全文获取类型
收费全文 | 717篇 |
免费 | 18篇 |
国内免费 | 4篇 |
专业分类
化学 | 427篇 |
晶体学 | 3篇 |
力学 | 27篇 |
数学 | 166篇 |
物理学 | 116篇 |
出版年
2023年 | 5篇 |
2022年 | 18篇 |
2021年 | 26篇 |
2020年 | 22篇 |
2019年 | 18篇 |
2018年 | 12篇 |
2017年 | 13篇 |
2016年 | 33篇 |
2015年 | 23篇 |
2014年 | 28篇 |
2013年 | 40篇 |
2012年 | 49篇 |
2011年 | 49篇 |
2010年 | 35篇 |
2009年 | 24篇 |
2008年 | 37篇 |
2007年 | 38篇 |
2006年 | 35篇 |
2005年 | 36篇 |
2004年 | 28篇 |
2003年 | 19篇 |
2002年 | 19篇 |
2001年 | 10篇 |
1999年 | 9篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 12篇 |
1995年 | 7篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1973年 | 2篇 |
1921年 | 2篇 |
1919年 | 2篇 |
1915年 | 4篇 |
1909年 | 2篇 |
1901年 | 2篇 |
1875年 | 1篇 |
1868年 | 2篇 |
排序方式: 共有739条查询结果,搜索用时 31 毫秒
151.
152.
Margherita Calò Alessandra Bitto Patrizia Lo Cascio Filippo Giarratana Domenica Altavilla Teresa Gervasi 《Natural product research》2018,32(10):1136-1144
The aim of the present study is to determine if Ahr ligands as PCB-126, a dioxin-like, might contribute to inhibition of the tumour suppressor p53 by promoting its degradation through proteasome-ubiquitin system (UPS). The findings show, in the presence of PCB-126, a significant increase in p53 immunoreactivity in fish compared to the control. Subsequently, there is a decrease in p53 immunoreactivity at 24 h which is maintained even at 72 h. There is also a slight decrease in ubiquitin immunoreactivity to 12 h compared to the control and a marked decrease to 24 and 72 h. It’s very important to underline as in this study we demonstrate a marked decrease in ubiquitin and p53 immunoreactivity at 24 and 72 h. Our result emphasise the need to deeply the role of this receptor in UPS regulation as potential therapeutic target for cancer treatment. 相似文献
153.
We consider the model of a 2D surface above a fixed wall and attracted toward it by means of a positive magnetic fieldh in the solid-on-solid (SOS) approximation when the inverse temperature is very large and the external fieldh is exponentially small in . We improve considerably previous results by Dinaburg and Mazel on the competition between the external field and the entropic repulsion with the wall, leading, in this case, to the phenomenon of layering phase transitions. In particular, we show, using the Pirogov-Sinai scheme as given by Zahradník, that there exists a unique critical valueh
k
*
() in the interval (1/4e
–4k
, 4e
–4k
) such that, for allh(h
k+1
*
,h
k
*
) and large enough, there exists a unique infinite-volume Gibbs state. The typical configurations are small perturbation of the ground state represented by a surface at heightk+1 above the wall. Moreover, for the same choice of the thermodynamic parameters, the influence of the boundary conditions of the Gibbs measure in a finite cube decays exponentially fast with the distance from the boundary. Whenh=h
k
*
() we prove instead the convergence of the cluster expansion for bothk andk+1 boundary conditions. This fact signals the presence of a phase transition. In the second paper of this series we will consider a Glauber dynamics for the above model and we will study the rate of approach to equilibrium in a large finite cube with arbitrary boundary conditions as a function of the external fieldh. Using the results proven in this paper, we will show that there is a dramatic slowing down in the approach to equilibrium when the magnetic field takes one of the critical values and the boundary conditions are free (absent). 相似文献
154.
155.
Giorgio Montaudo Concetto Puglisi Filippo Samperi 《Journal of polymer science. Part A, Polymer chemistry》1993,31(1):13-25
The chemical reactions occurring in the thermal treatment of polycarbonate/polybuthyleneterephthalate (PC/PBT) blends have been investigated by gradual heating (10°C/min) using thermogravimetry and direct pyrolysis into the mass spectrometer. Exchange reactions occur already in the temperature range below 300°C but the transesterification equilibrium is affected by the evolution of thermal degradation products. Buthylenecarbonate, was detected in the first decomposition stage (320–380°C), which is evolved together with a series of cyclic compounds containing units of PC and PBT, in varying ratios. The overall thermal reaction evolves towards the formation of the most thermally stable polymer, i.e., a totally aromatic polyester (polymer III , Table I), which was found to be the end-product of the thermal processes occurring in the system investigated. The thermal decomposition products obtained from the PC/PBT blends in the range 320–600°C have mass sufficiently high to be structurally significant, since they contain at least one copolymer repeating unit. The reactions occurring in the thermal treatment of the PC/PBT blend are discussed in detail. © 1993 John Wiley & Sons, Inc. 相似文献
156.
