全文获取类型
收费全文 | 453085篇 |
免费 | 5053篇 |
国内免费 | 1277篇 |
专业分类
电工技术 | 7948篇 |
综合类 | 305篇 |
化学工业 | 70376篇 |
金属工艺 | 19936篇 |
机械仪表 | 14181篇 |
建筑科学 | 10230篇 |
矿业工程 | 3518篇 |
能源动力 | 10628篇 |
轻工业 | 36409篇 |
水利工程 | 5519篇 |
石油天然气 | 12654篇 |
武器工业 | 36篇 |
无线电 | 49014篇 |
一般工业技术 | 92850篇 |
冶金工业 | 79950篇 |
原子能技术 | 12128篇 |
自动化技术 | 33733篇 |
出版年
2021年 | 3955篇 |
2019年 | 3611篇 |
2018年 | 6587篇 |
2017年 | 6584篇 |
2016年 | 7080篇 |
2015年 | 4321篇 |
2014年 | 7280篇 |
2013年 | 19245篇 |
2012年 | 11448篇 |
2011年 | 15101篇 |
2010年 | 12262篇 |
2009年 | 13887篇 |
2008年 | 14234篇 |
2007年 | 14048篇 |
2006年 | 12273篇 |
2005年 | 11334篇 |
2004年 | 10503篇 |
2003年 | 10144篇 |
2002年 | 10069篇 |
2001年 | 10061篇 |
2000年 | 9543篇 |
1999年 | 9667篇 |
1998年 | 23503篇 |
1997年 | 17118篇 |
1996年 | 13218篇 |
1995年 | 10006篇 |
1994年 | 8848篇 |
1993年 | 8971篇 |
1992年 | 6854篇 |
1991年 | 6805篇 |
1990年 | 6514篇 |
1989年 | 6511篇 |
1988年 | 6438篇 |
1987年 | 5515篇 |
1986年 | 5580篇 |
1985年 | 6357篇 |
1984年 | 6026篇 |
1983年 | 5616篇 |
1982年 | 5216篇 |
1981年 | 5299篇 |
1980年 | 5212篇 |
1979年 | 5139篇 |
1978年 | 5251篇 |
1977年 | 5826篇 |
1976年 | 7277篇 |
1975年 | 4770篇 |
1974年 | 4536篇 |
1973年 | 4641篇 |
1972年 | 4056篇 |
1971年 | 3703篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
DAVID G ELMS 《Civil Engineering and Environmental Systems》2013,30(3):265-272
Learning about complex systems is a fundamental engineering skill; it is often the first task of an engineer when faced with a complex problem in an unfamiliar context. The nature of learning is discussed. Contributions from cognitive psychology, artificial intelligence, management and sociology are drawn together to show that fundamentally, system learning is a matter of forming well-constructed system or conceptual models. The skills needed for this are discussed. 相似文献
132.
Gül Asatekin 《The Journal of Architecture》2013,18(4):389-414
Traditional architecture and associated environments created by residential buildings provide an important focus of interest in contemporary Turkey.1 They are generally accepted as physical witnesses of the past to be preserved and studied. Continuity in the traditional characteristics of the social group living in these environments has been observed in many of the extant settlements in Turkey. The reciprocal relationship between the dwelling and its owners, or users, has led to a dual definition of the ‘traditional dwelling unit’: the social unit being the ‘family’, the architectural unit the ‘dwelling’. The existing, modest-scaled, traditional dwellings in Turkey, which constitute the subject of this study, were mostly constructed after the seventeenth century, but more recent buildings exhibiting similar characteristics are also covered by the term ‘traditional’.2 The concept of ‘privacy’ serves as the basis of evaluation in analysing the interrelation of any two units. The interface of two units can be defined as an hierarchy of privacy represented sociologically by the interrelations of person/family/neighbourhood relationships and architecturally through the interrelations of room/dwelling unit/street/neighbourhood.3 This approach will include a brief summary of some previous studies of traditional residential architecture (Fig. 1). 相似文献
133.
G. B. R. Wesenberg G. Fosse N.‐P. Berg Justesen P. Rasmussen 《The International journal of environmental studies》2013,70(3):223-230
Male Wistar rats received a combination of 25 ppm PbCl2 and 5 ppm CdCl2 in drinking water at different developmental stages. Pb and Cd levels of incisors, molars, epiphyses, diaphyses and kidney cortex were recorded by atomic absorption spectrophotometry. The results confirmed that Pb has an affinity for hard tissue and especially to teeth, but it also accumulated in soft tissues under the above conditions. In addition, the results indicated none or only a moderate placental or mammary barrier for Pb, and suggested a high absorption of lead from the intestine of sucklings. The results also confirmed that kidney cortex is a primary target for Cd, and indicated that Cd has crossed the placental and mammary barriers to some degree. The positive significant correlation between Cd levels in molars and kidney cortex suggested that rodent molars indicate a degree of Cd absorption, whereas incisors do not. It is supposed that rodent molars are comparable to human deciduous teeth. It is thus confirmed that human deciduous teeth indicate previous lead exposure. It is further inferred that they also can be used as indicators of previous Cd‐exposures. 相似文献
134.
D. Mohan V. N. Singh S. N. Kaul Y. C. Sharma 《The International journal of environmental studies》2013,70(1):115-124
Feasibility of a waste material, flyash, as a material for purification of wastewater containing Lissamine Red has been studied. Effects of time and concentration, temperature and pH on the removal of the dye have been studied. Lower concentrations favour the uptake of dye from water and the maximum removal was observed at a dye concentration of 20 mgL m 1 , 30°C, pH of 7 and adsorbent particle size of 53 µm. Dynamics of the uptake was studied using Lagergren's equation. The mass transfer coefficient was found to be 0.05 cmmin m 1 at a concentration of 20 mgL m 1 , 30°C and 53 µm particle size. 相似文献
135.
