全文获取类型
收费全文 | 10045篇 |
免费 | 860篇 |
国内免费 | 33篇 |
专业分类
电工技术 | 135篇 |
综合类 | 13篇 |
化学工业 | 2092篇 |
金属工艺 | 237篇 |
机械仪表 | 388篇 |
建筑科学 | 232篇 |
矿业工程 | 4篇 |
能源动力 | 402篇 |
轻工业 | 742篇 |
水利工程 | 31篇 |
石油天然气 | 4篇 |
无线电 | 1745篇 |
一般工业技术 | 1971篇 |
冶金工业 | 1687篇 |
原子能技术 | 125篇 |
自动化技术 | 1130篇 |
出版年
2024年 | 6篇 |
2023年 | 83篇 |
2022年 | 111篇 |
2021年 | 225篇 |
2020年 | 188篇 |
2019年 | 230篇 |
2018年 | 311篇 |
2017年 | 249篇 |
2016年 | 365篇 |
2015年 | 307篇 |
2014年 | 411篇 |
2013年 | 666篇 |
2012年 | 499篇 |
2011年 | 654篇 |
2010年 | 512篇 |
2009年 | 526篇 |
2008年 | 509篇 |
2007年 | 409篇 |
2006年 | 378篇 |
2005年 | 315篇 |
2004年 | 303篇 |
2003年 | 264篇 |
2002年 | 245篇 |
2001年 | 221篇 |
2000年 | 194篇 |
1999年 | 227篇 |
1998年 | 617篇 |
1997年 | 379篇 |
1996年 | 284篇 |
1995年 | 196篇 |
1994年 | 160篇 |
1993年 | 119篇 |
1992年 | 66篇 |
1991年 | 68篇 |
1990年 | 79篇 |
1989年 | 75篇 |
1988年 | 66篇 |
1987年 | 58篇 |
1986年 | 61篇 |
1985年 | 38篇 |
1984年 | 26篇 |
1983年 | 30篇 |
1982年 | 10篇 |
1981年 | 26篇 |
1980年 | 25篇 |
1979年 | 11篇 |
1978年 | 14篇 |
1977年 | 30篇 |
1976年 | 53篇 |
1975年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 25 毫秒
991.
Slot antennas on photonic band gap crystals 总被引:1,自引:0,他引:1
Leung W.Y. Biswas R. Shi-Di Cheng Sigalas M.M. McCalmont J.S. Tuttle G. Ho K.-M. 《Antennas and Propagation, IEEE Transactions on》1997,45(10):1569-1570
The radiation patterns of a slot antenna placed on a photonic band gap crystal have been measured. We used a layer-by-layer photonic band gap crystal having a three-dimensional stop band between 12 and 15 GHz. The slot antenna radiation depends sensitively on the relative position and orientation of the slot in the surface unit cell of the photonic crystal. We have found configurations of the slot antenna with an increase of radiated power by 2-3 dB. The photonic band gap crystal can considerably improve the performance of a simple slot antenna 相似文献
992.
AA Ferraz VE Cowles RE Condon S Carilli F Ezberci CT Frantzides WJ Schulte 《Canadian Metallurgical Quarterly》1995,61(12):1079-1083
Morphine inhibits propagating and stimulates nonpropagating colon contractions in monkeys and humans. The use of morphine or other opioids that inhibit propulsive contractions prolongs postoperative ileus. In contrast, ketorolac tromethamine, a nonsteroidal analgesic, has no effect on colon contractions in monkeys. In 14 patients having elective abdominal operations, bipolar electrodes were implanted on the right (n = 13) and left (n = 10) colon. Group A (n = 8) received ketorolac, 30 mg IM q6h, for pain relief. Group B (n = 6) needed supplemental morphine, 2-10 mg IV or IM, plus ketorolac to control their pain. Myoelectric activity was recorded from each subject on postop Days 1-5 and analyzed by computer for electrical control activity (ECA), short and long electrical response activity (ERA), and propagation of long ERA. There was a difference between the two groups in return of propagated long ERA bursts that correlated with clinical recovery from postoperative ileus. Postoperative analgesia with ketorolac resulted in faster resolution of ileus compared to morphine plus ketorolac because opioid-induced motor abnormalities in the colon were avoided. 相似文献
993.
