全文获取类型
收费全文 | 648篇 |
免费 | 32篇 |
国内免费 | 1篇 |
专业分类
化学 | 511篇 |
晶体学 | 4篇 |
力学 | 7篇 |
数学 | 103篇 |
物理学 | 56篇 |
出版年
2023年 | 2篇 |
2022年 | 11篇 |
2021年 | 27篇 |
2020年 | 11篇 |
2019年 | 9篇 |
2018年 | 4篇 |
2017年 | 7篇 |
2016年 | 29篇 |
2015年 | 18篇 |
2014年 | 18篇 |
2013年 | 38篇 |
2012年 | 40篇 |
2011年 | 44篇 |
2010年 | 38篇 |
2009年 | 29篇 |
2008年 | 36篇 |
2007年 | 37篇 |
2006年 | 46篇 |
2005年 | 41篇 |
2004年 | 28篇 |
2003年 | 30篇 |
2002年 | 27篇 |
2001年 | 11篇 |
2000年 | 6篇 |
1999年 | 8篇 |
1998年 | 4篇 |
1997年 | 10篇 |
1996年 | 8篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 6篇 |
1992年 | 6篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1921年 | 1篇 |
1919年 | 1篇 |
排序方式: 共有681条查询结果,搜索用时 328 毫秒
71.
Finocchio E Baccini I Cristiani C Dotelli G Gallo Stampino P Zampori L 《The journal of physical chemistry. A》2011,115(26):7484-7493
The intercalation of organic polymers molecules (i.e., PEGs and BRIJ) into a standard Ca-montmorillonite has been studied by XRD, TG, and IR spectroscopy. The polymer intercalation is confirmed by the increasing of the d(001) in XRD spectra as well as by the complex multisteps thermal decomposition behavior of the organo-clay materials. Mid-IR and diffuse reflectance near-IR spectra of the intercalated materials show the polymer diagnostic bands (CH stretching and deformation mode), shifted or changed in shape by the interaction with the clay matrix. Both PEG 1500 and PEG 4000 based materials are likely intercalated in an extended configuration, similar to the amorphous polymer form. BRIJ intercalated polymer spectra suggest the disordered conformation of the alkilic chain in a prevailing "gauche", poorly packed, conformation. Host montmorillonite IR bands, mainly OH and water stretching and deformation fundamentals, combination, and overtone bands, are reduced in intensity by polymer intercalation, pointing out an interaction, likely through H-bonding and/or a possible substitution of cations hydration water molecules. 相似文献
72.
In this paper, the connections between model theory and the theory of infinite permutation groups (see 11 ) are used to study the n‐existence and the n‐uniqueness for n‐amalgamation problems of stable theories. We show that, for any n ? 2, there exists a stable theory having (k + 1)‐existence and k‐uniqueness, for every k ? n, but has neither (n + 2)‐existence nor (n + 1)‐uniqueness. In particular, this generalizes the example, for n = 2, due to Hrushovski given in 3 . © 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim 相似文献
73.
74.
In this paper, two different structures for inverted files are analyzed and compared, when the relational join operation is taken into account. The structures are called shared and separate inverted files. The results are given of some experiments which show that the shared inverted organization is always advantageous when the inverted files are not sorted and is almost always advantageous when the files are sorted. 相似文献
75.
76.
77.
Realini M Colombo C Sansonetti A Rampazzi L Colombini MP Bonaduce I Zanardini E Abbruscato P 《Annali di chimica》2005,95(3-4):217-226
The analytical studies carried out during two different diagnostic surveys, respectively in 1983 and 2003, offered the opportunity to control decay phenomena development on stones facing Certosa of Pavia (Italy). Calcium oxalate films and red stains, present on Carrara marble surface, have been particularly focused; these are the only decay phenomena which apparently have remained unchanged during a period of twenty years. More sensitive and in-depth analytical studies (FTIR equipped with diamond cell, GC-MS, SEM-EDS and optical microscopy) achieved a better knowledge about their composition. Results allowed a critical evaluation of the role of oxalate films on the external marble surface and to suggest new hypotheses about the formation of red stains. 相似文献
78.
Rosaria D’Amato Mauro Falconieri Fabio Fabbri Valentina Bello Elisabetta Borsella 《Journal of nanoparticle research》2010,12(5):1845-1858
The preparation of sizeable quantities of luminescent Si nanoparticles (Si-np) with controlled morphology is a challenging
task. Here, we describe two strategies aiming at size reduction of the Si-np produced in a laser-assisted silane pyrolysis
reactor without detrimental effects on the process yield and on the nanoparticle structural and compositional properties.
