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81.
Rate coefficients, k, for the gas‐phase reaction of O(3P) atoms with Cl2O (dichlorine monoxide) over a range of temperatures (230–357 K) at pressures between 12 and 32 Torr (N2) are reported. Rate coefficients were measured under pseudo‐first‐order conditions in O(3P) using pulsed laser photolysis to produce O(3P) atoms and atomic resonance fluorescence to detect its temporal profile. The rate coefficient temperature dependence is given by the Arrhenius expression k(T) = (1.51 ± 0.20) × 10?11 exp[?(477 ± 30)/T] cm3 molecule?1 s?1, and k(296 K) was measured to be (2.93 ± 0.30) × 10?12 cm3 molecule?1 s?1. The quoted uncertainty limits are at the 2σ (95% confidence) level and include estimated systematic errors. The rate coefficients determined in the present study, under conditions that minimized secondary losses of O(3P), are compared with previous results from other laboratories and the discrepancies are discussed. © 2011 Wiley Peiodicals, Inc. 1 This article is a U.S. Government work and, as such, is in the public domain of the United States of America. Int J Chem Kinet 43: 312–321, 2011 相似文献
82.
Bomholt J Moth-Poulsen K Harboe M Karlson AO Qvist KB Bjørnholm T Stamou DG 《Langmuir : the ACS journal of surfaces and colloids》2011,27(3):866-869
The aggregation of casein micelles (CMs) induced by milk-clotting enzymes is a process of fundamental importance in the dairy industry for cheese production; however, it is not well characterized on the nanoscale. Here we enabled the monitoring of the kinetics of aggregation between single CMs (30-600 nm in diameter) by immobilizing them on a glass substrate at low densities and subsequently imaging them with fluorescence microscopy. We validated the new method by a quantitative comparison to ensemble measurements of aggregation. Single-particle statistics allowed us to observe for the first time several heterogeneities in CM aggregation. We observed two types of CM growth: a slow increase in the size of CMs and a stepwise increase attributed to interactions between aggregates preformed in solution. Both types of growth exhibit a lag phase that was very heterogeneous between different CMs, suggesting significant differences in their composition or structure. Detailed size histograms of CMs during aggregation also revealed the presence of two distinct subpopulations with different growth amplitudes and kinetics. The dependence of these distinct nanoscale processes/parameters on aggregation conditions is not accessible to bulk measurements that report only ensemble-average values and may prove important to an in-depth understanding of CM aggregation. 相似文献
83.
Ramona Pristavita Jean-Luc Meunier Dimitrios Berk 《Plasma Chemistry and Plasma Processing》2011,31(2):393-403
Carbon material was produced using an inductively coupled thermal plasma torch system of 35 kW and a conical shape reactor.
The carbon nanopowders were obtained by plasma decomposition of methane at various flow rates and show a uniform microstructure
throughout the reactor. The product has a crystalline graphitic structure, with a stacking of between 6 and 16 planes and
a nano-flake morphology with particles dimensions of approximately 100 nm long, 50 nm wide and 5 nm thick. Nitrogen was also
introduced in some synthesis experiments along with the methane precursor using flow rates of 0.1 and 0.2 slpm. The resulting
product has the same structural properties and the nitrogen is incorporated into the graphitic structure through pyridinic
type bonds. 相似文献
84.
Cox N Rapatskiy L Su JH Pantazis DA Sugiura M Kulik L Dorlet P Rutherford AW Neese F Boussac A Lubitz W Messinger J 《Journal of the American Chemical Society》2011,133(10):3635-3648
The electronic structures of the native Mn(4)O(x)Ca cluster and the biosynthetically substituted Mn(4)O(x)Sr cluster of the oxygen evolving complex (OEC) of photosystem II (PSII) core complexes isolated from Thermosynechococcus elongatus, poised in the S(2) state, were studied by X- and Q-band CW-EPR and by pulsed Q-band (55)Mn-ENDOR spectroscopy. Both wild type and tyrosine D less mutants grown photoautotrophically in either CaCl(2) or SrCl(2) containing media were measured. The obtained CW-EPR spectra of the S(2) state displayed the characteristic, clearly noticeable differences in the hyperfine pattern of the multiline EPR signal [Boussac et al. J. Biol. Chem.2004, 279, 22809-22819]. In sharp contrast, the manganese ((55)Mn) ENDOR spectra of the Ca and Sr forms of the OEC were remarkably similar. Multifrequency simulations of the X- and Q-band CW-EPR and (55)Mn-pulsed ENDOR spectra using the Spin Hamiltonian formalism were performed to investigate this surprising result. It is shown that (i) all four manganese ions contribute to the (55)Mn-ENDOR spectra; (ii) only small changes are seen in the fitted isotropic hyperfine values for the Ca(2+) and Sr(2+) containing OEC, suggesting that there is no change in the overall spin distribution (electronic coupling scheme) upon Ca(2+)/Sr(2+) substitution; (iii) the changes in the CW-EPR hyperfine pattern can be explained by a small decrease in the anisotropy of at least two hyperfine tensors. It is proposed that modifications at the Ca(2+) site may modulate the fine structure tensor of the Mn(III) ion. DFT calculations support the above conclusions. Our data analysis also provides strong support for the notion that in the S(2) state the coordination of the Mn(III) ion is square-pyramidal (5-coordinate) or octahedral (6-coordinate) with tetragonal elongation. In addition, it is shown that only one of the currently published OEC models, the Siegbahn structure [Siegbahn, P. E. M. Acc. Chem. Res.2009, 42, 1871-1880, Pantazis, D. A. et al. Phys. Chem. Chem. Phys.2009, 11, 6788-6798], is consistent with all data presented here. These results provide important information for the structure of the OEC and the water-splitting mechanism. In particular, the 5-coordinate Mn(III) is a potential site for substrate 'water' (H(2)O, OH(-)) binding. Its location within the cuboidal structural unit, as opposed to the external 'dangler' position, may have important consequences for the mechanism of O-O bond formation. 相似文献
85.
