全文获取类型
收费全文 | 3252篇 |
免费 | 147篇 |
国内免费 | 9篇 |
专业分类
化学 | 1902篇 |
晶体学 | 20篇 |
力学 | 108篇 |
数学 | 613篇 |
物理学 | 765篇 |
出版年
2023年 | 47篇 |
2022年 | 25篇 |
2021年 | 63篇 |
2020年 | 61篇 |
2019年 | 55篇 |
2018年 | 52篇 |
2017年 | 57篇 |
2016年 | 125篇 |
2015年 | 92篇 |
2014年 | 108篇 |
2013年 | 198篇 |
2012年 | 142篇 |
2011年 | 133篇 |
2010年 | 112篇 |
2009年 | 104篇 |
2008年 | 94篇 |
2007年 | 131篇 |
2006年 | 118篇 |
2005年 | 89篇 |
2004年 | 68篇 |
2003年 | 72篇 |
2002年 | 81篇 |
2001年 | 58篇 |
2000年 | 46篇 |
1999年 | 51篇 |
1998年 | 46篇 |
1997年 | 41篇 |
1996年 | 46篇 |
1995年 | 45篇 |
1994年 | 34篇 |
1993年 | 32篇 |
1992年 | 27篇 |
1991年 | 33篇 |
1990年 | 26篇 |
1987年 | 30篇 |
1986年 | 35篇 |
1985年 | 29篇 |
1983年 | 22篇 |
1982年 | 31篇 |
1981年 | 27篇 |
1980年 | 41篇 |
1979年 | 25篇 |
1978年 | 33篇 |
1977年 | 37篇 |
1976年 | 24篇 |
1975年 | 28篇 |
1974年 | 28篇 |
1973年 | 20篇 |
1972年 | 18篇 |
1938年 | 18篇 |
排序方式: 共有3408条查询结果,搜索用时 15 毫秒
21.
G. Rauprich H. J. Hähn M. Karus P. Nießen K. R. Nyga H. Oswald L. Sydow H. Paetz gen Schieck Y. Koike 《Few-Body Systems》1988,5(2):67-77
The
elastic scattering was investigated especially in the Coulomb sensitive scattering regions. Angular distributions of the differential cross section and of the analyzing powerA
y, with emphasis on small scattering angles, were measured at 10.0 and 14.1 MeV. For extreme backward angles up toJ
c.m.=179° the differential cross section was measured at 12.0, 14.1 and 16.5 MeV. The data have been compared with recent Faddeev calculations based on the realistic meson-exchange Paris potential and including an approximate Coulomb correction. There are discrepancies between the data and the calculations especially for the analyzing power. This indicates that the approximate treatment of Coulomb effects and possibly also the purely nuclear part of the calculations need to be improved. 相似文献
22.
A. Türler H. W. Gäggeler D. T. Jost P. Armbruster W. Brüchle H. Folger F. P. Heßberger S. Hofmann G. Münzenberg V. Ninov M. Schädel K. Sümmerer J. V. Kratz U. Scherer 《Zeitschrift für Physik A Hadrons and Nuclei》1988,331(3):363-364
The isotope254No was produced in the fusion reaction48Ca +208Pb. Using the velocity filter SHIP and radiochemical techniques it was found that the nuclide254No with a half-life of 55 s decays byα, EC, and spontaneous-fission. Deduced partial half-lives are (61±2) s forα-decay, (550 ?160 +370 ) s for EC and [2.2 ?1.0 +2.0 ]×104 s for spontaneous fission. 相似文献
23.