The first method is based on the addition of a sensitizer gas to dilute silane and consequently reduce the nucleation centres
density without decreasing the reaction temperature. The second consists in the introduction of a collector at a variable
distance from the irradiated region to freeze the particle growth and decrease the inter-particle sintering probability. We
report on the characterization of the produced Si-np, and we show that by combining the two methods, we are able to prepare
4 nm crystalline core size nanoparticles with a productivity of 1 g per hour. We also describe the enhancement effect of the
wet-chemical oxidation processes on the luminescence emission intensity of the Si-np. 相似文献
79.
Scavia G Agostinelli E Laureti S Varvaro G Paci B Generosi A Albertini VR Kaciulis S Mezzi A 《The journal of physical chemistry. B》2006,110(11):5529-5536
A combined ultrahigh vacuum scanning tunneling microscopy (STM-UHV) and energy dispersive X-ray diffractometry/reflectometry (EDXD/EDXR) study of the evolution of face-centered cubic (fcc) Pt layer growth on MgO(100) by pulsed laser deposition as a function of the process parameters such as deposition temperature and deposition duration has been carried out. The aim of this study is to define the best experimental conditions to obtain a controlled film deposition selective on the Pt growth direction (either [111] or [002]). The evolution of the Pt surface morphology as a function of the deposition temperature (T(dep)) from 300 to 700 degrees C has been studied with STM and ED techniques. Results show that the Pt surface, characterized at T(dep) = 300 degrees C by a 3D island morphology, evolves at higher temperatures to a morphology in which the original islands coexist with a distribution of orthogonal 2D stripes. The two features can be associated with the [111] and [002] Pt growth directions of the fcc phase, respectively. For T(dep) = 700 degrees C, the island morphology of the (111) face completely disappears, while the merging process of the (002) stripes reaches completion. The evolution of the morphology at T(dep) = 600 degrees C as a function of the deposition time and thickness has then been studied with STM-UHV, revealing an initial growth of mosaic-like 3D islands. These independent islands, already interconnected, expand along two orthogonal directions and, for longer deposition times, lead to the texture of orthogonal stripes. The EDXR characterization providing the morphological parameters of the films, i.e., thickness and roughness, confirms the above observation and quantifies the effect of such morphological changes on the surface roughness of the Pt film, an important parameter for applications of Pt films as underlayer in magnetic recording media. 相似文献
80.
Sara Salucci Michela Battistelli Sabrina Burattini Cesare Squillace Barbara Canonico Pietro Gobbi Stefano Papa Elisabetta Falcieri 《Micron (Oxford, England : 1993)》2010,41(8):966-973
Apoptosis is a form of cell death crucial for normal development and tissue homeostasis. Its typical features include chromatin changes, nuclear breakdown, plasma membrane blebbing and splitting of cellular content into apoptotic bodies, that progressively undergo phagocytosis.Apoptosis is considered essential for skeletal muscle development, where defective cells are deleted during differentiation. In addition, it plays a relevant role in several muscle myopathies, as well as in denervation and disuse.The aim of this study was to evaluate muscle cell sensitivity to different apoptotic triggers, acting through different mechanisms of action. Chemical agents, active against distinct intracellular targets, such as mitochondrial respiratory chain and DNA, have been chosen to better highlight cell death mechanisms. To induce apoptosis, C2C12 myoblasts have been exposed to H2O2, staurosporine, cisplatin and etoposide, at different doses and incubation times, and they have been analysed by flow cytometry, scanning and transmission electron microscopy.Flow cytometry analysis revealed a certain subdiploid peak after all treatments. The best apoptotic effect was observable, as confirmed at reverted microscope, at minimum doses and after the major exposure time.At ultrastructural level programmed cell death has been observed. Characteristic chromatin condensation and margination, as well as apoptotic bodies, frequently appeared, even if in the presence of secondary necrosis; surface blebs were also observed during scanning microscopic observation.In particular, exposure to H2O2 or staurosporine showed the largest number of myoblasts in late apoptotic stages and in secondary necrosis. Cisplatin treatments revealed few early apoptotic cells. The analysis of etoposide-induced apoptosis was in agreement with data obtained from flow cytometry, indicating a significant increase of apoptotic cell number.These results suggest that all conditions are able to induce apoptosis in C2C12 myoblasts, which occurs, considering trigger mechanisms of action, mostly following the mitochondrial pathway, if not excluding that due to DNA damage. Therefore, mitochondria permeability alteration is an important step in skeletal muscle programmed cell death. This last conclusion seems to have a significant relevance in understanding the mechanisms involved in muscle disorders, denervation and chronic muscle disuse, conditions frequently characterized by a decline in mitochondrial content and by an increase of mitochondrial apoptosis susceptibility. 相似文献