全文获取类型
收费全文 | 421496篇 |
免费 | 7197篇 |
国内免费 | 1146篇 |
专业分类
电工技术 | 7128篇 |
综合类 | 2896篇 |
化学工业 | 63537篇 |
金属工艺 | 15401篇 |
机械仪表 | 12415篇 |
建筑科学 | 11051篇 |
矿业工程 | 1466篇 |
能源动力 | 10301篇 |
轻工业 | 38910篇 |
水利工程 | 4031篇 |
石油天然气 | 4151篇 |
武器工业 | 12篇 |
无线电 | 50470篇 |
一般工业技术 | 79163篇 |
冶金工业 | 67681篇 |
原子能技术 | 5867篇 |
自动化技术 | 55359篇 |
出版年
2021年 | 3063篇 |
2020年 | 2301篇 |
2019年 | 2748篇 |
2018年 | 18459篇 |
2017年 | 17299篇 |
2016年 | 14228篇 |
2015年 | 4081篇 |
2014年 | 5840篇 |
2013年 | 16847篇 |
2012年 | 12329篇 |
2011年 | 20727篇 |
2010年 | 17108篇 |
2009年 | 15590篇 |
2008年 | 17420篇 |
2007年 | 18069篇 |
2006年 | 9625篇 |
2005年 | 9862篇 |
2004年 | 9595篇 |
2003年 | 9304篇 |
2002年 | 8440篇 |
2001年 | 8012篇 |
2000年 | 7743篇 |
1999年 | 8090篇 |
1998年 | 20427篇 |
1997年 | 14489篇 |
1996年 | 11181篇 |
1995年 | 8487篇 |
1994年 | 7765篇 |
1993年 | 7438篇 |
1992年 | 5464篇 |
1991年 | 5269篇 |
1990年 | 5110篇 |
1989年 | 4962篇 |
1988年 | 4835篇 |
1987年 | 4025篇 |
1986年 | 4155篇 |
1985年 | 4893篇 |
1984年 | 4428篇 |
1983年 | 4135篇 |
1982年 | 3738篇 |
1981年 | 3905篇 |
1980年 | 3584篇 |
1979年 | 3518篇 |
1978年 | 3325篇 |
1977年 | 3966篇 |
1976年 | 5197篇 |
1975年 | 2855篇 |
1974年 | 2717篇 |
1973年 | 2741篇 |
1972年 | 2258篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
991.
Review on testers for measuring flow properties of bulk solids 总被引:3,自引:2,他引:1
Jörg Schwedes 《Granular Matter》2003,5(1):1-43
The author was asked by the International Fine Particle Research Institue (IFPRI) to write a critical review on shear testers
for IFPRI-members. The review was delivered to IFPRI in summer 1999. Following the contract with IFPRI it was not allowed
to publish the review elsewhere for at least two years. Granular Matter invited the author to submit the review in the original
form; during the refereeing process (besides other changes) it turned out that some remarks should be added here for clarification:
- Since 1999, the author is not aware of a really new device for testing bulk solid properties, which could lead to a change
of the general comments and conclusions provided in the review.
It was argued, that the review is referring too much to the work of Jenike, while the works of Johanson and Peschl were not
adequately cited. Both are excellent engineers with a lot of experience, but their basic ideas are not available in published
form, and if, they are not set in relation to alternative approaches so that an objective comparison in detail would be a
future research issue rather than a topic in this report.
A discussion on the influence of electrostatic charges was missing. There hardly is an influence, since the particles are
in continuous contact. Only with non-conducting plastic particles electrostatic charges could cause problems. But no relevant
experiments and results are known. In closed systems, the effect of electric charges is thus mainly neglected, but it is clear
that electrostatic forces are eminent in flows with a free surface – an issue not addressed in this review.
Received: 1 November 2002 相似文献
992.
Combined time and wavelength multiplexing technique of optical fiber grating sensor arrays using commercial OTDR equipment 总被引:1,自引:0,他引:1
Valente L.C.G. Braga A.M.B. Ribeiro A.S. Regazzi R.D. Ecke W. Chojetzki C. Willsch R. 《IEEE sensors journal》2003,3(1):31-35
The use of a commercial optical time domain reflectometry device for simultaneous wavelength and time domain multiplexing of fiber-optic Bragg grating sensors is proposed and demonstrated. The realization of such systems provides an inexpensive way of interrogating several hundreds of sensors in a single fiber. Strain resolution of 30 /spl mu/m/m over a strain measuring range of 0.5% was obtained. 相似文献
993.
