全文获取类型
收费全文 | 1852篇 |
免费 | 27篇 |
国内免费 | 2篇 |
专业分类
化学 | 1429篇 |
晶体学 | 21篇 |
力学 | 37篇 |
数学 | 40篇 |
物理学 | 354篇 |
出版年
2022年 | 11篇 |
2020年 | 11篇 |
2019年 | 18篇 |
2018年 | 14篇 |
2017年 | 9篇 |
2016年 | 20篇 |
2015年 | 14篇 |
2014年 | 29篇 |
2013年 | 66篇 |
2012年 | 84篇 |
2011年 | 82篇 |
2010年 | 47篇 |
2009年 | 58篇 |
2008年 | 96篇 |
2007年 | 90篇 |
2006年 | 108篇 |
2005年 | 90篇 |
2004年 | 96篇 |
2003年 | 81篇 |
2002年 | 67篇 |
2001年 | 49篇 |
2000年 | 58篇 |
1999年 | 34篇 |
1998年 | 27篇 |
1997年 | 41篇 |
1996年 | 26篇 |
1995年 | 26篇 |
1994年 | 20篇 |
1993年 | 28篇 |
1992年 | 46篇 |
1991年 | 23篇 |
1990年 | 22篇 |
1989年 | 17篇 |
1988年 | 34篇 |
1987年 | 27篇 |
1986年 | 31篇 |
1985年 | 39篇 |
1984年 | 25篇 |
1983年 | 16篇 |
1982年 | 21篇 |
1981年 | 17篇 |
1980年 | 12篇 |
1979年 | 24篇 |
1978年 | 17篇 |
1977年 | 14篇 |
1976年 | 8篇 |
1975年 | 9篇 |
1974年 | 14篇 |
1973年 | 7篇 |
1966年 | 8篇 |
排序方式: 共有1881条查询结果,搜索用时 15 毫秒
101.
Tetsuo Yamasaki Yuji Yoshihara Yoshinari Okamoto Tadashi Okawara Mitsuru Furukawa 《Journal of heterocyclic chemistry》1992,29(5):1313-1316
The reaction of 5-hydrazinopyridazin-3(2H)-ones 1 with α-keto diester 2 in acetic acid afforded the corresponding 4,6-dihydropyridazino[4,5-c]pyridazin-5(1H)-ones 3 and pyrrolo[2,3-d)pyridazin-4(5H)-ones 4 . Compounds 3 were also obtained from 4-bromo-5-hydrazinopyridazin-3(2H)-ones 8 and 2 under milder conditions. 5-Bromo-4-hydrazinopyridazin-3(2H)-one 9 , the regioisomer of 8b , also reacted readily with 2a to give 4,7-dihydropyridazino[4,5-c]pyridazin-8(1H)-one 10b , the regioisomer of 3b . 相似文献
102.
For a nontrivial connected graph G, let ${c: V(G)\to {{\mathbb N}}}For a nontrivial connected graph G, let
c: V(G)? \mathbb N{c: V(G)\to {{\mathbb N}}} be a vertex coloring of G, where adjacent vertices may be colored the same. For a vertex v of G, let N(v) denote the set of vertices adjacent to v. The color sum σ(v) of v is the sum of the colors of the vertices in N(v). If σ(u) ≠ σ(v) for every two adjacent vertices u and v of G, then c is called a sigma coloring of G. The minimum number of colors required in a sigma coloring of a graph G is called its sigma chromatic number σ(G). The sigma chromatic number of a graph G never exceeds its chromatic number χ(G) and for every pair a, b of positive integers with a ≤ b, there exists a connected graph G with σ(G) = a and χ(G) = b. There is a connected graph G of order n with σ(G) = k for every pair k, n of positive integers with k ≤n if and only if k ≠ n − 1. Several other results concerning sigma chromatic numbers are presented. 相似文献
103.
Futaba Okamoto Ping Zhang Varaporn Saenpholphat 《Czechoslovak Mathematical Journal》2008,58(1):271-287
For a nontrivial connected graph G of order n and a linear ordering s: v
1, v
2, …, v
n
of vertices of G, define . The traceable number t(G) of a graph G is t(G) = min{d(s)} and the upper traceable number t
+(G) of G is t
+(G) = max{d(s)}, where the minimum and maximum are taken over all linear orderings s of vertices of G. We study upper traceable numbers of several classes of graphs and the relationship between the traceable number and upper
traceable number of a graph. All connected graphs G for which t
+(G) − t(G) = 1 are characterized and a formula for the upper traceable number of a tree is established.
Research supported by Srinakharinwirot University, the Thailand Research Fund and the Commission on Higher Education, Thailand
under the grant number MRG 5080075. 相似文献
104.
