全文获取类型
收费全文 | 196437篇 |
免费 | 2353篇 |
国内免费 | 629篇 |
专业分类
电工技术 | 4032篇 |
综合类 | 123篇 |
化学工业 | 26091篇 |
金属工艺 | 7495篇 |
机械仪表 | 5426篇 |
建筑科学 | 4019篇 |
矿业工程 | 746篇 |
能源动力 | 4643篇 |
轻工业 | 14157篇 |
水利工程 | 1689篇 |
石油天然气 | 2792篇 |
武器工业 | 7篇 |
无线电 | 27263篇 |
一般工业技术 | 37327篇 |
冶金工业 | 45374篇 |
原子能技术 | 3560篇 |
自动化技术 | 14675篇 |
出版年
2021年 | 1233篇 |
2019年 | 1280篇 |
2018年 | 2123篇 |
2017年 | 2104篇 |
2016年 | 2171篇 |
2015年 | 1489篇 |
2014年 | 2615篇 |
2013年 | 7949篇 |
2012年 | 4461篇 |
2011年 | 6109篇 |
2010年 | 4930篇 |
2009年 | 5771篇 |
2008年 | 6145篇 |
2007年 | 6195篇 |
2006年 | 5633篇 |
2005年 | 5303篇 |
2004年 | 5249篇 |
2003年 | 5088篇 |
2002年 | 4898篇 |
2001年 | 5305篇 |
2000年 | 4915篇 |
1999年 | 5435篇 |
1998年 | 15616篇 |
1997年 | 10294篇 |
1996年 | 7715篇 |
1995年 | 5746篇 |
1994年 | 4979篇 |
1993年 | 4984篇 |
1992年 | 3347篇 |
1991年 | 3228篇 |
1990年 | 3197篇 |
1989年 | 2997篇 |
1988年 | 2755篇 |
1987年 | 2202篇 |
1986年 | 2270篇 |
1985年 | 2591篇 |
1984年 | 2297篇 |
1983年 | 2046篇 |
1982年 | 1885篇 |
1981年 | 2023篇 |
1980年 | 1778篇 |
1979年 | 1643篇 |
1978年 | 1644篇 |
1977年 | 2015篇 |
1976年 | 2692篇 |
1975年 | 1416篇 |
1974年 | 1358篇 |
1973年 | 1305篇 |
1972年 | 1113篇 |
1971年 | 941篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
91.
Effect of Supports and Promoters on the Performance of Ni-Based Catalysts in Ethanol Steam Reforming
Thanh Khoa Phung Thong Le Minh Pham Anh-Nga T. Nguyen Khanh B. Vu Ha Ngoc Giang Tuan-Anh Nguyen Thanh Cong Huynh Hong Duc Pham 《化学工程与技术》2020,43(4):672-688
Ethanol steam reforming (ESR) is one of the potential processes to convert ethanol into valuable products. Hydrogen produced from ESR is considered as green energy for the future and can be an excellent alternative to fossil fuels with the aim of mitigating the greenhouse gas effect. The ESR process has been well studied, using transition metals as catalysts coupled with both acidic and basic oxides as supports. Among various reported transition metals, Ni is an inexpensive material with activity comparable to that of noble metals, showing promising ethanol conversion and hydrogen yields. Additionally, different promoters and supports were utilized to enhance the hydrogen yield and the catalyst stability. This review summarizes and discusses the influences of the supports and promoters of Ni-based catalysts on the ESR process. 相似文献
92.
93.
Robert Groth Luke T. Cravigan Sadegh Niazi Zoran Ristovski Graham R. Johnson 《Journal of the Royal Society Interface》2021,18(178)
The airborne dynamics of respiratory droplets, and the transmission routes of pathogens embedded within them, are governed primarily by the diameter of the particles. These particles are composed of the fluid which lines the respiratory tract, and is primarily mucins and salts, which will interact with the atmosphere and evaporate to reach an equilibrium diameter. Measuring organic volume fraction (OVF) of cough aerosol has proved challenging due to large variability and low material volume produced after coughing. Here, the diametric hygroscopic growth factors (GF) of the cough aerosol produced by healthy participants were measured in situ using a rotating aerosol suspension chamber and a humidification tandem differential mobility analyser. Using hygroscopicity models, it was estimated that the average OVF in the evaporated cough aerosol was 0.88 ± 0.07 and the average GF at 90% relative humidity (RH) was 1.31 ± 0.03. To reach equilibrium in dry air the droplets will reduce in diameter by a factor of approximately 2.8 with an evaporation factor of 0.36 ± 0.05. Hysteresis was observed in cough aerosol at RH = ∼35% and RH = ∼65% for efflorescence and deliquescence, respectively, and may depend on the OVF. The same behaviour and GF were observed in nebulized bovine bronchoalveolar lavage fluid. 相似文献
94.
