全文获取类型
收费全文 | 9417篇 |
免费 | 785篇 |
国内免费 | 89篇 |
专业分类
电工技术 | 180篇 |
综合类 | 41篇 |
化学工业 | 2615篇 |
金属工艺 | 213篇 |
机械仪表 | 394篇 |
建筑科学 | 354篇 |
矿业工程 | 20篇 |
能源动力 | 615篇 |
轻工业 | 910篇 |
水利工程 | 190篇 |
石油天然气 | 140篇 |
武器工业 | 5篇 |
无线电 | 976篇 |
一般工业技术 | 1613篇 |
冶金工业 | 210篇 |
原子能技术 | 67篇 |
自动化技术 | 1748篇 |
出版年
2024年 | 40篇 |
2023年 | 191篇 |
2022年 | 346篇 |
2021年 | 612篇 |
2020年 | 550篇 |
2019年 | 680篇 |
2018年 | 775篇 |
2017年 | 732篇 |
2016年 | 723篇 |
2015年 | 429篇 |
2014年 | 711篇 |
2013年 | 1037篇 |
2012年 | 651篇 |
2011年 | 731篇 |
2010年 | 471篇 |
2009年 | 404篇 |
2008年 | 244篇 |
2007年 | 181篇 |
2006年 | 148篇 |
2005年 | 101篇 |
2004年 | 101篇 |
2003年 | 58篇 |
2002年 | 57篇 |
2001年 | 28篇 |
2000年 | 23篇 |
1999年 | 25篇 |
1998年 | 22篇 |
1997年 | 18篇 |
1996年 | 23篇 |
1995年 | 19篇 |
1994年 | 10篇 |
1993年 | 15篇 |
1992年 | 10篇 |
1991年 | 17篇 |
1990年 | 16篇 |
1989年 | 12篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 14篇 |
1983年 | 12篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1973年 | 2篇 |
1967年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
This paper describes a simple method based on three-phase hollow-fibre liquid-phase microextraction (HF-LPME) for the determination of phenolic acids in fruit juices. Analytes including gallic acid, p-hydroxy benzoic acid, caffeic acid, syringic acid, p-coumaric acid, ferulic acid, and cinnamic acid were separated and determined using high-performance liquid chromatography–photodiode array detection (HPLC–DAD). Parameters affecting the enrichment factors (EFs) were investigated. These compounds were extracted from 5 mL aqueous samples (pH 2) to a thin layer of organic solvent (hexyl acetate) phase impregnated into the pores of the polypropylene hollow fibre wall, and then back extracted to a basic acceptor solution (0.02 M NaOH). EFs ranged from 15 (gallic acid) to 408 (cinnamic acid). The RSD of the method for the analysis of spiked water and fruit juice samples varied from 3.1% to 11.3%. The LODs ranged from 0.01 (cinnamic acid) to 2.0 (caffeic acid) μg/L. 相似文献
992.
Somayeh Keypour Hasan Rafati Hossain Riahi Fateme Mirzajani Mohammad Fata Moradali 《Food chemistry》2010
Ganoderma lucidum is used as a health food and medicine in Far East and produces different ganoderic acids which are well known for their valuable bioactivities. In this study, two different strains of G. lucidum from Iran and China were investigated for ganoderic acids, using reversed phase HPLC (RP-HPLC) in combination with UV and electrospray ionisation-mass spectrometry (ESI-MS). The results showed a relatively low intensity ganoderic acid C2 peak in the chromatogram of the Iranian sample. However, three high intensity peaks attributed to the well known ganoderic acids including ganoderic acids T, Me and H from the Chinese strain. These findings clearly indicated that different strains of G. lucidum could posses a range of active compounds and hence, bioactivities. Moreover, the variation in the triterpenoid components encourages more studies on the rest of bioactive molecules, and also different strains grown in a variety of climatic and geographical conditions. 相似文献
993.
Mohammad Reza Karafi Ramin Narimani Yousef Hojjat Mojtaba Gheybi 《The International Journal of Advanced Manufacturing Technology》2010,50(9-12):953-960
This paper presents a method for automatic control of arc length in tungsten inert gas (TIG) welding process using the arc voltage. By using this method, the role of operator in arc length control is played by an automatic control system based on a predefined arc voltage value for any special welding operation. A dynamic model for feed-rate mechanism and the relation between variations of arc length and voltage are described in details. Using a proportional-integral controller, variations of arc length in welding path is compensated with an automatic feed-rate mechanism in a normal direction to the welding path. By keeping the voltage constant during the process, a stable weld with higher quality and better appearance is obtained specially in welding of uneven surfaces. Theoretical and practical investigations show that the suggested method is able to control the TIG welding process successfully. Test results show that an accurate weld is obtained without the interference of the operator, and by comparing the predefined values of arc voltage with what is practically obtained, the welding gap is automatically adjusted. 相似文献
994.
