全文获取类型
收费全文 | 586篇 |
免费 | 10篇 |
国内免费 | 2篇 |
专业分类
化学 | 382篇 |
力学 | 20篇 |
数学 | 100篇 |
物理学 | 96篇 |
出版年
2022年 | 8篇 |
2021年 | 11篇 |
2020年 | 6篇 |
2019年 | 7篇 |
2018年 | 13篇 |
2017年 | 3篇 |
2016年 | 13篇 |
2015年 | 12篇 |
2014年 | 17篇 |
2013年 | 37篇 |
2012年 | 32篇 |
2011年 | 39篇 |
2010年 | 26篇 |
2009年 | 18篇 |
2008年 | 31篇 |
2007年 | 38篇 |
2006年 | 33篇 |
2005年 | 27篇 |
2004年 | 28篇 |
2003年 | 34篇 |
2002年 | 20篇 |
2001年 | 7篇 |
2000年 | 13篇 |
1999年 | 9篇 |
1998年 | 7篇 |
1997年 | 9篇 |
1996年 | 6篇 |
1995年 | 8篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1985年 | 10篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1974年 | 8篇 |
1973年 | 4篇 |
1967年 | 1篇 |
1947年 | 1篇 |
1940年 | 1篇 |
1938年 | 1篇 |
排序方式: 共有598条查询结果,搜索用时 15 毫秒
591.
Pelin Sözen Jean-Claude Daran Eric Manoury Funda Demirhan Rinaldo Poli 《Journal of organometallic chemistry》2011,696(11-12):2275-2279
The reaction of Cp12W2O5 with HS(CH2)nCOOH (n = 1, 2) in MeOH or in CH2Cl2 solutions at room temperature proceeds in slightly different ways depending on the value of n. For n = 2, it selectively yields compound Cp1WO2(SCH2CH2CO2H), which has been isolated and characterized by elemental analysis, NMR and single crystal X-ray diffraction. The reaction is equilibrated, being shifted to the product by absorption of water by anhydrous Na2SO4 in CH2Cl2, and to the reactants by addition of water. Contrary to the Mo analogue, no products resulting from metal reduction are obtained. The corresponding reaction for n = 1 occurs similarly at low substrate/W ratios (<0.5), but proceeds further to several uncharacterized products for greater substrate amounts. The primary product could not be isolated, but its 1H NMR spectrum suggests a different, asymmetric structure. 相似文献
592.
Marini JC 《Rapid communications in mass spectrometry : RCM》2011,25(9):1291-1296
The enteral metabolisms of glutamine and citrulline are intertwined because, while glutamine is one of the main fuel sources for the enterocyte, citrulline is one of its products. It has been shown that the administration of 15N‐labeled glutamine results in the incorporation of the 15N label into citrulline, but it is not clear which of the three nitrogen groups of citrulline is actually labeled. To determine the 15N‐enrichment of the positional isomers of glutamine and citrulline, a rapid liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed. The amino acids were analyzed as their dansyl derivatives. The product ion resulting from the loss of NH3 from the omega carbon allows for the determination of the enrichment of the ureido (citrulline) or amido groups (glutamine). The protonated pyrrolidine (citrulline) or 5‐oxopyrrolidine (glutamine) product ion contains the 2‐N (amino group) and is used to determine its enrichment. The method described showed no ion suppression and a wide dynamic range ranging from 1.3 picomoles to 2 nanomoles for citrulline. Background samples and standards resulted in enrichments not different from those theoretically expected. The enrichment curves for the different glutamine and citrulline isotopomers were linear (R2 > 0.998) over the range of enrichments studied. The method developed provides an additional insight into the metabolism of glutamine and citrulline tracing the precursor‐product relationship between these two amino acids. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
593.
