全文获取类型
收费全文 | 12055篇 |
免费 | 2402篇 |
国内免费 | 1247篇 |
专业分类
化学 | 1550篇 |
晶体学 | 66篇 |
力学 | 620篇 |
综合类 | 108篇 |
数学 | 816篇 |
物理学 | 3866篇 |
无线电 | 8678篇 |
出版年
2024年 | 73篇 |
2023年 | 173篇 |
2022年 | 279篇 |
2021年 | 296篇 |
2020年 | 379篇 |
2019年 | 357篇 |
2018年 | 351篇 |
2017年 | 466篇 |
2016年 | 579篇 |
2015年 | 595篇 |
2014年 | 876篇 |
2013年 | 973篇 |
2012年 | 888篇 |
2011年 | 1014篇 |
2010年 | 780篇 |
2009年 | 826篇 |
2008年 | 815篇 |
2007年 | 811篇 |
2006年 | 780篇 |
2005年 | 618篇 |
2004年 | 564篇 |
2003年 | 571篇 |
2002年 | 426篇 |
2001年 | 375篇 |
2000年 | 376篇 |
1999年 | 265篇 |
1998年 | 190篇 |
1997年 | 166篇 |
1996年 | 128篇 |
1995年 | 124篇 |
1994年 | 81篇 |
1993年 | 86篇 |
1992年 | 68篇 |
1991年 | 53篇 |
1990年 | 52篇 |
1989年 | 59篇 |
1988年 | 40篇 |
1987年 | 35篇 |
1986年 | 17篇 |
1985年 | 18篇 |
1984年 | 21篇 |
1983年 | 12篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 5篇 |
1979年 | 10篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1973年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
251.
基于Wigner-Hough变换的多分量LFM信号 检测及离散计算方法 总被引:12,自引:1,他引:12
Wigner-Hough变换对LFM信号有压缩和聚焦的作用,这种作用的又具有阈值特性,本文简述Wigner-Hough变换的方法及对该方法的评价.重点讨论Wigner-Hough变换的离散计算,提出了一种对Wigner变换的结果再进行Hough变换的类似二维搜索的离散计算方法. 相似文献
252.
LTCC基板制造工艺研究 总被引:8,自引:0,他引:8
低温共烧多层陶瓷(LTCC)基板是制造复杂微电子产品多芯片组件(MCM)的重要部件。详细地讨论了LTCC基板制造工艺,介绍了多年研究之经验及国外的有关技术,还指出了目前工艺中存在的技术问题及在工艺水平上与国外的差距。采用目前工艺,可做出20层布线、线宽及间距均为0.20mm、80mm×80mm的多层共烧基板 相似文献
253.
Wei Jiang Hongping Li Sheng Yin Xin Wang Wei Liu Hui Liu Wenshuai Zhu Huaming Li 《应用有机金属化学》2016,30(9):753-758
Two hexacyanoferrate‐based ionic liquids, [C4Py]3Fe(CN)6 and [C16Py]3Fe(CN)6, were synthesized and characterized using Fourier transform infrared and mass spectroscopies and CHN analysis. They were employed as Fenton‐like catalysts in extraction and catalytic oxidative desulfurization of model oil with dibenzothiophene (DBT), benzothiophene (BT), 4,6‐dimethyldibenzothiophene (4,6‐DMDBT), 4‐methyldibenzothiophene (4‐MDBT) and 3‐methylbenzothiophene (3‐MBT) as substrates. Various polar solvents, such as ionic liquids, water and organic solvents, were applied to choose a suitable extractant. The results showed the removal of DBT reached 97.1% with [C4Py]3Fe(CN)6 as a catalyst and 1‐n‐octyl‐3‐methylimidazolium hexafluorophosphate ([C8mim]PF6) as an extractant under optimal conditions. The activity of sulfur removal followed the order DBT > 3‐MBT > BT > 4‐MDBT >4,6‐DMDBT. The effect of water content on sulfur removal was investigated by adding various concentrations of H2O2. It was found that excess water had a positive effect on sulfur removal but the catalysts were less sensitive than [FeCl4?]‐based catalysts to water. The mechanism was studied using electron spin‐resonance spectroscopy and gas chromatography–mass spectrometry. O2?? may be the active oxygen species in the catalytic oxidative desulfurization process and the oxidation products of various sulfur compounds were the corresponding sulfoxides and sulfones. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
254.
