全文获取类型
收费全文 | 34664篇 |
免费 | 3026篇 |
国内免费 | 1294篇 |
专业分类
电工技术 | 1807篇 |
技术理论 | 5篇 |
综合类 | 2206篇 |
化学工业 | 6176篇 |
金属工艺 | 2052篇 |
机械仪表 | 2062篇 |
建筑科学 | 2571篇 |
矿业工程 | 1035篇 |
能源动力 | 903篇 |
轻工业 | 1969篇 |
水利工程 | 524篇 |
石油天然气 | 2580篇 |
武器工业 | 229篇 |
无线电 | 4147篇 |
一般工业技术 | 4248篇 |
冶金工业 | 1565篇 |
原子能技术 | 478篇 |
自动化技术 | 4427篇 |
出版年
2024年 | 496篇 |
2023年 | 678篇 |
2022年 | 1017篇 |
2021年 | 1479篇 |
2020年 | 1159篇 |
2019年 | 898篇 |
2018年 | 1078篇 |
2017年 | 1188篇 |
2016年 | 987篇 |
2015年 | 1278篇 |
2014年 | 1632篇 |
2013年 | 2016篇 |
2012年 | 2087篇 |
2011年 | 2329篇 |
2010年 | 1967篇 |
2009年 | 1802篇 |
2008年 | 1732篇 |
2007年 | 1621篇 |
2006年 | 1790篇 |
2005年 | 1621篇 |
2004年 | 1100篇 |
2003年 | 931篇 |
2002年 | 863篇 |
2001年 | 747篇 |
2000年 | 859篇 |
1999年 | 1012篇 |
1998年 | 786篇 |
1997年 | 704篇 |
1996年 | 682篇 |
1995年 | 556篇 |
1994年 | 456篇 |
1993年 | 343篇 |
1992年 | 261篇 |
1991年 | 192篇 |
1990年 | 146篇 |
1989年 | 127篇 |
1988年 | 112篇 |
1987年 | 69篇 |
1986年 | 53篇 |
1985年 | 24篇 |
1984年 | 18篇 |
1983年 | 19篇 |
1982年 | 30篇 |
1981年 | 14篇 |
1980年 | 11篇 |
1979年 | 2篇 |
1977年 | 6篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
通过对总变电站6k V系统备用电源自动投入装置误动作进行分析,指出存在的缺陷,提出相应的改进措施,试验及现场运行表明这些措施是可靠有效的。 相似文献
22.
Ruwei Shen Jianlin Yang Bing Luo Lixiong Zhang Li‐Biao Han 《Advanced Synthesis \u0026amp; Catalysis》2016,358(23):3897-3906
The copper‐catalyzed reaction of 5‐substituted penta‐1,4‐diyn‐3‐yl acetates with P(O)H compounds to efficiently give a new class of phosphonyl diynes is reported. The reaction may take place through a regioselective nucleophilic attack of phosphorus nucleophiles on Cu‐allenylidene intermediates to form allenyl intermediates followed by a rapid allene‐alkyne isomerization process. The synthetic utility of the obtained products is demonstrated.
24.
Municipal solid waste incineration(MSWI) fly ash is a by-product from municipal waste incineration.According to incomplete statistics, each year more than one million tons MSWI fly ash was produced in China. Owing to high heavy elements content, widely used disposal methods of landfill are not suitable for MSWI fly ash treatment. In this study, by using MSWI fly ash as raw materials, glassceramics was synthesized for the solidification of heavy metals and waste recycle. Process parameters, including composition, heat treatment temperature and time, were studied and optimized. Under optimizing conditions, the product has good properties of density of 3.42 g·cm~(-3) and Vickers hardness of 6.91 GPa. Moreover, the leaching concentration of heavy metal elements meets allowable values of toxicity characteristic leaching procedure(TCLP).This study offers an alternative for MSWI fly ash recycle. 相似文献
25.
Evolutionary Algorithms(EAs)mimicking the principles of natural evolution can be used as powerful search and optimization methods.These Evolutionary Optimization methods are superior to traditional optimization methods especially in situations where gradient information is not readily available.EAs are generic and robust optimization methods since they do not make any assumption about the underlying search space.This is clearly evident by the success of EAs in a diverse range of real-world applications.T... 相似文献
26.
