全文获取类型
收费全文 | 563篇 |
免费 | 16篇 |
国内免费 | 2篇 |
专业分类
化学 | 362篇 |
晶体学 | 3篇 |
力学 | 25篇 |
数学 | 101篇 |
物理学 | 90篇 |
出版年
2023年 | 4篇 |
2022年 | 5篇 |
2021年 | 15篇 |
2020年 | 8篇 |
2019年 | 9篇 |
2018年 | 8篇 |
2017年 | 13篇 |
2016年 | 23篇 |
2015年 | 19篇 |
2014年 | 18篇 |
2013年 | 48篇 |
2012年 | 33篇 |
2011年 | 35篇 |
2010年 | 31篇 |
2009年 | 19篇 |
2008年 | 25篇 |
2007年 | 31篇 |
2006年 | 33篇 |
2005年 | 23篇 |
2004年 | 22篇 |
2003年 | 17篇 |
2002年 | 8篇 |
2001年 | 9篇 |
2000年 | 3篇 |
1999年 | 8篇 |
1998年 | 6篇 |
1997年 | 9篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1991年 | 5篇 |
1989年 | 4篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 6篇 |
1970年 | 1篇 |
1969年 | 5篇 |
1967年 | 2篇 |
1966年 | 2篇 |
1963年 | 1篇 |
排序方式: 共有581条查询结果,搜索用时 718 毫秒
91.
92.
Daniel Ha??ko Jaroslav Bruncko Andrej Vincze Franti??ek Uherek 《Central European Journal of Physics》2009,7(2):345-349
Two series of polycrystalline zinc oxide (ZnO) layers, from Zn or ZnO targets, were grown on silicon (1 1 1) substrates by
pulsed laser deposition (PLD) at ambient oxygen pressure levels, stepwise increased from 1 to 35 Pa. For ablation of targets,
a pulsed Nd:YAG laser was used. The structural and morphological properties of the layers were investigated by scanning electron
microscopy (SEM), atomic force microscopy (AFM), and secondary ion mass spectrometry (SIMS). The SEM images of ZnO layers
in SE mode show a uniform granular structure and modified surface morphology, depending on oxygen pressure. The mean grain
size in height and lateral directions decreases with an increase of oxygen pressure from 1 to 5 Pa, while a subsequent rise
of oxygen pressure from 5 to 35 Pa will cause an increase in the grain size. The AFM measurement revealed that the surface
structures of zinc oxide layers grown from different targets were similar, and the layers formed at an ambient oxygen pressure
of 5 Pa exhibited the smallest values of calculated roughness and granularity. SIMS depth profiling analyses confirmed that
the ZnO composition was homogenous across the layer, up to the abrupt change of chemical composition at the interface between
the ZnO layer and the Si substrate.
相似文献
93.
Andrej Vincze Ján Jakabovi? Rudolf Srnánek Alexander ?atka Jaroslav Kovac Jr. 《Central European Journal of Physics》2009,7(2):270-278
To improve Organic Thin Film Transistor (OTFT) properties we study OTFT semiconductor/dielectric interfacial properties via
examination of the gate dielectric using thin Parylene C layer. Structural and morphology properties of pentacene layers deposited
on parylene layer and SiO2/Si substrate structure were compared. The surface morphology was investigated using atomic force microscopy (AFM) and scanning
electron microscopy (SEM). AFM topography of pentacene layer in non-contact mode confirmed the preferable pentacene grain
formation on parylene surface in dependence on layer thickness. The distribution of chemical species on the surfaces and composition
depth profiles were measured by secondary ion mass spectroscopy (SIMS) and surface imaging. The depth profiles of the analyzed
structures show a homogenous pentacene layer, characterized with C or C2 ions. Relatively sharp interface between pentacene and parylene layers was estimated by characteristic increased intensity
of CCl ions peak. For revealing the pentacene phases in the structures the Micro-Raman spectroscopy was utilized. Conformal
coatings of parylene and pentacene layers without pinholes resulted from the deposition process as was confirmed by SIMS surface
imaging. For the pentacene layers thicker than 20 nm, both thin and bulk pentacene phases were detected by Micro-Raman spectroscopy,
while for the pentacene layer thickness of 5 and 10 nm the preferable thin phase was detected. The complete characterisation
of pentacene layers deposited on SiO2 and parylene surface revealed that the formation of large grains suggests 3D pentacene growth at parylene layer with small
voids between grains and more than one monolayer step growth. The results will be utilized for optimization of the deposition
process.
