全文获取类型
收费全文 | 226946篇 |
免费 | 22889篇 |
国内免费 | 13174篇 |
专业分类
电工技术 | 17592篇 |
技术理论 | 6篇 |
综合类 | 18100篇 |
化学工业 | 33308篇 |
金属工艺 | 13860篇 |
机械仪表 | 15305篇 |
建筑科学 | 18605篇 |
矿业工程 | 7557篇 |
能源动力 | 6671篇 |
轻工业 | 16345篇 |
水利工程 | 5250篇 |
石油天然气 | 11858篇 |
武器工业 | 2493篇 |
无线电 | 27505篇 |
一般工业技术 | 23746篇 |
冶金工业 | 9302篇 |
原子能技术 | 2534篇 |
自动化技术 | 32972篇 |
出版年
2024年 | 983篇 |
2023年 | 3554篇 |
2022年 | 6914篇 |
2021年 | 9841篇 |
2020年 | 7330篇 |
2019年 | 5856篇 |
2018年 | 6541篇 |
2017年 | 7563篇 |
2016年 | 6646篇 |
2015年 | 9766篇 |
2014年 | 12302篇 |
2013年 | 14686篇 |
2012年 | 17008篇 |
2011年 | 17979篇 |
2010年 | 16245篇 |
2009年 | 15357篇 |
2008年 | 15083篇 |
2007年 | 14333篇 |
2006年 | 13644篇 |
2005年 | 10855篇 |
2004年 | 7587篇 |
2003年 | 6405篇 |
2002年 | 6048篇 |
2001年 | 5376篇 |
2000年 | 4665篇 |
1999年 | 4144篇 |
1998年 | 3056篇 |
1997年 | 2530篇 |
1996年 | 2322篇 |
1995年 | 1966篇 |
1994年 | 1653篇 |
1993年 | 1072篇 |
1992年 | 836篇 |
1991年 | 662篇 |
1990年 | 489篇 |
1989年 | 420篇 |
1988年 | 319篇 |
1987年 | 205篇 |
1986年 | 177篇 |
1985年 | 91篇 |
1984年 | 64篇 |
1983年 | 40篇 |
1982年 | 57篇 |
1981年 | 54篇 |
1980年 | 59篇 |
1979年 | 35篇 |
1978年 | 16篇 |
1976年 | 24篇 |
1975年 | 17篇 |
1951年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
92.
在伯克氏菌Bth264野生株产新型抗癌药物Thailandepsin A以及调节基因tdp R正向调控Thailandepsin A生物合成的基础上,利用基因工程菌Bth264/p BMTL3-tdp R发酵生产Thailandepsin A,以提高产量。以0.5%乳糖为诱导剂,确定最佳诱导条件:发酵15 h添加乳糖,诱导时间6 h;通过单因素实验,确定葡萄糖和胰蛋白胨作为碳氮源、装液量65/250 m L以及接种量1%;同时结合优化发酵培养基进行发酵,Thailandepsin A产量达到252.14 mg·L-1,比优化前的产量提高56%;另外在发酵过程中,添加大孔树脂HP-20原位吸附产物,Thailandepsin A产量可达283.75 mg·L-1,比不加树脂提高13.8%;最后,基于RT-PCR和比较Ct值法,基因工程菌和野生菌相比,Thailandepsin A生物合成基因tdp B、tdp C1的转录水平分别提高11.4倍和6.0倍,对应的产量增加4.6倍,从而在很大程度上说明调节基因tdp R的过表达促进生物合成基因转录水平的提高以及产量的增加。 相似文献
93.
94.
Yafei Liu Zhilong Fu Xingyu Chen Yaxin Wei Bo Zhang Aimin Chang 《Journal of the American Ceramic Society》2021,104(5):2134-2142
Rare-earth ions doped Ca0.9R0.1CeNbMoO8 (R = Y, Sm, Nd, La) ceramics have been successfully prepared by solid-state method, and their modifications to the microstructure and electrical properties are also investigated. The rare-earth ions doped ceramics exhibit the scheelite structure. With the increase in the radius of rare-earth ions, the lattice distortion and bond interaction will be enhanced, and the consistency of grain size will be reduced. The ceramics exhibit negative temperature coefficient (NTC) thermistor characteristics in the temperature range of 473 K-1273 K, and the activation energy decreases with the increase of the radius of rare-earth ions. Rare-earth ions doping can increase the content of Ce3+ ions and promote the conductivity of ceramics. Except for Sm3+-doped ceramics, the high-temperature aging rate of other ceramics is less than 2%. The existence of some metastable Sm2+ ions in Sm3+-doped ceramics not only increases the activation energy, but also reduces the high-temperature stability of the ceramics. 相似文献
95.
