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271.
The interfacial and aggregation behavior of the nonionic surfactant decanoyl-N-methyl-glucamide (Mega-10) with the cationic surfactant hexadecyltriphenylphosphonium bromide (HTPB) have been studied using
interfacial tension measurements and fluorescence techniques. From interfacial tension measurements, the critical micellar
concentrations (cmc) and various interfacial thermodynamic parameters have been evaluated. The experimental results were analyzed
in the context of the pseudophase separation model, the regular solution theory, and the Maeda’s approach. These approaches
allowed us to determine the interaction parameter and composition in the mixed state. By using the static quenching method,
the mean micellar aggregation numbers of pure and mixed micelles of HTPB+Mega-10 were obtained. It was found that that the
aggregation number decreases with increasing mole fraction of HTPB. This behavior is attributed to the presence of the bulky
head group of HTPB, which creates steric head group incompatibility and/or electrostatic repulsion. The micropolarity of the
micelle was monitored with pyrene fluorescence intensity ratio. It was observed that the increasing participation of HTPB
induces the formation of micelles with a hydrated structure. The polarization of the fluorescent probe Rhodamine B was monitored
in micellar medium and found to increase with the increase of ionic content. This behavior suggests the formation of mixed
micelles with a more ordered or rigid structure. 相似文献
272.
Osamu Kosaka Shunsuke Iida Pankaj Sehgal Hidekazu Doe 《Colloid and polymer science》2008,286(5):545-551
The interaction of endocrine disruptor chemicals (EDCs) such as nonylphenol (NP) and β-estradiol with cationic micelle of
hexadecyltrimethylammonium ion (HTA+) and a monolayer of HTA+ ion adsorbed at the electrode surface has been investigated in the presence of hydrophilic modified (2-hydroxypropyl)-β-cyclodextrin.
NP, which has a similar structure to HTA+, decreased the critical micelle concentration (cmc) of hexadecyltrimethylammonium bromide more effectively. At the low HTA+ concentration, HTA+ inhibited the adsorption of I2. However, as the HTA+ concentration increased, a monolayer of HTA+ was formed at the electrode surface and caused the adsorption of iodine molecule (I2). In the presence of micelle, the I2 was dissolved in the micelle. Both EDCs caused the formation of HTA+ monolayer even at the HTA+ concentration below the cmc. 相似文献
273.
A detailed computational study on a series of spiroquinazolinones showing phosphodiesterase 7 (PDE7) inhibitory activity was performed to understand the binding mode and the role of stereoelectronic properties in binding. Our docking studies reproduced the essential hydrogen bonding and hydrophobic interactions for inhibitors of this class of enzymes. The N1 proton of the quinazolinone scaffold was involved in H-bonding to an amide side chain of the conserved glutamine residue in the active site. The central bicyclic ring of the molecules showed hydrophobic and pi-stacking interactions with hydrophobic and aromatic amino acid residues, respectively, present in the PDE7 active site. The docked conformations were optimized with density functional theory (DFT) and DFT electronic properties were calculated. Comparison of molecular electrostatic potential (MEP) plots of inhibitors with the active site of PDE7 suggested that the electronic distribution in the molecules is as important as steric factors for binding of the molecules to the receptor. The hydrogen bonding ability and nucleophilic nature of N1 appeared to be important for governing the interaction with PDE7. For less active inhibitors (pIC(50) < 6.5), the MEP maximum at N1 of the spiroquinazolinone ring was high or low based on the electronic properties of the substituents. All the more active molecules (pIC(50) > 6.5) had MEP highest at N3, not N1. Efficient binding of these inhibitors may need some rearrangement of side chains of active-site residues, especially Asn365. This computational modeling study should aid in design of new molecules in this class with improved PDE7 inhibition. 相似文献
274.
The analysis of nitrogen containing amino alcohols, which are the precursors and degradation products of nitrogen mustards and nerve agent VX, constitutes an important aspect for verifying the compliance to the CWC (Chemical Weapons Convention). This work devotes on the development of solid-phase extraction method using silica- and polymer-based SCX (strong cation-exchange) and MCX (mixed-mode strong cation-exchange) cartridges for N,N-dialkylaminoethane-2-ols and alkyl N,N-diethanolamines, from water. The extracted analytes were analyzed by GC-MS (gas chromatography-mass spectrometry) in the full scan and selected ion monitoring modes. The extraction efficiencies of SCX and MCX cartridges were compared, and results revealed that SCX performed better. Extraction parameters, such as loading capacity, extraction solvent, its volume, and washing solvent were optimized. Best recoveries were obtained using 2 mL methanol containing 10% NH(4)OH and limits of detection could be achieved up to 5 x 10(-3) microg mL(-1) in the selected ion monitoring mode and 0.01 microg mL(-1) in full scan mode. The method was successfully employed for the detection and identification of amino alcohol present in water sample sent by Organization for Prohibition of Chemical Weapons (OPCW) in the official proficiency tests. The method was also applied to extract the analytes from human plasma. The SCX cartridge showed good recoveries of amino alcohols from human plasma after protein precipitation. 相似文献
275.
Baruah PK Sreedevi NK Majumdar B Pasricha R Poddar P Gonnade R Ravindranathan S Sanjayan GJ 《Chemical communications (Cambridge, England)》2008,(6):712-714
Abiotic hetero oligomers, adopting a well-defined extended self-assembled sheet-like structure, derived from conformationally constrained aliphatic and aromatic amino acid residues repeating at regular intervals are reported. 相似文献
276.
