全文获取类型
收费全文 | 58663篇 |
免费 | 2921篇 |
国内免费 | 85篇 |
专业分类
电工技术 | 447篇 |
综合类 | 76篇 |
化学工业 | 13146篇 |
金属工艺 | 1070篇 |
机械仪表 | 1157篇 |
建筑科学 | 2054篇 |
矿业工程 | 128篇 |
能源动力 | 1753篇 |
轻工业 | 9383篇 |
水利工程 | 553篇 |
石油天然气 | 255篇 |
武器工业 | 3篇 |
无线电 | 2858篇 |
一般工业技术 | 9400篇 |
冶金工业 | 10187篇 |
原子能技术 | 334篇 |
自动化技术 | 8865篇 |
出版年
2024年 | 105篇 |
2023年 | 534篇 |
2022年 | 1144篇 |
2021年 | 1818篇 |
2020年 | 1284篇 |
2019年 | 1404篇 |
2018年 | 2022篇 |
2017年 | 1973篇 |
2016年 | 2179篇 |
2015年 | 1758篇 |
2014年 | 2190篇 |
2013年 | 4269篇 |
2012年 | 3494篇 |
2011年 | 3885篇 |
2010年 | 2930篇 |
2009年 | 2744篇 |
2008年 | 2677篇 |
2007年 | 2440篇 |
2006年 | 1849篇 |
2005年 | 1618篇 |
2004年 | 1396篇 |
2003年 | 1317篇 |
2002年 | 1175篇 |
2001年 | 820篇 |
2000年 | 752篇 |
1999年 | 834篇 |
1998年 | 2992篇 |
1997年 | 1963篇 |
1996年 | 1380篇 |
1995年 | 835篇 |
1994年 | 701篇 |
1993年 | 696篇 |
1992年 | 302篇 |
1991年 | 250篇 |
1990年 | 252篇 |
1989年 | 271篇 |
1988年 | 237篇 |
1987年 | 239篇 |
1986年 | 215篇 |
1985年 | 252篇 |
1984年 | 201篇 |
1983年 | 154篇 |
1982年 | 183篇 |
1981年 | 195篇 |
1980年 | 179篇 |
1979年 | 124篇 |
1978年 | 115篇 |
1977年 | 259篇 |
1976年 | 428篇 |
1975年 | 102篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
41.
42.
Survival of pure and mixed cultures of Yersinia enterocolitica and Escherichia coli in sterile spring water stored at 4 degrees C was evaluated. Y. enterocolitica increased two or three logs during the first 3 weeks of incubation, and at the end of 64 weeks viable cells in numbers corresponding to the initial inoculum level were still detectable. However, after 1 week of incubation, the number of E. coli in water started to decrease and in 13 weeks time no E. coli was detected. More rapid decrease of E. coli was observed in mixed cultures. 相似文献
43.
Summary The thermal properties of an epoxy resin (diglycidyl ether Bisphenol A, DGEBA) cured with a primary amine (ethylenediamine, ETDA) and filled with 10, 20 and 30 wt. % of ultra fine copper particles were analyzed. The thermal results were evaluated by means of the Romero-Garcia method, which allowed to obtain the resin degradation kinetic parameters, as well as the possible decomposition mechanism. From the obtained results is possible to infer that higger copper content strongly affects the degradation process of the epoxy resin, which causes a drop off on the composites thermal stability. This behavior could be attributed to water presence, being this effect less pronounced for the resin with 10 wt. % copper and unfilled resin. Regarding to decomposition mechanism, three way transport showed the best correlation for all samples. 相似文献
44.
Lime mortars are often used for repairs to historic buildings. This paper investigates two forms of lime binder: fat and feebly-hydraulic,
in order to predict their long-term behaviours and hence ascertain which of the two possesses greater durability, so that
they may be used more efficiently in restoration. Mortars were tested for properties governing moisture movement and also
subject to durability cycles. The resistance to damage under freezing conditions was evaluated with the saturation coefficient.
Thermal cycles had no effect on the mortars and gave no indication of the relative durabilities of the binders. Salt crystallization
cycles, though effective in distinguishing the more durable of the two, were too aggressive to gauge a clear profile of salt
weathering and succeeded in rapidly decomposing the samples. Tests on the properties governing moisture movement produced
good indications of the degree to which the mortars permit flow through their fabrics. According to the results obtained,
fat lime mortars are more durable than those made with feebly-hydraulic lime. The results also suggest that the feebly-hydraulic
lime mortars are at a higher risk of decomposition by granular disintegration whereas fat lime mortars are better suited to
damp, slightly exposed conditions. These results disagree with the general opinion that hydraulic limes are more durable than
fat limes due to the additional strength and water insolubility arising from their hydraulicity. 相似文献
45.
