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951.
Improving boron isotope ratio measurement precision with quadrupole inductively coupled plasma-mass spectrometry 总被引:2,自引:0,他引:2
Assad Al-Ammar Eva Reitznerov Ramon M. Barnes 《Spectrochimica Acta Part B: Atomic Spectroscopy》2000,55(12):1861-1867
A method was developed to improve the precision of inductively coupled plasma quadrupole mass spectrometry (ICP-QMS) for the determination of boron isotope ratios (11B/10B) in various environmental materials including seawater. This approach is based on the common analyte internal standardization (CAIS) chemometric algorithm. The sample solution obtained after digestion is spiked with lithium, and both 7Li/6Li and 11B/10B values are measured using long-counting periods (20 min). The CAIS algorithm corrects the measured 11B/10B values for (a) statistical fluctuations resulting from short-term noise; (b) drift in 11B-to-10B ratio as a result of long-term deviation in instrumental parameters likely to occur during long counting times; (c) change in 11B-to-10B ratio caused by variation in matrix elements concentrations; and (d) drift in mass bias correction factor. Comparing boron isotopic ratios in seawater measured by conventional and the new isotope ratio methods validates the procedure. A synthetic isotopic mixture of boron SRM 951 and enriched 10B SRM 952 also was examined. The CAIS method provided a measured boron isotopic ratio precision of 0.05% R.S.D. while eliminating 5.1% matrix concentration error and 0.25% instrumental drift error. 相似文献
952.
Chiral separation of deprenyl-N-oxide isomers is presented using capillary electrophoresis in the presence of various cyclodextrin (CD) derivatives. This recently identified metabolite of R-(-)-deprenyl may possess desirable pharmacological activities. The effect of the cavity size and the substituents of the CD are examined on the enantiomer resolution of the compound having an asymmetric center on a heteroatom. The importance of hydrophilic or hydrogen bonding interaction, as well as the position of the interacting groups is demonstrated. Outstanding selectivity and resolution values are achieved using the chargeable carboxymethyl-beta-CD. 2-Hydroxypropyl-beta-CD is also suitable for the enantiomer separation of the analyte. Native beta-CD and carboxyethyl-beta-CD provide only poor enantioselectivity, whereas heptakis-(2,6-di-O-methyl)-beta-CD is capable of separating only the diastereomers. No chiral resolution can be observed in the presence of gamma-CD. 相似文献
953.
The existence of multiple periodic solutions and their exponential stability are investigated for impulsive hybrid Hopfield-type neural networks with both time-dependent and distributed delays, using the Leray-Schauder fixed point theorem and Lyapunov functionals. The criteria given are easily verifiable, possess many adjustable parameters, and depend on impulses, providing flexibility for the analysis and design of delayed neural networks with impulse effects. Examples are given. 相似文献
954.
Eva‐Maria Laux Xenia Knigge Frank F. Bier Christian Wenger Ralph Hlzel 《Electrophoresis》2015,36(17):2094-2101
The combination of alternating electric fields with nanometer‐sized electrodes allows the permanent immobilization of proteins by dielectrophoretic force. Here, atomic force microscopy is introduced as a quantification method, and results are compared with fluorescence microscopy. Experimental parameters, for example the applied voltage and duration of field application, are varied systematically, and the influence on the amount of immobilized proteins is investigated. A linear correlation to the duration of field application was found by atomic force microscopy, and both microscopical methods yield a square dependence of the amount of immobilized proteins on the applied voltage. While fluorescence microscopy allows real‐time imaging, atomic force microscopy reveals immobilized proteins obscured in fluorescence images due to low S/N. Furthermore, the higher spatial resolution of the atomic force microscope enables the visualization of the protein distribution on single nanoelectrodes. The electric field distribution is calculated and compared to experimental results with very good agreement to atomic force microscopy measurements. 相似文献
955.
Concellón JM Bardales E Concellón C García-Granda S Díaz MR 《The Journal of organic chemistry》2004,69(20):6923-6926
The use of samarium diiodide as a source of iodides is reported. Thus, 2-hydroxy-3-iodoamides were obtained, with total regioselectivity, by treatment of 2,3-epoxyamides, in which the oxirane ring is 2,3-disubstituted or 2,2,3-trisubstituted, with SmI2. The ring-opening reaction was diastereospecific and (2R*,3R*)- or (2R*,3S*)-2-hydroxy-3-iodoamides were obtained from cis- or trans-epoxyamides, respectively. The relative configuration of 2-hydroxy-3-iodoamides was established by X-ray analysis. A mechanism to explain this transformation has been proposed. The starting compounds 1 are easily prepared by the reaction of enolates derived from 2-chloroamides with aldehydes at -78 degrees C. 相似文献
956.
The performance of the contactless conductivity (C4D) and diode array photometric (DAD) detectors has been compared for CE separations of creatinine, arginine and 3‐methylhistidine in acetic acid background electrolytes. The contactless conductivity detector response has also been modeled. It has been found that the two detectors provide similar responses and can readily be used for dual CE detection. Changes in the acetic acid concentration affect the C4D noise less than the DAD noise, but their effect on the C4D response to the analytes is greater than with DAD. In general, C4D provides better detection results at higher acetic acid concentrations, while DAD is more sensitive and reliable at very low ones. Capillaries with greater internal diameters are preferable for both detectors, provided that the separation efficiency is not adversely affected. Acetic acid is a suitable background electrolyte for CE separations of small, basic organic molecules. 相似文献
957.
