全文获取类型
收费全文 | 360725篇 |
免费 | 29155篇 |
国内免费 | 19000篇 |
专业分类
电工技术 | 28278篇 |
技术理论 | 52篇 |
综合类 | 43808篇 |
化学工业 | 50186篇 |
金属工艺 | 19382篇 |
机械仪表 | 19638篇 |
建筑科学 | 45541篇 |
矿业工程 | 17296篇 |
能源动力 | 12676篇 |
轻工业 | 20210篇 |
水利工程 | 14674篇 |
石油天然气 | 13656篇 |
武器工业 | 3573篇 |
无线电 | 23655篇 |
一般工业技术 | 36136篇 |
冶金工业 | 19744篇 |
原子能技术 | 3632篇 |
自动化技术 | 36743篇 |
出版年
2024年 | 1071篇 |
2023年 | 3584篇 |
2022年 | 6864篇 |
2021年 | 8513篇 |
2020年 | 8853篇 |
2019年 | 7466篇 |
2018年 | 7003篇 |
2017年 | 8827篇 |
2016年 | 10166篇 |
2015年 | 11102篇 |
2014年 | 19744篇 |
2013年 | 18443篇 |
2012年 | 24229篇 |
2011年 | 25950篇 |
2010年 | 20336篇 |
2009年 | 21171篇 |
2008年 | 19387篇 |
2007年 | 25742篇 |
2006年 | 24330篇 |
2005年 | 21170篇 |
2004年 | 18061篇 |
2003年 | 16361篇 |
2002年 | 13567篇 |
2001年 | 11602篇 |
2000年 | 9745篇 |
1999年 | 7962篇 |
1998年 | 6127篇 |
1997年 | 5273篇 |
1996年 | 4747篇 |
1995年 | 4029篇 |
1994年 | 3493篇 |
1993年 | 2681篇 |
1992年 | 2269篇 |
1991年 | 1662篇 |
1990年 | 1399篇 |
1989年 | 1210篇 |
1988年 | 951篇 |
1987年 | 660篇 |
1986年 | 459篇 |
1985年 | 406篇 |
1984年 | 404篇 |
1983年 | 311篇 |
1982年 | 275篇 |
1981年 | 185篇 |
1980年 | 157篇 |
1979年 | 124篇 |
1978年 | 67篇 |
1977年 | 74篇 |
1976年 | 59篇 |
1975年 | 60篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
81.
82.
83.
Kazuo Tsubota Stephen C. Pflugfelder Zuguo Liu Christophe Baudouin Hyo Myung Kim Elisabeth M. Messmer Friedrich Kruse Lingyi Liang Jimena Tatiana Carreno-Galeano Maurizio Rolando Norihiko Yokoi Shigeru Kinoshita Reza Dana 《International journal of molecular sciences》2020,21(23)
Over the past decades, the number of patients with dry eye disease (DED) has increased dramatically. The incidence of DED is higher in Asia than in Europe and North America, suggesting the involvement of cultural or racial factors in DED etiology. Although many definitions of DED have been used, discrepancies exist between the various definitions of dry eye disease (DED) used across the globe. This article presents a clinical consensus on the definition of DED, as formulated in four meetings with global DED experts. The proposed new definition is as follows: “Dry eye is a multifactorial disease characterized by a persistently unstable and/or deficient tear film (TF) causing discomfort and/or visual impairment, accompanied by variable degrees of ocular surface epitheliopathy, inflammation and neurosensory abnormalities.” The key criteria for the diagnosis of DED are unstable TF, inflammation, ocular discomfort and visual impairment. This definition also recommends the assessment of ocular surface epitheliopathy and neurosensory abnormalities in each patient with suspected DED. It is easily applicable in clinical practice and should help practitioners diagnose DED consistently. This consensus definition of DED should also help to guide research and clinical trials that, to date, have been hampered by the lack of an established surrogate endpoint. 相似文献
84.