相似文献
94.
Bogdan Kralj Andrej Šmidovnik Jože Kobe 《Rapid communications in mass spectrometry : RCM》2009,23(1):171-180
The mass spectrometric characterization of aqueous solutions of α‐ and β‐cyclodextrins (CDs) and o‐, m‐ and p‐coumaric acids (CAs) by negative ion electrospray ionization (ESI) indicates that the [CD+CA]? ions were sourced from the inclusion complex present in solution and from the anion attached to CD molecules formed in the spray processes. The anion adducts formed in the spray process contribute significantly to the signal intensity of an ionized inclusion complex thus overestimating the calculated stability constant (K) of solution‐phase complexes by one to two orders of magnitude. The relative intensities of anion adducts in mass spectra depend on the concentration ratio of the anion and the CD in spray droplets, while the relative intensity of the ionized inclusion complex depends on CD and CA concentrations in solutions and the value of K. Ion Mobility Spectrometry Mass Spectrometry [IMS‐MS] measurements show that the collision cross‐section (Ω) values of the [CD+CA]? or [(CD)2+CA]2? and [CD+CA] complex ions are 5–6% larger than or equal to CD? or [CD], respectively. Therefore, in the gas phase the anion adducts [CD+CA?] on cyclodextrin molecules possess the same conformations as the ionized inclusion complexes [CD+CA]?. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
95.
Ion Gutiérrez-Aguirre Marko Banjac Andrej Steyer Mateja Poljšak-Prijatelj Matjaž Peterka Aleš Štrancar Maja Ravnikar 《Journal of chromatography. A》2009,1216(13):2700-2704
Rotaviruses are the leading cause of diarrhoea in infants around the globe and, under certain conditions they can be present in drinking water sources and systems. Ingestion of 10–100 viral particles is enough to cause disease, emphasizing the need for sensitive diagnostic methods. In this study we have optimized the concentration of rotavirus particles using methacrylate monolithic chromatographic supports. Different surface chemistries and mobile phases were tested. A strong anion exchanger and phosphate buffer (pH 7) resulted in the highest recoveries after elution of the bound virus with 1 M NaCl. Using this approach, rotavirus particles spiked in 1 l volumes of tap or river water were efficiently concentrated. The developed concentration method in combination with a real time quantitative polymerase chain reaction assay detected rotavirus concentrations as low as 100 rotavirus particles/ml. 相似文献
96.
Perdih F Pevec A Petricek S Petric A Lah N Kogej K Demsar A 《Inorganic chemistry》2006,45(19):7915-7921
Organotitanium fluorides (C5Me4R)TiF3 (R = H, Me, Et) sublimate with formation of crystalline dimers. From solution, we obtained crystals of dimers and tetramers. The tetramer [{(C5Me5)TiF3}4] irreversibly dissociates in the solid state to dimers (DeltaH = 8.33 kcal mol(-1)). The variable-temperature (1)H and (19)F NMR spectroscopy measurements of the toluene-d(8) solution of [{(C5Me5)TiF3}2] revealed at 202 K one monomeric, two dimeric (with C2h and Cs symmetry), two tetrameric (with D2 and C2v symmetry), and two trimeric (both C2 symmetry) molecules. With the increase in temperature and dilution of the solution, the composition of the solution shifts to the smaller molecules. The thermodynamic and activation parameters for the reversible dissociation of dimers to monomers in the solution are DeltaH = 9.2 kcal mol(-1), DeltaS = 24.2 cal mol(-1) K(-1), DeltaH(double dagger) = 12.2 kcal mol(-1), DeltaS(double dagger) = 9.7 cal mol(-1) K(-1). The dissociation path with a weakly double-bridged transition-state dimer was proposed. The thermodynamic parameters for the reversible dissociation of the C2v tetramer to the dimers in solution are DeltaH = 7.9 kcal mol(-1) and DeltaS = 26.8 cal mol(-1) K(-1). From both tetramers, the D2 molecule is 0.34(5) kcal mol(-1) lower in enthalpy and 6.5(5) cal mol(-1) K(-1) lower in entropy than the C2v molecule. The structures of both trimers were proposed. The low-temperature 19F NMR spectra of the CDCl3 solution of [{(C5Me5)TiF3}2] are consistent with equilibria of a monomer, two dimers (with C2h and Cs symmetry), and a trimer. The vapor pressure osmometric molecular mass determination of CDCl3 solution of [{(C5Me5)TiF3}2] at 302 K is consistent with the equilibrium of the dimer and the monomer. 相似文献
97.
