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   74748篇
  免费   706篇
  国内免费   689篇
电工技术   1428篇
综合类   47篇
化学工业   11161篇
金属工艺   3444篇
机械仪表   2637篇
建筑科学   1638篇
矿业工程   503篇
能源动力   1851篇
轻工业   6377篇
水利工程   845篇
石油天然气   2303篇
武器工业   41篇
无线电   7193篇
一般工业技术   16438篇
冶金工业   12405篇
原子能技术   2627篇
自动化技术   5205篇
  2022年   573篇
  2021年   904篇
  2020年   696篇
  2019年   777篇
  2018年   1549篇
  2017年   1562篇
  2016年   1760篇
  2015年   944篇
  2014年   1555篇
  2013年   3562篇
  2012年   2355篇
  2011年   2817篇
  2010年   2367篇
  2009年   2638篇
  2008年   2614篇
  2007年   2551篇
  2006年   2181篇
  2005年   1911篇
  2004年   1837篇
  2003年   1786篇
  2002年   1703篇
  2001年   1676篇
  2000年   1669篇
  1999年   1562篇
  1998年   3665篇
  1997年   2598篇
  1996年   1934篇
  1995年   1521篇
  1994年   1326篇
  1993年   1348篇
  1992年   994篇
  1991年   1050篇
  1990年   1071篇
  1989年   1050篇
  1988年   940篇
  1987年   874篇
  1986年   877篇
  1985年   934篇
  1984年   777篇
  1983年   766篇
  1982年   675篇
  1981年   689篇
  1980年   661篇
  1979年   646篇
  1978年   620篇
  1977年   773篇
  1976年   930篇
  1975年   580篇
  1974年   551篇
  1973年   543篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Recent developments of stability control in mines, essentially based on Ge-doped fiber Bragg gratings (FBG) are reported including results about the different aspects of the system: accurate characterizations of FBG, sensor network topology and multiplexing method, user interface design and sensor packaging  相似文献   
102.
103.
This study focuses on the perception of large scale application of nuclear energy and coal in the Netherlands and France. The application of these energy-sources and the risks and benefits are judged differently by various group in society. In Europe, France has the highest density of nuclear power plants and the Netherlands has one of the lowest. In both countries scientists and social scientists completed a questionnaire assessing the perception of the large scale application of both energy sources. Furthermore, a number of variables relating to the socio cultural and political circumstances were measured. The results indicate that the French had a higher risk perception and a more negative attitude toward nuclear power than the Dutch. But they also assess the benefits of the use of nuclear power to be higher. Explanations for these differences are discussed.  相似文献   
104.
This paper describes the construction of four probes adjusted for fast transient monitoring in 123 kV SF6 insulated substations. The primary requirement was the ability to monitor without distortion very fast transients containing frequencies up to 200 MHz. The measuring system was tested and calibrated with the help of computer modeling techniques. The verified experimental apparatus was then used for testing and calibrating the measuring probes. During the test, various effects on the measuring system characteristics were analyzed with respect to materials used for the components of the system  相似文献   
105.
While cellular transformation by small DNA tumour viruses usually involves targeting the product of the p53 tumour suppressor gene by a virally encoded protein, none of the three polyoma virus (Py) specified T antigens have been observed to interact with p53. We show that primary mouse embryo fibroblasts and REF52 cells, which resemble primary cells in requiring co-operating oncogenes for transformation, cannot be transformed by the Py oncogene, middle T-antigen (PyMT), alone. These cells can be transformed by the complete Py early region, which encodes the Py large, middle and small T-antigens. We find that PyMT can transform rodent cells lacking a functional p53 protein (p53 null mouse embryo fibroblasts and DN-REF52 cells which contain a dominant negative p53). In Py transformed REF52 cells (Py-REF52) there is no significant accumulation of p53 protein, as opposed to SV40 transformed REF52 cells (SV-REF52) in which the amount of steady state p53 protein is elevated. However accumulation of p53 is observed following exposure of Py-REF52 cells to u.v. Treatment of Py-REF52 cells with X-rays results in a rapid increase in the levels of the p53-induced proteins p21/WAF1 and MDM2. In untransformed REF52 cells, X-irradiation causes p53 activation, which results in induction of both G1/S and G2/M blocks. In SV-REF52 and DN-REF52 cells, p53 abrogation results in the absence of both the G1/S and G2/M blocks. Only the absence of a G1/S block is observed in Py-REF52 cells exposed to X-irradiation. Together these results indicate that in contrast to most other DNA tumour viruses, Py does not appear to interfere with the DNA damage induced transactivation activities of the p53 protein but absence of a functional p53 protein can mediate transformation by the PyMT oncogene in the absence of other co-operating oncogenes. Possible modes of transformation by Py are discussed.  相似文献   
106.
Translated from Khimicheskoe i Neftyanoe Mashinostroenie, No. 4, pp. 32–33, April, 1991.  相似文献   
107.
108.
109.
110.
Microbial deterioration of materials – case histories and countermeasures: Legal aspects of environmental protection Biofouling is a natural process. Usually, it does not cause too much harm if taken care of properly. If biofouling is fought by special means, problems may arise. The waste water does not meet the due standards. Sometimes the recipe of the treatment agent is not known. If the treatment causes more problems than it can solve help is needed quickly. Yet, it is advisable to keep one's mind clear. Wrong help can become very expensive. In addition, legal punishment will follow, if environmental legislation is hurt. Damages of the environment will be payed by an insurance company only, if the risk is covered by the insurance contract in advance. The best way to be sure is to have a good lawyer, a good expert in environmental techniques and environmental legislation, a good insurance, and to anticipate possible risks.  相似文献   
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