全文获取类型
收费全文 | 537篇 |
免费 | 23篇 |
国内免费 | 2篇 |
专业分类
化学 | 335篇 |
晶体学 | 4篇 |
力学 | 48篇 |
数学 | 110篇 |
物理学 | 65篇 |
出版年
2023年 | 6篇 |
2022年 | 10篇 |
2021年 | 21篇 |
2020年 | 3篇 |
2019年 | 8篇 |
2018年 | 12篇 |
2017年 | 9篇 |
2016年 | 29篇 |
2015年 | 25篇 |
2014年 | 20篇 |
2013年 | 35篇 |
2012年 | 26篇 |
2011年 | 40篇 |
2010年 | 29篇 |
2009年 | 30篇 |
2008年 | 26篇 |
2007年 | 41篇 |
2006年 | 29篇 |
2005年 | 31篇 |
2004年 | 21篇 |
2003年 | 15篇 |
2002年 | 18篇 |
2001年 | 4篇 |
1999年 | 6篇 |
1998年 | 2篇 |
1996年 | 6篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1992年 | 3篇 |
1990年 | 2篇 |
1988年 | 2篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1972年 | 2篇 |
1969年 | 1篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1941年 | 1篇 |
1937年 | 1篇 |
1926年 | 1篇 |
1913年 | 1篇 |
1907年 | 1篇 |
1869年 | 1篇 |
排序方式: 共有562条查询结果,搜索用时 31 毫秒
441.
Shock structure in separated nozzle flows 总被引:2,自引:1,他引:1
In the case of high overexpansion, the exhaust jet of the supersonic nozzle of rocket engines separates from nozzle wall because
of the large adverse pressure gradient. Correspondingly, to match the pressure of the separated flow region, an oblique shock
is generated which evolves through the supersonic jet starting approximately at the separation point. This shock reflects
on the nozzle axis with a Mach reflection. Thus, a peculiar Mach reflection takes place whose features depend on the upstream
flow conditions, which are usually not uniform. The expected features of Mach reflection may become much difficult to predict,
depending on the nozzle shape and the position of the separation point along the divergent section of the nozzle.
相似文献
442.
Dr. Erika M. Dematteis Dr. Claudio Pistidda Prof. Martin Dornheim Prof. Marcello Baricco 《Chemphyschem》2019,20(10):1348-1359
Binary combinations of borohydrides have been extensivly investigated evidencing the formation of eutectics, bimetallic compounds or solid solutions. In this paper, the investigation has been extended to ternary and quaternary systems in the LiBH4-NaBH4-KBH4-Mg(BH4)2-Ca(BH4)2 system. Possible interactions among borohydrides in equimolar composition has been explored by mechanochemical treatment. The obtained phases were analysed by X-ray diffraction and the thermal behaviour of the mixtures were analysed by HP-DSC and DTA, defining temperature of transitions and decomposition reactions. The release of hydrogen was detected by MS, showing the role of the presence of solid solutions and multi-cation compounds on the hydrogen desorption reactions. The presence of LiBH4 generally promotes the release of H2 at about 200 °C, while KCa(BH4)3 promotes the release in a single-step reaction at higher temperatures. 相似文献
443.
The postbuckling behavior of an asymmetric one-bay, two-storey frame with clamped edges is analyzed. Columns have different bending stiffnesses and are pairwise of the same length. By assuming columns to be inextensible and shear undeformable, and beams to be rigid, two buckling modes are possible which are described by the sidesway of the lower floor with a rigid horizontal displacement of the upper floor and a sidesway of the upper floor, the lower floor undergoing no displacement. By properly selecting the ratios EI/h2 (EI being the bending stiffness of a column and h its length) the two buckling modes may occur simultaneously. A third buckling mode is also possible which is characterized by no displacement of the horizontal beams and local deflection of one or more columns in the shape of a beam with fixed edges. This third case will not be considered in this paper. The Koiter general nonlinear theory of elastic stability recast in a form convenient for the development of finite elment models along lines similar to the recent presentation by Budiansky has been employed in the analysis. Nonlinear constraints on the field variable φ (φ being the cross-section rotation) are accounted for by means of Lagrangian multipliers. Results show that the postbuckling behavior of a single buckling mode is always asymmetric unstable and depends both on the degree of asymmetry of the structure and on the ratio h/l, l being the frame span. The occurrence of simultaneous buckling modes exacerbates the imperfection sensitivity of the structure. 相似文献
444.