Stepanka Kuckova Jiri Santrucek Martin Adamec Radovan Hynek Antonin Zeman 《液相色谱法及相关技术杂志》2016,39(16):739-744
In this paper, a Gothic mortar originating from the remains of a bridge pier in Roudnice nad Labem (Czech Republic) was analyzed. The inorganic composition of the mortar showing special mechanical properties was studied using polarizing light microscopy, scanning electron microscopy coupled with energy dispersive X-ray spectrometry, and X-ray diffraction, while the protein content was analyzed by peptide mass mapping using matrix-assisted laser desorption/ionization—time of flight mass spectrometry and nanoliquid chromatography coupled to tandem mass spectrometry. Two types of inorganic binders having a composition similar to mineral wollastonite and hydraulic lime and milk protein additive were detected. We believe that organic and inorganic binders added together to the mortar increase its hardness and firmness in the aquatic environment. 相似文献
98.
P. Lukes P. Sunka P. Hoffer V. Stelmashuk P. Pouckova M. Zadinova J. Zeman L. Dibdiak H. Kolarova K. Tomankova S. Binder J. Benes 《Shock Waves》2014,24(1):51-57
The generator of two focused successive (tandem) shock waves (FTSW) in water produced by underwater multichannel electrical discharges at two composite electrodes, with a time delay between the first and second shock waves of 10 $\upmu $ s, was developed. It produces, at the focus, a strong shock wave with a peak positive pressure of up to 80 MPa, followed by a tensile wave with a peak negative pressure of up to $-80$ MPa, thus generating at the focus a large amount of cavitation. Biological effects of FTSW were demonstrated in vitro on hemolysis of erythrocytes and cell viability of human acute lymphoblastic leukemia cells as well as on tumor growth delay ex vivo and in vivo experiments performed with B16 melanoma, T-lymphoma, and R5-28 sarcoma cell lines. It was demonstrated in vivo that FTSW can enhance antitumor effects of chemotherapeutic drugs, such as cisplatin, most likely due to increased permeability of the membrane of cancer cells induced by FTSW. Synergetic cytotoxicity of FTSW with sonosensitive porphyrin-based drug Photosan on tumor growth was observed, possibly due to the cavitation-induced sonodynamic effect of FTSW. 相似文献
99.
We investigate the relationship between the synthetic approach to topology, in which every set is equipped with an intrinsic topology, and constructive theory of metric spaces. We relate the synthetic notion of compactness of Cantor space to Brouwer’s Fan Principle. We show that the intrinsic and metric topologies of complete separable metric spaces coincide if they do so for Baire space. In Russian Constructivism the match between synthetic and metric topology breaks down, as even a very simple complete totally bounded space fails to be compact, and its topology is strictly finer than the metric topology. In contrast, in Brouwer’s intuitionism synthetic and metric notions of topology and compactness agree. 相似文献
100.
Schuhmann K Almeida R Baumert M Herzog R Bornstein SR Shevchenko A 《Journal of mass spectrometry : JMS》2012,47(1):96-104
Top-down shotgun lipidomics relies on direct infusion of total lipid extracts into a high-resolution tandem mass spectrometer and implies that individual lipids are recognized by their accurately determined m/z. Lipid ionization efficiency and detection specificity strongly depend on the acquisition polarity, and therefore it is beneficial to analyze lipid mixtures in both positive and negative modes. Hybrid LTQ Orbitrap mass spectrometers are widely applied in top-down lipidomics; however, rapid polarity switching was previously unfeasible because of the severe and immediate degradation of mass accuracy. Here, we report on a method to rapidly acquire high-resolution spectra in both polarity modes with sub-ppm mass accuracy and demonstrate that it not only simplifies and accelerates shotgun lipidomics analyses but also improves the lipidome coverage because more lipid classes and more individual species within each class are recognized. In this way, shotgun analysis of total lipid extracts of human blood plasma enabled to quantify 222 species from 15 major lipid classes within 7?min acquisition cycle. 相似文献