Railway wheelset experiences the problem of hunting above a critical speed, which is a kind of self-excited oscillation. At the critical speed, it is known that the system undergoes a subcritical Hopf bifurcation. Therefore, for clarifying the nonlinear characteristics of hunting it is very important to detect, for example, the nonlinear forces in the wheelset due to the creep forces acting between the wheels and rails, and the nonlinear component of the resorting forces by the suspensions. However, it is impossible to determine each force quantitatively. In the present paper, it is first shown, by using the center manifold theory and the method of normal form, that the nonlinear characteristics of the bifurcation in a wheelset model with two degrees of freedom are governed by a single parameter, hence each nonlinear force need not be detected when examining the nonlinear characteristics. Also, a method of determining the governing parameter from experimentally observed radiuses of the unstable limit cycle is proposed. Next, we experimentally investigate the variation of the parameter due to the presence of linear spring suspensions in the lateral direction and discuss the variation of the nonlinear characteristics of the hunting motion, which depends on the lateral stiffness. As a result, the improvement of the stability of the wheelset against the disturbance by the linear spring suspensions is clarified. 相似文献
105.
Several dereverberation algorithms have been studied. The sampling frequencies used in conventional studies are typically 8–16 kHz because their main purpose is preprocessing for improving the intelligibility of speech communication and articulation for automatic speech recognition. However, in next-generation communication systems, techniques to analyze and reproduce not only semantic information of sound but also more high-definition components such as spatial information and directivity will be increasingly necessary. To decompose these sound field characteristics with high definition, a dereverberation algorithm that is useful at high sampling frequencies is an important technique to process sound that includes high-frequency spectra such as musical sounds. The LInear-predictive Multichannel Equalization (LIME) algorithm is a promising dereverberation method. Using the LIME algorithm, however, a dereverberation signal cannot be solved at high sampling frequencies when the source signal is colored, such as in the case of speech and sound of musical signals. Because the rank of the correlation matrix calculated from such a colored signal is not full, the characteristic polynomial cannot be calculated precisely. To alleviate this problem, we propose preprocessing of all input signals with filters to whiten their spectra so that this algorithm can function for colored signals at high sampling frequencies. 相似文献
106.
S. Tanabete Y. Nakagawa T. Okamoto M. Haraguchi T. Isu G. Shinomiya 《Applied Physics A: Materials Science & Processing》2013,112(3):605-611
Many researching efforts have been reported to seek various fundamental LC resonance structures, recently. But still the Split Ring Resonator (SRR) is the most famous and major fundamental LC-resonance structure used in the metamaterial. We employed SRR structure as the fundamental LC-resonance mechanism to fabricate photonic crystal with periodic arrangement of two different metamaterial areas composed from SRR arrays on the dielectric substrate. We developed Photonic Metamaterial Crystal (PMC) to realize the more advanced and versatile functions of the metamaterial by 1 dimensional or 2 dimensional periodic arranging of two metamaterial sections which have different dispersion properties due to the different size of SRR structures each other. In this paper, we report the fabrication process, estimation of PMC properties and some possible future application prospects, for instance the PMC waveguide structures and nonlinear properties of PMC observed as selective LC-resonant properties in Raman mapping analysis of PMC. These are quite interesting characters of PMC and the attractive applications as the PMC devices. 相似文献
107.
Background
Decrements of auditory evoked responses elicited by repeatedly presented sounds with similar frequencies have been well investigated by means of electroencephalography and magnetoencephalography (MEG). However the possible inhibitory interactions between different neuronal populations remains poorly understood. In the present study, we investigated the effect of proceeding notch-filtered noises (NFNs) with different frequency spectra on a following test tone using MEG. 相似文献108.
Optical Review - We propose a new single-shot digital holography that measures the complex amplitude high precisely using a single image sensor. In this technology, a signal beam passes through a... 相似文献
109.
Junya Matsunami Mitsuaki Ooya Tohru Okamoto 《Physica E: Low-dimensional Systems and Nanostructures》2006,34(1-2):248
We report electrically detected electron spin resonance (ESR) measurements of a high mobility two-dimensional (2D) electron system formed in a Si/SiGe quantum well, with millimeter wave in a high magnetic field . The negative ESR signal observed under an in-plane magnetic field gives direct evidence that the spin polarization leads to a resistance increase in the 2D metallic state. Suppression of spin decoherence was observed in the quantum Hall state at the Landau level filling factor ν=2. Strength of the nuclear magnetic field in the resonance is evaluated to be less than , much smaller than that reported for GaAs/AlGaAs heterostructures. 相似文献
110.