全文获取类型
收费全文 | 108351篇 |
免费 | 12183篇 |
国内免费 | 8754篇 |
专业分类
化学 | 52758篇 |
晶体学 | 982篇 |
力学 | 5512篇 |
综合类 | 518篇 |
数学 | 10112篇 |
物理学 | 31411篇 |
无线电 | 27995篇 |
出版年
2024年 | 209篇 |
2023年 | 2136篇 |
2022年 | 2385篇 |
2021年 | 3213篇 |
2020年 | 3207篇 |
2019年 | 3029篇 |
2018年 | 2758篇 |
2017年 | 2554篇 |
2016年 | 3800篇 |
2015年 | 3946篇 |
2014年 | 4827篇 |
2013年 | 6651篇 |
2012年 | 7912篇 |
2011年 | 8405篇 |
2010年 | 6115篇 |
2009年 | 6205篇 |
2008年 | 6608篇 |
2007年 | 6255篇 |
2006年 | 6096篇 |
2005年 | 5209篇 |
2004年 | 4050篇 |
2003年 | 3291篇 |
2002年 | 2946篇 |
2001年 | 3045篇 |
2000年 | 2699篇 |
1999年 | 2706篇 |
1998年 | 2279篇 |
1997年 | 2047篇 |
1996年 | 2004篇 |
1995年 | 1760篇 |
1994年 | 1609篇 |
1993年 | 1421篇 |
1992年 | 1283篇 |
1991年 | 1099篇 |
1990年 | 910篇 |
1989年 | 741篇 |
1988年 | 594篇 |
1987年 | 494篇 |
1986年 | 419篇 |
1985年 | 433篇 |
1984年 | 305篇 |
1983年 | 247篇 |
1982年 | 201篇 |
1981年 | 159篇 |
1980年 | 113篇 |
1978年 | 83篇 |
1977年 | 85篇 |
1976年 | 91篇 |
1975年 | 90篇 |
1973年 | 90篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
本文简要叙述利用流变仪对覆铜箔层压板生产工序中的胶液和半固化片参数进行控制,从而更好地保证胶液和 半固化片性状的一致性,以有利于控制板材流胶和品质。 相似文献
132.
A discussion about the quantum mechanical effects on noise properties of ballistic (phase-coherent) nanoscale devices is presented. It is shown that quantum noise can be understood in terms of quantum trajectories. This interpretation provides a simple and intuitive explanation of the origin of quantum noise that can be very salutary for nanoelectronic engineers. In particular, an injection model is presented that, coupled with a standard Monte Carlo algorithm, provides an accurate modeling of quantum noise. As a test, the standard results of noise in tunneling junction devices are reproduced within this approach. 相似文献
133.
134.
Several kinds of waveguide components such as curved waveguide bends, arbitrary angle waveguide bends and T-junctions have been analyzed with boundary element method in this paper. A new discretization method for the boundary element method to solve the waveguide discontinuities has been given. The numerical results obtained agree well with the experimental results and numerical results in other literature. Especially, the scattering characteristics of Forded E-, H-plane T-junctions in 3mm band have been analyzed using boundary element method and the calculation results are presented. 相似文献
135.
Tsung-Hui Huang Han-Jan Chen Chin-Sheng Chang Lih-Shan Chen Yeong-Her Wang Mau-Phon Houng 《Microwave and Wireless Components Letters, IEEE》2006,16(6):360-362
In this letter, a novel compact ring dual-mode with adjustable second-passband for dual-band applications are presented. A ring resonator with two different geometric dimensions are derived and designed to have identical fundamental and the first higher-order resonant frequencies, and to establish appropriate couplings in the structure. Moreover, the proposed filter has smaller size as compared with the basic topology of stopband filters and stepped-impedance-resonator (SIR) filters. The measured filter performance is in good agreement with the simulated response. 相似文献
136.
欧盟的电信管制陷入了与国家政体冲突的泥潭中,尽管高层有一些关于改革的勇敢论调,但事实胜于雄辩。欧盟所规定的电信规则设想在这个有25个国家、超过4.5亿人口的市场,以远远超出这个范围的影响创造一个公平的竞争环境,它能奏效吗?于布鲁塞尔制定的电信政策在许多方面呈现多极化趋向,这反映了对泛欧“超级国家”实体更大的争议。根据每天问题的不同,随着观点的转移,欧洲电信规则被同等程度地喜爱和痛恨着。对一方来说很协调的东西,对另一方则成了毫无根据 相似文献
137.
Biao Chen Hao Wang 《Signal Processing, IEEE Transactions on》2004,52(7):2047-2057
Blind deterministic estimation of the orthogonal frequency division multiplexing (OFDM) frequency offset via oversampling is proposed in this paper. This method utilizes the intrinsic phase shift of neighboring sample points incurred by the frequency offset that is common among all subcarriers. The proposed method is data efficient - it requires only a single OFDM symbol to achieve reliable estimation, hence making it more suitable to systems with stringent delay requirement and mobility-induced channel variation. The proposed scheme is devised to perfectly retrieve frequency offset in the absence of noise. Quite remarkably, we show that in the presence of channel noise, this intuitive scheme is indeed the maximum likelihood estimate of the carrier frequency offset. The possible presence of virtual carriers are also accommodated in the system model, and some interesting observations are obtained. The Cramer-Rao lower bound is derived for the oversampling-based signal model, and we show through numerical simulation that the proposed algorithm is efficient. Practical issues such as identifiability, the front-end filter bandwidth, and the possible presence of correlated noises are also carefully addressed. 相似文献
138.
139.
In order to complement subjective evaluation of the quality of segmentation masks, this paper introduces a procedure for automatically assessing this quality. Algorithmically computed figures of merit are proposed. Assuming the existence of a perfect reference mask (ground truth), generated manually or with a reliable procedure over a test set, these figures of merit take into account visually desirable properties of a segmentation mask in order to provide the user with metrics that best quantify the spatial and temporal accuracy of the segmentation masks. For the sake of easy interpretation, results are presented on a peaked signal-to-noise ratio-like logarithmic scale. 相似文献
140.
GaN-MOCVD设备反应室流场的CFD数值仿真 总被引:11,自引:2,他引:9
采用计算流体力学方法对生长半导体材料GaN的重要设备MOCVD(金属有机物化学气相沉积)反应室中的流场结构进行了三维数值仿真.数值模拟采用基于非交错网格系统的SIMPLE算法,用有限体积方法对控制方程进行离散,并采用改进的压力-速度耦合方法进行求解.数值仿真给出了具有复杂几何结构和运动方式的GaN-MOCVD反应室中的流场结构,研究了改变几何尺寸和运行参数对MOCVD反应室流场结构的影响,对正在试制开发中的MOCVD设备的几何结构的改进和运行参数的优化提出了指导性建议. 相似文献