全文获取类型
收费全文 | 82750篇 |
免费 | 8766篇 |
国内免费 | 5441篇 |
专业分类
电工技术 | 7018篇 |
技术理论 | 2篇 |
综合类 | 7163篇 |
化学工业 | 11429篇 |
金属工艺 | 4923篇 |
机械仪表 | 5995篇 |
建筑科学 | 7441篇 |
矿业工程 | 2485篇 |
能源动力 | 2513篇 |
轻工业 | 6811篇 |
水利工程 | 2082篇 |
石油天然气 | 3713篇 |
武器工业 | 993篇 |
无线电 | 9771篇 |
一般工业技术 | 8070篇 |
冶金工业 | 3112篇 |
原子能技术 | 1050篇 |
自动化技术 | 12386篇 |
出版年
2024年 | 280篇 |
2023年 | 1197篇 |
2022年 | 2421篇 |
2021年 | 3261篇 |
2020年 | 2539篇 |
2019年 | 1985篇 |
2018年 | 2316篇 |
2017年 | 2569篇 |
2016年 | 2357篇 |
2015年 | 3358篇 |
2014年 | 4493篇 |
2013年 | 4978篇 |
2012年 | 5962篇 |
2011年 | 6279篇 |
2010年 | 5845篇 |
2009年 | 5721篇 |
2008年 | 5826篇 |
2007年 | 5278篇 |
2006年 | 5144篇 |
2005年 | 4148篇 |
2004年 | 3318篇 |
2003年 | 3137篇 |
2002年 | 3813篇 |
2001年 | 3219篇 |
2000年 | 1970篇 |
1999年 | 1448篇 |
1998年 | 822篇 |
1997年 | 696篇 |
1996年 | 564篇 |
1995年 | 466篇 |
1994年 | 394篇 |
1993年 | 255篇 |
1992年 | 192篇 |
1991年 | 173篇 |
1990年 | 114篇 |
1989年 | 102篇 |
1988年 | 59篇 |
1987年 | 57篇 |
1986年 | 40篇 |
1985年 | 14篇 |
1984年 | 17篇 |
1983年 | 7篇 |
1982年 | 18篇 |
1981年 | 22篇 |
1980年 | 15篇 |
1979年 | 15篇 |
1978年 | 3篇 |
1976年 | 5篇 |
1959年 | 17篇 |
1951年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
31.
为了提高设计创新效率,本研究基于心理图式提出了国庆彩车的设计程序与方法。研究按照浅层、中层和深层的次序递进,设计心理图式划分为“造型图式”“叙事与动作图式”以及“人物和情感图式”的基本类别,并提出了综合性、时态性、差异性和集体性四类基本属性。而后结合新中国成立70周年彩车设计,对不同心理图式的应用方法和属性进行了案例分析。本文所提出的方法在设计实践中得到了实证,具有一定的实用价值。 相似文献
32.
Basins with various mineral resources coexisting and enriching often occupy an important strategic position. The exploration of various mineral resources is repetitive at present due to unshared data and imperfect management mechanism. This situation greatly increases the cost of energy exploitation in the country. Traditional data-sharing mode has several disadvantages, such as high cost, difficulty in confirming the right of data, and lack of incentive mechanism, which make achieving real data sharing difficult. In this paper, we propose a data-sharing mechanism based on blockchain and provide implementation suggestions and technical key points. Compared with traditional data-sharing methods, the proposed data-sharing mechanism can realize data sharing, ensure data quality, and protect intellectual property. Moreover, key points in the construction are stated in the case study section to verify the feasibility of the data-sharing system based on blockchain proposed in this paper. 相似文献
33.
