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   245203篇
  免费   3087篇
  国内免费   1229篇
电工技术   4929篇
综合类   270篇
化学工业   35764篇
金属工艺   10914篇
机械仪表   7102篇
建筑科学   6306篇
矿业工程   482篇
能源动力   6355篇
轻工业   24319篇
水利工程   1918篇
石油天然气   1338篇
武器工业   3篇
无线电   31244篇
一般工业技术   45224篇
冶金工业   50297篇
原子能技术   3912篇
自动化技术   19142篇
  2021年   1680篇
  2019年   1438篇
  2018年   2349篇
  2017年   2247篇
  2016年   2471篇
  2015年   1973篇
  2014年   3212篇
  2013年   10860篇
  2012年   5482篇
  2011年   7847篇
  2010年   6334篇
  2009年   7011篇
  2008年   7608篇
  2007年   7714篇
  2006年   7080篇
  2005年   6576篇
  2004年   6283篇
  2003年   6293篇
  2002年   6281篇
  2001年   6393篇
  2000年   5829篇
  1999年   6447篇
  1998年   16628篇
  1997年   11659篇
  1996年   8995篇
  1995年   6719篇
  1994年   5941篇
  1993年   5745篇
  1992年   4065篇
  1991年   4011篇
  1990年   3597篇
  1989年   3510篇
  1988年   3457篇
  1987年   2922篇
  1986年   2851篇
  1985年   3425篇
  1984年   3062篇
  1983年   2753篇
  1982年   2557篇
  1981年   2581篇
  1980年   2439篇
  1979年   2282篇
  1978年   2243篇
  1977年   2816篇
  1976年   4181篇
  1975年   1903篇
  1974年   1796篇
  1973年   1788篇
  1972年   1464篇
  1971年   1318篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
The Jerada anthracite mine in Morocco was abandoned in 2001 after producing approximately 20 million tonnes of solid waste. The acid generating potential of these wastes was determined by performing tests on five samples collected from relatively older and more recent waste deposits. No carbonate minerals were identified. Pyrite was the only sulphide mineral observed and much of it had been completely transformed into Fe-oxides. Analysis of the waste indicated low levels (<1 %) of Ca and Mg, while Fe and Al concentrations generally exceeded 5 %. Modified Sobek static tests and column kinetic tests were conducted for 24 months. The static test results were not conclusive (20 <net neutralising potential <20 Kg CaCO3/t). Leachates from the kinetic tests for three of the five samples showed an initially acidic pH, while those of the remaining two became acidic by the end of the tests. Sulfate concentrations (SO4 2?) decreased over time from 5000 to 200 mg/L.  相似文献   
62.
Russian Journal of Non-Ferrous Metals - Using a Thermo-Calc software package (TCAl4.0 database), unexplored data concerning the phase composition and crystallization behavior of...  相似文献   
63.
Russian Journal of Non-Ferrous Metals - In this paper, using the AA 511 alloy of the Al–Mg–Si system as an example, it is shown that the irradiation of aluminum melts with nanosecond...  相似文献   
64.
Vehicle legislation for safety and emission control is led by the USA where half the world's cars and one‐third of the world's road deaths are found. The 1975/6 standards will cause confrontations between industry and government in the U.S.A. and have costly implications for the American people. The rest of the world is affected by what happens in the U.S.A. but for language and other reasons fragmented laws are normal with conflicting requirements for manufacturers who supply the many markets. The greatest force for harmonization of legislation may be the enlarged Common Market including, as it does, the four major European Car manufacturing countries. The Common Market Commission may displace WP 29 of the United Nations as the leading law‐making body. Type approval is the compliance system used in Europe, but the growth in scope of safety and other legislation is bringing into focus a weakness of the system which is reducing production efficiency to an alarming degree. American style self‐certification is not acceptable to European governments.  相似文献   
65.
The development of an enormous culture gap, in which no individuals of advanced societies possess even a billionth of the non‐genetic information possessed by their entire society, has threatened a global collapse of civilisation. Critical parts of that gap must be rapidly bridged so that problems such as climate disruption, toxification of the Earth, loss of biodiversity and ecosystem services, and the decay of the epidemiological environment can be satisfactorily attacked. The essential need is to alter human behaviour to put society on a route to sustainability; one cheering development is a growing interest in the Millennium Assessment of Human Behaviour (MAHB), whose goal is to do just that.  相似文献   
66.
The paper reports an assessment of the soil and water in the coastal strip between Marsa Alam and Shalateen at the southern part of the Red Sea coast of Egypt. There is limited potential for agricultural development. There is a need for water re-use and some potential for tourism.  相似文献   
67.
Processing municipal and industrial wastes on land and particularly near inhabited centra has met with increased opposition. An apparent remedy to the problem is the establishment of such facilities offshore, hence various projects to build them on artificial islands. The paper examines a concrete proposal to locate such an island offshore from the Belgian Coast. Oceanographic and environmental aspects of the site are discussed, construction methods reviewed, erosion and corrosion effects looked at. The possibility of utilizing ocean power to provide the necessary operation energy is likewise considered.  相似文献   
68.
69.
70.
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