全文获取类型
收费全文 | 41409篇 |
免费 | 13068篇 |
国内免费 | 40篇 |
专业分类
电工技术 | 825篇 |
综合类 | 39篇 |
化学工业 | 17673篇 |
金属工艺 | 381篇 |
机械仪表 | 859篇 |
建筑科学 | 1777篇 |
矿业工程 | 23篇 |
能源动力 | 901篇 |
轻工业 | 7274篇 |
水利工程 | 306篇 |
石油天然气 | 53篇 |
武器工业 | 2篇 |
无线电 | 7031篇 |
一般工业技术 | 11709篇 |
冶金工业 | 787篇 |
原子能技术 | 55篇 |
自动化技术 | 4822篇 |
出版年
2023年 | 15篇 |
2022年 | 63篇 |
2021年 | 266篇 |
2020年 | 1443篇 |
2019年 | 3202篇 |
2018年 | 3141篇 |
2017年 | 3441篇 |
2016年 | 3906篇 |
2015年 | 3989篇 |
2014年 | 3918篇 |
2013年 | 5087篇 |
2012年 | 2785篇 |
2011年 | 2489篇 |
2010年 | 2779篇 |
2009年 | 2669篇 |
2008年 | 2247篇 |
2007年 | 2061篇 |
2006年 | 1780篇 |
2005年 | 1528篇 |
2004年 | 1421篇 |
2003年 | 1402篇 |
2002年 | 1348篇 |
2001年 | 1150篇 |
2000年 | 1111篇 |
1999年 | 482篇 |
1998年 | 103篇 |
1997年 | 81篇 |
1996年 | 70篇 |
1995年 | 48篇 |
1994年 | 48篇 |
1993年 | 57篇 |
1992年 | 42篇 |
1991年 | 37篇 |
1990年 | 34篇 |
1989年 | 23篇 |
1988年 | 28篇 |
1987年 | 26篇 |
1986年 | 18篇 |
1985年 | 30篇 |
1984年 | 20篇 |
1983年 | 29篇 |
1982年 | 10篇 |
1981年 | 22篇 |
1980年 | 16篇 |
1979年 | 13篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1973年 | 3篇 |
1970年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
91.
J. Gegner Priv.‐Doz. Dr. W. Nierlich M. Brückner 《Materialwissenschaft und Werkstofftechnik》2007,38(8):613-623
Due to clearly distinguishable damage symptoms, it is differentiated between the surface and sub‐surface failure mode of rolling bearings. Material states red out by X‐ray diffraction (XRD) residual stress measurements point to a variety of loading conditions especially at raceway surfaces that are associated with several competing failure mechanisms. The corresponding lifetime reduction can range from the lower fatigue strength region to material ratcheting in extreme cases. Relevant position of the microstructural changes and nature of the failure mechanisms are characterized. The time alteration of the XRD material parameters measured at or near the surface and at the depth of the maximum equivalent stress correlates, in a different manner, with the statistical parameter of the 10 % bearing life. Both failure modes are illustrated by concrete examples. Contaminated lubricant and boundary lubrication, which represent practically important surface‐induced failures, are discussed in more detail. Gray staining, i.e. shallow pitting, often occurs without distinct indication of global material aging by means of XRD characteristics. Here, scanning electron microscopy observations and electron microprobe analyses point to corrosion fatigue as acting surface failure mechanism. The interaction between material and lubricant under complex loading regimes particularly of mixed friction and corrosion opens further failure research areas in the field of tribology. 相似文献
92.
