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   498篇
  免费   18篇
  国内免费   5篇
电工技术   43篇
化学工业   127篇
金属工艺   45篇
机械仪表   6篇
建筑科学   22篇
能源动力   9篇
轻工业   49篇
水利工程   2篇
无线电   31篇
一般工业技术   62篇
冶金工业   49篇
原子能技术   17篇
自动化技术   59篇
  2022年   10篇
  2021年   14篇
  2020年   5篇
  2019年   9篇
  2018年   15篇
  2017年   5篇
  2016年   18篇
  2015年   6篇
  2014年   11篇
  2013年   33篇
  2012年   23篇
  2011年   39篇
  2010年   23篇
  2009年   20篇
  2008年   22篇
  2007年   16篇
  2006年   17篇
  2005年   18篇
  2004年   22篇
  2003年   11篇
  2002年   7篇
  2001年   5篇
  2000年   7篇
  1999年   14篇
  1998年   24篇
  1997年   9篇
  1996年   15篇
  1995年   10篇
  1994年   6篇
  1993年   8篇
  1991年   5篇
  1990年   7篇
  1988年   6篇
  1987年   4篇
  1986年   9篇
  1985年   5篇
  1984年   2篇
  1982年   3篇
  1981年   6篇
  1980年   10篇
  1979年   2篇
  1978年   2篇
  1977年   3篇
  1976年   3篇
  1975年   1篇
  1974年   2篇
  1973年   4篇
  1969年   1篇
  1968年   1篇
  1957年   1篇
排序方式: 共有521条查询结果,搜索用时 15 毫秒
21.

The development of early warning systems for landslide hazards has long been a challenge because the accuracy of such systems is limited by both the complicated underlying mechanisms of landslides and the lack of in situ data. In this study, we implemented a multivariate threshold criterion that integrates in situ monitoring data and data from unsaturated hydro-mechanical analyses as an early warning system for rainfall-induced landslides in the Wenchuan earthquake region of China. The results indicate that rainfall intensity is closely correlated with the probability of landslide occurrence. Variations in matric suction and suction stress were obtained from in situ measurements and used to quantify the soil water retention curve, which presented clear hysteresis characteristics. The impacts of rainfall infiltration on slope failure in post-earthquake landslide areas under transient rainfall conditions were quantified by hydro-mechanical modelling theories. Variations in the suction stress of unsaturated soil were used to calculate the safety factor. The influence of hydrological hysteresis processes on the slope failure mechanism was analysed. Multivariate threshold criteria that include the intensity–probability (I-P) threshold, soil moisture and matric suction based on in situ big data and unsaturated slope stability analysis benchmarks are proposed for use in an early warning system for rainfall-induced landslides.

  相似文献   
22.
The unsaponifiables from threeTheaceae (Camellia japonica L.,Camellia Sasanqua Thunb., andThea sinensis L.) oils and alfalfa, garden balsam, and spinach seed oils and shea fat were separated into four fractions: sterols, 4-methylsterols, triterpene alcohols, and less polar compounds by thin layer chromatography. While the sterol fraction was the major one for the unsaponifiables from alfalfa and spinach seed oils, the triterpene alcohol fraction was predominant for the unsaponifiables from all other oils. The sterol, 4-methylsterol, and triterpene alcohol fractions were analyzed by gas chromatography. All the sterol fractions were alike in their compositions, consisting exclusively of Δ7-sterols, such as α-spinasterol and Δ7-stigmastenol as predominant components together with Δ7-avenasterol and 24-methylcholest-7-enol. Obtusifoliol, gramisterol (occasionally accompanied with cycloeucalenol), and citrostadienol, together with several other unidentified components, were found in the 4-methylsterol fractions from all of the oils except shea fat. The 4-methylsterol fraction from shea fat showed a characteristic composition containing a large proportion of unidentified components which had relative retention time greater than that of citrostadienol, while no citrostadienol was detected. β-Amyrin, lupeol, and butyospermol were major components of the triterpene alcohol fractions from most of the oils, but the fraction from spinach seed oil contained cycloartenol and 24-methylene-cycloartanol as predominant components. There is a close similarity in the compositions of unsaponifiables (sterols, 4-methylsterols, and triterpene alcohols) of the threeTheaceae oils. Two sterols, α-spinasterol and Δ7-stigmastenol, and five triterpene alcohols were isolated from tea seed oil. Moreover, five unidentified components beside parkeol, butyrospermol, α-amyrin, and lupeol were isolated from the triterpene alcohol fraction of shea fat.  相似文献   
23.
