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   2494篇
  免费   109篇
  国内免费   15篇
电工技术   32篇
化学工业   648篇
金属工艺   58篇
机械仪表   62篇
建筑科学   57篇
矿业工程   2篇
能源动力   170篇
轻工业   219篇
水利工程   23篇
石油天然气   13篇
无线电   274篇
一般工业技术   625篇
冶金工业   144篇
原子能技术   31篇
自动化技术   260篇
  2023年   59篇
  2022年   103篇
  2021年   132篇
  2020年   84篇
  2019年   99篇
  2018年   135篇
  2017年   102篇
  2016年   116篇
  2015年   74篇
  2014年   93篇
  2013年   195篇
  2012年   122篇
  2011年   144篇
  2010年   109篇
  2009年   113篇
  2008年   109篇
  2007年   86篇
  2006年   44篇
  2005年   32篇
  2004年   34篇
  2003年   38篇
  2002年   36篇
  2001年   32篇
  2000年   24篇
  1999年   21篇
  1998年   30篇
  1997年   30篇
  1996年   23篇
  1995年   17篇
  1994年   18篇
  1993年   21篇
  1992年   20篇
  1991年   12篇
  1990年   11篇
  1989年   17篇
  1988年   26篇
  1987年   14篇
  1986年   19篇
  1985年   26篇
  1984年   21篇
  1983年   26篇
  1982年   18篇
  1981年   28篇
  1980年   18篇
  1979年   12篇
  1978年   13篇
  1977年   9篇
  1976年   14篇
  1975年   13篇
  1974年   8篇
排序方式: 共有2618条查询结果,搜索用时 46 毫秒
1.
Wireless Personal Communications - Recently, the theory of effective rate has attracted much attention, since it can take the delay aspect into account when performing channel capacity analysis. In...  相似文献   
2.
3.
Wireless Personal Communications - Traffic network is basically a “network of networks” consisting of mainly two types of networks: road network and a travel network. Due to drastic...  相似文献   
4.
5.
Multimedia Tools and Applications - In the way of communication, facial expression act as non-verbal communication and play an important role in social interaction by providing some contextual...  相似文献   
6.
Building useful systems with an ability to understand "real" natural language input has long been an elusive goal for Artificial Intelligence. Well-known problems such as ambiguity, indirectness, and incompleteness of natural language inputs have thwarted efforts to build natural language interfaces to intelligent systems. In this article, we report on our work on a model of understanding natural language design specifications of physical devices such as simple electrical circuits. Our system, called KA, solves the classical problems of ambiguity, incompleteness and indirectness by exploiting the knowledge and problem-solving processes in the situation of designing simple physical devices. In addition, KA acquires its knowledge structures (apart from a basic ontology of devices) from the results of its problem-solving processes. Thus, KA can be bootstrapped to understand design specifications and user feedback about new devices using the knowledge structures it acquired from similar devices designed previously.In this paper, we report on three investigations in the KA project. Our first investigation demonstrates that KA can resolve ambiguities in design specifications as well as infer unarticulated requirements using the ontology, the knowledge structures, and the problem-solving processes provided by its design situation. The second investigation shows that KA's problem-solving capabilities help ascertain the relevance of indirect design specifications, and identify unspecified relations between detailed requirements. The third investigation demonstrates the extensibility of KA's theory of natural language understanding by showing that KA can interpret user feedback as well as design requirements. Our results demonstrate that situating language understanding in problem solving, such as device design in KA, provides effective solutions to unresolved problems in natural language processing.  相似文献   
7.
Results of scanning electron microscopy (SEM) and energy dispersive X-ray analytical (EDAX) investigations, conducted on some elevated structures displayed by flux grown rare earth orthochromite, RCrO3 (R = La, Yb) crystals, are presented. The peculiar structures exhibited by crystal surfaces indicate imperfections and impurity phases. EDAX of elevated structures reveals the various phases to be composed of lead associated materials which may probably be either Pb2CrO5 or Pb2OF2 (flux). Other secondary crystallization of impurity phases, ROF (R = La, Yb) is illustrated in the case of RCrO3 (R = La, Yb) crystals. The elevated structures illustrate their non-stoichiometric behaviour. Precipitation of impurity phases and formation of imperfections during the growth of RCrO3 (R = La, Yb) crystals and their effect on the crystalline quality is discussed.  相似文献   
8.
An attempt is made to elucidate the electrochemical aspects of the electroosmotic dewatering (EOD) of clays as reported in some recent work, especially that on interrupted DC power electroosmotic dewatering published by Rabie, Mujumdar and Weber (2). These authors showed that the dewatering by EOD stops after the DC power has been on for several minutes or hours; on interruption of their power and on short-circuiting of the electrodes, conditions can be created again for some further dewatering by DC power EOD. This discovery, of Rabie et al. is interpreted as a fuel cell effect and it is shown that it affords clues to several other electrochemical strategies for the possible enhancement of the efficiency of the EOD by DC power.

Further, the open circuit potentials observed by Rabie et al. (2) on the interruption of DC power are given an electrochemical interpretation which leads to quantitative estimates in agreement with the experimental values.  相似文献   
9.
The effectiveness of a combined regimen of mifepristone and vaginal misoprostol for termination of pregnancies of 9-13 weeks of gestation was investigated in 120 UK abortion patients (median age, 22.1 years; median duration of amenorrhea, 10.3 weeks). Each woman received a single oral dose of 200 mg of mifepristone 36-48 hours before admission, at which time 800 mcg of misoprostol was administered vaginally. Where indicated, a further two doses of 400 mcg of misoprostol (vaginal or oral) were provided every 3 hours. All 120 women aborted on the day of prostaglandin administration; however, 6 women (5%) required exploratory curettage after the procedure for retained placenta. The median prostaglandin dose was 1200 mcg (range, 800-1600 mcg). The median time from misoprostol administration to abortion was 4.33 hours (range, 1.3-16.0 hours). 60 women (50%) required oral analgesics and 26 (22%) received parenteral analgesia. Diarrhea occurred in 38 women (32%). The median duration of bleeding after abortion was 12.5 days (range, 3-43 days). In questionnaires administered to 73 women, only 3 (4%) expressed dissatisfaction with medical abortion, because of pain or prolonged bleeding. The relatively high dose of misoprostol used in this study and the vaginal route of administration are presumed to account for the 95% success rate. Extension of medical abortion to later gestation times would decrease the need for surgery and expand women's choice of methods of pregnancy termination.  相似文献   
10.
Higher order elastic constants have been calculated in ZnS at 300 K and 500 K following the interaction potential model. Ultrasonic attenuation, velocity and other related parameters have been calculated using the higher order elastic constants for the different size of the material at 500 K. The size dependency of the ultrasonic properties is discussed in correlation with elastic, thermal and electrical properties. It has been found that the thermal conductivity is the main contributor to the behaviour of the ultrasonic attenuation as a function of the size and the responsible cause of attenuation is phonon-phonon interaction. The semiconducting nature of ZnS film has been achieved with the study of size variation of thermal relaxation time and ultrasonic attenuation.  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