首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   507篇
  免费   18篇
  国内免费   1篇
电工技术   12篇
化学工业   104篇
金属工艺   10篇
机械仪表   11篇
建筑科学   8篇
能源动力   20篇
轻工业   55篇
水利工程   2篇
无线电   20篇
一般工业技术   99篇
冶金工业   123篇
原子能技术   19篇
自动化技术   43篇
  2022年   3篇
  2021年   23篇
  2020年   7篇
  2019年   6篇
  2018年   8篇
  2017年   8篇
  2016年   21篇
  2015年   10篇
  2014年   8篇
  2013年   24篇
  2012年   20篇
  2011年   27篇
  2010年   19篇
  2009年   27篇
  2008年   15篇
  2007年   27篇
  2006年   19篇
  2005年   7篇
  2004年   14篇
  2003年   8篇
  2002年   7篇
  2001年   7篇
  2000年   8篇
  1999年   13篇
  1998年   49篇
  1997年   28篇
  1996年   17篇
  1995年   12篇
  1994年   8篇
  1993年   14篇
  1992年   3篇
  1991年   3篇
  1990年   6篇
  1989年   6篇
  1988年   5篇
  1987年   2篇
  1986年   3篇
  1985年   5篇
  1984年   4篇
  1983年   4篇
  1982年   3篇
  1980年   2篇
  1977年   1篇
  1976年   4篇
  1975年   2篇
  1974年   2篇
  1971年   1篇
  1970年   1篇
  1968年   1篇
  1957年   1篇
排序方式: 共有526条查询结果,搜索用时 187 毫秒
511.
In order to evaluate the numerical simulation method for solid oxide fuel cell anode polarization, three-dimensional lattice Boltzmann method simulation is carried out using Ni–YSZ microstructures reconstructed by a focused ion beam scanning electron microscope. The effects of reconstructed sample volume size on the three phase boundary length, tortuosity factors and overpotential are first investigated. The YSZ tortuosity factor has remained nearly unchanged when the cross-sectional area exceeds approximately 200 μm2, while the pore tortuosity factor is almost independent of the sample volume size. On the other hand, the Ni tortuosity shows very large variation regardless of the sample volume size. The overpotential predicted with the largest volume size sample is slightly larger than those of smaller volume samples. Two exchange current models based on patterned electrodes are assessed presently. Both models give weaker dependence on the steam concentration than the experimental data. From the predicted three-dimensional current stream lines, it is found that the mirrored computational structure gives a thinner reactive layer because of the factitious connection of Ni phase. Thus, it is recommended to use larger volume size samples which can cover whole reactive thickness when discussing the local potential and flux distributions.  相似文献   
512.
The kinetics of intercalation are discussed using a pulsed laser deposition (PLD) film electrode and electrochemical impedance analysis. Films of LiNi0.8Co0.2O2, deposited on single crystal substrates, were used for the study. The films have intercalative or blocking orientations on different crystal surfaces of the substrates. Impedance spectra show that there are at least three elemental processes in intercalation. Two processes at higher frequencies suggest that they occur at the electrode surface and are influenced by the orientation of the film. The third process appearing at low frequencies below 1 Hz indicates lithium motion in the bulk structure and shows the largest resistance among the three processes. This lithium conduction in a thin PLD film shows a semicircular response and is considered to be influenced more by the structure due to the nanometer-scale thickness.  相似文献   
513.
Nanoporous polyethersulfone (PES) membranes are widely used in dialysis systems due to their permeability and diffusion characteristics. However, PES membranes lack blood compatibility, which influences their permeability performance when employed in blood contact devices. Parylene film was deposited on a PES membrane surface and the membrane permeability and blood compatibility were investigated by long‐term blood diffusion testing. After 28 days of testing, 90% of a bare PES membrane was covered with platelets, while the parylene film coated PES membrane had improved biocompatibility with a platelet coverage of only 20–30%. The permeability of the bare PES membrane significantly declined during the first 7 days of the blood diffusion and became stable after 8 days. In contrast, the permeability of the parylene film coated PES membrane exhibited more consistent performance during the entire test. Thus, parylene film coating on PES membrane has potential for application in hemodialysis systems. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40024.  相似文献   
514.
