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221.
Fernando De Andrés Mohammed Zougagh Gregorio Castañeda Angel Ríos 《Analytical and bioanalytical chemistry》2010,397(1):223-231
A rapid and simple method for separation and detection of six heterocyclic aromatic amines (2-amino-1-methyl-6-phenylimidazo
[4,5-b]-pyridine, 2-amino-1-methyl-imidazo [4,5-f]-quinoline, 2-amino-3,8-dimethyl-imidazo [4,5-f]-quinoxaline, 2-amino-3,7,8-trimethyl-imidazo [4,5-f]-quinoxaline, 2-amino-3,4,8-trimethyl-imidazo [4,5-f]-quinoxaline, and 2-amino-3,4-dimethyl-imidazo [4,5-f]-quinoline) in human urine samples is proposed to reflect daily intake and recent HAAs exposure. This method comprises previous
clean-up and preconcentration of the analytes on Strata-X reversed phase extraction cartridges followed by capillary liquid
chromatography (CLC) and evaporative light-scattering detection (ELSD). A mobile phase of acetonitrile and ammonium acetate
35 mM at pH 5.15 through a gradient of composition and a flow rate of 15 μL min−1 resulted in good separations of the analytes. Temperature and gas pressure were optimized for detection. The CLC-ELSD allows
the separation and quantification of HAAs with good resolution, precision, and sensitivity. The usefulness of the proposed
method was demonstrated by the analysis of synthetic and natural human urine samples spiked with different concentration levels
of heterocyclic amines. 相似文献
222.
Abdel-Ghani Boudjahem Tahar Mokrane Affef Redjel Mohammed M. Bettahar 《Comptes Rendus Chimie》2010,13(12):1433-1439
Palladium catalysts (1–10 wt.% Pd) supported on silica were prepared by hydrazine reduction of palladium chloride at room temperature. They were characterized by XRD, TEM, EDX, H2-adsorption, and H2-TPD and tested in the gas phase hydrogenation of benzene in the temperature range 75–250 °C. A conventional catalyst (1 wt.% Pd) obtained by calcination then hydrogen reduction of the same metal precursor was studied for comparison. Metal particles with a size range 6.8–28.4 nm were obtained. Dispersion, hydrogen storage and activity in benzene hydrogenation increased with decreasing particle size. In comparison, the classical catalyst was found much more dispersed (mean particle size of 1.6 nm) and more active (specific rate 1.6–3.7 times higher) than the homolog hydrazine catalyst. However, unexpectedly, turnover frequency (TOF) calculations indicated a greater reactivity of the metal surface atoms for the hydrazine catalyst. It also stored more hydrogen. These contrasting results are discussed in relation with the metal particle morphology. 相似文献
223.
Marco L. Hennrich Shabaz Mohammed A. F. Maarten Altelaar Albert J. R. Heck 《Journal of the American Society for Mass Spectrometry》2010,21(12):1957-1965
Here, we explore a de novo sequencing strategy in which we combine Lys-N protein digestion with differential isotopic dimethyl
labeling to facilitate the (de novo) identification of multiply charged peptides in ESI-MS, both under CID and ETD conditions.
For a large fraction of the Lys-N generated peptides, all primary amines are present at the N-terminal lysine, enabling specific
labeling of the N-terminus. Differential derivatization of only the peptide N-terminus in combination with the simultaneous
fragmentation of the corresponding isotopologues allows the straightforward distinction of N-terminal fragments from C-terminal
and internal fragments. Furthermore, also singly and multiply charged N-terminal fragments can easily be distinguished due
to the mass differences of the isotope labeled fragment pairs. As a proof of concept, we applied this approach to proteins
isolated from an avocado fruit, and were able to partially de novo sequence and correctly align, with green plant homologues,
a previously uncharacterized avocado ascorbate peroxidase. 相似文献
224.
Low-temperature pyrolysis of methionine-enkephalin-Arg-Gly-Leu has been carried out and the non-volatile residues have been analyzed. The fragments were separated and characterized by LC-UV/Vis-MS/MS. Two major types of pyrolysis products were identified by matching the experimental results with a theoretical list that contains the expected fragments. These products were mainly composed of cyclic oligopeptides and linear fragments produced from the peptide backbone. These fragments have preserved the sequence of amino acids in the peptide. In some cases, a complete or partial loss of an amino-acid side group was observed. Tandem mass spectrometry and cyanogen bromide cleavage experiments were used to confirm the nature of the cyclic and linear pyrolysates, in addition to chromatographic and mass spectrometric data of actual standard synthetic cyclic peptides. 相似文献
225.
Phytochemical investigation of the ethyl acetate extract of the leaves of Juniperus procera growing in south Saudi Arabia Enemas region led to the isolation of a new flavonoid using different chromatographic methods (i.e. paper, thin layer and column chromatography). The isolated flavonoid was identified and established by m.p., 1H-NMR, 13C-NMR, UV and MS spectral analysis. The isolated compound was identified as 3′,4′,3,7-tetrahydroxyflavone. 相似文献
226.
227.
