全文获取类型
收费全文 | 9296篇 |
免费 | 612篇 |
国内免费 | 12篇 |
专业分类
电工技术 | 156篇 |
综合类 | 3篇 |
化学工业 | 2449篇 |
金属工艺 | 221篇 |
机械仪表 | 336篇 |
建筑科学 | 297篇 |
矿业工程 | 22篇 |
能源动力 | 378篇 |
轻工业 | 1738篇 |
水利工程 | 81篇 |
石油天然气 | 53篇 |
无线电 | 566篇 |
一般工业技术 | 1440篇 |
冶金工业 | 773篇 |
原子能技术 | 60篇 |
自动化技术 | 1347篇 |
出版年
2024年 | 32篇 |
2023年 | 107篇 |
2022年 | 278篇 |
2021年 | 482篇 |
2020年 | 324篇 |
2019年 | 399篇 |
2018年 | 400篇 |
2017年 | 433篇 |
2016年 | 400篇 |
2015年 | 297篇 |
2014年 | 417篇 |
2013年 | 753篇 |
2012年 | 579篇 |
2011年 | 648篇 |
2010年 | 486篇 |
2009年 | 507篇 |
2008年 | 422篇 |
2007年 | 384篇 |
2006年 | 329篇 |
2005年 | 217篇 |
2004年 | 207篇 |
2003年 | 194篇 |
2002年 | 168篇 |
2001年 | 110篇 |
2000年 | 119篇 |
1999年 | 110篇 |
1998年 | 217篇 |
1997年 | 172篇 |
1996年 | 143篇 |
1995年 | 85篇 |
1994年 | 74篇 |
1993年 | 70篇 |
1992年 | 35篇 |
1991年 | 22篇 |
1990年 | 36篇 |
1989年 | 23篇 |
1988年 | 32篇 |
1987年 | 16篇 |
1986年 | 23篇 |
1985年 | 20篇 |
1984年 | 16篇 |
1983年 | 17篇 |
1982年 | 11篇 |
1981年 | 12篇 |
1980年 | 10篇 |
1978年 | 11篇 |
1977年 | 10篇 |
1976年 | 22篇 |
1975年 | 10篇 |
1974年 | 8篇 |
排序方式: 共有9920条查询结果,搜索用时 15 毫秒
981.
VB de Carvalho EF Sousa JH Vila JP da Silva MR Caiado SR Araujo R Macruz EJ Zerbini 《Canadian Metallurgical Quarterly》1996,94(8):1815-1817
BACKGROUND: Heart transplantation (HT) as a therapeutic option for end-stage chronic Chagas' heart disease (CCHD) is controversial. Reactivation of Trypanosoma cruzi infection and recurrence of the disease in the allograft are likely to occur. Furthermore, active myocarditis has been reported to predispose patients to an increased incidence and severity of rejection. METHODS AND RESULTS: We prospectively investigated the long-term follow-up of 10 patients with CCHD who underwent HT. Immunosuppression was based on cyclosporine A and azathioprine. T cruzi reactivation was prevented with benzonidazole. Besides allograft rejection surveillance, T cruzi infection was monitored through blood tests, myocardial biopsies, and serological tests. Over a mean follow-up period of 34 +/- 38 months (range, 73 to 124 months), 7 patients are alive and in NYHA functional class I. Life expectancy was 78% for the second year and 65% for 10 years. Rejection was less frequent in chagasic than in age- and sex-matched control patients (mean +/- SD, 1.60 +/- 1.26 versus 5.70 +/- 1.89 episodes per patient, respectively; P = .0001); decreased severity of rejection was also observed (P = .006). T cruzi parasitemias detected on three occasions were successfully treated with benzonidazole. There were no signs of recurrence of the disease in the allograft. CONCLUSIONS: These results suggest an important role of HT in the treatment of CCHD. There was a low frequency of T cruzi infection reactivation and no signs of recurrence of the disease in the allograft. The surprisingly decreased rejection incidence and severity require further studies for elucidation. 相似文献
982.
Two cases of eumycotic mycetomas in the head and neck region are reported. The first case is the localized mycetoma which involved only the soft tissue of the neck. It was completely excised and the patient needed no further treatment. In the second case, the lesion extensively involved the structures in the parapharyngeal space, submandibular space and carotid sheath. The upper limit is the skull base. The patient was treated by combination of wide excision with radial forearm flap and antifungal agents, however, the prognosis is fair. 相似文献
983.
The identification of contaminated observations or outliers is an important part of data analysis since such observations can have a profound influence and distort the analysis. One simple graphical method, based on the box-plot, consists of constructing fences. The fences method is not only appealing in its simplicity but more importantly because it does not use the extreme potential outliers which can inflate the computing of a measure of dispersion and hence lessen the sensitivity for identifying outliers. The commonly used fences procedure may be too liberal in some situations and too conservative in others. That is, it sets one criteria for all scenarios and does not afford the data analyst the flexibility of specifying the probability or criterion for designating an observation as an outlier in a variety of circumstances. Furthermore, the most commonly used procedure is a “one size fits all” style and does not incorporate sample size. Unfortunately, a value that is extreme in a small data set might be expected in a much larger sample. In this paper, a method is proposed to include sample size in constructing fences as well as a sequential procedure to identify multiple outliers at a specified probability. 相似文献
984.
