全文获取类型
收费全文 | 16294篇 |
免费 | 1511篇 |
国内免费 | 1239篇 |
专业分类
化学 | 9328篇 |
晶体学 | 309篇 |
力学 | 1100篇 |
综合类 | 84篇 |
数学 | 1784篇 |
物理学 | 6439篇 |
出版年
2024年 | 17篇 |
2023年 | 185篇 |
2022年 | 395篇 |
2021年 | 398篇 |
2020年 | 432篇 |
2019年 | 512篇 |
2018年 | 436篇 |
2017年 | 377篇 |
2016年 | 552篇 |
2015年 | 527篇 |
2014年 | 672篇 |
2013年 | 963篇 |
2012年 | 1260篇 |
2011年 | 1325篇 |
2010年 | 938篇 |
2009年 | 945篇 |
2008年 | 993篇 |
2007年 | 843篇 |
2006年 | 853篇 |
2005年 | 674篇 |
2004年 | 614篇 |
2003年 | 517篇 |
2002年 | 553篇 |
2001年 | 707篇 |
2000年 | 518篇 |
1999年 | 386篇 |
1998年 | 307篇 |
1997年 | 234篇 |
1996年 | 247篇 |
1995年 | 189篇 |
1994年 | 180篇 |
1993年 | 133篇 |
1992年 | 169篇 |
1991年 | 147篇 |
1990年 | 136篇 |
1989年 | 100篇 |
1988年 | 75篇 |
1987年 | 60篇 |
1986年 | 56篇 |
1985年 | 55篇 |
1984年 | 43篇 |
1983年 | 32篇 |
1982年 | 33篇 |
1981年 | 34篇 |
1980年 | 26篇 |
1979年 | 21篇 |
1978年 | 25篇 |
1977年 | 19篇 |
1976年 | 18篇 |
1975年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
81.
We obtain sufficient conditions for the oscillation of all solutions of the higher order neutral differential equation dn/dm[y(t) + P(t) y(t - μ)] + Q(t) y(t ?σ) = 0, t ≧ t0 where n ≧ 1, P ? C[t0, ∞), R ], Q ? C[t0, ∞), R ] and τ, μ ? R +. Our results extend and improve several known results in the literature. 相似文献
82.
83.
The Hawking radiation of Dirac particles in an arbitrarily rectilinearly accelerating Kinnersley black hole with electromagnetic charge and cosmological constant is investigated by using the generalized tortoise coordinate transformation. Both the location and the temperature of the event horizon depend on the time and the polar angle. The Hawking thermal radiation spectrum of Dirac particles is also derived. 相似文献
84.
85.
Hui-Zhen Li Cheng-tian Xue 《International Journal of Infrared and Millimeter Waves》1991,12(12):1437-1449
This paper describes a global optimization design of quasi-optics power combiner of solid-state millimeterwave resonator. It is operated in the frequency range from 50 to 300 GHz using GaAs Gunn diodes. It is shown that sourcearrays containing N2 (N=3,5,...2K+1, where k is positive integer) individual elements. It is very efficient power transfer of energy from the source-array to the fractional power of the fundamental beam mode etc.. The RF output power exceeded the sum of the individual diodes to be threefold to sevenfold. And this data is the global optimization solution. 相似文献
86.
87.
The blends composed of polyamide 6 (PA6) and polyamide 66 (PA66) were obtained using two different preparation methods, one of which was the melt‐mixing through a twin‐screw extruder and the subsequent injection molding; and the other, the in situ blending through anionic polymerization of ε‐caprolactam in the presence of PA66. For the former, there existed a remarkable improvement in toughness but a drastic drop in strength and modulus; however, for the latter, a reverse but less significant trend of mechanical properties change appeared. Various characterizations were conducted, including the analyses of crystalline morphology, crystallographic form, and crystallization and melting behaviors using polarized optical microscopy (POM), wide‐angle X‐ray diffraction (WAXD), and differential scanning calorimetry (DSC), respectively; observation of morphology of fractured surface with scanning electron microscope (SEM); measurement of glass transition through dynamic mechanical analysis (DMA); and the intermolecular interaction as well as the interchange reaction between the two components by Fourier transform infrared spectrometry (FT‐IR) and 13C solution NMR. The presence and absence of interchange reaction was verified for the in situ and melt‐mixed blends, respectively. It is believed that the transreaction resulted in a drop in glass transition temperature (Tg) for the in situ blends, contrary to an increase of Tg with increasing PA66 content for the melt‐mixed ones. And the two kinds of fabrication methods led to significant differences in the crystallographic form, spherulite size and crystalline content and perfection as well. Accordingly, it is attempted to explain the reasons for the opposite trends of changes in the mechanical properties for these two blends. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1176–1186, 2007 相似文献
88.
All-optical wavelength conversion of 10-Gb/s signal based on four-wave mixing is experimentally demonstrated in a 30-m-long dispersion-flattened microstructure fiber with small positive dispersion. For an average pump power of 26 dBm, the conversion efficiency was around -19.5 dB with the fluctuation less than ±1.4 dB, covering a conversion bandwidth of 20 nm. The eye diagram of the converted signal shows good eye opening. 相似文献
89.
有限维路代数的K_1群 总被引:1,自引:0,他引:1
本文通过计算有限维路代数k△的单位群和单位群的阿贝尔化,完全刻划了 任意域上有限维路代数的K1群. 相似文献
90.
A. I. Golovashkin G. N. Izmaïlov G. V. Kuleshova T. Q. Khánh A. M. Tskhovrebov L. N. Zherikhina 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(3):243-249
A scheme of magnetic calorimeter for registration of rare events
characterized by small energy release (cosmic rays, WIMPs, solitary X-ray
quanta) is proposed. The calorimeter is brought to operation by adiabatic
demagnetization, and its magnetic response is measured by a quantum
interferometer (SQUID, A. Barone and G. Paterno, Physics and applications of Josephson Effect). Special consideration is given to the specific
features of calorimeter operation in the ferromagnetic transition region.
The trigger registration of ultrasmall energy release by a ferromagnetic
system in the metastable state is described. 相似文献