全文获取类型
收费全文 | 14707篇 |
免费 | 379篇 |
国内免费 | 22篇 |
专业分类
电工技术 | 198篇 |
综合类 | 12篇 |
化学工业 | 3280篇 |
金属工艺 | 237篇 |
机械仪表 | 303篇 |
建筑科学 | 688篇 |
矿业工程 | 101篇 |
能源动力 | 392篇 |
轻工业 | 1040篇 |
水利工程 | 132篇 |
石油天然气 | 165篇 |
武器工业 | 1篇 |
无线电 | 901篇 |
一般工业技术 | 2123篇 |
冶金工业 | 3607篇 |
原子能技术 | 142篇 |
自动化技术 | 1786篇 |
出版年
2022年 | 120篇 |
2021年 | 178篇 |
2020年 | 149篇 |
2019年 | 167篇 |
2018年 | 200篇 |
2017年 | 204篇 |
2016年 | 229篇 |
2015年 | 181篇 |
2014年 | 256篇 |
2013年 | 864篇 |
2012年 | 480篇 |
2011年 | 656篇 |
2010年 | 426篇 |
2009年 | 473篇 |
2008年 | 595篇 |
2007年 | 582篇 |
2006年 | 582篇 |
2005年 | 479篇 |
2004年 | 388篇 |
2003年 | 377篇 |
2002年 | 391篇 |
2001年 | 245篇 |
2000年 | 249篇 |
1999年 | 261篇 |
1998年 | 263篇 |
1997年 | 265篇 |
1996年 | 267篇 |
1995年 | 260篇 |
1994年 | 275篇 |
1993年 | 315篇 |
1992年 | 254篇 |
1991年 | 196篇 |
1990年 | 216篇 |
1989年 | 240篇 |
1988年 | 184篇 |
1987年 | 229篇 |
1986年 | 212篇 |
1985年 | 267篇 |
1984年 | 241篇 |
1983年 | 219篇 |
1982年 | 186篇 |
1981年 | 201篇 |
1980年 | 179篇 |
1979年 | 186篇 |
1978年 | 183篇 |
1977年 | 146篇 |
1976年 | 155篇 |
1975年 | 176篇 |
1974年 | 140篇 |
1973年 | 145篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
Ashraf Qadir William Semke Jeremiah Neubert 《Journal of Intelligent and Robotic Systems》2014,74(3-4):1029-1047
This paper presents the development of a vision-based neuro-fuzzy controller for a two axes gimbal system mounted on a small Unmanned Aerial Vehicle (UAV). The controller uses vision-based object detection as input and generates pan and tilt motion and velocity commands for the gimbal in order to keep the interest object at the center of the image frame. A readial basis function based neuro-fuzzy system and a learning algorithm is developed for the controller to address the dynamic and non-linear characteristics of the gimbal movement. The controller uses two separate, but identical radial basis function networks, one for pan and one for tilt motion of the gimbal. Each system is initialized with a fixed number of neurons that act as rules basis for the fuzzy inference system. The membership functions and rule strengths are then adjusted with the feedback from the visual tracking system. The controller is trained off-line until a desired error level is achieved. Training is then continued on-line to allow the system to accommodate air speed changes. The algorithm learns from the error computed from the detected position of the object in image frame and generates position and velocity commands for the gimbal movement. Several tests including lab tests and actual flight tests of the UAV have been carried out to demonstrate the effectiveness of the controller. Test results show that the controller is able to converge effectively and generate accurate position and velocity commands to keep the object at the center of the image frame. 相似文献
142.
William M. Tracy 《Computational Economics》2014,43(1):83-103
The classical game theoretic resolutions to Selten’s Chain Store game are unsatisfactory; they either alter the game to avoid the paradox or struggle to organize the existing experimental data. This paper applies co-evolutionary algorithms to the Chain Store game and demonstrates that the resulting system’s dynamics are neither intuitively paradoxical nor contradicted by the existing experimental data. Specifically, some parameterizations of evolutionary algorithms promote genetic drift. Such drift can lead the system to transition among the game’s various Nash Equilibria. This has implications for policy makers as well as for computational modelers. 相似文献
143.
