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   4854篇
  免费   95篇
  国内免费   14篇
电工技术   217篇
综合类   4篇
化学工业   875篇
金属工艺   122篇
机械仪表   144篇
建筑科学   50篇
矿业工程   1篇
能源动力   158篇
轻工业   249篇
水利工程   23篇
石油天然气   4篇
无线电   560篇
一般工业技术   731篇
冶金工业   1327篇
原子能技术   168篇
自动化技术   330篇
  2023年   20篇
  2022年   45篇
  2021年   86篇
  2020年   40篇
  2019年   39篇
  2018年   56篇
  2017年   59篇
  2016年   70篇
  2015年   58篇
  2014年   93篇
  2013年   226篇
  2012年   150篇
  2011年   207篇
  2010年   135篇
  2009年   162篇
  2008年   189篇
  2007年   145篇
  2006年   151篇
  2005年   127篇
  2004年   113篇
  2003年   124篇
  2002年   110篇
  2001年   95篇
  2000年   100篇
  1999年   134篇
  1998年   530篇
  1997年   311篇
  1996年   219篇
  1995年   142篇
  1994年   123篇
  1993年   126篇
  1992年   43篇
  1991年   51篇
  1990年   40篇
  1989年   44篇
  1988年   42篇
  1987年   40篇
  1986年   55篇
  1985年   34篇
  1984年   50篇
  1983年   39篇
  1982年   48篇
  1981年   43篇
  1980年   38篇
  1979年   17篇
  1978年   35篇
  1977年   34篇
  1976年   61篇
  1975年   10篇
  1969年   8篇
排序方式: 共有4963条查询结果,搜索用时 93 毫秒
111.
BACKGROUND: This article presents results of the acute treatment phase of a 2-site study comparing cognitive behavioral group therapy (CBGT) and treatment with the monoamine oxidase inhibitor phenelzine sulfate for social phobia. METHODS: One hundred thirty-three patients from 2 sites received 12 weeks of CBGT, phenelzine therapy, pill placebo administration, or educational-supportive group therapy (an attention-placebo treatment of equal credibility to CBGT). The "allegiance effect," ie, the tendency for treatments to seem most efficacious in settings of similar theoretical orientation and less efficacious in theoretically divergent settings, was also examined by comparing responses to the treatment conditions at both sites: 1 known for pharmacological treatment of anxiety disorders and the other for cognitive behavioral treatment. RESULTs: After 12 weeks, phenelzine therapy and CBGT led to superior response rates and greater change on dimensional measures than did either control condition. However, response to phenelzine therapy was more evident after 6 weeks, and phenelzine therapy was also superior to CBGT after 12 weeks on some measures. There were few differences between sites, suggesting that these treatments can be efficacious at facilities with differing theoretical allegiances. CONCLUSIONS: After 12 weeks, both phenelzine therapy and CBGT were associated with marked positive response. Although phenelzine therapy was superior to CBGT on some measures, both were more efficacious than the control conditions. More extended cognitive behavioral treatment and the combination of modalities may enhance treatment effect.  相似文献   
112.
Yamamoto H  Uenoyama H  Hirai K  Dou X  Ozaki Y 《Applied optics》1998,37(13):2640-2645
We describe the quantitative analysis of some metabolic gases bymultichannel Raman spectroscopy. Raman spectra were measured forair, acetone, ammonia, carbon dioxide, and mixed gas consisting ofacetone, ammonia, and air. We designed a new elliptic-sphericalintegration type of cell holder to obtain the Raman spectra of gaseswith a high signal-to-noise ratio. Concentrations of acetone, ammonia, and carbon dioxide were determined by the peak intensities ofRaman bands at 2940, 3228, and 1385 cm(-1), respectively. To compensate for the fluctuations of Ramanintensities caused by several factors, such as the fluctuations oflaser power, the peak intensity of a band at 2324 cm(-1) dueto nitrogen gas was used as an internal intensity standard. Thecorrelation coefficient between the corrected Raman intensity at 2940cm(-1) and the concentration of acetone was calculated to be0.984 for a concentration range of 2-12 ppm. The detection limitof acetone gas was found to be 2 ppm.  相似文献   
113.
We measured the interfacial tension of 3 He-4 He mixtures under pressure of 21 atm down to about 0.2K by using the resonance of the interfacial wave and found that the decrease from absolute zero is proportional to T2 up to about 0.4 K. From the simple extrapolation of this T2-dependence the interfacial tension at absolute zero is obtained as i (0) = 19.3 ± 1.3 mdyne/cm. Compared with saturated vapor pressure, the interfacial tension at absolute zero decreases by about 20%, and the coefficient of the T2-dependence does not depend strongly on pressure. The large T2-dependence both at saturated vapor pressure and at 21 atm may be attributable to the change in density difference between the two phases.  相似文献   
114.
This paper presents a novel method to predict the starting performance of synchronous motors. This proposed strategy is based on a simple standstill response testing method using a small-capacity DC power supply unit, tentatively named the DC decay testing method in this paper, and can be applied to standstill synchronous motors with the rotor in any arbitrary position. The proposed testing method is carried out on a 10 kW, 200 V, 31.9 A, 50 Hz four-pole laminated salient-pole synchronous motor with damper windings. The results measured by on-load test and those predicted by the proposed method on starting performance clearly show the validity of the proposed method  相似文献   
115.
