全文获取类型
收费全文 | 227237篇 |
免费 | 25838篇 |
国内免费 | 17951篇 |
专业分类
电工技术 | 20867篇 |
技术理论 | 3篇 |
综合类 | 22170篇 |
化学工业 | 28829篇 |
金属工艺 | 15708篇 |
机械仪表 | 15797篇 |
建筑科学 | 18464篇 |
矿业工程 | 8323篇 |
能源动力 | 6525篇 |
轻工业 | 21661篇 |
水利工程 | 7481篇 |
石油天然气 | 8337篇 |
武器工业 | 3159篇 |
无线电 | 25694篇 |
一般工业技术 | 20957篇 |
冶金工业 | 8810篇 |
原子能技术 | 3789篇 |
自动化技术 | 34452篇 |
出版年
2024年 | 1272篇 |
2023年 | 3389篇 |
2022年 | 7522篇 |
2021年 | 10098篇 |
2020年 | 7388篇 |
2019年 | 5605篇 |
2018年 | 5949篇 |
2017年 | 7060篇 |
2016年 | 6269篇 |
2015年 | 9778篇 |
2014年 | 12413篇 |
2013年 | 14478篇 |
2012年 | 17992篇 |
2011年 | 19387篇 |
2010年 | 18231篇 |
2009年 | 17947篇 |
2008年 | 18215篇 |
2007年 | 17840篇 |
2006年 | 15977篇 |
2005年 | 12885篇 |
2004年 | 9558篇 |
2003年 | 6783篇 |
2002年 | 6422篇 |
2001年 | 5794篇 |
2000年 | 4541篇 |
1999年 | 2338篇 |
1998年 | 1145篇 |
1997年 | 921篇 |
1996年 | 757篇 |
1995年 | 624篇 |
1994年 | 481篇 |
1993年 | 418篇 |
1992年 | 303篇 |
1991年 | 242篇 |
1990年 | 181篇 |
1989年 | 192篇 |
1988年 | 119篇 |
1987年 | 91篇 |
1986年 | 85篇 |
1985年 | 35篇 |
1984年 | 32篇 |
1983年 | 36篇 |
1982年 | 28篇 |
1981年 | 28篇 |
1980年 | 45篇 |
1979年 | 42篇 |
1977年 | 8篇 |
1976年 | 3篇 |
1959年 | 40篇 |
1951年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
42.
43.
44.
Joon‐Young Jun Sosuke Nakajima Koji Yamazaki Yuji Kawai Hajime Yasui Yasuyuki Konishi 《International Journal of Food Science & Technology》2015,50(4):871-877
Cystoseira hakodatensis is an unutilised brown algae belonging to family Sargassaceae. A crude methanol extract from the algae showed inhibitory effects on the growths of Bacillus cereus and Bacillus licheniformis. To isolate the major antimicrobial agent, a sequential active‐guided isolation procedure was applied: liquid–liquid extraction, column chromatography and bio‐autography. A marked antimicrobial agent (active α) was isolated in hydrophobic fraction and was determined to phenolics without carbohydrates and proteins by phytochemical test. Regarding the antimicrobial potential, the isolated active α showed better inhibitory effects against B. cereus and B. licheniformis at 2 and 4 times of lower concentrations (62.5 and 31.3 μg mL?1) in comparison with epigallocatechin gallate. These results showed that C. hakodatensis is a potential source of antimicrobial agent capable of preventing the growth of the two bacteria. 相似文献
45.
47.
马尔可夫跳变线性系统(MJLS)是一种具有多个模态的随机系统,系统在各个模态之间的跳变转移由一组马尔可夫链来决定。MJLS模型因其在表示过程中可以产生突变而更能精确的描述实际工程应用中的系统。近年来,MJLS的最优控制问题成为了研究的热点,动态规划、极大值原理以及线性矩阵不等式等成为了解决此类问题的主流方法。本文对MJLS最优控制领域的研究现状进行了综述。分别对一般情况下、带有噪声的情况下、带有时滞的情况下以及某些特定情况下的MLJS最优控制问题的国内外研究现状进行论述。最后进行了总结并提出MJLS最优控制领域未来值得关注的研究方向。 相似文献
48.
针对现有混合入侵检测模型仅定性选取特征而导致检测精度较低的问题,同时为了充分结合误用检测模型和异常检测模型的优势,提出一种采用信息增益率的混合入侵检测模型.首先,利用信息增益率定量地选择特征子集,最大程度地保留样本信息;其次,采用余弦时变粒子群算法确定支持向量机参数构建误用检测模型,使其更好地平衡粒子在全局和局部的搜索能力,然后,选取灰狼算法确定单类支持向量机参数构建异常检测模型,以此来提高对最优参数的搜索效率和精细程度,综合提高混合入侵检测模型对攻击的检测效果;最后,通过两种数据集进行仿真实验,验证了所提混合入侵检测模型具有较好的检测性能. 相似文献
49.
Wang Hay Kan Chenxi Wei Dongchang Chen Tao Bo Bao‐Tian Wang Yan Zhang Yangchao Tian Jun‐Sik Lee Yijin Liu Guoying Chen 《Advanced functional materials》2019,29(17)
Lithium‐rich disordered rock‐salt oxides have attracted great interest owing to their promising performance as Li‐ion battery cathodes. While experimental and theoretical efforts are critical in advancing this class of materials, a fundamental understanding of key property changes upon Li extraction is largely missing. In the present study, single‐crystal synthesis of a new disordered rock‐salt cathode material, Li1.3Ta0.3Mn0.4O2 (LTMO), and its use as a model compound to investigate Li concentration–driven evolution of local cationic ordering, charge compensation, and chemical distribution are reported. Through the combined use of 2D and 3D X‐ray nanotomography, it is shown that Li removal accompanied by oxygen oxidation is correlated with the development of morphological defects such as particle cracking. Chemical heterogeneity, quantified by subparticle level distribution of Mn valence state, is minimal during Mn redox, which drastically increases upon the formation of cracks during oxygen redox. Density functional theory and bond valence sum mismatch calculations reveal the presence of local short‐range ordering in the pristine oxide, which gradually disappears along with the extraction of Li. The study suggests that with cycling the transformation into true cation–disordered state can be expected, which likely impacts the voltage profile and obtainable energy density of the oxide cathodes. 相似文献
50.
Biyun Fang Chuanfeng Zhang Zeliang Qi Chunyan Li Jun Ni Xiuyun Wang Jianxin Lin Chak-Tong Au Bingyu Lin Lilong Jiang 《American Institute of Chemical Engineers》2022,68(11):e17849
The design of an efficient non-noble metal catalyst is of burgeoning interest for ammonia synthesis. Herein, we report a Mo2C/CeO2 catalyst that is superior in ammonia synthesis activity. In this catalyst, molybdenum carbide coexisted with the ceria overlayers which is from the ceria support as the strong metal–support interaction. There is a high proportion of low-valent Mo species, as well as high concentration of Ce3+ and surface oxygen species. The presence of Mo2C and CeO2 overlayers not only leads to enhancement of hydrogen and nitrogen adsorption, but also facilitates the desorption and exchange of adsorbed species with the gaseous reagents. Compared with the Mo/CeO2 catalyst prepared without carbonization, the Mo2C/CeO2 catalyst is more than sevenfold higher in ammonia synthesis rate. This work not only presents an explicit example of designing Mo-based catalyst that is highly efficient for ammonia synthesis by tuning the adsorption and desorption properties of the reactant gases, but opens a perspective for other elements in ammonia synthesis. 相似文献