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201.
Greenblatt HM Guillou C Guénard D Argaman A Botti S Badet B Thal C Silman I Sussman JL 《Journal of the American Chemical Society》2004,126(47):15405-15411
Bifunctional derivatives of the alkaloid galanthamine, designed to interact with both the active site of the enzyme acetylcholinesterase (AChE) and its peripheral cation binding site, have been assayed with Torpedo californica AChE (TcAChE), and the three-dimensional structures of their complexes with the enzyme have been solved by X-ray crystallography. Differences were noted between the IC(50) values obtained for TcAChE and those for Electrophorus electricus AChE. These differences are ascribed to sequence differences in one or two residues lining the active-site gorge of the enzyme. The binding of one of the inhibitors disrupts the native conformation of one wall of the gorge, formed by the loop Trp279-Phe290. It is proposed that flexibility of this loop may permit the binding of inhibitors such as galanthamine, which are too bulky to penetrate the narrow neck of the gorge formed by Tyr121 and Phe330 as seen in the crystal structure. 相似文献
202.
[reaction: see text] A recently discovered multicomponent coupling reaction is used to give direct access to a late intermediate in the synthesis of frondosin B. This intermediate can also be efficiently converted to a ring-expanded analogue of frondosin B by sustained heating of the reaction mixture. An unprecedented tandem 1,7-hydrogen shift, 8pi-electrocyclization is proposed to explain the formation of this ring-expanded species. 相似文献
203.
The decay rate of vinyl unsaturation in high-density polyethylenes irradiated at temperatures from about 310 to 450 K, changes significantly in the melting range up to the crystalline melting point as does free radical mobility and the polymer crystallinity. However, orienting the polymer, or slow cooling or quenching from the melt, prior to irradiation, do not alter the decay process or its rate, although they do alter the rate of increase of insoluble gel and of elastic modulus in the molten state. It is suggested that, below 340 K, the marked deviations from a first-order decay result from the limited mobility of polymeric free radicals in the crystalline phase and from scavenging, by vinyl groups, segregated into the amorphous phase, of radiolytic hydrogen atoms (H). In the melting range, the mobility of polymeric free radicals increases as the crystallinity decreases, reducing the importance of scavenging, so vinyl decay approximates more closely to a first-order relation. In the melt, the vinyl decay relation is not changed qualitatively by H atom scavenging, but the effective vinyl concentration is lower, so the decay rate drops sharply. 相似文献
204.
Céline Pascal Claude Merlet Rose-Marie Marin-Ayral Jean-Claude Tedenac Bernard Boyer 《Mikrochimica acta》2004,145(1-4):147-151
The phases formed at the interface between an intermetallic (NiAl) and a nickel base superalloy joined by combustion synthesis were investigated, particularly the eutectic phases. Owing to their small size, the characterisation of these phases using a Castaings electron microprobe encounters difficulties. The analysis volume size is generally too large to differentiate the phases from their surrounding matrix, even by using low accelerating voltage. Moreover, the eutectic phases contain boron, which is difficult to characterise by EPMA. Independently of the phases shape, the characterisation can be solved by viewing this complex system as a surrounding matrix and a multi layer system. The results of these simulations revealed the presence of two categories of borides: the eutectic boride MM2B2 (M=Mo and M=Co, Cr) and the solid solution boride [Cr1–x (Mo, W)x]B. 相似文献
205.
Bruno Jean Georges Bokias Lay-Theng Lee Ilias Iliopoulos Bernard Cabane 《Colloid and polymer science》2002,280(10):908-914
The structures of aqueous copolymer solutions have been examined through small angle neutron scattering. The copolymers contained mostly N-isopropylacrylamide (NIPAM) monomers. Poly (NIPAM) solutions have a lower critical solution temperature (LCST), above which the macromolecules separate from water. A small fraction of ionizable N,N-[(dimethylamino) propyl] methacrylamide (MADAP) monomers was introduced into the macromolecules. This had dramatic consequences on the solution behavior at temperatures above the LCST of PNIPAM, where phase separation would have been expected for the homopolymer. When all MADAP monomers were ionized, it was found that the solutions resisted the phase separation. At short spatial scales, the chains were collapsed but at large scales they formed branched aggregates that did not separate out of water. When only half of the MADAP monomers are ionized, the electrical charges were able to redistribute themselves along the chains. In this case, the rise in temperature caused a microphase separation where the electrical charges were relocated on a fraction of the chains that remained in solution.The other chains (or section of chains) formed large nodules of a polymer rich phase. 相似文献
206.
Various operating conditions have been applied on tetrakis[p‐(halogenomethyl)]‐ and tetrakis[p‐(aminomethyl)]calix[4]arene derivatives to improve the synthesis of the 5,11,17,23‐tetrakis[(diethylphosphono)methyl]‐25,26,27,28‐tetrahydroxycalix[4]arene. Two new, high yield, synthetic pathways have been selected, involving, for the first one, the 25,26,27,28‐tetrahydroxy‐5,11,17,23‐tetrakis[(trimethylamino)methyl]calix[4]arene, tetraiodide, DMF, and 10 equiv. of triethyl phosphite ((EtO)3P), and, for the other one, the 5,11,17,23‐tetra(bromomethyl)‐25,26,27,28‐tetrahydroxycalix[4]arene, CH2Cl2, and only 4 equiv. of (EtO)2P. 相似文献
207.
