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   238篇
  免费   6篇
电工技术   18篇
化学工业   64篇
金属工艺   1篇
机械仪表   3篇
建筑科学   2篇
能源动力   3篇
轻工业   17篇
水利工程   1篇
无线电   20篇
一般工业技术   41篇
冶金工业   42篇
原子能技术   7篇
自动化技术   25篇
  2023年   2篇
  2021年   8篇
  2020年   1篇
  2019年   2篇
  2018年   4篇
  2017年   5篇
  2016年   4篇
  2015年   2篇
  2014年   5篇
  2013年   11篇
  2012年   3篇
  2011年   9篇
  2010年   8篇
  2009年   5篇
  2008年   6篇
  2007年   13篇
  2006年   5篇
  2005年   10篇
  2004年   8篇
  2003年   5篇
  2002年   5篇
  2001年   2篇
  2000年   5篇
  1999年   7篇
  1998年   27篇
  1997年   13篇
  1996年   10篇
  1995年   3篇
  1994年   5篇
  1993年   6篇
  1992年   2篇
  1991年   5篇
  1990年   2篇
  1989年   2篇
  1988年   2篇
  1987年   2篇
  1985年   3篇
  1983年   2篇
  1982年   4篇
  1981年   6篇
  1980年   2篇
  1979年   7篇
  1978年   1篇
  1976年   1篇
  1975年   1篇
  1974年   2篇
  1968年   1篇
排序方式: 共有244条查询结果,搜索用时 437 毫秒
1.
A fault section detection system that uses optical magnetic field sensors and instantly detects the section in which a ground fault occurred was developed for 66 kV underground multiterminal systems having Y-branch joint boxes. The optical magnetic field sensor, which is based on the Faraday effect in Bi-doped YIG ((BiYbGd)3Fe5O12) having a large Verdet constant, detects cable conductor currents of 0 to 2000 A with high precision with the use of a laminated magnetic ring core of silicon steel plates. Sensors and a fault section detector/indicator of a system are connected with optical fibers capable of nonrepeated transmission of over 6 km  相似文献   
2.
The objectives of the present study were to investigate autonomic nervous system influence on heart rate during physical exercise and to examine the relationship between the fractal component in heart rate variability (HRV) and the system's response. Ten subjects performed incremental exercise on a cycle ergometer, consisting of a 5-min warm-up period followed by a ramp protocol, with work rate increasing at a rate of 2.0 W/min until exhaustion. During exercise, alveolar gas exchange, plasma norepinephrine (NE) and epinephrine (E) responses, and beat-to-beat HRV were monitored. HRV data were analyzed by "coarse-graining spectral analysis" (Y. Yamamoto and R. L. Hughson. J. Appl. Physiol. 71: 1143-1150, 1991) to break down their total power (Pt) into harmonic and nonharmonic (fractal) components. The harmonic component was further divided into low-frequency (0.0-0.15 Hz) and high-frequency (0.15-0.8 Hz) components, from which low-frequency and high-frequency power (Pl and Ph, respectively) were calculated. Parasympathetic (PNS) and sympathetic (SNS) nervous system activity indicators were evaluated by Ph/Pt and Pl/Ph, respectively. From the fractal component, the fractal dimension (DF) and the spectral exponent (beta) were calculated. The PNS indicator decreased significantly (P < 0.05) when exercise intensity exceeded 50% of peak oxygen uptake (VO2 peak). Conversely, the SNS indicator initially increased at 50-60% VO2peak (P < 0.05) and further increased significantly (P < 0.05) at > 60% VO2peak when there were also more pronounced increases in NE and E.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
3.
It has been said that nuclear energy is an important option for especially developing countries to satisfy their increasing energy demand. However, it will be difficult to deploy first of a kind nuclear power plant in developing countries because extensive safety demonstration has to be conducted in industrialized countries. On the other hand, it will be essential to present rigid proof of reliable operational experience to develop proper understanding of the safety features of new reactor systems among the people around the demonstration plant sites. One of the ways to solve the issue is to integrate existing technologies supported by a great deal of data and experience into a new reactor design. Based on the consideration, a small-sized district heating reactor system based on the pressurized water reactor (PWR) technologies combined with the fuel concept of high temperature gas cooled reactors (HTGRs) has been studied. The purpose of the combination of these two existing concepts is to take the best advantages of both excellent operational experience of PWRs and the integrity of HTGR fuel, coated particle fuel, against fission products release even at high temperature. We expect that this approach will help create a breakthrough to the current stagnation of nuclear power deployment.  相似文献   
4.
We have characterized the electronic structure of FeSe1−xTex for various x values using soft x-ray photoemission spectroscopy (SXPES), high-resolution photoemission spectroscopy (HRPES) and inverse photoemission spectroscopy (IPES). The SXPES valence band spectral shape shows that the 2 eV feature in FeSe, which was ascribed to the lower Hubbard band in previous theoretical studies, becomes less prominent with increasing x. HRPES exhibits systematic x dependence of the structure near the Fermi level (EF): its splitting near EF and filling of the pseudogap in FeSe. IPES shows two features, near EF and approximately 6 eV above EF; the former may be related to the Fe 3d states hybridized with chalcogenide p states, while the latter may consist of plane-wave-like and Se d components. In the incident electron energy dependence of IPES, the density of states near EF for FeSe and FeTe has the Fano lineshape characteristic of resonant behavior. These compounds exhibit different resonance profiles, which may reflect the differences in their electronic structures. By combining the PES and IPES data the on-site Coulomb energy was estimated at 3.5 eV for FeSe.  相似文献   
5.
