全文获取类型
收费全文 | 80182篇 |
免费 | 7025篇 |
国内免费 | 2903篇 |
专业分类
电工技术 | 3768篇 |
技术理论 | 2篇 |
综合类 | 4130篇 |
化学工业 | 14550篇 |
金属工艺 | 4350篇 |
机械仪表 | 5016篇 |
建筑科学 | 5070篇 |
矿业工程 | 2148篇 |
能源动力 | 2338篇 |
轻工业 | 5629篇 |
水利工程 | 1121篇 |
石油天然气 | 3941篇 |
武器工业 | 524篇 |
无线电 | 10255篇 |
一般工业技术 | 11286篇 |
冶金工业 | 4661篇 |
原子能技术 | 864篇 |
自动化技术 | 10457篇 |
出版年
2024年 | 376篇 |
2023年 | 1313篇 |
2022年 | 2131篇 |
2021年 | 3085篇 |
2020年 | 2361篇 |
2019年 | 2190篇 |
2018年 | 2434篇 |
2017年 | 2645篇 |
2016年 | 2552篇 |
2015年 | 3013篇 |
2014年 | 3776篇 |
2013年 | 4755篇 |
2012年 | 5102篇 |
2011年 | 5722篇 |
2010年 | 4624篇 |
2009年 | 4468篇 |
2008年 | 4236篇 |
2007年 | 3927篇 |
2006年 | 4216篇 |
2005年 | 3529篇 |
2004年 | 2590篇 |
2003年 | 2225篇 |
2002年 | 1977篇 |
2001年 | 1730篇 |
2000年 | 1827篇 |
1999年 | 2001篇 |
1998年 | 2068篇 |
1997年 | 1671篇 |
1996年 | 1406篇 |
1995年 | 1159篇 |
1994年 | 1020篇 |
1993年 | 745篇 |
1992年 | 557篇 |
1991年 | 469篇 |
1990年 | 365篇 |
1989年 | 311篇 |
1988年 | 252篇 |
1987年 | 180篇 |
1986年 | 154篇 |
1985年 | 137篇 |
1984年 | 100篇 |
1983年 | 65篇 |
1982年 | 70篇 |
1981年 | 60篇 |
1980年 | 65篇 |
1979年 | 49篇 |
1978年 | 39篇 |
1977年 | 56篇 |
1976年 | 93篇 |
1975年 | 50篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
NO2 fission is regarded to be the most important initial decomposition process of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20). In this study, four CL-20 conformers based on the ε-CL-20 were obtained after the optimization at m062x/cc-pvtz level, and the bond length, bond order and bond dissociation energy of the N-N bonds were examined to investigate the stability of these bonds. In addition, the rate constants and activation energy of the NO2 fission were evaluated using the microcanonical variational transition state theory (μVT). The calculation results have shown that N-N bonds in the case of pseudo-equatorial and axial of nitro groups are the most stable and the least stable, respectively, by evaluating the bond length, bond order and minimum energy path (MEP). The NO2 fission rate constants are affected by not only the stability of N-N bonds but also the repulsion forces from the other nitro groups, and the fission process for pseudo-equatorial positioning of nitro groups is easier to be accelerated due to the increase of the repulsion forces. The decomposition of CL-20 conformer may mainly originate from the fission of the pseudo-equatorial positioning of nitro groups, especially for CL-20 III conformer because of the significant low activation energy. 相似文献
53.
Jiaao Yan Gao Zhiming Tan Qingchao Yang Xian Hu Wenbin 《Protection of Metals and Physical Chemistry of Surfaces》2020,56(5):965-972
Protection of Metals and Physical Chemistry of Surfaces - The Al2O3 powder was added as a filler to polyurea and the effect of doping amount on Shore hardness and wetting property were... 相似文献
54.
Properties and applications of β‐glycosidase from Bacteroides thetaiotaomicron that specifically hydrolyses isoflavone glycosides 下载免费PDF全文
Da‐Hye Byun Hye‐Jeong Choi Hye‐Won Lee Hye‐Yeon Jeon Woo‐Jae Choung Jae‐Hoon Shim 《International Journal of Food Science & Technology》2015,50(6):1405-1412
To modify the glycan part of glycosides, the gene encoding β‐glycosidase was cloned from Bacteroides thetaiotaomicron VPI‐5482. The cloned gene, bt_1780, was expressed in Escherichia coli MC1061 and the expressed enzyme was purified using Ni‐NTA affinity chromatography. The purified enzyme, BTBG, showed optimal activity at 50 °C and pH 5.5. Interestingly, this enzyme did not have any hydrolysing activity on ordinary β‐linkage–containing substrates such as xylobiose, lactose and cello‐oligosaccharide, but specifically hydrolysed isoflavone glycosides such as daidzin, genistin and glycitin. Compared to a commercial beta glucosidase, BTBG selectively hydrolysed isoflavone glycosides in soybean extract mixture solution. These results suggest that BTBG may be a specialized enzyme for the hydrolysis of glycosides and that the substrate specificity of BTBG is applicable for the bioconversion of isoflavone glycosides in the food industry. 相似文献
55.
56.
Yanlong Shi Xiaojuan Feng Haiyu Guan Jiahua Zhang Zhongai Hu 《International Journal of Hydrogen Energy》2021,46(12):8557-8566
Constructing high-efficient and nonprecious electrocatalysts is of primary importance for improving the efficiency of water splitting. Herein, a novel sunflower plate-like NiFe2O4/CoNi–S nanosheet heterostructure was fabricated via facile hydrothermal and electrodeposition methods. The as-fabricated NiFe2O4/CoNi–S heterostructure array exhibits remarkable bifunctional catalytic activity and stability toward oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline media. It presents a small overpotential of 219 mV and 149 mV for OER and HER, respectively, to produce a current density of 10 mA cm?2. More significantly, when the obtained electrodes are used as both the cathode and anode in an electrolyzer, a voltage of 1.57 V is gained at 10 mA cm?2, with superior stability for 72 h. Such outstanding properties are ascribed to: the 3D porous network structure, which exposes more active sites and accelerates mass transfer and gas bubble emission; the high conductivity of CoNi–S, which provides faster charge transport and thus promotes the electrocatalytic reaction of the composites; and the effective interface engineering between NiFe2O4 (excellent performance for OER) and CoNi–S (high activity for HER), which leads to a shorter transport pathway and thus expedites electron transfer. This work provides a new strategy for designing efficient and inexpensive electrocatalysts for water splitting. 相似文献
57.
Tingen Zhu Wenping Li Qiqing Wang Yanbo Hu Kaifang Fan Jiafa Du 《Mine Water and the Environment》2020,39(1):57-67
A method to calculate the height of a water-conducting fractured zone (HWCFZ) was developed based on the plate and shell theory, and the development of the HWCFZ in bedrock and Q2l loess strata is discussed in detail. First, the subsidence-deflection curve equation of the overlying stratum is theoretically derived, and then the ultimate deflection and free space height of rock strata are calculated. Moreover, the strata tensile strain is calculated by using integral calculus. In addition, the failure state of the rock is analyzed by comparing the theoretically calculated tensile strain with the experimentally measured yield tensile strain, allowing one to attain the maximum value of HWCFZ. This approach was tested at the Jinjitan coal mine; the theoretically predicted, experimentally measured, and numerically computed maximum HWCFZ values were 189.5, 187.3, and 188.5 m, respectively, demonstrating the accuracy of the proposed method. These results are highly significant for safe and environment-friendly coal mining in northwest Shaanxi, China. 相似文献
58.
60.