Mirko Salinitro Alessandro Zappi Sonia Casolari Marcello Locatelli Annalisa Tassoni Dora Melucci 《Molecules (Basel, Switzerland)》2022,27(6)
Bioindicator plants are species that have the capacity to linearly uptake some elements (metal and metalloids) from the growing substrate, thus reflecting their concentration in the soil. Many factors can influence the uptake of these elements by plants, among which is the simultaneous presence of several metals, a common situation in contaminated or natural soils. A novel approach that can be used to validate the bioindication ability of a species growing on a polymetallic substrate is the design of experiment (DoE) approach. The aim of the present study was to apply the DoE in full factorial mode to model the Cu, Cd, Pb, Zn, and Cr bioindication capacity of Polygonum aviculare, used as the model plant. The results showed that P. aviculare has the ability to bioindicate Cd and Cr with a linear uptake (from 0.35 to 6.66, and 0.1 to 3.4 mg kg−1, respectively) unaffected by the presence of other metals. Conversely, the uptake of Pb, Cu, and Zn is strongly influenced by the presence of all the studied metals, making their concentration in the plant shoot not proportional to that of the soil. In conclusion, these preliminary results confirmed that the DoE can be used to predict the bioindicator abilities of a plant for several elements at the same time and to evaluate the interactions that can be established between variables in the growing medium and in the plant itself. However, more studies including other plant species are needed to confirm the effectiveness of this method. 相似文献
445.
Daniel Josiane S. P. Cruz Jonas C. Catelani Tiago A. Garcia Jerusa S. Trevisan Marcello G. 《Journal of Thermal Analysis and Calorimetry》2021,143(4):3127-3135
Journal of Thermal Analysis and Calorimetry - This study aims to characterize erythromycin (ERY) estolate by thermogravimetry analysis and differential scanning calorimetry. For such a purpose,... 相似文献
446.
447.
Lucia Cavigli Franco Bogani Anna Vinattieri Lorenzo Cortese Marcello Colocci Valentina Faso Giovanni Baldi 《Solid State Sciences》2010,12(11):1877-1880
We present an experimental study of the radiative recombination dynamics in size-controlled TiO2 nanoparticles in the range 20–130 nm. Time-integrated photoluminescence spectra clearly show a dominance of self-trapped exciton (STE) emission, with main features not dependent on the nanoparticle size and on its environment. From picosecond time-resolved experiments as a function of the excitation density and the nanoparticle size we address the STE recombination dynamics as the result of two main processes related to the direct STE formation and to the indirect STE formation mediated by non-radiative surface states. 相似文献
448.
Dr. Emeline Descamps Dr. Khoa Nguyen Dr. Christelle Bouchain‐Gautier Dr. Arianna Filoramo Dr. Laurence Goux‐Capes Dr. Marcello Goffman Dr. Jean‐Philippe Bourgoin Dr. Pascal Mailley Dr. Thierry Livache 《Chemphyschem》2010,11(16):3541-3546
Surface modification at the nanometer scale is a challenge for the future of molecular electronics. In particular, the precise anchoring and electrical addressing of biological scaffolds such as complex DNA nanonetworks is of importance for generating bio‐directed assemblies of nano‐objects for nanocircuit purposes. Herein, we consider the individual modification of nanoelectrodes with different oligonucleotide sequences by an electrochemically driven co‐polymerization process of pyrrole and modified oligonucleotide sequences bearing pyrrole monomers. We demonstrate that this one‐step technique presents the advantages of simplicity, localization of surface modification, mechanical, biological and chemical stability of the coatings, and high lateral resolution. 相似文献
449.
Lino Colombo Marcello Di Giacomo Massimo Serra Simone M. Tambini 《Tetrahedron》2009,65(29-30):5838-5843
We report two different synthetic approaches for the stereoselective synthesis of (2E,4E)-4-(4,4-dimethylpent-2-ynylidene)-N1,N5-dimethyl-N1,N5-bis(naphthalen-1-ylmethyl)pent-2-ene-1,5-diamine 1, an important impurity-reference standard for the chemical characterization of terbinafine. The diamine 1 was obtained in only six steps with a good overall yield starting from commercially available glutaconic acid. 相似文献
450.
M. Abdel-Bary S. Abdel-Samad K. -Th. Brinkmann H. Clement J. Dietrich E. Doroshkevich S. Dshemuchadse K. Ehrhardt A. Erhardt W. Eyrich A. Filippi H. Freiesleben M. Fritsch W. Gast A. Gillitzer J. Gottwald H. J?ger B. Jakob R. J?kel L. Karsch K. Kilian H. Koch M. Krapp J. Kre? E. Kuhlmann A. Lehmann S. Marcello S. Mauro P. Michel K. Móller H. P. Morsch L. Naumann N. Paul C. Pizzolotto Ch. Plettner S. Reimann M. Richter J. Ritman E. Roderburg A. Schamlott P. Sch?nmeier W. Schroeder M. Schulte-Wissermann T. Sefzick M. Steinke G. Y. Sun A. Teufel W. Ullrich G. J. Wagner M. Wagner R. Wenzel A. Wilms P. Wintz P. Wüstner P. Zupranski 《The European Physical Journal A - Hadrons and Nuclei》2010,44(1):7-22