全文获取类型
收费全文 | 200922篇 |
免费 | 3470篇 |
国内免费 | 808篇 |
专业分类
电工技术 | 3586篇 |
综合类 | 328篇 |
化学工业 | 32201篇 |
金属工艺 | 8285篇 |
机械仪表 | 5622篇 |
建筑科学 | 5265篇 |
矿业工程 | 962篇 |
能源动力 | 5489篇 |
轻工业 | 19811篇 |
水利工程 | 1923篇 |
石油天然气 | 3259篇 |
武器工业 | 8篇 |
无线电 | 21710篇 |
一般工业技术 | 36665篇 |
冶金工业 | 38448篇 |
原子能技术 | 4457篇 |
自动化技术 | 17181篇 |
出版年
2021年 | 1997篇 |
2020年 | 1376篇 |
2019年 | 1792篇 |
2018年 | 2694篇 |
2017年 | 2752篇 |
2016年 | 2817篇 |
2015年 | 2062篇 |
2014年 | 3463篇 |
2013年 | 8999篇 |
2012年 | 5647篇 |
2011年 | 7730篇 |
2010年 | 6035篇 |
2009年 | 6920篇 |
2008年 | 6788篇 |
2007年 | 6658篇 |
2006年 | 5649篇 |
2005年 | 5396篇 |
2004年 | 5242篇 |
2003年 | 4872篇 |
2002年 | 4803篇 |
2001年 | 4730篇 |
2000年 | 4369篇 |
1999年 | 4476篇 |
1998年 | 12072篇 |
1997年 | 8500篇 |
1996年 | 6430篇 |
1995年 | 4796篇 |
1994年 | 4002篇 |
1993年 | 4010篇 |
1992年 | 2786篇 |
1991年 | 2774篇 |
1990年 | 2595篇 |
1989年 | 2600篇 |
1988年 | 2545篇 |
1987年 | 2260篇 |
1986年 | 2214篇 |
1985年 | 2528篇 |
1984年 | 2290篇 |
1983年 | 2084篇 |
1982年 | 1981篇 |
1981年 | 2045篇 |
1980年 | 1879篇 |
1979年 | 1890篇 |
1978年 | 1834篇 |
1977年 | 2220篇 |
1976年 | 2884篇 |
1975年 | 1625篇 |
1974年 | 1583篇 |
1973年 | 1649篇 |
1972年 | 1372篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
53.
Catalysis Letters - In this work we studied the reactivity of the Trifluoroacetic acid hydroxylamine system in the one step salt free synthesis of amides from ketones. A particular regards was paid... 相似文献
54.
55.
56.
Zhang Xi Wang Xianhai Zhao Hongke Ordóñez de Pablos Patricia Sun Yongqiang Xiong Hui 《Scientometrics》2019,119(3):1311-1344
Scientometrics - Altmetrics indices are increasingly applied to measure scholarly influence in recent years because they can reflect the influence of research outputs more timely comparing with... 相似文献
57.
Fabíola Azanha de Carvalho Amanda Aleixo Moreira André Luiz Martinez de Oliveira Fabio Yamashita 《应用聚合物科学杂志》2021,138(28):50667
Neat poly (lactic acid) (PLA) and PLA/cassava bagasse (CB) composites were used to produce seedling tubes by extrusion and injection molding. The tubes were buried in simulated soil, and their biodegradation was investigated by weight loss, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). After 180 days, the composites' biodegradation was higher than neat PLA material, and the higher the CB content, the higher the biodegradation, which caused fissures and voids in the material. The biodegradation of PLA/CB composites increased the phosphorus content in the soil after 180 days. Composites of PLA with CB, an abundant agro-industrial residue in Brazil, are promising because they can reduce the environmental impact due to CB's proper destination, and the composites' costs and biodegradation are faster than pure PLA material. Both the faster biodegradation of the tube and the higher P content are advantageous for seedling tubes. 相似文献
58.
Gabriel Rodrigues de Almeida Neto Cesar Augusto Gonçalves Beatrice Daniel Rodrigo Leiva Luiz Antonio Pessan 《International Journal of Hydrogen Energy》2021,46(46):23767-23778
This study investigates the preparation of polyetherimide (PEI) – LaNi5 composites films for hydrogen storage. Prior to the polymer addition, LaNi5 was ball-milled at different conditions (250, 350, and 450 RPM) and annealed at 500 °C for 1 h under vacuum. The composites were produced with BM-LaNi5-350 (PEI/LaNi5-350) and annealed BM-LaNi5-350 (PEI/LaNi5-350-TT). Membranes were successfully produced through solvent casting assisted by an ultrasonic bath. The particles dispersion and the film morphology did not change after hydrogenation cycles. In the H2 sorption experiments at 43 °C and 20 bar, the films stored H2 without incubation time; both samples reached a capacity of ~0.6 wt%. The H2 sorption kinetics of PEI/LaNi5-350 was comparable to that of BM-LaNi5-350, whereas PEI/LaNi5-350-TT presented significantly slower kinetics. LaNi5 oxidation was hindered by PEI, showing that it can be explored to improve metal hydrides air resistance. The results demonstrated that PEI films filled with LaNi5 are promising materials for hydrogen storage. 相似文献
59.
Maria A. Ospina Monica Pizarro Thierry Tran Julien Ricci John Belalcazar Jorge L. Luna Luis F. Londoño Sandra Salazar Hernan Ceballos Dominique Dufour Luis A. Becerra Lopez-Lavalle 《International Journal of Food Science & Technology》2021,56(3):1343-1353
The objective of this study was to characterise the nutritional potential of leaves and identify a diversity centre with low cyanide and high nutrient content among 178 Latin American cassava genotypes. This field-based collection represents the seven diversity centres, held at The International Center for Tropical Agriculture (CIAT Palmira, Colombia) by the Cassava Program. The cyanide, all-trans-β-carotene and lutein concentrations in cassava leaves ranged from 346 to 7484 ppm dry basis (db), from 174–547 μg g−1 db and 15–181 μg g−1 db, respectively. Cassava leaves also showed significant levels of essential amino acids leucine, lysine, phenylalanine, valine and threonine, and average total protein content of 26.24 g 100 g−1 db. Among seven diversity centres, South American rainforest group showed low cyanide and high carotene content in leaves. In addition, VEN77 and PAN51 genotypes stood out for having low cyanide in leaves and roots and high carotene in leaves. This genetic diversity can be used to select high potential progenitors for breeding purposes. 相似文献
60.
Kooij Julian F. P. Flohr Fabian Pool Ewoud A. I. Gavrila Dariu M. 《International Journal of Computer Vision》2019,127(3):239-262
International Journal of Computer Vision - Anticipating future situations from streaming sensor data is a key perception challenge for mobile robotics and automated vehicles. We address the problem... 相似文献