全文获取类型
收费全文 | 49711篇 |
免费 | 4690篇 |
国内免费 | 2286篇 |
专业分类
电工技术 | 3404篇 |
技术理论 | 1篇 |
综合类 | 3176篇 |
化学工业 | 7992篇 |
金属工艺 | 2967篇 |
机械仪表 | 3177篇 |
建筑科学 | 3967篇 |
矿业工程 | 1612篇 |
能源动力 | 1284篇 |
轻工业 | 3837篇 |
水利工程 | 919篇 |
石油天然气 | 2830篇 |
武器工业 | 430篇 |
无线电 | 5924篇 |
一般工业技术 | 6107篇 |
冶金工业 | 2216篇 |
原子能技术 | 550篇 |
自动化技术 | 6294篇 |
出版年
2024年 | 285篇 |
2023年 | 976篇 |
2022年 | 1819篇 |
2021年 | 2286篇 |
2020年 | 1781篇 |
2019年 | 1454篇 |
2018年 | 1582篇 |
2017年 | 1812篇 |
2016年 | 1469篇 |
2015年 | 2077篇 |
2014年 | 2648篇 |
2013年 | 2928篇 |
2012年 | 3184篇 |
2011年 | 3299篇 |
2010年 | 2886篇 |
2009年 | 2850篇 |
2008年 | 2740篇 |
2007年 | 2501篇 |
2006年 | 2667篇 |
2005年 | 2303篇 |
2004年 | 1483篇 |
2003年 | 1428篇 |
2002年 | 1347篇 |
2001年 | 1138篇 |
2000年 | 1142篇 |
1999年 | 1192篇 |
1998年 | 982篇 |
1997年 | 856篇 |
1996年 | 740篇 |
1995年 | 659篇 |
1994年 | 498篇 |
1993年 | 356篇 |
1992年 | 315篇 |
1991年 | 213篇 |
1990年 | 183篇 |
1989年 | 168篇 |
1988年 | 125篇 |
1987年 | 74篇 |
1986年 | 44篇 |
1985年 | 45篇 |
1984年 | 27篇 |
1983年 | 29篇 |
1982年 | 31篇 |
1981年 | 13篇 |
1980年 | 13篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1975年 | 3篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
De Jun Mu Guan-Zhong Dai Liu K.J.R. Yao K. 《Signal Processing, IEEE Transactions on》1995,43(2):555-556
Comments that the paper by Liu and Yao (see ibid., vol.40, no.1, p.190, 1992) presented an efficient algorithm for spectral decomposition, but the parallel algorithm and architecture for the Hessenberg reduction has a problem. The matrix obtained from the unitary similarity transformation is not necessarily a Hessenberg matrix. The authors reply that the Hessenberg reduction described is not in the Hessenberg form. Only the first column is in its proper form. There are many ways to overcome such a problem. One simple way is to use the multiphase rectangular systolic array 相似文献
82.
An analytical solution of the dependence of the field distribution on the three-spatial coordinates in a permanent-magnet (PM) disk machine is obtained using the concept of magnetic charge and the method of images. A good correlation between the analytical solution and experimental data validates the method described. It is further indicated how this method can be extended to more complex problems. It is applicable to other PM machines, such as permanent-magnet linear synchronous motors.<> 相似文献
83.
84.
In this letter, based on the exact pairwise-error probability, we derive the union bound on the symbol-error probability (SEP) of the differential unitary space-time (DUST) modulation employing group codes. Instead of using the rank-and-determinant or Euclidean distance criteria, we optimize the cyclic group codes such that the union bound on the SEP is minimized for a predetermined scenario, taking into account the number of transmit and receive antennas and the operating signal-to-noise ratio (SNR). Our simulation results show that for a wide range of SNRs, the codes with the minimum union bound for a particular SNR outperform the codes designed based on rank-and-determinant or Euclidean distance criteria. 相似文献
85.
1“居山”与”隐贵山居“
回想一下人类的聚居行为颇为有趣,当年我们的祖先拼命从险山恶水的自然环境中挣脱出来,为的是得到更加安全和便利的聚居条件,但似乎从那一刻起本能式的回归意识便时刻魂牵梦绕,隐隐作响。其实无论是脱离自然还是回归自然,对于现实而言两者皆是虚幻和理想的。 相似文献
86.
87.
Meng Yan Minyu Yao Hongming Zhang Li Xia Ye Zhang 《Photonics Technology Letters, IEEE》2008,20(10):788-790
A novel en/decoder for spectral phase-coded optical code-division multiple-access system based on amplitude sampled fiber Bragg grating (FBG) is proposed. Both equivalent chirp and equivalent phase shift are achieved by amplitude sampling. Compared with previous en/decoder based on step chirped FBG, it is easier to fabricate. The performance of the proposed en/decoder is verified by both numerical simulation and experimental demonstration. 相似文献
88.
Branched polyacrylonitrile (PAN) was prepared through a self‐condensing vinyl copolymerization of acrylonitrile and 2‐(2‐bromopropionyloxy)ethyl acrylate (BPEA). The branched architecture of the product was confirmed by NMR spectra and the average degree of branching (DB ) was estimated. Through a comparison of the intrinsic viscosity of the product with that of its linear analogue, the contraction factor g′ was calculated. It was found that the viscosity of the branched PAN was obviously lower that that of linear PAN. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
89.
Yongxian Zhao Baochen Huang Wei Yao Hailin Cong Huafeng Shao Aihua Du 《应用聚合物科学杂志》2008,107(5):2986-2993
A new organic‐solvent‐free water‐phase suspension method was used to synthesize partially epoxidized high trans‐1,4‐polyisoprene (TPI) to improve its properties, including oil resistance and wet‐skid resistance. The epoxidation was conducted in an aqueous peracetic acid solution and on the TPI granules prepared by a bulk precipitation method with supported titanium catalyst. The effects of the synthesis conditions, including reaction temperature, reaction time, and pH value, on the epoxy content were investigated. Epoxidized trans‐1,4‐polyisoprene (ETPI) with epoxy contents between 10 and 80% were obtained within 4 h. Both the amorphous and crystalline regions of TPI were epoxidized. The crystallization properties decreased with increasing epoxy content. ETPIs possessed lower mechanical properties than TPI but could be enhanced by vulcanization. The oil resistance and wet‐skid resistance were significantly improved after epoxidation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
90.
A novel mixed‐mode expanded bed adsorbent with anion‐exchange properties was explored with benzylamine as the functional ligand. The cellulose composite matrix, densified with stainless steel powder, was prepared with the method of water‐in‐oil suspension thermal regeneration. High activation levels of the cellulose matrix were obtained with allyl bromide because of the relative inertness of the allyl group under the conditions of the activation reaction. After the formation of the bromohydrin with N‐bromosuccinimide and coupling with benzylamine, the activated matrix was derived to function as a mixed‐mode adsorbent containing both hydrophobic and ionic groups. The protein adsorption capacity was investigated with bovine serum albumin as a model protein. The results indicated that the prepared adsorbent could bind bovine serum albumin with a high adsorption capacity, and it showed salt tolerance. Effective desorption was achieved by a pH adjustment across the isoelectric point of the protein. The interactions between the cell and adsorbent were studied, and the bioadhesion was shielded by the adjustment of the salt concentration above 0.1M. Stable fluidization in the expanded bed was obtained even in a 2% (dry weight) yeast suspension. The direct capture of target proteins from a biomass‐containing feedstock without extra dilution steps could be expected with the mixed‐mode adsorbent prepared in this work, and this would be especially appropriate for expanded bed adsorption applications. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献