The effects of Ta addition on the magnetic properties of permalloy thin films have been investigated. The alloy compositions on a weight basis are (Ni81Fe19)1-x Ta x with 0 x 0.105, and the films are sputtered onto a glass substrate at between room temperature and 300 C. The saturation magnetization and anisotropic magnetic field decrease with increasing Ta content. The saturation magnetization is 0.75 T at 5 wt % Ta. The coercivity remains constant at 125 Am-1. The electrical resistivity increases linearly with increasing Ta content, then saturates at approximately 7.5 wt% Ta. The saturation resistivity is approximately 1.00 m. The magnetoresistivity ratio (/) decreases with increasing Ta content, mainly due to increased electrical resistivity (). The magnetostriction changes from negative to positive with increasing Ta content and reaches nearly zero at 2 wt% Ta. The NiFeTa films containing 5–6 wt% Ta have potential for use as the soft-biasing film in magnetoresistive elements.  相似文献   
116.
We propose an explanatory mechanism for multilayered neural networks (NN). In spite of the effective learning capability as a uniform function approximator, the multilayered NN suffers from unreadability, i.e., it is difficult for the user to interpret or understand the "knowledge" that the NN has by looking at the connection weights and thresholds obtained by backpropagation (BP). This unreadability comes from the distributed nature of the knowledge representation in the NN. In this paper, we propose a method that reorganizes the distributed knowledge in the NN to extract approximate classification rules. Our rule extraction method is based on the analysis of the function that the NN has learned, rather than on the direct interpretation of connection weights as correlation information. More specifically, our method divides the input space into "monotonic regions" where a monotonic region is a set of input patterns that belongs to the same class with the same sensitivity pattern. Approximate classification rules are generated by projecting these monotonic regions.  相似文献   
117.
The tangential momentum accommodation coefficient (TMAC) was investigated experimentally from the mass flow rate through a single microtube under the slip flow and the early part of the transition regime. The measurements were carried out by the constant-volume method under the mean Knudsen number smaller than 0.3, which is based on the mean pressure of the inlet and the outlet of the microtube, to apply the second-order slip boundary condition. To measure TMACs on various materials, quite large microtube was employed, which require the reduction in leakage. TMAC was obtained from the slip coefficient determined by the relation of the mass flow rate to the mean Knudsen number. The obtained mass flow rate was well explained by the theoretical equation. TMACs of deactivated-fused silica with argon, nitrogen, and oxygen were measured, showing the tangential momentum was not accommodated completely to the surface, and the values showed good agreement with previous studies. From the comparison between microtubes with different inner diameter, it is showed that TMAC is determined mainly by gas species and surface material.  相似文献   
118.
Abstract— To understand actual viewing conditions at home is important for TV design. And the preferred luminance level of LCD TVs under actual viewing conditions is also important in order to obtain both good picture quality and low power consumption. The actual viewing conditions of households and the preferred luminance levels was investigated. In a field test of 83 households, the display luminance, screen illuminance, and viewing locations were measured on site. In laboratory experiments, young and elderly subjects adjusted the luminance of an LCD‐TV screen to their preferred levels under different screen illuminance levels, angular screen sizes, and average luminance levels (ALL) of the images. As a result, two equations, which represent the preferred luminance level of LCD‐TV screens corresponding to different viewing conditions for young and elderly subjects were obtained. When the ALL of the images was 25% and the screen illuminance and angular screen size were set at 100 lx and 20°, respectively, the preferred luminance was 1 60 cd/m2 for the young subjects and 248 cd/m2 for the elderly subjects. By using the setting of the preferred luminance of an LCD TV under actual viewing conditions, it is possible to conserve energy consumption.  相似文献   
119.
For sustainable manufacturing, manufacturers should construct and design inverse manufacturing systems consisting of assembly and disassembly systems. The sorting process in the disassembly system is the first process of the whole inverse manufacturing system. Therefore, it can become a bottleneck and decrease the productivity of the whole inverse manufacturing systems.This study focuses on a disassembly system with reverse blocking in a sorting process [Yamada, T., & Matsui, M. (2003). Disassembly production systems and its design issues. Reprints of Japan Industrial Management Association, Spring meeting, Chofu, Japan, May, 144–145 (in Japanese)]. It generalizes the queuing model and discusses the performance of the disassembly system by mathematical and numerical analysis. First, the sorting process with reverse blocking is generally modeled as a queuing system. Next, the stationary state equations of the system are formulated, and the objective function is set as the throughput. Finally, the system performance is discussed by mathematical and numerical analysis in cases of a different number of stations and buffers, and also an example of the system design is shown and discussed in view of the busy rate, blocking probability and throughput.  相似文献   
120.
Organic light‐emitting diode displays have a cathode composed of a layer of highly reflective metal. Reflection of external light from this layer can be suppressed with a broadband quarter‐wave plate. Although various types of quarter‐wave plate retardation films have been prepared by copolymerizing, mixing, or laminating multiple polymers, ideal wavelength dispersion has not been achieved with thin retardation films because of their relatively low birefringence and the complexity of the procedure required manufacturing them. In this study, we developed (i) new liquid‐crystalline monomers with negative wavelength dispersion birefringence that we used to obtain thin, single‐layered retardation films suitable for coating and (ii) retardation films with different molecular alignments. We found that the monomers showed high solubility and high regularity of molecular alignment, with less damage to the substrate and alignment films. We also investigated the wavelength dispersion and thermal stability of the films. We succeeded in developing retardation films that had a homeotropic alignment or a hybrid alignment with negative wavelength dispersion. These alignments can be used to obtain antireflection films with an improved viewing angle for organic light‐emitting diode displays or next‐generation thin displays.  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