Kovatsi L Rentifis K Giannakis D Njau S Samanidou V 《Journal of separation science》2011,34(14):1716-1721
The availability of a sensitive and rapid analytical method for the determination of opiates, and other substances of forensic interest, in a variety of biological specimens is of utmost importance to forensic laboratories. Solid-phase extraction is very popular in the pre-treatment of forensic samples. Nevertheless, a new approach, disposable pipette extraction (DPX), is gaining increasing interest in sample preparation. DPX has already been applied to the analysis of drugs of abuse in common biological matrices, such as urine and blood, but has not yet been evaluated on alternative biological samples, such as vitreous humor. The objective of this study was to evaluate the applicability of DPX on the analysis of opiates in vitreous humor. The currently developed method is fast, reliable, and easy to perform. The sensitivity, precision, and accuracy are satisfactory. Recoveries obtained are within the range of 72-91%, whereas the sample volume of vitreous humor required is only 100 μL. 相似文献
86.
Vasilios N. Katsikis Dimitrios Pappas Athanassios Petralias 《Applied mathematics and computation》2011,217(23):9828-9834
In this article we provide a fast computational method in order to calculate the Moore-Penrose inverse of singular square matrices and of rectangular matrices. The proposed method proves to be much faster and has significantly better accuracy than the already proposed methods, while works for full and sparse matrices. 相似文献
87.
88.
Tsikas D 《The Analyst》2011,136(5):979-987
Nitric oxide (˙NO) and superoxide (O(2)(-)˙) are ubiquitous in nature. Their reaction product peroxynitrite (ONOO(-)) and notably its conjugated peroxynitrous acid (ONOOH) are highly unstable in aqueous phase. ONOO(-)/ONOOH (referred to as peroxynitrite) isomerize and decompose to NO(3)(-), NO(2)(-) and O(2). Here, we report for the first time GC-MS and HPLC methods for the analysis of peroxynitrite in aqueous solution. For GC-MS analysis peroxynitrite in alkaline solution was derivatized to a pentafluorobenzyl derivative using pentafluorobenzyl bromide. O(15)NOO(-) was synthesized from H(2)O(2) and (15)NO(2)(-) and used as internal standard. HPLC analysis was performed on stationary phases consisting of Nucleosil? 100-5C(18)AB or Nucleodur? C(18) Gravity. The mobile phase consisted of a 10 mM aqueous solution of tetrabutylammonium hydrogen sulfate and had a pH value of 11.5. UV absorbance detection at 300 nm was used. HPLC allows simultaneous analysis of ONOO(-), NO(2)(-) and NO(3)(-). The GC-MS and HPLC methods were used to study stability, synthesis, formation from S-[(15)N]nitrosoglutathione (GS(15)NO) and KO(2), and isomerization/decomposition of peroxynitrite to NO(2)(-) and NO(3)(-) in aqueous buffer. 相似文献
89.
zkan Grmez Bar Sal Uur alayan Dimitrios Kalderis Belgin Gzmen 《Molecules (Basel, Switzerland)》2022,27(22)
A weak aspect of the electro-Fenton (EF) oxidation of contaminants is the dependence of the Fenton reaction on acidic pH values. Therefore, the rationale of this work was to develop a novel catalyst capable of promoting the EF oxidation process at near-neutral and basic pH values. In this framework, rhombohedral FeCO3 was synthesized hydrothermally and used as a catalyst in the EF oxidation of p-benzoquinone (BQ). The catalyst was characterized using various surface and spectroscopic methods. Moreover, the effects of applied current (100–500 mA), time (1–9 h), catalyst dosage (0.25–1.00 g L−1), and initial concentration of BQ (0.50–1.00 mM) on the total organic carbon removal efficiency were determined. The results indicated that a 400 mA current was sufficient for a 95% total organic carbon removal and that the increase in catalyst dosage had a positive effect on the mineralization of BQ. It was determined that at pH 3, FeCO3 behaved like a homogeneous catalyst by releasing Fe3+ ions; whereas, at the pH range of 5–7, it shifted to a homogeneous/heterogeneous catalyst. At pH 9, it worked solely as a heterogeneous catalyst due to the decrease of Fe ions passing into the solution. Finally, the spent catalyst did not undergo structural deformations after the EF treatment at higher pH values and could be regenerated and used several times 相似文献
90.
Dimitrios G. Birbas 《Rendiconti del Circolo Matematico di Palermo》1923,47(3):431-446
We investigate subadditivity of Pták function as a sufficient and necessary condition for symmetry in the class of involutive spectrally bounded algebras. Among others it is proved an analogue of Raikov's criterion for complete lmc*-algebras in which the hermitian elements have finite spectral radius. 相似文献