27.
基于模糊PID控制的循环水自动加药与监测系统 总被引:1,自引:0,他引:1
工业生产中加强对循环水质的处理变得越来越重要,在对循环水系统存在问题进行分析后,利用西门子S7-200 PLC和WinCC组态软件开发设计了新型工业循环水水质在线监测与自动加药系统,解决了传统控制难以保证加药量准确与均匀的问题;针对加酸中pH值过程具有非线性、时变和大时滞等特点,采用了以控制人员的经验为基础的模糊控制方法,结果表明pH值控制误差完全满足系统要求;系统已在化工厂中投入运行,经实践证明,该系统人机交互性好、可靠性高、抗干扰能力强,满足了现代工业循环水质监管的要求。 相似文献
28.
29.
Zhi He Li Zheng Qiqi Chen Sen Xiong Zhide He Jiaxiang Hu Zhijun Ma Qian Zhang Jiayang He Lijuan Ye Liang He Jie Luo Xiaobin Gu Mingwang Zhang Ziting Tang Yuanyuan Jiao Yong Pu Jinxin Xiong Kuo Gao Bolin Lai Shiyong Yang Deying Yang Taiming Yan 《International journal of molecular sciences》2022,23(23)
Bmpr2 plays a central role in the regulation of reproductive development in mammals, but its role during ovarian development in fish is still unclear. To ascertain the function of bmpr2 in ovarian development in the ricefield eel, we isolated and characterized the bmpr2 cDNA sequence; the localization of Bmpr2 protein was determined by immunohistochemical staining; and the expression patterns of bmpr2 in ovarian tissue incubated with FSH and hCG in vitro were analyzed. The full-length bmpr2 cDNA was 3311 bp, with 1061 amino acids encoded. Compared to other tissues, bmpr2 was abundantly expressed in the ovary and highly expressed in the early yolk accumulation (EV) stages of the ovary. In addition, a positive signal for Bmpr2 was detected in the cytoplasm of oocytes in primary growth (PG) and EV stages. In vitro, the expression level of gdf9, the ligand of bmpr2, in the 10 ng/mL FSH treatment group was significantly higher after incubation for 4 h than after incubation for different durations. However, bmpr2 expression in the 10 ng/mL FSH treatment group at 2 h, 4 h and 10 h was significantly lower. Importantly, the expression level of bmpr2 and gdf9 in the 100 IU/mL hCG group had similar changes that were significantly decreased at 4 h and 10 h. In summary, Bmpr2 might play a pivotal role in ovarian growth in the ricefield eel, and these results provide a better understanding of the function of bmpr2 in ovarian development and the basic data for further exploration of the regulatory mechanism of gdf9 in oocyte development. 相似文献
30.
Dongdong Li Guoliang Li Haoying Wang Yuhang Guo Meng Wang Xiaohuan Lu Zhiheng Luo Xintian Zhu Thea Mi Weiß Sandra Roller Shaojiang Chen Lixing Yuan Tobias Würschum Wenxin Liu 《International journal of molecular sciences》2022,23(22)
Genotype-by-environment interaction (G-by-E) is a common but potentially problematic phenomenon in plant breeding. In this study, we investigated the genotypic performance and two measures of plasticity on a phenotypic and genetic level by assessing 234 maize doubled haploid lines from six populations for 15 traits in seven macro-environments with a focus on varying soil phosphorus levels. It was found intergenic regions contributed the most to the variation of phenotypic linear plasticity. For 15 traits, 124 and 31 quantitative trait loci (QTL) were identified for genotypic performance and phenotypic plasticity, respectively. Further, some genes associated with phosphorus use efficiency, such as Zm00001eb117170, Zm00001eb258520, and Zm00001eb265410, encode small ubiquitin-like modifier E3 ligase were identified. By significantly testing the main effect and G-by-E effect, 38 main QTL and 17 interaction QTL were identified, respectively, in which MQTL38 contained the gene Zm00001eb374120, and its effect was related to phosphorus concentration in the soil, the lower the concentration, the greater the effect. Differences in the size and sign of the QTL effect in multiple environments could account for G-by-E. At last, the superiority of G-by-E in genomic selection was observed. In summary, our findings will provide theoretical guidance for breeding P-efficient and broadly adaptable varieties. 相似文献