describe the acid-base behavior of clays is illustrated by the electrokinetic behavior of smectites, which is independent from the pH and the ionic strength. Therefore, there is still a need on one hand for accurate data recorded in controlled conditions, and on the other hand for new models taking into account the complex nature of the charge of clays. 相似文献
109.
Wiecko M Girnt D Rastätter M Panda TK Roesky PW 《Dalton transactions (Cambridge, England : 2003)》2005,(12):2147-2150
The chiral phosphanylamido ligand, (N(CHMePh)(PPh2))-, has been introduced into co-ordination chemistry. As starting material the oily amines HN(R-*CHMePh)(PPh2)(1a) and HN(S-*CHMePh)(PPh2)(1b) were used. To reconfirm their absolute structure, 1b was oxidized with H2O2 in air to obtain HN(S-*CHMePh)(P(O)Ph2)(2) as a solid compound. The solid-state structure of 2 was established by single-crystal X-ray diffraction. The lithium salts of both enantiomers Li(N(R-*CHMePh)(PPh2))(3a) and Li(N(S-*CHMePh)(PPh2))(3b) were prepared by deprotonation reaction of 1a,b. Compounds 3a,b were further reacted with zirconocen dichloride to give the chiral metallocenes [(eta5-C5H5)2Zr(Cl)(eta2-N(R-*CHMePh)(PPh2))](4a) and [(eta5-C5H5)2Zr(Cl)(eta2-N(S-*CHMePh)(PPh2))](4b). In an alternative approach to give chiral zirconium compounds, the neutral amine 1b was reacted with [(PhCH2)4Zr] to give the enantiomeric pure complex [(PhCH2)3Zr(eta2-N(S-*CHMePh)(PPh2))](5). The solid-state structures of all zirconium complexes were determined by single-crystal X-ray diffraction. 相似文献
110.