全文获取类型
收费全文 | 24289篇 |
免费 | 480篇 |
国内免费 | 123篇 |
专业分类
电工技术 | 517篇 |
综合类 | 67篇 |
化学工业 | 3518篇 |
金属工艺 | 961篇 |
机械仪表 | 668篇 |
建筑科学 | 600篇 |
矿业工程 | 72篇 |
能源动力 | 636篇 |
轻工业 | 1909篇 |
水利工程 | 218篇 |
石油天然气 | 181篇 |
武器工业 | 1篇 |
无线电 | 2702篇 |
一般工业技术 | 4289篇 |
冶金工业 | 6219篇 |
原子能技术 | 425篇 |
自动化技术 | 1909篇 |
出版年
2022年 | 146篇 |
2021年 | 225篇 |
2020年 | 164篇 |
2019年 | 224篇 |
2018年 | 297篇 |
2017年 | 296篇 |
2016年 | 325篇 |
2015年 | 230篇 |
2014年 | 364篇 |
2013年 | 887篇 |
2012年 | 569篇 |
2011年 | 867篇 |
2010年 | 596篇 |
2009年 | 660篇 |
2008年 | 761篇 |
2007年 | 793篇 |
2006年 | 664篇 |
2005年 | 734篇 |
2004年 | 602篇 |
2003年 | 648篇 |
2002年 | 685篇 |
2001年 | 682篇 |
2000年 | 607篇 |
1999年 | 624篇 |
1998年 | 2186篇 |
1997年 | 1417篇 |
1996年 | 1053篇 |
1995年 | 724篇 |
1994年 | 621篇 |
1993年 | 644篇 |
1992年 | 359篇 |
1991年 | 348篇 |
1990年 | 343篇 |
1989年 | 347篇 |
1988年 | 294篇 |
1987年 | 271篇 |
1986年 | 247篇 |
1985年 | 280篇 |
1984年 | 220篇 |
1983年 | 203篇 |
1982年 | 186篇 |
1981年 | 218篇 |
1980年 | 205篇 |
1979年 | 164篇 |
1978年 | 153篇 |
1977年 | 281篇 |
1976年 | 389篇 |
1975年 | 128篇 |
1974年 | 110篇 |
1973年 | 117篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
We report on picosecond time resolved spectroscopy of photogenerated infrared active vibrations in thin films of 2,5-dioctyloxy poly(phenylene vinylene). We excited the films by ?4 ps long pulses of 565 nm laser light with 2×1013 photons/cm2 per pulse and repetition rate of 76 MHz. We then followed the temporal evolution of the infrared active vibrational (IRAV) spectrum using a subsequent, variably delayed, weak tunable IR probe pulses of similar temporal duration. Under these conditions, we show clear spectroscopic evidence for photogenerated infrared active vibrations at times which are shorter than our temporal resolution (<4 ps). We suggest that the transient IRAV absorption is due to secondary polarons formation following exciton dissociation. 相似文献
12.
13.
Infant malnutrition and mortality are common in Africa, although Africa is endowed with agricultural produce that could be harnessed through processing to produce adequate infant food. This project was set up to explore the possibility of using local raw materials to develop a nutritious, low‐dietary‐bulk, cheap infant food. The materials used included cereal (maize), pulses (soybean and groundnut) and tuberiferous plants (cooking banana). The grains were first germinated and dried or kilned before milling and formulation. The malted products were compared with fermented ones in terms of nutritional, dietary bulk and acceptability criteria. Malting increased the nutrient content, reduced the dietary bulk and enhanced the taste of the infant food. In terms of protein content, least gelation concentration and overall acceptability, malted samples had values in the range of 138–151 mg g?1, 150–175 g l?1 and 7.2–8.82 respectively, while the control (fermented) sample had values of 54 mg g?1, 100 g l?1 and 6.29 respectively. Roasting of malted cereals above 55 °C reduced the bulk reduction ability but enhanced the taste of the products. A combination of malted maize and soybean, roasted groundnut and cooking banana in the ratio of 50:15:15:20 gave a very recommendable weaning food for infants between the ages of 6 months and 2 years. © 2002 Society of Chemical Industry 相似文献
14.
Cicalese F. Vaccaro U. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2002,48(4):933-938
We prove that the entropy is a supermodular and subadditive function on the lattice of all n-dimensional probability distributions, ordered according to the partial order relation defined by majorization among vectors 相似文献
15.
