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   1819篇
  免费   44篇
  国内免费   2篇
电工技术   108篇
综合类   1篇
化学工业   301篇
金属工艺   60篇
机械仪表   38篇
建筑科学   21篇
矿业工程   1篇
能源动力   59篇
轻工业   143篇
水利工程   4篇
石油天然气   2篇
无线电   182篇
一般工业技术   292篇
冶金工业   534篇
原子能技术   32篇
自动化技术   87篇
  2023年   8篇
  2022年   19篇
  2021年   31篇
  2020年   14篇
  2019年   19篇
  2018年   30篇
  2017年   21篇
  2016年   35篇
  2015年   17篇
  2014年   36篇
  2013年   87篇
  2012年   47篇
  2011年   73篇
  2010年   42篇
  2009年   58篇
  2008年   65篇
  2007年   42篇
  2006年   45篇
  2005年   54篇
  2004年   41篇
  2003年   49篇
  2002年   34篇
  2001年   49篇
  2000年   40篇
  1999年   55篇
  1998年   181篇
  1997年   128篇
  1996年   92篇
  1995年   51篇
  1994年   64篇
  1993年   51篇
  1992年   26篇
  1991年   16篇
  1990年   15篇
  1989年   20篇
  1988年   11篇
  1987年   19篇
  1986年   17篇
  1985年   30篇
  1984年   10篇
  1983年   16篇
  1982年   9篇
  1981年   11篇
  1980年   13篇
  1979年   5篇
  1978年   8篇
  1977年   19篇
  1976年   19篇
  1975年   6篇
  1968年   4篇
排序方式: 共有1865条查询结果,搜索用时 15 毫秒
1.
2.
This paper proposes a technique for monitoring the longitudinal motion of geosynchronous satellites. A two‐antenna interferometer is used, with the baseline orientation adjusted to a particular horizontal azimuth. The interferometer then becomes insensitive to the north–south motion of the satellite, and this enables direct measurement of the satellite's longitudinal motion. Longitudes are monitored continuously, with no delay when orbital manoeuvres occur. The proposed technique is particularly useful when two or more satellites are operating in close proximity and their longitudes must be precisely monitored for safety control. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   
3.
In recent years, computer technology has made remarkable progress and a computer has become an indispensable tool for both engineers and scientists. In this article, utilization of computers in welding research is briefly summarized. Their use in numerical analysis is particularly discussed and applied to physical phenomena in molten pool, hydrogen diffusion and residual stresses due to welding. A comparison is made between theoretical and experimental results.  相似文献   
4.
This study investigated the impact of Difficulty Level and Type of Suggestion upon the durability of posthypnotic suggestion over an 8-week period. Seventy-eight highly susceptible subjects selected by both the Harvard Group Scale of Hypnotic Susceptibility: Form A (HGSHS:A) and Stanford Hypnotic Scale of Susceptibility: Form C (SHSS:C) were assigned to six groups (two levels of Difficulty x three Types of Suggestion). S's were tested for posthypnotic suggestion at 1, 3, 6, and 8 weeks. A 2 x 3 x 4 (Difficulty x Suggestion x Time) factorial ANOVA was conducted, with Time treated as a repeated-measure. The outcome variable at each time was either pass or fail for relevant suggestion. We found a significant Time effect, a significant Difficulty effect, and a significant Time x Difficulty interaction. Fewer subjects passed the difficult suggestions than passed the easy suggestions; fewer passed suggestions at a latter time; and the decay in pass rate was more pronounced for the easy suggestion condition, due largely to the higher initial pass rate. Type of Suggestion was not significant, nor were any of the other interactions. Clinical implications were discussed.  相似文献   
5.
A CMOS integrated circuit for a noninvasive biological-signal telemetry system specified for use in medical and physiological studies of the influence of weightlessness in space is presented. The system can monitor multichannel (4 channels maximum) biological signals from multiple subjects (4 subjects maximum) in real time by using time multiplexing. A key technique so-called synchronized multiple-subject telemetry, to achieve multiple-subject telemetry has been proposed. This technique utilizes bidirectional optical transmissions with direct and scattered infrared lights between an observer and each of the subjects. An experimental CMOS IC to give a small light-weight low-power, and smart telemetry instrument for use on animals has been developed. This IC is for evaluating circuit blocks of the implantable monolithic telemetry instrument. The major circuit blocks include CMOS digital circuits for synchronization, subject selection and time multiplexing, analog circuits for pulse interval modulation, and other blocks such as a CMOS optical pulse receiver and an LED driver. A preliminary experimental multichannel telemetry from two subjects has been performed with the implemented IC chips, and the principal operation of the multiple-subject optical biotelemetry has been demonstrated  相似文献   
6.
