全文获取类型
收费全文 | 333050篇 |
免费 | 5281篇 |
国内免费 | 823篇 |
专业分类
电工技术 | 6523篇 |
综合类 | 824篇 |
化学工业 | 50707篇 |
金属工艺 | 10837篇 |
机械仪表 | 9325篇 |
建筑科学 | 8776篇 |
矿业工程 | 952篇 |
能源动力 | 9377篇 |
轻工业 | 34373篇 |
水利工程 | 3051篇 |
石油天然气 | 3810篇 |
武器工业 | 14篇 |
无线电 | 41417篇 |
一般工业技术 | 61709篇 |
冶金工业 | 61840篇 |
原子能技术 | 5624篇 |
自动化技术 | 29995篇 |
出版年
2021年 | 2955篇 |
2020年 | 2110篇 |
2019年 | 2666篇 |
2018年 | 4204篇 |
2017年 | 4123篇 |
2016年 | 4179篇 |
2015年 | 3032篇 |
2014年 | 5187篇 |
2013年 | 15476篇 |
2012年 | 8404篇 |
2011年 | 11501篇 |
2010年 | 8920篇 |
2009年 | 10135篇 |
2008年 | 10524篇 |
2007年 | 10381篇 |
2006年 | 9194篇 |
2005年 | 8600篇 |
2004年 | 8569篇 |
2003年 | 8223篇 |
2002年 | 8059篇 |
2001年 | 8142篇 |
2000年 | 7649篇 |
1999年 | 7963篇 |
1998年 | 19283篇 |
1997年 | 13927篇 |
1996年 | 10831篇 |
1995年 | 8360篇 |
1994年 | 7583篇 |
1993年 | 7351篇 |
1992年 | 5468篇 |
1991年 | 5307篇 |
1990年 | 5113篇 |
1989年 | 4942篇 |
1988年 | 4841篇 |
1987年 | 4012篇 |
1986年 | 4131篇 |
1985年 | 4862篇 |
1984年 | 4379篇 |
1983年 | 4085篇 |
1982年 | 3695篇 |
1981年 | 3860篇 |
1980年 | 3554篇 |
1979年 | 3491篇 |
1978年 | 3290篇 |
1977年 | 3931篇 |
1976年 | 5040篇 |
1975年 | 2844篇 |
1974年 | 2692篇 |
1973年 | 2713篇 |
1972年 | 2243篇 |
排序方式: 共有10000条查询结果,搜索用时 984 毫秒
131.
132.
133.
134.
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
135.
Radiochemistry - Leaching of uranium and REEs with oxalic acid from the Egyptian Abu-Tartur phosphate rock (PR) was studied. The effect exerted on the leaching process by oxalic acid concentration,... 相似文献
136.
ABSTRACTThis paper proposes the multiple-hypotheses image segmentation and feed-forward neural network classifier for food recognition to improve the performance. Initially, the food or meal image is given as input. Then, the segmentation is applied to identify the regions, where a particular food item is located using salient region detection, multi-scale segmentation, and fast rejection. Then, the features of every food item are extracted by the global feature and local feature extraction. After the features are obtained, the classification is performed for each segmented region using a feed-forward neural network model. Finally, the calorie value is computed with the aid of (i) food volume and (ii) calorie and nutrition measure based on mass value. The experimental results and performance evaluation are validated. The outcome of the proposed method attains 0.947 for Macro Average Accuracy (MAA) and 0.959 for Standard Accuracy (SA), which provides better classification performance. 相似文献
137.
138.
Kinetic,thermodynamic parameters and in vitro digestion of tannase from Aspergillus tamarii URM 7115
Amanda Reges de Sena Tonny Cley Campos Leite Talita Camila Evaristo da Silva Nascimento Anna Carolina da Silva Catiane S. Souza Antônio Fernando de Mello Vaz 《Chemical Engineering Communications》2018,205(10):1415-1431
Tannase is an enzyme used in various industries and produced by a large number of microorganisms. The aim of this study was to evaluate tannase production to determine the biochemical, kinetic, and thermodynamic properties and to simulate tannase in vitro digestion. The tannase-producing fungal strain was isolated from “jamun” leaves and identified as Aspergillus tamarii. Temperature at 26°C for 67?h was the best combination for maximum tannase activity (6.35-fold; initial activity in Plackett–Burman design—15.53?U/mL and average final activity in Doehlert design—98.68?U/mL). The crude extract of tannase was optimally active at 40°C, pH 5.5 and 6.5. Moreover, tannase was stimulated by Na+, Ca2+, Mg2+, and Mn2+. The half-life at 40°C lasted 247.55?min. The free energy of Gibbs, enthalpy, and entropy, at 40°C, was 81.47, 16.85, and ?0.21?kJ/mol?·?K, respectively. After total digestion, 123.95% of the original activity was retained. Results suggested that tannase from A. tamarii URM 7115 is an enzyme of interest for industrial applications, such as gallic acid production, additive for feed industry, and for beverage manufacturing, due to its catalytic and thermodynamic properties. 相似文献
139.
Meza-Espinoza Libier de los Ángeles Vivar-Vera María de Lourdes García-Magaña María Sáyago-Ayerdi Sonia G. Chacón-López Alejandra Becerrea-Verdín Eduardo M. Montalvo-González Efigenia 《Food science and biotechnology》2018,27(2):509-517
Food Science and Biotechnology - The enzymatic activity and partial characterization of proteases from Bromelia karatas fruits were evaluated and compared with Bromelia pinguin proteases. The... 相似文献
140.
Electrodewatering is a technique in which pressure dewatering is combined with electrokinetic effects to realize an improved solid/liquid separation and hence increased filter cake dry matter contents. In order to be energy efficient, it is shown that sludge should be dewatered by pressure dewatering to a high extent prior to electric field application, and a sufficient contact time for the electric field must be guaranteed. In order to realize these goals, a bench- and pilot-scale diaphragm filter press suited for electrodewatering were constructed for treatment of sewage and other types of sludges. It was shown that electrodewatering of sludge is a feasible technique, especially for biological sludge types. Other types of sludge are less suited for electrodewatering because of the restricted improvements that can be realized in cake dry matter content and the high electric energy consumption. Furthermore, it was shown in pilot-scale tests that the use of a diaphragm filter press with electrodewatering facilities was very well suited to deliver dry filter cakes of sewage sludge at a moderate energy consumption. Depending on local market prices for investment, operating and sludge disposal costs, this technology may therefore lead to important savings in the sludge management process. 相似文献