全文获取类型
收费全文 | 539篇 |
免费 | 22篇 |
国内免费 | 2篇 |
专业分类
化学 | 280篇 |
晶体学 | 8篇 |
力学 | 7篇 |
数学 | 133篇 |
物理学 | 135篇 |
出版年
2024年 | 2篇 |
2023年 | 7篇 |
2022年 | 3篇 |
2021年 | 23篇 |
2020年 | 13篇 |
2019年 | 16篇 |
2018年 | 12篇 |
2017年 | 11篇 |
2016年 | 33篇 |
2015年 | 19篇 |
2014年 | 31篇 |
2013年 | 67篇 |
2012年 | 26篇 |
2011年 | 27篇 |
2010年 | 37篇 |
2009年 | 18篇 |
2008年 | 19篇 |
2007年 | 13篇 |
2006年 | 14篇 |
2005年 | 8篇 |
2004年 | 8篇 |
2003年 | 7篇 |
2002年 | 5篇 |
2001年 | 9篇 |
2000年 | 4篇 |
1999年 | 7篇 |
1998年 | 3篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 10篇 |
1994年 | 4篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1990年 | 7篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 13篇 |
1984年 | 2篇 |
1982年 | 5篇 |
1981年 | 9篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 7篇 |
1973年 | 3篇 |
1961年 | 2篇 |
1913年 | 2篇 |
1909年 | 2篇 |
排序方式: 共有563条查询结果,搜索用时 15 毫秒
91.
Marian Żenkiewicz Józef Richert Piotr Rytlewski Krzysztof Moraczewski Magdalena Stepczyńska Tomasz Karasiewicz 《Polymer Testing》2009,28(4):412-418
The effect of multiple (up to 10 times) extrusion of polylactide on its mechanical properties (determined by a static tension test), Charpy impact strength, melt flow rate, phase transition temperatures, degradation temperature, and permeability of water vapour and oxygen is presented. It was found that, with raising the number of the extrusion cycles, the tensile strength at break slightly diminished and the impact strength clearly decreased, while the melt flow rate and water vapour and oxygen transmission rates steadily increased. Variation of the number of extrusion cycles did not affect the glass transition temperature, whereas it did cause a lowering of the cold crystallisation temperature and slight diminishing of the melting point. The presented results indicate that PLA technological waste is suitable to be reused as an additive to a neat polymer. 相似文献
92.
Synthesis of siloxy-modified second generation Hoveyda-Grubbs catalysts and their catalytic activity
Szymon Rogalski 《Journal of organometallic chemistry》2009,694(24):3918-5077
Efficient syntheses of the first ruthenium alkylidene complexes bearing siloxide ligands are described. Second generation Hoveyda-Grubbs catalyst is shown to undergo efficient functionalization with a number of potassium silanolates to give disiloxy derivatives. The complexes obtained are found catalytically active in selected metathesis transformations. 相似文献
93.
Szymon Godlewski Grzegorz Goryl Andre Gourdon Dr. Jacek J. Kolodziej Dr. Bartosz Such Dr. Marek Szymonski Prof. Dr. 《Chemphyschem》2009,10(12):2026-2033
The adsorption of individual Violet Lander molecules self‐assembled on the c(8×2) reconstructed InSb(001) surface in its native form and on the surface passivated with one to three monolayers of KBr is investigated by means of low‐temperature scanning tunneling microscopy (STM). Preferred adsorption sites of the molecules are found on flat terraces as well as at atomic step edges. For molecules immobilized on flat terraces, several different conformations are identified from STM images acquired with submolecular resolution and are explained by the rotation of the 3,5‐di‐tert‐butylphenyl groups around σ bonds, which allows adjustment of the molecular geometry to the anisotropic substrate structure. Formation of ordered molecular chains is found at steps running along substrate reconstruction rows, whereas at the steps oriented perpendicularly no intermolecular ordering is recorded. It is also shown that the molecules deposited at two or more monolayers of the epitaxial KBr spacer do not have any stable adsorption sites recorded with STM. Prospects for the manipulation of single molecules by using the STM tip on highly anisotropic substrates are also explored, and demonstrate the feasibility of controlled lateral displacement in all directions. 相似文献
94.
The paper presents a process of technical diagnostic applied to a fleet of vehicles utilized in the delivery system of express mail. It is focused on evaluation of diagnostic capacity of particular characteristics, reduction of a set of initially selected characteristics to a minimal and satisfactory subset, recognition of a technical condition of vehicles resulting in their condition-based classification. In addition, the decision rules facilitating technical diagnostic and management of a fleet of vehicles are generated and utilized. N-fold cross validation is applied to estimate the efficiency of the decision rules. The rough set theory is applied to support the diagnostic process of vehicles. Classical rough set (CRS) theory is compared with the dominance-based rough set (DRS) approach. The results of computational experiments for both approaches are compared. 相似文献
95.
