全文获取类型
收费全文 | 28293篇 |
免费 | 4259篇 |
国内免费 | 3879篇 |
专业分类
化学 | 15660篇 |
晶体学 | 350篇 |
力学 | 993篇 |
综合类 | 247篇 |
数学 | 2219篇 |
物理学 | 7047篇 |
无线电 | 9915篇 |
出版年
2024年 | 112篇 |
2023年 | 609篇 |
2022年 | 876篇 |
2021年 | 1063篇 |
2020年 | 1044篇 |
2019年 | 995篇 |
2018年 | 921篇 |
2017年 | 948篇 |
2016年 | 1159篇 |
2015年 | 1350篇 |
2014年 | 1627篇 |
2013年 | 2087篇 |
2012年 | 2406篇 |
2011年 | 2445篇 |
2010年 | 2038篇 |
2009年 | 1878篇 |
2008年 | 2065篇 |
2007年 | 1927篇 |
2006年 | 1709篇 |
2005年 | 1420篇 |
2004年 | 1078篇 |
2003年 | 970篇 |
2002年 | 912篇 |
2001年 | 809篇 |
2000年 | 671篇 |
1999年 | 521篇 |
1998年 | 383篇 |
1997年 | 306篇 |
1996年 | 350篇 |
1995年 | 302篇 |
1994年 | 216篇 |
1993年 | 168篇 |
1992年 | 148篇 |
1991年 | 140篇 |
1990年 | 137篇 |
1989年 | 100篇 |
1988年 | 68篇 |
1987年 | 67篇 |
1986年 | 46篇 |
1985年 | 42篇 |
1984年 | 28篇 |
1983年 | 33篇 |
1982年 | 31篇 |
1981年 | 18篇 |
1979年 | 32篇 |
1978年 | 29篇 |
1977年 | 18篇 |
1976年 | 18篇 |
1975年 | 21篇 |
1973年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
We propose a minimum mean absolute error linear interpolator (MMAELI), based on theL
1 approach. A linear functional of the observed time series due to non-normal innovations is derived. The solution equation
for the coefficients of this linear functional is established in terms of the innovation series. It is found that information
implied in the innovation series is useful for the interpolation of missing values. The MMAELIs of the AR(1) model with innovations
following mixed normal andt distributions are studied in detail. The MMAELI also approximates the minimum mean squared error linear interpolator (MMSELI)
well in mean squared error but outperforms the MMSELI in mean absolute error. An application to a real series is presented.
Extensions to the general ARMA model and other time series models are discussed.
This research was supported by a CityU Research Grant and Natural Science Foundation of China. 相似文献
102.
103.
104.
Gwang Hui Kim 《Journal of Mathematical Analysis and Applications》2004,299(2):375-391
In this paper we investigate a generalization of the Hyers-Ulam-Rassias stability for a functional equation of the form f(φ(X))=?(X)f(X)+ψ(X) and the stability in the sense of Ger for the functional equation of the form f(φ(X))=?(X)f(X), where X lie in n-variables. As a consequence, we obtain a stability result in the sense of Hyers-Ulam-Rassias, Gǎvruta, and Ger for some well-known equations such as the gamma, beta, and G-function type's equations. 相似文献
105.
LI Na ZHAO Degang & YANG Hui State Key Laboratory on Integrated Optoelectronics Institute of Semiconductors Chinese Academy of Sciences Beijing China 《中国科学G辑(英文版)》2004,47(6):694-701
Because of their large band-gap, large high-field electron velocity, large breakdownfield, and large thermal conductivity, GaN and its heterojunction with AlGaN and InGaNhave foreseeable potential in the applications of high-power/temperature electronics, andoptoelectronic devices operative in UV and visible wavelength. Polarization inducedelectric field can reach the magnitude of ~MV/cm[1,2]. For AlGaN/GaN based FETs theconcentration of sheet carrier induced by polarization in the cha… 相似文献
106.
Chongyi Wan Shiming Liu Rongqing Tan Jin Wu Jinwen Zhou Yan Lv Yanning Yu Hua Yang 《Optics & Laser Technology》2004,36(8):2389-649
A high average power, high-repetition-rate TEA CO2 laser employing printed-circuit-board preionizer is described. The power scaling of this preionization configuration has been demonstrated. The average output power reaches 3.6 kW at pulse repetition rate of 180 pps. Furthermore, the scaling-up ability of the rotating spark gap as high-voltage switch for high-average-power gas laser has been validated. 相似文献
107.
108.
当外电路的电阻等于电源内电阻时,电源输出功率最大,应用这个结论,可以省去许多计算步骤.但实际应用时还要注意一些问题,下面从几个方面加以讨论.1 电源实际输出功率与最大输出功率的区别 这是两个不同的概念,一些学生往往会用Pm=(?)/4r计算电源输出最大功率,其实,(?)/4r只是电源输出功率的极限,电源一般不在该状态下工作. 相似文献
109.
Two new polyacid derivative ligands of thienyl-substituted terpyridine analogues, N,N,N1,N1-[4′-(2?-thienyl)-2,2′:6′,2″-terpyridine-6,6″-diyl]bis(methylenenitrilo) tetrakis(acetic acid) (TTTA) and N,N,N1,N1-[2,6-bis(3′-aminomethyl-1′-pyrazolyl)-4-(2″-thienyl)pyridine] tetrakis(acetic acid) (BTTA), were synthesized, and the luminescence properties of their Eu3+ and Tb3+ chelates were investigated. The Eu3+chelates of the two ligands are strongly luminescent having luminescence quantum yields of 0.150 (TTTA-Eu3+) and 0.114 (BTTA-Eu3+), and lifetimes of 1.284 ms (TTTA-Eu3+) and 1.352 ms (BTTA-Eu3+), whereas their Tb3+ chelates are weakly luminescent. The TTTA-Eu3+ chelate was used for streptavidin (SA) labeling, and the labeled SA was used for time-resolved fluoroimmunoassay of insulin in human sera. The method gives the detection limits of 33 pg ml−1. 相似文献
110.
QiaoHongYAO FuYouLI LuSHAN ChunHuiHUANG DongDongYIN 《中国化学快报》2003,14(11):1185-1188
A new photoresponsive D-π-A dye, mPS, has been designed and synthesized.Compared to the parent dye PS, IPCE values in the region from 400 nm to 560 nm was greatly improved upon changing the attaching group from the p- position to the o- position of the π-conjugation bridge. A solar cell based on mPS generated a remarkably high overall yield η of 5.4% under irradiation of 80.0 mW cm^-2 white light from a Xe lamp, Compared with PS, the overall yield η increased by 64%. 相似文献