全文获取类型
收费全文 | 1851篇 |
免费 | 98篇 |
国内免费 | 20篇 |
专业分类
电工技术 | 24篇 |
综合类 | 3篇 |
化学工业 | 571篇 |
金属工艺 | 37篇 |
机械仪表 | 63篇 |
建筑科学 | 90篇 |
矿业工程 | 6篇 |
能源动力 | 138篇 |
轻工业 | 162篇 |
水利工程 | 24篇 |
石油天然气 | 48篇 |
无线电 | 149篇 |
一般工业技术 | 349篇 |
冶金工业 | 69篇 |
原子能技术 | 23篇 |
自动化技术 | 213篇 |
出版年
2024年 | 11篇 |
2023年 | 34篇 |
2022年 | 63篇 |
2021年 | 118篇 |
2020年 | 104篇 |
2019年 | 119篇 |
2018年 | 150篇 |
2017年 | 149篇 |
2016年 | 94篇 |
2015年 | 59篇 |
2014年 | 115篇 |
2013年 | 204篇 |
2012年 | 129篇 |
2011年 | 161篇 |
2010年 | 102篇 |
2009年 | 74篇 |
2008年 | 63篇 |
2007年 | 43篇 |
2006年 | 28篇 |
2005年 | 17篇 |
2004年 | 18篇 |
2003年 | 18篇 |
2002年 | 6篇 |
2001年 | 6篇 |
2000年 | 6篇 |
1999年 | 4篇 |
1998年 | 18篇 |
1997年 | 14篇 |
1996年 | 5篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 6篇 |
1991年 | 2篇 |
1989年 | 2篇 |
1987年 | 3篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有1969条查询结果,搜索用时 15 毫秒
91.
Abolfazl Jomekian Reza Mosayebi Behbahani Toraj Mohammadi Ali Kargari 《Korean Journal of Chemical Engineering》2017,34(2):440-453
Modified ultra-porous ZIF-8 particles were used to prepare novel ZIF-8/Pebax 1657 mixed matrix membranes (MMMs) on PES support for separation of CO2 from CH4 using spin coating method. TEM and SEM were used to characterize modified ZIF-8 particles. SEM was also used to investigate the morphology of synthesized MMMs. The MMMs with thinner selective layer showed higher CO2 permeability and lower CO2/CH4 selectivity in permeation tests compared to MMMs with thicker selective layer. The plasticization was recognized as the main reason for rise in CO2 permeability and drop in CO2/CH4 selectivity of thinner MMMs. The gas sorption results showed that the high permeability of CO2 in MMMs is mainly due to the high solubility of this gas in MMMs, leading to high CO2/CH4 solubility selectivity for MMMs. The fractional free volume and void volume fraction of MMMs increased as the thickness of membrane decreased. Applying higher mixed feed pressures and permeation tests temperatures resulted in increase in CO2 permeability and decrease in CO2/CH4 selectivity. At highest testing temperature (60 °C), the CO2 permeability of synthesized MMMs with thinner selective layer remarkably increased. 相似文献
92.
Akbar Ghaffar Pour Rahbar 《Photonic Network Communications》2009,17(3):226-237
Optical Packet Switching (OPS) can provide the ever-increasing bandwidth required for Internet traffic and new applications
for future networks. However, optical packet loss is the major problem for an OPS network. Moreover, by increasing the number
of hops between a pair of ingress–egress switches in an OPS network, optical Packet Loss Rate (PLR) between this pair is increased.
Therefore, due to a higher PLR for long-hop TCP connections, the throughput of these connections may be much lower than the
short-hop TCP connections. To overcome this problem, it is proposed in this paper to use the retransmission idea in the optical
domain not only to increase TCP throughput but also to improve the throughput of multi-hop TCP connections, and also to have
a loss-free OPS network. Under retransmission in the optical domain, a copy of the transmitted traffic is kept in the electronic
buffers of ingress switches and retransmitted in the optical domain whenever required. Note that the TCP layer has its own
retransmission at the client packet level as well. By retransmission of lost packets in the optical domain, TCP would be unaware
of the lost client packets, and therefore, TCP would not reduce its sending rate. In this paper, TCP throughput is studied
in a bufferless slotted OPS network and the effectiveness of the proposed mechanism is evaluated.