Ruan Ke-He; Milfeld Kent; Kulmacz Richard J.; Wu Kenneth K. 《Protein engineering, design & selection : PEDS》1994,7(11):1345-1351
A 3-D model of human thromboxane A2 synthase (TXAS) was constructedusing a homology modeling approach based on information fromthe 2.0 crystal structure of the hemoprotein domains of cytochromeP450BM-3 and P450cam. P450BM-3 is a bacterial fatty acid monooxygenaseresembling eukaryotic microsomal cytochrome P450s in primarystructure and function. TXAS shares 26.4% residue identity and48.4% residue similarity with the P450BM-3 hemoprotein domain.The homology score between TXAS and P450BM-3 is much higherthan that between TXAS and P450cam. Alignment between TXAS andthe P450BM-3 hemoprotein domain or P450cam was determined throughsequence searches. The P450BM-3 or P450cam main-chain coordinateswere spplied to the TXAS main chain in those sements where thetwo sequences were well aligned. These segments were linkedto one another using a fragment search method, and the sidechains were added to produce a 3-D model for TXAS. A TXAS substrate,prostaglandin H2 (PGH2) was docked into the TXAS cavity correspondingto the arachidonic acid binding pocket in P450BM-3 or camphorbinding site in P450cam. Regions of the heme and putative PGH2binding cavities in the TXAS model were identified and analyzed.The segments and residues involved in the active-site pocketof the TXAS model provide reasonable candidates for TXAS proteinengineering and inhibitor design. Comparison of the TXAS modelbased on P450BM-3 with another TXAS model based on the P450BM-3with another TXAS model based on the P450cam structure indicatedthat P450BM-3 is a more suitable template for homology modelingof TXAS. 相似文献
144.
William R. Chase Muraleedharan G. Nair Alan R. Putnam Saroj K. Mishra 《Journal of chemical ecology》1991,17(8):1575-1584
Acinetobacter calcoaceticus, a gram-negative bacterium isolated from field soil, was found to be responsible for the biotransformation of 2(3H)-benzoxazolinone (BOA) to 2,2-oxo-1,1-azobenzene (AZOB). Experiments were conducted to evaluate the transformation of BOA to AZOB by this microbe in sterile and nonsterile soil. Transformation studies with soils inoculated withA. calcoaceticus indicated that the production of AZOB increased linearly with the concentration of BOA in sterile soil and showed a quadratic trend in nonsterile soils. This also indicated that all soil types studied for the transformation experiments might containA. calcoaceticus capable of the conversion of benzoxazolinones. 相似文献
145.
Reactive Laser Ablation Synthesis of Nanosize Alumina Powder 总被引:1,自引:0,他引:1
Gregory P. Johnston Ross Muenchausen Douglas M. Smith William Fahrenholtz Steve Foltyn 《Journal of the American Ceramic Society》1992,75(12):3293-3298
An aluminum (Al) target was laser ablated in an oxygen (O2 ) atmosphere, producing nanosize alumina (Al2 O3 ) powder. The powder surface area decreased (and the particle size increased) with both increasing oxygen pressure and laser fluence. All powders produced had surface areas between 135 and 250 m2 /g, corresponding to primary particle sizes ranging from 7 to 3 nm in radius. Phase evolution with temperature was studied via X-ray diffraction. These powders showed a direct transformation from γ- to α-alumina at approximately 1200°C, bypassing other transition alumina phases, while still maintaining small particle size ( 30 nm). Despite the nanosize particles, green densities equal to 54% of the skeletal density (i.e., true density of the solid phase) were obtained by uniaxial pressing at 40 MPa. 相似文献
146.
Sam V. Shelton William J. Wepfer Daniel J. Miles 《Chemical Engineering Communications》1988,71(1):39-52
This work deals with the thermal analysis of externally heated porous beds of finite length. A one dimensional model was developed that includes conduction and storage in both the fluid and bed, convective exchange between the fluid and bed, and the effect of adsorption/desorption in the bed. This model results in two coupled differential equations for the fluid and bed temperatures as functions of four independent dimensionless parameters. These equations were solved numerically using finite difference approximations. A truncation error analysis was carried out to maintain an accurate solution. The method of normalization is such that the results of this analysis are of use in bed design when the breakthrough characteristics in finite length beds are of interest. A method to measure bed thermal performance is defined and a means to optimize bed thermal performance is presented. An experiment was conducted to validate the numerically obtained results. A comparison of numerical to experimental results is presented 相似文献
147.
