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   1168篇
  免费   51篇
电工技术   15篇
综合类   1篇
化学工业   286篇
金属工艺   38篇
机械仪表   19篇
建筑科学   52篇
矿业工程   1篇
能源动力   30篇
轻工业   186篇
水利工程   37篇
石油天然气   5篇
无线电   82篇
一般工业技术   148篇
冶金工业   192篇
原子能技术   11篇
自动化技术   116篇
  2023年   6篇
  2022年   15篇
  2021年   40篇
  2020年   19篇
  2019年   18篇
  2018年   23篇
  2017年   25篇
  2016年   34篇
  2015年   24篇
  2014年   41篇
  2013年   67篇
  2012年   64篇
  2011年   80篇
  2010年   61篇
  2009年   61篇
  2008年   56篇
  2007年   48篇
  2006年   55篇
  2005年   30篇
  2004年   35篇
  2003年   35篇
  2002年   36篇
  2001年   21篇
  2000年   20篇
  1999年   17篇
  1998年   56篇
  1997年   42篇
  1996年   21篇
  1995年   22篇
  1994年   17篇
  1993年   23篇
  1992年   8篇
  1991年   8篇
  1990年   4篇
  1989年   6篇
  1988年   9篇
  1987年   13篇
  1985年   9篇
  1984年   9篇
  1983年   2篇
  1982年   3篇
  1981年   2篇
  1980年   7篇
  1979年   5篇
  1978年   2篇
  1977年   6篇
  1976年   3篇
  1975年   2篇
  1974年   3篇
  1970年   2篇
排序方式: 共有1219条查询结果,搜索用时 578 毫秒
101.
This article describes the effect of educational level on the decision to continue smoking among 1,354 initially smoking participants (age≥20 years) in the Dutch GLOBE study. The effect of education continued smoking was explained from baseline information (1991) on smoking characteristics, individual characteristics, and environmental factors. Smoking status was reassessed after 6.5 years. Lower educated smokers more often continued smoking (odds ratio 2.09). Poor perceived health and earlier smoking initiation in lower educated groups were main predictors of educational differences in smoking maintenance. Educational differences in chronic illness, perceived control, neuroticism, and emotional support also contributed to the explanation of educational differences in continued smoking. These results have important implications for intervention programs and policy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
102.
Different types of coatings were characterised for: swelling by moisture, moisture permeability, elastic modulus and extensibility. These data were used to calculate maximum internal stress. Internal stress was also measured directly whilst changing temperature and humidity. The stress data were compared to cracking and flaking results in both natural and accelerated weathering tests. Results showed that high levels of stress occur if there is a difference in swelling between coating and wood. In most cases stress relaxation took place rapidly. Comparing maximum stress, extensibility and cracking, a good correlation between these data was found. The ratio between maximum stress and extensibility appeared to be a very good predictor for crack formation.  相似文献   
103.
An Initial Experimental Assessment of the Dynamic Modelling in UML   总被引:1,自引:1,他引:0  
The goal of this empirical study is to compare the semantic comprehension of three different notations for representing the dynamic behaviour in unified modelling language (UML): (a) sequence diagrams, (b) collaboration diagrams, and (c) state diagrams. Eighteen students of Informatics analysed the three types of diagrams within three different application domains. We performed a 3 × 3 factorial experimental design with repeated measures. The metrics collected were total time and total score. The main conclusion of this study is that the comprehension of the dynamic modelling in object-oriented designs depends on the diagram type and on the complexity of the document. The software project design written in the UML notation is more comprehensible, when the dynamic behaviour is modelled in a sequence diagram. While if it is implemented using a collaboration diagram, the design turns out to be less comprehensible as the application domain, and consequently, the document is more complex.  相似文献   
104.
Design-Operation of Multi-Hydropower Reservoirs: HBMO Approach   总被引:6,自引:5,他引:1  
To illustrate and test the applicability and performance of the innovative honey-bee mating optimization (HBMO) algorithm in highly non-convex hydropower system design and operation, two problems are considered: single reservoir and multi-reservoir. Both hydropower problems are formulated to minimize the total present net cost of the system, while achieving the maximum possible ratio for generated power to installed capacity. The single hydropower reservoir problem is approached by the developed algorithm in 10 different runs. The first feasible solution was generated initially and later improved significantly and solutions converged to a near optimal solution very rapidly. In the application of the proposed algorithm to a five-reservoir hydropower system with 48 periods and a total of 230 decision variables, in early mating flights, the first feasible solution was identified and the results converged to a near optimal solution in later mating flights. In the case of the multi-reservoir problem, an efficient gradient-based nonlinear-programming solver (LINGO 8.0) failed to find a feasible solution and for the single hydropower reservoir design problem it performed much worse than the proposed algorithm.  相似文献   
105.