Todor Baramov Karlijn Keijzer Dr. Elisabeth Irran Eva Mösker Prof. Dr. Mu‐Hyun Baik Prof. Dr. Roderich Süssmuth 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(32):10536-10542
The E. coli siderophore enterobactin, one of the strongest FeIII chelators known to date, is also capable of binding SiIV under physiological conditions. We report on the synthesis and structural characterization of the tris(catecholate) SiIV–enterobactin complex and its GeIV and TiIV analogues. Comparative structural analysis, supported by quantum‐chemical calculations, reveals the correlation between the ionic radius and the structural changes in enterobactin upon complexation. 相似文献
958.
Scheer M Himmel D Kuntz C Zhan S Leiner E 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(29):9020-9029
Thermolysis of [Cp*P{W(CO)5}2] (1) in the presence of [{CpMo(CO)2}2] leads to the novel complexes [{(CO)2Cp*W}{CpMo(CO)2}(micro,eta2:eta1:eta1-P2{W(CO)5}2)] (6; Cp=eta5-C5H5, Cp*=eta5-C5Me5), [{(micro-O)(CpMoWCp*)W(CO)4}{micro3-PW(CO)5}2] (7), [{CpMo(CO)2}2{Cp*W(CO)2}{micro3-PW(CO)5}] (8) and [{CpMo(CO)2}2{Cp*W(CO)2}(micro3-P)] (9). The structural framework of the main products 8 and 9 can be described as a tetrahedral Mo2WP unit that is formed by a cyclisation reaction of [{CpMo(CO)2}2] with an [Cp*(CO)2W[triple chemical bond]P-->W(CO)5] intermediate containing a W--P triple bond and subsequent metal-metal and metal-phosphorus bond formation. Photolysis of 1 in the presence of [{CpMo(CO)2}2] gives 8, 9 and phosphinidene complex [(micro3-PW(CO)5){CpMo(CO)2W(CO)5}] (10), in which the P atom is in a nearly trigonal-planar coordination environment formed by one {CpMo(CO)2} and two {W(CO)5} units. Comprehensive structural and spectroscopic data are given for the products. The reaction pathways are discussed for both activation procedures, and DFT calculations reveal the structures with minimum energy along the stepwise Cp* migration process under formation of the intermediate [Cp*(CO)2W[triple chemical bond]P-->W(CO)5]. 相似文献
959.
A new, simple, fast and sensitive ion chromatography (IC) method, for the simultaneous analysis of fluoride, chloride, nitrite, bromide, nitrate, phosphate and sulphate in edible seaweeds was developed and reported for the first time. The validation of the analytical method was studied in terms of linearity, sensitivity, precision and accuracy. All standard calibration curves showed very good correlation between anion peak area and concentration (r > 0.999). Limits of detection and quantitation ranged between 0.002-0.05 mg/L and 0.01-0.1 mg/L, respectively and indicated the high sensitivity of the method. Relative standard deviation values of repeatability and inter-day precision for standard anions with the same sample were less than 2%. Anion recoveries ranged from 97 to 113% for chloride and from 87 to 105% for sulphate, respectively and showed the fairly good accuracy of the method. The method was applied to the analysis of inorganic anions in brown and red edible seaweeds. Brown seaweeds were characterized by higher chloride content up to 33.7-36.9%, while red seaweeds were characterized by higher sulphate content (45-57%). Sulphate content in seaweeds is related to the presence of sulphated polysaccharides of biological importance. The method developed was well applicable to mineral anion analysis in edible seaweeds and shows suitability and reliability of use in other food samples of nutritional importance. 相似文献
960.
Polysulfonylamines. CLXVI. Crystal Structures of Metal Di(methanesulfonyl)amides. 15. The Isotypic Crystal Structures of Ammonium and Cesium Dimesylamide: Crystallographic Congruency of Hydrogen Bonds N—H···O/N and Metal‐Ligand Interactions Cs—O/N The ammonium salt NH4[N(SO2CH3)2] and its previously reported cesium analogue Cs[N(SO2CH3)2] are isostructural (monoclinic, space group P21/n, Z = 4, V at —140 °C: 0.761 and 0.832 nm3 respectively). The cesium ion adopts an irregular (O6N)‐heptacoordination by forming close contacts to one (O, N)‐chelating, one (O, O)‐chelating and three κ1O‐bonding anions, whereas in the ammonium‐based structure each of the seven Cs—O/N interactions is perfectly mimicked by an N—H···O/N hydrogen‐bond component. To this effect, three N—H donors are engaged in asymmetric three‐centre bonds, the fourth in a moderately strong and approximately linear two‐centre bond. The crystal packings consist of anion monolayers that intercalate planar zigzag rows of cations propagating around symmetry centres (Cs···Cs alternatingly 422.5 and 487.5 pm, Cs···Cs···Cs 135.7°; N···N alternatingly 397.4 and 474.1 pm, N···N···N 136.1°). Each cation row is surrounded by and bonded to four translation‐generated anion stacks, and each anion stack connects two cation rows. The net effect is that the packings display congruent three‐dimensional networks of metal‐ligand bonds or hydrogen bonds, respectively. Moreover, close C—H···O/N interanion contacts consistent with weak hydrogen bonding are observed in both structures. 相似文献