全文获取类型
收费全文 | 540篇 |
免费 | 7篇 |
国内免费 | 4篇 |
专业分类
化学 | 324篇 |
晶体学 | 1篇 |
力学 | 27篇 |
数学 | 45篇 |
物理学 | 154篇 |
出版年
2020年 | 4篇 |
2019年 | 5篇 |
2018年 | 6篇 |
2016年 | 5篇 |
2015年 | 5篇 |
2014年 | 16篇 |
2013年 | 19篇 |
2012年 | 22篇 |
2011年 | 21篇 |
2010年 | 14篇 |
2009年 | 9篇 |
2008年 | 23篇 |
2007年 | 25篇 |
2006年 | 33篇 |
2005年 | 21篇 |
2004年 | 23篇 |
2003年 | 17篇 |
2002年 | 12篇 |
2001年 | 9篇 |
2000年 | 15篇 |
1999年 | 5篇 |
1998年 | 12篇 |
1997年 | 4篇 |
1996年 | 15篇 |
1995年 | 5篇 |
1994年 | 10篇 |
1993年 | 7篇 |
1992年 | 8篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1987年 | 4篇 |
1985年 | 13篇 |
1984年 | 5篇 |
1983年 | 8篇 |
1982年 | 11篇 |
1981年 | 9篇 |
1980年 | 13篇 |
1979年 | 9篇 |
1978年 | 17篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1975年 | 8篇 |
1973年 | 7篇 |
1970年 | 4篇 |
1969年 | 4篇 |
1968年 | 4篇 |
1967年 | 4篇 |
1966年 | 4篇 |
1938年 | 3篇 |
1870年 | 4篇 |
排序方式: 共有551条查询结果,搜索用时 46 毫秒
1.
International Intercomparison of Solar UVR Spectral Measurement Systems in Melbourne in 2013 下载免费PDF全文
Peter Gies Rebecca Hooke Richard McKenzie John O'Hagan Stuart Henderson Andy Pearson Marina Khazova John Javorniczky Kerryn King Matt Tully Michael Kotkamp Bruce Forgan Stephen Rhodes 《Photochemistry and photobiology》2015,91(5):1237-1246
Monitoring ambient solar UVR levels provides information on how much there is in both real time and historically. Quality assurance of ambient measurements of solar UVR is critical to ensuring accuracy and stability and this can be achieved by regular intercomparisons of spectral measurement systems with those of other organizations. In October and November of 2013 a solar UVR spectroradiometer from Public Health England (PHE) was brought to Melbourne for a campaign of intercomparisons with a new Bentham spectrometer of Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) and one at the Australian Bureau of Meteorology (BOM), supported by New Zealand's National Institute for Water and Atmosphere (NIWA). Given all three spectroradiometers have calibrations that are traceable to various national standards, the intercomparison provides a chance to determine measurement uncertainties and traceability that support UV measurement networks in Australia, New Zealand and the UK. UV Index measurements from all three systems were compared and ratios determined for clear sky conditions when the scans from each instrument were within 2 min of each other. While wavelengths below 305 nm showed substantial differences between the PHE unit and the two other systems, overall the intercomparison results were encouraging, with mean differences in measured UV Index between the BOM/NIWA and those of PHE and ARPANSA of <0.1% and 7.5%, respectively. 相似文献
2.
Dev Raj Chopra Justin Seth Pearson Darius Durant Ritesh Bhakta Anil R. Chourasia 《Surface and interface analysis : SIA》2019,51(2):246-253
The Ti/CuO interface has been studied by the techniques of X-ray photoelectron spectroscopy and atomic force microscopy. Thin films of titanium were deposited on a CuO substrate at room temperature by the e-beam technique. The photoelectron spectra of titanium and copper were found to exhibit significant chemical interaction at the interface. The titanium overlayer was observed to get oxidized to TiO2, while the CuO was observed to get reduced to elemental copper. This chemical interaction was observed to occur until a thickness of 7 nm of the titanium overlayer. For thicknesses greater than this value, the presence of unreacted titanium in the sample was detected. Barrier characteristics at the Ti/CuO interface were also carried out for substrate temperatures of 300°C, 400°C, 500°C, and 600°C as a function of the titanium overlayer thickness. A linear trend in the barrier thickness of the overlayer was observed between 400°C and 600°C substrate temperatures. The atomic force microscopy micrographs of the unannealed samples depicted layer-by-layer growth of elemental titanium on copper. At the Ti/CuO interface in such samples, the micrographs exhibited island formation of TiO2 corresponding to the Volmer-Weber growth model. This formation has been interpreted as the relaxation in the strain energy. The percentage coverage of the underlying substrate by the TiO2 islands showed a linear trend for the thicknesses of the titanium overlayer investigated. The average size of these islands also showed a linear trend as a function of the thickness of the overlayer. 相似文献
3.
