全文获取类型
收费全文 | 109613篇 |
免费 | 21746篇 |
国内免费 | 4657篇 |
专业分类
电工技术 | 6919篇 |
技术理论 | 4篇 |
综合类 | 6061篇 |
化学工业 | 26962篇 |
金属工艺 | 4858篇 |
机械仪表 | 5608篇 |
建筑科学 | 7828篇 |
矿业工程 | 1967篇 |
能源动力 | 2974篇 |
轻工业 | 12278篇 |
水利工程 | 2001篇 |
石油天然气 | 3433篇 |
武器工业 | 788篇 |
无线电 | 15707篇 |
一般工业技术 | 18979篇 |
冶金工业 | 3381篇 |
原子能技术 | 987篇 |
自动化技术 | 15281篇 |
出版年
2024年 | 370篇 |
2023年 | 1193篇 |
2022年 | 2444篇 |
2021年 | 3617篇 |
2020年 | 3879篇 |
2019年 | 4953篇 |
2018年 | 5026篇 |
2017年 | 5644篇 |
2016年 | 5901篇 |
2015年 | 6873篇 |
2014年 | 7574篇 |
2013年 | 9242篇 |
2012年 | 7999篇 |
2011年 | 7850篇 |
2010年 | 7579篇 |
2009年 | 7386篇 |
2008年 | 6996篇 |
2007年 | 6431篇 |
2006年 | 5954篇 |
2005年 | 4865篇 |
2004年 | 3801篇 |
2003年 | 3564篇 |
2002年 | 3796篇 |
2001年 | 3353篇 |
2000年 | 2815篇 |
1999年 | 1802篇 |
1998年 | 1006篇 |
1997年 | 881篇 |
1996年 | 747篇 |
1995年 | 563篇 |
1994年 | 448篇 |
1993年 | 324篇 |
1992年 | 274篇 |
1991年 | 214篇 |
1990年 | 155篇 |
1989年 | 124篇 |
1988年 | 89篇 |
1987年 | 70篇 |
1986年 | 45篇 |
1985年 | 35篇 |
1984年 | 26篇 |
1983年 | 18篇 |
1982年 | 23篇 |
1981年 | 15篇 |
1980年 | 20篇 |
1979年 | 9篇 |
1976年 | 3篇 |
1973年 | 2篇 |
1959年 | 5篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
将环隙式离心萃取器(ACCs)与电喷雾飞行时间质谱(ESI-TOF-MS)相结合,在线监测了回收过程中的钨萃取行为(宏观)和钨形态的转化路径(微观),发现宏观萃取反应和微观离子形态转化同时发生并相互补充。伯胺N1923萃取钨在144 s内即可达到萃取平衡,萃取率高达98%以上,同时,酸钨比n(H)/n(W)是一个关键变量,当酸钨比n(H)/n(W)=2.4时,全流程钨回收率超过93%。最后,得到了基于钨形态监测的萃取机理,同时,减少原料液中W1含量,增加W10含量,可有效提高钨回收效率。 相似文献
62.
Junyu Chen Yuze Li Yuming Jiang Liucheng Mao Mi Lai Lixia Jiang Huihui Liu Zongxiu Nie 《Advanced functional materials》2021,31(52):2106743
Cancer remains an intractable medical problem. Rapid diagnosis and identification of cancer are critical to differentiate it from nonmalignant diseases. High-throughput biofluid metabolic analysis has potential for cancer diagnosis. Nevertheless, the present metabolite analysis method does not meet the demand for high-throughput screening of diseases. Herein, a high-throughput, cost-effective, and noninvasive urine metabolic profiling method based on TiO2/MXene-assisted laser desorption/ionization mass spectrometry (LDI-MS) is presented for the efficient screening of bladder cancer (BC) and nonmalignant urinary disease. Combined with machine learning, TiO2/MXene-assisted LDI-MS enables high diagnostic accuracy (96.8%) for the classification of patient groups (including 47 BC and 46 ureteral calculus (UC) patients) from healthy controls (113 cases). In addition, BC patients can also be identified from noncancerous UC individuals with an accuracy of 88.3% in the independent test cohort. Furthermore, metabolite variations between BC and UC individuals are investigated based on relative quantification, and related pathways are also discussed. These results suggest that this method, based on urine metabolic patterns, provides a potential tool for rapidly distinguishing urinary diseases and it may pave the way for precision medicine. 相似文献
63.