相似文献
Akbar Ghaffar Pour RahbarEmail: Email: |
93.
Atena Shaterian Mohammadi Heshmatolah Aminian Arsalan Jamshidnia 《Journal of Food Safety》2020,40(6):e12847
Aflatoxin (AF) contamination of the Iranian exporting pistachio has become a major problem in the last decades. In this study, the antifungal effects of smoke produced from the smoldering of several herbal plants were investigated. Four different ratios of plant weight/exposure time (5/5, 10/15, 15/30, and 20 g/45 min) were used from each plant material to smoke two isolates of Aspergillus flavus (A47 and A3), grown in potato dextrose agar (PDA). The results showed that the 20 g/45 min treatment using smoldering cinnamon bark, neem leaves, and clove flowers had efficient inhibitions of 100, 85, and 75%, respectively. Furthermore, the smoking of pistachio inoculated with a spore concentration of 1 × 106 / ml using 30 g of cinnamon bark, neem leaves, and clove flowers for 75 min was capable of preventing the production of different types of AF, that is, B1, B2, G1, and G2 in the treated products. There is a good potential to smoke pistachio with these three herbal plants and prevent the production of AF in pistachio during the handling, storage, and transportation. 相似文献
94.
The spun tapes of synthesized PAN, its copolymer with 1 wt% itaconic acid, and doped version with 1 wt% sodium dodecyl sulfate (SDS) all showed stripy, even, and compact cross-sections as the hallmark of gel forming products. PAN doping with SDS and acrylonitrile copolymerization with itaconic acid reduced its dimethylformamide (DMF) solution structural viscosity index (Δη) by 50% and 30%, respectively, at 675 s??1. In addition, the modification of synthesized PAN through doping and acrylonitrile copolymerization with itaconic acid led to severe and mild gelation temperature decrease, respectively. The stabilization peak of the synthesized PAN tape was enhanced as much as 25 °C by 900% hot drawing, decreased by about 10 °C through copolymerization, while experienced small temperature changes through doping. The second derivative of Fourier transform infrared and Gaussian fitting was used to analyze the tapes cyclization due to stabilization treatment through introducing Isd index. 10 min Isd index was raised as much as 430% and 800% in comparison with the synthesized PAN through its doping or acrylonitrile copolymerization with itaconic acid, respectively. Further 180 min of Isd index, however, showed the same proportional increase as toughness of the drawn tapes versus their heat of stabilization through their physical and chemical modifications. 相似文献
95.
In the last decades, heat recovery systems have received much attention due to the increase in fuel cost and the increase in environmental issues. In this study, different heat recovery systems for a cement plant are compared in terms of electricity generation and exergy analysis. The heat sources are available in high temperature (HT) and low temperature (LT). For the HT section a dual pressure Rankine cycle, a simple dual pressure Organic Rankine Cycle (ORC) and a regenerative dual pressure ORC are compared. Also, for the LT section, a simple ORC is compared with transcritical carbon dioxide cycle. To find the best system, an optimisation algorithm is applied to all proposed cycles. The results show that for the HT section, regenerative ORC has the highest exergy efficiency and has the capability of producing nearly 7?MW electricity for a cement factory with the capacity of 3400 ton per day. The main reason for this is introducing the regenerative heat exchanger to the cycle. For the LT section, ORC showed a better performance than the CO2 cycle. It is worth mentioning that the generated power in this section is far lower than that of the HT section and is equal to nearly 300?kW. 相似文献
96.
97.