The activity of Rh/CeO2 for NO reduction by C3H6 was gradually deceased by mixing with ZrO2 until 68 mol%. Rh supported on CeO2–ZrO2 with higher OSC was found to show lower catalytic activity. High OSC of CeO2–ZrO2 would probably stabilize the surface of Rh in oxidized state, resulting in low activity and low efficiency of C3H6 utilization for NO reduction. In situ FT-IR spectroscopy suggested that mononitrosyl species such as Rh(NO)δ? and Rh(NO)δ+ are reaction intermediates in the NO–C3H6–O2 reaction over Rh/CeO2–ZrO2 catalysts.  相似文献   
24.
A thin film (60 μm thick) of a gadolinium-doped ceria (GDC) electrolyte was prepared by the doctor blade method. This film was laminated with freeze-dried 42 vol% NiO–58 vol% GDC mixed powder and pressed uniaxially or isostatically under a pressure of 294 MPa. This laminate was cosintered at 1100 °–1500 °C in air for 4–12 h. The laminate warped because of the difference in the shrinkage of the electrolyte and electrode during the sintering. A higher shrinkage was measured for the electrode at 1100 °–1200 °C and for the electrolyte at 1300 °–1500 °C. The increase of the thickness of anode was effective in decreasing the warp and in increasing the density of the laminated composite. The maximum electric power density with a SrRuO3 cathode using 3 vol% H2O-containing H2 fuel was 100 mW/cm2 at 600 °C and 380 mW/cm2 at 800 °C, respectively, for the anode-supported GDC electrolyte with 30 μm thickness.  相似文献   
25.
The deposition rate plays an important role in determining the thickness, stress state, and physical properties of plasma-sprayed coatings. In this article, the effect of the deposition rate on the stress evolution during the deposition (named evolving stress) of yttria-stabilized zirconia coatings was systematically studied by varying the powder feed rate and the robot-scanning speed. The evolving stress during the deposition tends to increase with the increased deposition rate, and this tendency was less significant at a longer spray distance. In some cases, the powder feed rate had more significant influence on the evolving stress than the robot speed. This tendency can be associated with a deviation of a local deposition temperature at a place where sprayed particles are deposited from an average substrate temperature. At a further higher deposition rate, the evolving stress was relieved by introduction of macroscopic vertical cracks as well as horizontal branching cracks.  相似文献   
26.
The extraction equilibria of Am(III) and Eu(III) by using a tripodal ligand, tris(2‐pyridylmethyl)amine (tpa), with various lipophilic anions have been investigated. The extractability of both Am(III) and Eu(III) was increased by the combination of tpa and counteranions due to a synergistic effect. The separation factors between Am(III) and Eu(III) were also increased from 7.6 to 49 by the combination of counteranions and organic solvents. The extraction equilibria of Am(III) and Eu(III) with tpa in 1,2‐dichloroethane were determined by slope analysis. It was found that three anions and one molecule of the ligand coordinated to Am(III) and Eu(III) was extracted regardless of the anions.  相似文献   
27.