The coastal zone acts as a major interface between the ocean and continents. Harbours located in this zone face grave problems from sedimentation, which is a global issue for most of the harbours of the world. Dredging which counter acts sedimentation, brings about innumerable environmental impacts — both positive and negative. As a case study, this paper reports the impacts of dredging conducted at Cochin harbour which is the second largest port along the west coast of India; this port is a nodal center in trade and commerce connecting south east Asia to European sector. The harbour operation mainly depends on maintenance form of dredging bringing about impacts which have both direct and indirect effects in the long term. The important parameters selected for this study are salinity, current, extinction coefficient, turbidity, nutrients, chlorophyll and bottom fauna. An assessment is made on both positive and negative impacts which indicate rise in turbidity, changes in nutrient content and biota. The current practice on dredging is conducive to harbour operations, regulating the material made available to the near shore areas and highlights the possible venues for utilization of spoil for reclamation of land and wetland development. A flow chart identifies the areas vulnerable to impacts arising out of dredging and its consequential environmental issues. 相似文献
136.
Ifechukwu E. Adieze Justina C. Orji Rose N. Nwabueze G.O.C. Onyeze 《The International journal of environmental studies》2013,70(3):490-500
Responses to hydrocarbon stress of four tropical plants Panicum maximum, Zea mays, Centrosema sp. and Pueraria sp. grown in crude oil contaminated soils (1%, 5% and 10% w/w) were evaluated in a green house. Plants’ percentage survival, shoot heights, biomass development, and phytotoxicity susceptibility were used as indicators of growth, stress response and hydrocarbon tolerance. Relative to control, shoot heights and biomass of plants reduced with increasing hydrocarbon concentration, but 1% w/w oil-in-soil, stimulated shoot heights (5.9% and 6.4%) and weights (21.9% and 2.3%) in P. maximum and Centrosema sp. respectively. P. maximum tolerated the contaminant stress with biomass yields of 113% and 57% of control respectively in 1% and 10% w/w oil-in-soil. All the plants had 100% survival in 1% w/w, but considerably reduced survival in 10% w/w oil-in-soil. These results show that P. maximum has great potential for phytoremediation of petroleum contaminated soil. 相似文献
137.
The 1101 km length of the Andalusian coast (Spain) was assessed for coastal scenery at 45 specific locations. Selected areas covered resort (3), urban (19), village (8), rural (10) and remote (5) bathing areas. Scenery was analyzed for physical and human parameters via 26 selected parameters. These parameters were obtained by interviews of >500 people on European beaches. Each parameter was assessed via a one-to-five-point attribute scale, which essentially ranged from presence/absence or poor quality (1), to excellent/outstanding (5). Results were subsequently weighted by interviewing >600 bathing area users (not all 26 parameters have equal weight) and subjected to fuzzy logic mathematics in order to reduce recorder subjectivity. High weighted averages for attributes 4 and 5 (excellent/outstanding) reflected high scenic quality, vice versa for attributes 1 and 2. Sites were classified into five classes ranging from Class 1 sites having top grade scenery to Class 5, poor scenery. Seven sites each were found in Classes 1 and 2; 10 sites each in Classes 3 and 5; 11 sites in Class 4. The finest coastal scenery was found in remote areas whilst urban areas scored mainly as Class 3 or 4. Three out of the ten rural sites had Class 3 and 4 values assigned them whereas the rest scored as Class 1 and 2; village sites invariably had scores within Class 3 and 4. Of the three resort sites investigated, one scored as a Class 1 site, the others as Class 3. 相似文献
138.
Landscape and law cross-influence each other. Legal rules shape landscapes, while landscapes shape the culture from which rules emerge. In describing this interplay, landscape can seem passive, as a canvas on which laws paint visions of society; or active, as a matrix for the creation of law and culture. An alternative view is suggested: landscapes are opportunities for action, fields within which individuals interact with context in a mutually adaptive relationship. Lawyers are specialized constituents of this adaptation. Lawyers' acts and practices help to constitute the adaptations that shape a given landscape. A teaching module in which it was sought to prompt law students to become aware of the adaptive role of lawyering in landscape is described. The results suggest useful theoretical and methodological insights into landscape as a field of human activity, and the need for further study of lawyering as a force in the construction of landscape. 相似文献
139.
140.
Alazar G. Ejigu 《Urban Forum》2014,25(3):267-293
A body of scholarship in urban theory of global South over the last two decades has begun to present counterhegemonic notions of modernity and urbanism thereby charting new ways to conceptualize and study African cities. While the need for fuller, richer, and more textured accounts of ordinariness of African cities is often emphasized, the usefulness of differentiated accounts of cities to understanding their spatiality is also highlighted. This article attempts to supplement the ongoing discussion by exploring Addis Ababa as an African city with particular cultural and political historical contexts that gave it distinct experiences of modernity. Data is primarily drawn from historical study of modernizations of the city, supplemented with an ethnographic study that documents contemporary changes and lived experiences in the city and its emerging modern residential places. The study shows that the local experience of modernity is primarily situated in the isolated and noncolonial history of the nation, which on the one hand helps preserve indigenous qualities and on the other becomes a source of envy contributing to the consciousness of belatedness compared to other colonized and Western countries. This consciousness coordinates political intentions with people’s everyday practices in the co-making of a new, modern Addis Ababa and the reassertion of its unofficial identity as “the Diplomatic Capital of Africa.” Potentials and challenges of place-based conceptions of urbanism are implicated. 相似文献