Average-optimal string matching 总被引:2,自引:0,他引:2
The exact string matching problem is to find the occurrences of a pattern of length m from a text of length n symbols. We develop a novel and unorthodox filtering technique for this problem. Our method is based on transforming the problem into multiple matching of carefully chosen pattern subsequences. While this is seemingly more difficult than the original problem, we show that the idea leads to very simple algorithms that are optimal on average. We then show how our basic method can be used to solve multiple string matching as well as several approximate matching problems in average optimal time. The general method can be applied to many existing string matching algorithms. Our experimental results show that the algorithms perform very well in practice. 相似文献
96.
ABSTRACTA broad-frequency dielectric spectroscopy (100 Hz to 10 MHz) was used to investigate newly synthesized fluorinated compound. This compound exhibits a wide-temperature ferroelectric phase. Due to the fact that the compound does not crystallize at temperatures available in our DSC equipment, additional measurements were done at the very low temperatures (down to ?100 °C) to find the crystallization temperature. Finally, we did not manage to crystallize the investigated compound. Compound under studies seems to be overcooled. Observed dielectric modes are described and their parameters are shown in this paper. Additionally, DC field influence on dielectric response is shown and analyzed here. Both modes observed at the low temperature are recognized as the molecular ones. 相似文献
97.
Sodium hexafluorophosphate, perchlorate and tetrafluoroborate were applied as the ion‐pair reagents in reversed‐phase chromatography of several imidazolium‐based ionic liquids. The optimization of the retention was performed by changing the kind of organic modifier (methanol, acetonitrile), concentration and the kind of the ion‐pair reagents in the mobile phase and the column kind (Zorbax SB‐C18, Zorbax SB‐Phenyl, Zorbax SB‐CN, Zorbax SB‐NH2 and Supelcosil LC‐F). The selectivity of the proposed chromatographic systems according to the cation kind was compared on the basis of the resolution of ionic liquid mixture. The perturbation method was applied to identify the anion kind. The formation of ion‐associated complexes between promethazine as counter‐cation and chaotropic anions controlling their retention was confirmed. 相似文献
98.
K. Bodek J. Golak L. Jarczyk St. Kistryn J. Kuroś-Żołnierczuk J. Lang A. Micherdzińska R. Skibiński J. Smyrski M. Sokołowski J. Sromicki A. Strzałkowski H. Witała J. Zejma W. Zipper 《Few-Body Systems》2001,30(1-2):65-79
Cross sections and vector-analyzing powers for four unspecific configurations of the 2H(p,pp)n breakup reaction at E
lab
p
= 65MeV were measured in a kinematically complete experiment. Measured observables are compared with rigorous Faddeev calculations
using four realistic charge-dependent interaction models, the CD Bonn, Argonne v
18, Nijmegen I, and Nijmegen II potentials with or without inclusion of the Tucson-Melbourne three-nucleon force. Coulomb effects
are completely omitted. A satisfactory agreement between theory and experiment has been found. There exist, however, some
discrepancies between measured and calculated analyzing-power distributions in certain kinematical regions. The effects of
the Tucson-Melbourne three-body force are either negligible or slightly increasing the disagreement.
Received May 12, 1999; revised March 3, 2000; accepted for publication April 26, 2000 相似文献
99.
β-sialon ceramics sintered with yttria additives have been studied with the use of an electron probe X-ray analysis (EPMA).
Sialon ceramics were prepared from a carbothermally derived β-sialon powder and then sintered in a nitrogen atmosphere with
yttria admixture. The above process was followed by annealing in flowing nitrogen. Scanning electron microscope (SEM) observations
have shown that the sintered material contains a glassy phase (Y-Si-Al-O-N) on the grain boundaries. X-ray diffraction (XRD)
after annealing in nitrogen revealed the presence of a considerable amount of yttrium aluminium garnet (YAG). The higher voltage
of 30 kV was used in order to excite the yttrium Kα radiation (14.96 keV) at an appropriate overvoltage ratio because in some phases of the material, the disappearance of the
yttrium Lα line has been observed during EPMA examination at an accelerating voltage of 15 kV in energy dispersive spectra (EDS). The
intensity of the yttrium Kα line was sufficiently high, while the Y Lα line was not seen in the ED spectrum. Because the position of the yttrium Lα line (1.922 keV) is very close to the Si (K) absorption edge (1.84 keV), the strong absorption at this edge is probably responsible
for the effect. This result should be considered as a serious warning in the case of EPMA (EDS) studies on compounds or mixtures
suspected to contain both silicon and yttrium, because at electrons energies lower than 15 keV, the presence of yttrium in
materials can go unnoticed. In wavelength dispersive spectra (WDS) obtained at 15 keV the intensity of the yttrium Lα line was also very low but measurable. 相似文献
100.
We study nonlinear wave and heat equations on ℝ
d
driven by a spatially homogeneous Wiener process. For the wave equation we consider the cases of d = 1, 2, 3. The heat equation is considered on an arbitrary ℝ
d
-space. We give necessary and sufficient conditions for the existence of a function-valued solution in terms of the covariance
kernel of the noise.
Received: 1 April 1998 / Revised version: 23 June 1999 / Published online: 7 February 2000 相似文献