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   2259篇
  免费   74篇
  国内免费   4篇
电工技术   8篇
综合类   8篇
化学工业   499篇
金属工艺   22篇
机械仪表   26篇
建筑科学   173篇
矿业工程   16篇
能源动力   65篇
轻工业   260篇
水利工程   30篇
石油天然气   8篇
无线电   129篇
一般工业技术   391篇
冶金工业   281篇
原子能技术   9篇
自动化技术   412篇
  2023年   10篇
  2022年   17篇
  2021年   44篇
  2020年   34篇
  2019年   33篇
  2018年   40篇
  2017年   36篇
  2016年   35篇
  2015年   51篇
  2014年   64篇
  2013年   155篇
  2012年   84篇
  2011年   158篇
  2010年   98篇
  2009年   97篇
  2008年   124篇
  2007年   118篇
  2006年   99篇
  2005年   81篇
  2004年   65篇
  2003年   65篇
  2002年   53篇
  2001年   38篇
  2000年   39篇
  1999年   39篇
  1998年   57篇
  1997年   42篇
  1996年   37篇
  1995年   33篇
  1994年   44篇
  1993年   32篇
  1992年   29篇
  1991年   15篇
  1990年   25篇
  1989年   20篇
  1988年   27篇
  1987年   17篇
  1986年   17篇
  1985年   35篇
  1984年   24篇
  1983年   20篇
  1982年   22篇
  1981年   14篇
  1980年   15篇
  1979年   24篇
  1978年   14篇
  1977年   18篇
  1976年   24篇
  1975年   17篇
  1973年   10篇
排序方式: 共有2337条查询结果,搜索用时 15 毫秒
81.
An event-related brain potential experiment was carried out to investigate the temporal relationship between lexical selection and the semantic integration in auditory sentence processing. Participants were presented with spoken sentences that ended with a word that was either semantically congruent or anomalous. Information about the moment in which a sentence-final word could uniquely be identified, its isolation point (IP), was compared with the onset of the elicited N400 congruity effect, reflecting semantic integration processing. The results revealed that the onset of the N400 effect occurred prior to the IP of the sentence-final words. Moreover, the factor early or late IP did not affect the onset of the N400. These findings indicate that lexical selection and semantic integration are cascading processes, in that semantic integration processing can start before the acoustic information allows the selection of a unique candidate and seems to be attempted in parallel for multiple candidates that are still compatible with the bottom-up acoustic input. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
82.
This paper reports on research carried out in 1999–2001 on the use of e-business applications in enterprise resource planning (ERP)-based organisations. Multiple structured interviews were used to collect data on 11 established organisations from a diverse range of industries. The findings are analysed according to the level of sophistication of e-business models and their transformational impact on the organisation. Early adopters of e-business show a trend towards cost reductions and administrative efficiencies from e-procurement and self-service applications used by customers and employees. More mature users focus on strategic advantage and generate this through an evolutionary model of organisational change. Two complex case studies of e-business integration with global suppliers and their corporate customers are analysed to identify specific stages of benefits accrual through the e-business transformation process. Collectively, the set of case studies is used to demonstrate the increased benefits derived from an e-business architecture based on a network of ERP-enabled organisations.  相似文献   
83.
Combining implicit polynomials and algebraic invariants for representing and recognizing complicated objects proves to be a powerful technique. In this paper, we explore the findings of the classical theory of invariants for the calculation of algebraic invariants of implicit curves and surfaces, a theory largely disregarded in the computer vision community by a shadow of skepticism. Here, the symbolic method of the classical theory is described, and its results are extended and implemented as an algorithm for computing algebraic invariants of projective, affine, and Euclidean transformations. A list of some affine invariants of 4th degree implicit polynomials generated by the proposed algorithm is presented along with the corresponding symbolic representations, and their use in recognizing objects represented by implicit polynomials is illustrated through experiments. An affine invariant fitting algorithm is also proposed and the performance is studied.  相似文献   
84.
In this paper, we review an extension of the learning rules in a Principal Component Analysis network which has been derived to be optimal for a specific probability density function. We note that this probability density function is one of a family of pdfs and investigate the learning rules formed in order to be optimal for several members of this family. We show that, whereas we have previously (Lai et al., 2000; Fyfe and MacDonald, 2002) viewed the single member of the family as an extension of PCA, it is more appropriate to view the whole family of learning rules as methods of performing Exploratory Projection Pursuit. We illustrate this on both artificial and real data sets.  相似文献   
85.
