全文获取类型
收费全文 | 34357篇 |
免费 | 2893篇 |
国内免费 | 955篇 |
专业分类
电工技术 | 1328篇 |
综合类 | 1038篇 |
化学工业 | 6584篇 |
金属工艺 | 1931篇 |
机械仪表 | 2280篇 |
建筑科学 | 1543篇 |
矿业工程 | 618篇 |
能源动力 | 1266篇 |
轻工业 | 2703篇 |
水利工程 | 354篇 |
石油天然气 | 992篇 |
武器工业 | 115篇 |
无线电 | 4672篇 |
一般工业技术 | 6059篇 |
冶金工业 | 2687篇 |
原子能技术 | 367篇 |
自动化技术 | 3668篇 |
出版年
2024年 | 121篇 |
2023年 | 564篇 |
2022年 | 946篇 |
2021年 | 1395篇 |
2020年 | 1038篇 |
2019年 | 948篇 |
2018年 | 1134篇 |
2017年 | 1139篇 |
2016年 | 1229篇 |
2015年 | 1299篇 |
2014年 | 1652篇 |
2013年 | 2158篇 |
2012年 | 2166篇 |
2011年 | 2530篇 |
2010年 | 2000篇 |
2009年 | 1952篇 |
2008年 | 1850篇 |
2007年 | 1466篇 |
2006年 | 1365篇 |
2005年 | 1195篇 |
2004年 | 987篇 |
2003年 | 957篇 |
2002年 | 879篇 |
2001年 | 728篇 |
2000年 | 678篇 |
1999年 | 702篇 |
1998年 | 944篇 |
1997年 | 709篇 |
1996年 | 548篇 |
1995年 | 423篇 |
1994年 | 380篇 |
1993年 | 309篇 |
1992年 | 227篇 |
1991年 | 171篇 |
1990年 | 165篇 |
1989年 | 158篇 |
1988年 | 106篇 |
1987年 | 86篇 |
1986年 | 88篇 |
1985年 | 98篇 |
1984年 | 86篇 |
1983年 | 53篇 |
1982年 | 50篇 |
1981年 | 57篇 |
1980年 | 51篇 |
1979年 | 43篇 |
1978年 | 38篇 |
1977年 | 57篇 |
1976年 | 88篇 |
1975年 | 42篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
De Young RJ 《Applied optics》1986,25(21):3850-3854
Beam profile measurements have been made as a function of time within the laser pulse and C2F5I pressure. Measurements indicate that the profile is determined directly by the optical excitation volume, produced by the solar simulator, and that media distortion plays a minor role compared to the build up of quenching species during the lasing pulse. 相似文献
42.
T. Yang B.H. LiDepartment of Materials Physics University of Science Technology Beijing Beijing ChinaK. Kang T. SuzukiInformation Storage Materials Laboratory Toyota Technological Institute Nagoya - Japan 《金属学报(英文版)》2003,16(4):261-265
(FePt/Ag)n nano-multilayers were deposited on MgO (100) single crystal with laser ablation and then subjected to annealing. FePt L1o grains with (001) texture and thus a large perpendicular magnetic anisotropy constant Ku of the order of 106 J/m3 were formed. A thick Ag layer is found to be favorable for decreasing the dispersion of the easy axis for magnetization. The measurement of time decay of magnetization gave rise to a small activation volume of the order of 10-25m3, showing the promising of being the recording medium for future high density perpendicular recording. 相似文献
43.
The dependent deformations and evidence of structural changes were measured on pastes of C3S containing CaCl2, and on pastes of C3S or a C3S/C2S blend cured at 65°C. It was concluded that the addition of CaCl2 enhances the role of the “pore component” in controlling irreversible strains even when well-hydrated pastes are dried. The formation of ore stable CSH at 65°C can explain the reduction in time-dependent deformations observed for these pastes. Even though a change in pore size distribution occurs at 65°C, it is not considered to affect irreversible strains in well-hydrated pastes. 相似文献
44.
