全文获取类型
收费全文 | 1029篇 |
免费 | 20篇 |
国内免费 | 1篇 |
专业分类
化学 | 652篇 |
晶体学 | 13篇 |
力学 | 51篇 |
数学 | 35篇 |
物理学 | 299篇 |
出版年
2021年 | 9篇 |
2020年 | 5篇 |
2019年 | 6篇 |
2018年 | 5篇 |
2017年 | 9篇 |
2016年 | 15篇 |
2015年 | 11篇 |
2014年 | 14篇 |
2013年 | 58篇 |
2012年 | 50篇 |
2011年 | 46篇 |
2010年 | 34篇 |
2009年 | 30篇 |
2008年 | 44篇 |
2007年 | 41篇 |
2006年 | 43篇 |
2005年 | 37篇 |
2004年 | 43篇 |
2003年 | 42篇 |
2002年 | 31篇 |
2001年 | 27篇 |
2000年 | 27篇 |
1999年 | 20篇 |
1998年 | 11篇 |
1997年 | 14篇 |
1996年 | 12篇 |
1995年 | 14篇 |
1994年 | 18篇 |
1993年 | 26篇 |
1992年 | 24篇 |
1991年 | 23篇 |
1990年 | 17篇 |
1989年 | 15篇 |
1988年 | 18篇 |
1987年 | 13篇 |
1986年 | 11篇 |
1985年 | 18篇 |
1984年 | 32篇 |
1983年 | 11篇 |
1982年 | 16篇 |
1981年 | 15篇 |
1980年 | 12篇 |
1979年 | 8篇 |
1978年 | 12篇 |
1977年 | 13篇 |
1976年 | 6篇 |
1975年 | 6篇 |
1974年 | 9篇 |
1973年 | 6篇 |
1970年 | 4篇 |
排序方式: 共有1050条查询结果,搜索用时 15 毫秒
141.
Seven organic dyes were adsorbed on photoconductive zinc oxide powder and their sensitizing efficiencies were examined. The adsorption of dye induced a change in the dark conductivity, the magnitude of which appeared to represent the sensitizing power of the dye. The initial slope of sensitized photocurrent was found to be an exponential function of σ0, the pre-exponential factor in the conductivity equation. A model is proposed, which is consistent with all the observations. In this model, the sensitized photoinjection of electrons is assumed to occur from surface states to the bulk, depending upon the population of the surface states. A critical surface level for the spectral sensitization is introduced to account for the observed temperature effect. Surface states located below the critical energy are assumed not to contribute for the sensitization. 相似文献
142.
143.
144.
The addition of 1,10-phenanthroline improves both the extraction and the spectrophotometric sensitivity of the determination of cadmium with diphenylcarbazone. Slope analysis suggests the formation of a 1:2:2 extracted species. The molar absorptivity is 9.4 × 104 l cm-1 mol-1 at 536 nm and extraction is maximal at pH 8.2–9.8. Extraction is rapid and absorbances remain constant at room temperature for 48 h. Various divalent metal ions interfere. 相似文献
145.
Yu?Nakayama 《Journal of High Energy Physics》2010,2010(4):102
We investigate universal time-dependent exact deformations of Schrödinger geometry. We present 1) scale invariant but non-conformal deformation, 2) non-conformal but scale invariant deformation, and 3) both scale and conformal invariant deformation. All these solutions are universal in the sense that we could embed them in any supergravity constructions of the Schrödinger invariant geometry. We give a field theory interpretation of our time-dependent solutions. In particular, we argue that any time-dependent chemical potential can be treated exactly in our gravity dual approach. 相似文献
146.
The role of the In/Si(111)-(4 x 1)-In surface as an atomic-scale geometrical template for the growth of Ag thin films is clarified by scanning tunneling microscopy and low energy electron diffraction. Low-temperature grown Ag films are found to have stripe structures with a transverse periodicity equal to that of indium chains of the In/Si(111)-(4 x 1)-In. The stripes exhibit a structural transformation at the thickness of 6 monolayers (ML); this relaxation allows the stripes to persist up to a thickness as large as 30 ML (approximately = 7 nm) while maintaining their mean periodicity. We attribute this stability to a coincidental matching of the periodicity and the corrugation amplitude between the Ag film and the substrate, which is realized by periodic insertion of stacking faults into a Ag fcc crystal. 相似文献
147.
