全文获取类型
收费全文 | 314篇 |
免费 | 7篇 |
国内免费 | 5篇 |
专业分类
化学 | 204篇 |
力学 | 15篇 |
数学 | 47篇 |
物理学 | 60篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 1篇 |
2020年 | 5篇 |
2019年 | 7篇 |
2018年 | 6篇 |
2017年 | 3篇 |
2016年 | 11篇 |
2015年 | 6篇 |
2014年 | 11篇 |
2013年 | 13篇 |
2012年 | 14篇 |
2011年 | 25篇 |
2010年 | 8篇 |
2009年 | 14篇 |
2008年 | 29篇 |
2007年 | 23篇 |
2006年 | 23篇 |
2005年 | 19篇 |
2004年 | 14篇 |
2003年 | 6篇 |
2002年 | 12篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 6篇 |
1998年 | 8篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1965年 | 2篇 |
排序方式: 共有326条查询结果,搜索用时 15 毫秒
311.
Plastic-Adherent DNA Aptamer-Magnetic Bead and Quantum Dot Sandwich Assay for Campylobacter Detection 总被引:1,自引:0,他引:1
John G. Bruno Taylor Phillips Maria P. Carrillo Randy Crowell 《Journal of fluorescence》2009,19(3):427-435
DNA aptamers were developed against MgCl2-extracted surface proteins from Campylobacter jejuni. The two highest affinity aptamers were selected for use in a magnetic bead (MB) and red quantum dot (QD)-based sandwich
assay scheme. The assay was evaluated using both heat-killed and live C. jejuni and exhibits detection limits as low as an average of 2.5 colony forming unit (cfu) equivalents in buffer and 10–250 cfu
in various food matrices. The assay exhibits low cross-reactivity with bacterial species outside the Campylobacter genus, but exhibits substantial cross-reactivity with C. coli and C. lari. The assay was evaluated with a spectrofluorometer and a commercially available handheld fluorometer, which yielded comparable
detection limits and ranges. Remarkably, the sandwich assay components adhere to the inside face of polystyrene cuvettes even
in food matrices near neutral pH, thereby enabling a rapid homogeneous assay, because fluorescence is concentrated to a small,
thin planar area and background fluorescence from the bulk solution is minimized. The plastic cuvette-adherent technology
coupled to a sensitive handheld fluorometer may enable rapid (15–20 min), portable detection of foodborne pathogens from “farm-to-fork”
by obviating the slow enrichment culture phase used by other food safety tests. 相似文献
312.
PbTe colloidal nanocrystals: synthesis, characterization, and multiple exciton generation 总被引:1,自引:0,他引:1
Murphy JE Beard MC Norman AG Ahrenkiel SP Johnson JC Yu P Mićić OI Ellingson RJ Nozik AJ 《Journal of the American Chemical Society》2006,128(10):3241-3247
We report an alternative synthesis and the first optical characterization of colloidal PbTe nanocrystals (NCs). We have synthesized spherical PbTe NCs having a size distribution as low as 7%, ranging in diameter from 2.6 to 8.3 nm, with first exciton transitions tuned from 1009 to 2054 nm. The syntheses of colloidal cubic-like PbSe and PbTe NCs using a PbO "one-pot" approach are also reported. The photoluminescence quantum yield of PbTe spherical NCs was measured to be as high as 52 +/- 2%. We also report the first known observation of efficient multiple exciton generation (MEG) from single photons absorbed in PbTe NCs. Finally, we report calculated longitudinal and transverse Bohr radii for PbS, PbSe, and PbTe NCs to account for electronic band anisotropy. This is followed by a comparison of the differences in the electronic band structure and optical properties of these lead salts. 相似文献
313.