Effect of deformation route on microstructural development in aluminum processed by equal channel angular extrusion 总被引:3,自引:0,他引:3
Pei-Ling Sun Po-We Kao Chih-Pu Chang 《Metallurgical and Materials Transactions A》2004,35(4):1359-1368
Aluminum has been deformed by equal channel angular extrusion (ECAE) to obtain submicron-grained structures under different
deformation routes. The deformation routes were varied by rotating billets through 0, 90, and 180 deg between each extrusion
pass, and were designated as route A, BC, and C, respectively. Based on quantitative microstructural analysis, the effectiveness of the deformation route is shown
to depend upon the different definition used. The order of effectiveness is (a) A > BC > C for both 90 and 120 deg dies, in terms of the generation of high-angle grain boundaries (HAGBs); (b) BC > C > A for both 90 and 120 deg dies, in terms of the formation of equiaxed shape of grains; and (c) BC > A > C for 90 deg die and BC ∼ A > C for 120 die, in terms of reducing grain size. It is suggested that the generation of HAGBs can be related to the
accumulation of nonredundant strain, while the shape and orientation of grains may be linked to the shearing patterns of the
deformation route. 相似文献
994.
The present study explores the relation among 4 personality traits associated with impulsive behavior and alcohol abuse. Personality traits were measured using the 4 subscales of the UPPS Impulsive Behavior Scale (UPPS: S. P. Whiteside & D. R. Lynam. 2001). The UPPS and measures of psychopathology were administered to clinical samples of alcohol abusers high in antisocial personality traits (AAPD), alcohol abusers low in antisocial personality traits (AA), and a control group (total N = 60). Separate analyses of variance indicated that AAPDs had significant elevations on all 4 UPPS scales, whereas the AAs and controls differed only on the Urgency subscale. However, when controlling for psychopathology, group differences on the UPPS scales disappeared. The results suggest that personality traits related to impulsive behavior are not directly related to alcohol abuse but rather are associated with the elevated levels of psychopathology found in a subtype of alcohol abusers. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
995.
A fully-dense Cu-75 vol pct ZrW2O8 metal matrix composite was fabricated by hot isostatic pressing of Cu-coated ZrW2O8 particles. A small amount of the high-pressure γ-ZrW2O8 phase was created during the cooldown and depressurization following densification; near complete transformation to γ-ZrW2O8 was achieved by subsequent cold isostatic pressing. The thermal expansion behavior of the composite between 25°C and 325°C
was altered by the cold isostatic pressing treatment, and also depended on the length of time that had passed between thermal
cycles. The measured thermal expansion coefficients within specific temperature ranges varied from −6·10−6 K−1 to far above the thermal expansion coefficient of the copper matrix. The complex temperature-dependent expansion/contraction
behavior could be justified by considering the evolution of phase transformations taking place in the ZrW2O8 phase, which were observed by in-situ synchrotron X-ray diffraction measurements. 相似文献
996.
O. R. Dornyak 《Journal of Engineering Physics and Thermophysics》2003,76(3):648-654
A rheological equation of state for wood which allows for the running values of its porosity and humidity is considered. 相似文献
997.
998.
999.
Wilcox Sara; Evenson Kelly R.; Aragaki Aaron; Wassertheil-Smoller Sylvia; Mouton Charles P.; Loevinger Barbara Lee 《Canadian Metallurgical Quarterly》2003,22(5):513
This study examined whether widowhood was associated with physical and mental health, health behaviors, and health outcomes using a cross-sectional (N=72,247) and prospective (N=55,724) design in women aged 50-79 years participating in the Women's Health Initiative observational study (85.4% White). At baseline, married women reported better physical and mental health and generally better health behaviors than widowed women. Whereas women who remained married over the 3-year period showed stability in mental health, recent widows experienced marked impairments and longer term widows showed stability or slight improvements. Both groups of widows reported more unintentional weight loss over the 3-year period. Changes in physical health and health behaviors were inconsistent, with generally small effect sizes. Findings underscore the resilience of older women and their capacity to reestablish connections, but point to the need for services that strengthen social support among women who have difficulty during this transition. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
1000.
The biological decolorization of two industrial, spent textile reactive dyebaths was investigated using a suspended-growth, halophilic mixed culture fed with glucose. Dyebath I contained mainly Reactive Blue 19 (RB19), an anthraquinone dye, whereas dyebath II contained mainly Reactive Blue 21 (RB21), a phthalocyanine dye. Batch assays under anaerobic conditions with the two neutralized dyebaths resulted in 87 and 37% extent of decolorization for dyebaths I and II, respectively. The rate of glucose utilization and the extent of acetate production were impacted in the presence of each dyebath as compared to the control culture. However, dyebath decolorization occurred despite moderate culture inhibition. Reuse of a biologically renovated RB19-containing dyebath in the dyeing process resulted in reproducible but not identical cotton fabric shades as compared to a standard dyeing (i.e., control) using fresh water. This difference is attributed to a variable degree of RB19 aggregation during the dyeing process and is not related to the efficiency of the biodecolorization process. Further improvement of the redyeing efficiency will lead to the development of an in-plant, closed-loop decolorization system resulting in significant water conservation and minimization of textile pollutants such as salt and dyes. 相似文献