Lu Xu Baijun Liu Mingyao Zhang Yang Bai Jinming Zhang Jiayin Song 《Polymer Engineering and Science》2020,60(6):1194-1201
A series of methacrylate-acrylonitrile-butadiene-styrene (MABS) resins was prepared using bulk polymerization. The polarity of the continuous phase and the compatibility of two phases were changed by adjusting the methyl methacrylate (MMA) content, choosing values that were close to styrene-butadiene rubber solubility value. The possibility of controlling the microstructure of the MABS resin by changing the polarity of the components and the compatibility of two phases was assessed. The dynamic mechanical analysis shows that the compatibility of two phases varies with the MMA content. The morphological analysis shows that increasing MMA contents results in a gradual decrease in the sub-inclusion structure with a network skeleton of rubber particles, and that all the particles become solid rubber when the MMA content reaches 75%. The sub-inclusion structure reappears but does not have a network skeleton when the MMA content is 90%. The impact strength and morphological analysis indicate that the solid rubber particles and the sub-inclusion structure with a network skeleton provide excellent toughness, while the sub-inclusion structure without a network skeleton does not. In contrast, the transmittance of the ABS resin first increased and then decreased with increasing MMA content. 相似文献
85.
Izyan Najwa Mohd Norsham Siti Nor Atika Baharin Muggundha Raoov Syed Shahabuddin Jaroon Jakmunee Kavirajaa Pandian Sambasevam 《Polymer Engineering and Science》2020,60(12):3170-3182
A simple, cost-effective, and novel chemical sensor for ammonia (NH3) gas detection was developed from polyaniline (PANI)/quail eggshell (QES) composites. QES is a natural waste enriched in calcium carbonate. In this work, pure PANI was synthesized from chemical oxidation method and PANI/QES composites were prepared from physical mixing of QES with the synthesized PANI at different mass ratio. A series of complementary techniques including Fourier transform infrared and ultraviolet-visible spectrometers, scanning electron microscope with energy dispersive detection coupled with mapping, thermogravimetric analysis, and X-ray diffractometer were used to characterize the physicochemical and textural properties of the biocomposites. From the results, PANI/QES composite with a mass ratio of 1 exhibited the lowest NH3 detection limit of 5.24 ppm with a linear correlation coefficient (R2) of close to unity (0.9932) between the signal and NH3 gas concentration. As a whole, the PANI/QES biocomposites synthesized from this work exhibited excellent selectivity toward NH3 gas even in the presence of other gas impurities, such as acetone, ethanol, and hexane. For the sensor reusability, the PANI/QES biocomposites can be reused in the application of NH3 gas detection for at least 4 cycles. 相似文献
86.
87.
88.
Reliability based criteria are quite popular for optimal sensor network design. We present a modified definition of system reliability for sensor network design for two applications: reliable estimation of variables in a steady state linear flow process, and reliable fault detection and diagnosis for any process. Unlike the weakest-link based definition of system reliability in the literature, the proposed definition considers the entire system and is consistent with the reliability concept used in classical reliability literature. For each application, dual approaches for defining system reliability are proposed, and their analogy with the reliability problem in the classical reliability literature is established. Using examples and stochastic simulations, the advantage of using the proposed system reliability in contrast to the existing definition is illustrated. Part II of this series of articles presents methods for efficient generation of the system reliability function and its use in optimization-based approaches for designing optimal sensor networks. 相似文献
89.
与传统比例-积分-微分(PID)控制方法相比,滑模控制(SMC)方法可以比较容易地将不确定性纳入控制器设计中,从而增强系统的鲁棒性。探索了SMC技术在运载器主动段姿态控制中的工程应用,首先通过分析基于趋近律的SMC系统,提出了降低不连续切换项系数的需求,然后研究了基于干扰上界的SMC方法。三通道小偏差仿真结果验证了两种方法的控制效果,表明第2种控制器的鲁棒性更好,稳态误差小,同时发动机喷管摆角需求较小。 相似文献
90.
泛在电力物联网是物联网在电力领域的具体体现,建设泛在电力物联网是推进"三型两网"建设的关键环节,也是实现能源转型的必要手段。阐述了泛在电力物联网的定义,从供电公司角度出发,根据北京经济技术开发区实际情况,讨论了依托地区特点的泛在电力物联网实施策略和实际应用场景,分析了可能遇到的问题。得出结论:随着泛在电力物联网的深入建设,供电公司能够为电力客户提供多元化服务,提高客户满意度;地市供电公司能够依托泛在电力物联网开展更多电力相关业务;泛在电力物联网的安全性、实用性、有效性是发展面临的首要问题。 相似文献