全文获取类型
收费全文 | 90099篇 |
免费 | 7918篇 |
国内免费 | 3874篇 |
专业分类
电工技术 | 5050篇 |
技术理论 | 10篇 |
综合类 | 5551篇 |
化学工业 | 15143篇 |
金属工艺 | 5017篇 |
机械仪表 | 5502篇 |
建筑科学 | 6628篇 |
矿业工程 | 2413篇 |
能源动力 | 2715篇 |
轻工业 | 6791篇 |
水利工程 | 1595篇 |
石油天然气 | 4606篇 |
武器工业 | 638篇 |
无线电 | 11166篇 |
一般工业技术 | 11991篇 |
冶金工业 | 4640篇 |
原子能技术 | 895篇 |
自动化技术 | 11540篇 |
出版年
2024年 | 413篇 |
2023年 | 1614篇 |
2022年 | 2837篇 |
2021年 | 3925篇 |
2020年 | 3035篇 |
2019年 | 2431篇 |
2018年 | 2833篇 |
2017年 | 2883篇 |
2016年 | 2866篇 |
2015年 | 3567篇 |
2014年 | 4433篇 |
2013年 | 5198篇 |
2012年 | 5711篇 |
2011年 | 6284篇 |
2010年 | 5249篇 |
2009年 | 5038篇 |
2008年 | 4890篇 |
2007年 | 4445篇 |
2006年 | 4236篇 |
2005年 | 3696篇 |
2004年 | 2779篇 |
2003年 | 2515篇 |
2002年 | 2309篇 |
2001年 | 2037篇 |
2000年 | 2146篇 |
1999年 | 2467篇 |
1998年 | 2157篇 |
1997年 | 1742篇 |
1996年 | 1697篇 |
1995年 | 1400篇 |
1994年 | 1208篇 |
1993年 | 830篇 |
1992年 | 653篇 |
1991年 | 470篇 |
1990年 | 412篇 |
1989年 | 370篇 |
1988年 | 262篇 |
1987年 | 188篇 |
1986年 | 143篇 |
1985年 | 103篇 |
1984年 | 78篇 |
1983年 | 51篇 |
1982年 | 59篇 |
1981年 | 48篇 |
1980年 | 43篇 |
1979年 | 18篇 |
1978年 | 12篇 |
1977年 | 15篇 |
1976年 | 23篇 |
1974年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
32.
33.
Maqbool Ali Jamil Hussain Sungyoung Lee Byeong Ho Kang Kashif Sattar 《Expert Systems》2020,37(1):e12401
The case-based learning (CBL) approach has gained attention in medical education as an alternative to traditional learning methodology. However, current CBL systems do not facilitate and provide computer-based domain knowledge to medical students for solving real-world clinical cases during CBL practice. To automate CBL, clinical documents are beneficial for constructing domain knowledge. In the literature, most systems and methodologies require a knowledge engineer to construct machine-readable knowledge. Keeping in view these facts, we present a knowledge construction methodology (KCM-CD) to construct domain knowledge ontology (i.e., structured declarative knowledge) from unstructured text in a systematic way using artificial intelligence techniques, with minimum intervention from a knowledge engineer. To utilize the strength of humans and computers, and to realize the KCM-CD methodology, an interactive case-based learning system(iCBLS) was developed. Finally, the developed ontological model was evaluated to evaluate the quality of domain knowledge in terms of coherence measure. The results showed that the overall domain model has positive coherence values, indicating that all words in each branch of the domain ontology are correlated with each other and the quality of the developed model is acceptable. 相似文献
34.
Yue Gao Miao-miao Zhang Xiao-peng Guo Wen-jian Li Dong Lu 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2020,95(5):1290-1297
Toxicity caused by the accumulation of butanol in fermentation media is an important factor limiting the concentration of butanol. There is currently no systematic research in place investigating the butanol tolerance mechanism of bacteria such as Clostridium acetobutylicum, which adapts to butanol stress and regulates its growth and metabolism. Here, research results related to the butanol tolerance of C. acetobutylicum are reviewed to understand the molecular basis of changes in butanol-tolerant strains. Organic solvent-tolerant bacteria play an important role in the fields of biofuel production, enzyme preparation and bioremediation. An analysis of limitations of the application of organic solvent-tolerant bacteria has revealed that future research should focus on combining the microbial tolerance phenotype with specific utilization to achieve an optimal balance between organic solvent tolerance and production. This review serves as a reference for the improvement and engineering of strains that tolerate organic solvents. © 2019 Society of Chemical Industry 相似文献
35.