64.
Qiang Liu Xinyu Mao Xiaoying Li Penghui Chen Xin Liu Ziyu Liu Danyang Zhu Haohong Chen Tengfei Xie Jiang Li 《Journal of the American Ceramic Society》2021,104(10):4927-4931
0.5 at.% Cr:ZnGa2O4 precursor was synthesized by the co-precipitation method with nitrates as raw materials, using ammonium carbonate as the precipitant. Low-agglomerated Cr:ZnGa2O4 powders with an average particle size of 43 nm were obtained by calcining the precursor at 900℃ for 4 h. Using the powders as starting materials, 0.5 at.% Cr:ZnGa2O4 ceramics with an average grain size of about 515 nm were prepared by presintering at 1150℃ for 5 h in air and HIP post-treatment at 1100℃ for 3 h under 200 MPa Ar. The in-line transmittance of 0.5 at.% Cr:ZnGa2O4 ceramics with a thickness of 1.3 mm reaches 59.5% at the wavelength of 700 nm. The Cr:ZnGa2O4 ceramics can be effectively excited by visible light and produce persistent luminescence at 700 nm. For Cr:ZnGa2O4 transparent ceramics, the brightness of afterglow was larger than 0.32 mcd/m2 after 30 min, which is far superior to that of Cr:ZnGa2O4 persistent luminescence powders. 相似文献
65.
从老旧建筑结构现状展开论述,详细阐述了砌体墙加固设计、构造柱与圈梁加固设计、基础结构加固设计这几种老旧建筑结构改造加固设计,实现了对建筑结构改造工程施工技术的深入分析,希望能够为城乡建设事业的发展提供助力。 相似文献
66.
Tong Le Fan Ronggui Yang Shuangchun Zhang Qiushi Pan Yi 《Chemistry and Technology of Fuels and Oils》2022,57(6):991-999
Chemistry and Technology of Fuels and Oils - Application of water flooding technologies in the oilfield causes intensive heterogeneity of the oil reservoir and improper circulation of the injected... 相似文献
67.
This paper considers the state‐dependent interference relay channel (SIRC) in which one of the two users may operate as a secondary user and the relay has a noncausal access to the signals from both users. For discrete memoryless SIRC, we first establish the achievable rate region by carefully merging Han‐Kobayashi rate splitting encoding technique, superposition encoding, and Gelfand‐Pinsker encoding technique. Then, based on the achievable rate region that we derive, the capacity of the SIRC is established in many different scenarios including (a) the weak interference regime, (b) the strong interference regime, and (c) the very strong interference regime. This means that our capacity results contain all available known results in the literature. Next, the achievable rate region and the associated capacity results are also evaluated in the case of additive Gaussian noise. Additionally, many numerical examples are investigated to show the value of our theoretical derivations. 相似文献
68.
D.R. Santos‐Peñate C.M. Campos‐Rodríguez J.A. Moreno‐Pérez 《International Transactions in Operational Research》2019,26(1):340-363
The ‐centroid problem or leader–follower problem is generalized considering different customer choice rules where a customer may use facilities belonging to different firms, if the difference in travel distance (or time) is small enough. Assuming essential goods, some particular customer choice rules are analyzed. Linear programming formulations for the generalized ‐medianoid and ‐centroid problems are presented and an exact solution approach is applied. Some computational examples are included. 相似文献
69.
When solving a mathematical problem, students who do not have sufficient conceptual understanding may perform poorly and exhibit misconceptions. This study was aimed to examine students' conceptual understanding and significant misconceptions when solving number sense‐related problems. An online three‐tier diagnostic test was administered to 125 fifth‐grade students with varied socio‐economic backgrounds in Hong Kong. Only 14.40% of the students exhibited high performance with high confidence, indicating that these students had a profound conceptual understanding of number sense. In addition, the majority of the students (66.40%) did not demonstrate number sense; these students exhibited several significant misconceptions and could solve the questions only by using a rule‐based method or guessing. Accordingly, most students performed unsatisfactorily on number sense‐related problems. This study is imperative in identifying early predictors and provides information for further compatible interventions in the teaching and learning of number sense in Hong Kong in particular and worldwide in general. 相似文献
70.