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   61713篇
  免费   4230篇
  国内免费   1011篇
电工技术   1443篇
综合类   1726篇
化学工业   13763篇
金属工艺   1755篇
机械仪表   1878篇
建筑科学   2646篇
矿业工程   517篇
能源动力   1660篇
轻工业   10891篇
水利工程   892篇
石油天然气   975篇
武器工业   138篇
无线电   3667篇
一般工业技术   8386篇
冶金工业   6891篇
原子能技术   386篇
自动化技术   9340篇
  2024年   187篇
  2023年   713篇
  2022年   1784篇
  2021年   2417篇
  2020年   1772篇
  2019年   1713篇
  2018年   2256篇
  2017年   2333篇
  2016年   2342篇
  2015年   2259篇
  2014年   3020篇
  2013年   4834篇
  2012年   4490篇
  2011年   4711篇
  2010年   3792篇
  2009年   3607篇
  2008年   3337篇
  2007年   3029篇
  2006年   2354篇
  2005年   1846篇
  2004年   1398篇
  2003年   1268篇
  2002年   1011篇
  2001年   775篇
  2000年   641篇
  1999年   633篇
  1998年   2276篇
  1997年   1505篇
  1996年   980篇
  1995年   568篇
  1994年   459篇
  1993年   436篇
  1992年   183篇
  1991年   145篇
  1990年   118篇
  1989年   129篇
  1988年   134篇
  1987年   132篇
  1986年   102篇
  1985年   121篇
  1984年   97篇
  1983年   68篇
  1982年   68篇
  1981年   87篇
  1980年   93篇
  1979年   52篇
  1978年   61篇
  1977年   123篇
  1976年   243篇
  1973年   52篇
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
121.
122.
The martensitic transformation temperatures and the types of martensitic phases have been determined in a wide concentration range of technological interest for Cu-Al-Ni shape-memory alloys (SMAs) A stability diagram of martensitic phases as a function of alloy concentration has been determined. It is found that when the aluminum content increases, the transformation changes from β 3β3 to β 3γ3, with an intermediate concentration range where both martensites coexist due to a β 3γ3+β3 transformation. On the other hand, an increase of nickel content stabilizes the martensite β3, changing from a mixed β 3γ3 + β3 to a single β 3β3 transformation. Furthermore, linear relationships between M s and Al and Ni concentrations have been obtained for all types of martensitic phases.  相似文献   
123.
124.
介绍了本钢不停产安装再造煤气管道鼓形膨胀器的实践,并对制造、安装方法进行了叙述,特别是在结构上采用了独特的构槽密封焊缝和完整的安装程序,保证了实施的安全。  相似文献   
125.
126.
PURPOSE OF THE STUDY: Impaction in pertrochanteric fracture sites is a well known phenomenon; the screw-plate system is designed to stabilise the fracture. Although easier to use, the risk with the nail-plate system is postoperative penetration of the nail into the joint. The present study was conducted to determine the exact conditions of the impaction, and to identify possible ways to improve the nail-plate system. MATERIAL-METHOD: The study included 129 cases of pertrochanteric fracture, excluding sub-trochanteric fractures. All fractures were fixed with a 130 degrees angulated nail-plate. In all cases, consolidation was uneventful after 8 to a 12 weeks. The anatomical type of fracture, i.e. stable or unstable, was determined according to the size of the intermediary fragment, including the trochanter minor. The displacement was measured as the difference between the length of the nail and the length of the femoral head and neck measured along the axis of the femoral neck. The parameters examined were: fracture stability degree, bony mineralisation (Singh Index), nail length, femoral neck, length nail position in the femoral head, and above all, fracture reduction. All these parameters were computerised and compared using Stat View statistics software. RESULTS: Impaction was observed in 43 per cent of cases. Among these, 25 per cent were rated as slight (1 to 5 mm), 18 per cent as moderate (over 5 mm) and 9 per cent as marked (10 to 25 mm). Impaction was associated with demineralisation of the bone tissue (p = 0.001). The anatomical classification of the fracture was not a determining factor (p = 0.19), as marked displacements were also recorded in stable fractures. A posterior and inferior position of the intramedullary nail in the femoral head is one of displacement determining factors (p = 0.004, two-sided 1 test). Valgus over-correction is the most important factor, especially when it is associated with bony demineralisation (p = 0.02) and an inadequately centred intramedullary pin (p = 0.02). Shorter the femoral neck, and shorter the nail, greater was the frequency of nail articular penetration. DISCUSSION: The risk of articular penetration therefore reaches 15 per cent in petrochanteric fractures repaired with a nail plate, set at an angle of 130 degrees. A short neck, a cervicodiaphyseal angle superior to 140 degrees, and demineralisation are the three determining parameters. Stable or unstable fracture has in fact little effect on displacement incidence, and therefore does not, on its own, warrant the use of a prosthesis in comminuted fractures. The authors compared their results to literature on progressive sliding system: the incidence of complications associated with this type of fracture treatment is identical, but the determining parameters are different. CONCLUSION: The study shows that the nail-plate is efficient and provides simple and solid fracture fixation. However, this osteosynthesis material needs to be modified in order to improve its fixation in the femoral head.  相似文献   
127.
