全文获取类型
收费全文 | 502317篇 |
免费 | 4705篇 |
国内免费 | 1745篇 |
专业分类
电工技术 | 8513篇 |
综合类 | 2676篇 |
化学工业 | 74015篇 |
金属工艺 | 18854篇 |
机械仪表 | 14940篇 |
建筑科学 | 14223篇 |
矿业工程 | 1428篇 |
能源动力 | 12449篇 |
轻工业 | 47761篇 |
水利工程 | 4690篇 |
石油天然气 | 2202篇 |
武器工业 | 14篇 |
无线电 | 64952篇 |
一般工业技术 | 93449篇 |
冶金工业 | 78671篇 |
原子能技术 | 5918篇 |
自动化技术 | 64012篇 |
出版年
2021年 | 2921篇 |
2020年 | 2249篇 |
2019年 | 2916篇 |
2018年 | 17816篇 |
2017年 | 16864篇 |
2016年 | 13974篇 |
2015年 | 4097篇 |
2014年 | 6085篇 |
2013年 | 19926篇 |
2012年 | 13395篇 |
2011年 | 23881篇 |
2010年 | 19324篇 |
2009年 | 18367篇 |
2008年 | 20552篇 |
2007年 | 21870篇 |
2006年 | 13192篇 |
2005年 | 13336篇 |
2004年 | 12787篇 |
2003年 | 12557篇 |
2002年 | 11575篇 |
2001年 | 11334篇 |
2000年 | 10557篇 |
1999年 | 10944篇 |
1998年 | 24169篇 |
1997年 | 17713篇 |
1996年 | 14047篇 |
1995年 | 11101篇 |
1994年 | 9878篇 |
1993年 | 9456篇 |
1992年 | 7239篇 |
1991年 | 6875篇 |
1990年 | 6461篇 |
1989年 | 6187篇 |
1988年 | 5949篇 |
1987年 | 4964篇 |
1986年 | 4910篇 |
1985年 | 6057篇 |
1984年 | 5679篇 |
1983年 | 4903篇 |
1982年 | 4546篇 |
1981年 | 4509篇 |
1980年 | 4266篇 |
1979年 | 4127篇 |
1978年 | 3827篇 |
1977年 | 4585篇 |
1976年 | 6131篇 |
1975年 | 3152篇 |
1974年 | 3045篇 |
1973年 | 2919篇 |
1972年 | 2353篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
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
132.
134.
135.
136.
F. Ellwood Allen J. Martin Frissel 《Journal of the American Planning Association. American Planning Association》2013,79(3):79-80
AN ANALYSIS OF THE PROBLEN OF “LOW COST HOUSING FOR THE LOWER INCOME GROUP”, By George F. Lindsay. Dec. 10, 1937. 80 pages. 81/2 × 11 inches. Mimeographed. 相似文献
137.
Roger L. Creighton J. Douglas Carroll Jr. Graham S. Finney 《Journal of the American Planning Association. American Planning Association》2013,79(2):96-103
In city planning, data-processing machines permit the rapid handling and summarization of data in housing, renewal, land use, transportation, and basic urban research. Electronic computers. specifically, are exciting because they offer a means of solving complex city planning problems, especially in forecasting land use and travel demand. For most planning operations punched card data processing is superior to other processes. The functions of these machines are described herein and three examples of data processing are elaborated on. In future years, planning techniques may have to be altered considerably to take advantage of the potentials of data processing. 相似文献
138.
D. J. Walmsley 《Urban Policy and Research》2013,31(4):509-523
Examination of the changing composition of shopping centres in suburban Sydney between 1969 and 1998 suggests that retail restructuring is linked to lifestyle changes. The growth in the number of shops appears to have matched population growth in the 1990s, suggesting that the suburbanisation of retailing has stabilised. At the same time there has been increasing diversification in terms of the retail functions which are available and in terms of the places where these are available. These changes appear linked to a blurring of the distinction between shopping and leisure and to the use of shopping as a way of signifying identity. 相似文献
139.
A. N. Clarke W. W. Eckenfelder E. D. McMullen J. A. Roth B. A. Young 《Water research》1978,12(10):799-804
A continuous oxygen uptake meter or continuous respirometer was developed which produced a rapid and reliable response to systemic shocks. The respirometer basically is a 101. Plexiglas laboratory activated sludge unit with a variable volume air tight side car. The feed enters the completely mixed aeration basin and is pumped into the side car. The side car is the site of the oxygen uptake measurements as indicated by a continuously monitoring dissolved oxygen probe. The system was most sensitive to changes in influent concentrations when run at an F/M = 0.1. Response time for a change in DO of 0.1 ppm was less than 4 min. The continuous respirometer was tested employing both synthetic and raw industrial wastes. 相似文献
140.
Herbert BM Halsall CJ Villa S Fitzpatrick L Jones KC Lee RG Kallenborn R 《The Science of the total environment》2005,342(1-3):145-160
PCNs were measured in air and snow during separate field campaigns at Ny-Alesund (April 2001) and Troms? (February/March 2003) in the Norwegian Arctic. Air concentrations ranged from 27 to 48 and 9 to 47 pg sigmaPCN m(-3) for Ny-Alesund (n=6) and Troms? (n=10), respectively. These concentrations (including the tri-chlorinated naphthalenes) greatly exceeded concentrations previously measured in the Canadian Arctic, but did fall within the upper range of concentrations observed over the eastern Arctic Ocean and regional seas. Local sources appear to be affecting concentrations observed at both sites, with the presence of several hexa-chlorinated naphthalenes at Troms? probably attributed to local/regional sources. Use of air mass back trajectories at Troms? revealed that background air concentrations in the Norwegian Arctic are likely to range between <9 and 20 pg sigmaPCN m(-3) and that contemporary concentrations derived close to potential sources (i.e. arctic towns) may equal or exceed those of PCBs. The mean concentration in surface snow was 350 and 240 pg sigmaPCN L(-1) (meltwater) (or 0.014 and 0.01 pg g(-1) (snow)) at Ny-Alesund and Troms?, respectively. The wide variation in concentrations observed between fresh snowfalls could be explained by different snow densities (as a surrogate of snow surface area), rather than attributed to varying air concentrations. A statistically significant inverse relationship was found between snow density and concentrations of tri- to penta-chlorinated homologues and compliments similar findings for the polychlorinated biphenyls (PCBs). This suggests that the vapour-sorbed quantity changes rapidly with snow ageing/compaction; with implications for the fate of these chemicals in the Arctic. 相似文献