全文获取类型
收费全文 | 1146篇 |
免费 | 60篇 |
国内免费 | 19篇 |
专业分类
化学 | 711篇 |
晶体学 | 3篇 |
力学 | 14篇 |
数学 | 215篇 |
物理学 | 282篇 |
出版年
2023年 | 6篇 |
2022年 | 30篇 |
2021年 | 30篇 |
2020年 | 40篇 |
2019年 | 35篇 |
2018年 | 23篇 |
2017年 | 22篇 |
2016年 | 56篇 |
2015年 | 45篇 |
2014年 | 41篇 |
2013年 | 75篇 |
2012年 | 80篇 |
2011年 | 77篇 |
2010年 | 58篇 |
2009年 | 39篇 |
2008年 | 50篇 |
2007年 | 55篇 |
2006年 | 53篇 |
2005年 | 65篇 |
2004年 | 39篇 |
2003年 | 31篇 |
2002年 | 35篇 |
2001年 | 32篇 |
2000年 | 21篇 |
1999年 | 14篇 |
1998年 | 12篇 |
1997年 | 10篇 |
1996年 | 8篇 |
1995年 | 3篇 |
1994年 | 5篇 |
1993年 | 10篇 |
1992年 | 5篇 |
1990年 | 7篇 |
1989年 | 8篇 |
1987年 | 4篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 11篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1976年 | 5篇 |
1975年 | 2篇 |
1974年 | 5篇 |
1973年 | 4篇 |
1970年 | 2篇 |
1967年 | 2篇 |
1915年 | 2篇 |
排序方式: 共有1225条查询结果,搜索用时 15 毫秒
71.
Odysseas Paschos Alexander N. Simonov Alesya N. Bobrovskaya Moritz Hantel Matthias Rzepka Petra Dotzauer Anton N. Popov Pavel A. Simonov Valentin N. Parmon Ulrich Stimming 《Electrochemistry communications》2010,12(11):1490-1492
The electrocatalytic activity of bimetallic BiPd catalysts supported on Sibunit carbon towards hydrogen oxidation/evolution reactions (HOR/HER) was studied in a gas diffusion electrode (GDE) setup. Catalysts were synthesized by deposition of Pd on the carbon support, followed by impregnation of Pd/C precursor with Bi(NO3)3 solution and reduction in hydrogen. Transmission electron microscopy and local EDX elemental analysis revealed that BiPd/C catalysts contain bimetallic particles with narrow size distribution with maxima at 3.2–4.1 nm. X-ray diffraction evidenced that bimetallic particles are constituted by Pd–Bi solid solution. It was shown that modification of Pd/C by bismuth increases the specific activity of palladium towards HOR/HER by a factor of 3. 相似文献
72.
Levina EV Kalinovsky AI Dmitrenok PS Martyyas EA Stonik VA 《Natural product communications》2010,5(11):1737-1742
New steroid glycosides, hylodoside A (1) and novaeguinoside Y (2), along with previously known polyhydroxylated steroids (3-7) were isolated from the ethanolic extracts of the starfish Leptasterias hylodes reticulata and Culcita novaeguineae (juvenile). The structures have been elucidated using 1D and 2D NMR spectra (1H, 13C, DEPT, COSY-45, 1D-TOCSY, HSQCGP, ROESY, HSQC and HMBCGP) and mass spectrometry. Compound 3 was shown to inhibit the growth of Staphylococcus aureus up to 10% from the control at a concentration of 1 mg/mL. Steroids 1, 2 and 5 showed moderate hemolytic activity in the mouse erythrocytes assay. Compounds 3, 4 and 6 displayed pH-depended hemolytic properties. 相似文献
73.
74.
Francesco Napoli Dr. Mario Chiesa Dr. Elio Giamello Prof. Gloria Preda Dr. Cristiana Di Valentin Dr. Gianfranco Pacchioni Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(23):6776-6785
The formation of O2? radical anions by contact of O2 molecules with a Na pre‐covered MgO surface is studied by a combined EPR and quantum chemical approach. Na atoms deposited on polycrystalline MgO samples are brought into contact with O2. The typical EPR signal of isolated Na atoms disappears when the reaction with O2 takes place and new paramagnetic species are observed, which are attributed to different surface‐stabilised O2? radicals. Hyperfine sublevel correlation (HYSCORE) spectroscopy allows the superhyperfine interaction tensor of O2?Na+ species to be determined, demonstrating the direct coordination of the O2? adsorbate to surface Na+ cations. DFT calculations enable the structural details of the formed species to be determined. Matrix‐isolated alkali superoxides are used as a standard to enable comparison of the formed species, revealing important and unexpected contributions of the MgO matrix in determining the electronic structure of the surface‐stabilised Na+? O2? complexes. 相似文献
75.