This paper presents a new self-routing packet network called the plane interconnected parallel network (PIPN). In the proposed design, the traffic arriving at the network is shaped and routed through two banyan network based interconnected planes. The interconnections between the planes distribute the incoming load more homogeneously over the network. The throughput of the network under uniform and heterogeneous traffic requirements is studied analytically and by simulation. The results are compared with the results of the baseline network and another banyan network based parallel interconnection network. It is shown that, for the proposed design, a higher degree of heterogeneity results in better performance 相似文献
16.
In this paper the approach of BRASIL in modelling digitalintegrated circuits is presented. BRASIL consists of a timingsimulator for digital MOS circuits coupled with an algorithmfor circuit simulation. The timing simulation is based upon afast macromodelling approach and the calculation of time-variantRC networks. The circuit simulator takes advantage of structuringthe system of nodal equations. With BRASIL a fast and accuratesimulation of digital circuits, with special regard to the analogbehaviour of highly integrated systems is possible. 相似文献
17.
For two applications of fuel cells (SOFC and IMFC) system configurations and energy balances are presented. A decentralized combined heat and power plant on SOFC basis can be designed as a flexible system with high efficiency. A drive system with methanol reformer and fuel cell (IMFC) in comparison with a natural gas combustion engine has lower energy comsumption and much lower emissions. 相似文献
18.
ME Sutherlin I Nishimori T Caffrey EP Bennett H Hassan U Mandel D Mack T Iwamura H Clausen MA Hollingsworth 《Canadian Metallurgical Quarterly》1997,57(21):4744-4748
The levels of mRNA expression of three UDP-N-acetyl-alpha-D-galactosamine:polypeptide GalNAc N-acetylgalactosaminyltransferases (GalNAc-transferases) were quantified for human adenocarcinoma cell lines from pancreas, colon, stomach, and breast. Two of the GalNAc-transferases, GalNAc-T1 and GalNAc-T2, were expressed constitutively and at low levels in most or all cell lines examined. A third GalNAc-transferase, GalNAc-T3, was differentially expressed. Well-differentiated adenocarcinoma cell lines expressed high levels and moderately differentiated cell lines expressed lower levels of GalNAc-T3. Cell lines classified as poorly differentiated failed to express GalNAc-T3 mRNA at levels that could be detected by Northern blot analysis. Differential expression of the GalNAc-T3 protein was confirmed in these cell lines by Western blotting. We propose that glycosylation in tumor cell lines may be regulated in part by differential expression of GalNAc-transferases, and we suggest that GalNAc-T3 gene expression may be a molecular indicator of differentiated adenocarcinoma. 相似文献
19.
P Virsik-Peuckert M Rave-Fr?nk U Langebrake H Schmidberger 《Canadian Metallurgical Quarterly》1997,148(3):209-215
The modulatory role of locally produced cyclooxygenase products and endothelium-derived nitric oxide in controlling vascular tone was investigated in bovine intra-mammary artery. Vascular reactivity initiated by vasoactive compounds, endothelin-1 (ET-1), bradykinin (BK), and substance P (SP) was measured isometrically in an isolated tissue bath. The effects of a cyclooxygenase inhibitor, indomethacin (10(-5) M) and an inhibitor of nitric oxide production, N omega-Nitro L-Arginine (L-NNA: 3 x 10(-4) M) were determined during agonist-mediated responses. Indomethacin alone markedly enhanced vascular contraction produced by ET-1, while L-NNA did not. Inhibition of endothelium-derived nitric oxide synthesis by L-NNA, however, significantly attenuated BK- and SP-induced vascular relaxations, whereas indomethacin had slight influence. The potentiation between indomethacin and L-NNA in regulating vasomotor tone was not observed in this vascular bed. Thus, it appeared that both the cyclooxygenase and endothelium-derived nitric oxide pathways participated in modifying vascular reactivity. Domination of one pathway over the other depended upon the agonist used to stimulate vascular tissue. 相似文献
20.
The dynamical behavior of distributed Bragg reflector lasers with detuned Bragg reflectors is investigated theoretically. The model is based on the traveling wave equations, which are solved by expanding the solution in terms of the longitudinal eigenmodes. It is shown that for a drastic enhancement of the modulation bandwidth the interplay of the dominant mode and one side mode has to be enforced. Under these conditions, the modulation bandwidth can be enhanced to more than 70 GHz 相似文献