全文获取类型
收费全文 | 22844篇 |
免费 | 826篇 |
国内免费 | 83篇 |
专业分类
电工技术 | 293篇 |
综合类 | 44篇 |
化学工业 | 5146篇 |
金属工艺 | 478篇 |
机械仪表 | 461篇 |
建筑科学 | 1720篇 |
矿业工程 | 160篇 |
能源动力 | 686篇 |
轻工业 | 2136篇 |
水利工程 | 182篇 |
石油天然气 | 56篇 |
武器工业 | 1篇 |
无线电 | 1484篇 |
一般工业技术 | 4162篇 |
冶金工业 | 2773篇 |
原子能技术 | 137篇 |
自动化技术 | 3834篇 |
出版年
2023年 | 152篇 |
2022年 | 308篇 |
2021年 | 534篇 |
2020年 | 312篇 |
2019年 | 327篇 |
2018年 | 493篇 |
2017年 | 425篇 |
2016年 | 530篇 |
2015年 | 479篇 |
2014年 | 689篇 |
2013年 | 1506篇 |
2012年 | 1082篇 |
2011年 | 1518篇 |
2010年 | 1092篇 |
2009年 | 1043篇 |
2008年 | 1265篇 |
2007年 | 1099篇 |
2006年 | 939篇 |
2005年 | 865篇 |
2004年 | 774篇 |
2003年 | 690篇 |
2002年 | 660篇 |
2001年 | 392篇 |
2000年 | 376篇 |
1999年 | 412篇 |
1998年 | 412篇 |
1997年 | 372篇 |
1996年 | 341篇 |
1995年 | 294篇 |
1994年 | 301篇 |
1993年 | 297篇 |
1992年 | 250篇 |
1991年 | 214篇 |
1990年 | 201篇 |
1989年 | 230篇 |
1988年 | 186篇 |
1987年 | 177篇 |
1986年 | 174篇 |
1985年 | 239篇 |
1984年 | 214篇 |
1983年 | 184篇 |
1982年 | 168篇 |
1981年 | 195篇 |
1980年 | 130篇 |
1979年 | 147篇 |
1978年 | 143篇 |
1977年 | 127篇 |
1976年 | 138篇 |
1975年 | 120篇 |
1974年 | 105篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
End of life management (EOL) is currently a hot topic in the electronics industry. Currently, mostly IT equipment and goods of consumer electronics are considered. In the nearest future automation equipment has also to be taken into account. There are three possibilities depending on the age and kind of the device: resell–reuse–recycle, called the “3Rs”. For recycling fully or semi-automated disassembly will gain in importance in the nearest future also for robots. Producers of robots have to take into account EoL because of regulations and laws as well as according to ethical codes contributing to protection of the environment. Based on previous works a real example will be presented and discussed. 相似文献
962.
The main objective of this paper was to study the effect of precipitation on the geological development of badlands in arid
regions. Field observations and laboratory investigations were carried out to characterize the surface soils of the Avonlea
badlands in southern Saskatchewan, Canada, which is currently experiencing a rapid development in infrastructure. Three distinct
surface sediments were identified: an upper slope of cemented sandstone, a mid-slope on weathered mudrock and a relatively
flat basal pediment. Each of these soils reacts differently to rainfall events. Precipitation results in grain size reduction
which, together with the consistency limits, explains the water sensitivity of the soils; the fines increased by 16% in the
cemented sandstone, 78% in the weathered mudrock and 33% in the basal pediment. Erosion susceptibility was highest in the
basal pediment (2% clays) followed by cemented sandstone (cementation by 6% active clays) and then by weathered mudrock (cohesion
due to the 40% clay). 相似文献
963.
Poorya Hosseini Sudarshan Martins Tristan Martin Peter Radziszewski Francois-Raymond Boyer 《Minerals Engineering》2011,24(13):1440-1447
Knowledge of the internal variables of a mill is of importance in design and performance optimization of the mill, notwithstanding the difficulty in measuring these variables within the harsh mill environment. To overcome this problem, the research has focused on measuring the internal parameters through non-invasive measurement methods such as the use of the vibration/acoustic signal obtained from the mill. Alternatively, virtual instruments, such as discrete element methods (DEM), are employed. Here, a methodology is developed to simulate on-the-shell acoustic signal emitted from tumbling mills using the information extracted from a DEM simulator. The transfer function which links the forces exerted on the internal surface of the mill and the acoustic signal measured on the outer surface is measured experimentally. Given this transfer function and the force distribution obtained from the DEM simulation, and assuming a linear time-invariant response, the on-the-shell acoustic of a laboratory scale ball mill has been simulated. Comparison of this simulated signal with the signal measured experimentally can be used as a criterion to judge the validity of the DEM simulations, and as a tool for enhancing our understanding of both DEM simulations and the use of acoustics within the context of mineral processing. The results derived from preliminary experiments on a laboratory scale mill shows satisfactory agreement between the actual measurement and the simulated acoustic signal. 相似文献
964.