Statistical models are presented to describe the evolution of the surface roughness of polishing pads during the pad-conditioning process in chemical-mechanical polishing. The models describe the evolution of the surface-height probability-density function of solid pads during fixed height or fixed cut-rate conditioning. An integral equation is derived for the effect of conditioning on a foamed pad in terms of a model for a solid pad. The models that combine wear and conditioning are then discussed for both solid and foamed pads. Models include the dependence of the surface roughness on the shape and density of the cutting tips used in the conditioner and on other operating parameters. Good agreement is found between the model, Monte Carlo simulations and with experimental data.  相似文献   
86.
Dairy calf nutrition is traditionally one of the most overlooked aspects of dairy management, despite its large effect on the efficiency and profitability of dairy operations. Unfortunately, among all animals on the dairy farm, calves suffer from the highest rates of morbidity and mortality. These challenges have catalyzed calf nutrition research over the past decade to mitigate high incidences of disease and death, and improve animal health, growth, welfare, and industry sustainability. However, major knowledge gaps remain in several crucial stages of development. The purpose of this review is to summarize the key concepts of nutritional physiology and programming from conception to puberty and their subsequent effects on development of the calf, and ultimately, future performance. During fetal development, developmental plasticity is highest. At this time, maternal energy and protein consumption can influence fetal development, likely playing a critical role in calf and heifer development and, importantly, future production. After birth, the calf's first meal of colostrum is crucial for the transfer of immunoglobulin to support calf health and survival. However, colostrum also contains numerous bioactive proteins, lipids, and carbohydrates that may play key roles in calf growth and health. Extending the delivery of these bioactive compounds to the calf through a gradual transition from colostrum to milk (i.e., extended colostrum or transition milk feeding) may confer benefits in the first days and weeks of life to prepare the calf for the preweaning period. Similarly, optimal nutrition during the preweaning period is vital. Preweaning calves are highly susceptible to health challenges, and improved calf growth and health can positively influence future milk production. Throughout the world, the majority of dairy calves rely on milk replacer to supply adequate nutrition. Recent research has started to re-evaluate traditional formulations of milk replacers, which can differ significantly in composition compared with whole milk. Transitioning from a milk-based diet to solid feed is critical in the development of mature ruminants. Delaying weaning age and providing long and gradual step-down protocols have become common to avoid production and health challenges. Yet, determining how to appropriately balance the amount of energy and protein supplied in both liquid and solid feeds based on preweaning milk allowances, and further acknowledging their interactions, shows great promise in improving growth and health during weaning. After weaning and during the onset of puberty, heifers are traditionally offered high-forage diets. However, recent work suggests that an early switch to a high-forage diet will depress intake and development during the time when solid feed efficiency is greatest. It has become increasingly clear that there are great opportunities to advance our knowledge of calf nutrition; yet, a more concentrated and rigorous approach to research that encompasses the long-term consequences of nutritional regimens at each stage of life is required to ensure the sustainability and efficiency of the global dairy industry.  相似文献   
87.
88.
89.
The study focuses on the design and construction, as well as the theoretical and experimental optimization of electrochemical filter press microreactors for the electrosynthesis of molecules with a high added value. The main characteristics of these devices are firstly a high-specific electrochemical area to increase conversion and selectivity, and secondly the shape and size of the microchannels designed for a uniform residence time distribution of the fluid. A heat exchanger is integrated into the microstructured electrode to rapidly remove (or supply) the heat required in exo- or endothermic reactions. The microreactors designed are used to perform-specific electrosynthesis reactions such as thermodynamically unfavorable reactions (continuous NADH regeneration), or reactions with high enthalpy changes.  相似文献   
90.
The implementation of synthetic guided wave focusing to locate axially aligned defects in pipes has been investigated. Results from both finite element computer models and experiments on real pipes are presented and the data show good agreement. Focusing is necessary to improve the reflection coefficient from axially aligned defects, as the signals are very weak. The Common Source Method (CSM) of synthetic focusing has been applied which makes it possible to apply focusing via post processing to previously collected data. The dependence of reflection coefficient on crack length was measured for both through thickness and part depth axially aligned defects, at a range of frequencies, using the torsional guided wave family. The results show that the reflection coefficient is approximately doubled when focusing is employed, compared to the sensitivity for unfocused fundamental torsional waves. However the sensitivity is still very low, so in practise this approach could only be used to find severe defects.  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