为了保证上海光源X射线干涉光刻光束线的稳定性,减小热变形对实验结果的影响,对X射线干涉光刻光束线的3个关键光学元件——偏转镜、聚焦镜和精密四刀狭缝进行热-结构耦合分析。首先,计算偏转镜、聚焦镜和精密四刀狭缝所承载的功率密度;然后,建立其有限元模型;最后,获得光学元件的温度场和热变形的结果。结果表明,偏转镜和聚焦镜采用间接水冷方式可有效抑制热变形,冷却后的最大面形误差分别为7.2μrad和9.2μrad。精密四刀狭缝未冷却时,刀片组件温度介于271.56~273.27℃,刀口热变形为0.19 mm,直线导轨热变形为0.08 mm;经过铜辫子冷却后,刀片组件温度降至22.24~23.94℃,刀口热变形降至0.2μm,直线导轨热变形降至0.1μm;采用影像法和接触探头法测试后,刀口直线度、平行度和重复精度均满足技术要求。偏转镜、聚焦镜和精密四刀狭缝的热变形通过间接水冷和铜辫子的冷却方式可以得到很大程度的抑制,进而保证光斑质量。 相似文献
36.
37.
38.
Zu Guoqing Lu Yukuan Yan Yi Zhang Xiaoming Zhao Jingwei Du Wei Ran Xu Jiang Zhengyi 《Metals and Materials International》2020,26(2):248-259
Metals and Materials International - The flow behaviour and microstructure characteristics of a ferritic stainless steel were investigated using plain strain compression test on a Gleeble 3500... 相似文献
39.
Tao Li Zehui Du Nobumichi Tamura Mao Ye Saikumar Inguva Wei Lu Xierong Zeng Shanming Ke Haitao Huang 《Journal of the European Ceramic Society》2018,38(4):1488-1497
(1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 ((1-x)PZN-xPT in short) is one of the most important piezoelectric materials. In this work, we extensively investigated (1-x)PZN-xPT (x = 0.07–0.11) ferroelectric single crystals using in-situ synchrotron μXRD, complemented by TEM and PFM, to correlate microstructures with phase transitions. The results reveal that (i) at 25 °C, the equilibrium state of (1-x)PZN-xPT is a metastable orthorhombic phase for x = 0.07 and 0.08, while it shows coexistence of orthorhombic and tetragonal phases for x = 0.09 and x = 0.11, with all ferroelectric phases accompanied by ferroelastic domains; (ii) upon heating, the phase transformation in x = 0.07 is Orthorhombic → Monoclinic → Tetragonal → Cubic. The coexistence of ferroelectric tetragonal and paraelectric cubic phases was in-situ observed in x = 0.08 above Curie temperature (TC), and (iii) phase transition can be explained by the evolution of the ferroelectric and ferroelastic domains. These results disclose that (1-x)PZN-xPT are in an unstable regime, which is possible factor for its anomalous dielectric response and high piezoelectric coefficient. 相似文献
40.
Baizhan Li Chenqiu Du Hong Liu Wei Yu Jie Zheng Meilan Tan Zhenxing Jin Wenjie Li Jing Wu Lu Chen Runming Yao 《Indoor air》2019,29(2):308-319
The extensive research interests in environmental temperature can be linked to human productivity / performance as well as comfort and health; while the mechanisms of physiological indices responding to temperature variations remain incompletely understood. This study adopted a physiological sensory nerve conduction velocity (SCV) as a temperature‐sensitive biomarker to explore the thermoregulatory mechanisms of human responding to annual temperatures. The measurements of subjects’ SCV (over 600 samples) were conducted in a naturally ventilated environment over all four seasons. The results showed a positive correlation between SCV and annual temperatures and a Boltzmann model was adopted to depict the S‐shaped trend of SCV with operative temperatures from 5°C to 40°C. The SCV increased linearly with operative temperatures from 14.28°C to 20.5°C and responded sensitively for 10.19°C‐24.59°C, while tended to be stable beyond that. The subjects’ thermal sensations were linearly related to SCV, elaborating the relation between human physiological regulations and subjective thermal perception variations. The findings reveal the body SCV regulatory characteristics in different operative temperature intervals, thereby giving a deeper insight into human autonomic thermoregulation and benefiting for built environment designs, meantime minimizing the temperature‐invoked risks to human health and well‐being. 相似文献