全文获取类型
收费全文 | 623043篇 |
免费 | 7223篇 |
国内免费 | 1899篇 |
专业分类
电工技术 | 11413篇 |
综合类 | 470篇 |
化学工业 | 94432篇 |
金属工艺 | 25071篇 |
机械仪表 | 19585篇 |
建筑科学 | 14008篇 |
矿业工程 | 3583篇 |
能源动力 | 16717篇 |
轻工业 | 49291篇 |
水利工程 | 6658篇 |
石油天然气 | 12860篇 |
武器工业 | 28篇 |
无线电 | 72342篇 |
一般工业技术 | 124875篇 |
冶金工业 | 115831篇 |
原子能技术 | 14230篇 |
自动化技术 | 50771篇 |
出版年
2021年 | 5349篇 |
2020年 | 4156篇 |
2019年 | 5183篇 |
2018年 | 8950篇 |
2017年 | 8881篇 |
2016年 | 9600篇 |
2015年 | 6089篇 |
2014年 | 10090篇 |
2013年 | 29061篇 |
2012年 | 16204篇 |
2011年 | 21992篇 |
2010年 | 17621篇 |
2009年 | 20054篇 |
2008年 | 20551篇 |
2007年 | 20229篇 |
2006年 | 18028篇 |
2005年 | 16407篇 |
2004年 | 15468篇 |
2003年 | 15311篇 |
2002年 | 14742篇 |
2001年 | 14552篇 |
2000年 | 13723篇 |
1999年 | 14182篇 |
1998年 | 35739篇 |
1997年 | 25313篇 |
1996年 | 19535篇 |
1995年 | 14645篇 |
1994年 | 13017篇 |
1993年 | 12905篇 |
1992年 | 9503篇 |
1991年 | 9069篇 |
1990年 | 8976篇 |
1989年 | 8699篇 |
1988年 | 8428篇 |
1987年 | 7206篇 |
1986年 | 7170篇 |
1985年 | 8132篇 |
1984年 | 7575篇 |
1983年 | 6899篇 |
1982年 | 6445篇 |
1981年 | 6564篇 |
1980年 | 6184篇 |
1979年 | 6027篇 |
1978年 | 6150篇 |
1977年 | 7015篇 |
1976年 | 9047篇 |
1975年 | 5398篇 |
1974年 | 5070篇 |
1973年 | 5203篇 |
1972年 | 4424篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Results are presented for experimental investigations on the traffic-induced oscillations of two full-scale foundations of a metallic tunnel, one of which is installed directly on the ground, and the other on cast-in-place piles. The foundations are close to one another with respect to mass and the load applied to them. Differences are revealed between the parameters of the actual oscillations of these foundations and their computed values. 相似文献
103.
The paper outlines some of the actions taken by Severn Trent Water to achieve compliance with consent limits since the implementation of the Control of Pollution Act (Part II) in 1985.
Prior to and since 1985, Severn Trent Water has undertaken an extensive programme to analyse the reasons for failure and carry out remedial work. A major feature of this programme, which has been further stimulated by privatization, has been the need to reduce the lead time for carrying out improvements.
The paper discusses the means by which this has been achieved, including the introduction of the 'fast-track'initiative and the 'process matrix'.
Other aspects are outlined including initiatives to develop more robust processes, computerized work scheduling, extensive training programmes and best practice studies. 相似文献
Prior to and since 1985, Severn Trent Water has undertaken an extensive programme to analyse the reasons for failure and carry out remedial work. A major feature of this programme, which has been further stimulated by privatization, has been the need to reduce the lead time for carrying out improvements.
The paper discusses the means by which this has been achieved, including the introduction of the 'fast-track'initiative and the 'process matrix'.
Other aspects are outlined including initiatives to develop more robust processes, computerized work scheduling, extensive training programmes and best practice studies. 相似文献
104.
A matrix method for the analysis of structural systems composed of thin-walled members is presented. The matrix displacement analysis includes the effects of thin-walled non-uniform torsion theory, cross-section asymmetry, eccentric restraint as well as joint types peculiar to thin-walled members. The method is used for a prediction of the elastic behaviour of a set of representative test frames. The test frames were pitched-roof portals constructed from channel sections bent about their major-axis and supported by eccentric restraints simulating purlins and girts. 相似文献
105.
Sorption of P to the filter material Filtralite-P was examined at a small, medium and large scale. In the small- and meso-scale laboratory models, the sorbed amount of total phosphorus (P) was heterogeneously distributed with more P sorbed in the inlet zone and the bottom layers. The full-scale system had, on the other hand, the highest sorbed concentration in the outlet region. The overall P sorption capacity of the material was 8030, 4990 and 521 mg P kg(-1) Filtralite-P for Box 1, Box 2 and meso scale, respectively. This equals 4.4, 2.8 and 0.29 kg P m(-3) material, respectively. However, the maximum sorption capacities found were 2500, 3887 and 4500 mg P kg(-1) Filtralite-P for the two small-scale box systems and the meso-scale container, respectively. In the full-scale system the overall P sorption capacity of the material was 52 mg P kg(-1) Filtralite-P (0.029 kg P m(-3) Filtralite-P with a maximum sorbed amount of P of 249 mg P kg(-1). Results from both the small- and meso-scale system show that when a constructed wetland (CW) is saturated, i.e. when the outlet concentration has reached its maximum allowed concentration of 1.0 mg P l(-1), only parts of the filter material will have reached the sorption capacity. Sequential extractions of Filtralite-P showed that the loosely bound P, Ca-P and Al-P were the primary P sorption pools both in the small-scale models and in the full-scale CW. However, the proportion of these three fractions varied with time and change in pH. A white product precipitated in the outlet zone of both the small-scale box models as well as the onsite CW. The surface of these precipitation particles was identified by X-ray diffraction and SEM method as CaCO3 and precipitated Ca- and Mg-phosphates. 相似文献
106.