Declercq R Van Aerschot A Read RJ Herdewijn P Van Meervelt L 《Journal of the American Chemical Society》2002,124(6):928-933
A huge variety of chemically modified oligonucleotide derivatives has been synthesized for possible antisense applications. One such derivative, hexitol nucleic acid (HNA), is a DNA analogue containing the standard nucleoside bases, but with a phosphorylated 1',5'-anhydrohexitol backbone. Hexitol nucleic acids are some of the strongest hybridizing antisense compounds presently known, but HNA duplexes are even more stable. We present here the first high-resolution structure of a double helical nucleic acid with all sugars being hexitols. Although designed to have a restricted conformational flexibility, the hexitol oligomer h(GTGTACAC) is able to crystallize in two different double helical conformations. Both structures display a high x-displacement, normal Watson-Crick base pairing, similar base stacking patterns, and a very deep major groove together with a minor groove with increased hydrophobicity. One of the conformations displays a major groove which is wide enough to accommodate a second HNA double helix resulting in the formation of a double helix of HNA double helices. Both structures show most similarities with the A-type helical structure, the anhydrohexitol chair conformation thereby acting as a good mimic for the furanose C3'-endo conformation observed in RNA. As compared to the quasi-linear structure of homo-DNA, the axial position of the base in HNA allows efficient base stacking and hence double helix formation. 相似文献
314.
Paul C. Painter Richard E. Kessler Randy W. Snyder 《Journal of Polymer Science.Polymer Physics》1980,18(4):723-729
Infrared spectra of isotactic polystyrene gel films are observed to be significantly different from those of amorphous and crystalline polymer, indicating that the gel form is in a different conformation than the usual 31 helical crystal structure. Computer-assisted subtraction indicates that approximately 35% of the chains participate in the gel component, effectively ruling out structural defects as the origin of the ordered gel component. 相似文献
315.
316.
The need for a new avionic interconnection scheme that can provide superior performance, installability and maintainability as compared with copper has become evident. Fiber optics, which has been proposed for this role, is expected to improve environmental immunity, decrease system weight, and increase bandwidth. It has also been suggested that sensors based on fiber optics can offer significant advantages in aerospace applications. Realizing these advantages is a difficult challenge because mature sensing technologies have done a good job at reasonable cost. Furthermore, it has been demonstrated that a wide variety of aircraft electrical sensors can be addressed by a few standard interfaces. Therefore, future fiber optic sensor suites will also need to be interrogated through only a few standard interfaces, and standardization of the fiber optic sensor interface will be a primary issue in furthering fiber optic sensing technology for aerospace applications. This paper discusses the fiber optic sensor standardization process underway in the Avionic Systems Division of the Society of Automotive Engineers. 相似文献
317.
Randy A. Baadhio 《Communications in Mathematical Physics》1991,136(2):251-264
A new mechanism for the cancellation of gauge residue symmetries in the framework of heterotic superstring compactification theories is revealed. The model preserves all the string features and fits naturally in the consistent topological structure of the homogeneousCP
4 Calabi-Yau manifold. 相似文献
318.
Auditory discontinuities interact with categorization: implications for speech perception 总被引:2,自引:0,他引:2
Behavioral experiments with infants, adults, and nonhuman animals converge with neurophysiological findings to suggest that there is a discontinuity in auditory processing of stimulus components differing in onset time by about 20 ms. This discontinuity has been implicated as a basis for boundaries between speech categories distinguished by voice onset time (VOT). Here, it is investigated how this discontinuity interacts with the learning of novel perceptual categories. Adult listeners were trained to categorize nonspeech stimuli that mimicked certain temporal properties of VOT stimuli. One group of listeners learned categories with a boundary coincident with the perceptual discontinuity. Another group learned categories defined such that the perceptual discontinuity fell within a category. Listeners in the latter group required significantly more experience to reach criterion categorization performance. Evidence of interactions between the perceptual discontinuity and the learned categories extended to generalization tests as well. It has been hypothesized that languages make use of perceptual discontinuities to promote distinctiveness among sounds within a language inventory. The present data suggest that discontinuities interact with category learning. As such, "learnability" may play a predictive role in selection of language sound inventories. 相似文献
319.
Randy McCarthy 《Transactions of the American Mathematical Society》2001,353(6):2371-2390
We compute the stabilization of functors from exact categories to abelian groups derived from -fold tensor products. Rationally, this gives a new computation for the relative algebraic -theory of dual numbers.
320.