The performance of a partially packed charcoal pellet bioreactor was compared to that of a fully packed bioreactor for aerobic acetic acid production. In the fully packed charcoal pellet bioreactor, it was considered that the shortening of an actual retention time of the culture broth limited the bioreactor performance under high dilution rate and high aeration conditions. By reducing the filling ratio of charcoal pellets to 44%, which increased the actual retention time of the culture broth, the maximum productivity increased from 3.9 g/l/h in the fully packed bed bioreactor to 5.7 g/l/h in the partially packed bioreactor without affecting the operational stability.  相似文献   
515.
516.
Racemic 8-[2-(2-pentyl-cyclopropylmethyl)-cyclopropyl]-octanoic acid (DCP-LA), a linoleic acid derivative with cyclopropane rings instead of cis-double bonds, contains possible four diastereomers such as α,α-, α,β-, β,α-, and β,β-DCP-LA. The present study examined the effect of racemic and diastereomeric DCP-LA on age-related learning and memory disorders using accelerated-senescence-prone mice 8 (SAMP8) and accelerated-senescence-resistant mice 1 (SAMR1). In the water maze test, the acquisition and retention latencies for SAMP8 mice were significantly longer than the latency for SAMR1 mice, indicating spatial learning and memory impairment for SAMP8 mice. All the racemic (1?mg/kg, per os) and diastereomeric DCP-LA (0.25?mg/kg, per os) significantly shortened the acquisition latency for SAMP8 mice, and racemic, α,α- and α,β-DCP-LA significantly shortened the retention latency, with the advantage greater than the acetylcholine (ACh) esterase inhibitor galanthamine. The results of the present study show that all the racemic and diastereomeric DCP-LA, has the potential to improve age-related learning and memory deterioration, the potential varying among them.  相似文献   
517.
518.
Dimensionality is one of the most important parameters of physical phenomena. Only two things determine the universality class of a phase transition: the dimensionality of a given system and the symmetry of the order parameter. In most cases, the dimensionality of a substance is predetermined by its crystal structure. Examples in which the effective dimensionality is reduced are quite rare. Here we show that the three-dimensional cubic system of Tl(2)Ru(2)O(7) most probably evolves into a one-dimensional spin-one Haldane system with a spin gap below 120 K, accompanied by anomalies in the structure, resistivity and susceptibility. We argue that these anomalies are due to an orbital ordering of Ru 4d electrons, with a strong coupling among three degrees of freedom: orbital, spin and lattice. Our work provides a unique example of the spontaneous formation of Haldane system with an insight into the intriguing interplay of different degrees of freedom.  相似文献   
519.
Epoxidized soybean oil (ESBO) was surveyed in the 103 samples of cap sealing for bottled foods on the Japanese market. Most of the sealings were made of polyvinyl chloride, while a few were made of polyethylene or acrylic resin. All the sealings contained ESBO in the range of 0.006-42.4%. Sealings for baby food, jam, etc. contained higher levels of ESBO, though those for beverages contained lower levels. Sealings in lug caps and press-on twist caps contained higher levels of ESBO, though that in pilfer-proof caps contained lower levels. Some sealings in screw caps and lug caps also contained other plasticizers, for example, di-2-ethylhexyl phthalate and diisononyl phthalate, and their ESBO contents were 1/10 of those in sealings containing only ESBO. In this survey, ESBO was the most common plasticizer in cap sealing resin for bottled foods on the Japanese market.  相似文献   
520.
A determination method was developed for epoxidized soybean oil (ESBO) and epoxidized linseed oil (ELO), which are used as plasticizers and/or stabilizers, in wrapping film and cap sealings. The ESBO method reported by Castle et al. was improved. Samples were extracted with acetone-hexane (3: 7), transmethylated under alkaline conditions, then derivatized to the 1,3-dioxolanes and analyzed by GC/MS. The recoveries of spiked ESBO and ELO were between 92.6% and 104.4%. The determination limits were 0.01 mg/g for ESBO and 0.02 mg/g for ELO in the wrapping film, and 0.04 mg/g and 0.08 mg/g in the cap sealing. ESBO and ELO were surveyed in 10 samples each of wrapping film and cap sealings currently available on the Japanese market. ESBO was found at 34.7-82.8 mg/g in polyvinyl chloride (PVC) wrapping films and at 5.47-399 mg/g in cap sealings. ELO was detected at 8.6-11.4 mg/g in polyvinylidene chloride (PVDC) wrapping films, and at 46.4 mg/g in a PVC wrapping film.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号