Keang-Po Ho 《Photonics Technology Letters, IEEE》2003,15(9):1213-1215
The error probability is calculated for phase-modulated systems with nonlinear phase noise. Using the assumption that the phase of amplifier noise and nonlinear phase noise are independent of each other, the error probability and penalty are calculated for both phase-shift keying (PSK) and differential phase-shift keying (DPSK) systems. The mean nonlinear phase shift must be less than about 1.00 and 0.63 rad for a penalty less than 1 dB for PSK and DPSK systems, respectively. 相似文献
994.
Numerical Simulation of scattering of electromagnetic waves from traveling and/or vibrating perfect conducting planes 总被引:2,自引:0,他引:2
Mingtsu Ho 《Antennas and Propagation, IEEE Transactions on》2006,54(1):152-156
This paper presents the one-dimensional computational results for electromagnetic waves scattered from traveling and/or vibrating perfect conducting planes via the application of the characteristic-based method. Relativistic boundary conditions combined with the characteristic variable boundary conditions are employed to account for relativistic effects due to the very high-speed motion of the conductor. The variations in both magnitude and frequency of the reflected electric field were investigated by comparing the computational results with the theoretical double-Doppler shift values. A maximum error percentage of less than 0.50% was found. It is also concluded that when the perfect conducting plane travels and vibrates simultaneously, the Doppler effects in frequency that are impressed on the reflected fields can be predicted, on the basis of computational results, simply dividing the vibrating frequency of perfect conducting plane by the factor (1+/spl beta//sub t/) where /spl beta//sub t/ is the ratio of the traveling velocity to the speed of light. 相似文献
995.
Yunhua Kuang Pratap Pullammanappallil Muriel Lepesteur Goen E Ho 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2006,81(6):1057-1063
Four laboratory‐scale anaerobic digesters were deliberately and completely inhibited by feeding sodium oleate to such an extent that no methane was produced from the digesters. Three of them were then respectively fed glucose, cysteine or glucose and cysteine along with sodium oleate, while the remaining digester was operated as control reactor and continued to be fed with only sodium oleate. Oligonucleotide probes ARC915, EUB338, MB310, MC1109, MSMX860 and MG1200 were used to target and quantify specific groups of microbes, Archaea, Bacteria, Methanobacteriales, Methanococcales, Methanosarcinaceae, and Methanomicrobiaceae, Methanocorpusculaceae and Methanoplanaceae respectively throughout the operation of reactors. Addition of glucose and/or cysteine assisted with the recovery of methane production from oleate inhibition. The addition of glucose was more effective than cysteine, while the combination of glucose and cysteine was most effective on this recovery. The addition of these substrates also stimulated the degradation of oleate in the reactor. Daily methane production from the digesters correlated negatively with residual oleate concentration and positively with Archaea counts. Addition of glucose was more effective than cysteine on increasing the number of Archaea cells, while cysteine was more effective in increasing the number of Bacteria cells. All microbial populations recovered to pre‐inhibition levels within 40 days when glucose together with cysteine was fed. Copyright © 2006 Society of Chemical Industry 相似文献
996.
We propose a sequential approach called Random Approximated Greedy Search (RAGS) in this paper and apply it to the feature subset selection for regression. It is an extension of GRASP/Super‐heuristics approach to complex stochastic combinatorial optimization problems, where performance estimation is very expensive. The key points of RAGS are from the methodology of Ordinal Optimization (OO). We soften the goal and define success as good enough but not necessarily optimal. In this way, we use more crude estimation model, and treat the performance estimation error as randomness, so it can provide random perturbations mandated by the GRASP/Super‐heuristics approach directly and save a lot of computation effort at the same time. By the multiple independent running of RAGS, we show that we obtain better solutions than standard greedy search under the comparable computation effort. 相似文献
997.