The supercharged flap is one which is expected to attain better survival, by anastomosing the distal vessels of the flap to the recipient vessels. An experimental study is reported to determine whether the vessel to be anastomosed should be an artery, a vein, or both. The authors advise anastomosing an artery and a vein, but they believe that arterial inflow is more important than venous drainage.  相似文献   
7.
For multi-step heterogeneous consecutive reactions affected entirely by interphase diffusion under isothermal condition, the equations for the effectiveness factors, the surface concentrations and the point yields were derived in terms of the Damkoehler numbers or the measurables from the mass balances set up on the assumption that the mass-transfer rate balances the surface-reaction rate at steady state. From the analyses of the equations derived, the effectiveness factors for the intermediate steps and the surface concentrations of intermediates were understood to be enhanced by the measurables inclusive of the concentrations and the mass-transfer coefficients. Then the effect of the concentrations was concluded to be most significant. The effects of these measurables to the effectiveness factors and the surface concentrations were qualitatively discussed for simple consecutive reactions and also for additive consecutive reactions. Especially, as for two-step additive consecutive reactions, the effects of measurables η Da and the concentrations to the effectiveness factors were examined with graphical presentations. Finally, the brief discussion of the dependency of the Damkoehler number upon reaction time and the effect of the Renolds number and diffusivity to the extent of the mass-transfer resistance were presented.  相似文献   
8.
We have investigated the characteristics of transparent metal-insulator-semiconductor field-effect transistors (MISFETs) fabricated using InGaO3(ZnO)m (m=integer) single-crystalline thin films as n-channel layers and amorphous alumina as gate insulator films. The MISFETs exhibit good characteristics such as insensitivity to visible light illumination, off-current as low as ∼1 nA with a positive threshold voltage of ∼3 V and on/off current ratio of 105. The field-effect mobility increased from ∼1 to ∼10 cm2 (V s)−1 as the m-value increased. Room temperature Hall mobility also increased. However, unexpectedly these values were lower than the field-effect mobility. It is explained by existence of shallow localized state in the homologous compounds.  相似文献   
9.
Preliminary experiments using two chemicals (CaO, a quicklime, and a cationic nitrogen-bearing precipitant, EC-004) to remove silica from geothermal brine were undertaken at the Mokai geothermal plant, New Zealand. The brine was mixed with the reagent (CaO or EC-004). The reaction was studied from the start of the experiment (NRT, 0 min, no retaining time) and after 15 min (15RT) at 90 °C. The concentration of silica in the brine was initially 954 mg/l, and decreased linearly with increasing reagent concentration. When CaO is added, the silica concentration at 15RT was 200 mg/l lower than at NRT and became almost zero on addition of 1.5 g/l. In contrast, when EC-004 is added, the total silica concentration nearly reaches the solubility of amorphous silica at 90 °C. In order to prevent silica scaling in Mokai brines cooled to 90 °C, the CaO and EC-004 added should be individually adjusted to 0.5 g/l and 80 mg/l, respectively.  相似文献   
10.
One of the anaphylatoxins, C5a, is known to increase the expression of the complement receptors, CR1 and CR3, on PMNs which play important roles in the phagocytosis. We measured the expression of these receptors before and after the stimulation with C5a and C5a-receptors (C5aR) on PMNs in patients with systemic lupus erythematosus (SLE). PMNs from 16 patients and 11 normal controls were tested. All the patients with SLE were administered with prednisolone orally and were in the inactive stage. The CR1 expression in SLE was significantly weak (p < 0.01) before and after stimulation with 4.55 nM (50 micrograms/ml) of C5a. There was no significant difference of CR3 expression before stimulation. However, after the stimulation with C5a, the increase of CR3 on PMNs from SLE was significantly small (p < 0.01). C5aR on PMNs showed no difference between the two groups. However, the expression of C5aR was significantly suppressed in patients treated with a high dosage of prednisolone (> = 10 mg/day) compared to those with a low dosage of prednisolone (< 10 mg/day). There was no significant difference of CR1 and CR3 expression between these groups. It is concluded that the increase of CR1 and CR3 on PMNs by C5a in small in SLE, of which impaired increase is not due to C5aR on PMNs, and that the expression of C5aR is suppressed by prednisolone.  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