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   6958篇
  免费   235篇
  国内免费   15篇
电工技术   195篇
综合类   31篇
化学工业   1441篇
金属工艺   184篇
机械仪表   122篇
建筑科学   367篇
矿业工程   54篇
能源动力   171篇
轻工业   1231篇
水利工程   69篇
石油天然气   22篇
无线电   429篇
一般工业技术   941篇
冶金工业   958篇
原子能技术   95篇
自动化技术   898篇
  2022年   54篇
  2021年   122篇
  2020年   83篇
  2019年   102篇
  2018年   124篇
  2017年   115篇
  2016年   137篇
  2015年   127篇
  2014年   188篇
  2013年   312篇
  2012年   212篇
  2011年   262篇
  2010年   234篇
  2009年   247篇
  2008年   253篇
  2007年   221篇
  2006年   200篇
  2005年   156篇
  2004年   169篇
  2003年   150篇
  2002年   157篇
  2001年   109篇
  2000年   95篇
  1999年   115篇
  1998年   215篇
  1997年   172篇
  1996年   122篇
  1995年   109篇
  1994年   95篇
  1993年   81篇
  1992年   66篇
  1991年   65篇
  1990年   76篇
  1989年   73篇
  1988年   61篇
  1987年   69篇
  1986年   59篇
  1985年   72篇
  1984年   70篇
  1983年   69篇
  1982年   62篇
  1981年   51篇
  1980年   52篇
  1979年   53篇
  1978年   68篇
  1977年   71篇
  1976年   81篇
  1975年   65篇
  1974年   62篇
  1973年   69篇
排序方式: 共有7208条查询结果,搜索用时 296 毫秒
71.
72.
Twenty-nine selected styles of subprimals or sections of veal were obtained from a commercial facility to assist in the development of a support program for retailers. They were fabricated into bone-in or boneless retail cuts and associated components by trained meat cutters. Each style selected (n = 6) was used to generate mean retail yields and labor requirements, which were calculated from wholesale and retail weights and processing times. Means and standard errors for veal ribs consisting of five different styles (n = 30) concluded that style #2, 7-rib 4 (10 cm) x 4 (10 cm), had the lowest percentage of total retail yield (P < .05) owing to the greatest percentage of bone. Furthermore, rib style #2 required the longest total processing time (P < .05). Rib styles #3, 7-rib chop-ready, and #5, 6-rib chop ready, yielded the greatest percentage of total retail yield and also had the shortest total processing time (P < .05). Within veal loins, style #2, 4 (10 cm) x 4 (10 cm) loin kidney fat in, had the greatest percentage fat (P < .05). Loin styles #2 and #3, 4 (10 cm) x 4 (10 cm) loin special trimmed, generated more lean and fat trimmings and bone, resulting in lower percentage of total retail yields than loin style #1, 0 (0 cm) x 1 (2.5 cm) loin special trimmed (P < .05). Results indicated that bone-in subprimals and sections required more processing time if fabricated into a boneless end point. In addition, as the number of different retail cuts increased, processing times also increased.  相似文献   
73.
Buck变换器又称降压变换器、串联开关稳压电源、三端开关型降压稳压器。广泛用于计算机、家用电器、控制系统和通信系统中的电源几乎都是开关电源,具有超快速负载动态响应、高功率变换效率、高功率密度、低电压、大电流的特性.开关变换器作为它的主要电路,故障率较高,对它故障诊断研究是有意义的。基于强跟踪滤波理论,给出了一种开关变换器电路故障实时诊断的一种方法。该方法以建立一种开关变换器电路状态空间模型为基础,利用强跟踪滤波器对电路状态及元件参数进行估计,当元件参数发生软、硬型故障时,根据强跟踪滤波器对元件参数的跟踪结果及修正的Bayes分类算法,可实时诊断开关变换器电路中的元件故障。仿真结果证明了该方法的有效性。  相似文献   
74.
For stochastic multi-objective combinatorial optimization (SMOCO) problems, the adaptive Pareto sampling (APS) framework has been proposed, which is based on sampling and on the solution of deterministic multi-objective subproblems. We show that when plugging in the well-known simple evolutionary multi-objective optimizer (SEMO) as a subprocedure into APS, ε-dominance has to be used to achieve fast convergence to the Pareto front. Two general theorems are presented indicating how runtime complexity results for APS can be derived from corresponding results for SEMO. This may be a starting point for the runtime analysis of evolutionary SMOCO algorithms.  相似文献   
75.
