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   4237篇
  免费   152篇
  国内免费   16篇
电工技术   80篇
综合类   18篇
化学工业   1032篇
金属工艺   107篇
机械仪表   140篇
建筑科学   119篇
矿业工程   15篇
能源动力   254篇
轻工业   595篇
水利工程   39篇
石油天然气   29篇
无线电   267篇
一般工业技术   752篇
冶金工业   281篇
原子能技术   58篇
自动化技术   619篇
  2023年   52篇
  2022年   98篇
  2021年   141篇
  2020年   118篇
  2019年   120篇
  2018年   152篇
  2017年   160篇
  2016年   168篇
  2015年   112篇
  2014年   139篇
  2013年   318篇
  2012年   231篇
  2011年   241篇
  2010年   184篇
  2009年   229篇
  2008年   232篇
  2007年   184篇
  2006年   133篇
  2005年   109篇
  2004年   95篇
  2003年   87篇
  2002年   80篇
  2001年   54篇
  2000年   52篇
  1999年   43篇
  1998年   63篇
  1997年   51篇
  1996年   35篇
  1995年   29篇
  1994年   32篇
  1993年   42篇
  1992年   39篇
  1991年   29篇
  1990年   25篇
  1989年   24篇
  1988年   17篇
  1987年   25篇
  1986年   23篇
  1985年   28篇
  1984年   26篇
  1983年   28篇
  1982年   16篇
  1981年   24篇
  1980年   19篇
  1979年   31篇
  1978年   22篇
  1977年   17篇
  1976年   14篇
  1975年   17篇
  1974年   25篇
排序方式: 共有4405条查询结果,搜索用时 15 毫秒
91.
Turkey has a great number of hazelnut trees that possess nutritious components. However, only the inside part of the hazelnut is used as a nutrient, while the rest of it is waste. This study suggests that the waste parts of the Turkish hazelnut could be used as a natural dye for dyeing textile fabrics. The dyeing properties of the leaves, coat, shell and dice of the hazelnut were studied on wool, cotton and viscose fabric by using three different mordants: copper sulphate, iron sulphate and aluminium sulphate. The selected dyed fibre sample surfaces were observed using a scanning electron microscope. The colour strength (K/S), light, washing, rubbing, and perspiration fastness levels of the dyed fabrics were investigated. The experimental natural dyeing results indicate that waste hazelnut‐based products can be used as a natural dye for textile coloration.  相似文献   
92.
In this article, the characterization of the interfacial structure of diffusion bonding a TiAl alloy is presented. The joining surfaces were modified by Ni/Al reactive multilayer deposition as an alternative approach to conventional diffusion bonding. TiAl substrates were coated with alternated Ni and Al nanolayers. The nanolayers were deposited by dc magnetron sputtering with 14 nm of period (bilayer thickness). Joining experiments were performed at 900 °C for 30 and 60 min with a pressure of 5 MPa. Cross sections of the joints were prepared for characterization of their interfaces by scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), high resolution TEM (HRTEM), energy dispersive x-ray spectroscopy (EDS), and electron backscatter diffraction (EBSD). Several intermetallic compounds form at the interface, assuring the bonding of the TiAl. The interface can be divided into three distinct zones: zone 1 exhibits elongated nanograins, very small equiaxed grains are observed in zone 2, while zone 3 has larger equiaxed grains. EBSD analysis reveals that zone 1 corresponds to the intermetallic Al2NiTi and AlNiTi, and zones 2 and 3 to NiAl.  相似文献   
93.
Learners need to have good reasons to engage and accept e-learning. They need to understand that unless they do, the outcomes will be less favourable. The technology acceptance model (TAM) is the most widely recognized model addressing why users accept or reject technology. This study describes the development and evaluation of a virtual environment, the online 3D world Second Life (SL), for learning rapid sequence intubation (RSI). RSI is an increasingly frequently used method of acute airway management in healthcare settings. The intention of learners to use the system was explored based on the TAM, with the computer self-efficacy construct as an external variable. Two hundred and six nursing students participated in this study. The findings suggest that the system was perceived as useful, and that the students felt confident working with computers and intended to review RSI in SL as often as needed. However, they remained neutral regarding the ease of use of the system. Strategies were suggested for boosting the students’ self-confidence in using the system. Overall use of the TAM in this context was successful, indicating the robustness of the model. The limitations of the study were discussed and further areas of research on the TAM were proposed.  相似文献   
94.
The objective of this study is to characterise the gross chemical and microbiological status and identify the volatile compounds of mouldy Civil cheeses. A total of forty‐one samples were surveyed, and gross compositional status of the cheeses was (as mean values): 6.5 for pH, 6.2% for fat‐in‐dry matter, 51.8% for moisture and 15.3% for water‐soluble nitrogen (as% of total nitrogen). Chemical composition of the cheese samples varied widely. Mouldy Civil cheese has similar pH values and moisture contents when compared with blue‐type cheeses, but it has distinct feature for fat contents. The microbiological counts of the samples were found to be high and some samples contained coliform bacteria. A total of 95 volatiles, including esters (28), acids (6), ketones (12), aldehydes (3), alcohols (15), terpenes (10), sulphur compounds (3) and miscellaneous (18), were identified in the volatile fractions of the cheeses, and principal volatile groups were esters, alcohols and ketones.  相似文献   
95.
