全文获取类型
收费全文 | 276篇 |
免费 | 30篇 |
国内免费 | 31篇 |
专业分类
化学 | 175篇 |
晶体学 | 2篇 |
力学 | 17篇 |
综合类 | 1篇 |
数学 | 57篇 |
物理学 | 85篇 |
出版年
2023年 | 5篇 |
2022年 | 9篇 |
2021年 | 7篇 |
2020年 | 6篇 |
2019年 | 6篇 |
2018年 | 11篇 |
2017年 | 3篇 |
2016年 | 5篇 |
2015年 | 18篇 |
2014年 | 12篇 |
2013年 | 20篇 |
2012年 | 20篇 |
2011年 | 18篇 |
2010年 | 17篇 |
2009年 | 16篇 |
2008年 | 23篇 |
2007年 | 8篇 |
2006年 | 9篇 |
2005年 | 5篇 |
2004年 | 11篇 |
2003年 | 7篇 |
2002年 | 9篇 |
2001年 | 8篇 |
2000年 | 4篇 |
1999年 | 16篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1990年 | 5篇 |
1988年 | 2篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1969年 | 2篇 |
1968年 | 1篇 |
1929年 | 1篇 |
1909年 | 1篇 |
1887年 | 1篇 |
排序方式: 共有337条查询结果,搜索用时 15 毫秒
111.
A. Basile F. Gallucci A. Iulianelli G.F. Tereschenko M.M. Ermilova N.V. Orekhova 《Journal of membrane science》2008,310(1-2):44-50
In this experimental work the influence of co-existing gases on the hydrogen permeation through a Ti–Ni–Pd membrane was studied. It was found that nitrogen, carbon dioxide and helium do not influence the hydrogen permeation through the dense membrane. However, carbon monoxide influences the hydrogen flux at each temperature investigated (400–500 °C). The results show that for low CO concentration (i.e. at H2 upstream >80%), the hydrogen flux through the membrane decreases faster than linearly, while, at H2 upstream <80%, the slope is linear but smaller than the theoretical one. 相似文献
112.
G. Basile L. Delfini S. Lepri R. Livi S. Olla A. Politi 《The European physical journal. Special topics》2007,151(1):85-93
After reviewing the main features of anomalous
energy transport in 1D systems, we report simulations performed with
chains of noisy anharmonic oscillators. The stochastic terms are added
in such a way to conserve total energy and momentum, thus keeping the
basic hydrodynamic features of these models. The addition of this
“conservative noise" allows to obtain a more efficient estimate of the
power-law divergence of heat conductivity κ(L) ∼Lα
in the limit of small noise and large system size L.
By comparing the numerical results
with rigorous predictions obtained for the harmonic chain, we show
how finite-size and time
effects can be effectively controlled. For low noise amplitudes, the
α values are close to 1/3 for asymmetric potentials and to 0.4
for symmetric ones. These results support the previously conjectured
two-universality-classes scenario. 相似文献
113.
Brønsted Acid‐Mediated Annulation of α‐Oxo Ketene Dithioacetals with Pyrroles: Efficient Synthesis of Structurally Diverse Cyclopenta[b]pyrroles
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Xiaoge Yang Kaikai Wu Ping Wu Prof. Dr. Jiping Chen Prof. Chenglin Sun Prof. Dr. Zhengkun Yu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(26):9323-9327
Brønsted acid‐mediated annulation of internal olefins α‐oxo ketene dithioacetals to pyrroles was efficiently achieved to afford cyclopenta[b]pyrroles. A pair of Brønsted acids with acid strengths, that is, trifluoroacetic acid, and para‐toluenesulfonic acid hydrate, were applied to promote the annulation reactions. The resultant products were readily oxidized to sulfones by meta‐chloroperoxybenzoic acid. Subsequent treatment with 1,8‐diazabicyclo[5.4.0]undec‐7‐ene gave desulfurized terminal olefins or [2+2] cycloaddition products from the desulfurized olefin intermediates. The present protocol provides facile access to structurally diverse cyclopenta[b]pyrrole derivatives under mild conditions. 相似文献
114.
Characterization of the dehydration products due to thermal decomposition of peptides by liquid chromatography‐tandem mass spectrometry
下载免费PDF全文
![点击此处可从《Journal of mass spectrometry : JMS》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Chenglin Liu Elena Topchiy Teresa Lehmann Franco Basile 《Journal of mass spectrometry : JMS》2015,50(3):625-632
Thermal decomposition (TD) of proteins is being investigated as a rapid digestion step for bottom‐up proteomics. Mass spectrometry (MS) analyses of the TD products of simple peptides and intact proteins have revealed several nonvolatile products at masses lower than the precursor biomolecule (M). In addition to products stemming from site‐specific cleavages, many signals are also observed at a corresponding M‐18, most likely because of dehydration (M‐H2O) during the heating process. Understanding the structural nature of the water loss product is important in establishing the utility of their tandem mass spectra (collision‐induced dissociation) in determining the precursor ion amino acid sequence in a bottom‐up proteomic workflow. Dehydration of a peptide can take place from a variety of sources including side chain groups, C‐terminus, and/or intramolecular cyclization (C to N‐terminus cyclization). In this work, liquid chromatography‐tandem MS (LC‐MS/MS) and a series of standard peptides (angiotensin II, DRVYIHPF and its cyclic analog) are implemented to decipher the structure of the TD dehydration product. In addition, a derivatization strategy incorporating N‐terminus acetylation was developed that allowed the direct comparison of tandem mass spectra of standard cyclic peptides with those resulting from the TD process, thus eliminating any ambiguity from the direct comparison of their mass spectra (due to gas‐phase cyclization of b‐ions, which can result in sequence scrambling of the precursor ion). Results from these investigations indicated that peptide dehydrated TD products were mostly linear in nature, and water loss was favored from the C‐terminus carboxyl group or, when present, the aspartic acid side chain. Given the predictable nature of the formation of TD dehydration products, their MS/MS analysis can be of utility in providing complementary and confirmatory sequence information of the precursor peptide. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
115.
