全文获取类型
收费全文 | 408864篇 |
免费 | 4688篇 |
国内免费 | 2448篇 |
专业分类
电工技术 | 6711篇 |
综合类 | 2969篇 |
化学工业 | 58689篇 |
金属工艺 | 19201篇 |
机械仪表 | 13734篇 |
建筑科学 | 9540篇 |
矿业工程 | 2494篇 |
能源动力 | 9406篇 |
轻工业 | 28199篇 |
水利工程 | 4836篇 |
石油天然气 | 7972篇 |
武器工业 | 55篇 |
无线电 | 47001篇 |
一般工业技术 | 84178篇 |
冶金工业 | 61161篇 |
原子能技术 | 8610篇 |
自动化技术 | 51244篇 |
出版年
2021年 | 2832篇 |
2020年 | 2176篇 |
2019年 | 2786篇 |
2018年 | 18903篇 |
2017年 | 17896篇 |
2016年 | 15143篇 |
2015年 | 4123篇 |
2014年 | 6104篇 |
2013年 | 15327篇 |
2012年 | 12226篇 |
2011年 | 21140篇 |
2010年 | 17532篇 |
2009年 | 16565篇 |
2008年 | 17822篇 |
2007年 | 18840篇 |
2006年 | 9710篇 |
2005年 | 9819篇 |
2004年 | 9469篇 |
2003年 | 9113篇 |
2002年 | 8251篇 |
2001年 | 8009篇 |
2000年 | 7764篇 |
1999年 | 7906篇 |
1998年 | 18434篇 |
1997年 | 13285篇 |
1996年 | 10244篇 |
1995年 | 7724篇 |
1994年 | 6699篇 |
1993年 | 6752篇 |
1992年 | 4936篇 |
1991年 | 4714篇 |
1990年 | 4535篇 |
1989年 | 4483篇 |
1988年 | 4095篇 |
1987年 | 3724篇 |
1986年 | 3705篇 |
1985年 | 4071篇 |
1984年 | 3732篇 |
1983年 | 3469篇 |
1982年 | 3268篇 |
1981年 | 3283篇 |
1980年 | 3322篇 |
1979年 | 3122篇 |
1978年 | 3128篇 |
1977年 | 3509篇 |
1976年 | 4666篇 |
1975年 | 2678篇 |
1974年 | 2629篇 |
1973年 | 2657篇 |
1972年 | 2237篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
The state of the art of debugging is examined. A debugged process model that serves as the basis of a general debugging framework is described. The relationship of the model to traditional debugging processes and support tools is discussed. A minimal set of requirements for a general debugging framework is described in terms of both the theory behind debugging methodologies and the support tools. An execution monitor, Eden, that serves as a debugging tool within this general framework is described 相似文献
72.
73.
O Baeder-Bederski M Dürr M Borneff-Lipp P Kuschk R Netter G Daeschlein P Mosig R A Müller 《Water science and technology》2005,51(9):205-212
Different types of constructed wetlands in a pilot-plant system were fed with identical municipal waste water to compare the sanitisation process in two-stage systems. With combinations of a vertical and a horizontal flow filter an E. coli reduction of 5 log10 with an E. coli influent concentration of 10(7) MPN/100 ml was achieved. Using different filter materials in each stage the total performance of the two-stage system was independent from the sequence of these materials. However, using coarser filter material in the first stage makes the filter less prone to clogging and is thus the preferential option with regard to operational reliability. 相似文献
74.
P Dugan 《Water science and technology》2005,51(8):157-161
The growing attention being given to improving water productivity at the catchment level has given rise to increased interest in the contribution of aquatic ecosystems and in particular fisheries to reducing rural poverty and improving food security. There is growing recognition that these natural resources have an important role to play in pro-poor water management in many of the world's river basins, but that capacity to optimize these benefits is constrained by a lack of appropriate technologies and tools to do so. The present paper provides an overview of the current state of understanding of these issues and identifies a number of challenges to be addressed, namely the need to: (i) build wider understanding of the value of river fisheries; (ii) understand the water requirements for sustaining river fisheries; and (iii) develop governance arrangements that bring fisheries to the decision-making table. It concludes by distilling from recent reviews of river fisheries valuation, environmental flows, and governance, a set of specific directions that need to be taken in order to meet these challenges. 相似文献
75.