Ahluwalia Jasjit S.; Nollen Nicole; Kaur Harsohena; James Aimee S.; Mayo Matthew S.; Resnicow Ken 《Canadian Metallurgical Quarterly》2007,26(2):214
Objectives: Examine the effectiveness of an intervention to increase fruits and vegetables (FV) consumption among smokers. Design: Cluster-randomized trial of 20 public housing developments; 10 randomly assigned to an FV intervention and 10 to a smoking cessation intervention. Main outcome measures: Usual (past 7 days) and past 30 days change in daily FV intake at 8 weeks and 6 months postbaseline. Results: Greater increases were seen in the FV group. At Week 8 and Month 6, the FV group had consumed 1.58 (p = .001) and 0.78 (p = .04), respectively, more daily FV servings in the past 7 days than the cessation group. At the same time points, the FV group had consumed 3.61 (p = .01) and 3.93 (p = .01), respectively, more FV servings in the past 30 days than the cessation group. Completing more motivational interviewing sessions (p = .02) and trying more recipes (p = .02) led to significantly greater increases at Month 6 among FV participants. Conclusions: Motivational interviewing counseling and lifestyle modification through trying out healthy recipes may be effective in helping a high-risk population increase their FV intake. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
93.
94.
Argues that psychoanalysts have repeatedly attempted to (dis)locate homosexuals within a theory of gender that rests on essential distinctions between what is feminine and what is masculine. The best illustration of this (dis)location is the manner in which the male homosexual has been regarded as feminine. Calling gay men feminine neither sufficiently problematizes their experience of gender nor adequately captures the vicissitudes of gender. The author contends that male homosexuality is a differently structured masculinity, not a simulated femininity. Though both heterosexual and homosexual men readily identify themselves as men, the gay man's gender identity is distinguished by his experience of passivity in relation to another man. A crucial step in the treatment of any gay man is the recognition of his early gender experience. The heterosexual male analyst's countertransference difficulties with homosexual male patients are addressed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
95.
96.
97.
Y. Nakamura Ichiro Tanaka N. Takeuchi S. Koshiba H. Sakaki 《Journal of Electronic Materials》1998,27(11):1240-1243
We studied morphology of GaAs surfaces and the transport properties of two-dimensional electron gas (2DEG) on vicinal (111)B
planes. Multi-atomic steps (MASs) are found on the vicinal (111)B facet grown by molecular beam epitaxy, which will affect
electron transport on the facet. We also studied how the morphology of GaAs epilayers on vicinal (111)B substrates depends
on growth conditions, especially on the As4 flux. The uniformity of MASs on the substrates have been improved and smooth surfaces were obtained when the GaAs was grown
with high As4 flux, providing step periodicity of 20 nm. The channel resistance of the 2DEG perpendicular to the MASs is reduced drastically
with this smooth morphology. These findings are valuable not only for fabricating quantum devices on the (111)B facets but
also those on the vicinal (111)B substrates. 相似文献
98.
Richard D. Dick William L. Fourney Deborah J. Goodings Chaun‐Ping Lin Leonhard E. Bernold 《Canadian Metallurgical Quarterly》1992,5(1):59-69
The utilization of explosives for excavation on the lunar surface is under serious consideration as a part of the design for construction of temporary and permanent bases. An excavation research program has shown that small‐scale explosives blasting in a lunar‐soil simulant will greatly reduce the digging forces required for scoop and dragline excavators. Some crater‐blasting parameters were determined for the lunar soil simulant at one Earth gravity and at 10 Earth gravities using a centrifuge. The size of the craters produced at 10 Earth gs matched those formed at one earth g by scaling according to the weight of the explosive. These data can be applied to explosive‐excavation problems such as habitat construction, burial of nuclear power sources, and the rapid construction of shelters remote from the main base to shield against solar‐flare activity. 相似文献
99.
100.
J. Weise Dr.‐Ing. O. Yezerska M. Busse M. Haesche V. Zanetti‐Bueckmann M. Schmitt 《Materialwissenschaft und Werkstofftechnik》2007,38(11):901-906
Micro‐porous syntactic foams were produced by means of integration of glass bubbles into aluminium and zinc matrices. Preforms of glass bubbles were pressure infiltrated with the alloys AlSi9Cu9 ans ZnAl4Cu using squeeze casting. The preforms were sintered thermically without the use of bonding agents. Using the combination of different sintering steps syntactic foams with locally different densities could be produced. The mechanical properties of the foams were tested indicating a high compression strength of the foams and a very good compression energy absorption. Furthermore, corrosion behaviour and behaviour at higher temperatures were investigated. 相似文献