Karen Hovsepian Peter Anselmo Subhasish Mazumdar 《Knowledge and Information Systems》2011,26(2):195-223
We present a classification algorithm built on our adaptation of the Generalized Lotka–Volterra model, well-known in mathematical
ecology. The training algorithm itself consists only of computing several scalars, per each training vector, using a single
global user parameter and then solving a linear system of equations. Construction of the system matrix is driven by our model
and based on kernel functions. The model allows an interesting point of view of kernels’ role in the inductive learning process.
We describe the model through axiomatic postulates. Finally, we present the results of the preliminary validation experiments. 相似文献
965.
966.
Molenaar Peter C. M.; Sinclair Katerina O.; Rovine Michael J.; Ram Nilam; Corneal Sherry E. 《Canadian Metallurgical Quarterly》2009,45(1):260
Individuals change over time, often in complex ways. Generally, studies of change over time have combined individuals into groups for analysis, which is inappropriate in most, if not all, studies of development. The authors explain how to identify appropriate levels of analysis (individual vs. group) and demonstrate how to estimate changes in developmental processes over time using a multivariate nonstationary time series model. They apply this model to describe the changing relationships between a biological son and father and a stepson and stepfather at the individual level. The authors also explain how to use an extended Kalman filter with iteration and smoothing estimator to capture how dynamics change over time. Finally, they suggest further applications of the multivariate nonstationary time series model and detail the next steps in the development of statistical models used to analyze individual-level data. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
968.
Richard Weinkamer Peter Fratzl 《Materials science & engineering. C, Materials for biological applications》2011,31(6):1164-1173
Many biological materials have the property of being responsive to their environment combined with the ability to adapt to possible changes in this environment. Two prototypical responsive biological materials are presented and confronted with each other: bone and wood. These biomaterials have attracted research interest of materials scientists mainly investigating structure–property relationships. Ageing and diseases of bone and the widespread use of wood as construction material, fuel research from a medical and technological perspective. After describing the structure of bone and wood, the mechanisms of adaptation – adaptive growth and remodelling – are introduced, which allow structural changes in these biomaterials. Four examples are presented how these mechanisms are used for adaptation on different length scales starting from the shape at the macroscopic scale to the composite structure at the nanoscopic scale. In all these examples the biomaterials respond to mechanical stimuli and try to improve their mechanical performance. While some of the embarked strategies are very similar in bone and wood, like the arrangement of fibres and the architecture of the nanocomposite, differences can be observed in other situations like growing a supportive cylindrical structure or in the reorientation of structures. At the core of these differences is the capacity of living bone to deposit material where needed, but also to remove superfluous material. In contrast, a tree can only grow by adding new material. 相似文献
969.
Maike Gleichenhagen Benno F. Zimmermann Birgit Herzig Ingar Janzik Siegfried Jahnke Markus Boner Peter Stehle Rudolf Galensa 《Food chemistry》2013
The intrinsic isotopic labelling of plants with 13CO2 is an effective method to generate highly labelled compounds using photosynthesis and avoiding labour-intensive complex organic syntheses. In this study, the intrinsic isotopic labelling of polyphenols in parsley, spinach and peppermint is shown for the first time. The plants were grown in an atmosphere where 12CO2 was replaced by 13CO2, in order to generate highly labelled compounds. The total content of 13C as well as the individual polyphenols were analysed by Isotopic Ratio-MS and HPLC–Iontrap-MSn. 相似文献
970.
Heat pre-treated and non heat pre-treated whey protein isolate (WPI) were hydrolysed using α-chymotrypsin (chymotrypsin), pepsin and trypsin. The in vitro antioxidant activity, ACE-inhibition activity and surface hydrophobicities of the hydrolysates were measured in order to determine if peptides with dual functionalities were present. Dual functional peptides have both biological (e.g. antioxidant, ACE-inhibition, opioid activities) and technological (e.g. nanoemulsification abilities) functions in food systems. Heat pre-treatment marginally enhanced the hydrolysis of WPI by pepsin and trypsin but had no effect on WPI hydrolysis with chymotrypsin. With the exception of the hydrolysis by trypsin, heat pre-treatment did not affect the peptide profile of the hydrolysates as analysed using size exclusion chromatography, or the antioxidant activity (P > 0.05). Heat pre-treatment significantly affected the ACE-inhibition activities and the surface hydrophobicities of the hydrolysates (P < 0.05), which was a function of the specificity of the hydrolysing enzyme. Extended hydrolysis (up to 24 h) had no significant effect on the DH and the molecular weight profiles (P > 0.05) but in some instances caused a reduction in the antioxidant activity of WPI hydrolysates. The chymotrypsin hydrolysate showed a broad MW size range, and was followed by pepsin and then trypsin. The bioactivities of the hydrolysates generally decreased in the order; chymotrypsin > trypsin > pepsin. This study showed that by manipulating protein conformation with pre-hydrolysis heat treatment, combined with careful enzyme selection, peptides with dual functionalities can be produced from WPI for use as functional ingredients in the manufacture of functional foods. 相似文献