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排序方式: 共有374条查询结果,搜索用时 31 毫秒
361.
Bojan Orel 《BIT Numerical Mathematics》2001,41(5):1089-1100
This paper describes the use of extrapolation with Magnus methods for the solution of a system of linear differential equations. The idea is a generalization of extrapolation with symmetric methods for the numerical solution of ODEs, where each extrapolation step increases the order of the method by 2.This revised version was published online in October 2005 with corrections to the Cover Date. 相似文献
362.
The equivalence of several definitions of convolution of two Roumieu ultradistributions is proved. For that purpose, the $\varepsilon $ tensor product of $\dot{\tilde{\mathcal{B }}}^{\{M_p\}}$ and a locally convex space $E$ is considered. 相似文献
363.
364.
Methods for the asymmetric transfer hydrogenation (ATH) of ketones and imines are still being intensively studied and developed. Of foremost interest is the use of Noyori's [RuCl(η?-arene)(N-TsDPEN)] complexes in the presence of a hydrogen donor (i-PrOH, formic acid). These complexes have found numerous practical applications and have been extensively modified. The resulting derivatives have been heterogenized, used in ATH in water or ionic liquids and even some attempts have been made to approach the properties of biocatalysts. Therefore, an appropriate modification of the catalyst that suits the specific requirements for the reaction conditions is very often readily available. The mechanism of the reaction has also been explored to a great extent. Model substrates, acetophenone (a ketone) and 6,7-dimethoxy-1-methyl-3,4-dihydroisoquinoline (an imine), are both reduced by this Ru catalytic system with almost perfect selectivity. However, in each case the major product is a different enantiomer (S- for an alcohol, R- for an amine when the S,S-catalyst is used), which demanded an in-depth mechanistic investigation. Full-scale molecular modelling of this system enabled us to visualize the plausible 3D structures of the transition states, allowing the proposition of a viable explanation of previous experimental findings. 相似文献
365.
Markovic BD Dobricic VD Vladimirov SM Cudina OA Savic VM Karljikovic-Rajic KD 《Molecules (Basel, Switzerland)》2011,16(3):2658-2671
In this study the solvolysis of newly synthesized fluocinolone acetonide C-21 esters was analysed in comparison with fluocinonide during a 24-hour period of time. The solvolysis was performed in an ethanol-water (90:10 v/v) mixture using the excess of NaHCO?. The solvolytic mixtures of each investigated ester have been assayed by a RP-HPLC method using isocratic elution with methanol-water (75:25 v/v); flow rate 1 mL/min; detection at 238 nm; temperature 25 °C. Solvolytic rate constants were calculated from the obtained data. Geometry optimizations and charges calculations were carried out by Gaussian W03 software. A good correlation (R = 0.9924) was obtained between solvolytic rate constants and the polarity of the C-O2 bond of those esters. The established relation between solvolytic rate constant (K) and lipophilicity (cLogP) with experimental anti-inflammatory activity could be indicative for topical corticosteroid prodrug activation. 相似文献
366.
Pejov L Ristova M Soptrajanov B 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2011,79(1):27-34
The 1:1 p-toluenesulfonic acid-water complex, p-toluenesulfonic acid itself and the p-toluenesulfonate anion were studied at HF and B3LYP/6-31+G(d,p) levels of theory. Full geometry optimizations of the aforementioned species reveal non-existence of ionic minima on the explored 1:1 p-toluenesulfonic acid-water complex potential-energy hypersurfaces (PEHSs), implying that two or three p-toluenesulfonate ions (+crystal field) are required to stabilize the ionic H(3)O(+)?C(6)H(4)(CH(3))SO(3)(-) species found in the crystal structure of p-toluenesulfonic acid monohydrate (in fact, oxonium p-toluenesulfonate). Harmonic vibrational analyses of the p-toluenesulfonic acid-water complex as well as of the p-toluenesulfonate anion were used to confirm some of our previous reassignments of bands in the vibrational spectra of p-toluenesulfonic acid monohydrate and several metal p-toluenesulfonates. According to the quantum chemical results, the symmetric SO(3) bending mode should appear at higher frequencies than the antisymmetric one. A more consistent interpretation of the region of appearance of the SO(3) stretching modes is proposed which is in excellent agreement with the experimental spectroscopic data. The frequency of the multireference benzenoid ν(14) (B(2u)) mode (the "Kekulé" type vibration) is excellently predicted at the B3LYP level of theory, while the HF methodology performs significantly poorer in this respect. The interaction energies as well as the vibrational frequency shifts of the most relevant modes are also presented for the 1:1 p-toluenesulfonic acid-water complex. The NBO analysis is employed to analyze the charge transfer interaction within the complex. 相似文献
367.
