全文获取类型
收费全文 | 16668篇 |
免费 | 1261篇 |
国内免费 | 405篇 |
专业分类
电工技术 | 726篇 |
综合类 | 482篇 |
化学工业 | 3089篇 |
金属工艺 | 584篇 |
机械仪表 | 622篇 |
建筑科学 | 845篇 |
矿业工程 | 155篇 |
能源动力 | 526篇 |
轻工业 | 1554篇 |
水利工程 | 227篇 |
石油天然气 | 274篇 |
武器工业 | 76篇 |
无线电 | 2220篇 |
一般工业技术 | 2367篇 |
冶金工业 | 1872篇 |
原子能技术 | 182篇 |
自动化技术 | 2533篇 |
出版年
2024年 | 65篇 |
2023年 | 240篇 |
2022年 | 482篇 |
2021年 | 700篇 |
2020年 | 522篇 |
2019年 | 466篇 |
2018年 | 538篇 |
2017年 | 506篇 |
2016年 | 544篇 |
2015年 | 580篇 |
2014年 | 754篇 |
2013年 | 1005篇 |
2012年 | 989篇 |
2011年 | 1140篇 |
2010年 | 851篇 |
2009年 | 764篇 |
2008年 | 813篇 |
2007年 | 713篇 |
2006年 | 610篇 |
2005年 | 489篇 |
2004年 | 422篇 |
2003年 | 370篇 |
2002年 | 409篇 |
2001年 | 278篇 |
2000年 | 262篇 |
1999年 | 268篇 |
1998年 | 584篇 |
1997年 | 416篇 |
1996年 | 328篇 |
1995年 | 210篇 |
1994年 | 209篇 |
1993年 | 179篇 |
1992年 | 121篇 |
1991年 | 121篇 |
1990年 | 117篇 |
1989年 | 120篇 |
1988年 | 71篇 |
1987年 | 66篇 |
1986年 | 64篇 |
1985年 | 86篇 |
1984年 | 78篇 |
1983年 | 75篇 |
1982年 | 83篇 |
1981年 | 62篇 |
1980年 | 46篇 |
1979年 | 53篇 |
1978年 | 33篇 |
1977年 | 63篇 |
1976年 | 81篇 |
1973年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
11.
The ring shape is a good solution to the study of the magnetization processes of magnetic materials because demagnetizing fields are easily avoided. However, when small samples are investigated, the magnitude of the field applied is necessarily limited by the low number of primary winding turns, and by the cross section of the wire itself. The use of sequential-type techniques for high current supply allows this problem to be avoided. One-cycle power production from the 50 Hz AC-line voltage is a simple example of such techniques. An electronic device designed around a commercial integrated circuit is described. A full period of current of 20-ms duration is applied to the load with a magnitude ranging from 0 to 100 A. Magnetization parameters of soft polycrystalline ring ceramics approaching the saturation region are studied as an application. The fitness to measure such characteristic parameters as saturation magnetization and magnetic hardness is shown 相似文献
12.
In "Stationary distributions for the random waypoint mobility model" (TMC, Vol. 3, No, 1), Navidi and Camp find the stationary distribution of the random waypoint model, with or without pause on a rectangular area. In this short note, we show that, under the stationary regime, speed and location are independent. 相似文献
13.
O Bernard B Chachuat A Hélias B Le Dantec B Sialve J-P Steyer L Lardon P Neveu S Lambert J Gallop M Dixon P Ratini A Quintabà S Frattesi J M Lema E Roca G Ruiz J Rodriguez A Franco P Vanrolleghem U Zaher D J W De Pauw K De Neve K Lievens D Dochaine O Schoefs H Fibrianto R Farina V Alcaraz Gonzalez V Gonzalez Alvarez P Lemaire J A Martinez F Esandi O Duclaud J F Lavigne 《Water science and technology》2005,52(1-2):457-464
The TELEMAC project brings new methodologies from the Information and Science Technologies field to the world of water treatment. TELEMAC offers an advanced remote management system which adapts to most of the anaerobic wastewater treatment plants that do not benefit from a local expert in wastewater treatment. The TELEMAC system takes advantage of new sensors to better monitor the process dynamics and to run automatic controllers that stabilise the treatment plant, meet the depollution requirements and provide a biogas quality suitable for cogeneration. If the automatic system detects a failure which cannot be solved automatically or locally by a technician, then an expert from the TELEMAC Control Centre is contacted via the internet and manages the problem. 相似文献
14.
