全文获取类型
收费全文 | 353篇 |
免费 | 12篇 |
国内免费 | 2篇 |
专业分类
化学 | 282篇 |
晶体学 | 3篇 |
力学 | 6篇 |
数学 | 21篇 |
物理学 | 40篇 |
无线电 | 15篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 14篇 |
2021年 | 10篇 |
2020年 | 12篇 |
2019年 | 13篇 |
2018年 | 11篇 |
2017年 | 8篇 |
2016年 | 16篇 |
2015年 | 14篇 |
2014年 | 12篇 |
2013年 | 22篇 |
2012年 | 27篇 |
2011年 | 27篇 |
2010年 | 22篇 |
2009年 | 12篇 |
2008年 | 25篇 |
2007年 | 20篇 |
2006年 | 19篇 |
2005年 | 16篇 |
2004年 | 12篇 |
2003年 | 10篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 5篇 |
1999年 | 2篇 |
1998年 | 5篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1889年 | 1篇 |
排序方式: 共有367条查询结果,搜索用时 15 毫秒
141.
142.
143.
Ivanchina NV Kalinovsky AI Kicha AA Malyarenko TV Dmitrenok PS Ermakova SP Stonik VA 《Natural product communications》2012,7(7):853-858
Two new asterosaponins, lethasteriosides A (1) and B (2), were isolated along with previously known thornasteroside A (3), anasteroside A (4), and luidiaquinoside (5) from the ethanolic extract of the Far Eastern starfish Lethasterias fusca. The structures of the new compounds were elucidated by extensive NMR and ESIMS techniques, and chemical transformations. Compounds 1 and 3-5 did not show any apparent cytotoxicity against cancer cell lines T-47D, RPMI-7951, and HCT-116, but glycoside 1, at concentration of 20 microM, demonstrated considerable inhibition of the T-47D (97%), RPMI-795I (90%) and HCT-116 (90%) cell colony formations in a soft agar clonogenic assay. 相似文献
144.
145.
D. S. Shaitura A. A. Teplov E. A. Chikina A. M. Klevachev I. Yu. Efimochkin S. V. Fedotov M. I. Petrzhik E. A. Levashov Yu. A. Abuzin 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2010,4(6):951-955
Copper-based composite coatings with addition of 34 wt % of Al—Cu—Fe quasicrystalline powder of dispersity less than 20 fum,
as well as 70 wt % of quasicrystalline powder of dispersity less than 40fum and less than 3 fum, were produced by the cold
spray process. The phase composition during annealing of samples at various temperatures was studied by X-ray phase analysis.
Tribological properties of each composite coating and pure copper were investigated. The experimental results showed a considerable
improvement of the tribological properties of the material at the addition of quasicrystals. The least wear was observed in
the composite sample containing quasicrystalline inclusions of less than 3 fum subjected to thermal treatment. In this case
the counterbody wear was practically absent. 相似文献
146.
Amir Qamar Muhammad Ruhul Amin Oleksandr Grynko Oleksii Semeniuk Prof. Alla Reznik Prof. Alexander Moewes 《Chemphyschem》2019,20(24):3328-3335
We investigate how the electronic structure of amorphous lead oxide (a-PbO) films deposited on ITO substrate is changed after annealing at various temperatures. Both experimental soft X-ray spectroscopic and density functional theory (DFT) based computational techniques are used to explore the electronic structure of this material. X-ray emission, resonant X-ray inelastic scattering, and X-ray absorption spectroscopic techniques are employed to directly probe the valence and conduction bands. We discover that the films are very stable and remain amorphous when exposed to temperatures below 300 °C. An amorphous-to-polycrystalline (α-PbO phase) transformation occurs during annealing at 400 °C. At 500 °C, an alpha to beta phase change is observed. These structural modifications are accompanied by the band gap value changing from 1.4±0.2 eV to 2.0±0.2 eV upon annealing at 400 °C and to 2.6±0.2 eV upon annealing at 500 °C. A difference between surface and bulk structural properties is found for all samples annealed at 500 °C and above; these samples also exhibit an unexpected suppression of O : 2p density of states (DOS) near the bottom of the conduction band, whereas additional electronic states appear well within the valence band. This study provides a significant step forward to understanding the electronic properties of two polymorphic forms of PbO needed for optimization of this material for use in X-ray sensors. 相似文献
147.
