全文获取类型
收费全文 | 14697篇 |
免费 | 647篇 |
国内免费 | 2篇 |
专业分类
化学 | 7890篇 |
晶体学 | 42篇 |
力学 | 265篇 |
数学 | 1901篇 |
物理学 | 4643篇 |
无线电 | 605篇 |
出版年
2023年 | 132篇 |
2021年 | 145篇 |
2020年 | 176篇 |
2019年 | 109篇 |
2018年 | 174篇 |
2017年 | 180篇 |
2016年 | 381篇 |
2015年 | 374篇 |
2014年 | 354篇 |
2013年 | 663篇 |
2012年 | 627篇 |
2011年 | 815篇 |
2010年 | 354篇 |
2009年 | 318篇 |
2008年 | 717篇 |
2007年 | 696篇 |
2006年 | 674篇 |
2005年 | 542篇 |
2004年 | 423篇 |
2003年 | 419篇 |
2002年 | 376篇 |
2001年 | 357篇 |
2000年 | 289篇 |
1999年 | 232篇 |
1998年 | 203篇 |
1997年 | 213篇 |
1996年 | 201篇 |
1995年 | 191篇 |
1994年 | 176篇 |
1993年 | 201篇 |
1992年 | 196篇 |
1991年 | 162篇 |
1990年 | 135篇 |
1989年 | 128篇 |
1988年 | 116篇 |
1987年 | 130篇 |
1986年 | 140篇 |
1985年 | 152篇 |
1984年 | 185篇 |
1983年 | 167篇 |
1982年 | 174篇 |
1981年 | 184篇 |
1980年 | 162篇 |
1979年 | 150篇 |
1978年 | 167篇 |
1977年 | 159篇 |
1976年 | 138篇 |
1975年 | 131篇 |
1974年 | 122篇 |
1973年 | 112篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
U. Täuber C.E.M. Carvalho R.F. dos Santos C.G. Carvalhaes C.E. Fellows 《Applied physics. B, Lasers and optics》2007,87(3):475-481
A six level rate equation system was used to investigate the impact of photodepletion to amplified spontaneous emission (ASE)
of intramolecular proton-transfer (IPT) dyes incorporated into polymeric hosts. The model includes the most important transitions
for the normal and tautomer form of the molecule as well as intersystem crossing and triplet–triplet transitions. The experimentally
observed pulse shape as well as photodepletion phenomena, i.e. a first order exponential decay of the ASE intensity and a
shortening in ASE pulse width, have been simulated successfully. Additionally, the model was used to propose an explanation
of the unexpected high photodepletion of proton-transfer dyes in solids. The results show that the emission cross section
and reabsorption cross section of the tautomer form of the molecule are the most important parameter not only for efficiency
but also for photodepletion. The model was tested by comparison with experimental results of 2-(2’-hydroxyphenyl)benzimidazole
in polymethylmethacrylate (PMMA), polystyrene (PS) and a 1:1 alternating copolymer matrix PS-co-PMMA.
PACS 78.45.th; 42.55.Mv; 42.70.Jk 相似文献
32.
Hyperfine Interactions - In this paper, the conditions for which three-dimensional crystalline ion beams were attained in the rf quadrupole storage ring PALLAS at a velocity of around 2800 m/s are... 相似文献
33.
Ledzewicz U. Nowakowski A. Schättler H. 《Journal of Optimization Theory and Applications》2004,122(2):345-370
It is shown that, if a parametrized fämily of extremals F can be stratified in a way compatible with the flow map generated by F, then those trajectories of the family which realize the minimal values of the cost in F are indeed optimal in comparison with all trajectories which lie in the region R covered by the trajectories of F. It is not assumed that F is a field covering the state space injectively. As illustration, an optimal synthesis is constructed for a system where the flow of extremals exhibits a simple cusp singularity. 相似文献
34.
We determine the stationary two-point correlation function of the one-dimensional KPZ equation through the scaling limit of a solvable microscopic model, the polynuclear growth model. The equivalence to a directed polymer problem with specific boundary conditions allows one to express the corresponding scaling function in terms of the solution to a Riemann–Hilbert problem related to the Painlevé II equation. We solve these equations numerically with very high precision and compare our, up to numerical rounding exact, result with the prediction of Colaiori and Moore(1) obtained from the mode coupling approximation. 相似文献
35.
36.
L. G. Lumbreras R. Gebhard W. Häusler F. Kauffmann-Doig J. Riederer G. Sieben U. Wagner 《Hyperfine Interactions》2003,150(1-4):51-72
Ceramic finds from the Galería de las Ofrendas at Chavín de Huántar and surface finds from the settlement of Chavín were characterised by combining the results of archaeological typology with archaeometric studies using neutron activation analysis, Mössbauer spectroscopy, X-ray diffraction and thin-section microscopy. Sherds from the pyramid Tello are included in the study as representative of local material. The analyses show that the vessels were made from different raw materials and that different firing procedures were used in their production. Sherds of certain styles largely exhibit similar types of Mössbauer patterns and in many instances also have similar element compositions. This supports the archaeological notion that the vessels were brought to Chavín from the provinces, perhaps on the occasion of a festivity. 相似文献
37.
38.
Christian J. Bordé Claus Lämmerzahl Ernst M. Rasel 《General Relativity and Gravitation》2004,36(10):2193-2196
39.
Lancaster G.P.T. Häffner H. Wilson M.A. Becher C. Eschner J. Schmidt-Kaler F. Blatt R. 《Applied physics. B, Lasers and optics》2003,76(8):805-808
We present a scheme for employing a violet extended-cavity diode laser in experiments with single, trapped ions. For this the grating-stabilised laser is spatially and spectrally filtered and referenced to a Fabry–Pérot cavity. We measure an upper limit to the line width by observing a 305-kHz FWHM beat note with the second harmonic of a titanium sapphire laser. The laser is subsequently used to optically cool a single 40Ca+ ion close to the Doppler limit. PACS 03.67.Lx; 32.80.Pj; 42.55.Px 相似文献
40.
W. B. Krätzig 《Archive of Applied Mechanics (Ingenieur Archiv)》1993,64(1):1-19
Übersicht Konsistente Schalentheorien lassen sich in einer besonders anschaulichen Weise durch lineare Approximation der Erhaltungssätze eines als Multi-Direktor-Körper beschriebenen, dreidimensionalen Kontinuums herleiten. Im vorliegenden Beitrag entstchen auf diesem Wege bestmögliche, in Geschwindigkeiten formulierte innere Schalengleichungen für beliebig große Deformationen und willkürliche, in eine Leistungsaussage einpaßbare Materialgesetze. Dabei finden Schub- und Querdeformationen Berücksichtigung. Der optimale Charakter der Schalentheorie mit gleichen Unschärfen in allen Einzelbeziehungen wird durch den Herleitungsgang sichergestellt und durch Einschrankungen mittels lokaler Tensornormen bewiesen.
Best interior shell equations including transverse shear deformations and thickness changes
Summary Consistent shell theories can be derived in a particular correct manner by linear approximation of conservation laws of a three-dimensional continuum, described as a multi-director-body. In the present paper best interior shell equations-formulated in velocities—are developed, valid for arbitrarily large deformations and rather optional material laws, incorporating shear distorsions and thickness changes. The optimal character of the theory is guaranteed by the derivation process and proven by bounding techniques using tensor norms.相似文献