The energy transfer from the upper triplet states of diphenylamine, naphthalene and triphenylene to toluene and hexene-1 is studed. Two mechanisms of dissipation transferred energy in solvents are discussed. 相似文献
255.
The periodic structure of the underlying support of paintings on canvas can become quite prominent and disturbing in high resolution digital recordings. In this paper, we construct a new model and method for the digital removal of canvas which is considered as a noise component superimposed on the painting artwork. The high resolution of the images prohibits the efficient application of existing adaptive denoising filters. Hence, a two-step approach is proposed. First a (smoothing) Wiener filter is applied to the complete image. The second step consists of a spatially adaptive extension with low-complexity to obtain a generic digital canvas removal filter. 相似文献
256.
We will focus on estimating the integrated covariance of two diffusion processes observed in a nonsynchronous manner. The observation data is contaminated by some noise, which possibly depends on the time and the latent diffusion processes, while the sampling times also possibly depend on the observed processes. In a high-frequency setting, we consider a modified version of the pre-averaged Hayashi–Yoshida estimator, and we show that such a kind of estimator has the consistency and the asymptotic mixed normality, and attains the optimal rate of convergence. 相似文献
257.
Bobby D. Ellis Charles L. B. Macdonald 《Phosphorus, sulfur, and silicon and the related elements》2013,188(4-5):775-778
We have synthesized a new As(I) salt and performed a Density Functional Theory investigation into the use of such compounds as pnicta-Wittig reagents. 相似文献
258.
It is shown that the probability law of a diffusion process conditioned on weakly corrupted observations is asymptotically Gaussian when properly scaled. The method of proof involves Fisher information matrices and a Cramér-Rao inequality. 相似文献
259.
Zhaojie Gu Lijun Deng Hao Luo Xia Guo Haohao Li Zhencai Cao Xunshan Liu Xinwei Li Hongyan Huang Yingzi Tan Yong Pei Songting Tan 《Journal of polymer science. Part A, Polymer chemistry》2012,50(18):3848-3858
A series of novel low band gap polymers containing conjugated side chains with 4,7‐dithien‐5‐yl‐2,1,3‐benzodiathiazole and different electron‐withdrawing end groups of aldehyde ( PT‐DTBTCHO ), 2‐ethylhexyl cyanoacetate ( PT‐DTBTCN ), 1,3‐diethyl‐2‐thiobarbituric acid ( PT‐DTBTDT ), and electron‐donating end group of 2‐methylthiophene ( PT‐DTBTMT ) have been designed and synthesized. All polymers exhibit good solubility in common organic solvents, film‐forming ability, and thermal stability. These conjugated polymers show the broad ultraviolet‐visible absorption and the narrow optical band gaps in the range of 1.65–1.90 eV. Through changing the end group of conjugated side chains, the photophysical properties and energy levels of the polymers were tuned effectively. Bulk heterojunction solar cells based on the blend of these polymers and (6,6)‐phenyl‐C61‐butyric acid methyl ester (PC61BM) reached the best power conversion efficiency (PCE) of 2.72%. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
260.
凌云 《微电子学与计算机》2012,29(10):47-50
针对物联传感网络由于数据类型不一致造成散粒噪声.提出一种物联传感网络散粒噪声过滤的自适应线性权值算法.提取物联传感网络散粒噪声特征参数,对上述参数进行线性变换,获取噪声关联特征参数自适应线性权值,完成物联传感网络散粒噪声过滤.实验表明,该算法能够有效过滤物联传感网络中的散粒噪声,取得了令人满意的结果. 相似文献