全文获取类型
收费全文 | 357224篇 |
免费 | 6688篇 |
国内免费 | 4937篇 |
专业分类
化学 | 172938篇 |
晶体学 | 5303篇 |
力学 | 20789篇 |
综合类 | 325篇 |
数学 | 50810篇 |
物理学 | 118684篇 |
出版年
2021年 | 4675篇 |
2020年 | 5140篇 |
2019年 | 5920篇 |
2018年 | 7910篇 |
2017年 | 7950篇 |
2016年 | 10040篇 |
2015年 | 5377篇 |
2014年 | 9264篇 |
2013年 | 15455篇 |
2012年 | 13756篇 |
2011年 | 15496篇 |
2010年 | 12760篇 |
2009年 | 12867篇 |
2008年 | 14344篇 |
2007年 | 13871篇 |
2006年 | 12519篇 |
2005年 | 10808篇 |
2004年 | 10263篇 |
2003年 | 9415篇 |
2002年 | 9740篇 |
2001年 | 9215篇 |
2000年 | 7292篇 |
1999年 | 5599篇 |
1998年 | 5281篇 |
1997年 | 4962篇 |
1996年 | 4568篇 |
1995年 | 4004篇 |
1994年 | 4099篇 |
1993年 | 4081篇 |
1992年 | 4002篇 |
1991年 | 4403篇 |
1990年 | 4386篇 |
1989年 | 4314篇 |
1988年 | 4031篇 |
1987年 | 4082篇 |
1986年 | 3747篇 |
1985年 | 4309篇 |
1984年 | 4515篇 |
1983年 | 3892篇 |
1982年 | 4058篇 |
1981年 | 3699篇 |
1980年 | 3456篇 |
1979年 | 3997篇 |
1978年 | 4075篇 |
1977年 | 4203篇 |
1976年 | 4362篇 |
1975年 | 4059篇 |
1974年 | 3963篇 |
1973年 | 4085篇 |
1972年 | 3544篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The effect of variation of the scattered light intensity in a magnetic fluid with aggregates of magnetite particles several microns in size under the action of a magnetic field is studied. The effect relaxation times are determined when the magnetic field is turned on and off. This effect is found to be caused by the orientation of anisotropically magnetized aggregates. Experimental data are used to calculate the average anisotropy of the magnetic susceptibility of the aggregate and estimate its magnetic permeability. 相似文献
992.
Within the framework of the kinetic theory of strength, relations for estimation of durability of thermoplastic materials
under stationary and non-stationary thermomechanical impacts are obtained It is shown that durability decreases linearly with
increase in the natural (Napierian) logarithm of the mean size of microcracks formed during manufacturing of polymer products.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 3–6, July, 2007. 相似文献
993.
A model for the interaction of near-infrared laser pulses with metal powders in selective laser sintering 总被引:4,自引:0,他引:4
P. Fischer N. Karapatis V. Romano R. Glardon H.P. Weber 《Applied Physics A: Materials Science & Processing》2002,74(4):467-474
A thermal model of the interaction of pulsed near-infrared laser radiation from a Nd:YAG laser was made, taking the measured
powder properties such as reflectance, optical penetration depth and thermal conductivity into account. It allows an estimation
of the evolution of two different temperatures: the average temperature of the powder (taken over the grains in a volume given
by the laser beam diameter and the optical penetration depth) and the temperature distinction within a single grain. It showed
that in pulsed mode consolidation can be achieved at much lower average power as the surface of the powder particles are molten
but their cores remain at nearly room temperature. This leads to a much lower average temperature and therefore a dramatic
decrease in residual thermal stresses in the finished piece. The results of the model were experimentally tested and confirmed.
Received: 26 July 2001 / Accepted: 23 November 2001 / Published online: 23 January 2002 相似文献
994.
995.
E. S. Voropai M. P. Samtsov K. N. Kaplevskii A. A. Maskevich V. I. Stepuro O. I. Povarova I. M. Kuznetsova K. K. Turoverov A. L. Fink V. N. Uverskii 《Journal of Applied Spectroscopy》2003,70(6):868-874
Comparative analysis of the absorption and fluorescence spectra and fluorescence excitation spectra of thioflavin T (ThT) in various solvents and in the composition of amyloid fibrils has shown that ThT, when excited in the region of the long-wavelength absorption band, fluoresces in the spectral region with a maximum at 478–484 nm. The appearance in aqueous and alcohol solutions of a fluorescence band with a maximum near 440 nm has been attributed to the presence in the composition of the ThT preparations of an impurity with an absorption band in the 340–350-nm range. The literature data showing that in glycerol ThT has a wide fluorescence spectrum with two maxima are due to the artifact connected with the use of a high concentration of the dye. It has been suggested that the cause of the low quantum yield of ThT aqueous and alcohol solutions is the breakage of the system of conjugated bonds due to the reorientation of the benzothiozole and benzaminic rings of ThT in the excited state with respect to one another. The main factor determining the high quantum yield of fluorescence of ThT incorporated in fibrils is the steric restriction of the rotation of the rings about one another under these conditions. The suggestions made have been verified by the quantum-chemical calculation of the ThT molecule geometry in the ground and excited states. 相似文献
996.
997.
998.
D. V. Treschev 《Proceedings of the Steklov Institute of Mathematics》2007,259(1):196-235
We propose a method for constructing noncommutative analogs of objects from classical calculus, differential geometry, topology,
dynamical systems, etc. The standard (commutative) objects can be obtained from noncommutative ones by natural projections
(a set of canonical homomorphisms). The approach is ideologically close to the noncommutative geometry of A. Connes but differs
from it in technical details. 相似文献
999.
Madhu V. Nayakkankuppam 《Mathematical Programming》2007,109(2-3):477-504
We describe an approach to the parallel and distributed solution of large-scale, block structured semidefinite programs using
the spectral bundle method. Various elements of this approach (such as data distribution, an implicitly restarted Lanczos
method tailored to handle block diagonal structure, a mixed polyhedral-semidefinite subdifferential model, and other aspects
related to parallelism) are combined in an implementation called LAMBDA, which delivers faster solution times than previously
possible, and acceptable parallel scalability on sufficiently large problems.
This work was supported in part by NSF grants DMS-0215373 and DMS-0238008. 相似文献
1000.
V. I. Maslov 《Russian Physics Journal》2007,50(5):425-428
An abrupt rise of the field electron emission (FEE) current from a high-temperature superconductor (HTSC) being in the normal
state has been detected. The current amplification with a factor reaching ∼106 occurs as an HTSC emitter is heated in the temperature range 110–170 K. The features of the temperature dependence of FEE
are discussed. Measured parameters of the effect observed are presented. Possible mechanisms of the process under consideration
are discussed.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 13–16, May, 2007. 相似文献