全文获取类型
收费全文 | 33240篇 |
免费 | 867篇 |
国内免费 | 66篇 |
专业分类
电工技术 | 366篇 |
综合类 | 35篇 |
化学工业 | 6801篇 |
金属工艺 | 861篇 |
机械仪表 | 622篇 |
建筑科学 | 1844篇 |
矿业工程 | 247篇 |
能源动力 | 1019篇 |
轻工业 | 2764篇 |
水利工程 | 335篇 |
石油天然气 | 207篇 |
武器工业 | 2篇 |
无线电 | 2224篇 |
一般工业技术 | 5236篇 |
冶金工业 | 6666篇 |
原子能技术 | 322篇 |
自动化技术 | 4622篇 |
出版年
2022年 | 196篇 |
2021年 | 388篇 |
2020年 | 335篇 |
2019年 | 401篇 |
2018年 | 491篇 |
2017年 | 512篇 |
2016年 | 527篇 |
2015年 | 465篇 |
2014年 | 741篇 |
2013年 | 2138篇 |
2012年 | 1251篇 |
2011年 | 1602篇 |
2010年 | 1173篇 |
2009年 | 1266篇 |
2008年 | 1444篇 |
2007年 | 1477篇 |
2006年 | 1259篇 |
2005年 | 1176篇 |
2004年 | 1057篇 |
2003年 | 1027篇 |
2002年 | 1034篇 |
2001年 | 637篇 |
2000年 | 621篇 |
1999年 | 582篇 |
1998年 | 611篇 |
1997年 | 504篇 |
1996年 | 607篇 |
1995年 | 548篇 |
1994年 | 540篇 |
1993年 | 535篇 |
1992年 | 486篇 |
1991年 | 321篇 |
1990年 | 440篇 |
1989年 | 428篇 |
1988年 | 379篇 |
1987年 | 425篇 |
1986年 | 382篇 |
1985年 | 516篇 |
1984年 | 491篇 |
1983年 | 444篇 |
1982年 | 464篇 |
1981年 | 445篇 |
1980年 | 354篇 |
1979年 | 365篇 |
1978年 | 329篇 |
1977年 | 307篇 |
1976年 | 270篇 |
1975年 | 320篇 |
1974年 | 243篇 |
1973年 | 279篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
31.
John Prescott 《Food quality and preference》1998,9(6):393-402
A program of research that compared the taste perceptions and preferences of Japanese and Australian consumer panels is reviewed from the point of view of the general issues that have emerged. These studies revealed few cross-cultural differences in the perceptions of the panels, implicating an important role for dietary experience in differences in preference. There was also little evidence for cross-cultural influences on panellists' assessment behaviour, such as scale usage. Studies of predominantly sweet and salty foods from both Australia and Japan illustrated the importance of familiarity with the overall product as an influence on the assessment of individual sensory characteristics. Subsequent attempts to overcome this influence by comparing cross-cultural responses to the manipulation of tastes within foods common to both cultures revealed no differences in the optimum tastant level within each of the foods. The implications of these studies for future cross-cultural research is addressed, and it is argued that future studies need to develop methods for determining the acceptability of relatively novel foods specifically developed for export markets, and also to address the complexity of food preferences from the point of view of both sensory and non-sensory influences. 相似文献
32.
A new seismic support device and its application in piping systems is described. The device, E-BAR (patented), can be cost effectively used for snubber replacement programs, mitigation of hydraulic transients, pipe whip and as a thermal stop. The device has pre-set gaps to allow free thermal movement. During a seismic or other dynamic load event, if the pipe movement exceeds the gap dimension, the device acts as an elastic or elastic-plastic restraint. The device also has a unique design feature for not exceeding the restraint force beyond a specified limit design value. To analyze piping systems with gap supports having elastic-plastic characteristics, modal analysis procedures for both response spectrum and time history methods are developed. The comparison of responses obtained from the procedures with nonlinear time history analysis and test results available in the literature shows excellent correlation. A pilot program conducted for snubber replacement with E-BARs demonstrates that the limit force feature of E-BAR makes them very attractive for snubber replacement. This is because a particular E-BAR with a specified limit design force can be selected, such that, the E-BAR replacing the snubber does not require any modifications be made to the existing support steel and hardware. 相似文献
33.
34.
