全文获取类型
收费全文 | 54163篇 |
免费 | 5358篇 |
国内免费 | 2855篇 |
专业分类
电工技术 | 3662篇 |
技术理论 | 6篇 |
综合类 | 4099篇 |
化学工业 | 8889篇 |
金属工艺 | 2950篇 |
机械仪表 | 3445篇 |
建筑科学 | 4638篇 |
矿业工程 | 1618篇 |
能源动力 | 1774篇 |
轻工业 | 4074篇 |
水利工程 | 1143篇 |
石油天然气 | 2586篇 |
武器工业 | 553篇 |
无线电 | 6324篇 |
一般工业技术 | 6130篇 |
冶金工业 | 2284篇 |
原子能技术 | 662篇 |
自动化技术 | 7539篇 |
出版年
2024年 | 293篇 |
2023年 | 1076篇 |
2022年 | 1967篇 |
2021年 | 2649篇 |
2020年 | 1918篇 |
2019年 | 1599篇 |
2018年 | 1734篇 |
2017年 | 1916篇 |
2016年 | 1709篇 |
2015年 | 2374篇 |
2014年 | 2845篇 |
2013年 | 3368篇 |
2012年 | 3790篇 |
2011年 | 3820篇 |
2010年 | 3619篇 |
2009年 | 3426篇 |
2008年 | 3306篇 |
2007年 | 2896篇 |
2006年 | 2901篇 |
2005年 | 2297篇 |
2004年 | 1646篇 |
2003年 | 1378篇 |
2002年 | 1478篇 |
2001年 | 1295篇 |
2000年 | 1142篇 |
1999年 | 1177篇 |
1998年 | 868篇 |
1997年 | 740篇 |
1996年 | 701篇 |
1995年 | 530篇 |
1994年 | 472篇 |
1993年 | 321篇 |
1992年 | 282篇 |
1991年 | 206篇 |
1990年 | 152篇 |
1989年 | 137篇 |
1988年 | 84篇 |
1987年 | 61篇 |
1986年 | 47篇 |
1985年 | 33篇 |
1984年 | 25篇 |
1983年 | 17篇 |
1982年 | 18篇 |
1981年 | 13篇 |
1980年 | 17篇 |
1979年 | 7篇 |
1974年 | 2篇 |
1970年 | 2篇 |
1959年 | 8篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
斜程红外辐射大气透射率的简易计算 总被引:3,自引:2,他引:3
简述了计算红外辐射大气中透射比常用的方法,利用实验数据计算得到了大气中水汽(H2O)、CO2的光谱吸收系数,给出了水汽吸收系数与温度、相对湿度之间的关系.给出了计算高空红外辐射透射比的方法.对于斜程的透射比,将路程按照一定的精度分成小段,各小段透射比相乘可以得到总的透射比,根据高度、压强、透射比之间的关系,通过推导得到了计算斜程红外辐射透射比的简易公式,可以简化斜程透射率的计算.本方法在工程应用中具有一定的参考价值. 相似文献
992.
鄂尔多斯盆地奥陶系马家沟组五段膏盐下白云岩储层形成的主控因素 总被引:1,自引:0,他引:1
近期勘探实践表明,鄂尔多斯盆地东部奥陶系马家沟组五段膏盐下白云岩具有良好的天然气勘探开发潜力。为此,综合岩心观察、薄片鉴定、物性分析及地球化学特征等资料,对其岩石学、储集空间和孔渗特征等开展了系统研究。结果表明,鄂尔多斯盆地奥陶系膏盐下储集层为孔隙型白云岩储层,纵向上分布在马五6亚段、马五7亚段和马五9亚段。马五6亚段储集层岩性主要为颗粒白云岩和斑状粉晶白云岩,马五7亚段和马五9亚段储集层岩性主要为颗粒白云岩和粉-细晶白云岩。三个储层段储集空间均以溶蚀孔洞为主,次为残余粒间孔、晶间溶孔、晶间孔和微裂缝,平均孔隙度分别为5.84%、6.81%和7.03%。沉积古地貌、海平面变化和准同生期大气淡水溶蚀作用等因素共同控制膏盐下白云岩储集层的发育与分布。研究认为位于盐岩边界线外侧的中央古隆起带和榆林-横山隆起带地势相对较高,颗粒滩沉积厚度大,在准同生期和浅埋藏期易于发生大气淡水溶蚀作用,其内部赋存的孔隙不易被膏盐岩充填,是盆地内膏盐下有利白云岩储集层的发育区。 相似文献
993.