ABSTRACTA growing number of workers, particularly in the knowledge and service sectors, can perform their work at multiple locations, and it is decreasingly realistic to assume, as researchers and planners have traditionally done, that employment in cities occurs in fixed locations. This suggests that census data or establishment registries do not fully capture where economic activity takes place. Given the role that ICTs play in enabling daytime workplace mobility, and given that they generate substantial amounts of real-time, geolocated data, we ask whether these Big Data can shed light upon the trajectories of mobile workers at the urban scale. 相似文献
107.
E.P. Koster B.C.J. Zoeteman G.J. Piet E. De Greef H. Van Oers B.G. Van Der Heijden A.J. Van Der Veer 《The Science of the total environment》1981
The human senses play an important role in assessing the quality of food and of the environment. Particularly the chemical senses of taste and smell determine the pleasantness of foods and drinks and may provide a warning mechanism for the presence of more or less toxic contaminants. Even after the recent rapid development of powerful analytical techniques the human nose can easily detect trace amounts of chemicals at levels manytimes lower than the analytical detection limits.Although taste and odour assessment of drinking water has been practized inmany waterworks laboratories by small panels, relatively unreliable results were obtained and such sensory data played up till now only a minor role in the management of the water treatment plant. More sophisticated and reliable methods for sensory water quality evaluation are discussed. Special attention is given to the characteristics of the human senses of taste and smell, to which the methodology of sensory assessment should be better adapted. High numbers of observations on a sample are generally needed, for which purpose the use of large panels has to be realized. In this respect the help of large consumer panels is an alternative for the presently often used small laboratory groups. As an example the preliminary results of a large ongoing experiment of sensory water quality assessment by 2 consumer panels of 100 persons each in the Rotterdam area are discussed. Drinking water quality is judged at the consumer homes every week. The experiment started September 1979 and will be continued for one year. 相似文献
108.
Philip J. Bourque Dominique Gambier Raymond J. Burby III Jack E. Adams Jeffrey B. Nugent D. van der Werf William J. Serow Edward L. Prill Willard Tim Chow R. J. Johnston Craig Zumbrunnen Kingsley E. Haynes Nolin Masih Robert Hines Wilson Philip S. Morrison Debnath Mookherjee Robin Flowerdew Noel D. Uri Panayotis H. Mavrakis Leo E. Zonn Joseph A. Ziegler J. S. L. McCombie Ronald A. Oliveira Jacob J. van Duijn Douglas M. Brown Robert G. Fletcher Lawrence Hugg W. T. Trulove Alene Anderson Bruce Domazllcky 《The Annals of Regional Science》1978,12(1):105-164
109.
The direct determination of 238U in various soil samples was done by measuring the 63.3-keV transition from the decay of the first daughter 234Th. Potential errors resulting from the chemical non-equilibrium of 238U with its daughters are thus avoided. The method sensitivity is 1 ppm compared to the 35 ppm obtainable by employing the 1001-keV gamma ray. A Ge(Li) gamma-ray spectrometer is the only analytical tool required. Examples are offered that demonstrate the usefulness of the technique for routine, inexpensive environmental monitoring of uranium. The technique also has the capability of providing information on the 238U/235U isotopic ratio. 相似文献
110.
Shamshuddin J Muhrizal S Fauziah I Husni MH 《The Science of the total environment》2004,323(1-3):33-45
Acid sulfate soils having a pH of less than 3.5 are widespread in Malaysia. Some of these soils are planted to cocoa, but the yield is reported to be low due to soil infertility related to Al toxicity. Cocoa growth is sensitive to the presence of Al in the soil. To a certain extent, Al toxicity in soils can be reduced by organic matter application and to a greater extent in iron-poor acid sulfate soil. A study was conducted to determine the efficacy of various types of organic materials easily available in the country to ameliorate acid sulfate soil infertility for growing cocoa seedlings. The treatments were control (nil), lime (3 t/ha), peat (10% w/w), peat plus green manure (10% w/w), peat plus rice straw (10% w/w), peat plus chicken dung (10% w/w) and peat plus POMS (Palm oil mill sludge) (10% w/w). The growth of cocoa seedlings was affected significantly by the presence of Al in the cocoa tissues. As the amount of Al in the leaves increased, the relative top dry weight of cocoa seedlings decreased. Likewise, the relative plant height was negatively correlated with Al in the leaves. Peat as well as peat in combination with green manure, rice straw, chicken dung or palm oil mill sludge was able to reduce Al toxicity in acid sulfate soil; the highest top dry weight of cocoa seedlings were obtained in the peat plus green manure treatment. The best cocoa seedlings root growth was found for the peat treatment alone. The relative top dry weight of cocoa seedlings was negatively correlated with Al(3+) as well as Al(3+)+Al(OH)(2+)+Al(OH)(2)(+) activity in the soil solution. The critical values for Al(3+) and the combination of Al(3+)+Al(OH)(2+)+Al(OH)(2)(+) activity in the soil solution were 10 microM and 15 microM, respectively. 相似文献