全文获取类型
收费全文 | 436095篇 |
免费 | 4853篇 |
国内免费 | 1230篇 |
专业分类
化学 | 233806篇 |
晶体学 | 6489篇 |
力学 | 18765篇 |
综合类 | 13篇 |
数学 | 49933篇 |
物理学 | 133172篇 |
出版年
2021年 | 3774篇 |
2020年 | 4187篇 |
2019年 | 4521篇 |
2018年 | 5855篇 |
2017年 | 5749篇 |
2016年 | 8837篇 |
2015年 | 5562篇 |
2014年 | 8543篇 |
2013年 | 20186篇 |
2012年 | 15649篇 |
2011年 | 19261篇 |
2010年 | 13499篇 |
2009年 | 13352篇 |
2008年 | 17648篇 |
2007年 | 17541篇 |
2006年 | 16252篇 |
2005年 | 14550篇 |
2004年 | 13524篇 |
2003年 | 11892篇 |
2002年 | 11729篇 |
2001年 | 13429篇 |
2000年 | 10085篇 |
1999年 | 7916篇 |
1998年 | 6569篇 |
1997年 | 6314篇 |
1996年 | 6081篇 |
1995年 | 5470篇 |
1994年 | 5392篇 |
1993年 | 5197篇 |
1992年 | 5828篇 |
1991年 | 5924篇 |
1990年 | 5664篇 |
1989年 | 5472篇 |
1988年 | 5493篇 |
1987年 | 5374篇 |
1986年 | 5091篇 |
1985年 | 6560篇 |
1984年 | 6694篇 |
1983年 | 5301篇 |
1982年 | 5387篇 |
1981年 | 5367篇 |
1980年 | 4955篇 |
1979年 | 5352篇 |
1978年 | 5491篇 |
1977年 | 5385篇 |
1976年 | 5328篇 |
1975年 | 4914篇 |
1974年 | 4885篇 |
1973年 | 4880篇 |
1972年 | 3455篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
VICENTE LUIS N.; JUDICE JOAQUIM J.; PARDALOS PANOS M. 《IMA Journal of Management Mathematics》1992,4(4):343-349
In this paper, we discuss a multiparametric technique for findinga global minimum for an indefinite quadratic programming problembased on the spectral decomposition of the matrix of the quadraticform. Special attention is given to the case where this matrixhas only rank 1, where the multiparametric linear program turnsout to be a single-parameter linear program. An extension ofthe traditional linear parametric procedure is introduced whichin general solves this problem efficiently. However, an exampleis presented showing that this technique may take an exponentialnumber of steps. 相似文献
992.
J Perkell H Lane M Svirsky J Webster 《The Journal of the Acoustical Society of America》1992,91(5):2961-2978
Acoustic parameters were measured for vowels spoken in /hVd/ context by four postlingually deafened recipients of multichannel (Ineraid) cochlear implants. Three of the subjects became totally deaf in adulthood after varying periods of partial hearing loss; the fourth became totally deaf at age four. The subjects received different degrees of perceptual benefit from the prosthesis. Recordings were made before, and at intervals following speech processor activation. The measured parameters included F1, F2, F0, SPL, duration, and amplitude difference between the first two harmonic peaks in the log magnitude spectrum (H 1-H2). Numerous changes in parameter values were observed from pre- to post-implant, with differences among subjects. Many changes, but not all, were in the direction of normative data, and most changes were consistent with hypotheses about relations among the parameters. Some of the changes tended to enhance phonemic contrasts; others had the opposite effect. For three subjects, H 1-H2 changed in a direction consistent with measurements of their average air flow when reading; that relation was more complex for the fourth subject. The results are interpreted with respect to: characteristics of the individual subjects, including vowel identification scores; mechanical interactions among glottal and supraglottal articulations; and hypotheses about the role of auditory feedback in the control of speech production. Almost all the observed differences could be attributed to changes in the average settings of speaking rate, F0 and SPL, which presumably can be perceived without the need for spectral place information. Some observed F2 realignment may be attributable to the reception of spectral cues. 相似文献
993.
994.
Starting from a model of free Fermions in two dimensions with an arbitrary strong effective interaction, we derive a Ginzburg-Landau theory describing the crossover from BCS-superconductivity to Bose-condensation. We find a smooth crossover from the standard BCS-limit to a Gross-Pitaevski type equation for the order parameter in a Bose superfluid. The mean field transition temperature exhibits a maximum at a coupling strength, where the behaviour crosses over from BCS to Bose like with corresponding values of 2 Δ0/Tc ≈ 5 which are characteristic for high Tc superconductors. 相似文献
995.
The Borel-Weil (BW) construction for unitary irreps of a compact Lie group is extended to a construction of all unitary irreps of the quantum groupU
q(n). Thisq-BW construction uses a recursion procedure forU
q(n) in which the fiber of the bundle carries an irrep ofU
q(n–1)×U
q(1) with sections that are holomorphic functions in the homogeneous spaceU
q(n)/U
q(n–1)×U
q(1). Explicit results are obtained for theU
q(n) irreps and for the related isomorphism of quantum group algebras.Supported in part by the National Science Foundation, No. PHY-9008007 相似文献
996.
M. D. Roberts 《Czechoslovak Journal of Physics》1992,42(2):151-158
It is shown that: i) the Weyl tensor can be expressed in terms of the sum of a tensor and its double dual, where the tensor is constructed from the covariant derivatives of the Lanczos tensor, ii) a similar expression does not exist for the Riemann tensor in electromagnetic theory, iii) the electromagnetic field cannot be identified with the differential gauge freedom of the Lanczos tensor, iv) the symmetries of Einstein Maxwell theory and the Lanczos tensor do not prohibit the identification of the electromagnetic field with the algebraic gauge freedom of the Lanczos tensor, these symmetries require a differential equation relating the electromagnetic field tensor to the algebraic gauge vector and this is given. 相似文献
997.
An intensity-modulated optical fibre sensor system is described which employs a single LED source to provide the measurand and the reference signals with two separate wavelength bands. The allocated wavelength bands are selected to minimize any differential intensity effects that may arise from LED thermal variations. The sensor system, comprising a transceiver unit connected to an optical displacement sensor using a single optical fibre, provides an output fully referenced for all major common-mode variations that are likely to occur. Performance characteristics for the prototype system are reported which show a linear displacement range of over 20 mm. 相似文献
998.
O. M. Kiselev 《Mathematical Notes》1995,58(2):833-840
An asymptotic expansion uniform with respect to a parameter is obtained for a multiple Cauchy integral with a rapidly oscillating exponential in the integrand under the assumption that the singularity lines are in a general position.Translated fromMatematicheskie Zametki, Vol. 58, No. 2, pp. 231–242, August, 1995.The work was financially supported by the Russian Foundation for Basic Research under grant No. 94-01-00193-a. 相似文献
999.
1000.
The spectral dependence of the photoionization cross-section is calculated for shallow donors in GaAs/GaAlAs heterojunctions. The resulting spectra is found to be different for light polarized along and perpendicular to the growth direction. The calculations are repeated for both infinite- and finite-barrier models. 相似文献