Victor T. Wyatt Alberto Nuñez Thomas A. Foglia William N. Marmer 《Journal of the American Oil Chemists' Society》2006,83(12):1033-1039
Novel oligomeric prepolymers were synthesized by acid-catalyzed condensation of glycerol with iminodiacetic, azelaic, or succinic
acid. The prepolymers were obtained, on average, in 62% yield and were characterized by 13C NMR, 1H NMR, matrix-assisted laser desorption ionization-time of flight-mass spectrometry, and gel permeation chromatography. The
synthesized oligomers had an average M.W. of 1543 Daltons (average polydispersity (PD)=1.34, average degree of polymerization
(DOP)=5.5). Hyperbranching was evident in the oligomers produced when using azelaic acid and succinic acid as co-monomers
with glycerol, whereas the reaction between iminodiacetic acid and glycerol resulted in linear products bearing cyclic urethane
structures. 相似文献
148.
In studies of feeding by the bark beetle, Ips paraconfusus, two pine stilbenes (pinosylvin and pinosylvin methyl ether), ferulic acid glucoside, and enantiomers of the four most common sugars present in ponderosa pine phloem (sucrose, glucose, fructose, and raffinose) did not stimulate or reduce male feeding when assayed on wet -cellulose with or without stimulatory phloem extractives present. When allowed to feed on wet -cellulose containing sequential extracts (hexane, methanol, and water) of ponderosa pine phloem, methanol and water extractives stimulated feeding, but hexane extractives did not. Males confined in wet -cellulose containing aqueous or organic extracts of culture broths derived from phloem tissue and containing the root pathogen, Heterobasidion annosum, ingested less substrate than beetles confined to control preparations. In an assay using logs from uninoculated ponderosa pines, the mean lengths of phloem in the digestive tracts increased as time spent feeding increased. Males confined to the phloem of basal logs cut from ponderosa pines artificially inoculated with H. annosum ingested significantly less phloem than beetles in logs cut from trees that were (combined) mock-inoculated or uninoculated and did not contain the pathogen. However, individual pathogen-containing treatments were not significantly different from uninoculated controls. It was concluded that altered feeding rates are not a major factor which may explain why diseased ponderosa pines are colonized by I. paraconfusus. 相似文献
149.
J. William Maisel 《乙烯基与添加剂工艺杂志》1986,8(3):112-115
Plate-out is the undesired deposition of materials from a compound onto the surface of processing equipment. Plate-out causes problems with quality control and down-time. Changes in processing conditions can help alleviate plate-out, but adjustments in the formulation are usually needed for significant improvements in plate-out, the deposition. The addition of precipitated silica to a PVC formulation is a simple and effective method to reduce plate-out. This study explores the relationship between plate-out reduction and the physical properties of precipitated silica. Silica properties such as surface area, average particle size, and oil absorption can all be controlled by a patented process developed by the Chemicals Division of J. M. Huber Corporation. Plate-out reduction is related to the properties of precipitated silica, the loading of the silica, the order of addition, and type of PVC formulation. The effect of precipitated silica on the physical properties of the PVC compound, such as, tensile strength, tear strength, elongation and stiffness, are explored. Finally, the effectiveness of plate-out reduction by precipitated silica as compared to fumed silica will be discussed. 相似文献
150.
Stephen Q. Zhou Liming Wang Xiugao Liao Georges Manuel William P. Weber 《Journal of Inorganic and Organometallic Polymers and Materials》1991,1(2):199-210
High molecular weight poly(1,1-dimethyl-1-germa-cis-pent-3-ene), poly(1,1-diphenyl-1-germa-cis-pent-3-ene), poly(1,1-dimethyl-1-sila-cis-pent-3-ene), and poly(1-methyl-1-phenyl-1-sila-cis-pent-3-ene) have been prepared. The thermal stability of these polymers is found to increase with their molecular weight. 相似文献