全文获取类型
收费全文 | 33300篇 |
免费 | 3224篇 |
国内免费 | 3812篇 |
专业分类
化学 | 27554篇 |
晶体学 | 458篇 |
力学 | 1590篇 |
综合类 | 217篇 |
数学 | 3197篇 |
物理学 | 7320篇 |
出版年
2024年 | 47篇 |
2023年 | 349篇 |
2022年 | 999篇 |
2021年 | 923篇 |
2020年 | 1095篇 |
2019年 | 1064篇 |
2018年 | 956篇 |
2017年 | 1193篇 |
2016年 | 1287篇 |
2015年 | 1182篇 |
2014年 | 1484篇 |
2013年 | 2367篇 |
2012年 | 1845篇 |
2011年 | 2092篇 |
2010年 | 1739篇 |
2009年 | 2148篇 |
2008年 | 1951篇 |
2007年 | 2024篇 |
2006年 | 1809篇 |
2005年 | 1646篇 |
2004年 | 1674篇 |
2003年 | 1301篇 |
2002年 | 1598篇 |
2001年 | 952篇 |
2000年 | 791篇 |
1999年 | 645篇 |
1998年 | 547篇 |
1997年 | 497篇 |
1996年 | 532篇 |
1995年 | 498篇 |
1994年 | 476篇 |
1993年 | 337篇 |
1992年 | 347篇 |
1991年 | 210篇 |
1990年 | 163篇 |
1989年 | 163篇 |
1988年 | 176篇 |
1987年 | 133篇 |
1986年 | 103篇 |
1985年 | 85篇 |
1984年 | 86篇 |
1983年 | 32篇 |
1982年 | 84篇 |
1981年 | 108篇 |
1980年 | 123篇 |
1979年 | 121篇 |
1978年 | 99篇 |
1977年 | 72篇 |
1976年 | 64篇 |
1973年 | 36篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
The increasing use of Ultraviolet (UV) light in medicine, industrial environments, for cosmetic use, and even in consumer products necessitates that greater attention be paid to the potential hazards of this type of electromagnetic radiation. To avoid any adverse effects of exposure to this type of radiation, four suitable protection filters were produced to block three UV bands (UVA, UVB, and UVC). The design structure of the required dielectric multilayer filters was done by optical thin film technology using the absorbing property of UV radiation for the substrates and dielectric materials. The computer analyses of the multilayer filter formulas were prepared using Macleod Software for the production processes. The deposition technique was achieved on optical substrates (Glass BK-7 and Infrasil 301) by dielectric material combinations including Titanium dioxide (Ti2O3), Hafnium dioxide (HfO2), and Lima (mixture of oxides SiO2/Al2O3); deposition being achieved using an electron beam gun. The output results of the theoretical and experimental transmittance values for spectral band from 200 nm to 800 nm were discussed in four processes. To analyze the suitability for use in ‘real world’ applications, the test pieces were subjected to the durability tests (adhesion, abrasion resistance, and humidity) according to Military Standard MIL-C-675C and MIL-C-48497A. 相似文献
162.
A palladium‐TPPTS catalyst heterogenized on KF/alumina has been shown to be effective and recyclable for the selective formation of monooctadienylxylopyranosides via the telomerization of butadiene with D ‐xylose. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
163.
164.
This paper studies the tail behavior of the fundamental period in the MAP/G/1 queue. We prove that if the service time distribution
has a regularly varying tail, then the fundamental period distribution in the MAP/G/1 queue has also regularly varying tail,
and vice versa, by finding an explicit expression for the asymptotics of the tail of the fundamental period in terms of the
tail of the service time distribution. Our main result with the matrix analytic proof is a natural extension of the result
in (de Meyer and Teugels, J. Appl. Probab. 17: 802–813, 1980) on the M/G/1 queue where techniques rely heavily on analytic expressions of relevant functions.
I.-S. Wee’s research was supported by the Korea Research Foundation Grant KRF 2003-070-00008. 相似文献
165.
Highly ordered composite nanowires with multilayer Ni/Cu and NiFe/Cu have been fabricated by pulsed electrodeposition into
nanoporous alumina membrane. The diameter of wires can be easily varied by pore size of alumina, ranging from 30 to 100 nm.
The applied potential and the duration of each potential square pulse determine the thickness of the metal layers. The nanowires
have been characterized by transmission electron microscopy (TEM), magnetic force microscopy (MFM), and vibrating sample magnetometer
(VSM) measurements. The MFM images indicate that every ferromagnetic layer separated by Cu layer was present as single isolated
domain-like magnet. This technique has potential use in the measurement and application of magnetic nanodevices. 相似文献
166.
微纳米加工技术及其应用综述 总被引:2,自引:0,他引:2
材料与结构在微纳米尺度展现了许多不同于宏观尺度的新特征,纳米技术已经成为当前科学研究与工业开发的热门领域之一。微小型化依赖于微纳米尺度的功能结构与器件,实现功能结构微纳米化的基础是先进的微纳米加上技术,文章对微纳米加上技术做了一个综合的介绍,简要说明了微纳米加工技术与传统加工技术的区别,在微纳米加工技术的应用方面提出了一些合理选择加工技术的原则,并对当前微纳米加工技术面临的挑战和今后发展的趋势作了预测。 相似文献
167.
采用溶胶-凝胶工艺与原位生长技术,制备了ZnSe/SiO2复合薄膜.X射线衍射分 析表明薄膜中ZnSe晶体呈立方闪锌矿结构.X射线荧光分析结果显示薄膜中Zn与Se摩尔比为1 ∶1.01—1∶1.19.利用场发射扫描电子显微镜观察了复合薄膜的表面形貌,结果表明复合薄 膜表面既存在尺寸约为400nm的ZnSe晶粒,也存在尺寸小于100nm的ZnSe晶粒.利用椭偏仪测 量了薄膜椭偏角Ψ,Δ与波长λ的关系,采用Maxwell-Garnett有效介质理论对薄膜的光学 常数、厚度、气孔率、ZnS
关键词:
2复合薄膜')" href="#">ZnSe/SiO2复合薄膜
光学性质
椭偏光度法
荧光光谱 相似文献
168.
Karl Sigman 《Operations Research Letters》2007,35(5):581-583
In Mandelbaum and Yechiali [The conditional residual service time in the M/G/1 queue, http://www.math.tau.ac.il/∼uriy/publications (No. 30a), 1979] and in Fakinos [The expected remaining service time in a single-server queue, Oper. Res. 30 (1982) 1014-1018] a simple formula is derived for the (stationary) expected remaining service time in a M/G/1 queue, conditional on the number of customers in the system. We give a short new proof of the formula using Rate Conservation Law, and generalize to handle higher moments. 相似文献
169.
We study theoretically a nonlinear response of the planar metal/dielectric nanostructures constituted from periodical array
of ultra thin silver layers and the layers of Kerr-like nonlinear dielectric. We predict hysteresis-type dependences of the
components of the tensor of effective dielectric permittivity on the field intensity allowing the change in material transmission
properties from transparent to opaque and back at extremely low intensities of the light. It makes possible to control the
light by light in all-optical nanoscale devices and circuits. 相似文献
170.