A novel bio‐based phthalonitrile resin derived from catechin: synthesis and comparison of curing behavior with petroleum‐based counterpart 下载免费PDF全文
Yu Qi Zhihuan Weng Jinyan Wang Shouhai Zhang Lishuai Zong Cheng Liu Xigao Jian 《Polymer International》2018,67(3):322-329
The development of bio‐based thermosetting resins with good thermal stability can potentially afford sustainable polymers as replacements for petroleum‐based polymers. We report a practical route to a novel catechin‐based phthalonitrile resin precursor (CA‐Ph), which contains free phenolic hydroxyl groups that result in ‘self‐curing’ at elevated temperatures to afford a thermostable polymer. Comparison of the performance of this CA‐Ph resin with that of a conventional petroleum‐based bisphenol A phthalonitrile resin (BPA‐Ph; containing 5 wt% of the curing agent 4,4′‐diaminodiphenylsulfone) revealed that CA‐Ph exhibits a lower melting point and curing temperature. Cured CA‐Ph resin retains 95% of its weight at 520 °C under a nitrogen atmosphere, which compares favorably with results obtained for BPA‐Ph resin that retains 95% of its weight at a lower temperature of 484 °C. Kinetic results indicated that the curing reactions of both CA‐Ph and BPA‐Ph systems follow an autocatalytic mechanism. These results suggest that catechin is a useful bio‐based feedstock for the preparation of self‐curing and thermally stable phthalonitrile resins for advanced technological applications. © 2017 Society of Chemical Industry 相似文献
34.
Functional expression and synergistic cooperation of xylan‐degrading enzymes from Hypocrea orientalis and Aspergillus niger 下载免费PDF全文
35.
36.
This paper considers a novel distributed iterative learning consensus control algorithm based on neural networks for the control of heterogeneous nonlinear multiagent systems. The system's unknown nonlinear function is approximated by suitable neural networks; the approximation error is countered by a robust term in the control. Two types of control algorithms, both of which utilize distributed learning laws, are provided to achieve consensus. In the provided control algorithms, the desired reference is considered to be an unknown factor and then estimated using the associated learning laws. The consensus convergence is proven by the composite energy function method. A numerical simulation is ultimately presented to demonstrate the efficacy of the proposed control schemes. 相似文献
37.
Yao Dajie Liu Xiaofei Wu Jian 《International Journal of Control, Automation and Systems》2020,18(9):2251-2258
International Journal of Control, Automation and Systems - In this paper, the tracking problem for a class of uncertain nonlinearly parameterized systems with input delay based the adaptive... 相似文献
38.
针对电牵引采煤机渐开线行走轮在ANSYS分析中存在的问题,提出运用APDL语言命令直接建模,并通过VB与ANSYS的交互运行途径,设计了基于VB界面和程序的软件,实现了利用VB界面直接输入参数并调用ANSYS对行走轮自动建模、加载和计算的有限元分析。验证结果表明,该软件减少了设计人员的重复劳动,提高了行走轮的设计效率和水平,具有一定的工程实用价值。 相似文献
39.
40.
The red grape berry pigments, anthocyanins, were characterized in the early 20th century, but investigations of wine pigments were stymied during that era. The question of their identity was a major challenge for wine chemists. A number of techniques showed that the pigments were polymeric in nature. Some structures were postulated by mid-century based on reactions between anthocyanins and condensed tannin, and later postulated wine pigments were observed in model reactions. Some related compounds were then observed in wine. By the end of the 20th century, the ionization of non-volatiles for mass spectrometry opened the door to these compounds. In addition, a new class of compounds was observed, the pyranoanthocyanins, a product of fermentation and aging metabolites with anthocyanins. These compounds possess the pigment stability to SO2 and pH change that is characteristic of aged red wine. Aging experiments show a dynamic situation with shifts in the population of pigment classes over time. The very large number of diverse pigments explains why it has been so difficult to answer the century-old question of the structure of wine pigments. Our current understanding is founded on the use of mass spectral analysis using electrospray and related ionization techniques over the last 25 years. Future progress will rely on more sophisticated analysis of this very complex mixture of substances. © 2019 Society of Chemical Industry 相似文献