全文获取类型
收费全文 | 354335篇 |
免费 | 2304篇 |
国内免费 | 975篇 |
专业分类
化学 | 149649篇 |
晶体学 | 5091篇 |
力学 | 20819篇 |
综合类 | 5篇 |
数学 | 71752篇 |
物理学 | 110298篇 |
出版年
2021年 | 1700篇 |
2020年 | 1807篇 |
2019年 | 2012篇 |
2018年 | 18811篇 |
2017年 | 19293篇 |
2016年 | 12177篇 |
2015年 | 3774篇 |
2014年 | 4008篇 |
2013年 | 9521篇 |
2012年 | 13981篇 |
2011年 | 27861篇 |
2010年 | 16988篇 |
2009年 | 17278篇 |
2008年 | 22680篇 |
2007年 | 27665篇 |
2006年 | 8097篇 |
2005年 | 14370篇 |
2004年 | 10837篇 |
2003年 | 10454篇 |
2002年 | 7670篇 |
2001年 | 6775篇 |
2000年 | 5469篇 |
1999年 | 3960篇 |
1998年 | 3249篇 |
1997年 | 3189篇 |
1996年 | 3099篇 |
1995年 | 2798篇 |
1994年 | 2613篇 |
1993年 | 2489篇 |
1992年 | 2798篇 |
1991年 | 2793篇 |
1990年 | 2705篇 |
1989年 | 2518篇 |
1988年 | 2581篇 |
1987年 | 2577篇 |
1986年 | 2401篇 |
1985年 | 3091篇 |
1984年 | 3348篇 |
1983年 | 2756篇 |
1982年 | 2920篇 |
1981年 | 2892篇 |
1980年 | 2752篇 |
1979年 | 2848篇 |
1978年 | 2950篇 |
1977年 | 2863篇 |
1976年 | 2961篇 |
1975年 | 2728篇 |
1974年 | 2694篇 |
1973年 | 2866篇 |
1972年 | 1809篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
Joseph Shipman 《Mathematical Intelligencer》2007,29(4):9-14
Theorems 2 and 3 establish the minimum algebraic conditions necessary for a field to be algebraically closed, and they can
therefore be said to “optimize” the Fundamental Theorem of Algebra. But each specific“degree implication” is a first-order
consequence of the axioms for fields, and could have been discovered two centuries ago; the existence of these finitary relationships
appears to have been unsuspected by practically everyone, with one important exception. 相似文献
982.
T. Hansel J. Müller C. Falldorf C. von Kopylow W. Jüptner R. Grunwald G. Steinmeyer U. Griebner 《Applied physics. B, Lasers and optics》2007,89(4):513-516
Digital holographic shape measurements using femtosecond laser pulses are reported. For contouring of very fast moving objects,
the simultaneous generation of at least two spectrally separated ultrashort pulses is required. To deliver this particular
spectral signature at high pulse energies, a chirped-pulse Ti:sapphire laser amplifier was modified to emit two spectrally
separated pulses with energies above 1 μJ each. The wavelength separation of these pulses was adjustable within the 50 nm
gain bandwidth, cutting out two distinct wavelength peaks by a variable double-slit assembly in a prism sequence. A Michelson-type
interferometer was employed to perform the two-wavelength contouring. The phases of the holograms and the phase differences
are calculated numerically, which allow us to deduce the contour lines of the topology of the object. The suitability of the
light source for digital holography is demonstrated with contouring of stationary objects and the potential for high-speed
applications is indicated.
PACS 42.40.-i; 42.60.By 相似文献
983.
Ling-yan Tang Song-he Song 《应用数学学报(英文版)》2007,23(2):303-310
In this paper,we use Daubechies scaling functions as test functions for the Galerkin method,and discuss Wavelet-Galerkin solutions for the Hamilton-Jacobi equations.It can be proved that the schemesare TVD schemes.Numerical tests indicate that the schemes are suitable for the Hamilton-Jacobi equations.Furthermore,they have high-order accuracy in smooth regions and good resolution of singularities. 相似文献
984.
