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   13708篇
  免费   1132篇
  国内免费   410篇
电工技术   675篇
综合类   537篇
化学工业   2176篇
金属工艺   553篇
机械仪表   592篇
建筑科学   739篇
矿业工程   163篇
能源动力   413篇
轻工业   1358篇
水利工程   217篇
石油天然气   310篇
武器工业   76篇
无线电   1784篇
一般工业技术   1873篇
冶金工业   1681篇
原子能技术   174篇
自动化技术   1929篇
  2024年   50篇
  2023年   206篇
  2022年   406篇
  2021年   661篇
  2020年   469篇
  2019年   413篇
  2018年   490篇
  2017年   449篇
  2016年   474篇
  2015年   510篇
  2014年   660篇
  2013年   840篇
  2012年   860篇
  2011年   967篇
  2010年   726篇
  2009年   651篇
  2008年   663篇
  2007年   569篇
  2006年   475篇
  2005年   391篇
  2004年   330篇
  2003年   291篇
  2002年   316篇
  2001年   235篇
  2000年   215篇
  1999年   240篇
  1998年   560篇
  1997年   360篇
  1996年   275篇
  1995年   172篇
  1994年   166篇
  1993年   142篇
  1992年   84篇
  1991年   88篇
  1990年   67篇
  1989年   79篇
  1988年   48篇
  1987年   44篇
  1986年   45篇
  1985年   52篇
  1984年   44篇
  1983年   47篇
  1982年   44篇
  1981年   32篇
  1980年   35篇
  1979年   27篇
  1978年   25篇
  1977年   53篇
  1976年   75篇
  1973年   19篇
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
51.
Polyarteritis nodosa is a rare disorder and a form of systemic vasculitis. A 48 year-old female was admitted to the hospital because menorrhagia and pelvic pain in February 1993. The patient underwent exploratory laparotomy resulting in a total hysterectomy and bilateral salpingo-oophorectomy for myoma of uterus and a right adnexal cystic mass. Histopathologic examination revealed left ovarian periarteritis nodosa. Further investigation and 9 months follow-up failed to show any systemic involvement. To our knowledge the isolated ovarian polyarteritis nodosa is the first case in the literature.  相似文献   
52.
53.
For the first time, a direct optically injection-locked oscillator based on the Esaki-Tsu effect in superlattices is reported. The microwave output power is -7 dBm at 20 GHz with an optical input power of -10 dBm at a wavelength of 1.3 μm  相似文献   
54.
In this paper, we study the dynamic survivable routing problem, both in optical networks without wavelength conversion and in optical networks with sparse wavelength conversion, and propose a novel hybrid algorithm for it based on the combination of mobile agents technique and genetic algorithms (GA). By keeping a suitable number of mobile agents in the network to cooperatively explore the network states and continuously report cycles (that are formed by two disjoint-link routes) into the routing tables, our new hybrid algorithm can promptly determine the first population of cycles for a new request based on the routing table of its source node, without the time consuming process associated with current GA-based lightpath protection schemes. We further improve the performance of our algorithm by introducing a more advanced fitness function that is suitable for both the above networks. Extensive simulation studies on the ns-2 network simulator show that our hybrid algorithm achieves a significantly lower blocking probability than the conventional survivable routing algorithms for all the cases we studied.  相似文献   
55.
The Mn0.23Ga1.85S3 phase belongs to the solid solution ф0, stable at low temperature in the Ga2S3MnS system. It is hexagonal superstructure of the wurtzite, with the Ga2S3α′ type (a = 6.397 A?; c = 18.027 A?Z = 6; space groupe P61 or P65). Its crystal structure has been refined by the least squares method to a final R = 0.06 with 323 independant reflections. This structure is closely related to Ga2S3 α described by Hahn and Frank, and differs only by the partial occupation of the vacant metal site of Ga2S3 by Mn atoms in statistical disorder.  相似文献   
56.
强化措施抓好落实全面推进农村饮水安全工作   总被引:6,自引:0,他引:6  
陈雷 《中国水利》2007,(10):I0001-I0001
民以食为天,食以水为先。获得安全饮用水是人类生存的基本需求。 党中央、国务院领导高度重视饮水安全工作,要求把“切实保护好饮用水源,让群众喝上放心水”作为首要任务,把“让人民群众喝上干净的水、呼吸清新的空气,有更好的工作和生活环境”作为政府工作的目标。  相似文献   
57.
Among the new semiconductor materials for telecom devices, the GaInNAs-GaAs structure presents interesting properties for low-cost applications, like high differential gain and high T/sub 0/. Another key aspect of the performance is the behavior of the GaInNAs-GaAs based lasers under high bit rate direct modulation. Here, we demonstrate the dynamic capabilities of GaInNAs-GaAs three-quantum-well ridge structure through 2.5-Gb/s directly modulated laser emission and transmission on standard fiber, in the temperature range 25/spl deg/C-85/spl deg/C. Besides transmission is demonstrated up to 10 Gb/s at 25/spl deg/C on the same fiber, without penalty and bit-error-rate floor.  相似文献   
58.
In this paper we consider two performance modelling techniques from the perspectives of model construction, generation of an underlying continuous time Markov process, and the potential for reduction in the Markov process. Such careful comparison of modelling techniques allows us to appreciate the strengths and weaknesses of different approaches, and facilitates cross-fertilization between them. In the present case we take a characteristic of one formalism, functional rates in Stochastic Automata Networks, and introduce it to the other formalism, Performance Evaluation Process Algebra. We investigate the benefits of this cross-fertilization, particularly from the perspectives of Markov process generation and reduction.  相似文献   
59.
In this work we present a bulk silicon technology platform able to cointegrate gate-all-around (GAA) MOSFETs and local SOI waveguides with pentagonal cross section. Wire diagonals of 100-800 nm are obtained using a lithographic resolution of 0.8 mum. Well-functioning triangular multigate MOSFETs are reported, and tested up to 150 degC. A significant increase is observed in the low-field mobility mu0 for small devices (Weffles500 nm), which is attributed to local volume inversion in the corners. Preliminary characterization of the optical waveguides is carried out, showing optical losses of a few dB/cm. The processing is entirely CMOS compatible, does not require access to advanced lithography equipment, and is based on a silicon bulk substrate. Thus, this technology might serve as the basis for a low-cost, high-performance optical signaling platform  相似文献   
60.
In Part I of this paper, a theoretical basis is presented using a two-degrees-of-freedom model. In this second part of the study, the passive control and the two types of semiactive controls introduced in Part I are examined numerically for a taut cable experiencing wind-induced galloping motion. The passive and the semiactive control schemes for taut cables show a good similarity with the results obtained for the two-degrees-of-freedom model. The potential of using these control schemes in practical applications to flexible structures is demonstrated.  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