全文获取类型
收费全文 | 266篇 |
免费 | 7篇 |
专业分类
化学 | 208篇 |
晶体学 | 4篇 |
力学 | 7篇 |
数学 | 19篇 |
物理学 | 35篇 |
出版年
2022年 | 4篇 |
2021年 | 4篇 |
2017年 | 5篇 |
2016年 | 4篇 |
2015年 | 8篇 |
2014年 | 2篇 |
2013年 | 11篇 |
2012年 | 15篇 |
2011年 | 12篇 |
2010年 | 8篇 |
2009年 | 11篇 |
2008年 | 14篇 |
2007年 | 12篇 |
2006年 | 12篇 |
2005年 | 10篇 |
2004年 | 4篇 |
2003年 | 5篇 |
2002年 | 7篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 8篇 |
1990年 | 7篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1971年 | 2篇 |
1969年 | 3篇 |
1963年 | 2篇 |
1936年 | 3篇 |
1928年 | 3篇 |
1877年 | 2篇 |
排序方式: 共有273条查询结果,搜索用时 46 毫秒
141.
A strategy for the stepwise annulation of pyrrolic rings of a porphyrin to imidazole rings is presented. Mono(imidazole), Janus and corner bis(imidazole), T-shaped tris(imidazole), and tetrakis(imidazole) porphyrins have been synthesized and characterized. 相似文献
142.
Colorectal cancer (CRC) is the second most common cause of cancer-related deaths worldwide with an annual incidence of almost a million cases and an annual mortality around 500,000. The fecal occult blood test is currently the first line method for CRC screening, but has unacceptably low sensitivity and specificity. Improved screening tests are therefore urgently required for early-stage CRC screening when therapy is most likely to be effective. We describe a discovery-based proteomics hypothesis using orthogonal multi-dimensional fractionation (1-D SDS-PAGE, RP-HPLC, size exclusion chromatography) to mine deep into the fecal proteome for the initial discovery process, which generated a library containing 108 human fecal proteins with the associated peptide and MS/MS data. These data were then used to develop and optimize a multiplex multiple reaction monitoring assay for 40 non-redundant human proteins present in the feces. To show proof of principal for clinical analysis, multiplex screening of these 40 proteins was carried out on fecal samples from eight CRC patient and seven normal volunteers. We identified 24 proteins consistently found in all samples and nine proteins found only in the CRC patients, showing the potential of this approach for the analysis of potential CRC biomarkers. Absolute quantitation using C-terminal isotopically labeled synthetic peptides corresponding to hemoglobin and carcinoembryonic antigen 5 was also performed. 相似文献
143.
Kadda Medjoubi Nicolas Leclercq Florent Langlois Alain Buteau Stephane Lé Stéphane Poirier Pascal Mercère Marie Catherine Sforna Cameron M. Kewish Andréa Somogyi 《Journal of synchrotron radiation》2013,20(2):293-299
A distributed fast‐acquisition system for synchronized multi‐technique experiments is presented, in which the collection of metadata and the asynchronous merging of large data volumes from multiple detectors are managed as part of the data collection process. This fast continuous scanning scheme, named FLYSCAN, enables measurement of microscopy data on a timescale of milliseconds per pixel. Proof‐of‐principle multi‐technique experiments, namely scanning X‐ray fluorescence spectrometry combined with absorption, differential phase contrast and dark‐field imaging, have been performed on biological and geological samples. 相似文献
144.
Edouard Boivin Jean-Noël Chotard Christian Masquelier Laurence Croguennec 《Molecules (Basel, Switzerland)》2021,26(5)
Vanadium phosphate positive electrode materials attract great interest in the field of Alkali-ion (Li, Na and K-ion) batteries due to their ability to store several electrons per transition metal. These multi-electron reactions (from V2+ to V5+) combined with the high voltage of corresponding redox couples (e.g., 4.0 V vs. for V3+/V4+ in Na3V2(PO4)2F3) could allow the achievement the 1 kWh/kg milestone at the positive electrode level in Alkali-ion batteries. However, a massive divergence in the voltage reported for the V3+/V4+ and V4+/V5+ redox couples as a function of crystal structure is noticed. Moreover, vanadium phosphates that operate at high V3+/V4+ voltages are usually unable to reversibly exchange several electrons in a narrow enough voltage range. Here, through the review of redox mechanisms and structural evolutions upon electrochemical operation of selected widely studied materials, we identify the crystallographic origin of this trend: the distribution of PO4 groups around vanadium octahedra, that allows or prevents the formation of the vanadyl distortion (O…V4+=O or O…V5+=O). While the vanadyl entity massively lowers the voltage of the V3+/V4+ and V4+/V5+ couples, it considerably improves the reversibility of these redox reactions. Therefore, anionic substitutions, mainly O2− by F−, have been identified as a strategy allowing for combining the beneficial effect of the vanadyl distortion on the reversibility with the high voltage of vanadium redox couples in fluorine rich environments. 相似文献
145.