A. M. Kharitonov 《Thermophysics and Aeromechanics》2007,14(1):3-11
Sergey Alekseevich Khristianovich is one of the famous Russian mechanical engineers of the 20th century together with N.E.
Zhukovsky, S.A. Chaplygin, N.E. Kochin, and others. He made an immense contribution to some aspects of mechanics, such as
aerogasdynamics, rock mechanics, theory of plasticity, filtration theory, and environmental power engineering. All this was
preceded by a long, hard, and fruitful life full of outstanding events. 相似文献
985.
E. Granot S. Sternklar D. Schermann Y. Ben-Aderet M.H. Itzhaq 《Applied physics. B, Lasers and optics》2006,82(3):359-362
We use the spectral ballistic imaging technique to measure the impulse response of a Fabry–Pérot etalon with less than 0.2 ps
temporal resolution. The results show excellent agreement with the theoretical predictions and negligible noise. Comparison
to the Kramers–Kronig method along with its limitations is also presented.
PACS 42.65.Re; 07.60.Ly; 42.30.Kq 相似文献
986.
987.
D. Kawamura A. Takita Y. Hayasaki N. Nishida 《Applied Physics A: Materials Science & Processing》2006,85(1):39-43
The morphology of a glass surface having a transparent coating processed with focused femtosecond laser pulses is investigated. The transparent coating is formed of poly-methyl methacrylate (PMMA). When the glass was coated with a PMMA film with a thickness of 2.8 μm, bumps were formed over a wide range of axial focus positions. The same laser pulse energy produced cavities when processing bare glass with no coating. The bumps were formed as a result of suppressing material emission from the glass surface by a shielding effect of plasma generated by ablation of the PMMA film and by physical blocking of the PMMA film. A thinner film with a thickness of 0.7 μm produced a reduced shielding effect, forming an exploded bump with a small pit at its center and debris around the periphery. PACS 44.10.+i; 61.80.Ba; 79.20.Ds 相似文献
988.
There are many advantages in being able to perform positron annihilation lifetime spectroscopy (PALS) using a variable energy positron beam, the most obvious being the easy identification of different defect types at different depths. The difficulty in conducting variable energy (VE) PALS studies lies in the fact that a “start” signal is required to signal the entry of the positron into the target. Two methods have been used to overcome this problem, namely the bunching technique, which employs radio frequency (RF) cavities and choppers, and secondly the use of secondary electrons emitted from the target. The latter technique is in terms of experimental complexity much simpler, but has in the past suffered from poor time resolution (typically ∼500 ps). In this work, we present a series of computer simulations of a design based on the secondary electron emission from thin C-foils in transmission mode which shows that significant improvements in time resolution can be made with resolutions ∼200 ps being in principle possible. 相似文献
989.
D. K. Kuznetsov I. S. Baturin V. Ya. Shur N. Menou C. Muller T. Schneller A. Sternberg 《Physics of the Solid State》2006,48(6):1174-1176
The effect of irradiation with electrons and neutrons and of exposure to synchrotron radiation on cyclic switching of polarization in thin films of lead zirconate titanate Pb(Zr,Ti)O3 (PZT) was studied. It is shown that variations in the shape of switching currents are due to the generation of a spatially nonuniform bound internal field with account for an increase in the rate of bulk screening caused by irradiation. A correlation between structural variations and the evolution of the switching current measured during and after irradiation is established. 相似文献
990.
V. P. Nekhoroshev Yu. P. Turov A. V. Nekhorosheva V. D. Ogorodnikov K. N. Gaevoi 《Russian Journal of Applied Chemistry》2006,79(5):833-840
The composition and structure of low-molecular-weight products of thermal oxidative degradation of atactic polypropylene were studied. 相似文献