Strength of Materials - A metallographic method, dilatometry, and X-ray diffraction were applied to investigate the effects of undercooling and holding time on bainitic transformation,... 相似文献
97.
Qin-yu Zhou Shan Zhao Yan-yan Huang Jin-shuang Hu Jia-hua Kuang Dong-mei Liu Charles S. Brennan 《International Journal of Food Science & Technology》2021,56(6):2992-3003
Yogurt preserves and enhances nutritional value of milk. In this study, we have compared several strains to determine the physicochemical, sensory, rheological and aroma characteristics of different yogurts. We used Lactobacillus gasseri LGZ 1029 (LG), commercial probiotic L. rhamnosus (LGG) and traditional fermentation strains Streptococcus thermophilus and L. bulgaricus (SL). Results showed that the flavour and texture characteristics of mixed-strain yogurts were obviously better than in single-strain yogurts. Addition of LG increased pseudoplastic behaviour, as shown by Herschel–Bulkley model analysis of rheological behaviour. The LG + SL group also had both the highest viscosity consistency index and thickening ability. In addition, a total of 57 volatile compounds were detected in yogurts and the fermentation with the addition of LG was mainly affected by ketones. Our study suggested that a yogurt with new attributes can be produced by using LGZ 1029. 相似文献
98.
Bin Zhang Xuesong Jiang Fei Shen Xueming He Yong Fang Qiuhui Hu 《International Journal of Food Science & Technology》2021,56(6):2588-2595
This work intends to develop an online experimental system for screening of deoxynivalenol (DON) contamination in whole wheat meals by visible/near-infrared (Vis/NIR) spectroscopy and computer vision coupling technology. Spectral and image information of samples with various DON levels was collected at speed of 0.15 m s−1 on a conveyor belt. The two-type data were then integrated and subjected to chemometric analysis. Discriminant analysis showed that samples could be classified by setting 1000 μg kg−1 as the cut-off value. The best correct classified rate obtained in prediction was 93.55% based on fusion of spectral and image features, with reduced prediction uncertainty as compared to single feature. However, quantification of DON by quantitative analysis was not successful due to poor model performance. These results indicate that, although not accurate enough to provide conclusive result, this coupling technology could be adopted for rapid screening of DON contamination in cereals and feeds during processing. 相似文献
99.
Wei-Fei Hu Shuo Chen Hong-Chao Hao Hong Jiang 《American Institute of Chemical Engineers》2022,68(11):e17879
Herein, we propose a novel method to enhance the photoreactivity of an MOF catalyst by grafting isocyanate bonds ( NCO) and sulfhydryl-complexed copper ( SCu) onto ZIF-8 (NIF-SCu). The grafting process intercalated interlayer bands between the conduction and valence bands of ZIF-8, thereby providing a “ladder” for facile electron transition. The extreme improvement in the photoreactivity of NIF-SCu could be attributed to the enhancement in light responses in the range of 350–450 nm by NCO groups and the widening of the visible light range of the MOF by SCu groups. The formation of staggered energy levels in NIF-SCu could also narrow the band gap, lower the resistance, and facilitate the transfer of photogenerated carriers, thereby generating electrons with strong reduction potential in the SCu conduction band. This study provides a new strategy for improving or even endowing the photoactivity of environmental functional materials with wide bandgaps. 相似文献
100.
Gang Zheng Xiaoxuan Yu Haizuo Zhou Xinyu Yang Wei Guo Pengbo Yang 《Geotextiles and Geomembranes》2021,49(1):180-187
Incompressible dipping substrata are commonly encountered in engineering practice. Compared to horizontal underlying strata, the inclined underlying stratum increase the risk of collapse of embankments reinforced with columns because it weakens the restraint of the column base. The objective of this study is to investigate the effectiveness of geosynthetics on improving the embankment stability when the underlying stratum is inclined. The influence of geosynthetic tensile stiffness on the ultimate surcharge and failure mechanism is studied. A deep-seated failure with column tilting occurs when the geosynthetic tensile stiffness is low, whereas a lateral sliding occurs when the geosynthetic tensile stiffness is high. To illustrate the contribution of geosynthetics, the distribution of the lateral pressures acting on the columns is analyzed. 相似文献