全文获取类型
收费全文 | 2738篇 |
免费 | 125篇 |
国内免费 | 8篇 |
专业分类
化学 | 1830篇 |
晶体学 | 21篇 |
力学 | 75篇 |
数学 | 300篇 |
物理学 | 449篇 |
无线电 | 196篇 |
出版年
2023年 | 20篇 |
2022年 | 43篇 |
2021年 | 43篇 |
2020年 | 36篇 |
2019年 | 35篇 |
2018年 | 44篇 |
2017年 | 39篇 |
2016年 | 86篇 |
2015年 | 78篇 |
2014年 | 87篇 |
2013年 | 156篇 |
2012年 | 187篇 |
2011年 | 191篇 |
2010年 | 131篇 |
2009年 | 138篇 |
2008年 | 182篇 |
2007年 | 173篇 |
2006年 | 157篇 |
2005年 | 143篇 |
2004年 | 101篇 |
2003年 | 98篇 |
2002年 | 95篇 |
2001年 | 57篇 |
2000年 | 67篇 |
1999年 | 46篇 |
1998年 | 28篇 |
1997年 | 28篇 |
1996年 | 34篇 |
1995年 | 23篇 |
1994年 | 15篇 |
1993年 | 16篇 |
1992年 | 26篇 |
1991年 | 22篇 |
1990年 | 22篇 |
1989年 | 19篇 |
1988年 | 22篇 |
1987年 | 20篇 |
1986年 | 14篇 |
1985年 | 18篇 |
1984年 | 12篇 |
1983年 | 12篇 |
1982年 | 10篇 |
1981年 | 14篇 |
1980年 | 14篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1975年 | 5篇 |
1974年 | 10篇 |
1973年 | 5篇 |
排序方式: 共有2871条查询结果,搜索用时 15 毫秒
121.
C. Mocuta A. Barbier A. V. Ramos M.-J. Guittet J.-B. Moussy S. Stanescu C. Gatel R. Mattana C. Deranlot F. Petroff 《The European physical journal. Special topics》2009,167(1):53-58
Epitaxial metal/oxide based magnetic tunnel-junctions
(MTJ) are valuable model systems to investigate the influence of the
crystallinity of individual layers on the magnetic properties. We
have non-destructively studied the effect of the optical lithography
procedure on the crystalline structure of MTJ’s with lateral spatial
resolution by performing local x-ray diffraction experiments using a
microfocused x-ray spot. We demonstrate that the lithography process
produces distortion effects on the crystalline structure of the
layers near the edges of the lithographed junction. These
distortions are present on all the constituent layers and are most
probably driven by the elastic constants of the materials. They
translate into tilts of the crystalline planes in the vicinity of
the edges and propagate towards the center of the junction; the
tilt’s amplitude (up to several degrees) and sign (concave or
convex) depend on the junction’s shape, size and the type of
materials (interfaces) used. We report results for junctions made
with two types of metal-oxide interfaces (Co/CoFe2O4 and
Co/Fe3O4), with sizes from 10 to 150 μm and various shapes
(square-, rectangle- and disk-like). 相似文献
122.
123.
Yoann Lalatonne Farah Benyettou Nicole Lièvre Marc Lecouvey Laurence Motte 《Journal of magnetism and magnetic materials》2009,321(10):1653-1657
Magnetic nanoparticles differing by their size have been synthesized to use them for multiparametric testing, based on their differing magnetic properties. The nanoparticle has two essential roles: to act as a probe owing to its specific magnetic properties and to carry on its surface precursor groups for the covalent coupling of biological recognition molecules, such as antibodies, nucleic acids. A totally unique, newly patented, method has been used to characterize magnetic signatures using the MIAplex technology. The MIAplex reader, developed by Magnisense, measures the non-linear response of the magnetic labels when they are exposed to a multi-frequency alternating magnetic field. This specific signature based on d2B(H)/dH2 was correlated to other more conventional magnetic detection methods (superconducting quantum interference devices (SQUID) and Mössbauer). 相似文献
124.
