全文获取类型
收费全文 | 628篇 |
免费 | 69篇 |
国内免费 | 112篇 |
专业分类
化学 | 288篇 |
晶体学 | 5篇 |
力学 | 9篇 |
数学 | 184篇 |
物理学 | 323篇 |
出版年
2024年 | 1篇 |
2023年 | 11篇 |
2022年 | 16篇 |
2021年 | 21篇 |
2020年 | 17篇 |
2019年 | 15篇 |
2018年 | 7篇 |
2017年 | 14篇 |
2016年 | 12篇 |
2015年 | 17篇 |
2014年 | 33篇 |
2013年 | 44篇 |
2012年 | 63篇 |
2011年 | 51篇 |
2010年 | 51篇 |
2009年 | 57篇 |
2008年 | 43篇 |
2007年 | 51篇 |
2006年 | 63篇 |
2005年 | 59篇 |
2004年 | 36篇 |
2003年 | 21篇 |
2002年 | 17篇 |
2001年 | 12篇 |
2000年 | 16篇 |
1999年 | 8篇 |
1998年 | 13篇 |
1997年 | 6篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1988年 | 6篇 |
1987年 | 9篇 |
1986年 | 5篇 |
排序方式: 共有809条查询结果,搜索用时 15 毫秒
701.
分析了两个各向同性材料界面处的本征模,从另一个角度来分析解释了布儒斯特定律.当入射光与界面处的表面模匹配时,入射光的能量就会全部转移到界面的本征场上,如果电磁波在折射介质中为行波,界面的本征场又会在折射介质中激发新的电磁波,形成透射波,也就是布儒斯特定律描述的横电波或者横磁波的全透射现象,这也可以看作是一种光学共振现象.横磁波的全透射现象往往出现在两个具有相同磁导率的介质的界面处,而横电波的全透射现象则往往出现在两个具有相同介电常数的介质的界面处. 相似文献
702.
703.
Mao-Sheng YangXiu-Bo Liu Ji-Wei FanXiang-Ming He Shi-Hong ShiGe-Yan Fu Ming-Di WangShu-Fa Chen 《Applied Surface Science》2012,258(8):3757-3762
The high temperature self-lubricating wear-resistant NiCr/Cr3C2-30%WS2 coating and wear-resistant NiCr/Cr3C2 coating were fabricated on 0Cr18Ni9 austenitic stainless steel by laser cladding. Phase constitutions and microstructures were investigated, and the tribological properties were evaluated using a ball-on-disc wear tester under dry sliding condition at room-temperature (17 °C), 300 °C and 600 °C, respectively. Results indicated that the laser clad NiCr/Cr3C2 coating consisted of Cr7C3 primary phase and γ-(Fe,Ni)/Cr7C3 eutectic colony, while the coating added with WS2 was mainly composed of Cr7C3 and (Cr,W)C carbides, with the lubricating WS2 and CrS sulfides as the minor phases. The wear tests showed that the friction coefficients of two coatings both decrease with the increasing temperature, while the both wear rates increase. The friction coefficient of laser clad NiCr/Cr3C2-30%WS2 is lower than the coating without WS2 whatever at room-temperature, 300 °C, 600 °C, but its wear rate is only lower at 300 °C. It is considered that the laser clad NiCr/Cr3C2-30%WS2 composite coating has good combination of anti-wear and friction-reducing capabilities at room-temperature up to 300 °C. 相似文献
704.
C. G. Jin T. Yu Z. F. Wu F. Wang M. Z. Wu Y. Y. Wang Y. M. Yu L. J. Zhuge X. M. Wu 《Applied Physics A: Materials Science & Processing》2012,106(4):961-966
Al-doped zinc oxide (AZO) films are prepared on quartz substrates by dual-ion-beam sputtering deposition at room temperature
(∼25°C). An assisting argon ion beam (ion energy E
i
=0–300 eV) directly bombards the substrate surface to modify the properties of AZO films. The effects of assisted-ion beam
energy on the characteristics of AZO films were investigated in terms of X-ray diffraction, atomic force microscopy, Raman
spectra, Hall measurement and optical transmittance. With increasing assisting-ion beam bombardment, AZO films have a strong
improved crystalline quality and increased radiation damage such as oxygen vacancies and zinc interstitials. The lowest resistivity
of 4.9×10−3Ω cm and highest transmittance of above 85% in the visible region were obtained under the assisting-ion beam energy 200 eV.
It was found that the bandgap of AZO films increased from 3.37 to 3.59 eV when the assisting-ion beam energy increased from
0 to 300 eV. 相似文献
705.
Let (X,T) be a topological dynamical system and be a sub-additive potential on C(X,R). Let U be an open cover of X. Then for any T-invariant measure μ, let . The topological pressure for open covers U is defined for sub-additive potentials. Then we have a variational principle:
706.
For large sparse saddle point problems, Chen and Jiang recently studied a class of generalized inexact parameterized iterative methods (see [F. Chen, Y.-L. Jiang, A generalization of the inexact parameterized Uzawa methods for saddle point problems, Appl. Math. Comput. 206 (2008) 765-771]). In this paper, the methods are modified and some choices of preconditioning matrices are given. These preconditioning matrices have advantages in solving large sparse linear system. Numerical experiments of a model Stokes problem are presented. 相似文献
707.
Chu Li-zhong 《东北数学》2010,26(3):230-238
Let (R, m) be a commutative Noetherian local ring, I an ideal of R and M a finitely generated R-module. Let limnHm^i(M/I^nM)be the ith formal local cohomology module of M with respect to I.In this paper, we discuss some properties of formal local cohomology modules limnHm^i(M/I^nM),which are analogous to the finiteness and Artinianness of local cohomology modules of a finitely generated module. 相似文献
708.
S. Zhu J. Fang X. Luo 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(1):123-128
A linear array of three lasers that are coupled mutually in space is investigated. It is shown that the phase of the laser
fields is locked with intermediate coupling while the laser intensities are totally chaotic and chaotically synchronized.
When the intensities of lasers reenter the regime of chaotic synchronization at smaller coupling constant, the laser fields
show low degree of phase locking. The phase differences in the fields between three lasers show rich patterns when the coupling
is changed.
Received 3 August 2001 and Received in final form 27 September 2001 相似文献
709.
The reaction of α-halo ketones (α-iodocycloalkanones, α-bromocycloalkanones, α-iodo-β-alkoxy esters, and α-iodoacyclicketones) with irradiation under a high-pressure mercury lamp gave the corresponding α-hydroxyketones in good yields. For α-bromoketones, it was found that α-hydroxylation does not occur. However, α-bromoketones were converted into α-hydroxyketones in the presence of KI. In the case of α,α′-diiodo ketones, α,α′-dihydroxyketones, which up to now have scarcely been reported, were obtained. This reaction affords a new, clean and convenient synthetic method for α-hydroxy- and α,α′-dihydroxyketones. 相似文献