The detection and dosimetry of radiosterilization of pharmaceuticals is a growing concern to numerous government regulatory agencies worldwide. In the absence of suitable detection methods, attention was focused on electron spin resonance (ESR) spectrometry. This paper reports experimental data on ESR dosimetry of irradiated nitrofurans (nitrofurantoin, nifuroxazide, nifurzide and nifurtoinol). Whereas the ESR spectrum of a non-irradiated sample shows no signal, a signal, that is dependent on the irradiation dose is observed with irradiated samples. The number of free radicals was calculated by comparing the second integral from radiosterilized samples and a Bruker strong pitch reference; the values were in the range 1.1 x 10(18)-1.5 x 10(19) radicals mol-1 (G = 0.003-0.03). In addition to qualitative detection, ESR spectrometry can be used for dose determination. When a bi-exponential function is applied to the variation of the peak-to-peak amplitude versus dose, the function correlates well with the data. However, an exponential function, easier to use than a bi-exponential function, will probably be sufficient for dose determination by retrospective dosimetry. Decay of radicals upon storage was modelled using a bi-exponential function. From this, the time limit from the irradiation (25 kGy) for identification of irradiated nitrofurans by ESR can be evaluated. With regard to the commercial aspects of drugs, radicals should be detected up to 2 years after irradiation. The kinetic decrease makes discrimination between irradiated and non-irradiated nitrofurans possible even after storage for up to 2 years, except for nifurtoinol. 相似文献
208.
Cytotoxicity and Antiproliferative Effect of Hypericin and Derivatives after Photosensitization 总被引:3,自引:1,他引:3
Ann L. Vandenbogaerde Els M. Delaey Annelies M. Vantieghem Bernard E. Himpens Wilfried J. Merlevede Peter A. de Witte 《Photochemistry and photobiology》1998,67(1):119-125
The toxicity on three human tumor cell lines (A431, HeLa and MCF7) of five phenanthroperylenequinones (hypericin and derivatives) and two perylenequinones (cercosporin and calphostin C) was investigated after photosensitization (4 J/cm2 ). Furthermore, the antiproliferative effect on HeLa cells was studied for the phenanthroperylenequinones. Hypericin, 2,5-dibromohypericin, 2,5,9,12-tetrabromohypericin and perylenequinones displayed a potent cytotoxic and antiproliferative effect in the nanomolar range. Hypericin dicarboxylic acid exhibited no photoactivity. In general, the antiproliferative activity correlated well with the photocytotoxicity. However, the nonphotocytotoxic compound hexamethylhypericin showed potent antiproliferative activity in the nanomolar range, probably exerting its action by protein kinase C inhibition. Without light irradiation, no cytotoxic and antiproliferative effect was observed for any photocytotoxic phenanthroperylenequinone compound. Furthermore, confocal laser microscopy revealed that the subcellular localization in A431 cells was similar for the photoactive compounds; the photosensitizers were mainly concentrated in the perinuclear region, probably corresponding with the Golgi apparatus and the endoplasmic reticulum. In addition, the accumulation of the photosensitizers in HeLa cells was investigated. All compounds except hypericin dicarboxylic acid were found to concentrate to a large extent in the cells. The compound 2,5,9,12-tetrabromohypericin seemed intrinsically more effective than hypericin since the intracellular concentration of the bromoderivative was a magnitude of order lower than that of hypericin although both compounds showed similar photobiological activity. 相似文献
209.
Dynamic arsenic removal on a MnO2-loaded resin 总被引:2,自引:0,他引:2
Lenoble V Chabroullet C al Shukry R Serpaud B Deluchat V Bollinger JC 《Journal of colloid and interface science》2004,280(1):62-67
Previous batch studies on a polystyrene matrix loaded with manganese dioxide, synthesized from an anionic commercial resin in chloride form, have proven the efficiency of this sorbent in As(V) and As(III) removal. This solid is now tested with column experiments to predict its behavior in a treatment process. An artificial water, with a composition in major ions similar to that of granitic water, often contaminated with arsenic, was prepared. This artificial water was used to simulate arsenic removal processes under near-natural conditions and with a stable composition. Furthermore, the hydride generation AAS analytical method was optimized to measure low arsenic concentrations (1 to 20 microg/L). 相似文献
210.
Grancher D Jaussaud P Durix A Berthod A Fenet B Moulard Y Bonnaire Y Bony S 《Journal of chromatography. A》2004,1059(1-2):73-81
This paper describes a new method of purification of the Lolitrem B, a tremorgenic mycotoxin produced in planta by the endophytic fungus Neotyphodium lolii. The method is based on the large-scale isolation of the toxin by countercurrent chromatography (CCC). The lolitrem B content in endophyted ryegrass seed, 11 microg/g or 11 ppm, is extracted by stirring finely ground seeds with ethanol for 3 h at room temperature. The concentrated crude extract contains about 0.6 mg/g or 600 ppm of lolitrem B. It is then submitted to CCC purification with a biphasic four-solvent liquid system. A 160-fold enrichment was obtained in one step producing a raffinate containing 10% or 100 mg/g of the toxin. Further purifications were then performed by thin layer and low pressure liquid chromatography. Twenty-eight micrograms of lolitrem B with a 96% purity grade were obtained from 8 kg of seeds (yield 32%). 相似文献