Da Silva M.J. Schleicher E. Hampel U. 《IEEE transactions on instrumentation and measurement》2007,56(4):1249-1256
For the investigation of multiphase or multicomponent flows, which are of interest, for instance, in oil extraction and processing or in chemical engineering, there are only few suitable measuring techniques. For this reason, we have developed a high-speed complex permittivity needle probe. Such probes are able to distinguish the different phases or components of a flow by measuring the complex value of the electrical permittivity at a high data rate (up to 20 000 samples/s). The performance of the system, as well as its ability to differentiate organic substances, has been analyzed. A time-resolved experiment in an oil-water-gas flow, as well as a two-substance mixing experiment in a stirred tank, is presented. 相似文献
985.
The use of an iron dispersed catalyst, derived from Fe3(CO)12, for extra-heavy crude oil upgrading using methane as source of hydrogen was studied. The upgrading reactions were carried out batchwise in a stainless-steel 300 ml Parr reactor with 250 ppm of Fe at a temperature of 410-420 °C, a pressure of 11 MPa of CH4, and a residence time of 1 h. In the presence of Fe3(CO)12, the reaction of Hamaca extra-heavy crude oil led to a reduction of two orders of magnitude in the viscosity (from 500 to 1.3 Pa s), 14% reduction in sulfur content, and 41% conversion of the >500 °C fraction in the upgraded product with respect to the original crude. The iron catalyst was isolated from the coke produced from the upgrading reaction and was analyzed by XPS, EDAX, and Mössbauer spectroscopy. The results indicated the presence of a Fe-V mixed sulfide species with a composition ca. (Fe0.6V0.4)zS, where z is in the range 0.8-0.9. 相似文献
986.
Rabbiteye blueberries were osmoconcentrated for 12 h, and for 3 h with and without continuous high-frequency ultrasound (CHFU) and then air dehydrated (70°C, 10 h). Osmoconcentration increased solids gain, moisture loss, soluble solids, and bulk density. Long osmoconcentration for 12 h can be reduced with CHFU with similar results. Scanning electron microscopy (SEM) micrographs indicated that berries without pretreatment suffered the highest degree of tissue collapse. They also had the highest rehydration ratio and may be ideal for use in breakfast cereals. Osmoconcentrated berries may be used as snack food or in cereal bars due to high bulk density and low rehydration ratio. 相似文献
987.
The advances of using carbon-nanotube (CNT) triode structure field-emission (FE) devices for display applications require an accurate and efficient SPICE-compatible device model for evaluating their electrical behaviors in the early circuit and system design stage. This letter presents a simple and efficient macromodeling approach that can accurately model the CNT triode FE devices independent of the device process and physical structures for circuit simulations. 相似文献
988.
Ana Costa e Silva Alípio M. Jorge Luís Torgo 《International Journal on Document Analysis and Recognition》2006,8(2-3):144-171
This paper plans an end-to-end method for extracting information from tables embedded in documents; input format is ASCII, to which any richer format can be converted, preserving all textual and much of the layout information. We start by defining table. Then we describe the steps involved in extracting information from tables and analyse table-related research to place the contribution of different authors, find the paths research is following, and identify issues that are still unsolved. We then analyse current approaches to evaluating table processing algorithms and propose two new metrics for the task of segmenting cells/columns/rows. We proceed to design our own end-to-end method, where there is a higher interaction between different steps; we indicate how back loops in the usual order of the steps can reduce the possibility of errors and contribute to solving previously unsolved problems. Finally, we explore how the actual interpretation of the table not only allows inferring the accuracy of the overall extraction process but also contributes to actually improving its quality. In order to do so, we believe interpretation has to consider context-specific knowledge; we explore how the addition of this knowledge can be made in a plug-in/out manner, such that the overall method will maintain its operability in different contexts.The opinions expressed in this article are the responsibility of the authors and do not necessarily reflect those of Banco de Portugal. 相似文献
989.
Monodisperse and Corrosion-Resistant Metallic Nanoparticles Embedded into Sepiolite Particles for Optical and Magnetic Applications 总被引:2,自引:0,他引:2
Carlos Pecharromán Antonio Esteban-Cubillo Isabel Montero José S. Moya Eduardo Aguilar Julio Santarén Antonio Alvarez 《Journal of the American Ceramic Society》2006,89(10):3043-3049
The preparation of large quantities of heterogeneous materials containing non-agglomerated and monodispersed nanoparticles is becoming one of the bottlenecks that hinders the development of commercial devices. Here we describe a method to prepare monodispersed metallic (Cu, Ag, Au, Ni, Co, and Fe) nanoparticles in a silicate matrix (sepiolite) by means of a reduction process of metallic cations associated with a dehydration process of the matrix. This process is characterized by the huge amount of monodispersed metallic nanoparticles that it produces. Additionally, these nanoparticles have been revealed to be remarkably stable against oxidation because the transformed sepiolite matrix becomes a diffusion barrier for oxygen. Furthermore, the nanoparticles present suitable properties to be used for optical and magnetic applications. 相似文献
990.
The effects of reprocessing on the mechanical, physical, and rheological properties of a commercial plasticized PVC compound are investigated. Reprocessing experiments at lower, identical, and higher temperatures than those attained during the initial extrusion in a capillary rheometer are undertaken. Repetitive reprocessing is also considered. With the exception of the mean surface roughness—and when the effects of degradation are discarded—the other characteristics of processed and reprocessed PVC are essentially similar. Nevertheless, changes at both the molecular and the morphological level take place during reprocessing, as demonstrated by the results of thermal analysis and surface appearance. 相似文献