S Wakatsuki SC Ho M Arioka M Yamasaki K Kitamoto 《Canadian Metallurgical Quarterly》1997,122(6):1146-1152
By screening with monoclonal antibodies (mAbs) raised against growth cone membrane fraction from fetal porcine brains, we have identified a 230 kDa antigen, termed p230. Western blot analysis of extracts from various tissues demonstrated that p230 is specifically expressed in brains, in which its expression is temporally restricted; it was especially prominent in the embryonic and the early postnatal stage, and decreased to subdetectable levels in the adult brain. Further characterization of p230 revealed that it is a peripherally-membrane associated, cell surface protein produced by astrocytes. Neurite outgrowth of E18 rat cerebral cortex neurons cultured on a monolayer of astrocytes was significantly reduced in the presence of anti-p230 polyclonal antibody. Partial amino acid sequences of p230 purified from fetal porcine brains were highly homologous to an extracellular matrix protein, tenascin-C. These lines of evidence suggest that p230, a tenascin-C-like molecule present in fetal porcine brains, plays important roles during early brain development, particularly in growth cone guidance. 相似文献
998.
Jung Wook Lim Sun Jin Yun Jin Ho Lee 《Journal of the Society for Information Display》2003,11(3):505-509
Abstract— It is important to select an optimal insulator for an electroluminescent (EL) device, and this insulator have a large dielectric constant, large breakdown field, and few defects. Generally, an insulator with a high dielectric constant shows a considerably low breakdown field; however, none of them should be abandoned. Therefore, it is required that insulators with high breakdown fields should be developed without lowering the dielectric constant. In this article, we present aluminum oxinitride films grown by plasma‐enhanced atomic layer deposition (PEALD). The dielectric breakdown field of this film is considerably higher than that of alumina grown by conventional atomic layer deposition (ALD), and this film is also more stable than alumina grown by PEALD as well as by ALD after post‐annealing process. Furthermore, aluminum oxinitride films, grown by PEALD as the upper insulator of a ZnS:Mn‐based EL device, shows an excellent long‐lasting property for an applied voltage and a reasonable luminance. 相似文献
999.
1000.
Brain acetylhydrolase that inactivates platelet-activating factor is a G-protein-like trimer 总被引:1,自引:0,他引:1
YS Ho L Swenson U Derewenda L Serre Y Wei Z Dauter M Hattori T Adachi J Aoki H Arai K Inoue ZS Derewenda 《Canadian Metallurgical Quarterly》1997,385(6611):89-93
The platelet-activating factor PAF (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) is a potent lipid first messenger active in general cell activation, fertilization, inflammatory and allergic reactions, asthma, HIV pathogenesis, carcinogenesis, and apoptosis. There is substantial evidence that PAF is involved in intracellular signalling, but the pathways are poorly understood. Inactivation of PAF is carried out by specific intra- and extracellular acetylhydrolases (PAF-AHs), a subfamily of phospholipases A2 that remove the sn-2 acetyl group. Mammalian brain contains at least three intracellular isoforms, of which PAF-AH(Ib) is the best characterized. This isoform contains a heterodimer of two homologous catalytic subunits alpha1 and alpha2, each of relative molecular mass 26K, and a non-catalytic 45K beta-subunit, a homologue of the beta-subunit of trimeric G proteins. We now report the crystal structure of the bovine alpha1 subunit of PAF-AH(Ib) at 1.7 A resolution in complex with a reaction product, acetate. The tertiary fold of this protein is closely reminiscent of that found in p21(ras) and other GTPases. The active site is made up of a trypsin-like triad of Ser 47, His 195 and Asp 192. Thus, the intact PAF-AH(Ib) molecule is an unusual G-protein-like (alpha1/alpha2)beta trimer. 相似文献