Nakayama T Kurosawa Y Furui S Kerman K Kobayashi M Rao SR Yonezawa Y Nakano K Hino A Yamamura S Takamura Y Tamiya E 《Analytical and bioanalytical chemistry》2006,386(5):1327-1333
Polymerase chain reaction (PCR) is an essential part of research based on genomics or cell analysis. The development of a
microfluidic device that would be suitable for high-temperature-based reactions therefore becomes an important contribution
towards the integration of micro-total analysis systems (μTAS). However, problems associated with the generation of air bubbles
in the microchannels before the introduction of the assay liquid, which we call the “initial start-up” in this study, made
the flow irregular and unstable. In this report, we have tried to address these problems by adapting a novel liquid-flow method
for high-temperature-based reactions. A PDMS-based microfluidic device was fabricated by soft-lithography techniques and placed
on a cartridge heater. The generation of the air bubbles was prevented by introducing the fluorinated oil, an inert and highly
viscous liquid, as the cap just before the introduction of the sample solutions into the microchannels. The technique was
applied for continuous-flow PCR, which could perform PCR on-chip in a microfluidic system. For the evaluation of practical
accuracy, plasmid DNA that serves as a reference molecule for the quantification of genetically modified (GM) maize was used
as the template DNA for continuous-flow PCR. After PCR, the products were collected in a vial and analyzed by gel electrophoresis
to confirm the accuracy of the results. Additionally, quantitative continuous-flow PCR was performed using TaqMan technology
on our PCR device. A laser detection system was also used for the quantitative PCR method. We observed a linear relationship
between the threshold cycle (Ct) and the initial DNA concentration. These results showed that it would be possible to quantify
the initial copies of the template DNA on our microfluidic device. Accurate quantitative DNA analysis in microfluidic systems
is required for the integration of PCR with μTAS, thus we anticipate that our device would have promising potential for applications
in a wide range of research. 相似文献
148.
Hisahiro Nakayama Jiro Kasahara Akiko Matsuo Ikkoh Funaki 《Proceedings of the Combustion Institute》2013,34(2):1939-1947
The propagation of curved detonation waves of gaseous explosives stabilized in rectangular-cross-section curved channels is investigated. Three types of stoichiometric test gases, C2H4 + 3O2, 2H2 + O2, and 2C2H2 + 5O2 + 7Ar, are evaluated. The ratio of the inner radius of the curved channel (ri) to the normal detonation cell width (λ) is an important factor in stabilizing curved detonation waves. The lower boundary of stabilization is around ri/λ = 23, regardless of the test gas. The stabilized curved detonation waves eventually attain a specific curved shape as they propagate through the curved channels. The specific curved shapes of stabilized curved detonation waves are approximately formulated, and the normal detonation velocity (Dn)?curvature (κ) relations are evaluated. The Dn nondimensionalized by the Chapman–Jouguet (CJ) detonation velocity (DCJ) is a function of the κ nondimensionalized by λ. The Dn/DCJ?λκ relation does not depend on the type of test gas. The propagation behavior of the stabilized curved detonation waves is controlled by the Dn/DCJ?λκ relation. Due to this propagation characteristic, the fully-developed, stabilized curved detonation waves propagate through the curved channels while maintaining a specific curved shape with a constant angular velocity. Self-similarity is seen in the front shock shapes of the stabilized curved detonation waves with the same ri/λ, regardless of the curved channel and test gas. 相似文献
149.
Tone Takahashi Hideki Tomita Motoi Nakayama Yoshitaka Adachi Volker Sonnenschein Tetsuo Iguchi Klaus Wendt 《Hyperfine Interactions》2013,218(1-3):133-138
2D coordination polymer iron(II) spin crossover complexes containing 3,5-lutidine with host framework Fe(3,5-lutidine)2Ni(CN)4were synthesized. Their spin crossover properties were studied by temperature dependent 57Fe Mössbauer spectroscopy. Materials show gradual incomplete spin crossover with distinct thermochromism, while only 25 % of iron(II) ions are switched to the low spin state at 80 K, as determined by a detailed 57Fe Mössbauer study. 相似文献
150.
We have investigated the quantum-statistics behavior of the exciton-biexciton system from the photoluminescence properties in (GaAs) m /(AlAs) m type-II superlattices with m = 12 and 13 monolayers, where the lowest-energy type-II exciton consists of the n = 1 X electron of AlAs and n = 1 o heavy hole of GaAs. The long exciton lifetime of the order of w s due to the indirect transition nature enables us to obtain precisely the density relation between the exciton and biexciton from the line-shape analysis of time-resolved photoluminescence spectra. In a relatively low exciton-density region, the biexciton density obeys a well-known square law. At an exciton density around 1 2 10 10 cm m 2 , the biexciton density suddenly increases with a threshold-like nature. This behavior, which is realized at a bath temperature up to 8 K under an excitation power of the order of 100 mW/cm 2 , results from the characteristics of Bose-Einstein statistics of the exciton-biexciton system. 相似文献