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991.
DNA oligonucleotides that form intramolecular G-quartet structures were investigated as stationary phase reagents for separation of mixtures of the isomeric dipeptides Trp-Arg and Arg-Trp in open-tubular capillary electrochromatography (OTCEC). The oligonucleotides included a thrombin-binding aptamer that forms a biplanar G-quartet structure and an oligonucleotide that forms a 4-plane G-quartet structure. Fluorescence, circular dichroism and UV-visible absorbance spectroscopies were used in batch solution studies to indicate interactions between the dipeptides and the biplanar G-quartet structure. Results for OTCEC separations were compared with results obtained for capillary zone electrophoresis separations on a bare capillary. Temperature studies suggest that resolution is improved when the G-quartet structure is partially destabilized, but control experiments in which potassium chloride was not included in the mobile phase indicate that the G-quartet structure nevertheless plays a role in the separations. 相似文献
992.
The oxidation and enhanced detection of traditionally 'non-electroactive' amino acids at a single-wall carbon nanotube (SWNT) surface and at a nickel hydroxide film electrochemically deposited and generated upon the SWNT layer is reported. Different CNT are compared, with Nafion-dispersed SWNT offering the most favorable layer for constant-potential amperometric detection. Factors affecting the oxidation process, including the pH or applied potential, are assessed. The response of the SWNT-Nafion coated electrode compares favorably with that of copper and nickel disk electrodes under flow injection analysis (FIA) conditions. The electrodeposition of nickel onto the SWNT-Nafion layer (Ni-CNT) led to a dramatic enhancement of the analytical response (vs. that observed at the SWNT or nickel electrodes alone). The oxidative process at the Ni(OH)(2) layer has been studied and the increase in sensitivity rationalized. In the presence of amino acid the Ni-CNT layer undergoes an electrocatalytic process in which the amino acid reduces the newly formed NiO(OH) species. Furthermore, the attractive response of both the CNT and Ni-CNT layers has allowed these electrodes to be used for constant-potential FIA of various amino acids and indicates great promise for monitoring chromatographic effluents. Once again an improved signal was observed at the Ni-CNT electrode compared to nickel deposited upon a bare glassy carbon electrode (Ni-GC). 相似文献
993.
Mehtap E. Eanes George L. Schimek Joseph W. Kolis 《Journal of chemical crystallography》2000,30(4):223-226
The syntheses and structure determinations of CsAg5Se3 (I) and RbAg3Te2 (II) are reported. Both compounds were prepared by using supercritical ethylenediamine at 300°C for 6 days reacting alkali polychalcogenides with silver. For the compound I; tetragonal space group P42/mnm, a = 14.083(2)Å, c = 4.410(2)Å, V = 874.5(4)Å3, Z = 4, D = 6.905 Mg/m3, MoK radiation, = 0.71073, = 27.493 mm–1, F(000) = 1568, R = 0.022, Rw = 0.026 for 472 independent reflection. For compound II; monoclinic space group C2/m, a = 17.546(2)Å, b = 4.617(2)Å, c = 9.165(2)Å, = 113.04(2)°, V = 683.31(12)Å3, Z = 2, D = 6.457 Mg/m3, MoK radiation, = 0.71073, = 23.825 mm–1, F(000) = 1128, R = 0.019, Rw = 0.027 for 690 independent reflection. 相似文献
994.
The set of hyponormal operators whose squares are not hyponormal is norm dense in the set of all hyponormal operators. 相似文献
995.
Berger EL Harris BW Kaplan DE Sullivan Z Tait TM Wagner CE 《Physical review letters》2001,86(19):4231-4234
A long-standing discrepancy between the bottom-quark production cross section and predictions of perturbative quantum chromodynamics is addressed. We show that pair production of light gluinos, of mass 12 to 16 GeV, with two-body decays into bottom quarks and light bottom squarks, yields a bottom-quark production rate in agreement with hadron collider data. We examine constraints on this scenario from low-energy data and make predictions that may be tested at the next run of the Fermilab Tevatron collider. 相似文献
996.
The reaction of dialkyl alkylphosphonates with trivalent metal chlorides has recently been reported (1,2). The typical products of these reactions is a solid which is insoluble in most organic solvents and water. A monomeric structure was postulated for the iron phosphonates(1), while polynuclear structure was proposed for titanium, vanadium, and chromium phosphonates(2). Infrared(1) and Mossbauer-effect(3) studies were unable to differentiate between the monomeric or polynuclear structure for the iron phosphonates, In an attempt to further characterize the iron phosphonates, an x-ray diffration study was undertaken. The results of these studies are reported herein. 相似文献
997.
998.
Two new synthetic approaches to the title compounds are reported. In the first of these, starting with N-carbobenzyloxysarcosine, four synthetic steps are employed to finally assemble the C3? C4 bond of the 1,2-benzothiazine ring. In the second approach, an enol ether is employed as a protecting group to allow formation of the 3-carboxamide function, which is followed by cleavage of the ether function to yield the desired 4-hydroxy-1,2-benzothiazine-3-carboxamide 1,1-dioxide. 相似文献
999.
Joseph G. Lombardino 《Journal of heterocyclic chemistry》1968,5(1):35-39
The synthesis of 6-methoxyimidazo[1,2-b]pyridazine and its 2-methyl analog is reported. Carboxylic acids, esters and quaternary salts derived from this ring system are described and the heterocyclic system is shown to undergo the Mannich reaction. A condensation reaction of the 2-methyl group is reported and nuclear magnetic resonance (nmr) spectra and acidity constants of some imidazo[1,2-b]pyridazines are recorded. 相似文献
1000.
Kenji Maeda Ross A. Miller Ali Shafiee Joseph D. Armstrong III 《Tetrahedron letters》2005,46(9):1545-1549
Highly diastereoselective (>20:1) bromo-lactonization of N-sulfonyl-2-allyl-2-phenylglycine methyl ester (11) was observed. Successive treatment of the chiral lactone with MeONa gave the desired (2S,4R)-4-hydroxy-2-phenylproline derivative in high yield without erosion of the diastereoselectivity. The starting chiral non-racemic compound (5) was prepared from the racemic 2-phenylglycine using a classical kinetic resolution (crystallization), an asymmetric phase transfer alkylation, and an enzyme-catalyzed kinetic resolution. 相似文献