The article established the regularities of change of the physicomechanical characteristics and strength of glass textolites in single and repeated thermal loading. It shows that under multiple loading the intense loss of strength of the investigated materials is due to increased porosity on account of the large number of microcracks appearing in the structure. A correlation is obtained between the elastic and strength characteristics and porosity in dependence on the temperature of multiple heating which in the first approximation is described by a polynomial of second degree with respect to temperature, multiplied by the reciprocal of porosity.Translated from Problemy Prochnosti, No. 6, pp. 53–58, June, 1991. 相似文献
76.
P.O. Fanger B.M. Ipsen G. Langkilde B.W. Olessen N.K. Christensen S. Tanabe 《Energy and Buildings》1985,8(3):225-236
Groups of 32 and 16 subjects of both sexes were exposed in an environmental chamber to radiant asymmetry caused by a cool wall, a warm wall, and a cool ceiling. Each subject was tested individually while seated and clothed at 0.6 clo. During each 3.5-hour experiment the subject was exposed to six radiant temperature asymmetries. He was asked whether and where he experienced any local cool or warm sensation, and whether it was felt to be uncomfortable. During the entire experiment he was kept thermally neutral by changing the air temperature according to his wishes.For cool walls, warm walls, and cool ceilings curves have been established showing the percentage of dissatisfied subjects as a function of the radiant asymmetry. Radiant asymmetry at a warm wall caused less discomfort than a cool wall. A cool ceiling caused less discomfort than a warm ceiling. Accepting that 5% of the subjects may feel uncomfortable. a radiant temperature asymmetry of 10°C is allowable at a cool wall, 23°C at a warm wall, and 14°C under a cool ceiling. A previous study showed that 4°C is allowable under a warm ceiling. Radiant asymmetry had no significant impact on the operative temperatures preferred by the subjects. No significant differences were observed between the responses of men and women exposed to radiant asymmetry. 相似文献
77.
78.
V. Ya. Chubar' Zaporozhe Machine Building Institute. Translated from Problemy Prochnosti, No. 3, pp. 62–65, March, 1989. 相似文献
79.
Indoor body-area channel model for narrowband communications 总被引:1,自引:0,他引:1
Fort A. Desset C. Wambacq P. Biesen L.V. 《Microwaves, Antennas & Propagation, IET》2007,1(6):1197-1203
Using wireless sensors placed on a person to continuously monitor health information is a promising new application. At the same time, new low-power wireless standards such as Bluetooth and Zigbee have been proposed for short range, low data-rate communication matching the requirements of these bio-medical applications. However, there are currently few measurements or models describing propagation around the body. To address this problem, electromagnetic waves near the torso are measured and a statistical model is derived for communication in the 915 MHz and 2.45 GHz industrial, scientific and medical bands associated with Zigbee and Bluetooth. Measurement setup and statistical analysis are described. 相似文献
80.
R. Oliva A. L. Gemal A. W. N brega A. C. P. Araú jo 《Food Additives & Contaminants》2003,20(8):758-763
The structure of the recently introduced Brazilian government programme for monitoring pesticide residues in six major agricultural products is described. Residues found from the analysis of samples of tomatoes and strawberries are discussed in detail. The much greater frequency of detection of pesticide residues, many of which are not approved for use in Brazil, in produce being sold on the domestic market, as opposed to that produced for export, is of major concern. It is perceived that this new monitoring programme will become permanent and be used to underpin enforcement actions that will need to be taken to reduce the numbers of incidents of illegal residues occurring, particularly in fresh fruits and vegetables. 相似文献