Polonca Trebše Boris Recelj Tanja Lukanc Simona Golič Grdadolnik Andrej Petrič Bojan Verček 《合成通讯》2013,43(15):2637-2644
6, 7-Dihydrocyclopenta[b]pyran-2, 5-dione 1 was converted with hydrazines to fused pyridine-2(1H)-ones of type a. In contrast, 2H-1-benzopyran-2, 5-diones 2–4 gave under the same reaction conditions 5-hydrazonobenzopyrans of type b. Calculated heats of formation matched experimental findings. 相似文献
368.
Syslová K Rambousek L Kuzma M Najmanová V Bubeníková-Valešová V Slamberová R Kačer P 《Journal of chromatography. A》2011,1218(21):3382-3391
A sensitive assay method was developed for a parallel, rapid and precise determination of dopamine and its metabolites, homovanillic acid, 3-methoxytyramine and 3,4-dihydroxyphenylacetic acid, from brain microdialysates. The method consisted of a pre-treatment step, freeze-drying (lyophilization), to concentrate dopamine and its metabolites from the microdialysates, and a detection step using liquid chromatography combined with electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). In particular, the reaction monitoring mode was selected for its extremely high degree of selectivity and the stable-isotope-dilution assay for its high precision of quantification. The developed method was characterized by the following parameters: the precision of the developed method was determined as ≥88.6% for dopamine, ≥89.9% for homovanillic acid, ≥86.1% for 3-methoxytyramine and ≥88.1% for 3,4-dihydroxyphenylacetic acid; the mean accuracy was determined as ≥88.2% for dopamine, ≥88.3% for homovanillic acid, ≥85.9% for 3-methoxytyramine and ≥88.6% for 3,4-dihydroxyphenylacetic acid. The developed method was compared to (1) other combinations of pre-treatment methods (solid phase extraction and nitrogen stripping) with LC-MS and (2) another detection method, liquid chromatography, with electrochemical detection. The novel developed method using combination of lyophilization with LC-ESI-MS/MS was tested on real samples obtained from the nucleus accumbens of rat pups after an acute methamphetamine administration. It was proven that the developed assay could be applied to both a simultaneous analysis of all four substrates (dopamine, homovanillic acid, 3-methoxytyramine and 3,4-dihydroxyphenylacetic acid) in microdialysis samples acquired from the rat brain and the monitoring of their slight concentration changes on a picogram level over time following methamphetamine stimulus. 相似文献
369.
Monica Ari Kimberly J. Miller Bojan A. Marinkovic Paula M. Jardim Roberto de Avillez Fernando Rizzo Mary Anne White 《Journal of Sol-Gel Science and Technology》2011,58(1):121-125
Aluminum molybdate was successfully synthesized using a simplified PVA assisted sol–gel method resulting in highly crystalline,
monophasic (monoclinic P21/a) samples. These materials could readily be obtained at temperatures of 600 and 700 °C after calcining for as little as
15–20 min. Scanning electron microscopy and X-ray powder diffraction indicated that even the sample calcined at 600 °C for
20 min was free of impurities and composed of submicron sized particles (~300 nm). Transmission electron microscopy was used
to confirm the monophasic character and submicron dimensions of the as-prepared powders. In addition to producing high quality
samples, it was also observed that the metal to PVA ratio used during this simplified synthesis, could be used as a control
parameter for tailoring the particle sizes of the final product. 相似文献
370.
Gurumurthy Ramachandran Susan M. Wolf Jordan Paradise Jennifer Kuzma Ralph Hall Efrosini Kokkoli Leili Fatehi 《Journal of nanoparticle research》2011,13(4):1345-1371
Federal oversight of nanobiotechnology in the U.S. has been fragmented and incremental. The prevailing approach has been to
use existing laws and other administrative mechanisms for oversight. However, this “stay-the-course” approach will be inadequate
for such a complex and convergent technology and may indeed undermine its promise. The technology demands a new, more dynamic
approach to oversight. The authors are proposing a new oversight framework with three essential features: (a) the oversight
trajectory needs to be able to move dynamically between “soft” and “hard” approaches as information and nano-products evolve;
(b) it needs to integrate inputs from all stakeholders, with strong public engagement in decision-making to assure adequate
analysis and transparency; and (c) it should include an overarching coordinating entity to assure strong inter-agency coordination
and communication that can meet the challenge posed by the convergent nature of nanobiotechnology. The proposed framework
arises from a detailed case analysis of several key oversight regimes relevant to nanobiotechnology and is informed by inputs
from experts in academia, industry, NGOs, and government. 相似文献