全文获取类型
收费全文 | 280526篇 |
免费 | 3429篇 |
国内免费 | 1319篇 |
专业分类
电工技术 | 4842篇 |
综合类 | 527篇 |
化学工业 | 40771篇 |
金属工艺 | 11213篇 |
机械仪表 | 8491篇 |
建筑科学 | 6435篇 |
矿业工程 | 1589篇 |
能源动力 | 7118篇 |
轻工业 | 22621篇 |
水利工程 | 3060篇 |
石油天然气 | 5786篇 |
武器工业 | 43篇 |
无线电 | 33960篇 |
一般工业技术 | 57063篇 |
冶金工业 | 51139篇 |
原子能技术 | 7511篇 |
自动化技术 | 23105篇 |
出版年
2021年 | 2285篇 |
2019年 | 2134篇 |
2018年 | 3679篇 |
2017年 | 3745篇 |
2016年 | 3992篇 |
2015年 | 2545篇 |
2014年 | 4439篇 |
2013年 | 12131篇 |
2012年 | 7163篇 |
2011年 | 9855篇 |
2010年 | 7641篇 |
2009年 | 8871篇 |
2008年 | 9198篇 |
2007年 | 9215篇 |
2006年 | 7883篇 |
2005年 | 7317篇 |
2004年 | 7247篇 |
2003年 | 7025篇 |
2002年 | 6757篇 |
2001年 | 6889篇 |
2000年 | 6531篇 |
1999年 | 6800篇 |
1998年 | 16373篇 |
1997年 | 11625篇 |
1996年 | 8952篇 |
1995年 | 6884篇 |
1994年 | 6060篇 |
1993年 | 6098篇 |
1992年 | 4440篇 |
1991年 | 4226篇 |
1990年 | 4108篇 |
1989年 | 4078篇 |
1988年 | 3770篇 |
1987年 | 3412篇 |
1986年 | 3415篇 |
1985年 | 3760篇 |
1984年 | 3487篇 |
1983年 | 3230篇 |
1982年 | 3039篇 |
1981年 | 3046篇 |
1980年 | 3044篇 |
1979年 | 2843篇 |
1978年 | 2877篇 |
1977年 | 3153篇 |
1976年 | 4115篇 |
1975年 | 2418篇 |
1974年 | 2385篇 |
1973年 | 2401篇 |
1972年 | 2020篇 |
1971年 | 1785篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
112.
P. Sampath Brijesh Kakarla Raghava Reddy C. Venkata Reddy Nagaraj P. Shetti Raghavendra V. Kulkarni Anjanapura V. Raghu 《化学工程与技术》2020,43(7):1240-1248
Hydrogen fuel is a promising alternative to fossil fuels because of its energy content, clean nature, and fuel efficiency. However, it is not readily available. Most current producion processes are very energy intensive and emit carbon dioxide. Therefore, this article reviews technological options for hydrogen production that are eco-friendly and generate clean hydrogen fuel. Biological methods, such different fermentation processes and photolysis are discussed together with the required substrates and the process efficiency. 相似文献
113.
F. Schröder R. M. Ward A. R. Walpole R. P. Turner M. M. Attallah J.-C. Gebelin 《Materials Science & Technology》2015,31(3):372-384
Linear friction welding of the Ti6Al4V alloy is studied. A new definition of the energy input rate is proposed, based on an integration over time of the in-plane force and velocity; a strong correlation with the upset rate is then found. The effective friction coefficient is estimated to be 0·5±0·1 for varying frequencies and amplitudes, with only a weak dependence on the processing conditions displayed. A model is proposed that accounts for both the conditioning and equilibrium stages of the process, which is shown to be in good agreement with the experimental data. The model is used to study the mechanism by which the flash is formed. A criterion is proposed by which the rippled nature of its morphology can be predicted. 相似文献
114.