Ochratoxin A (OTA) is a secondary metabolite produced by several species of Aspergillus and Penicillium; among them Aspergillus ochraceus and Penicillium verrucosum are two ochratoxigenic species capable of growing in different climates and thus contamination of food crops with OTA can occur worldwide. OTA can be found in a wide range of foods such as cereals, coffee, cocoa, spices, beer, wine, dried vine fruit, grapes and meat products. OTA is toxic to animals, it presents neurotoxic, immunotoxic and nephrotoxic effects. It has been implicated in a human kidney disorder known as Balkan Endemic Nephropathy. This review focuses on the ecophysiology of ochratoxin-producing Aspergillus ochraceus and Penicillium verrucosum, the effect of environmental factors on their germination, mycelial growth, and OTA production. Knowledge of environmental conditions required for sucessive stages of fungal development represent the first step towards preventing mycotoxin formation. Predictive models for different stages of fungal development are presented, which allow prediction of the time before spoilage as a function of the abiotic factors. Finally, the implications of these studies in management of barley, coffee and grapes are described. This can help to identify the critical control points in their production, storage and distribution processes. 相似文献
46.
47.
The transition from basic automation to flexible manufacturing is an expensive and tedious procedure. It requires meticulous planning and almost clairvoyant forecasting to insure that the initial flexibility obtained is sufficient to allow growth and expansion in the future. This paper will suggest a systematic and methodological approach to achieve optimal flexibility and describe the present results of its application to an ongoing system transformation.
Conclusions based on existing levels of completion are presented along with identification of critical and non critical flexibility requirements. The considerations and steps taken are summarized in a procedural format which may then be applied to a wide variety of system transformations. 相似文献
48.
470 injured teeth of 370 patients who consulted the Dental Clinic of Ege University, Izmir, Turkey for examination or treatment between 1981-1993 were evaluated. Information concerning sex, age of patients at the time of injury, cause of trauma, number of injured teeth, type of tooth and type of trauma were recorded. More boys suffered traumatic injuries (64.8%) than girls (35.2%). Patients aged 11-15 years old exhibited the highest number of injuries (34.4%) followed by the 6-10 years old group (24.5%). Most injuries involved one tooth (60%) and maxillary central incisors were the most often affected teeth (66.2%). The leading cause of injury was undefined falls (45.1%). At the initial examination, cases seen after a long posttraumatic period showed more complications than those presented within a short time period. Educational programs about the importance of dental trauma, the benefits of immediate attendance and conservation of avulsed and fractured teeth would be very helpful for patients. Additionally improving the knowledge of the dental practitioner about trauma would be another important point in solving the problem. 相似文献
49.
María Esther Diupotex-Chong Néstor J Cazzaniga Alejandra Hernández-Santoyo José Miguel Betancourt-Rule 《Biocell》2004,28(3):279-285
Mitotic chromosomes of the freshwater snail Pomacea patula catemacensis (Baker 1922) were analyzed on gill tissue of specimens from the type locality (Lake Catemaco, Mexico). The diploid number of chromosomes is 2n = 26, including nine metacentric and four submetacentric pairs; therefore, the fundamental number is FN = 52, No sex chromosomes could be identified. The same chromosome number and morphology were already reported for P. flagellata, i.e., the other species of the genus living in Mexico. The basic haploid number for family Ampullariidae was reported to be n = 14 in the literature; so, its reduction to n = 13 is probably an apomorphy of the Mexican Pomacea snails. Lanistes bolteni, from Egypt, also shows n = 13, but its karyotype is much more asymmetrical, and seems to have evolved independently from P. flagellata and P. patula catemacensis. The nominotypical subspecies, P. patula patula (Reeve 1856), is a poorly known taxon, whose original locality is unknown. A taxonomical account is presented here, and a Mexican origin postulated as the most parsimonious hypothesis. 相似文献
50.
Imperfection in information can be considered a crosscutting concern that manifests itself in diverse kinds of imprecision, uncertainty, or inconsistency in the data models of a software system. The extension of existing programming and querying interfaces for the different aspects of information imperfection requires a proper modularization of the different concerns of numerical imprecision handling, so that the extensions do not interfere with existing programming practices and do not obscure the original design. Aspect‐oriented design (AOD) enables such a form of nonintrusive extensions to be added to existing software libraries, clearly separating fuzziness or other imperfections in data as a differentiated concern that can be considered from the early phases of development. In this article, a general framework for aspect‐based extension of data models and fuzzy databases is described, and some design and implementation issues of such AOD‐based extensions on OJB database libraries are described as a case study. © 2006 Wiley Periodicals, Inc. Int J Int Syst 21: 1199–1216, 2006. 相似文献