A series of organotin(IV) compounds R3Sn(A) where R = Me or Ph and A is a chromogenic nitrophenolate ligand were prepared and studied as possible colorimetric sensors for anions (F−, Cl−, Br−, AcO−, H2PO4−). Equilibrium constants for a complete set of reactions between R3Sn(A) with A = 2‐amino‐4‐nitrophenolate (ANP) or 4‐nitrophenolate and anions (X−) involving formation of complexes R3Sn(A)(X)− and substitution products R3Sn(X) and R3Sn(X)2− were determined by UV‐vis and 1H NMR titrations in MeCN and DMSO. The binding selectivity was AcO− > F− > H2PO4− > Cl− ≫ Br− in both solvents and both for R = Me and Ph with higher affinity for R = Ph. Compounds with A = ANP were found to have the optimum properties as anion sensors allowing optical detection of F−, AcO− and H2PO4− anions in the 5–100 µM range by appearance of an intense absorption band of free ANP resulting from its substitution with the analyte. Selectivity and affinity of anion interactions with R3Sn(ANP) are similar to those for thiourea receptors, but the organotin receptor produces a much larger naked eye detected optical signal, operates equally well in nonpolar and polar solvents and tolerates the presence of up to 20% vol. of water in DMSO. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
125.
Joaquim J. Moura Ramos 《Molecular physics》2013,111(5):644-660
This study of the thermal behaviour of two glass formers showed that rofecoxib has a good ability to vitrify while celecoxib displays a moderate glass forming ability. On the other hand, celecoxib forms an instable glass while rofecoxib displays moderate glass stability. The α-relaxation of the two amorphous drugs was studied by differential scanning calorimetry (DSC) and thermally stimulated depolarization currents (TSDC). The values of the dynamic fragility obtained by the two techniques are in good mutual agreement and suggest that both drugs are moderately fragile glass formers. These values are however considerably lower than those obtained by dielectric relaxation spectroscopy (DRS) and published in the literature. In the present work we will compare the values of the dynamic fragility obtained by TSDC and DRS for a set of ~30 glass-forming liquids, in order to evaluate their relative suitability for the determination of the m-index. The observed differences are discussed and interpreted. Finally, secondary mobility modes were detected by TSDC in both celecoxib and rofecoxib. The kinetic parameters are identical in both cases and similar to those found by DRS for the slow-b relaxation of celecoxib. These secondary relaxations, that are precursors of the main relaxation on its lower temperature side, are believed to be Johari-Goldstein relaxations. 相似文献
126.
Inês R. Ramos Fiona M. Lyng Ihtesham Ur Rehman Basil Sharrack M. Nicola Woodroofe 《应用光谱学评论》2017,52(10):868-882
Spectroscopy techniques are valuable tools in biomedical research and have been used extensively in the study of disease. However, neurological conditions such as multiple sclerosis (MS) have received little attention and the available spectroscopy studies are limited, both in overall numbers of patients studied and the disease samples considered. MS is a complex immune-mediated disease, with variable clinical courses and limited therapeutic options. This review aims to summarize current literature in the area, demonstrating how spectroscopy techniques can provide valuable information to inform and advance research into the most common neurological condition affecting young adults. 相似文献
127.
Laurence S. Rothman 《Journal of Quantitative Spectroscopy & Radiative Transfer》2010,111(11):1514-1515
The publication by G.H. Dieke and H.M. Crosswhite (JQSRT 1962;2:97-199) is a classic paper detailing the spectroscopy of the A2Σ+←X2Π bands of the hydroxyl radical (OH) in the ultraviolet region. It soon became the basis of astrophysical modeling, most subsequent theoretical and laboratory studies of the OH individual line parameters, and a host of other applications. 相似文献
128.
129.
The effect of storage time, the presence of light and oxygen on the decomposition rate of carotenoid pigments in paprika (Capsicum annuum) powders was determined by reversed-phase high-performance liquid chromatography (RP-HPLC). The similarities and dissimilarities of pigment composition of samples under various storage conditions was elucidated by principal component analysis (PCA) and stepwise regression analysis (SRA). Calculations proved that the overall decomposition rate of pigment sections equally depended on the storage time and on the presence of light and oxygen, the effect of storage time being the most decisive factor while the impact of oxygen was the lowest. The selectivity of decomposition also depended on the storage time and on the presence of oxygen the influence of storage time being the most important. RP-HPLC followed by PCA and SRA can be successfully used for the study of the impact of environmental conditions on the decomposition of carotenoid pigments of paprika powders. 相似文献
130.
Simpson CD Brand JD Berresheim AJ Przybilla L Räder HJ Müllen K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(6):1424-1429
In this paper we present the synthesis and characterization of the so far largest polycyclic aromatic hydrocarbon (PAH), containing 222 carbon atoms or 37 separate benzene units. First a suitable three-dimensional oligophenylene precursor molecule is built up by a sequence of Diels-Alder and cyclotrimerization reactions and then planarized in the final step by oxidative cyclodehydrogenation to the corresponding hexagonal PAH. Structural proof is based on isotopically resolved MALDI-TOF mass spectra and electronic characteristics are studied by UV/Vis spectroscopy. 相似文献