全文获取类型
收费全文 | 443篇 |
免费 | 3篇 |
专业分类
化学 | 278篇 |
晶体学 | 10篇 |
力学 | 3篇 |
数学 | 65篇 |
物理学 | 90篇 |
出版年
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 2篇 |
2019年 | 3篇 |
2018年 | 6篇 |
2017年 | 8篇 |
2016年 | 4篇 |
2015年 | 6篇 |
2014年 | 4篇 |
2013年 | 16篇 |
2012年 | 22篇 |
2011年 | 20篇 |
2010年 | 9篇 |
2009年 | 6篇 |
2008年 | 23篇 |
2007年 | 20篇 |
2006年 | 20篇 |
2005年 | 24篇 |
2004年 | 15篇 |
2003年 | 11篇 |
2002年 | 13篇 |
1999年 | 8篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1994年 | 2篇 |
1992年 | 3篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 8篇 |
1984年 | 14篇 |
1983年 | 15篇 |
1982年 | 7篇 |
1981年 | 9篇 |
1980年 | 12篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1977年 | 17篇 |
1976年 | 6篇 |
1975年 | 8篇 |
1974年 | 7篇 |
1973年 | 14篇 |
1971年 | 8篇 |
1970年 | 5篇 |
1969年 | 7篇 |
1967年 | 3篇 |
1909年 | 2篇 |
1882年 | 2篇 |
排序方式: 共有446条查询结果,搜索用时 15 毫秒
441.
A sub-model of multivariate regular variation called hidden regular variation facilitates more accurate estimation of joint tail probabilities in the presence of asymptotic independence. A related concept called hidden domain of attraction can sometimes offer similar estimation assistance in circumstances where hidden regular variation is absent. Examples and discussion illustrate strengths and limitations of this concept. We outline estimation techniques where applicable. 相似文献
442.
Freitas Neto ES Dantas NO Lourenço SA 《Physical chemistry chemical physics : PCCP》2012,14(4):1493-1501
Optical absorption (OA), magnetic force microscopy (MFM), and photoluminescence (PL) measurements were employed to study Cd(1-x)Mn(x)S nanoparticles (NPs), grown in a glass matrix, at different x-concentrations. The formation of two well defined groups of NPs with different sizes was detected by OA spectra at room temperature and confirmed by MFM images, from which they were identified as quantum dots (QDs) and bulk-like nanocrystals (NCs). Emissions from luminescent states were observed in the temperature dependent PL spectra of both groups of NPs, including those from deep defects which were attributed to the presence of divacancies (V(Cd)-V(S)) in the hexagonal wurtzite structure. Furthermore, we have come up with a model based on rate equations that describes energy transfers involving the excitonic states of QDs, the conduction band of bulk-like NCs, and the shallow virtual levels of NPs. This model was used to fit the integrated PL intensity of the corresponding NP groups, and a good agreement between them confirms that the model suitably describes the temperature dependent carrier dynamics of Cd(1-x)Mn(x)S NPs. 相似文献
443.
Extremes - Reciprocity characterizes the information exchange between users in a network, and some empirical studies have revealed that social networks have a high proportion of reciprocal edges.... 相似文献
444.
Dr. Shruti Trivedi Sidney G. Coombs Durgesh V. Wagle Nakara Bhawawet Prof. Gary A. Baker Prof. Frank V. Bright 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(33):11677-11684
To develop ionic liquid/porous silicon (IL/pSi) microarrays we have contact pin‐printed 20 hydrophobic and hydrophilic ionic liquids onto as‐prepared, hydrogen‐passivated porous silicon (ap‐pSi) and then determined the individual IL spot size, shape and associated pSi surface chemistry. The results reveal that the hydrophobic ionic liquids oxidize the ap‐pSi slightly. In contrast, the hydrophilic ionic liquids lead to heavily oxidized pSi (i.e., ox‐pSi). The strong oxidation arises from residual water within the hydrophilic ILs that is delivered from these ILs into the ap‐pSi matrix causing oxidation. This phenomenon is less of an issue in the hydrophobic ILs because their water solubility is substantially lower. 相似文献
445.
William J. Bailey Paul Y. Chen Shuh-Cheng Chen Wen-Bin Chiao Takeshi Endo Benjamin Gapud Vijaya Kuruganti Yin-Nian Lin Zhende Ni Cai-Yuan Pan Scott E. Shaffer Luann Sidney Shang-Ren Wu Noboru Yamamoto Noboro Yamazaki Kazuya Yonezawa Lin-Lin Zhou 《Macromolecular Symposia》1986,6(1):81-100
Since a carbon-oxygen double bond is considerably more stable than a carbon-carbon double bond, it has been possible to use this driving force to promote free radical ring-opening polymerization of unsaturated heterocyclic compounds. This process, for the first time, has permitted the introduction of functional groups, such as esters, amides and carbonates, into the backbone of addition polymers. Hydrolysis of the copolymers with common monomers produced oligomers capped with hydroxyl, amino or carboxylic acid groups. The presence of an ester group in a copolymer, such as in a copolymer of ethylene, render the copolymer biodegradable. 相似文献
446.
Lori Manoukian Robin S. Stein José A. Correa Dominic Frigon Sidney Omelon 《Electrophoresis》2023,44(15-16):1197-1205
Polyacrylamide gel electrophoresis is commonly used to characterize the chain length of polyphosphates (polyP), more generally called condensed phosphates. After separation, nonradioactive, optical polyP staining is limited to chain lengths greater than 15 monomers with toluidine blue or 4′,6-diamidino-2-phenylindole. PolyP chain lengths longer than 62monomers were correlated to the shortest DNA ladders. In this study, synthetic linear polyPs (Sigma-Aldrich “Type 45”, estimated mean length of 45 monomers), trimetaphosphate (trimetaP: 3 ring), tripolyphosphate (tripolyP), pyrophosphate (PPi), and inorganic orthophosphate (o-Pi) were visualized after separation by an in situ hydrolytic degradation process to o-Pi that was subsequently stained with methyl green. Statistically insignificant migration reduction of synthetic short-chain polyP after perchloric acid or phenol–chloroform extraction was confirmed with the Friedman test. 31P diffusion–ordered NMR spectroscopy confirmed that extraction also reduced PPi diffusivity by <10%. Linear regression between the Rf peak migration value and the logarithm of synthetic polyP molecular weights enabled estimation of extracted polyP chain lengths from 2 to 45 monomers. Linear polyP extracts from Saccharomyces cerevisiae grown in aerobic conditions were generally shorter than extracts cultured in anaerobic conditions. Extractions from both aerobic and anaerobic S. cerevisiae included tripolyP and o-Pi, but no PPi. 相似文献