We study both H and E/Z-eigenvalues of the adjacency tensor of a uniform multi-hypergraph and give conditions for which the largest positive H or Z-eigenvalue corresponds to a strictly positive eigenvector. We also investigate when the E-spectrum of the adjacency tensor is symmetric. 相似文献
4.
S. Aubin J. A. Behr R. Collister V. V. Flambaum E. Gomez G. Gwinner K. P. Jackson D. Melconian L. A. Orozco M. R. Pearson D. Sheng G. D. Sprouse M. Tandecki J. Zhang Y. Zhao 《Hyperfine Interactions》2013,214(1-3):163-171
We present a method for measuring the nuclear anapole in a string of francium isotopes. The anapole is a parity non-conserving electromagnetic moment that enables parity-forbidden transitions between ground state hyperfine levels of an atom. The experiment is run by the FrPNC collaboration and relies on a beam of artificially-produced francium from the ISAC facility at TRIUMF. 相似文献
5.
6.
Meredith J Layton Mirette Saad Nicole L Church Richard B Pearson Christina A Mitchell Wayne A Phillips 《BMC biochemistry》2012,13(1):1-9
Background
Hyaluronan (HA) is made at the plasma membrane and secreted into the extracellular medium or matrix by phospolipid-dependent hyaluronan synthase (HAS), which is active as a monomer. Since the mechanism by which HA is translocated across membranes is still unresolved, we assessed the presence of an intraprotein pore within HAS by adding purified Streptococcus equisimilis HAS (SeHAS) to liposomes preloaded with the fluorophore Cascade Blue (CB).Results
CB translocation (efflux) was not observed with mock-purified material from empty vector control E. coli membranes, but was induced by SeHAS, purified from membranes, in a time- and dose-dependent manner. CB efflux was eliminated or greatly reduced when purified SeHAS was first treated under conditions that inhibit enzyme activity: heating, oxidization or cysteine modification with N-ethylmaleimide. Reduced CB efflux also occurred with SeHAS K48E or K48F mutants, in which alteration of K48 within membrane domain 2 causes decreased activity and HA product size. The above results used liposomes containing bovine cardiolipin (BCL). An earlier study testing many synthetic lipids found that the best activating lipid for SeHAS is tetraoleoyl cardiolipin (TO-CL) and that, in contrast, tetramyristoyl cardiolipin (TM-CL) is an inactivating lipid (Weigel et al, J. Biol. Chem. 281, 36542, 2006). Consistent with the effects of these CL species on SeHAS activity, CB efflux was more than 2-fold greater in liposomes made with TO-CL compared to TM-CL.Conclusions
The results indicate the presence of an intraprotein pore in HAS and support a model in which HA is translocated to the exterior by HAS itself. 相似文献7.
A concise synthesis of 4,5-epi-11-hydroxy-saxitoxinol utilizing d-ribose to direct an asymmetric Mannich reaction. This approach allows many modes of reactivity, which can be used to access various analogs of saxitoxin. 相似文献
8.
9.
Polymeric versions of deacetylated auranofin, a gold complex with a sugar ligand, were prepared by post-modifying RAFT glycopolymers. Micellisation of a block copolymer containing pendant Au(I) units produced nanoparticles with an increased anti-proliferative effect against OVCAR-3 human ovarian carcinoma cells. 相似文献
10.
We report an NMR experimental realization of a rapid quantum deletion algorithm that deletes marked states in an unsorted database.Unlike classical deletion,where search and deletion are equivalent,quantum deletion can be implemented with only a single query,which achieves exponential speed-up compared to the optimal classical analog.In the experimental realization,the GRAPE algorithm was used to obtain an optimized NMR pulse sequence,and the efficient method of maximum-likelihood has been used to reconstruct the experimental output state. 相似文献