全文获取类型
收费全文 | 10426篇 |
免费 | 364篇 |
国内免费 | 88篇 |
专业分类
化学 | 7135篇 |
晶体学 | 93篇 |
力学 | 267篇 |
综合类 | 1篇 |
数学 | 1740篇 |
物理学 | 1642篇 |
出版年
2023年 | 81篇 |
2022年 | 121篇 |
2021年 | 193篇 |
2020年 | 210篇 |
2019年 | 250篇 |
2018年 | 158篇 |
2017年 | 159篇 |
2016年 | 384篇 |
2015年 | 288篇 |
2014年 | 320篇 |
2013年 | 603篇 |
2012年 | 607篇 |
2011年 | 653篇 |
2010年 | 453篇 |
2009年 | 404篇 |
2008年 | 586篇 |
2007年 | 630篇 |
2006年 | 494篇 |
2005年 | 547篇 |
2004年 | 440篇 |
2003年 | 350篇 |
2002年 | 336篇 |
2001年 | 162篇 |
2000年 | 144篇 |
1999年 | 96篇 |
1998年 | 103篇 |
1997年 | 109篇 |
1996年 | 113篇 |
1995年 | 93篇 |
1994年 | 84篇 |
1993年 | 100篇 |
1992年 | 78篇 |
1991年 | 79篇 |
1990年 | 74篇 |
1989年 | 64篇 |
1988年 | 51篇 |
1987年 | 55篇 |
1986年 | 69篇 |
1985年 | 103篇 |
1984年 | 101篇 |
1983年 | 80篇 |
1982年 | 69篇 |
1981年 | 73篇 |
1980年 | 68篇 |
1979年 | 64篇 |
1978年 | 68篇 |
1977年 | 41篇 |
1976年 | 40篇 |
1975年 | 50篇 |
1974年 | 54篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The steady-state movement of the spherical and non-spherical particles, such as prolate or oblate rotational ellipsoids, cylinders, or parallelepipeds, suspended in a liquid and exposed to a unidirectional temperature gradient, is analyzed theoretically. The differences in the ratios of the rotational to translational diffusion coefficients of the non-spherical to spherical particles, the heterogeneity of thermal conductivity of the particle body, and the heterogeneity in surface chemical nature make possible to separate the particles according to differences in shape. Preliminary experimental separations of Gram-positive and Gram-negative, nearly spherical and rod-shaped bacteria performed by Microthermal Field-Flow Fractionation confirmed that the fractionation of the cells according to differences in shape is possible. 相似文献
992.
Kundrat O Kroupa J Böhm S Budka J Eigner V Lhotak P 《The Journal of organic chemistry》2010,75(24):8372-8375
Nitration of thiacalix[4]arene, immobilized in the 1,3-alternate conformation, leads regioselectively to meta-substituted products. Depending on the reaction conditions, mono- and dinitro-derivatives can be isolated in acceptable yields. This unique substitution pattern is inaccessible in classical calixarene chemistry, and yields inherently chiral compounds, which makes thiacalixarenes very attractive as building blocks or molecular scaffolds. 相似文献
993.
Gerard A. van Albada Maarten G. van der Horst Simon J. Teat Patrick Gamez Olivier Roubeau Ilpo Mutikainen Urho Turpeinen Jan Reedijk 《Polyhedron》2009
In this study the synthesis, crystal structure and characterization of three new transition metal polynuclear compounds with formula [Cu(dipm)(μ-dca)2]n(H2O) (1), [Ni(dipm)(μ-dca)2]n(C2H6O)1/2 (2) and [Cd(dipm)(μ-dca)2]n (3) (in which dipm = bis(pyrimidin-2-yl)amine and dca = dicyanamide) are reported. The isostructural compounds 1 and 2 contain a double-bridging end-to-end dca unit connecting two metal ions and a single bridging end-to-end dca unit between subsequent metals. Compound 3 exhibits only single bridging end-to-end dca units, oriented in three directions, giving rise to a 3D framework. 相似文献
994.
We announce new structural properties of 1-homogeneous rank-1 convex integrands, and discuss some of their consequences. 相似文献
995.
Ofelia T. Alas Lucia R. Junqueira Jan van Mill Vladimir V. Tkachuk Richard G. Wilson 《Central European Journal of Mathematics》2011,9(3):603-615
For a topological property P, we say that a space X is star Pif for every open cover Uof the space X there exists Y ? X such that St(Y,U) = X and Y has P. We consider star countable and star Lindelöf spaces establishing, among other things, that there exists first countable pseudocompact spaces which are not star Lindelöf. We also describe some classes of spaces in which star countability is equivalent to countable extent and show that a star countable space with a dense σ-compact subspace can have arbitrary extent. It is proved that for any ω 1-monolithic compact space X, if C p (X)is star countable then it is Lindelöf. 相似文献
996.
