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   209篇
  免费   17篇
化学工业   50篇
金属工艺   8篇
机械仪表   4篇
建筑科学   9篇
矿业工程   2篇
能源动力   10篇
轻工业   41篇
水利工程   1篇
石油天然气   1篇
无线电   15篇
一般工业技术   43篇
冶金工业   21篇
自动化技术   21篇
  2023年   3篇
  2022年   4篇
  2021年   9篇
  2020年   3篇
  2019年   1篇
  2018年   15篇
  2017年   4篇
  2016年   10篇
  2015年   11篇
  2014年   11篇
  2013年   21篇
  2012年   12篇
  2011年   17篇
  2010年   15篇
  2009年   6篇
  2008年   16篇
  2007年   7篇
  2006年   8篇
  2005年   6篇
  2004年   3篇
  2003年   2篇
  2002年   10篇
  2001年   2篇
  2000年   4篇
  1999年   1篇
  1998年   6篇
  1997年   5篇
  1996年   3篇
  1995年   1篇
  1994年   3篇
  1993年   1篇
  1990年   1篇
  1988年   1篇
  1983年   1篇
  1977年   1篇
  1968年   2篇
排序方式: 共有226条查询结果,搜索用时 15 毫秒
81.
Scientific and other non-patent references (NPRs) in patents are important tools to analyze interactions between science and technology. This paper organizes a database with 514,894 USPTO patents granted globally in 1974, 1982, 1990, 1998 and 2006. There are 165,762 patents with at least one reference to science and engineering (S&E) literature, from a total of 1,375,503 references. Through a lexical analysis, 71.1% of this S&E literature is classified by S&E fields. These data serve as the basis for the elaboration of global and national 3-dimensional matrices (technological domains, S&E fields and number of references). Three indicators are proposed to analyze these matrices, allowing us to identify patterns of structured growth that differentiate developed and non-developed countries. This differentiation informs suggestions for public policies for development, emphasizing the need for an articulation between the industrial and technological dimension and scientific side. The intertwinement of these two dimensions is a key component of developmental policies for the twenty-first century.  相似文献   
82.
This report describes the meat quality of two INTA hybrids (hybrid females) sired by Duroc (D) or Yorkshire (Y) boars and a third one from PIC (S), a cross of females C22 to 412 boars. Starting at 30 kg live weight, 18 barrows and 18 gilts of each genotype were kept in identical conditions until slaughtered at 110 kg. Longissimus dorsi muscles were analyzed. Means differed significantly (P < 0.05) for drip loss (higher in S); tenderness (more tender in D), water holding capacity (higher in Y); cooking loss (higher in Y); colour parameter L (lower in D) and b (higher in S) and intramuscular fat content (higher in D). As a result of sensory analysis, it was found that D was the most tender and juicy. There were few sex effects and no genotype–sex interactions. Distinct differences in meat quality between hybrids do exist, with D superior, S the worst, and Y intermediate.  相似文献   
83.
Rapid evolution of pork production in Argentina requires new calibrations for predicting carcass lean meat percentage with the Fat-O-Meater (FOM) and Hennessy Grading Probe (HGP), first adopted in 1995. The second objective was to unify the lean percentage units with those applied by the European Union. Carcasses of 59 gilts and 56 barrows from different environments and breeds were tested. Carcass weights were from 65 to 117kg, and lean content was from 38% to 62%. Predicting lean content by multiple regression equations, the coefficients of determination R(2) were 0.801 and 0.794 for the FOM and HGP equations, and the residual standard deviations (RSD) were 2.40% and 2.45%, respectively. Both instruments had the same precision and were accurate enough to be adopted in national carcass grading classification. Hot carcass weight was not selected as a significant variable. The same prediction equations could be used for gilts and barrows. Quadratic terms did not improve predictions.  相似文献   
84.
Non-consumable electrodes are made of pure or alloyed tungsten for arc welding processes, and graphite for gouging. Yet the technical literature on arc welding has little consideration on the non-use of other materials such as thermionic emitters. Aiming to contribute to filling this knowledge gap, this study attempts to justify the unviability of the use of pure iron in the manufacture of non-consumable electrodes, and to demonstrate the thermionic emission potential of pure and thoriated tungsten and graphite electrodes. Initially, the emission areas and respective diameters for welding at 100 and 300 A at several temperatures were theoretically determined. Then, the maximum temperatures attained by the Joule effect on these electrodes at different diameters were calculated. The results were validated by means of comparison with the phenomena observed in practice. Non-consumable, pure iron electrodes were shown to be unviable, because they require extremely large diameters to emit at normal current levels below their melting temperatures. Furthermore, at these diameters, they would not be heated by the Joule effect up to the emission temperature. On the other hand, it has been demonstrated that pure and alloyed tungsten and graphite electrodes emit with smaller diameters at temperatures close to their melting/sublimation temperatures, and they quickly reach emission temperatures by the Joule effect. Despite the simplifications adopted, the need was shown for improvement of the electrodes for arc welding, and it was demonstrated that W electrode doping with lower uranium oxides limits the heating of the electrode tip, preventing the melting of its surface.  相似文献   
85.
To face innovation challenges of the twenty-first century, companies should learn from proven successful strategies and draw on technological evolutions as well. Our proposal consists in aligning ideation to innovation strategies through the use of avatars in a virtual world. On the basis of the Persona method and the Proteus effect, we design avatars’ appearance so as to implement a Need-seeker or a Technology-driver innovation strategy. To test the effectiveness of this avatar-mediated innovation tool, we conducted an experiment in a French company. Two groups of highly qualified employees from the innovation department had to find applications for smart windows in public transportation. Both groups experienced immersion in a virtual transportation situation: one group embodied avatars resembling Inventors, whereas the other group embodied Personas representing users of public transportation. As expected, avatars’ appearance proved to influence the creative production: the Inventor condition led to a techno-centered ideation profile, oriented toward technological solutions, while the Persona condition led to more user-centered, needs-oriented ideas. Consistently, Inventors’ production tended to be better evaluated through industrial criteria and Personas’ production tended to be better evaluated by transportation users. We discuss the use of avatar-mediated creativity as a strategic tool for companies seeking to innovate.  相似文献   
86.