M. Ghoranneviss S. Mohammadi A. Salar Elahi R. Arvin 《Fusion Engineering and Design》2013,88(2):94-99
Electrode biasing system was designed, constructed, and installed on the IR-T1 tokamak, and then biasing experiments were carried out. Also, using a Mach probes the effects of radial electric field (produced by biased electrode) on the poloidal and toroidal components of the edge plasma velocity were investigated. The results showed an increase in both toroidal and poloidal components of the edge plasma velocity during biasing regime. Results compared and discussed. During positive biasing, increased Er tends to slow the poloidal rotation in the electron diamagnetic drift direction, i.e., to speed up rotation in the ion diamagnetic drift direction. An increased toroidal rotation velocity has the opposite effect on the poloidal rotation. 相似文献
98.
Stimulated Raman scattering (SRS) with ordinary (O-mode) wave at phase space (x, v) is investigated. For this purpose Vlasov equation is solved with one simulation method. Evolution of distribution function for an early time and a later time is presented. Initial distribution function has Gaussian shape, that is important in plasma heating, but as the time passed, this function due to the perturbation extends over space and velocity. In this situation, the behavior of distribution function has an important role in instability rate. Then instability rate for SRS is obtained and these results are showed in some special times and special cells. Density fluctuations affect instability rate and there is no remarkable damping at early times. At later times instability rate reduces sensitively which is in accordance to electron plasma wave damping and then heating the electrons. Also with increase in frequency of the incident wave, the instability rate due to saturation decreases sensitively. 相似文献
99.
Roya Salehi Soodabeh Davaran Mohammad R. Rashidi Ali Akbar Entezami 《应用聚合物科学杂志》2009,111(4):1905-1910
Temperature‐responsive polymers have become increasingly attractive as carrier for the injectable drug delivery systems. In the present work, we have studied the preparation of poly(N‐isopropylacrylamide‐acrylamide‐vinilpyrrolidone) (NIPAAm‐AAm‐VP terpolymer) nanoparticulated terpolymer and its blend with poly(lactide‐co‐glycolide, PLGA; molar ratio of lactide/glycolid 1/3). Thermosensitive terpolymer, poly(NIPAAm‐AAm‐VP) was prepared by free‐radical polymerization in aqueous solution. The nanoparticles of poly(NIPAAm‐AAm‐VP) and its blend with PLGA containing naltrexone were prepared using the evaporation and w/o emulsion‐solvent evaporation methods, respectively. Nanoparticles prepared from terpolymer‐PLGA blend at low polymer concentration (5%) shows larger particle size (>300 nm) and higher drug content%. Various types of nanoparticles showed a burst release of less than 10% after 24 h . The results suggest that by regulating different variables, desired release profiles of naltrexone can be achieved using a blend of PLGA‐poly(NIPAAm‐AAm‐VP) nanoparticulate system. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 相似文献
100.
Isa MH Ibrahim N Aziz HA Adlan MN Sabiani NH Zinatizadeh AA Kutty SR 《Journal of hazardous materials》2008,152(2):662-668
This study proposed an oil palm by-product as a low-cost adsorbent for the removal of hexavalent chromium [Cr (VI)] from aqueous solution. Adsorption of Cr (VI) by sulphuric acid and heat-treated oil palm fibre was conducted using batch tests. The influence of pH, contact time, initial chromium concentration and adsorbent dosage on the removal of Cr (VI) from the solutions was investigated. The optimum initial pH for maximum uptake of Cr (VI) from aqueous solution was found to be 1.5. The removal efficiency was found to correlate with the initial Cr (VI) concentration, adsorbent dosage as well as the contact time between Cr (VI) and the adsorbent. The adsorption kinetics tested with pseudo first order and pseudo second order models yielded high R(2) values from 0.9254 to 0.9870 and from 0.9936 to 0.9998, respectively. The analysis of variance (ANOVA) showed significant difference between the R(2) values of the two models at 99% confidence level. The Freundlich isotherm (R(2)=0.8778) described Cr (VI) adsorption slightly better than the Langmuir isotherm (R(2)=0.8715). Difficulty in desorption of Cr (VI) suggests the suitability of treated oil palm fibre as a single-use adsorbent for Cr (VI) removal from aqueous solution. 相似文献