This paper proposes a technique for the detection of head nod and shake gestures based on eye tracking and head motion decision. The eye tracking step is divided into face detection and eye location. Here, we apply a motion segmentation algorithm that examines differences in moving people’s faces. This system utilizes a Hidden Markov Model-based head detection module that carries out complete detection in the input images, followed by the eye tracking module that refines the search based on a candidate list provided by the preprocessing module. The novelty of this paper is derived from differences in real-time input images, preprocessing to remove noises (morphological operators and so on), detecting edge lines and restoration, finding the face area, and cutting the head candidate. Moreover, we adopt a K-means algorithm for finding the head region. Real-time eye tracking extracts the location of eyes from the detected face region and is performed at close to a pair of eyes. After eye tracking, the coordinates of the detected eyes are transformed into a normalized vector of x-coordinate and y-coordinate. Head nod and shake detector uses three hidden Markov models (HMMs). HMM representation of the head detection can estimate the underlying HMM states from a sequence of face images. Head nod and shake can be detected by three HMMs that are adapted by a directional vector. The directional vector represents the direction of the head movement. The vector is HMMs for determining neutral as well as head nod and shake. These techniques are implemented on images, and notable success is notified. 相似文献
45.
PdOx/MnO2 has been examined as a catalyst for CO oxidation using a conventional flow reactor at reaction temperatures between 50 and 150°C. In the reaction conditions of GHSV (gashourlyspacevelocity) of 1.22 × 105/h and CO concentration of 2000 ppm, PdOx/MnO2 showed higher catalytic activity compared with PdOx/Mn2O3, which had been previously reported as an effective catalyst due to the cooperative action of Pd and Mn2O3 for this reaction. The reason for higher activity of PdOx/MnO2 than PdOx/Mn2O3 has been investigated using TPR (temperatureprogrammed reduction) and XPS studies. TPR showed that PdOx/MnO2 could be reduced by CO at much lower temperature than PdOx/Mn2O3. During the experiment of reduction and oxidation, XPS showed that the valence of Mn in the PdOx/MnO2 was between 4+ and 3+, which is higher than that of Mn in the PdOx/Mn2O3 catalyst of which the valence has been reported to be between 3+ and 2+. It is known that in this catalyst system the support supplies oxygen onto Pd, where the oxidation occurs with adsorbed CO, and the ability of the support to provide oxygen improves the performance of the catalyst. Therefore, it was concluded that the readiness of MnO2 to be reduced with maintaining a higher oxidation state showed higher CO oxidation activity than Mn2O3 as support for PdOx. 相似文献
46.
康继辉 《重庆科技学院学报(社会科学版)》2010,(18)
蒙元王朝是一个少数民族政权,在对汉人的任用问题上十分敏感,大部分蒙古最高统治者对汉臣的防范多于信任,甚至干脆不用汉臣,而元世祖忽必烈在元朝的统治者中算是比较开明的,特别是他即位之前及中统时期,大量任用汉臣,这些汉臣也给予了忽必烈充分的回报,他们在忽必烈还是亲王时,充当王府幕僚,为忽必烈出谋划策,积蓄力量,后来又为其夺取汗位立下了汗马功劳. 相似文献
47.
48.
49.
A class of networked control systems is investigated whose communication network is shared with other applications. The design objective for such a system setting is not only the optimization of the control performance but also the efficient utilization of the communication resources. We observe that at a large time scale the data packet delay in the communication network is roughly varying piecewise constant, which is typically true for data networks like the Internet. Based on this observation, a dynamic data packing scheme is proposed within the recently developed packet-based control framework for networked control systems. As expected this proposed approach achieves a fine balance between the control performance and the communication utilization: the similar control performance can be obtained at dramatically reduced cost of the communication resources. Simulations illustrate the effectiveness of the proposed approach. 相似文献
50.
德惠断陷下白垩统登娄库组、营城组、沙河子组储层物性差,勘探风险大.利用岩心观察、铸体薄片鉴定、扫描电镜分析、黏土X线衍射分析等方法,分析储层基本特征、储层成岩作用和控制因素.结果表明:德惠断陷下白垩统碎屑岩储层成分成熟度和结构成熟度较低,储层孔隙类型主要有残余原生孔、次生孔和混合孔,储层物性和孔隙结构较差;压实作用是导致储层物性变差的主要原因,溶蚀作用改善储层物性;纵向上发育2个次生孔隙带,主要形成于中成岩期,次生孔隙带的形成与有机质生烃排酸和断裂有关.研究结果为德惠断陷下白垩统进一步油田勘探提供地质依据,对其他地区类似储层研究有一定借鉴意义. 相似文献