Rozet E Rudaz S Marini RD Ziémons E Boulanger B Hubert P 《Analytica chimica acta》2011,702(2):160-171
Evaluation of analytical results reliability is of core importance as crucial decisions are taken with them. From the various methodologies to evaluate the fitness of purpose of analytical methods, overall measurement uncertainty estimation is more and more applied. Overall measurement uncertainty allows to combine simultaneously the remaining systematic influences to the random sources of uncertainty and allows assessing the reliability of results generated by analytical methods. However there are various interpretations on how to estimate overall measurement uncertainty, and thus various models for estimating it. Each model together with its assumptions has great impacts on the risks to abusively declare that analytical methods are suitable for their intended purpose. This review paper aims at (i) summarizing the various models used to estimate overall measurement uncertainty, (ii) provide their pros and cons, (iii) review the main areas of application and (iv) as a conclusion provide some recommendations when evaluating overall measurement uncertainty. 相似文献
594.
L<Superscript>1</Superscript> Stability of Spatially Periodic Solutions in Relativistic Gas Dynamics
Daniela Calvo Rinaldo M. Colombo Hermano Frid 《Communications in Mathematical Physics》2008,284(2):509-535
This paper proves the well posedness of spatially periodic solutions of the relativistic isentropic gas dynamics equations.
The pressure is given by a γ-law with initial data of large amplitude, provided γ − 1 is sufficiently small. As a byproduct of our techniques, we obtain the same results for the classical case. At the limit
c → + ∞, the solutions of the relativistic system converge to the solutions of the classical one, the convergence rate being
1/c
2. We also construct the semigroup of solutions of the Cauchy problem for initial data with bounded total variation, which
can be large, as long as γ − 1 is small. 相似文献
595.
We consider optical propagation through a centrosymmetric photorefractive crystal with the externally applied bias voltage modulated along the optical propagation direction. We analytically prove that, if the modulation scale is smaller than the optical diffraction length, the resulting effective nonlinearity has an even parity in the transverse plane for an even-symmetric intensity profile and supports bending-free solitons down to few-micrometer beam widths. Numerical integration of the full photorefractive model for light-matter interaction allows us to confirm the feasibility of these miniaturized solitons and, for longer modulation periods, to investigate the excitation of self-trapped wiggling optical beams. 相似文献
596.
597.
Claudia Scappaticci Stella Spera Alessandra Biancolillo Federico Marini 《Molecules (Basel, Switzerland)》2022,27(19)
In the present work, a fast, relatively cheap, and green analytical strategy to identify and quantify the fraudulent (or voluntary) addition of a drug (alprazolam, the API of Xanax®) to an alcoholic drink of large consumption, namely gin and tonic, was developed using coupling near-infrared spectroscopy (NIR) and chemometrics. The approach used was both qualitative and quantitative as models were built that would allow for highlighting the presence of alprazolam with high accuracy, and to quantify its concentration with, in many cases, an acceptable error. Classification models built using partial least squares discriminant analysis (PLS-DA) allowed for identifying whether a drink was spiked or not with the drug, with a prediction accuracy in the validation phase often higher than 90%. On the other hand, calibration models established through the use of partial least squares (PLS) regression allowed for quantifying the drug added with errors of the order of 2–5 mg/L. 相似文献
598.
Giora Peniakov Quirin Buchinger Mohamed Helal Simon Betzold Yorick Reum Michele B. Rota Giuseppe Ronco Mattia Beccaceci Tobias M. Krieger Saimon F. Covre da Silva Armando Rastelli Rinaldo Trotta Andreas Pfenning Sven Höfling Tobias Huber-Loyola 《Laser \u0026amp; Photonics Reviews》2024,18(4):2300835
Polarized , and unpolarized emission from a single emitter embedded in a single, cylindrically symmetric device design is presented. The polarization stems from a position offset of the single emitter with respect to the cavity center, which breaks the cylindrical symmetry, and a position-dependent coupling to the frequency degenerate eigenmodes of the resonator structure is shown. The experimental results are interpreted by using numerical simulations and by experimental mapping of the polarization-resolved far-field emission patterns. The findings can be generalized to any nanophotonic structure where two orthogonal eigenmodes are not fully spatially overlapping. 相似文献