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   320899篇
  免费   10315篇
  国内免费   5156篇
电工技术   9463篇
技术理论   7篇
综合类   5645篇
化学工业   51369篇
金属工艺   14664篇
机械仪表   11978篇
建筑科学   11667篇
矿业工程   3539篇
能源动力   7214篇
轻工业   29987篇
水利工程   4270篇
石油天然气   9090篇
武器工业   857篇
无线电   35245篇
一般工业技术   55746篇
冶金工业   49827篇
原子能技术   6322篇
自动化技术   29480篇
  2022年   3670篇
  2021年   5397篇
  2020年   3885篇
  2019年   3856篇
  2018年   5187篇
  2017年   5543篇
  2016年   5604篇
  2015年   5635篇
  2014年   8031篇
  2013年   15444篇
  2012年   12029篇
  2011年   15013篇
  2010年   12352篇
  2009年   12772篇
  2008年   13498篇
  2007年   13128篇
  2006年   11696篇
  2005年   10012篇
  2004年   8330篇
  2003年   7536篇
  2002年   7465篇
  2001年   7457篇
  2000年   6875篇
  1999年   6836篇
  1998年   13618篇
  1997年   10173篇
  1996年   7881篇
  1995年   6070篇
  1994年   5515篇
  1993年   5298篇
  1992年   4180篇
  1991年   3961篇
  1990年   3963篇
  1989年   3881篇
  1988年   3624篇
  1987年   3076篇
  1986年   3103篇
  1985年   3441篇
  1984年   3344篇
  1983年   3098篇
  1982年   2719篇
  1981年   2918篇
  1980年   2664篇
  1979年   2851篇
  1978年   2738篇
  1977年   2844篇
  1976年   3697篇
  1975年   2459篇
  1974年   2292篇
  1973年   2321篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
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   
52.
53.
Sol–gel films are actively investigated during the last decade as possible candidates for environmentally friendly pre-treatments. However, the important drawback in this case is the lack of active corrosion protection and self-healing ability.  相似文献   
54.
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   
55.
56.
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   
57.
In the approach to a cycle-invariant state in the forced feed concentration cycling of the CO oxidation over a NiO catalyst, a very long transient has been observed lasting 80 ks or more. This transient appears to be associated only with CO pretreatment of the catalyst and is not a general phenomenon. The slow convergence to the cycle-invariant state reported in certain modelling calculations in the literature appears to have a different cause.  相似文献   
58.
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   
59.
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   
60.
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