全文获取类型
收费全文 | 5291篇 |
免费 | 379篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 120篇 |
综合类 | 5篇 |
化学工业 | 1373篇 |
金属工艺 | 144篇 |
机械仪表 | 146篇 |
建筑科学 | 179篇 |
矿业工程 | 24篇 |
能源动力 | 200篇 |
轻工业 | 671篇 |
水利工程 | 33篇 |
石油天然气 | 27篇 |
无线电 | 329篇 |
一般工业技术 | 1405篇 |
冶金工业 | 130篇 |
原子能技术 | 50篇 |
自动化技术 | 840篇 |
出版年
2023年 | 50篇 |
2022年 | 48篇 |
2021年 | 141篇 |
2020年 | 115篇 |
2019年 | 128篇 |
2018年 | 193篇 |
2017年 | 201篇 |
2016年 | 222篇 |
2015年 | 202篇 |
2014年 | 288篇 |
2013年 | 634篇 |
2012年 | 341篇 |
2011年 | 367篇 |
2010年 | 310篇 |
2009年 | 226篇 |
2008年 | 248篇 |
2007年 | 209篇 |
2006年 | 171篇 |
2005年 | 114篇 |
2004年 | 80篇 |
2003年 | 105篇 |
2002年 | 87篇 |
2001年 | 64篇 |
2000年 | 68篇 |
1999年 | 50篇 |
1998年 | 41篇 |
1997年 | 44篇 |
1996年 | 52篇 |
1995年 | 37篇 |
1994年 | 50篇 |
1993年 | 45篇 |
1992年 | 35篇 |
1991年 | 38篇 |
1990年 | 30篇 |
1989年 | 34篇 |
1988年 | 20篇 |
1986年 | 18篇 |
1985年 | 43篇 |
1984年 | 52篇 |
1983年 | 48篇 |
1982年 | 35篇 |
1981年 | 55篇 |
1980年 | 42篇 |
1979年 | 37篇 |
1978年 | 30篇 |
1977年 | 25篇 |
1976年 | 31篇 |
1975年 | 21篇 |
1974年 | 20篇 |
1973年 | 20篇 |
排序方式: 共有5676条查询结果,搜索用时 218 毫秒
71.
The metabolism of 1-acyl-2-acetyl-sn-glycero-3-phosphocholine (1-acyl-PAF), a naturally occurring analogue of platelet activating factor (PAF), was investigated
in rabbit platelets. Our studies showed that 1-acyl-[3H]PAF (1-palmitoyl-2-acetyl-sn-glycero-3-phospho[N-methyl-3H]-choline) was converted by platelets into phosphatidyl-[3H]choline ([3H]PC) in a time-dependent fashion. The formation of [3H]PC occurred at a rate similar to that observed when lyso-[3H]PC (palmitoyl-sn-glycero-3-phospho[N-methyl-3H]choline) was used as substrate. In addition, a time-dependent increase in the level of water-soluble radioactivity was observed
during the incubation of platelets with either 1-acyl-[3H]PAF or lyso-[3H]PC. This increase was parallel to the formation of [3H]PC and was not observed in the presence of [14C]PAF (1-octadecyl-2-acetyl-sn-glycerol-3-phospho[N methyl-14C]choline). Analysis by thin-layer chromatography showed that the soluble radioactivity was mainly associated with glycerophosphocholine
(GPC). On the other hand, the preincubation of platelets with phenylmethylsulfonyl fluoride, an inhibitor of the acetylhydrolase,
reduced the hydrolysis of 1-acyl-[3H]PAF to [3H]GPC with a concomitant accumulation of radioactivity in 1-acyl-PAF. These findings suggest that 1-acyl-PAF is converted
into PC through deacetylation-reacylation with lysoPC as an obligatory intermediate. The findings also indicate that the lysoPC
resulting from 1-acyl-PAF is either reacylated to phosphatidylcholine (PC) or hydrolyzed to GPC by lysophospholipase. Finally,
we showed that the stimulation of platelets with PAF led to a time- and concentration-dependent increase in the conversion
of 1-acyl-[3H]PAF to [3H]PC. The stimulatory effect of PAF was not observed when platelets were lysed before incubation, suggesting that PAF enhances
the metabolism of 1-acyl-PAF, probably by accelerating its translocation through the plasma membrane. 相似文献
72.
The study of hydration of expansive cement prepared from 64% portland cement clinker, 23% metakaolinite and 13% CaSO4.2H2O is described. It was found that in the course of a 10-day hydration period, all the gypsum entered the reaction with the formation of ettringite. In 7–10 days, after the termination of the expansion processes, typical stalk-like crystals were transformed into leaf-shaped or other formations. Ettringite was identified even after 4 months of hydration. Monosulphate (3CaO.Al2O3.CaSO4.12H2O) was found in none of the investigated high-expansion cement paste samples. 相似文献
73.
Summary The electrical conductivity of polyphenylacetylenes and polyhalophenylacetylenes was measured in dependence on the temperature and on the type of catalyst used for polymerization. The electrical conductivity increased with increasing temperature. The energy gap was calculated from the temperature dependence on the electrical conductivity; it decreased with increasing number of conjugated double bonds in the polymer chain and with the regularity of structure of the polymer. The number of double bonds, cyclization and configurations were determined by 1H and 13C-NMR. In polyphenylacetylenes only aliphatic carbons deriving from cyclohexadiene units were found but no such units were found in polyhalophenylacetylenes. By UV-vis measurement the number of conjugated double bonds in segments was estimated. The synthesized polymers were amorphous. Their molecular weight was between 2000 and 74.000. 相似文献
74.