In this paper, a finance system with time delay is considered. By linearizing the system at the unique equilibrium and analyzing the associated characteristic equation, the asymptotic stability of the unique equilibrium is investigated and Hopf bifurcations are demonstrated. Furthermore, the direction of Hopf bifurcation and the stability of the bifurcating periodic solutions are determined by the normal form theory and the center manifold theorem for functional differential equations. Finally, some numerical simulations are carried out for illustrating the theoretical results. 相似文献
116.
AbstractWe have prepared novel nanohybrid Li2xMn1?xPS3/GO films consisting of graphene oxide (GO) and exfoliated MnPS3 nanosheets via an easy mixing protocol at room temperature. These films were investigated by SEM and AFM, as well as XRD, Raman and XPS spectroscopies, obtaining information about the nature of the interaction between MnPS3 and GO. In particular, the dark colour of the nanocomposite film and, more to the point, the analysis of (i) the C1s core level XPS spectra, (ii) the interlayer spacing obtained by XRD measurements and (iii) the increment in the intensity ratio ID/IG of the two bands typical of the carbon region of GO Raman spectra, suggest that a partial reduction of GO can be obtained right upon intercalation into Li2xMn1?xPS3. 相似文献
117.
Basile F. E. Curchod Thomas J. Penfold Ursula Rothlisberger Ivano Tavernelli 《Central European Journal of Physics》2013,11(9):1059-1065
We review our recent work on ab initio nonadiabatic molecular dynamics, based on linear-response timedependent density functional theory for the calculation of the nuclear forces, potential energy surfaces, and nonadiabatic couplings. Furthermore, we describe how nuclear quantum dynamics beyond the Born-Oppenheimer approximation can be performed using quantum trajectories. Finally, the coupling and control of an external electromagnetic field with mixed quantum/classical trajectory surface hopping is discussed. 相似文献
118.
Peter de B. Harrington Kent J. Voorhees Franco Basile Alan D. Hendricker 《Journal of the American Society for Mass Spectrometry》2002,13(1):10-21
Temperature constrained cascade correlation networks (TCCCNs) are computational neural networks that configure their own architecture, train rapidly, and give reproducible prediction results. TCCCN classification models were built using the Latin-partition method for five classes of pathogenic bacteria. Neural networks are problematic in that the relationships among the inputs (i.e., mass spectra) and the outputs (i.e., the bacterial identities) are not apparent. In this study, neural network models were constructed that successfully classified the targeted bacteria and the classification model was validated using sensitivity and target transformation factor analysis (TTFA). Without validation of the classification model, it is impossible to ascertain whether the bacteria are classified by peaks in the mass spectrum that have no causal relationships with the bacteria, but instead randomly correlate with the bacterial classes. Multiple single output network models did not offer any benefits when compared to single network models that had multiple outputs. A multiple output TCCCN model achieved classification accuracies of 96 +/- 2% and exhibited improved performance over multiple single output TCCCN models. Chemical ionization mass spectra were obtained from in situ thermal hydrolysis methylation of freeze-dried bacteria. Mass spectral peaks that pertain to the neural network classification model of the pathogenic bacterial classes were obtained by sensitivity analysis. A significant number of mass spectral peaks that had high sensitivity corresponded to known biomarkers, which is the first time that the significant peaks used by a neural network model to classify mass spectra have been divulged. Furthermore, TTFA furnishes a useful visual target as to which peaks in the mass spectrum correlate with the bacterial identities. 相似文献
119.
120.
Li S Zhang C Wang M Luo HQ Lu X Faulhaber E Schneidewind A Link P Hu J Xiang T Dai P 《Physical review letters》2010,105(15):157002
We use cold neutron spectroscopy to study the low-energy spin excitations of superconducting (SC) FeSe0.4Te0.6 and essentially nonsuperconducting (NSC) FeSe0.45Te0.55. In contrast with BaFe2-x(Co,Ni)xAs2, where the low-energy spin excitations are commensurate both in the SC and normal state, the normal-state spin excitations in SC FeSe0.4Te0.6 are incommensurate and show an hourglass dispersion near the resonance energy. Since similar hourglass dispersion is also found in the NSC FeSe0.45Te0.55, we argue that the observed incommensurate spin excitations in FeSe(1-x)Tex are not directly associated with superconductivity. Instead, the results can be understood within a picture of Fermi surface nesting assuming extremely low Fermi velocities and spin-orbital coupling. 相似文献