Differences between oculomotor and perceptual artifacts for temporally limited head mounted displays
Alexander Goettker Kevin J. MacKenzie T. Scott Murdison 《Journal of the Society for Information Display》2020,28(6):509-519
We used perceptual and oculomotor measures to understand the negative impacts of low (phantom array) and high (motion blur) duty cycles with a high‐speed, AR‐likehead‐mounted display prototype. We observed large intersubject variability for the detection of phantom array artifacts but a highly consistent and systematic effect on saccadic eye movement targeting during low duty cycle presentations. This adverse effect on saccade endpoints was also related to an increased error rate in a perceptual discrimination task, showing a direct effect of display duty cycle on the perceptual quality. For high duty cycles, the probability of detecting motion blur increased during head movements, and this effect was elevated at lower refresh rates. We did not find an impact of the temporal display characteristics on compensatory eye movements during head motion (e.g., VOR). Together, our results allow us to quantify the tradeoff of different negative spatiotemporal impacts of user movements and make subsequent recommendations for optimized temporal HMD parameters. 相似文献
95.
96.
Zareen S. Khan Niladri S. Chatterjee Ahammed Shabeer T.P. Shamim Shaikh Kaushik Banerjee 《European Journal of Lipid Science and Technology》2020,122(4)
The aim of the study is to investigate the biochemical composition of grapeseed oil and cake from an unexplored Indian grape‐juice cultivar, Manjari Medika (MM). The composition of oil and residual seed cake is evaluated using various chromatographic and spectroscopic techniques. The findings demonstrate that the vitamin E content of MM‐seed oil (1.15–1.35 g kg?1) is distinctively higher than the Codex standard, suggesting its superior quality as an edible oil. The predominant triacylglycerols include trilinolein (LLL, 43%), dilinoleoyl‐stearylglycerol (LSL, 19%), and dilinoleoyl‐palmitoylglycerol (LLP, 11%), which are earlier recognized as natural antioxidants. The seed‐cake is rich in polyphenols including acylated anthocyanins (e.g., pelargonidin‐3‐O‐coumaroyl glucoside) and certain other flavonoids (e.g., catechin). The profile of phytonutrients in MM seed‐oil and cake is significantly superior to its seeded female parent and two other widely cultivated wine‐grape varieties. In brief, the studied by‐products of this new grape‐juice cultivar can be an important source of high‐value ingredients for use in food supplements, nutraceuticals, and functional foods. Practical applications: This study reports the phytochemical profile of the seed‐oil and seed cake derived from a newly developed grape variety, Manjari Medika. High contents of selective antioxidants: lipids, vitamin E, and phenols in the seed‐oil and cake with health benefits suggest their potential for use in nutraceutical and functional foods. These byproducts can be utilised as ingredients of functional foods and nutraceuticals (e.g., grape seed oil capsule) and also as raw materials in food supply chains (e.g., for production of grape cookies or cake). MM can also be utilized as a colorant in the food industry. 相似文献
97.
Kuznetsova T. F. Ivanets A. I. Savka Yu. D. Kul’bitskaya L. V. 《Protection of Metals and Physical Chemistry of Surfaces》2020,56(1):30-37
Protection of Metals and Physical Chemistry of Surfaces - Mesoporous titanosilicate structures synthesized by the sol–gel method using the cetylpyridinium template at different Ti/Si ratios... 相似文献
98.
Yachao Dong Christos T. Maravelias Norman F. Jerome 《Optimization and Engineering》2018,19(4):937-976
We study a maritime inventory routing problem, in which shipments between production and consumption nodes are carried out by a fleet of vessels. The vessels have specific capacities and can be chartered under different agreements. The inventory levels of all consumption nodes and some production nodes should be maintained within specified bounds; for the remaining production nodes, orders should be picked up within pre-defined time windows. We propose a discrete-time mixed-integer programming model. In the face of new information and uncertainty, this optimization model has to be re-solved, as the horizon is rolled forward. We discuss how to account for different sources of uncertainty. We present a rolling-horizon reoptimization framework that allows us to study different policies that impact the quality of the implemented solution, so we can identify the optimal set of policies. 相似文献
99.
Chalykh A. E. Petrova T. F. Antipov Yu. V. Aliev A. D. Matveev V. V. Telitsyna M. Yu. 《Protection of Metals and Physical Chemistry of Surfaces》2020,56(1):20-29
Protection of Metals and Physical Chemistry of Surfaces - The degree of crystallinity of carbon fibers (CFs) of different manufacturers has been determined by means of the Raman scattering method.... 相似文献
100.