Natalia V. Ivanchina Alla A. Kicha Timofey V. Malyarenko Sofiya D. Ermolaeva Ekaterina A. Yurchenko Evgeny A. Pislyagin 《Natural product research》2019,33(18):2623-2630
Two new steroid glycosides, granulatosides D (1) and E (2), belonging to the group of bi- and monoglycosides of polyhydroxysteroids, respectively, were isolated from the ethanolic extract of the starfish Choriaster granulatus along with thirteen previously known glycosides of polyhydroxysteroids (3–15) and one steroid heptaol (16). The structures of the new compounds were elucidated by extensive NMR and ESIMS techniques. Cytotoxic and immunomodulatory activities of compounds 1, 3–8, and 10–16 using murine splenocytes and peritoneal macrophages were studied. At a dose of 0.1 μM new glycoside 1 showed immunomodulatory properties, increasing the intracellular ROS (reactive oxygen species) level in peritoneal murine macrophages by 20% and decreasing intracellular ROS level by 21% in pre-treated with endotoxic lipopolysaccharide from E. coli (LPS) peritoneal macrophages. 相似文献
148.
Mehmet F. Yilmaz Alla S. SafronovaVictor L. Kantsyrev Andrey A. EsaulovKenneth M. Williamson Ishor K. ShresthaMichael E. Weller Glenn C. OsborneVeronica V. Shlyaptseva 《High Energy Density Physics》2012,8(1):30-37
Radiative emission from alloyed Al single, double and compact cylindrical wire arrays have been studied using the 1 MA Zebra UNR generator. Single planar wire arrays using ten wires and double planar wire arrays and compact cylindrical wire arrays (CCWA) that both had sixteen wires were utilized. The wire composition is Al-5056 (95% of Al and 5% of Mg). We have observed that implosion of these alloyed Al wire loads generated optically thick Al plasmas that can be diagnosed using K-shell Mg lines. In particular, among the considered loads, the K-shell lines of Al from implosions of the double planar wire arrays have the highest optical depth for He-like Al resonance transitions, which occurred near the stagnation phase. X-ray time-gated and time-integrated spectra and pinhole images as well as photoconductive detectors signals were analyzed to provide information on the plasma parameters; electron temperatures and densities, implosion dynamics features and power and yields of the X-ray radiation. Previously developed non-LTE models were applied to model axially-resolved time-integrated, as well as time-gated spatially-integrated, K-shell spectra from Al and Mg. The derived time-dependent electron temperature, density and axial opacity were studied and compared. In addition, the wire ablation dynamics model (WADM) was used to calculate the kinetic energy of the plasma, which with the aid of a Local Thermal Equilibrium (LTE) magneto-hydrodynamics (MHD) simulation, allowed to estimate the precursor and stagnated z-pinch plasma electron temperatures from implosions of wire array loads. 相似文献
149.
Dr. Alla Vaskevych Dr. Maryna Dekhtyar Prof. Dr. Mykhailo Vovk 《Chemical record (New York, N.Y.)》2024,24(2):e202300255
Quinazolin-4-one, its heteroanalogues, and derivatives represent an outstandingly important class of compounds in modern organic, medicinal, and pharmaceutical chemistry, as these molecular structures are noted for their wide synthetic and pharmacological potential. In the last years, ever-increasing research attention has been paid to quinazolinone derivatives bearing alkenyl and alkynyl substituents on the pyrimidinone nucleus. The original structural combination of synthetically powerful endocyclic amidine (or amidine-related) and exocyclic unsaturated moieties provides a driving force for cyclizations, which offer an efficient toolkit to construct a variety of fused pyrimidine systems with saturated N- and N,S-heterocycles. In this connection, the present review article is mainly aimed at systematic coverage of the progress in using alkenyl(alkynyl)quinazolinones and their heteroanalogues as convenient bifunctional substrates for regioselective annulation of small- and medium-sized heterocyclic nuclei. Much attention is paid to elucidating the structural and electronic effects of reagents on the regio- and stereoselectivity of the cyclizations as well as to clarifying the relevant reaction mechanisms. 相似文献
150.
Conformational transitions in thermotropic main-chain polymers of complex chemical structure including homopolymers with possibility of conformational transformations in mesogens and random copolymers (CPLs) containing mesogens of the same type and spacers of different lengths were investigated. It was demonstrated that liquid crystalline (LC) state influences conformational transformations in fragments of chain restraining them in comparison with an isotropic melt. It was found that CPLs studied form LC order of smectic type. Peculiarities in spacers behaviour during transition to LC state ensure formation of such type of LC order. Conclusion about dependence of mechanism of smectic LC order formation on chemical structure of rigid components of CPLs is made. 相似文献