全文获取类型
收费全文 | 645397篇 |
免费 | 6123篇 |
国内免费 | 1565篇 |
专业分类
化学 | 326106篇 |
晶体学 | 9512篇 |
力学 | 32096篇 |
综合类 | 20篇 |
数学 | 85707篇 |
物理学 | 199644篇 |
出版年
2021年 | 5861篇 |
2020年 | 6500篇 |
2019年 | 7367篇 |
2018年 | 10036篇 |
2017年 | 9971篇 |
2016年 | 14177篇 |
2015年 | 8040篇 |
2014年 | 13310篇 |
2013年 | 28867篇 |
2012年 | 22690篇 |
2011年 | 27313篇 |
2010年 | 20412篇 |
2009年 | 20475篇 |
2008年 | 25657篇 |
2007年 | 25239篇 |
2006年 | 23183篇 |
2005年 | 20484篇 |
2004年 | 19227篇 |
2003年 | 17210篇 |
2002年 | 17368篇 |
2001年 | 18574篇 |
2000年 | 14378篇 |
1999年 | 11096篇 |
1998年 | 9583篇 |
1997年 | 9249篇 |
1996年 | 8760篇 |
1995年 | 7910篇 |
1994年 | 7872篇 |
1993年 | 7651篇 |
1992年 | 8247篇 |
1991年 | 8590篇 |
1990年 | 8313篇 |
1989年 | 8167篇 |
1988年 | 7945篇 |
1987年 | 7899篇 |
1986年 | 7421篇 |
1985年 | 9356篇 |
1984年 | 9567篇 |
1983年 | 7801篇 |
1982年 | 8050篇 |
1981年 | 7756篇 |
1980年 | 7240篇 |
1979年 | 7969篇 |
1978年 | 8161篇 |
1977年 | 8190篇 |
1976年 | 8157篇 |
1975年 | 7545篇 |
1974年 | 7397篇 |
1973年 | 7523篇 |
1972年 | 5750篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
Pre—Separation Axioms in Fuzzifying Topology 总被引:1,自引:0,他引:1
K.M.AbdEl-Hakeim F.M.Zeyada 《模糊系统与数学》2003,17(1):28-36
1 IntroductionYing[5,6 ] introduced and elementally developed so called fuzzifying topology with the semanticmethod of continuous valued L ogic.Shen[7] introduced and studied T0 -,T1-,T2 (Hausdorff) -,T3(regularity) -,T4 (normality) -separation axioms in fuzzifying topology.In [3 ]the concepts of thefamily of fuzzifying pre-open sets,fuzzifying pre-neighbourhood structure of a point and fuzzifyingpre-closure are introduced and studied.It is worth to mention that pre-separation axioms are … 相似文献
982.
983.
The projection approach is applied to construct and investigate an operator-difference scheme for fluid dynamics in Lagrangean variables which has first-order local approximation in the axisymmetric case near the symmetry axis. The scheme also has operator properties that make it suitable for rederiving and substantiating previous results, methods, and algorithms. 相似文献
984.
P. V. Yagodovskii 《Journal of Mathematical Sciences》2003,113(5):728-730
A linear deformation of a discrete group G is a special deformation of the group algebra of G resulting in the group algebra of a multivalued group. Basic results on linear deformations are presented. Bibliography: 5 titles. 相似文献
985.
We prove that given a simply connected compact manifold M and a
closed manifold N, any map in the Sobolev space W
1,2(M,N) can be
approximated weakly by smooth maps between M and N.
Submitted: September 2002, Final version: November 2002. 相似文献
986.
M.B. Xu 《Applied Acoustics》2003,64(7):731-752
The forced vibration of an infinite elastic circular cylindrical shell filled with fluid is studied. Three methods are employed to analyze the forced vibration problem of this shell-fluid coupled system, that is, wave propagation approach (wave mode superposition), theorem of residues and a numerical integral method. In order to explain these methods more explicitly, before being used to investigate the vibration of an infinite fluid-filled elastic circular cylindrical shell, all these three methods are employed firstly to analyze the forced vibration problem of an infinite beam and an infinite elastic circular cylindrical shell in vacuo. Advantage and disadvantage of these three methods are discussed and their interesting relationship is revealed. That is, to any circumferential wavenumber and frequency of the external force, there is an unchangeable relationship between the general coordinates of various waves in the wave propagation approach and the residuals in the theorem of residues. 相似文献
987.
In a Young–Michelson tandem interferometer a Michelson interferometer is illuminated through a pair of Young slits. The pattern produced by this set-up is analyzed theoretically. The consequences of small misalignments and uncompensated arms in the Michelson interferometer are studied. The effects of the spatial and temporal partial coherence of the source are also explored. Experimental results using a laser source are shown to be in good agreement with the predicted theoretical calculations. 相似文献
988.
Time-resolved electron transport studies on InGaAs/GaAs-QWIPs 总被引:1,自引:0,他引:1
S. Steinkogler H. Schneider R. Rehm M. Walther P. Koidl P. Grant R. Dudek H. C. Liu 《Infrared Physics & Technology》2003,44(5-6):355-361
Due to the short internal response time, quantum-well infrared photodetectors (QWIPs) are interesting for high-speed applications such as heterodyne spectroscopy or laser pulse monitoring. We studied the photocurrent transients of InGaAs/GaAs-QWIPs after irradiation with infrared laser pulses of 250 fs duration. The excitation wavelength of about 9 μm matches the peak wavelength of the QWIP structure. The photocurrent transient consists of two different dynamical components, representing the fast photoionization in the quantum-wells and the slow injection current that compensates the remaining space charge. The investigations of the different components as a function of temperature and bias voltage were performed on a nanosecond time-scale. The experimental separation of the two photocurrent contributions allows us to determine the photoconductive gain. The Fourier transform of the photocurrent transient was compared with other experimental methods including heterodyne detection and microwave rectification. The quantitative agreement between these different measurement techniques is excellent. 相似文献
989.
Glezer A.M. Blinova E.N. Pozdnyakov V.A. Shelyakov A.V. 《Journal of nanoparticle research》2003,5(5-6):551-560
Journal of Nanoparticle Research - It was shown that the thermoelastic martensite transformation B2 ? B19 inside nanoparticles surrounded by amorphous matrix in Ni–Ti–Cu alloys as... 相似文献
990.
N. Segovia M. A. Armienta C. Valdes M. Mena J. L. Seidel M. Monnin P. Pea M. B. E. Lopez A. V. Reyes 《Radiation measurements》2003,36(1-6):379-383
Soil radon has been monitored at two fixed stations in the northern flank of Popocatepetl Volcano, a high risk volcano located 60 km SE from Mexico City. Water samples from three springs were also studied for radon as well as major and trace elements. Radon in the soil was recorded using track detectors. Radon in the water samples was evaluated using the liquid scintillation method and an Alphaguard. The major elements were determined through conventional chemical methods and trace elements using an ICP-MS equipment. Soil radon levels were low, indicating a moderate diffuse degassing through the flanks of the volcano. Groundwater radon had almost no relation with the eruptive stages. Water chemistry was stable in the reported time (2000–2002). 相似文献