The prevalence of Campylobacter (>90%) and Salmonella (33%) in turkeys at slaughter has been estimated. This report describes studies to estimate the time of entry of Campylobacter and Salmonella into the brooder house, which is the first stage of commercial turkey production. In trial 1, birds (∼100 per time point) were monitored by conventional culture at three intervals (0, 9, and 16 days of age). Campylobacter spp. were not detected in poults at the day of hatch; Salmonella was isolated from the ceca (3.9%) and yolk sac (0.1%). By day 9, Salmonella were frequently isolated from the ceca (55%) and small intestine (45%) while Campylobacter was not cultured. By day 16, the prevalence of Salmonella in the ceca (21%) and small intestine (5.1%) had declined; Campylobacter was infrequently isolated from either the ceca (2%) or small intestine (3%). In trial 2, poults (50 per time point at 5, 20, and 33 days of age) were monitored for Campylobacter and Salmonella by real-time polymerase chain reaction (PCR); Salmonella was also monitored by conventional culture. Whereas Campylobacter was not detected by real-time PCR in the ceca of 5-day-old birds, it was detected on days 20 (92%) and 33 (90%). In contrast, Salmonella was isolated from young birds at days 5 (98%), 20 (98%), and 33 (98%), after which time the turkeys were moved to the finisher house. At slaughter at 138 days, Salmonella prevalence in the ceca had declined (4.5%) in contrast to the prevalence of Campylobacter (92%). Antimicrobial sensitivity profiles of the Salmonella isolates indicated an increase of sulfonamide-resistant isolates throughout the brooder stage. Genotyping by pulsed-field gel electrophoresis analysis of Salmonella (45 isolates per sampling time) indicated fluctuating populations as the birds matured.  相似文献   
6.
7.
Retention of the stationary phase of aqueous–aqueous polymer phase systems is improved by a spiral column configuration which utilizes the radially acting centrifugal force along the spiral pitch to retain the heavier phase in the outer portion and the lighter phase in the inner portion of the spiral channel. For the separation of proteins which has low mass transfer rates, the system needs further modification of the separation channel to interrupt the laminar flow and enhance mixing of the two phases.  相似文献   
8.
 To design contact-type gimbal system for a newly developed removable flexible disk drive called Card size flexible disk drive (CFDD) (Shinpuku et al., 2001; Ryoson et al., 2001), the gimbal's vibration characteristics in the disk-rotation direction were measured and simulated using FEM. To determine the relationship between vibration and friction in the head disk interface (HDI), a hard disk was also used. The friction characteristics were inserted into the FEM model based on the results. The gimbal was modified to suppress vibration amplitude to half in both simulation and experiment. Received: 5 July 2001/Accepted: 1 November 2001 Paper presented at the 12th Annual Symposium on Information Storage and Processing Systems, Santa Clara, CA, USA, 28–29 June, 2001.  相似文献   
9.
The increase in electric power consumption in industry has led to the development of modern distribution systems such as control centers having high kVA ratings and high prospective fault current. In such a situation, the improvement of the system usefulness such as reliability and cost effectiveness is the essential requirement. An index is presented to evaluate the system usefulness using the cost effectiveness for fault protection in a system of given bank kVA. The index is estimated on four different system structures of control centers, including one which utilizes Permanent Power Fuses (PPF). It is presented that the PPF combined with molded case circuit breaker in main circuit effectively improves the cost effectiveness in control centers with high fault current. Operating principles of the PPF and the control center utilizing the PPF are briefly outlined.  相似文献   
10.
Despite advances in medicine, cardiac disease remains an increasing health problem associated with a high mortality rate. Maladaptive cardiac remodeling, such as cardiac hypertrophy and fibrosis, is a risk factor for heart failure; therefore, it is critical to identify new therapeutic targets. Failing heart is reported to be associated with hyper-ubiquitylation and impairment of the ubiquitin–proteasome system, indicating an importance of ubiquitylation in the development of cardiac disease. Ubiquitylation is a post-translational modification that plays a pivotal role in protein function and degradation. In 1995, homologous to E6AP C-terminus (HECT) type E3 ligases were discovered. E3 ligases are key enzymes in ubiquitylation and are classified into three families: really interesting new genes (RING), HECT, and RING-between-RINGs (RBRs). Moreover, 28 HECT-type E3 ligases have been identified in human beings. It is well conserved in evolution and is characterized by the direct attachment of ubiquitin to substrates. HECT-type E3 ligase is reported to be involved in a wide range of human diseases and health. The role of HECT-type E3 ligases in the development of cardiac diseases has been uncovered in the last decade. There are only a few review articles summarizing recent advancements regarding HECT-type E3 ligase in the field of cardiac disease. This study focused on cardiac remodeling and described the role of HECT-type E3 ligases in the development of cardiac disease. Moreover, this study revealed that the current knowledge could be exploited for the development of new clinical therapies.  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