Mohammad Saidi-Mehrabad Rassoul Noorossana Mahmood Shafiee 《The International Journal of Advanced Manufacturing Technology》2010,46(1-4):253-265
Often, customers are uncertain about the performance and durability of the used/second-hand products. The warranties play an important role in reassuring the buyer. Offering the warranty implies that the dealer incurs additional costs to service any claims made by the customers. Reducing warranty costs is an issue of great interest to dealers. One way of improving the reliability and reducing the warranty servicing cost for second-hand items is through actions such as overhaul and upgrade which are carried out by the dealer or a third party. Improving actions allow the dealer to offer better warranty terms and to sell the item at a higher price. This paper deals with two effective approaches (virtual age approach and screening test approach) to decide on the reliability improvement strategies for second-hand products sold under various warranty policies (failure-free, rebate warranty, and a combination of free replacement and lump sum). A numerical example illustrates that from a dealer’s point of view, it is beneficial to carry out an improvement action only if the reduction in the warranty servicing cost is greater than the extra cost incurred due to this improvement action. 相似文献
995.
Mohammad Jafar Tarokh Sahar Sohrabi Farid Khoshalhan 《The International Journal of Advanced Manufacturing Technology》2010,48(5-8):823-828
B2B electronic market facilitates the transactions among businesses. It consists of buyers, sellers, and the market owner. But most of these markets could not generate the expected profits for all market participants. In this paper, expected profit for each market participant has been considered in a neutral market with double auction. Based on these profit functions, optimal quantities of bids and offers are determined for buyers and sellers. Then, a model based on game theory is proposed that leads to recognize optimal strategies for game players that include buyers, sellers, and the market owner. Using the optimal strategies will satisfy the game participants and maximize their benefits. Additionally, a numerical example is illustrated to better describe the proposed model. 相似文献
996.
Seyed Taghi Akhavan Niaki Mohammad Javad Ershadi Mahdi Malaki 《The International Journal of Advanced Manufacturing Technology》2010,48(1-4):283-296
Economic design of multivariate exponentially weighted moving average (MEWMA) control charts for monitoring the process mean vector involves determining economically the optimum values of the three control parameters: the sample size, the sampling interval between successive samples, and the control limits or the critical region of the chart. In the economic-statistical design, constraints (including the requirements of type I error probability and power) are added such that the statistical property of the chart is satisfied. In this paper, using the multivariate Taguchi loss approach, the Lorenzen–Vance (Technometrics 28:3-10, 1) cost function of implementing the control chart is extended to include intangible external costs along with the in-control average run length (ARL0) and out-of-control average run length (ARL1) as statistical constraints. A Markov chain model is then developed to estimate the ARLs and a genetic algorithm whose parameters are optimally obtained by design of experiments is used to solve the model and estimate the optimum values of the control chart parameters. A numerical example and a sensitivity analysis are provided to illustrate the solution procedure and to investigate the effects of cost parameters on the optimal designs. The results show that the proposed economic-statistical design of the chart has better statistical properties in comparison to the economic design while the difference between the costs is negligible. 相似文献
997.
Mohammad Jafar Haddad Fereshteh Alihoseini Mostafa Hadi Meysam Hadad Alireza Fadaei Tehrani Aminollah Mohammadi 《The International Journal of Advanced Manufacturing Technology》2010,46(9-12):1119-1132
The cylindrical wire electrical discharge turning (CWEDT) process was developed to generate precise cylindrical forms on hard, difficult to machine materials. A precise, flexible, and corrosion-resistant submerged rotary spindle was designed and added to a conventional five-axis CNC wire electrical discharge machine (EDM) to enable the generation of free-form cylindrical geometries. The hardness and strength of the work material are no longer the dominating factors that affect the tool wear and hinder the machining process. In this study, the effect of machining parameters on surface roughness (R a) and roundness in cylindrical CWEDT of a AISI D3 tool steel is investigated. The selection of this material was made taking into account its wide range of applications in tools, dies, and molds and in industries such as punching, tapping, reaming, and so on in cylindrical forms. Surface roughness and roundness are chosen as two of the machining performances to verify the process. In addition, power, pulse off-time, voltage, and spindle rotational speed are adopted for evaluation by full factorial design of experiments. In this case, a 22?×?32 mixed full factorial design has been selected considering the number of factors used in the present study. The main effects of factors and interactions were considered in this paper, and regression equations were derived using response surface methodology. Finally, the surfaces of the CWEDT parts were examined using scanning electron microscopy (SEM) to identify the macro-ridges and craters on the surface. Cross sections of the EDM parts were examined using the SEM and microhardness tests to quantify the sub-surface recast layers and heat-affected zones under specific process parameters. 相似文献
998.