In this paper, we discuss basic issues related to measurements performed in the domains of software engineering and metrology. Similarities and differences are highlighted, with the aim of analyzing the level of knowledge in both domains. A theoretical approach is followed, allowing the proposal of a measurement process model, which is used as a guiding scheme throughout the paper to illustrate peculiarities arising when taking software measurements. Common ground between metrologists and software engineers are described by discussing foundations of measurement in the software context.  相似文献   
106.
Review of book: Feminism and Its Discontents: A Century of Struggle with Psychoanalysis. Cambridge, MA: Harvard University Press, 1998, 448 pp. Reviewed by Elaine Hoffman Baruch. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
107.
In the present work, we studied the microstructure, phase constitution, and corrosion performance of Al88Pd12, Al77Pd23, Al72Pd28, and Al67Pd33 alloys (metal concentrations are given in at.%). The alloys were prepared by repeated arc melting of Al and Pd granules in argon atmosphere. The as-solidified samples were further annealed at 700 °C for 500 h. The microstructure and phase constitution of the as-solidified and as-annealed alloys were studied by scanning electron microscopy, energy-dispersive x-ray spectroscopy, and x-ray diffraction. The alloys were found to consist of (Al), ε n (~ Al3Pd), and δ (Al3Pd2) in various fractions. The corrosion testing of the alloys was performed in aqueous NaCl (0.6 M) using a standard 3-electrode cell monitored by potentiostat. The corrosion current densities and corrosion potentials were determined by Tafel extrapolation. The corrosion potentials of the alloys were found between ? 763 and ? 841 mV versus Ag/AgCl. An active alloy dissolution has been observed, and it has been found that (Al) was excavated, whereas Al in ε n was de-alloyed. The effects of bulk chemical composition, phase occurrence and microstructure on the corrosion behavior are evaluated. The local nobilities of ε n and δ are discussed. Finally, the conclusions about the alloy’s corrosion resistance in saline solutions are provided.  相似文献   
108.
The presence of denticles in the external surface, oral cavity, fins, and clasper of Elasmobranchii has been widely reported. These structures, called body denticles, may be observed on the body surface of sharks. Dermal and oral denticles are made up by a basal plate that is embedded in the dermis, forming a peduncle that grows from the base to the crown. These denticles may protect the skin against abrasion, and improve hydrodynamics and gill arches function. Rhizoprionodon lalandii is a widely distributed and very common species in Brazilian coastal areas. The aims of this study was to compare the morphology of oral and body denticles of R. lalandii to understand the implications of these structures in the behavior of these animals. Morphological analysis showed that there are differences between dermal and oral denticles, which are related to their role in different body regions. Body denticles have three cusps, and well‐defined crests and ridges, and literature data suggest that suggest that hydrodynamics is their main function. Most of the oral denticles have only one cusp, and their morphology and distribution showed that their main functions are preparing food to be swallowed and protecting the oral cavity against abrasion. Microsc. Res. Tech. 78:859–864, 2015. © 2015 Wiley Periodicals, Inc.  相似文献   
109.
Nanoparticles were prepared by the thermosensitive aggregation of the elastin model polypeptide, (GVGVP)251, and gamma-ray crosslinking. Three different heating processes, “slow heating,” “fast heating,” and “heat shock,” were used for the aggregation of the peptide, followed by gamma-ray crosslinking. Only the “heat shock” process successfully yielded stable nanoparticles with diameters of less than ca. 150 nm and a narrow size distribution. Circular dichroism (CD) spectrometry showed that this polypeptide formed a type-II β-turn structure when the temperature was increased to above the cloudy point in the case of the “heat shock” process; suggesting that this structure might contribute to stable nanoparticle formation by gamma-rays. CD spectrometry also suggested that this structure would be affected during the formation of stable crosslinked particles.  相似文献   
110.
Females of the solitary endoparasitoid Cotesia vestalis respond to a blend of volatile organic compounds (VOCs) released from plants infested with larvae of their host, the diamondback moth (Plutella xylostella), which is an important pest insect of cruciferous plants. We investigated the flight response of female parasitoids to the cruciferous plant Brassica rapa, using two-choice tests under laboratory conditions. The parasitoids were more attracted to plants that had been infested for at least 6 hr by the host larvae compared to intact plants, but they did not distinguish between plants infested for only 3 hr and intact plants. Although parasitoids preferred plants 1 and 2 days after herbivory (formerly infested plants) over intact plants they also preferred plants that had been infested for 24 hr over formerly infested plants. This suggests that parasitoids can distinguish between the VOC profiles of currently and formerly infested plants. We screened for differences in VOC emissions among the treatments and found that levels of benzyl cyanide and dimethyl trisulfide significantly decreased after removal of the host larvae, whereas terpenoids and their related compounds continued to be released at high levels. Benzyl cyanide and dimethyl trisulfide attracted parasitoids in a dose-dependent manner, whereas the other compounds were not attractive. These results suggest that nitrile and sulfide compounds temporarily released from plants under attack by host larvae are potentially more effective attractants for this parasitoid than other VOCs that are continuously released by host-damaged plants.  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