Trekin A. N. Ignatiev V. Yu. Yakubovskii P. Ya. 《Journal of Computer and Systems Sciences International》2020,59(5):755-767
Journal of Computer and Systems Sciences International - The height of a building is a basic characteristic needed for analytical services. It can be used to evaluate the population and functional... 相似文献
115.
Nilesh P. Vanikar Shantipal S. Ohol Saeede Goldar 《International Journal of Cast Metals Research》2018,31(4):249-259
Bottom pour ladles with stopper rod systems are commonly used in the metal casting industry. However, stopper rod bottom-pouring systems have not yet been developed for the lower thermal masses of alloys typically used in the investment casting industry. Large thermal masses used with bottom pour systems are typically limited for ladles larger than 700 kg and to certain alloys with higher fluidity and longer solidification time like cast iron, aluminum alloys etc. In this study, bottom pour ladle designs and low thermal mass refractory systems have been developed and evaluated in production investment foundry trials with 300 kg pouring ladle. The ladles system and pouring practices used will be described along with the results from the pouring trials for SS304 that represents typical alloys used in Investment casting industries. Optimization of the variables used in an experimentation using Genetic algorithm is also explained. 相似文献
116.
117.
Ana Rita Gomes Nasim Bahram Sangani Tiago G. Fernandes M. Margarida Diogo Leopold M. G. Curfs Chris P. Reutelingsperger 《International journal of molecular sciences》2020,21(24)
The central nervous system (CNS) is the most complex structure in the body, consisting of multiple cell types with distinct morphology and function. Development of the neuronal circuit and its function rely on a continuous crosstalk between neurons and non-neural cells. It has been widely accepted that extracellular vesicles (EVs), mainly exosomes, are effective entities responsible for intercellular CNS communication. They contain membrane and cytoplasmic proteins, lipids, non-coding RNAs, microRNAs and mRNAs. Their cargo modulates gene and protein expression in recipient cells. Several lines of evidence indicate that EVs play a role in modifying signal transduction with subsequent physiological changes in neurogenesis, gliogenesis, synaptogenesis and network circuit formation and activity, as well as synaptic pruning and myelination. Several studies demonstrate that neural and non-neural EVs play an important role in physiological and pathological neurodevelopment. The present review discusses the role of EVs in various neurodevelopmental disorders and the prospects of using EVs as disease biomarkers and therapeutics. 相似文献
118.
Brusov V. S. Korchagin P. O. Malyshev V. V. Piyavsky S. A. 《Journal of Computer and Systems Sciences International》2020,59(1):83-94
Journal of Computer and Systems Sciences International - The article considers the problem of making multicriteria decisions in which the decision maker (DM) has the opportunity to indicate the... 相似文献
119.
Pavel Strunz Debashis Mukherji Přemysl Beran Ralph Gilles Lukas Karge Michael Hofmann Markus Hoelzel Joachim Rösler Gergely Farkas 《Metals and Materials International》2018,24(5):934-944
An addition of boron largely increases the ductility in polycrystalline high-temperature Co–Re alloys. Therefore, the effect of boron on the alloy structural characteristics is of high importance for the stability of the matrix at operational temperatures. Volume fractions of ε (hexagonal close-packed—hcp), γ (face-centered cubic—fcc) and σ (Cr2Re3 type) phases were measured at ambient and high temperatures (up to 1500 °C) for a boron-containing Co–17Re–23Cr alloy using neutron diffraction. The matrix phase undergoes an allotropic transformation from ε to γ structure at high temperatures, similar to pure cobalt and to the previously investigated, more complex Co–17Re–23Cr–1.2Ta–2.6C alloy. It was determined in this study that the transformation temperature depends on the boron content (0–1000 wt. ppm). Nevertheless, the transformation temperature did not change monotonically with the increase in the boron content but reached a minimum at approximately 200 ppm of boron. A probable reason is the interplay between the amount of boron in the matrix and the amount of σ phase, which binds hcp-stabilizing elements (Cr and Re). Moreover, borides were identified in alloys with high boron content. 相似文献
120.