We have used the density functional theory to study the effect of molecular elongation on the isotropic-nematic, isotropic-smectic A and nematic-smectic A phase transitions of a fluid of molecules interacting via the Gay-Berne intermolecular potential. We have considered a range of length-to-width parameter 3.0 ⩽ x0 ⩽ 4.0 in steps of 0.2 at different densities and temperatures. Pair correlation functions needed as input information in density functional theory are calculated using the Percus-Yevick integral equation theory. Within the small range of elongation, the phase diagram shows significant changes. The fluid at low temperature is found to freeze directly from isotropic to smectic A phase for all the values of x0 considered by us on increasing the density while the nematic phase stabilizes in between isotropic and smectic A phases only at high temperatures and densities. Both isotropic-nematic and nematic-smectic A transition density and pressure are found to decrease as we increase x0. The phase diagram obtained is compared with computer simulation result of the same model potential and is found to be in good qualitative agreement. 相似文献
277.
Realizing the ubiquitous presence of rare-earth orthoborates in various applications involving their optical properties, the current investigation is directed towards the exploration of epoxide mediated rapid synthesis to make YBO3. Highly crystalline orthoborate with disordered vaterite structure resulted on calcining xerogel from the reaction of yttrium chloride, boric acid and propylene oxide at 900 °C as verified from diffraction, vibration spectroscopic and microscopic techniques. Following this approach, orthoborate containing 50 mol% of Y and Gd was obtained and characterized. Dissolution limit of Ce3+ in Y0.50Gd0.50BO3 has been determined. Cerium doping resulted in the reduction in the optical band gap of these samples and appended photocatalytic ability in terms of degradation of aqueous rhodamine-6G (Rh-6G) dye solution. The intensity of 4f → 5d transition of Ce3+ increased monotonously with increase in cerium content. The role of distortion on the blue emission from Ce3+ and photocatalytic properties of these samples were comprehended by characterizing Li+, Ca2+ and Al3+-doped samples (up to 10 mol%) for yttrium. The distortion of Y0.50?xMxGd0.45Ce0.05BO3 lattice decreased in the order, RCa2+ > RY3+ > RLi+ > RAl3+, with the emission intensity (5d → 4f transitions) from Ce3+ increasing in the reverse order. Optical band gap was found to decrease for the Li+, Ca2+ and Al3+ doped samples as compared to undoped one. These doped samples retained their catalytic ability as verified from their use in the photo degradation of rhodamine-B (Rh-B) dye. An insight in to possible mechanism operative in the present photo catalytic degradation experiments has been attempted by carrying out trapping experiments. 相似文献
278.
Pankaj Bandhoria Vivek K. Gupta D. K. Gupta S. M. Jain B. Varghese 《Journal of chemical crystallography》2006,36(3):161-166
The title compound, 3β-acetoxy-pregna-5,16-dien-20-one, C23H32O3, has been synthesized by acetylation followed by oxidation of diosgenin and its crystal structure has been solved from single crystal X-ray diffraction data. The compound crystallizes into orthorhombic space group P212121 with unit cell parameters: a = 6.031(4) ?, b = 12.481(2) ?, c = 27.162(5) ?, Z = 4. The crystal structure has been refined to R = 0.0597 for 1291 observed reflections. Rings A and C of the compound are in chair conformation whereas ring B is in half-chair conformation. Ring D is in envelop conformation. The A/B ring junction is quasi-trans, while ring systems B/C and C/D are trans fused about the C8–C9 and C13–C14 bonds, respectively. The steroid nucleus has a small twist, as shown by the C19–C10⋅C13–C18 pseudo-torsion angle of 9.5°. The crystal packing is determined by a pair of weak C–H⋅O hydrogen bonds in addition to van der Waals interactions. 相似文献
279.
Pankaj K. Agarwal 《Discrete and Computational Geometry》1990,5(1):449-483
In this paper we consider the following problem: Given a set ofn lines in the plane, partition the plane intoO(r
2) triangles so that no triangle meets more thanO(n/r) lines of . We present a deterministic algorithm for this problem withO(nr logn/r) running time, where is a constant <3.33.Work on this paper has been supported by Office of Naval Research Grant N00014-87-K-0129, by National Science Foundation Grant DCR-83-20085, and by grants from the Digital Equipment Corporation and the IBM Corporation. A preliminary version of this paper appears in theProceedings of the 5th Annual Symposium on Computational Geometry, 1989, pp. 11–22. 相似文献
280.
We show thatm distinct cells in an arrangement ofn planes in 3 are bounded byO(m
2/3
n+n
2) faces, which in turn yields a tight bound on the maximum number of facets boundingm cells in an arrangement ofn hyperplanes in
d
, for everyd3. In addition, the method is extended to obtain tight bounds on the maximum number of faces on the boundary of all nonconvex cells in an arrangement of triangles in 3. We also present a simpler proof of theO(m
2/3
n
d/3+n
d–1) bound on the number of incidences betweenn hyperplanes in
d
andm vertices of their arrangement.Work on this paper was supported by DIMACS (Center for Discrete Mathematics and Theoretical Computer Science), a National Science Foundation Science and Technology Center Grant NSF-STC88-09648, and by NSA Grant MDA 904-89-H-2030. 相似文献