Semi-insulating electrical properties of undoped inp after heat treatment in a phosphorus atmosphere 总被引:1,自引:0,他引:1
D. Hofmann G. Müller N. Streckfuß 《Applied Physics A: Materials Science & Processing》1989,48(4):315-319
Nominally undoped InP wafers have been annealed in a phosphorus atmosphere under a pressure of about 5 bar at temperatures of 900 °C for about 80 h. It was found that the electrical properties of the samples changed considerably after this treatment. A room temperature resistivity of up to 2×107cm (semi-insulating behaviour) was obtained in the bulk of the samples. The resistivity finally obtained depends on the starting carrier concentration of the untreated samples. The Hall coefficient and Hall mobility have been measured up to 600 °C. The results can be interpreted in terms of a deep electronic level (E
A=0.63 ... 0.65 eV below the conduction band). The Hall coefficient was always found to be negative resulting in a Hall mobility of 1.4 to 4.9×103 cm2/Vs. The highest resistivity in nominally undoped bulk InP so far reported in the literature [1] was =3.6 × 105cm. Therefore, this paper demonstrates for the first time that a really semi-insulating behaviour of >107 cm can be achieved for bulk InP with the purity of nominally undoped material (1015 to 1016cm–3). 相似文献
24.
The synthesis and properties of perchlorobi-9-fluorenylidene, a highly twisted ethylene, are reported. It is a diamagnetic chlorocarbon. 相似文献
25.
S Çak?r E Co?kunP Naumov E Biçer? Bulut H ?çbudakO Çak?r 《Journal of Molecular Structure》2002,608(1):101-107
Aspartame adduct of copper(II) chloride Cu(Asp)2Cl2·2H2O (Asp=aspartame) is synthesized and characterized by elemental analysis, FT IR, UV/vis, ESR spectroscopies, TG, DTG, DTA measurements and molecular mechanics calculations. Aqueous solution of the green solid absorbs strongly at 774 and 367 nm. According to the FT IR spectra, the aspartame moiety coordinates to the copper(II) ion via its carboxylate ends, whereas the ammonium terminal groups give rise to hydrogen bonding network with the water, the chloride ions or neighboring carboxylate groups. The results suggest tetragonally distorted octahedral environment of the copper ions. 相似文献
26.
27.
28.
29.
A new enantioselective synthesis of furan‐2‐yl amines and amino acids is described, in which the key step is the oxazaborolidine‐catalyzed enantioselective reduction of O‐benzyl (E)‐ and (Z)‐furan‐2‐yl ketone oximes to the corresponding chiral amines. The chirality of the furan‐2‐yl amines is fully controlled by the appropriate choice of the geometrical isomer of the O‐benzyl oxime. Oxidation of the furan ring furnished amino acids in high yields. 相似文献
30.
Dr.-Ing. H. Wißbrock 《Archive of Applied Mechanics (Ingenieur Archiv)》1987,57(5):349-360
Übersicht Die Fugen zusammengesetzter Bauteile sind einerseits für eine nachteilige Steifigkeitsminderung verantwortlich, tragen aber andererseits durch Reibungsvorgänge wesentlich zum Dämpfungsvermögen einer Konstruktion bei. Merkliche Reibungsdämpfung ohne gleichzeitigen Steifigkeitsverlust bewirken zusätzliche Fugen, die durch Anbringen sogenannter Scheuerleisten entstehen. Der Autor stellt ein Näherungsverfahren zur dämpfungsoptimalen Auslegung von Scheuerleisten vor. Ausgehend von der zu dämpfenden Schwingungsform liefert dieses Verfahren Kriterien für eine günstige Scheuerleistenanordnung, geeignete Leistenabmessungen und als wichtigstes Ergebnis eine dämpfungsoptimale Fugenpressung, die zu maximaler Energiedissipation führt. Schließlich kann das zu erwartende Dämpfungsmaß berechnet und damit das Ergebnis einer vorgesehenen Dämpfungsmaßnahme abgeschätzt werden.
Damping by friction ledges: a practical design concept
Summary On the one hand, mating surfaces of structures are responsible for a reduction of stiffness, on the other hand relative motion produces friction, which contributes considerably to the damping. Noticeable friction damping without simultaneous stiffness reduction can be achieved by adding further mating surfaces. Such interfaces are realized by fastening additional elements (e.g. beamlike) onto the structure. An analytic approximation method for these so-called friction ledges is described in this paper. Initiating from the mode shape to be damped the procedure yields criteria for the suitable positioning and design of the ledges. Most important of all is the damping optimized interface pressure, that leads to maximum energy dissipation. Finally, the expected damping rate can be computed, and therefore the result of the proposed measure assessed.相似文献