Future systems will be too complex to design and implement explicitly. Instead, we will have to learn to engineer complex behaviours indirectly: through the discovery and application of local rules of behaviour, applied to simple process components, from which desired behaviours predictably emerge through dynamic interactions between massive numbers of instances. This paper describes a process-oriented architecture for fine-grained concurrent systems that enables experiments with such indirect engineering. Examples are presented showing the differing complex behaviours that can arise from minor (non-linear) adjustments to low-level parameters, the difficulties in suppressing the emergence of unwanted (bad) behaviour, the unexpected relationships between apparently unrelated physical phenomena (shown up by their separate emergence from the same primordial process swamp) and the ability to explore and engineer completely new physics (such as force fields) by their emergence from low-level process interactions whose mechanisms can only be imagined, but not built, at the current time.  相似文献   
96.
97.
ABSTRACT

Wind turbine control is an important task to make the electricity generation secure in terms of energy demand and machine safety. It also yields to control the desired power level and optimized energy because of the assignment of turbine speed. The contactless piezoelectric wind energy harvester (CPWEH) used in this study has three piezoelectric layers located around the shaft with 120 degrees apart and they are buckled by the magnetic force without any physical contact. The superiority of this device is to generate energy for low wind speeds such as 1.5 m/s. However, for high speeds, high total harmonic distortions (THDs) govern the waveforms, thus controlling the turbine speed becomes necessary for optimizing the output power. Encouraged by this, a small low inertia dc generator is coupled with the wind turbine, and the generator terminals are connected to a resistor through a power switch to generate a braking torque that opposes to wind speed direction. By controlling the switch properly, turbine speed is ensured to remain within a certain band, which accordingly prevents the turbine from rotating very fast at damaging wind speeds. Several experiments are performed on the developed CPWEH with/without the presented control scheme which prove the existence of promising performance of our proposal.  相似文献   
98.
A new and simple solid‐phase extraction method for the determination of trace levels of sunset yellow has been developed on Diaion HP 2MG column system. The adsorbed sunset yellow on the resin was eluted with 3 mL of methanol and determined by UV–Vis spectrophotometry at 484 nm. Various experimental parameters such as pH, amount of sunset yellow, flow rates of sample and eluent solutions, resin amount, sample volumes, etc. were investigated. The influences of some alkali, alkali earth and transition metals on the recoveries of sunset yellow were investigated. The recovery values for sunset yellow were higher than 95%. Preconcentration factor was found as 150. The detection limit (three sigma) of the reagent blank for sunset yellow was 5.2 μg L?1. The relative standard deviations (RSD) of the procedure were found as 3.9%. The validation of the presented procedure was performed by the method of standard addition. The procedure was successfully applied to the determination of trace levels of sunset yellow in powdered beverage and confectionery products.  相似文献   
99.
We have worked on the structural and magnetic properties of Zn0.99?xMn0.01Gd x O δ (for x = 0.02, 0.03, and 0.04) compounds prepared by using a sol–gel method. The x-ray diffraction, scanning electron microscopy, and energy dispersive x-ray spectroscopy were used to understand the structural properties of the samples. We observed that co-substitution of Mn (1 %) and Gd (2–4 %) into the ZnO does not change the hexagonal structure. Scanning electron microscope (SEM) images show us that the grain size decreases with the increasing amount of the Gd into the ZnO matrix. The magnetic properties of the samples have been investigated by using magnetic hysteresis and DC susceptibility measurements. The ZMG1 sample shows a weak ferromagnetic behavior at room temperature, whereas the ZMG2 and ZMG3 samples exhibit a paramagnetic nature. Furthermore, it is also found that the magnetizations of the samples decrease with increasing Gd content in the ZnMnO system due to the enhancing interaction between Gd 3+ ions. We summarize that the co-substitution of Mn and Gd into the ZnO generates a room-temperature ferromagnetism, but it still needs more work to obtain strong and high coercivity magnetic loops for applications.  相似文献   
100.
The aim of this study was to determine the levels of copper (Cu), manganese (Mn), zinc (Zn), iron (Fe), cadmium (Cd), lead (Pb), chromium (Cr), nickel (Ni) and selenium (Se) in sunflower honeys obtained from Thrace Region of Turkey. Trace and toxic element determination was performed by atomic absorption spectrometry after microwave digestion. The accuracy of the method was checked by the standard reference material, NIST‐SRM 1515 Apple leaves. The maximum contents of trace and toxic elements in honey samples from Kesan (polluted area) were found as 0.46, 0.82, 1.98, 14.0, 9.86 μg kg?1, 0.48 mg kg?1, 137, 115 and 290 μg kg?1 for Cu, Mn, Zn, Fe, Cd, Pb, Cr, Ni and Se, respectively.  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