Nanogrinding was performed on the cross-sections of amorphous Si thin film solar panels, which are nanoscale multi-layer structures consisting of hard and brittle materials. The deformed structures of the panel cross-sectional surfaces after grinding were investigated using electron and atomic force microscopy. The nanogrinding results were compared with those obtained from polishing and nanoscratching, demonstrating that the three processes had produced consistent surface characteristics. Though nanogrinding produced nanometric surface roughness with ductile material removal, but could cause cracking, edge chipping and delamination at thin film interfaces. The results of this work are of value for developing the efficient machining process for thin film solar panels and other brittle multi-layer materials.  相似文献   
28.
Magnetic properties of manganese zinc ferrite (MZF) coatings deposited by atmospheric dc plasma spraying largely depend on zinc and oxygen loss during particle flight. The temperature and velocity of in-flight MZF particles were widely varied by changing plasma spray conditions to examine these chemistry changes and resultant magnetic properties. Zn loss increases with increased particle temperature or decreased particle velocity. Meanwhile, wüstite (FeO) formation, related to the oxygen loss, is more complicated, partly because oxygen, which is lost during flight in the high-temperature zone of the plasma jet, can be recovered at longer spray distances. As a result, the saturation magnetization of MZF coatings decreases and the coercivity increases with increased particle temperature or decreased particle velocity.  相似文献   
29.
To clarify the role of phosphate in the formation of corrosion products, the transformation of GRI(Cl) with the addition of phosphate was characterized through XRD, TEM, and solution analysis. Electrochemical analysis showed that the transformation of GRI(Cl) was delayed and the size of the final products, i.e., γ-FeOOH was reduced in the phosphate added case. X-ray absorption spectroscopy indicated that the neighboring Fe–Fe coordination number of FeO6 octahedral unit in γ-FeOOH was decreased. These effects of phosphate are attributed to its adsorption on GRI(Cl) and nucleated γ-FeOOH that prevented particle growth during oxidation process.  相似文献   
30.
The new cytostatics titanocene dichloride and vinorelbine were compared to cisplatin and paclitaxel using a human ovarian cancer xenografts model. Biopsy material from a native human ovarian carcinoma was expanded and transplanted into 96 nude mice. The animals were divided into six treatment groups: cisplatin 3 x 4 mg/kg, paclitaxel 5 x 26 mg/kg, vinorelbine 1 x 20 mg/kg, titanocene dichloride 3 x 30 mg/kg, titanocene dichloride 3 x 40 mg/kg and a control group treated with 0.9% saline. Each experiment was repeated with eight mice in each treatment group. Treatment groups were evaluated in terms of average daily increase in tumor volume and average daily body weight increase of nude mice based on slopes of least-square regressions performed on individual animals. The slope factors alpha and beta of the body weight (alpha) and tumor volume changes (beta) within each group during the course of an experiment were calculated. Both a statistically significant decrease (p<0.05) in the body weight of the experimental animals (cisplatin: alpha = -0.5163, vinorelbine: alpha = -0.6598, paclitaxel: alpha = -0.6746, titanocene dichloride 3 x 30 mg/kg: alpha = -0.6259, titanocene dichloride 3 x 40 mg/kg: alpha = -0.7758) and a significant reduction (p<0.05) of the increase in tumor volume (cisplatin: beta = 12.049, vinorelbine: beta = 0.504, paclitaxel: beta = -1.636, titanocene dichloride 3 x 30 mg/kg: beta = 6.212, titanocene dichloride 3 x 40 mg/kg: beta= -0.685) was shown in all treated groups compared to the control group (alpha = -0.1398; beta = 23.056). No significant weight changes were observed between the individually treated groups. A statistically significant reduction of the tumor growth occured under paclitaxel (beta = -1.636), vinorelbine (beta = 0.504) and titanocene dichloride medication 3 x 40 mg/kg (beta = -0.685), as compared to the group treated with cisplatin (beta = 12.049). We found titanocene dichloride to be as effective as paclitaxel and more effective than cisplatin. Vinorelbine seems to be a very effective antineoplastic agent exhibiting a significant higher cytostatic effect than cisplatin. Both titanocene dichloride and vinorelbine provide new therapeutic options in women with ovarian carcinoma not responding to standard chemotherapy.  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