Two-dimensional target characterization using inverse profiling approaches with total-field phaseless data is discussed. Two different inversion schemes are compared. In the first one, the intensity-only data are exploited in a minimization scheme, thanks to a proper definition of the cost functional. Specific normalization and starting guess are introduced to avoid the need for global optimization methods. In the second scheme [J. Opt. Soc. Am. A21, 622 (2004)], one exploits the field properties and the theoretical results on the inversion of quadratic operators to derive a two-step solution strategy, wherein the (complex) scattered fields embedded in the available data are retrieved first and then a traditional inverse scattering problem is solved. In both cases, the analytical properties of the fields allow one to properly fix the measurement setup and identify the more convenient strategy to adopt. Also, indications on the number and types of sources and receivers to be used are given. Results from experimental data show the efficiency of these approaches and the tools introduced.  相似文献   
87.
Background: Diabetes mellitus results in many complications, also compromising the salivary glands. The current treatment for this condition should be a substituting method to exogenous insulin. In this aspect, the immunotherapy has been tested, but, it can be inefficient as an agent for the control of damage caused by diabetes. Thus, the aim of this study was to evaluate the anti‐CD3 monoclonal antibody as alternative immunotherapy in the recovery of salivary glands of spontaneously diabetic NOD (nonobese diabetic) mice. Methods: NOD mice were divided into two groups of 10 animals: group I (untreated diabetic mice) and group II (anti‐CD3‐treated diabetic mice). After treatment, the samples of salivary glands were collected for histological examination under both transmitted and polarized light microscopy. Results: Alterations in tissue architecture; increase in extracellular matrix and presence of inflammatory process were observed in untreated animals. Recovery of the salivary acinar cells occurred in treated animals. The parotid glands demonstrated a smaller amount of collagen fibers and were not observed severe inflammatory processes. Conclusion: These results indicate that immunotherapy contributed to reestablishment of tissue damaged by the hyperglycemic condition, demonstrating that the immunomodulation plays an important role in the recovery of salivary glands. Microsc. Res. Tech., 2012. © 2012 Wiley Periodicals, Inc.  相似文献   
88.
Summary A framework is proposed for the structured specification and verification of database dynamics. In this framework, the conceptual model of a database is a many sorted first order linear tense theory whose proper axioms specify the update and the triggering behaviour of the database. The use of conceptual modelling approaches for structuring such a theory is analysed. Semantic primitives based on the notions of event and process are adopted for modelling the dynamic aspects. Events are used to model both atomic database operations and communication actions (input/output). Nonatomic operations to be performed on the database (transactions) are modelled by processes in terms of trigger/reaction patterns of behaviour. The correctness of the specification is verified by proving that the desired requirements on the evolution of the database are theorems of the conceptual model. Besides the traditional data integrity constraints, requirements of the form Under condition W, it is guaranteed that the database operation Z will be successfully performed are also considered. Such liveness requirements have been ignored in the database literature, although they are essential to a complete definition of the database dynamics.

Notation

Classical Logic Symbols (Appendix 1) for all (universal quantifier) - exists at least once (existential quantifier) - ¬ no (negation) - implies (implication) - is equivalent to (equivalence) - and (conjunction) - or (disjunction) Tense Logic Symbols (Appendix 1) G always in the future - G 0 always in the future and now - F sometime in the future - F 0 sometime in the future or now - H always in the past - H 0 always in the past and now - P sometime in the past - P 0 sometime in the past or now - X in the next moment - Y in the previous moment - L always - M sometime Event Specification Symbols (Sects. 3 and 4.1) (x) means immediately after the occurrence of x - (x) means immediately before the occurrence of x - (x) means x is enabled, i.e., x may occur next - { } ({w 1} x{w 2}) states that if w 1 holds before the occurrence of x, then w 2 will hold after the occurrence of x (change rule) - [ ] ([oa1, ..., oan]x) states that only the object attributes oa1, ..., oa n are modifiable by x (scope rule) - {{ }} ({{w}}x) states that if x may occur next, then w holds (enabling rule) Process Specification Symbols (Sects. 5.3 and 5.4) :: for causal rules - for behavioural rules Transition-Pattern Composition Symbols (Sects. 5.2 and 5.3) ; sequential composition - ¦ choice composition - parallel composition - :| guarded alternative composition Location Predicates (Sect. 5.2) (z) means immediately after the occurrence of the last event of z (after) - (z) means immediately before the occurrence of the first event of z (before) - (z) means after the beginning of z and before the end of z (during) - ( z) means before the occurrence of an event of z (at)  相似文献   
89.
90.
It was recently proposed that the induction period observed during the hydration of tricalcium silicate could be explained by the build‐up of ions in solution. Due to the importance of defects in this mechanism, this work describes the effect of different annealing effects on the defect structure and hydration behavior of C3S. The impact of annealing on the crystal structure was checked by X‐ray diffraction and the defect structure studied by transmission electron microscopy. The hydration kinetics were followed by isothermal calorimetry of pastes. Scanning electron microscopy was used to look at the microstructure formation. It was observed that grinding created a highly deformed layer on the surface of the grains, which disappeared after annealing. The defect structure was closely related to the length of the induction period observed in pastes by calorimetry. There was no observable effect on the morphology of C–S–H during hydration, but the number of calcium hydroxide nuclei was less in pastes from annealed material.  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