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   497501篇
  免费   5626篇
  国内免费   1825篇
电工技术   9247篇
综合类   410篇
化学工业   75614篇
金属工艺   21175篇
机械仪表   14582篇
建筑科学   12270篇
矿业工程   2260篇
能源动力   12185篇
轻工业   45719篇
水利工程   4733篇
石油天然气   8274篇
武器工业   19篇
无线电   57982篇
一般工业技术   94789篇
冶金工业   96466篇
原子能技术   10630篇
自动化技术   38597篇
  2021年   3437篇
  2019年   3205篇
  2018年   5636篇
  2017年   5515篇
  2016年   5997篇
  2015年   4130篇
  2014年   6954篇
  2013年   21464篇
  2012年   11458篇
  2011年   15878篇
  2010年   12926篇
  2009年   14560篇
  2008年   15369篇
  2007年   15322篇
  2006年   13799篇
  2005年   12793篇
  2004年   12097篇
  2003年   11917篇
  2002年   11933篇
  2001年   11902篇
  2000年   11092篇
  1999年   11759篇
  1998年   29444篇
  1997年   21240篇
  1996年   16417篇
  1995年   12358篇
  1994年   10995篇
  1993年   10804篇
  1992年   7951篇
  1991年   7897篇
  1990年   7347篇
  1989年   7297篇
  1988年   7188篇
  1987年   6111篇
  1986年   6067篇
  1985年   7082篇
  1984年   6583篇
  1983年   6024篇
  1982年   5618篇
  1981年   5768篇
  1980年   5541篇
  1979年   5304篇
  1978年   5373篇
  1977年   6373篇
  1976年   8749篇
  1975年   4791篇
  1974年   4570篇
  1973年   4587篇
  1972年   3913篇
  1971年   3601篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Thirty patients who had undergone either a right or left unilateral temporal lobectomy (14 RTL; 16 LTL) and 16 control participants were tested on a computerized human analogue of the Morris Water Maze. The procedure was designed to compare allocentric and egocentric spatial memory. In the allocentric condition, participants searched for a target location on the screen, guided by object cues. Between trials, participants had to walk around the screen, which disrupted egocentric memory representation. In the egocentric condition, participants remained in the same position, but the object cues were shifted between searches to prevent them from using allocentric memory. Only the RTL group was impaired on the allocentric condition, and neither the LTL nor RTL group was impaired on additional tests of spatial working memory or spatial manipulation. The results support the notion that the right anterior temporal lobe stores long-term allocentric spatial memories. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
62.
63.
Mathematical models of thermomechanical processes which are based on the laws of rational thermodynamics of irreversible processes are treated. Singular features of the unsteady-state behavior of a continuous medium are demonstrated within different models, such as a medium with internal parameters of state, a medium with memory, and a medium of the velocity type.  相似文献   
64.
Managing sewerage systems is a highly complex task due to the dynamic nature of the facilities. Their performance strongly depends on the know-how applied by the operators. In order to define optimal operational settings, two decision support tools based on mathematical models have been developed. Moreover, easy-to-use interfaces have been created as well, aiding operators who presumably do not have the necessary skills to use modelling software. The two developed programs simulate the behaviour of both wastewater treatment plants (WWTP) and sewer network systems, respectively. They have essentially the same structure, including raw data management and statistical analysis, a simulation layer using the application programming interface of the applied software and a layer responsible for the representation of the obtained results. Four user modes are provided in the two software including the simulation of historical data using the applied and novel operational settings, as well as modes concerning prediction of possible operation periods and updates. Concerning the WWTP software, it was successfully installed in Nantes (France) in June 2004. Moreover, the one managing sewer networks has been deployed in Saint-Malo (France) in January 2005. This paper presents the structure of the developed software and the first results obtained during the commissioning phase.  相似文献   
65.
66.
67.
Prodrugs of mitomycin C (MMC) based on soluble poly-[N-(2-hydroxyethyl)-L-glutamine] (pHEG) polymers have been evaluated as tumour-targeted drugs. These materials are designed to exploit the enhanced permeability of tumour vasculature, combining a passive tumour tropism with decreased systemic liberation of free MMC. A tri- or tetrapeptide linkage (e.g. Gly-Phe-Ala-Leu) between pHEG and the aziridine nitrogen of MMC can combine good hydrolytic stability with rapid cleavage by lysosomal enzymes, releasing free MMC. The conjugates showed decreased systemic toxicity and could be administered to mice at a total MMC dose of 15 mg/kg i.v., compared with just 6 mg/kg for free MMC. Conjugates also showed better activity against animal models of established tumours, achieving up to 77% increased life span (ILS) against solid P388 leukaemia, compared with only 23% for free MMC, and up to 121% ILS against solid C26 colorectal carcinoma, compared with no activity for the free drug. Improving the therapeutic index of anticancer drugs by combining tumour tropism with decreased systemic toxicity is a versatile approach that should produce a new generation of improved anticancer agents.  相似文献   
68.
The impact of crosstalk in an arrayed-waveguide N×N wavelength multiplexer is investigated precisely in relation to its application to wavelength-routing N×N all optical networks. In such systems multiple crosstalk light which has the same wavelength as the signal results in signal-crosstalk beat noise. We confirm that the noise is Gaussian and obtain the relation between crosstalk and power penalty. It is shown that the crosstalk must be less than -38 dB for a 16×16 system to keep the power penalty below 1 dB at a bit error rate of 10-9  相似文献   
69.
In summary, recent literature indicates that the complications of chronic otitis media have been decreasing. However, even with the advent of modern and more powerful antimicrobials and aggressive surgical eradication of disease, the morbidity and mortality are still high. Some complications may initially be quite obvious and some complications may be quite subtle. Therefore, the most important tools in making early diagnosis are careful history and physical examination, and a high index of suspicion for impending complications.  相似文献   
70.
For pt.I see ibid., vol.43, no.6, pp.1150-9 (1996). An exact solution of the electrostatic problem for calculating the surface charge and electric field distributions in an arbitrary periodic interdigital transducer (IDT) is given using the results of our companion paper. An arbitrary external electric field may be specified along the electrode structure with the unit cell containing one electrode, or several electrodes, of different widths. The potentials of the electrodes that may be specified are also arbitrary. It is shown that in the case without an external field, the solution includes all the known results as special cases. The case of shorted electrodes in the external electric field is investigated in detail. The surface charge and electric field distributions are calculated for a spatially harmonic external field with an arbitrary wavenumber. The results of the calculations are represented graphically for various ratios between the period of the electrode structure and the wavelength of the external field for the case of a unit cell containing one or two electrodes of different widths  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