A review of focused ion beam sputtering 总被引:1,自引:0,他引:1
Mohammad Yeakub Ali Wayne Hung Fu Yongqi 《International Journal of Precision Engineering and Manufacturing》2010,11(1):157-170
This paper reviews the applications of focused ion beam (FIB) sputtering for micro/nano fabrication. Basic principles of FIB
were briefly discussed, and then empirical and fundamental models for sputtering yield, material removal rate, and surface
roughness were presented and compared. The empirical models were more useful for application compared to fundamental models.
Fabrication of various micro and nano structures was discussed. Trimmed atomic force microscope (AFM) tips were tested in
measurement and imaging of high aspect ratio nanopillars where higher accuracy and clarity were observed. Micromilling tool
fabricated using FIB sputtering was used to machine microchannels. Slicing and dwell time control approaches on FIB sputtering
were presented for the fabrication of three dimensional microcavities. The first approach is preferred for practical applications.
The maximum aspect ratio of 13:1 of the microstructures was achieved. The minimum size of the nanopore was in the range of
2–10 μm. Cavities of microgear of 70 μm outside diameter were sputtered with submicrometer accuracy and 2–5 nm average surface
roughness. The microcavities were then filled with polymer in a subsequent micromodling process. The replicated microcomponents
were inspected with scanning electron microscope where faithful duplication of accuracy and surface texture of the cavity
was observed. 相似文献
999.
Mohammad Zareinejad Saeed Shiry Ghidary Seyed Mehdi Rezaei Amir Abdullah 《International Journal of Precision Engineering and Manufacturing》2010,11(1):55-65
Piezoelectric actuators are widely used in micro manipulation applications. However hysteresis nonlinearity limits accuracy
of these actuators. This paper presents a novel approach for utilizing a piezoelectric nano-stage as slave manipulator of
a teleoperation system. The Prandtl-Ishlinskii (PI) model is used to model actuator hysteresis in feedforward scheme to cancel
out this nonlinearity. To deal with the influence of parametric uncertainties, unmodeled dynamics, and PI identification error
a perturbation term is added to the slave model and apply a sliding mode based impedance control with perturbation estimation.
The stability of the entire system is guaranteed by Llewellyn’s absolute stability criterion. Performance of the proposed
controllers is verified through experiments. 相似文献
1000.
Surfactant injection is a promising method for enhanced oil recovery (EOR) due to its effective micro-displacement mechanisms. However, understanding the interaction of a surfactant solution with heavy oil in porous media is neither straightforward nor well understood, particularly in heterogeneous systems. By enabling in-situ real-time monitoring of flow transport, microfluidic studies have provided novel insights into the underlying multiphase physics of flow at the pore scale. This paper examines the two-phase displacement efficiency of a new surfactant in layered–fractured porous microfluidic patterns, a topic seldom discussed in the literature. To evaluate the performance of the proposed surfactant, we considered several heterogeneous media with varying layer and fracture geometrical characteristics, quantifying displacement efficiency for each case. Based on the analysis of pore-scale snapshots, it was inferred that the primary mechanisms responsible for EOR during surfactant flooding into heavy oil include pore wall transportation, emulsifications, the deformation of residual oil, inter-pore or intra-pore bridging, and wettability alteration. Macroscopic displacement experiments revealed that the width of the swept area from surfactant injection significantly exceeded that of water injection, resulting in a substantially higher oil recovery. Furthermore, it was demonstrated that the direction of fluid flow in relation to fracture orientation plays a critical role in the dynamics of surfactant solution movement and, consequently, the ultimate oil production. 相似文献