全文获取类型
收费全文 | 115889篇 |
免费 | 30173篇 |
国内免费 | 25168篇 |
专业分类
化学 | 76935篇 |
晶体学 | 1942篇 |
力学 | 7739篇 |
综合类 | 784篇 |
数学 | 14378篇 |
物理学 | 69452篇 |
出版年
2024年 | 554篇 |
2023年 | 1356篇 |
2022年 | 2196篇 |
2021年 | 2190篇 |
2020年 | 2504篇 |
2019年 | 2986篇 |
2018年 | 2770篇 |
2017年 | 3529篇 |
2016年 | 3964篇 |
2015年 | 4473篇 |
2014年 | 4810篇 |
2013年 | 7093篇 |
2012年 | 7926篇 |
2011年 | 9565篇 |
2010年 | 12154篇 |
2009年 | 12574篇 |
2008年 | 6784篇 |
2007年 | 5707篇 |
2006年 | 5314篇 |
2005年 | 5134篇 |
2004年 | 5388篇 |
2003年 | 4348篇 |
2002年 | 4220篇 |
2001年 | 4354篇 |
2000年 | 3501篇 |
1999年 | 3303篇 |
1998年 | 2666篇 |
1997年 | 2398篇 |
1996年 | 2651篇 |
1995年 | 3030篇 |
1994年 | 3084篇 |
1993年 | 3101篇 |
1992年 | 2649篇 |
1991年 | 2267篇 |
1990年 | 1937篇 |
1989年 | 1978篇 |
1988年 | 1950篇 |
1987年 | 1228篇 |
1986年 | 1281篇 |
1985年 | 911篇 |
1984年 | 1013篇 |
1982年 | 907篇 |
1981年 | 752篇 |
1980年 | 783篇 |
1979年 | 559篇 |
1978年 | 545篇 |
1977年 | 646篇 |
1976年 | 1046篇 |
1973年 | 442篇 |
1972年 | 536篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
T Utsunomiya M. Sekine 《International Journal of Infrared and Millimeter Waves》2005,26(11):1651-1660
We have conducted a millimeter wave propagation experiment at 103 GHz (2.9 mm) on a propagation path of 390 m. The results
were compared with the rain attenuation calculations from the Marshall-Palmer, Best, Joss-Thomas-Waldvogel and Weibull distributions
for raindrop-size. It has been shown that the Weibull distribution has a good agreement with the experiments. 相似文献
32.
33.
建立了相变热力学理论和场论的关系. 强调在量子场论中必须引进序参量场, 则相变的讨论就类似于Goldstone bosons 的产生. 如果只讨论一级相变, Goldstone bosons场就足够了; 如果要讨论二级相变, 则必须讨论一系列的场, 这些场构成一个对称群的表示. 另外, 也将这一思想用到色超导中. In this paper we built a relation between the thermodynamical theory of the phase transition and field theory. We emphasized that in the quantum field theory we have to introduce the order parameter fields. Then the discussion of the phase transition is closed to the creation of the Goldstone bosons. If we only discuss the first order transition, the Goldstone bosons fields are sufficient. If we want to discuss the second order transition, we have to discuss a set of fields that constructs a representation of a symmetry group. We also apply this concept to color superconductivity. 相似文献
34.
We present all-atom molecular dynamics simulations ofn-hexane on the basal plane of graphite at monolayer and multilayer coverages. In keeping with experimental data, we find the
presence of ordered adsorbed layers both at single monolayer coverage and when the adsorbed layer coexists with excess liquid
adsorbate. Using a simulation method that does not impose any particular periodicity on the adsorbed layer, we quantitatively
compare our results to the results of neutron diffraction experiments and find a structural transition from a uniaxially incommensurate
lattice to a fully commensurate structure on increasing the coverage from a monolayer to a multilayer. The zig-zag backbone
planes of all the alkane molecules lie parallel to the graphite surface at the multilayer coverage, while a few molecules
are observed to attain the perpendicular orientation at monolayer coverage.
Dedicated to Professor C N R Rao on his 70th birthday 相似文献
35.
36.
Abstract. We propose a general approach to deal with nonlinear, nonconvex variational problems based on a reformulation of the problem
resulting in an optimization problem with linear cost functional and convex constraints. As a first step we explicitly explore
these ideas to some one-dimensional variational problems and obtain specific conclusions of an analytical and numerical nature. 相似文献
37.
In this paper, we give the following dominated theorem: Let φ(g) ∈ L1(G//K),φε(t)=ε> 0, and the least radical decreasing dominatedfunction φ(t) = sup |φ(y)| ∈L1(G//K). If shtφ(t) is monotonically decreasingon (0, ∞), then for any f∈L1loc(G//K) , the following inequality holds:sup |φε * f(x)| ≤ Cmf(x),where mf(x) is the Hardy-Littlewood maximal function of f, and C = ||φ||1.An application of this dominated theorem is also given. 相似文献
38.
39.
Li Yingle Huang Jiying Gong Shuohong 《International Journal of Infrared and Millimeter Waves》2003,24(6):953-961
The dielectric constant for rain medium is investigated by utilizing the system identification method. The rain rate model and frequency model of permittivity in millimeter waves band for rain medium are presented. The results obtained with models are in very good agreement with references in calculating the attenuation of electromagnetic waves induced by rain, which Shows that the obtained models are valid and practicable. The cross-polar discrimination gotten with rain rate model is in agreement with references. 相似文献
40.
R. Pizzoferrato L. Lagonigro T. Ziller A. Di Carlo R. Paolesse F. Mandoj A. Ricci C. Lo Sterzo 《Chemical physics》2004,300(1-3):217-225
We study the infrared emission at 1.54 μm of an organolanthanide complex, Er(III)-tetraphenylporphyrin [Er(TPP)acac], both as a result of direct optical excitation and via energy transfer from host π-conjugate polymers of type poly(arylene–ethynylene) [PAE]. In the first case, the emission of the neat complex is characterized in inert transparent materials and a value of the quantum yield at 1.54 μm φIR=4×10−4 is measured. Then, fluorescence resonance transfer is investigated in blends of Er(TPP)acac with PAEs by monitoring the quenching of the polymer fluorescence along with the enhancement of both the visible emission of the ligand and the near-infrared band of Er3+. These different procedures allow a detailed analysis of the transfer efficiency within a specific implementation of the Förster model for polymeric donors. The experimental values of the critical radius R0, ranging from 1.3 to 2.5 nm for the different blends, are in good agreement with theory for a wide interval of the physical and spectroscopic parameters. This suggests that other mechanisms for excitation transfer do not play a significant role in these materials. 相似文献