Vampola T Laukkanen AM Horácek J Svec JG 《The Journal of the Acoustical Society of America》2011,129(1):310-315
Phonation into a glass tube is a voice training and therapy method that leads to beneficial effects in voice production. It has not been known, however, what changes occur in the vocal tract during and after the phonation into a tube. This pilot study examined the vocal tract shape in a female subject before, during, and after phonation into a tube using computer tomography (CT). Three-dimensional finite-element models (FEMs) of the vocal tract were derived from the CT images and used to study changes in vocal tract input impedance. When phonating on vowel [a:] the data showed tightened velopharyngeal closure and enlarged cross-sectional areas of the oropharyngeal and oral cavities during and after the tube-phonation. FEM calculations revealed an increased input inertance of the vocal tract and an increased acoustic energy radiated out of the vocal tract after the tube-phonation. The results indicate that the phonation into a tube causes changes in the vocal tract which remain also when the tube is removed. These effects may help improving voice production in patients and voice professionals. 相似文献
997.
Herbst CT Qiu Q Schutte HK Švec JG 《The Journal of the Acoustical Society of America》2011,129(4):2253-2262
While vocal fold adduction is an important parameter in speech, relatively little has been known on the adjustment of the vocal fold adduction in singing. This study investigates the possibility of separate adjustments of cartilaginous and membranous vocal fold adduction in singing. Six female and seven male subjects, singers and non-singers, were asked to imitate an instructor in producing four phonation types: "aBducted falsetto" (FaB), "aDducted falsetto" (FaD), "aBducted Chest" (CaB), and "aDducted Chest" (CaD). The phonations were evaluated using videostroboscopy, videokymography (VKG), electroglottography (EGG), and audio recordings. All the subjects showed less posterior (cartilaginous) vocal fold adduction in phonation types FaB and CaB than in FaD and CaD, and less membranous vocal fold adduction (smaller closed quotient) in FaB and FaD than in CaB and CaD. The findings indicate that the exercises enabled the singers to separately manipulate (a) cartilaginous adduction and (b) membranous medialization of the glottis though vocal fold bulging. Membranous adduction (monitored via videokymographic closed quotient) was influenced by both membranous medialization and cartilaginous adduction. Individual control over these types of vocal fold adjustments allows singers to create different vocal timbres. 相似文献
998.
Noise map validation by continuous noise monitoring 总被引:1,自引:0,他引:1
Piotr Mioduszewski Jerzy A. Ejsmont Jan Grabowski Daniel Karpiński 《Applied Acoustics》2011,72(8):582-589
This paper presents a comparison of two noise assessments in the Gdansk agglomeration in Poland. One is based on the noise map produced by computational method for the city in 2007, the second one is based on real data from continuous measurements acquired by a noise monitoring network operating in the city since 2008. Differences are shown and analyzed. Additionally, seasonal and weekday influence on noise indicators (LDEN, LD, LE and LN) is analyzed and discussed in this paper. 相似文献
999.
Resonant vibration control of rotating beams 总被引:3,自引:0,他引:3
Martin Nymann Svendsen Steen Krenk Jan Høgsberg 《Journal of sound and vibration》2011,330(9):1877-1256
Rotating structures, like e.g. wind turbine blades, may be prone to vibrations associated with particular modes of vibration. It is demonstrated, how this type of vibrations can be reduced by using a collocated sensor-actuator system, governed by a resonant controller. The theory is here demonstrated by an active strut, connecting two cross-sections of a rotating beam. The structure is modeled by beam elements in a rotating frame of reference following the beam. The geometric stiffness is derived in a compact form from an initial stress formulation in terms of section forces and moments. The stiffness, and thereby the natural frequencies, of the beam depend on the rotation speed and the controller is tuned to current rotation speed to match the resonance frequency of the selected mode. It is demonstrated that resonant control leads to introduction of the intended level of damping in the selected mode and, with good modal connectivity, only very limited modal spill-over is generated. The controller acts by resonance and therefore has only a moderate energy consumption, and successfully reduces modal vibrations at the resonance frequency. 相似文献
1000.
Using a coarse-grained molecular model we study the spatial distribution of lipid domains on a 20-nm-sized vesicle. The lipid mixture laterally phase separates into a raftlike, liquid-ordered (l(o)) phase and a liquid-disordered phase. As we uniaxially compress the mixed vesicle keeping the enclosed volume constant, we impart tension onto the membrane. The vesicle adopts a barrel shape, which is composed of two flat contact zones and a curved edge. The l(o) domain, which exhibits a higher bending rigidity, segregates to the highly curved edge. This inverted domain sorting switches to normal domain sorting, where the l(o) domain prefers the flat contact zone, when we release the contents of the vesicle. We rationalize this domain sorting by a pronounced reduction of the bending rigidity and area compressibility of the l(o) phase upon bending. 相似文献