Christian Ligoure Michel Cloitre Christille Le Chatelier Fabrice Monti 《Polymer》2005,46(17):6402-6410
A remarkable correlation exists between the degree of expansion of polyurethane foams and the structure of the reacting premixes. Polyurethane foams obtained from reacting premixes containing microemulsions are highly expanded. The expansion rate is proportional to the volume fraction of microemulsion in the premix. The stability of premixes with and without microemulsion is completely different suggesting distinct creaming mechanisms. We apply this idea to synthesize polyurethane foams from microemulsions successfully. This approach can be used to rationalize the design of polyurethane formulations leading to highly expanded foams. 相似文献
15.
Patrick DAstous Franoise Dtienne Willemien Visser Pierre N. Robillard 《Design Studies》2004,25(6):625-655
By contrast to design meetings, design evaluation meetings (DEMs) have generally been considered as situations in which, according to DEM methodologies, design activities are quite marginal. In a study of DEMs in software development, i.e. in technical review meetings following a particular review methodology, we showed: (i) the occurrence of design activities as part of an argumentation process; (ii) the relative importance of cognitive synchronisation as a prerequisite for evaluation; (iii) the important role played in evaluation by argumentation that makes explicit the underlying design rationale (DR). On the basis of our results, we discuss the potential for using DR methodologies in this kind of meetings. 相似文献
16.
Catherine J. Harrison Yann A. Le Gouellec Robert C. Cheng Amy E. Childress 《Canadian Metallurgical Quarterly》2007,133(11):1004-1014
A dual-staged nanofiltration process is being evaluated as an alternative to reverse osmosis for seawater desalination. The primary goal of this system is to reduce energy consumption while producing potable water at an acceptable recovery rate. Investigation of this system at the bench-scale level focused on membrane surface characterization, ion rejection (including boron, bromide, and iodide rejection), and flux decline. Results from this study showed that two commercially available nanofiltration membranes can effectively desalinate seawater. Although fouling was apparent—and resulted in approximately 20% flux decline over 3 days—a critical flux was not identifiable. Operation of the system at different cross-flow velocities revealed the significance of hydrodynamic conditions on the polarization modulus, and hence on membrane performance. 相似文献
17.
18.
Laparoscopic pelvic lymph node dissection has been applied as a minimally invasive staging technique for men with prostate cancer. This procedure has been shown to shorten markedly postoperative hospitalization, decrease analgesic requirements and shorten convalescence period compared to open pelvic node dissection. However, the laparoscopic procedure takes longer to perform and many disposable instruments are used, thus increasing the cost. We determine the overall cost of laparoscopic versus open pelvic lymph node dissection. Between January 1989 and April 1992, 61 men underwent only staging pelvic lymph node dissection for cancer of the prostate at a single university teaching hospital. Of these patients 11 and 50 underwent open and laparoscopic pelvic lymph node dissection, respectively. Information from the hospital business office was reorganized into preoperative, intraoperative and postoperative expenses. All individual charges were transformed up or down to the dollar amounts of the 1990 to 1991 fiscal year so as to correct for inflationary changes. Preoperative costs were not significantly different between the 2 operative approaches. Intraoperative expenses were 52% greater if laparoscopic pelvic lymph node dissection was performed and can be explained by the longer operative times and use of disposable instrumentation. However, the postoperative period lasted an average of 1.61 days following laparoscopic pelvic lymph node dissection. Postoperative nursing and analgesic requirements were significantly more for patients undergoing open pelvic lymph node dissection. The overall postoperative costs following open pelvic lymph node dissection were 280% more expensive than for the laparoscopic procedure. The overall total costs were approximately $1,250 more for laparoscopic pelvic lymph node dissection. Wages lost or earned during this period and rapid return to normal activity following laparoscopic pelvic lymph node dissection would, in our opinion, justify this additional cost. 相似文献
19.
Theory is presented to provide insight into the observation that attenuation through vegetation is proportional to vegetation water content. In this analysis, the canopy is modeled as a sparse layer of randomly oriented particles (leaves, stalks, etc.) over a flat, homogeneous ground plane (soil) and an expression is obtained for the “optical depth”. The formulas developed by Ulaby and El Rayes are used to relate this expression to the water content of the canopy. In the low frequency extreme (Rayleigh scatterers), the attenuation varies almost linearly with water content and inversely with wavelength. In contrast, in the high frequency limit, the attenuation is independent of both water content and frequency, in between, geometry dependent “resonances” occur even at the low frequency end of the microwave spectrum (e.g. L-band) making the dependence of attenuation on frequency and water content specific to canopy architecture 相似文献
20.