M. Hartmanová V. Šály F. Hanic M. Pisarčík H. Ullmann 《Journal of Materials Science》1991,26(16):4313-4317
The investigation of microstructure, some electrical and optical parameters of transparent ThO2-15 mol % yo1.5 ceramics has shown: (a) a very low porosity, close to zero; (b) a higher electrical conductivity than is usual for ThO2 ceramics of the same composition, with the activation energy 1.12 eV; (c) a relative permittivity r 33 under the given conditions; (d) confirmation of a single-phase fluorite-type cubic structure by means of Raman and infrared spectra. 相似文献
75.
Peter Tatarko Fabrizio Valenza Hakan Ünsal Alexandra Kovalčíková Jaroslav Sedláček Pavol Šajgalík 《Journal of the European Ceramic Society》2021,41(5):3051-3060
The wettability and infiltration of molten ZrSi2 and ZrSi2-Lu2O3 alloys into Cf/SiC and B4C-infiltrated Cf/SiC composites were investigated to understand the interfacial interactions that occur during the development of Cf/SiC-ZrC and Cf/SiC-ZrB2-ZrC-Lu2O3 materials. A significant evaporation of Si from the liquid affected the wetting behaviour of the alloy when tested in a vacuum at 1670 °C. The better wetting and spreading of the alloy over the surface was observed for the composites with lower overall porosity (12 %). On the other hand, the formation of an outer dense layer, followed up by the uniform infiltrated region up to ~ 1 mm was observed for the Cf/SiC with higher porosity (21 %). The infiltrated alloy reacted with SiC matrix to form ZrC or with B4C-infiltrated SiC matrix to form ZrB2-ZrC-SiC. The Lu2O3 particles were not wetted by the melt, and were pushed away of the reaction zone by the solidification front. 相似文献
76.
Over the last decade, enhanced suffix arrays (ESA) have replaced suffix trees in many applications. Algorithms based on ESAs require less space, while allowing the same time efficiency as those based on suffix trees. However, this is only true when a suffix structure is used as a static index. Suffix trees can be updated faster than suffix arrays, which is a clear advantage in applications that require dynamic indexing. We show that for some dynamic applications a suffix array and the derived LCP-interval tree can be used in such a way that the actual index updates are not necessary. We demonstrate this in the case of grammar text compression with longest first substitution and provide the source code. The proposed algorithm has O(N2) worst case time complexity but runs in O(N) time in practice. 相似文献
77.
78.
Boris Škorić Sebastiaan J. A. de Hoogh Nicola Zannone 《International Journal of Information Security》2016,15(4):381-402
The concept of reputation is widely used as a measure of trustworthiness based on ratings from members in a community. The adoption of reputation systems, however, relies on their ability to capture the actual trustworthiness of a target. Several reputation models for aggregating trust information have been proposed in the literature. The choice of model has an impact on the reliability of the aggregated trust information as well as on the procedure used to compute reputations. Two prominent models are flow-based reputation (e.g., EigenTrust, PageRank) and subjective logic-based reputation. Flow-based models provide an automated method to aggregate trust information, but they are not able to express the level of uncertainty in the information. In contrast, subjective logic extends probabilistic models with an explicit notion of uncertainty, but the calculation of reputation depends on the structure of the trust network and often requires information to be discarded. These are severe drawbacks. In this work, we observe that the ‘opinion discounting’ operation in subjective logic has a number of basic problems. We resolve these problems by providing a new discounting operator that describes the flow of evidence from one party to another. The adoption of our discounting rule results in a consistent subjective logic algebra that is entirely based on the handling of evidence. We show that the new algebra enables the construction of an automated reputation assessment procedure for arbitrary trust networks, where the calculation no longer depends on the structure of the network, and does not need to throw away any information. Thus, we obtain the best of both worlds: flow-based reputation and consistent handling of uncertainties. 相似文献
79.
80.
Boris Hudec Chung-Wei Hsu I-Ting Wang Wei-Li Lai Che-Chia Chang Taifang Wang Karol Fröhlich Chia-Hua Ho Chen-Hsi Lin Tuo-Hung Hou 《中国科学:信息科学(英文版)》2016,59(6):061403
In this article, we comprehensively review recent progress in the ReRAM cell technology for 3D integration focusing on a material/device level. First we briefly mention pioneering work on high-density crossbar ReRAM arrays which paved the way to 3D integration. We discuss the two main proposed 3D integration schemes—3D horizontally stacked ReRAM vs 3D Vertical ReRAM and their respective advantages and disadvantages. We follow with the detailed memory cell design on important work in both areas, utilizing either filamentary or interface-limited switching mechanisms. We also discuss our own contributions on HfO2-based filamentary 3D Vertical ReRAM as well as TaOx/TiO2 bilayer-based self-rectifying 3D Vertical ReRAM. Finally, we summarize the present status and provide an outlook for the nearterm future. 相似文献