William N. Gill Rajiv M. Ginde John Verhoeven 《Chemical Engineering Communications》1993,124(1):49-56
The linear theory of Pearson (1958) and Nield (1964) is modified here to study liquid tin and include the finite thermal resistances of the bounding layers of boron nitride, copper and air (∼10-2 torr) in the experiments of Ginde et al. (1989). The magnitude of the ΔTc across the layer of liquid tin required for the onset of convection depends on the ratios of the thermal conductivities and thicknesses of the supporting layers of boron nitride and copper to those of the tin.
According to our theory surface tension contributes more than buoyancy to the instability observed experimentally. The critical ΔTc observed required for the onset of convection in the layer of tin, is up to 25% lower than that predicted, which shows the layer is less stable than the theory indicates. Thus the surface of the tin was uncontaminated, or a significantly larger observed critical ΔTc would be expected.
The boundary condition on the thermal fluctuations at the base of the supporting layer of copper does not appear to be important in these experiments. However, the thermal resistance of the boron nitride would have to be assumed to be unrealistically large to obtain agreement within experimental error with the theory. 相似文献
According to our theory surface tension contributes more than buoyancy to the instability observed experimentally. The critical ΔTc observed required for the onset of convection in the layer of tin, is up to 25% lower than that predicted, which shows the layer is less stable than the theory indicates. Thus the surface of the tin was uncontaminated, or a significantly larger observed critical ΔTc would be expected.
The boundary condition on the thermal fluctuations at the base of the supporting layer of copper does not appear to be important in these experiments. However, the thermal resistance of the boron nitride would have to be assumed to be unrealistically large to obtain agreement within experimental error with the theory. 相似文献
35.
Many companies are using Just-In-Time (JIT) control systems in their mixed-model multi-level production facilities. When scheduling these facilities the most important objective is to keep a constant rate of usage for every part used by the system. In this paper a mathematical model for scheduling these facilities is studied and techniques for determining good schedules are developed. Procedures for solving very large problems are given. 相似文献
36.
John E. Lowther 《Journal of the American Ceramic Society》2002,85(1):55-58
Diamond and BN have common relatively soft precursor structures that are hexagonal. Electronic structure calculations have now revealed subtle energy differences between the two materials. Another hard material, stishovite, also has a relatively soft precursor phase, quartz, and here again electronic structure calculations have given insight into the nature of the phase transformation. On the other hand, with boron-related materials, the main focus is to connect basic icosahedra structures to produce a hard material. The structural aspects of these materials are examined and possible consequences for low- and high-coordination ultrahard nitrides considered. 相似文献
37.
Aqueous extracts of the coralline red algaeBossiella orbigniana have been shown to catalyze the enzymatic oxidation of arachidonic acid to a previously unreported ω6 eicosapentaenoic acid
product. This unique fatty acid contains a conjugated tetraene with absorption maxima at 293, 306, and 321 nm, and was identified
by spectral methods as 5(Z),8(Z),10(E),12(E),14(Z)-eicosapentaenoic acid. The compound was given the trivial name bosseopentaenoic
acid. Under experimental conditions, production of bosseopentaenoic acid was linear up to 2 hr and dioxygen was consumed.
Bosseopentaenoic acid, along with several other conjugated tetraenes, was also present in the algae endogenously as revealed
by a comparison of the ultraviolet (UV) spectra and the high-performance liquid chromatographic (HPLC) pattern of the purified
product and the organic extract ofBossiella. 相似文献
38.
Collaborative filtering (CF) involves predicting the preferences of a user for a set of items given partial knowledge of the user's preferences for other items, while leveraging a database of profiles for other users. CF has applications e.g. in predicting Web sites a person will visit and in recommending products. Fundamentally, CF is a pattern recognition task, but a formidable one, often involving a huge feature space, a large data set, and many missing features. Even more daunting is the fact that a CF inference engine must be capable of predicting any (user-selected) items, given any available set of partial knowledge on the user's other preferences. In other words, the model must be designed to solve any of a huge (combinatoric) set of possible inference tasks. CF techniques include memory-based, classification-based, and statistical modelling approaches. Among these, modelling approaches scale best with large data sets and are the most adept at handling missing features. The disadvantage of these methods lies in the statistical assumptions (e.g. feature independence), which may be unjustified. To address this shortcoming we propose a new model-based CF method, based on the maximum entropy principle. For the MS Web application, the new method is demonstrated to outperform a number of CF approaches, including naive Bayes and latent variable (cluster) models, support vector machines (SVMs), and the (Pearson) correlation method. 相似文献
39.
40.