首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   284898篇
  免费   3372篇
  国内免费   1518篇
电工技术   5980篇
技术理论   5篇
综合类   1297篇
化学工业   46010篇
金属工艺   11608篇
机械仪表   8201篇
建筑科学   7505篇
矿业工程   1821篇
能源动力   6251篇
轻工业   27770篇
水利工程   3321篇
石油天然气   6408篇
武器工业   289篇
无线电   29505篇
一般工业技术   52519篇
冶金工业   51178篇
原子能技术   6057篇
自动化技术   24063篇
  2021年   2918篇
  2020年   2253篇
  2019年   2735篇
  2018年   3765篇
  2017年   3761篇
  2016年   4271篇
  2015年   3185篇
  2014年   5071篇
  2013年   12563篇
  2012年   8401篇
  2011年   11103篇
  2010年   8813篇
  2009年   9407篇
  2008年   10336篇
  2007年   10457篇
  2006年   9150篇
  2005年   8045篇
  2004年   7232篇
  2003年   6771篇
  2002年   6767篇
  2001年   6654篇
  2000年   6236篇
  1999年   6197篇
  1998年   13285篇
  1997年   9916篇
  1996年   7608篇
  1995年   5858篇
  1994年   5380篇
  1993年   5285篇
  1992年   4240篇
  1991年   3955篇
  1990年   4070篇
  1989年   4012篇
  1988年   3766篇
  1987年   3256篇
  1986年   3300篇
  1985年   3683篇
  1984年   3581篇
  1983年   3333篇
  1982年   2909篇
  1981年   3119篇
  1980年   2858篇
  1979年   3061篇
  1978年   2949篇
  1977年   3051篇
  1976年   3872篇
  1975年   2629篇
  1974年   2442篇
  1973年   2479篇
  1972年   2081篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
In temperate seas such as the North Sea harmful (toxic) algal blooms will probably increase as a result of climate change. This conclusion was reached after investigating the projected effect of climate change for the year 2100 in Dutch coastal waters (4 degrees C temperature rise and increased water column stratification) on the growth rates of six harmful and two non-harmful phytoplankton species. Micro algae form the basis of the marine food chain. However, toxin-producing species may seriously disrupt the food web and lead to fish kills and human intoxication. Two species with estimated doubled growth rates in 2100, F. japonica and C. antiqua, entered Europe via ship's ballast water or shellfish imports. This stresses the need to legally regulate such invasion routes in order to prevent the import of novel species. Future toxic phytoplankton blooms may further devaluate ecosystem deliverables such as fish production or recreational use. This devaluation can be estimated by monetary value assessments that are needed in cost-benefit analyses for policy guidance. The lack of understanding of future climate, ecosystem functioning and its response to climate change calls for a scientific effort to improve our knowledge on present day coastal ecosystem functioning and its resilience.  相似文献   
32.
33.
Summary The effect of the addition of four commercial pectolytic preparations on the visual characteristics (colour and turbidity) of red wines has been evaluated. The effect of both clarifying and colour extracting enzymes and the effect of different doses used, were evaluated and compared. All the red wines treated enzymatically, independent of the type of enzyme and dose, present chromatic characteristics which can be considered better than those of the control wines. Also, those wines treated with enzymes had greater stability during 2 years storage in bottles, in particular the turbidity was better than untreated wines.  相似文献   
34.
35.
We present measurements of the electron, positive ion, and photon emission accompanying the fracture in vacuum of poly-crystalline 95/5 lead zirconate-titanate. The intensities of the charged-particle components of this fractoemission are shown to depend strongly on the direction (relative to the direction of fracture) and magnitude of polarization. The most intense emission is observed when the fracture surfaces are perpendicular to the polarization direction. The emission intensity increases monotonically with polarization. These results are interpreted in terms of a model involving charge separation on the fracture surfaces leading to a microdischarge during fracture. Implications to the interpretation of triboluminesence effects are discussed.  相似文献   
36.
The comfort diagrams and the so-called PMV-PPD values are already used today directly and indirectly in a wide field in technical practice, even at a standard level. This theory is known also in Hungary, and the PMV-PPD values have been used by us for the solution of a design problem. The task was to elaborate a calculation method, an index number suitable for the determination of the thermal confort effect in the case of occasional underheating of residential and communal buildings in winter.The results of this work are presented in this paper.  相似文献   
37.
New nanolayered coatings are designed and deposited on flexible plastic substrate having the thickness of 100 /spl mu/m, in order to realize lightweight ultrathin transparent shielding foils. The structure of the coating is optimized considering three figures of merit: the average transmittance in the visible range for normal incidence, the normalized average transmittance for oblique incidence at 550 nm, and the transmittance quality factor. The nanotechnology exploited for the deposition of the transparent metals is the dual ion beam sputtering. Tests of durability, optical transmission, and shielding effectiveness demonstrate that the film has a high adhesion under mechanical solicitation, high resistance against aging, peak transmittance in the visible range higher than 70%, omnidirectional properties in the range 0/spl deg/-60/spl deg/, and shielding effectiveness of 40 dB up to 6 GHz.  相似文献   
38.
39.
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   
40.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号