全文获取类型
收费全文 | 484607篇 |
免费 | 89027篇 |
国内免费 | 54539篇 |
专业分类
电工技术 | 44053篇 |
技术理论 | 33篇 |
综合类 | 39235篇 |
化学工业 | 73738篇 |
金属工艺 | 39787篇 |
机械仪表 | 26106篇 |
建筑科学 | 36592篇 |
矿业工程 | 21920篇 |
能源动力 | 16867篇 |
轻工业 | 38901篇 |
水利工程 | 12434篇 |
石油天然气 | 32096篇 |
武器工业 | 5937篇 |
无线电 | 62041篇 |
一般工业技术 | 64798篇 |
冶金工业 | 22592篇 |
原子能技术 | 4400篇 |
自动化技术 | 86643篇 |
出版年
2024年 | 2116篇 |
2023年 | 8790篇 |
2022年 | 11804篇 |
2021年 | 16858篇 |
2020年 | 17386篇 |
2019年 | 24887篇 |
2018年 | 27325篇 |
2017年 | 29355篇 |
2016年 | 28182篇 |
2015年 | 30468篇 |
2014年 | 32501篇 |
2013年 | 34461篇 |
2012年 | 35099篇 |
2011年 | 33458篇 |
2010年 | 29569篇 |
2009年 | 25644篇 |
2008年 | 23563篇 |
2007年 | 22178篇 |
2006年 | 22015篇 |
2005年 | 19671篇 |
2004年 | 17298篇 |
2003年 | 14649篇 |
2002年 | 13457篇 |
2001年 | 12079篇 |
2000年 | 12307篇 |
1999年 | 13006篇 |
1998年 | 11176篇 |
1997年 | 9504篇 |
1996年 | 8890篇 |
1995年 | 8145篇 |
1994年 | 6601篇 |
1993年 | 5252篇 |
1992年 | 4645篇 |
1991年 | 3509篇 |
1990年 | 2721篇 |
1989年 | 2397篇 |
1988年 | 1831篇 |
1987年 | 816篇 |
1986年 | 628篇 |
1985年 | 444篇 |
1984年 | 295篇 |
1983年 | 212篇 |
1982年 | 292篇 |
1981年 | 241篇 |
1980年 | 180篇 |
1976年 | 260篇 |
1975年 | 210篇 |
1972年 | 241篇 |
1971年 | 137篇 |
1960年 | 206篇 |
排序方式: 共有10000条查询结果,搜索用时 625 毫秒
1.
4.
5.
Kelin Hu Feipeng Wang Yuyang Yan Hongcheng Liu Zijia Shen 《Ceramics International》2021,47(11):15228-15236
In this paper, a novel hybrid structure of Pd doped ZnO/SnO2 heterojunction nanofibers with hexagonal ZnO columns was one step synthesized from electrospun precursor nanofibers. Due to the synergistic effect of hexagonal ZnO, SnO2 and Pd, the structure exhibited excellent hydrogen (H2) gas sensing properties. At low-temperature of 120 °C, the response (Ra/Rg) to 100 ppm H2 gas exceeded 160, the response/recovery time was only 20 s and 6 s respectively and the limit of detection was only 0.5 ppm. Meanwhile, it also had good selectivity for H2 gas and excellent linearity. In addition, the materials were characterized by XRD, FESEM, HRTEM, XPS, and the synthesis mechanism and gas sensing mechanism were proposed. 相似文献
6.
通过固液掺杂、等静压压制、中频烧结的方法,制备了不同的氧化镧、氧化钇、氧化锆三元掺杂成分比例的钨电极材料烧结棒材,探究了不同成分配比对样品显微组织、第二相粒子分布以及宏观力学性能的影响。结果表明,氧化镧、氧化钇、氧化锆三元复合添加能够有效改善第二相粒子在钨基体中的分布形态,降低第二相在晶界的过度富集,提高钨电极材料的综合力学性能。并且当添加成分镧、钇、锆质量比为3:1:1时,材料具有最好的综合力学性能,致密度可达96.04%,显微硬度可达549.37HV0.3,抗压强度可达3785MPa,原因是此配比下第二相粒子最为细小均匀,弥散程度最高,对基体晶粒的细化作用最好,该配比下钨基体平均晶粒尺寸达到10.3μm。 相似文献
8.
Shanshan Zhuang Wenxiong Zheng Yunong Na Naiyi Chen Fan Gong Bingxuan Huang Stephen Brennan Charles Congyi Liu Jian Cheng Lukai Ma Huifan Liu 《International Journal of Food Science & Technology》2022,57(2):1093-1103
The β-Carotene (BC), an important precursor of vitamin A (VA), possesses antioxidant activity but is fat-soluble and has low bioavailability. In previous in-vitro assays evaluating antioxidant and 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH) free radical scavenging, both BC and VA showed a strong ability to scavenge radicals and protected cells from oxidative stress. Here, we used artificially simulated gastrointestinal digestion and Caco-2 cell absorption models to evaluate the bioavailability of the BC during gastrointestinal digestion and absorption using high-performance liquid chromatography (HPLC) analysis. We observed high absorptive and transfer rates of BC and detected retinol metabolites (Vitamin A). Therefore, BC can be detected in the acidic gastrointestinal environment using HPLC. Optimised method provided better separation of BC and VA in the column, improving the accuracy of the test results. 相似文献
9.
Mengru Liu Weihai Zhang Limin Ma 《International Journal of Adaptive Control and Signal Processing》2022,36(1):69-87
The article investigates the finite-time adaptive fuzzy control for a class of nonlinear systems with output constraint and input dead-zone. First, by skillfully combining the barrier Lyapunov function, backstepping design method, and finite-time control theory, a novel adaptive state-feedback tracking controller is constructed, and the output constraint of the nonlinear system is not violated. Second, the fuzzy logic system is used to approximate unknown function in the nonlinear system. Third, the finite-time command filter is introduced to avoid the problem of “complexity explosion” caused by repeated differentiations of the virtual control signal in conventional backstepping control schemes. Meanwhile, a new saturation function is added in the compensating signal for filter error to improve control accuracy. Finally, based on Lyapunov stability analysis, all the signals of the closed-loop are proved to be semi-globally uniformly ultimately bounded, and the tracking error converges to a small neighborhood region of the origin in a finite time. A simulation example is presented to demonstrate the effectiveness for the proposed control scheme. 相似文献
10.
Xin Li Yurui Wang Minxuan Xu Yueqin Shi Hemiao Wang Xin Yang Haoting Ying Qi Zhang 《应用聚合物科学杂志》2021,138(19):50406
Polymer electrets have revealed great potential application in electromechanical devices because of the low weight, large quasi-piezoelectric sensitivity, and excellent flexibility. For an electret, a permanent and macroscopic electric field exists on the surface, principally led by a macroscopic electrostatic charge on the surface or a net orientation of polar groups inside the object. Here, progress in the development of polymer electrets is reviewed. After a brief retrospect of the research courses and those typical polymer electrets that are classified into fluorine polymer and nonfluorine polymer, we present a survey on the charging methods, including corona, soft X-ray, contact, thermal and monoenergetic particle beams. The latest representative applications (i.e., power harvesting, sensors, field effect transistors, and biomedicine) based on polymer electrets are also summarized. Finally, we complete this review with a discussion on perspectives and challenges in this field. 相似文献