全文获取类型
收费全文 | 389987篇 |
免费 | 5602篇 |
国内免费 | 1784篇 |
专业分类
化学 | 211356篇 |
晶体学 | 5886篇 |
力学 | 15756篇 |
综合类 | 64篇 |
数学 | 47306篇 |
物理学 | 117005篇 |
出版年
2020年 | 3316篇 |
2019年 | 3457篇 |
2018年 | 4486篇 |
2017年 | 4578篇 |
2016年 | 7095篇 |
2015年 | 4705篇 |
2014年 | 6951篇 |
2013年 | 17075篇 |
2012年 | 13542篇 |
2011年 | 16443篇 |
2010年 | 11483篇 |
2009年 | 11197篇 |
2008年 | 15554篇 |
2007年 | 15503篇 |
2006年 | 14551篇 |
2005年 | 13152篇 |
2004年 | 11801篇 |
2003年 | 10418篇 |
2002年 | 10261篇 |
2001年 | 11315篇 |
2000年 | 8631篇 |
1999年 | 6437篇 |
1998年 | 5418篇 |
1997年 | 5297篇 |
1996年 | 5255篇 |
1995年 | 4705篇 |
1994年 | 4784篇 |
1993年 | 4664篇 |
1992年 | 5080篇 |
1991年 | 5012篇 |
1990年 | 4815篇 |
1989年 | 4639篇 |
1988年 | 4579篇 |
1987年 | 4506篇 |
1986年 | 4372篇 |
1985年 | 5820篇 |
1984年 | 5936篇 |
1983年 | 5103篇 |
1982年 | 5421篇 |
1981年 | 5079篇 |
1980年 | 4831篇 |
1979年 | 5111篇 |
1978年 | 5348篇 |
1977年 | 5316篇 |
1976年 | 5328篇 |
1975年 | 4968篇 |
1974年 | 5064篇 |
1973年 | 5271篇 |
1972年 | 3795篇 |
1971年 | 3066篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
942.
The potential and polarization distributions in a planar emitting layer of PLZT-9/65/35 ferroelectric ceramic with a set of conductive strip electrodes on the emitting side and a continuous electrode on the opposite side are studied by numerical methods. The state arising immediately after polarization switching at the leading edge of an applied voltage pulse (i.e., before the polarization charges are screened by free charges) is considered. When the pulsed field strength far exceeds the double coercive field, regions with alternating polarization are found to form in the surface layer between the strips. The normal component of the polarization at its maxima is close to saturation. The electric field on both sides of the surface varies as the polarization vector and reaches 200 kV/cm. At surface microirregularities, the electric field strength is much higher. This means that field emission is responsible for electron escape from the ferroelectric ceramic during pulsed polarization switching. 相似文献
943.
The thermal decomposition of lead and manganese salts of mono(hydroxyethyl) phthalate was studied by thermogravimetry and differential scanning calorimetry. The kinetic parameters for the various stages of decomposition of these salts were calculated by different methods and mechanisms are proposed to explain the results. 相似文献
944.
The optimal return function for a Borel measurable gambling problem with a bounded utility function was shown by Strauch (1967)
to be universally measurable when the problem is leavable in the sense that the gambler may terminate play at any time. The
same is shown here for the more general class of nonleavable problems.
Research supported by National Science Foundation Grant DMS-8801085. 相似文献
945.
946.
W. Hufenbach R. Böhm A. Langkamp L. Kroll T. Ritschel 《Mechanics of Composite Materials》2006,42(2):151-162
The basic damage and failure models of multiaxially reinforced composites with a thermoplastic matrix are presented and verified.
Within the framework of continuum damage mechanics, a phenomenological model is introduced, where the damage is defined as
a change in the elasticity tensor. For damage identification, a specific ultrasonic device was developed. A combination of
an immersion set-up and a contact coupling device formed a system for an efficient determination of stiffness-tensor components
from convenient sets of velocity measurements. Linked to a tensile machine, it allowed us to measure the anisotropic damage
of the new materials group caused by tensile loading.
Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 2, pp. 221–234, March–April, 2006. 相似文献
947.
948.
L. Torrisi A.M. Mezzasalma J. Badziak J. Wolowski G. Franco 《Applied Surface Science》2006,252(24):8533-8538
High energy laser plasma-produced Cu ions have been implanted in silicon substrates placed at different distances and angles with respect to the normal to the surface of the ablated target. The implanted samples have been produced using the iodine high power Prague Asterix Laser System (PALS) using 438 nm wavelength irradiating in vacuum a Cu target. The high laser pulse energy (up to 230 J) and the short pulse duration (400 ps) produced a non-equilibrium plasma expanding mainly along the normal to the Cu target surface. Time-of-flight (TOF) technique was employed, through an electrostatic ion energy analyzer (IEA) placed along the target normal, in order to measure the ion energy, the ion charge state, the energy distribution and the charge state distribution. Ions had a Boltzmann energy distributions with an energy increasing with the charge state. At a laser fluence of the order of 6 × 106 J/cm2, the maximum ion energy was about 600 keV and the maximum charge state was about 27+.In order to investigate the implantation processes, Cu depth profiles have been performed with Rutherford backscattering spectrometry (RBS) of 1.5 MeV helium ions, Auger electron spectroscopy (AES) with 3 keV electron beam and 1 keV Ar sputtering ions in combination with scanning electron microscopy (SEM). Surface analysis results indicate that Cu ions are implanted within the first surface layers and that the ion penetration ranges are in agreement with the ion energy measured with IEA analysis. 相似文献
949.
We calculate the loss induced in a single-mode rectangular optical waveguide by the presence of a second waveguide, perpendicular to the first, which crosses over the first waveguide at a variable distance d. Our calculation is applied to the analysis of several doped silica waveguides of practical importance for optical circuit design. 相似文献
950.
The plastic deformation field near the horizontal surface of a half space of perfectly plastic material associated with an indenting rotating rigid tooth is studied using slip line theory. The tooth is one of many on a roll surface and indents first into the half-space material and then rotates about the roll center. A slip line field is proposed for the deforming plastic region and a solution scheme is outlined. The emphasis is on determining the shape of the deforming region, especially that of the free surface. The study has a potential application in roughness transfer in metal forming processing. 相似文献