全文获取类型
收费全文 | 69639篇 |
免费 | 16497篇 |
国内免费 | 986篇 |
专业分类
电工技术 | 2149篇 |
技术理论 | 4篇 |
综合类 | 1555篇 |
化学工业 | 22248篇 |
金属工艺 | 1876篇 |
机械仪表 | 2346篇 |
建筑科学 | 3305篇 |
矿业工程 | 758篇 |
能源动力 | 1965篇 |
轻工业 | 9012篇 |
水利工程 | 723篇 |
石油天然气 | 1050篇 |
武器工业 | 146篇 |
无线电 | 11729篇 |
一般工业技术 | 15597篇 |
冶金工业 | 3244篇 |
原子能技术 | 388篇 |
自动化技术 | 9027篇 |
出版年
2024年 | 105篇 |
2023年 | 450篇 |
2022年 | 866篇 |
2021年 | 1380篇 |
2020年 | 2291篇 |
2019年 | 3798篇 |
2018年 | 3826篇 |
2017年 | 4196篇 |
2016年 | 4567篇 |
2015年 | 4827篇 |
2014年 | 5079篇 |
2013年 | 6714篇 |
2012年 | 4491篇 |
2011年 | 4511篇 |
2010年 | 4319篇 |
2009年 | 4213篇 |
2008年 | 3830篇 |
2007年 | 3508篇 |
2006年 | 3106篇 |
2005年 | 2542篇 |
2004年 | 2365篇 |
2003年 | 2423篇 |
2002年 | 2589篇 |
2001年 | 2215篇 |
2000年 | 1809篇 |
1999年 | 1100篇 |
1998年 | 1011篇 |
1997年 | 721篇 |
1996年 | 587篇 |
1995年 | 478篇 |
1994年 | 401篇 |
1993年 | 340篇 |
1992年 | 255篇 |
1991年 | 232篇 |
1990年 | 232篇 |
1989年 | 200篇 |
1988年 | 172篇 |
1987年 | 158篇 |
1986年 | 134篇 |
1985年 | 128篇 |
1984年 | 111篇 |
1983年 | 77篇 |
1982年 | 70篇 |
1981年 | 59篇 |
1980年 | 82篇 |
1979年 | 49篇 |
1978年 | 61篇 |
1977年 | 59篇 |
1976年 | 76篇 |
1975年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
Joon‐Young Jun Sosuke Nakajima Koji Yamazaki Yuji Kawai Hajime Yasui Yasuyuki Konishi 《International Journal of Food Science & Technology》2015,50(4):871-877
Cystoseira hakodatensis is an unutilised brown algae belonging to family Sargassaceae. A crude methanol extract from the algae showed inhibitory effects on the growths of Bacillus cereus and Bacillus licheniformis. To isolate the major antimicrobial agent, a sequential active‐guided isolation procedure was applied: liquid–liquid extraction, column chromatography and bio‐autography. A marked antimicrobial agent (active α) was isolated in hydrophobic fraction and was determined to phenolics without carbohydrates and proteins by phytochemical test. Regarding the antimicrobial potential, the isolated active α showed better inhibitory effects against B. cereus and B. licheniformis at 2 and 4 times of lower concentrations (62.5 and 31.3 μg mL?1) in comparison with epigallocatechin gallate. These results showed that C. hakodatensis is a potential source of antimicrobial agent capable of preventing the growth of the two bacteria. 相似文献
43.
44.
【摘要】 目的 研究和探讨125I粒子条联合胆道支架植入治疗恶性梗阻性黄疸的临床疗效。方法 2011年6月—2013年9月收治恶性梗阻性黄疸患者40例。行胆道支架植入术治疗患者18例,为对照组;采用125I粒子条联合胆道支架植入患者22例,为观察组。两组均采用经皮肝穿刺胆道引流(PTCD)并胆道支架植入。结果 观察组与对照组的平均胆道开通时间分别为(8.7 ± 0.7)和(6.2 ± 0.4)个月,两组比较差异有统计学意义(P < 0.05)。观察组与对照组术后平均生存时间分别为(11.4 ± 0.8)和(8.7 ± 0.5)个月,生存时间的差异有统计学意义(P < 0.05)。术后近期疗效及并发症两组之间的比较无明显差异(P > 0.05),但是远期疗效有显著差异(P < 0.05)。结论 与对照组相比,观察组的术后生存时间及胆道开通时间明显延长,对于125I粒子条联合支架治疗恶性梗阻性黄疸值得进一步临床研究。
相似文献
相似文献
45.