Numerical simulations are used to estimate the dynamic behavior of new concepts of forming presses as well as to improve the dynamic properties of existing machines. These simulations are to be parametrized with appropriate values in order to yield most accurate results. In many cases neither the way of building up the simulation model for the specific problem nor an appropriate method for gathering the needed date are given in advance. Regarding these facts this paper intends both to characterize the way of building up complex simulation models by using basic simulation modules and to describe methods for the identification of the needed parameters that work even under conditions that hitherto made parameter identifications impossible or at least very time-consuming. In this context recent developments in simulating press dynamics will also be characterized as new modal analysis methods that are not yet established in the field of forming technique. The research activities were financed by the European Research Association for Sheet Metal Working.  相似文献   
76.
This paper describes the kinetics of attrition in the bubbling zone of a fluidized bed and focuses on the development of an equation for attrition in continuous fluidized beds operating at steady state.

Laboratory data describing batch attrition of a limestone sorbent are applied to the integrated equations to describe overall attrition rate in a full-scale continuous system.  相似文献   
77.
Two extruded-expelled physically refined soybean oils with reduced contents of linolenic acid, ultra-low- linolenic acid (ULL, 1.5%) and low-linolenic acid (LL, 2.6%), and a extruded-expelled physically refined control oil (control, 5.3% linolenic acid) were evaluated by frying French fries in a commercial-like setting for 6 h day−1 during 23 days. The oils became darker, increased in yellow color at the beginning, and became redder and less green throughout the process. Free fatty acids levels were not different among the oils until day 14, after which, ULL was different from the control for the remainder of frying. The conjugated dienoic acid values were greatest in the control. Generally, ULL and LL oils had lower percentages of polar compounds than did the control, providing a frying life 2 days longer than the control and ~30% increase in frying time. A trained sensory panel evaluated the French fries on days 2, 5, and 6. Buttery and potato flavors decreased, and rancid and painty flavors increased over frying time for all products. Rancid flavor was highest in the fries from the control oil. Overall, the ULL and LL oils performed better than did the control oil and ULL tended to perform better than the LL.  相似文献   
78.
The decomposition of 1,2-dichloroethane on polycrystalline copper has been studied using a microreactor. The reaction is found to have an activation energy of 81±5 kJ mol–1 generating gaseous ethene and chemisorbed chlorine. The reaction terminates on completion of a monolayer of chemisorbed chlorine and is followed by a much slower reaction. The rate limiting step is thought to be C2H4Cl2(phys)C2H4Cl(ads)+Clads The reaction is compared with a UHV study of the same molecule on Cu(l 11) and the possibility of a negative ion transition state is discussed.  相似文献   
79.
The secondary diamine 1,3,5,7-tetrahydro[1,2c:4,5c'] benzodipyrrole (3) and 1,2,4,5-tetrabromomethylbenzene (1) form a polymeric ionene with spirane structure through a repetitive alkylation reaction. The structure of the product could be proven by13C-NMR spectroscopy by comparison with suitable reference compounds. Solutions in aqueous methanol exhibit a typical polyelectrolyte effect. Variation of the counterions produces sufficient solubility in organic solvents. From the crystal structure of a similar model compound one can conclude that the synthesized polymer has a rod-like shape.  相似文献   
80.
Various plant secondary metabolites related to cinnamic acid are of interest because of their repellency to birds and their occurrence in ecologically important food items. Coniferyl benzoate (CB), a phenylpropanoid ester that occurs in quaking aspen (Populus tremuloides) is of particular ecological interest because of its effect on ruffed grouse (Bonasa umbellus) feeding behavior and its possible influence on the population dynamics of this bird. During detoxification processes, CB and other analogous compounds are metabolized into by-products, such as ferulic acid (FA), that can cause anti-reproductive effects. We tested whether consumption of CB produces antire-productive effects similar to FA using male and female Japanese quail (Coturnix coturnix) as avian models for ruffed grouse. The parameters we investigated included: the production, morphology, and development of eggs; reproductive characteristics influenced by estrogen; serum prolactin levels; and male reproductive behavior. Dietary CB did not produce antireproductive effects similar to FA at intake levels that Japanese quail and ruffed grouse would freely consume. Consumption of CB by Japanese quail significantly reduced egg production and body mass but did not affect male reproductive performance. Coniferyl benzoate's effect on egg production may be explained by lower energy acquisition and retention rather than endocrine changes per se. Contrary to previous reports, it is unlikely that FA, or similar compounds act directly as estrogen mimics or antagonists. Although, CB did reduce egg production in quail, it is unlikely that it would affect egg production in wild ruffed grouse. Detoxification costs and the effects of CB on nutrient utilization may explain why ruffed grouse avoid high dietary levels of CB.  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