Silvia Gennari Filippo Maglia Umberto Anselmi-Tamburini Giorgio Spinolo 《Monatshefte für Chemie / Chemical Monthly》2005,17(1):1871-1875
Computer simulation results for the Self-propagating High-temperature Synthesis (SHS) of the intermetallic compound NbSi2 are discussed in comparison with experiments for SHS of mechanically activated powders. The variation of wave speed of the
propagation front is considered while varying Nb grain size and thermal conductivity of the starting mixture. A co-operating
effect of these two parameters (due to the change in morphology of reactants after milling) is outlined. 相似文献
157.
Raffaella Ruffini Alessandro Borghi Roberto Cossio Filippo Olmi Gloria Vaggelli 《Mikrochimica acta》2002,139(1-4):151-158
Quartz is a common phenocryst in acidic volcanic rocks but rarely contributes to the understanding of the magmatic or eruptive
processes due to its apparent chemical homogeneity. Cathodoluminescence studies indicate that volcanic quartz is strongly
zoned with respect to the trace elements. The determination of this zoning can help to elucidate the crystallisation history
of the magmatic rock. Polished thin sections from rhyolitic and dacitic volcanic rocks were examined by cathodoluminescence
mounted on an optical microscope and analysed by electron probe microanalysis. X-ray mapping of the trace elements incorporated
in the zoned quartz was also performed. The interpretation of the data obtained from these different analytical methods provides
useful information on the chemical zoning of single crystals and therefore on the chemico-physical conditions of the melt
from which the quartz crystallised. Quartz from dacitic rock shows a complex cathodoluminescence oscillatory zoning, consisting
of large red-brown and blue bands concentric to a resorbed core. Quartz from rhyolite shows simpler cathodoluminescence zoning,
consisting of dark to bright blue luminescent bands. The EMPA analyses and the X-ray maps combined with the cathodoluminescence
images suggest a clear correlation between the concentrations of some trace element (mainly Al and Ti, acting as activators
of luminescence) and the cathodoluminescence colours pattern zoning. The incorporation of these trace elements during the
growth of the crystals is linked to small variations in the thermo-chemical properties of the magma such as temperature and
chemical composition. 相似文献
158.
Alessandro Borghi Roberto Cossio Filippo Olmi Raffaella Ruffini Gloria Vaggelli 《Mikrochimica acta》2002,139(1-4):17-25
A comparison between major and trace element concentrations in garnet performed by electron microprobe (EPMA) technique is
reported. Quantitative spot analyses and X-ray maps of major elements (Fe, Mg, Mn, Ca) and the trace element yttrium in garnets
from metamorphic rocks are presented. The selected garnet samples come from meta-pelitic and meta-basic specimens belonging
to the tectonic unit of the Monte Rosa Nappe (Western Alps).
In the metapelites, the quantitative Y distribution maps display a prominent increase at the core, the Y abundance varying
by over two orders of magnitude, from about 80 ppm (rim) to over 2100 ppm (core). The Y profiles show well defined patterns
with sharp features that do not correlate with major element distributions. A roughly comparable pattern can be supposed only
with Mn. The Y distribution suggests that the diffusion of Y through the garnet is very slow compared to the major elements,
thus the Y results are suitable for geothermometric estimates.
In the metabasites, the Y spatial distribution is characterised by an increasing content from the core to the rim, displaying
a zoning pattern opposite to the metapelite garnet. Quantitative EPMA analyses range from 1100 ppm at the rim to values lower
than the detection limit at the core.
Therefore, the Y content in the garnet can be related to several chemical and physical variables such as the bulk rock composition
and the phase assemblage. In particular, in the xenotime-bearing metapelitic system the Y distribution seems to be correlated
with metamorphic peak temperature. 相似文献
159.
Filippo Russo Andrea Santagati Maria Santagati 《Journal of heterocyclic chemistry》1985,22(2):297-299
Continuing preceeding studies, designed to obtain derivatives of 1,3,4-thiadiazolo[3,2-α]pyrimidin-5-one and of the isomeric 7-one of pharmacological interest, some of the above mentioned compounds were prepared. Their structural identification was obtained by mass spectra. 相似文献
160.
Filippo De Angelis Simona Fantacci Antonio Sgamellotti 《Theoretical chemistry accounts》2007,117(5-6):1093-1104
We present a combined computational strategy for the study of the optical properties of nanoscale systems, using a combination
of codes and techniques based on Density Functional Theory (DFT) and its Time Dependent extension (TDDFT). In particular,
we describe the use of Car–Parrinello molecular dynamics simulations for the study of nanoscale devices and show the integration
of the obtained results with available quantum chemistry codes for the calculation of TDDFT excitation energies, including
solvation effects by continuum solvation models. We review some prototypical applications of this integrated computational
strategy, ranging from the interaction of dye sensitizers with TiO2 nanoparticles, of interest in the field of dye-sensitized solar cells, to transition metal molecular wires exceeding 3 nm
length. 相似文献