Yafei Liu Zhilong Fu Xingyu Chen Yaxin Wei Bo Zhang Aimin Chang 《Journal of the American Ceramic Society》2021,104(5):2134-2142
Rare-earth ions doped Ca0.9R0.1CeNbMoO8 (R = Y, Sm, Nd, La) ceramics have been successfully prepared by solid-state method, and their modifications to the microstructure and electrical properties are also investigated. The rare-earth ions doped ceramics exhibit the scheelite structure. With the increase in the radius of rare-earth ions, the lattice distortion and bond interaction will be enhanced, and the consistency of grain size will be reduced. The ceramics exhibit negative temperature coefficient (NTC) thermistor characteristics in the temperature range of 473 K-1273 K, and the activation energy decreases with the increase of the radius of rare-earth ions. Rare-earth ions doping can increase the content of Ce3+ ions and promote the conductivity of ceramics. Except for Sm3+-doped ceramics, the high-temperature aging rate of other ceramics is less than 2%. The existence of some metastable Sm2+ ions in Sm3+-doped ceramics not only increases the activation energy, but also reduces the high-temperature stability of the ceramics. 相似文献
46.
47.
Matthew O'Sullivan Daire
hUallachin Patrícia Oliveira Antunes Eleanor Jennings Mary Kelly‐Quinn 《河流研究与利用》2019,35(2):146-158
Cattle access to streams has been linked globally with degradation of stream water quality, driven largely by bank erosion and resultant instream, fine sediment deposition. The majority of evidence on such effects is however based in arid and semiarid regions of the United States and Australia, with few studies relating to cool temperate climates such as Northwest Europe. In this study, “Quorer” resuspendable sediment samples were taken from riffle geomorphic units upstream (control) and at two points downstream (pressure and recovery) of cattle access points in headwater streams in agricultural catchments in Ireland to assess levels of deposited stream sediment. Samples were taken in April/May (2016) prior to the grazing season and in October (2016) at the end of the grazing season. Sites in good‐high ecological status catchments and less than good ecological status catchments were included in the study. Higher levels of sediment were found downstream of cattle access points in both good‐high status and less than good status catchments; however, the impacts of access points were spatially confined to, in most cases, the area immediately downstream of the point of access. There was a strong correlation between deposited sediment mass and organic matter (OM) mass, with levels of OM increasing linearly with deposited sediment mass. Levels of measured sediment were negatively correlated with riparian habitat health (measured using a qualitative habitat assessment). The results of this study highlight the need for measures to prevent cattle access to headwater streams where access points can be many in order to manage local habitat quality and downstream water quality issues. 相似文献
48.
Muhammad Sheeraz Mamoon Ur Rashid Asad Ali Fazli Akram Ho Jeong Lee Jin San Choi Jong-Seong Bae Yong Soo Kim Young-Han Shin Chang Won Ahn Tae Heon Kim 《Journal of the European Ceramic Society》2021,41(10):5155-5162
We demonstrate the structural evolution of polymorphic phases in Al2O3-inserted SrMnO3 ceramics synthesized by solid state reaction. While the 4H-hexagonal phase is predominant in pure SrMnO3 ceramics, a small amount of 6H-hexagonal polymorph is identified in addition to the primary 4H-hexagonal SrMnO3 and the secondary hexagonal SrAl2O4 phases in the as-sintered ceramics, evidenced by x-ray diffraction and subsequent Rietveld refinement analyses. The existence of the 6H-hexagonal SrMnO3 phase is corroborated using Raman spectroscopy. The chemical compositions and electronic structures of the Al2O3-inserted SrMnO3 compounds are also examined using energy dispersive spectroscopy and x-ray photoelectron spectroscopy, respectively. The first-principles calculations reveal that there is no clear difference between the total energies of 4H- and 6H-hexagonal polymorphs regardless of the presence/absence of Sr and oxygen vacancies. Possible origins are discussed with the estimation of actual strain based on the refined lattice parameter of 6H SrMnO3. 相似文献
49.
50.
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