Anina Wöhl Dr. Wolfgang Müller Dr. Stephan Peitz Normen Peulecke Dr. Bhaskar R. Aluri Dr. Bernd H. Müller Dr. Detlef Heller Dr. Uwe Rosenthal Prof. Dr. Mohammed H. Al‐Hazmi Dr. Fuad M. Mosa 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(26):7833-7842
In this paper we report the results of an extensive experimental kinetic study carried out on the novel ethylene trimerization catalyst system, comprising the chromium source [CrCl3(thf)3] (thf=tetrahydrofuran), a Ph2P‐N(iPr)‐P(Ph)‐N(iPr)H (PNPNH) ligand (Ph=phenyl, iPr=isopropyl), and triethylaluminum (AlEt3) as activator. It could be shown that the initial activity shows a first‐order dependency on the ethylene concentration. Also, a first‐order dependency was found for the catalyst concentration. The initial activity follows a typical Arrhenius behavior with an experimentally determined activation energy of 52.6 kJ mol?1. At elevated temperatures (ca. 80 °C), a significant deactivation was observed, which can be tentatively traced back to a ligand rearrangement in the presence of AlEt3. After a fast initial phase, a pronounced ‘kink’ in the ethylene‐uptake curve is observed, followed by a slow, almost linear, further increase of the total ethylene consumption. The catalyst composition, in particular the ligand/chromium and the cocatalyst/chromium molar ratio, has a strong impact on the catalytic performance of the trimerization of ethylene. 相似文献
228.
Wang J Aubry A Bolgar MS Gu H Olah TV Arnold M Jemal M 《Rapid communications in mass spectrometry : RCM》2010,24(22):3221-3229
Liquid chromatography/tandem mass spectrometry (LC/MS/MS) based on selected reaction monitoring (SRM) is the standard methodology in quantitative analysis of administered xenobiotics in biological samples. Utilizing two SRM channels during positive electrospray ionization (ESI) LC/MS/MS method development for a drug compound containing two basic functional groups, we found that the response ratio (SRM1/SRM2) obtained using an acidic mobile phase was dramatically different from that obtained using a basic mobile phase. This observation is different from the well-established phenomenon of mobile phase affecting the [M+H](+) response, which is directly related to the amount of the [M+H](+) ions produced during the ionization. Results from follow-up work reported herein revealed that the MS/MS fragmentation patterns of four drug or drug-like compounds are affected not only by the pH, but also by the aqueous-organic ratio of the mobile phase and the buffer concentration at a given apparent pH. The observed phenomenon can be explained by invoking that a mixture of [M+H](+) ions of the same m/z value for the analyte is produced that is composed of two or more species which differ only in the site of the proton attachment, which in turn affects their MS/MS fragmentation pattern. The ratio of the different protonated species changes depending on the pH, aqueous-organic ratio, or ionic strength of the mobile phase used. The awareness of the mobile phase dependency of the MS/MS fragmentation pattern of precursor ions of identical m/z value will influence LC/MS/MS-based bioanalytical method development strategies. Specifically, we are recommending that multiple SRM transitions be monitored during mobile phase screening, with the MS/MS parameters used for each SRM optimized for the composition of the mobile phase (pH, organic percentage, and ionic strength) in which the analyte elutes. 相似文献
229.
Mohammed Taghi Zafarani-Moattar Saeed Nasiri 《The Journal of chemical thermodynamics》2010,42(9):1071-1078
(Liquid + liquid) equilibrium (LLE) for the {poly ethylene glycol di-methyl ether 2000 (PEGDME2000) + Na2HPO4 + H2O} system have been determined experimentally at T = (298.15, 308.15, 313.15, and 318.15) K. The effects of temperature on the binodals and tie-lines for the investigated aqueous two-phase system (ATPS) have been studied. An empirical non-linear expression developed by Merchuk was used for reproducing the experimental binodal data. In this work, the three fitting parameters of the Merchuk equation were obtained with the temperature dependence expressed in the linear form with (T ? T0) K as a variable. Furthermore, the modified local composition segment-based NRTL and Wilson models and also osmotic virial equation were used to describe the LLE data of the studied system. Also, the effects of the type of salt on LLE are discussed. In addition, the effects of end groups of the polymers PEGDME2000 and poly ethylene glycol 2000 on phase forming ability were studied. The complete phase diagram for the poly ethylene {glycol di-methyl ether 2000 (PEGDME2000) + Na2HPO4 + H2O} system has also been determined at T = 298.15 K. 相似文献
230.
Mohammed Taghi Zafarani-Moattar Shokat Sarmad 《The Journal of chemical thermodynamics》2010,42(10):1213-1221
Density, sound velocity, and viscosity of 1-ethyl-3-methylimidazolium bromide, [Emim][Br], in aqueous solutions of tri-potassium phosphate with salt weight fractions (ws = 0.00, 0.10, 0.15, and 0.20) have been measured as a function of concentration of [Emim][Br] at atmospheric pressure and T = (298.15, 303.15, 308.15, 313.15, and 318.15) K. The apparent molar volume, isentropic compressibility, apparent isentropic compressibility, and relative viscosity values have been evaluated from the experimental data. The partial molar volume and isentropic compressibility at infinite dilution, and viscosity B-coefficient obtained from these data have been used to calculate the corresponding transfer parameters for the studied IL from water to the aqueous tri-potassium phosphate solutions. Also, an empirical equation was satisfactorily used to correlate the experimental viscosity data. 相似文献