Aline Gardez Ghassen Saidani Ludovic Biennier Robert Georges Edouard Hugo Vijayanand Chandrasekaran Vivien Roussel Bertrand Rowe K. P. J. Reddy E. Arunan 《国际化学动力学杂志》2012,44(11):753-766
More than 70 molecules of varied nature have been identified in the envelopes of carbon‐rich stars through their spectral fingerprints in the microwave or far infrared regions. Many of them are carbon chain molecules and radicals, and a significant number are unique to the circumstellar medium. The determination of relevant laboratory kinetics data is critical to keep up with the development of the high spectral and spatial resolution observations and of the refinement of chemical models. Neutral–neutral reactions of the CN radical with unsaturated hydrocarbons could be a dominant route in the formation of cyanopolyynes, even at low temperatures and deserve a detailed laboratory investigation. The approach we have developed aims to bridge the temperature gap between resistively heated flow tubes and shock tubes. The present kinetic measurements are obtained using a new reactor combining a high‐enthalpy source with a flow tube and a pulsed laser photolysis–laser‐induced fluorescence system to probe the undergoing chemical reactions. The high‐enthalpy flow tube has been used to measure the rate constant of the reaction of the CN radical with propane (C3H8), propene (C3H6), allene (C3H4), 1,3‐butadiene (1,3‐C4H6), and 1‐butyne (C4H6) over a temperature range extending from 300 to 1200 K. All studied reactions of CN with unsaturated hydrocarbons are rapid, with rate coefficients greater than 10?10 cm3 · molecule?1 · s?1 and exhibit slight negative temperature dependence above room temperature. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 753–766, 2012 相似文献
146.
H. Y. Lee X. Letartre J. L. Leclercq P. Viktorovitch L. Konczewicz M. Sadowski 《高压研究》2013,33(1-6):347-351
Abstract GaAlAs-based microstructures have been designed and realized in order to take advantage of their favorable intrinsic properties. Piezoresistive properties were determined on macrostructures. Microfabrication process was established and first micro-accelerometers were produced. 相似文献
147.
Mathematical Programming - Counterexamples to some old-standing optimization problems in the smooth convex coercive setting are provided. We show that block-coordinate, steepest descent with exact... 相似文献
148.
M. Touboul J. Crepin G. Rousselier F. Latourte S. Leclercq 《Experimental Mechanics》2013,53(3):455-468
A methodology to obtain visco-plastic laws in heterogeneous materials with digital image correlation (DIC) is proposed based on tensile and tensile-relaxation tests conducted at room temperature and at 625 °C. Tested samples are manufactured from a P91 weld in which a microstructural heterogeneity translates into graded mechanical properties. To simplify the problem, a classical decomposition of the weld into five different domains is considered. Strain field in each domain is obtained by means of digital image correlation applied to high magnification pictures recorded with an optical long distance microscope. The conducted identifications exhibit key features in the behaviour of each domain in terms of yield stress, ultimate tensile stress and hardening at both room temperature and 625 °C. Experimental fields are compared to the fields provided by finite element simulations. Eventually, the benefit of accounting for transverse strains in the identification procedure is examined, and the robustness of the procedure with addition of noise (representative of experimental conditions) in the measurement is characterized. 相似文献
149.
Ballistic imaging of liquid breakup processes in dense sprays 总被引:2,自引:0,他引:2
Mark A. Linne Megan Paciaroni Edouard Berrocal David Sedarsky 《Proceedings of the Combustion Institute》2009,32(2):2147-2161
Ballistic imaging is the name applied to a category of optical techniques that were originally developed for medical applications. Recently, ballistic imaging was adapted to acquire instantaneous images of the liquid core inside atomizing sprays; a region that has been heretofore inaccessible to spray researchers. An important difference between spray research and the medical imaging problem is the need for high fidelity single-shot (within 10 μs) imaging in a spray whereas stationary tissue images can be averaged. Transient ballistic imaging diagnostics have been used to reveal details of the primary breakup process in a LOX injector, a turbulent water jet, a water jet in cross-flow, a transient diesel fuel spray, a rocket fuel injector, and an aerated spray. This paper briefly discusses various methods for imaging the liquid core, it introduces ballistic imaging and provides specific examples, it describes detailed studies of photon transmission through dense media, and it then discusses incorporation of those results into a model for a ballistic imaging instrument that can evaluate and optimize various concepts. 相似文献
150.
We report an original optical method providing the probability of molecular ionization induced by femtosecond laser pulses. The approach consists of exploiting molecular alignment to extract reliable information about ionization. The cross defocusing technique implemented for this purpose reveals a sensitivity with respect to postpulse alignment, as well as to the free electron density induced by the ultrashort laser pulse. The analysis of the resulting signal thus gives access to absolute single-ionization probabilities calibrated through the degree of alignment, provided that free electrons are produced mainly by single ionization. The relevance of the method is assessed in N2. 相似文献