Peripheral Nerve‐Derived Matrix Hydrogel Promotes Remyelination and Inhibits Synapse Formation 下载免费PDF全文
Jian‐Long Zou Sheng Liu Jia‐Hui Sun Wei‐Hong Yang Yi‐Wei Xu Zi‐Long Rao Bin Jiang Qing‐Tang Zhu Xiao‐Lin Liu Jin‐Lang Wu Calvin Chang Hai‐Quan Mao Eng‐Ang Ling Da‐Ping Quan Yuan‐Shan Zeng 《Advanced functional materials》2018,28(13)
Regeneration of injured nerve tissues requires intricate interplay of complex processes like axon elongation, remyelination, and synaptic formation in a tissue‐specific manner. A decellularized nerve matrix‐gel (DNM‐G) and a decellularized spinal cord matrix‐gel (DSCM‐G) are prepared from porcine sciatic nerves and spinal cord tissue, respectively, to recapitulate the microenvironment cues unique to the native tissue functions. Using an in vitro dorsal root ganglion–Schwann cells coculture model and proteomics analysis, it is confirmed that DNM‐G promotes far stronger remyelination activity and reduces synapse formation of the regenerating axons in contrast to DSCM‐G, Matrigel, and collagen I, consistent with its tissue‐specific function. Bioinformatics analysis indicates that the lack of neurotrophic factors and presence of some axon inhibitory molecules may contribute to moderate axonal elongation activity, while laminin β2, Laminin γ1, collagens, and fibronectin in DNM‐G promote remyelination. These results confirm that DNM‐G is a promising matrix material for peripheral nerve repair. This study provides more insights into tissue‐specific extracellular matrix components correlating to biological functions supporting functional regeneration. 相似文献
994.
Emancipating Target‐Functionalized Carbon Dots from Autophagy Vesicles for a Novel Visualized Tumor Therapy 下载免费PDF全文
Jipeng Li Siwei Yang Yuan Deng Peiwei Chai Yucheng Yang Xiaoyu He Xiaoming Xie Zhenhui Kang Guqiao Ding Huifang Zhou Xianqun Fan 《Advanced functional materials》2018,28(30)
Killing the tumor cells by a visualized targeting system is a promising strategy with which to achieve high efficiency, low side effects, and a high survival rate for tumor therapy. Here, an autophagy regulation strategy is reported by emancipating target‐functionalized carbon dots from autophagy vesicles for the efficient visualized tumor therapy. The folic acid modified N‐doped carbon dots (FN‐CDs) are selectively endocytosed (specific cellular uptake rate >93.40%) and stably existed in autophagic vacuoles in tumor cells. Next, the autophagic vacuoles are “opened” by the autophagy inhibitors. Released FN‐CDs activate both the intrinsic and extrinsic apoptotic signaling pathway and kill tumor cells efficiently. This method achieves therapeutic effects with high performance in 26 types of tumor cell lines. Animal experiments show that the 30 d survival rate of this therapeutic strategy is much higher than that with traditional drug treatment. Real‐time imaging/monitoring and its effects on the intelligent tumor therapy are also demonstrated based on the stable, strong, green emission from FN‐CDs. 相似文献
995.