Valentin Todorov Matthias Templ Peter Filzmoser 《Advances in Data Analysis and Classification》2011,5(1):37-56
Many different methods for statistical data editing can be found in the literature but only few of them are based on robust estimates (for example such as BACON-EEM, epidemic algorithms (EA) and transformed rank correlation (TRC) methods of Béguin and Hulliger). However, we can show that outlier detection is only reasonable if robust methods are applied, because the classical estimates are themselves influenced by the outliers. Nevertheless, data editing is essential to check the multivariate data for possible data problems and it is not deterministic like the traditional micro editing where all records are extensively edited manually using certain rules/constraints. The presence of missing values is more a rule than an exception in business surveys and poses additional severe challenges to the outlier detection. First we review the available multivariate outlier detection methods which can cope with incomplete data. In a simulation study, where a subset of the Austrian Structural Business Statistics is simulated, we compare several approaches. Robust methods based on the Minimum Covariance Determinant (MCD) estimator, S-estimators and OGK-estimator as well as BACON-BEM provide the best results in finding the outliers and in providing a low false discovery rate. Many of the discussed methods are implemented in the R package ${\tt{rrcovNA}}$ which is available from the Comprehensive R Archive Network (CRAN) at http://www.CRAN.R-project.org under the GNU General Public License. 相似文献
76.
A combined experimental and first principles study of Cu defects in bulk ZnO is presented. Cu particles are epitaxially deposited on the polar O-ZnO(0001) surface at room temperature. Upon heating, a broadening of the quasielastic peak in high resolution electron energy loss spectra is observed, corresponding to an electronic doping effect of Cu atoms in bulk ZnO with an ionization energy of 88 meV. Cu impurities in ZnO, although commonly acting as acceptors, are presently observed to induce shallow donor states. We assign these to interstitial Cu species on the basis of a hybrid density functional study. 相似文献
77.
Magdalena Ulmeanu Iuliana Iordache Mihaela Filipescu Valentin Craciun Simona Cinta Pinzaru Andreas Hörner 《Central European Journal of Physics》2011,9(5):1280-1287
Experimental studies on patterning hexagonal Ge nanostructures have been conducted on Si substrates through deposition of
Ge with colloidal particles as a mask. The deposited Ge thin film possesses, according to the X-ray diffraction measurements,
in plane texture, being epitaxial and aligned with the (111) Si substrate. The size distribution of the patterned Ge nanostructures
is narrow, as indicated by the atomic force microscopy and scanning electron microscopy measurements. We have obtained Ge
nanostructures with lateral dimension of 490 nm (height 12 nm), 200 nm (height 6 nm) and 82 nm (height 6 nm) by using different
sizes of polystyrene spheres. We have performed in depth studies of the Ge nanostructures’ behavior due to thermal and rapid
thermal post-annealing processes. FT micro-Raman spectroscopy shows that there is no Si intermixing during the annealing process.
In order to quantify the changes in the height and lateral dimension, we have performed atomic force microscopy and white
light interferometry analysis. The changes in shape and the decrease in the area of a cross-section of Ge nanostructure will
be discussed in respect to similar results shown in the literature for Ge thin films during the annealing process. 相似文献
78.
研究了三种掺Yb钒酸盐混晶Yb0.005:Y0.298Gd0.697VO4, Yb0.007:Y0.407Gd0.586VO4和Yb0.009:Y0.575Gd0.416VO4的室温偏振吸收谱和发射谱. 结果表明,最强的吸收和发射相应于π偏振,位
关键词:
掺Yb钒酸盐混晶
吸收谱和发射谱
激光振荡
偏振态 相似文献
79.
80.
In this paper we consider aggregate Malmquist productivity index measures which allow inputs to be reallocated within the group (when in output orientation). This merges the single period aggregation results allowing input reallocation of Nesterenko and Zelenyuk (2007) with the aggregate Malmquist productivity index results of Zelenyuk (2006) to determine aggregate Malmquist productivity indexes that are justified by economic theory, consistent with previous aggregation results, and which maintain analogous decompositions to the original measures. Such measures are of direct relevance to firms or countries who have merged (making input reallocation possible), allowing them to measure potential productivity gains and how these have been realised (or not) over time. 相似文献