全文获取类型
收费全文 | 343896篇 |
免费 | 31472篇 |
国内免费 | 18982篇 |
专业分类
电工技术 | 24787篇 |
技术理论 | 7篇 |
综合类 | 27602篇 |
化学工业 | 50788篇 |
金属工艺 | 19887篇 |
机械仪表 | 21864篇 |
建筑科学 | 27070篇 |
矿业工程 | 9510篇 |
能源动力 | 10105篇 |
轻工业 | 27024篇 |
水利工程 | 7643篇 |
石油天然气 | 15737篇 |
武器工业 | 3265篇 |
无线电 | 42319篇 |
一般工业技术 | 37187篇 |
冶金工业 | 15367篇 |
原子能技术 | 4078篇 |
自动化技术 | 50110篇 |
出版年
2024年 | 1473篇 |
2023年 | 5002篇 |
2022年 | 9851篇 |
2021年 | 13681篇 |
2020年 | 10110篇 |
2019年 | 8178篇 |
2018年 | 9059篇 |
2017年 | 10736篇 |
2016年 | 9576篇 |
2015年 | 13838篇 |
2014年 | 17911篇 |
2013年 | 21826篇 |
2012年 | 24731篇 |
2011年 | 26532篇 |
2010年 | 24178篇 |
2009年 | 23201篇 |
2008年 | 22950篇 |
2007年 | 21855篇 |
2006年 | 20651篇 |
2005年 | 16647篇 |
2004年 | 12021篇 |
2003年 | 10273篇 |
2002年 | 10619篇 |
2001年 | 9185篇 |
2000年 | 7380篇 |
1999年 | 6313篇 |
1998年 | 4772篇 |
1997年 | 3990篇 |
1996年 | 3661篇 |
1995年 | 3070篇 |
1994年 | 2433篇 |
1993年 | 1763篇 |
1992年 | 1425篇 |
1991年 | 1071篇 |
1990年 | 872篇 |
1989年 | 670篇 |
1988年 | 578篇 |
1987年 | 395篇 |
1986年 | 310篇 |
1985年 | 251篇 |
1984年 | 204篇 |
1983年 | 148篇 |
1982年 | 142篇 |
1981年 | 131篇 |
1980年 | 118篇 |
1979年 | 88篇 |
1978年 | 53篇 |
1977年 | 56篇 |
1976年 | 88篇 |
1974年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
62.
小剂量辐射对肿瘤细胞K_(562)及肿瘤病人天然杀伤细胞(NK)活性的影响 总被引:2,自引:0,他引:2
已知小剂量辐射可增强机体免疫功能。从对高本底地区的调查发现,该地区居民肿瘤死亡率及某些肿瘤发病率有所降低(1)。NK细胞能直接杀伤肿瘤细胞,在肿瘤免疫中起着重要的作用。本文观察小剂量辐射对肿瘤病人和正常人外周血淋巴细胞NK活性的相对效应以及对人红白血病细胞(K(562)细胞)的影响,以期从体外买验来探索较小剂量辐射对肿瘤治疗的影响 相似文献
63.
Min-Shiang Hwang Chih-Wei Lin Cheng-Chi Lee 《Electronics letters》2002,38(23):1429-1431
An authenticated multiple-key agreement protocol is proposed. The protocol is not only secure against the unknown-key attack but also more efficient than other protocols. 相似文献
64.
65.
Using AuGeNiCr multilayered metals as the wafer bonding medium, long-wavelength GaInAsP/InP vertical cavity surface emitting lasers employing Al-oxide/Si as the upper and lower distributed Bragg reflectors were fabricated on Si substrate with the bonding interface formed outside the vertical cavity surface emitting laser cavity. Laser emission at 1.545 μm was measured under pulsed operations near room temperature. The low-temperature metallic bonding process demonstrates a great potential in device fabrication 相似文献
66.
The use of capillary electrophoresis (CE) for clinically relevant assays is attractive since it often presents many advantages over contemporary methods. The small-diameter tubing that holds the separation medium has led to the development of multicapillary instruments, and simultaneous sample analysis. Furthermore, CE is compatible with a wide range of detectors, including UV-Vis, fluorescence, laser-induced fluorescence, electrochemistry, mass spectrometry, radiometric, and more recently nuclear magnetic resonance, and laser-induced circular dichroism systems. Selection of an appropriate detector can yield highly specific analyte detection with good mass sensitivity. Another attractive feature of CE is the low consumption of sample and reagents. However, it is paradoxical that this advantage also leads to severe limitation, namely poor concentration sensitivity. Often high analyte concentrations are required in order to have injection of sufficient material for detection. In this regard, a series of devices that are broadly termed 'analyte concentrators' have been developed for analyte preconcentration on-line with the CE capillary. These devices have been used primarily for non-specific analyte preconcentration using packing material of the C18 type. Alternatively, the use of very specific antibody-containing cartridges and enzyme-immobilized microreactors have been demonstrated. In the current report, we review the likely impact of the technology of capillary electrophoresis and the role of the CE analyte concentrator-microreactor on the analysis of biomolecules, present on complex matrices, in a clinical laboratory. Specific examples of the direct analysis of physiologically-derived fluids and microdialysates are presented, and a personal view of the future of CE in the clinical environment is given. 相似文献
67.
通过密度测定和DSC热分析,观测了超高分子量聚乙烯的辐射效应。实验结果表明:在吸收剂量0—1.13MGy范围内,密度随吸收剂量的增加而增大,熔化热和熔点也有所增加,特别是在低剂量范围内增加十分明显。以上结果都说明,超高分子量聚乙烯在辐照过程中,结晶在完善或有新的结晶形成 相似文献
68.
Coplanar waveguide-fed uniplanar bow-tie antenna 总被引:3,自引:0,他引:3
Yu-De Lin Syh-Nan Tsai 《Antennas and Propagation, IEEE Transactions on》1997,45(2):305-306
The design of coplanar waveguide (CPW)-fed bow-tie antenna for the 2.4-GHz ISM band is described. A coplanar waveguide-to-coplanar strips (CPW-to-CPS) balun is used to obtain the balanced feed line for the printed bow-tie. An analysis method based on the mixed potential integral equation method is used to characterize the input characteristics of the bow-tie antenna. The numerical results obtained are in good agreement with the experimental data. Through experiments with bow-tie antennas of various extended angles, the bow-tie antenna with a 90° extended angle exhibits the widest bandwidth in the desired frequency band which has a bandwidth of 17% for a VSWR <1.5:1 相似文献
69.
Color image retrieval based on hidden Markov models 总被引:1,自引:0,他引:1
In this correspondence, a new approach to retrieving images from a color image database is proposed. Each image in the database is represented by a two-dimensional pseudo-hidden Markov model (2-D PHMM), which characterizes the chromatic and spatial information about the image. In addition, a flexible pictorial querying method is used, by which users can paint the rough content of the desired images in a query picture. Image matching is achieved by comparing the query picture with each 2-D PHMM in the database. Experimental results show that the proposed approach is indeed effective. 相似文献
70.
制作压力传感器时,在二氧化硅层上淀积多晶硅膜,既可利用优良的机械特性,又可保证压敏电阻与衬底间具有良好的绝缘性,由此可大大提高器件的温度特性。介绍了一种多晶硅压力传感器的原理和设计。实验结果表明,这类传感器具有灵敏度好,精度高等特点,电路工作范围为0-250℃,且具有良好的温度稳定性。 相似文献