Video transmission over IEEE 802.11e wireless networks still shows poor performance for large bandwidth demand and frequently changed environments. Thus, several enhancements of IEEE 802.11e were proposed. On the other hand, big frames and simultaneous sending of adjacent frames always cause packet dropping for buffer overflow. In the past, we proposed an IEEE 802.11e enhancement named DFAA and a content aware mechanism to solve the above problems. The motivation of this paper is to find a proper way to integrate these two mechanisms. A DFAA enhancement (DFAA-E) is proposed to make up the insufficiency of content aware mechanism. Experiments results show that the combination of DFAA-E and content aware mechanism improves the video decoded quality greatly. And its performance can be further enhanced by selecting the suitable settings of certain parameters. 相似文献
996.
Jun Ye Kai Wang Zhan Chen Fei-Fei An Yi Yuan Chi Zhang Xiao-Hong Zhang Chun-Sing Lee 《Organic Electronics》2014,15(12):3514-3520
A novel device concept was realized for simple single-layer small-molecule white organic light emitting devices. The single organic active layer here is simply comprised of a newly synthesized sky-blue fluorescent bipolar host (TPASO) and a common orange phosphorescent dopant. Suppressed singlet Föster energy transfer induced by a low-concentration doping and spontaneous high- to low-lying triplet energy transfer, respectively, lead to sky-blue fluorescence from TPASO and orange phosphorescence from the dopant. The resulting two-organic-component device exhibits a low turn-on voltage of 2.4 V, maximum current/power efficiencies up to 11.27 ± 0.02 cd A−1 and 14.15 ± 0.03 lm W−1, and a warm-white CIE coordinate of (0.42, 0.45) at 1000 cd m−2. 相似文献
997.
像素级数字积分探测是一种新型的红外探测技术,其具备电荷处理能力高、动态范围大等特点,能够有效提升红外系统探测灵敏度,在各类红外弱信号探测领域具有巨大的应用潜力。像素级数字积分技术中的二次量化技术,可对在总噪声中占比较大的量化噪声进行有效抑制。对像素级数字积分探测系统中的量化步长进行优化设计以及对二次量化技术进行研究,分析量化步长的改变对像素级数字积分红外探测系统性能的影响;分析二次量化的原理及特点,研究其在应用中的关键参数设计,从而推动二次量化技术的发展,实现像素级数字积分探测系统更高灵敏度探测应用。 相似文献
998.
999.
Yuanjing Lin Mallika Bariya Hnin Yin Yin Nyein Liisa Kivimki Sanna Uusitalo Elina Jansson Wenbo Ji Zhen Yuan Tuomas Happonen Christina Liedert Jussi Hiltunen Zhiyong Fan Ali Javey 《Advanced functional materials》2019,29(33)
Development of reliable glucose sensors for noninvasive monitoring without interruption or limiting users' mobility is highly desirable, especially for diabetes diagnostics, which requires routine/long‐term monitoring. However, their applications are largely limited by the relatively poor stability. Herein, a porous membrane is synthesized for effective enzyme immobilization and it is robustly anchored to the modified nanotextured electrode solid contacts, so as to realize glucose sensors with significantly enhanced sensing stability and mechanical robustness. To the best of our knowledge, this is the first report of utilizing such nanoporous membranes for electrochemical sensor applications, which eliminates enzyme escape and provides a sufficient surface area for molecular/ion diffusion and interactions, thus ensuring the sustainable catalytic activities of the sensors and generating reliable measureable signals during noninvasive monitoring. The as‐assembled nanostructured glucose sensors demonstrate reliable long‐term stable monitoring with a minimal response drift for up to 20 h, which delivers a remarkable enhancement. Moreover, they can be integrated into a microfluidic sensing patch for noninvasive sweat glucose monitoring. The as‐synthesized nanostructured glucose sensors with remarkable stability can inspire developments of various enzymatic biosensors for reliable noninvasive composition analysis and their ultimate applications in predictive clinical diagnostics, personalized health‐care monitoring, and chronic diseases management. 相似文献
1000.