BACKGROUND: It is not clear if old age is a risk factor for adverse drug reactions. AIM: To study the incidence of adverse drug reactions and the effect of age in patients admitted to an Internal Medicine Service in an university hospital. PATIENTS AND METHODS: Two hundred one patients, hospitalized at the Clinical Hospital of the Catholic University, were studied. These patients were followed using a prospective pharmacological surveillance method. For statistical purposes, patients aged 65 years old or older were compared with those younger than 65 years old. RESULTS: Patients over 65 years old had a 33% incidence of adverse drug reactions, mainly involving cardiovascular system and provoking metabolic disturbances. Younger subjects had a 24% incidence of adverse drug reactions, mainly involving the gastrointestinal system and the skin. Sixteen percent of adverse drug reactions were classified as severe and there was a direct relationship between its frequency and the number of drugs prescribed, the hospitalization length and the presence of renal failure. Younger patients with adverse drug reactions had lower serum albumin levels than those without adverse reactions. This relationship was not observed in older patients. CONCLUSIONS: The frequency of adverse drug reactions in hospitalized patients, is related to the number of drugs prescribed and the length of hospitalization.  相似文献   
128.
Proper integration of scheduling and control in Flexible Manufacturing Systems will make available the required level of decision-making capacity to provide a flexibly-automated, efficient, and quality manufacturing process. To achieve this level of integration, the developments in computer technology and sophisticated techniques of artificial intelligence (AI) should be applied to such FMS functions as scheduling. In this paper, we present an Intelligent Scheduling System for FMS under development that makes use of the integration of two AI technologies. These two AI technologies — Neural Networks and Expert Systems — provide the intelligence that the scheduling function requires in order to generate goodschedules within the restrictions imposed by real-time problems. Because the system has the ability to plan ahead and learn, it has a higher probability of success than conventional approaches. The adaptive behavior that will be achieved contribute to the integration of scheduling and control in FMS.  相似文献   
129.
Describes radio receivers that monitor transmissions from beacons on geosynchronous satellites. The receivers can detect ionospheric perturbations of a 300-3000 s period in the electron density integrated from beacon to receiver, for amplitudes as low as (1-2)×1013 m-2. Data are used in studies of atmospheric acoustic and acoustic-gravity waves  相似文献   
130.
This study, guided in part by G. A. Marlatt and J. R. Gordon's (1985) abstinence violation effect (AVE) model, examined whether variability in cognitive and emotional reactions to binges accounts for recurrence of binge eating. Attributional, cognitive, and affective reactions to 2 successive binges, as well as the latencies between each binge and a subsequent binge, were evaluated through a series of structured phone interviews with 50 nonpurging normal-weight female bingers. Reported mood after binging was unrelated to binge latency. However, when Ss made more intense internal, global, and uncontrollable causal attributions for a binge, a subsequent binge followed significantly sooner. Within-subject variations in AVEs across binges prospectively predicted within-subject variations in the speed with which another binge followed. Analyses suggested that cognitive states (e.g., AVE and guilt) evoked by particular events were better predictors of how quickly binging repeats than were stable differences in attributional style. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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