全文获取类型
收费全文 | 952篇 |
免费 | 64篇 |
专业分类
电工技术 | 9篇 |
综合类 | 1篇 |
化学工业 | 239篇 |
金属工艺 | 12篇 |
机械仪表 | 13篇 |
建筑科学 | 35篇 |
矿业工程 | 1篇 |
能源动力 | 8篇 |
轻工业 | 125篇 |
水利工程 | 7篇 |
石油天然气 | 2篇 |
无线电 | 66篇 |
一般工业技术 | 149篇 |
冶金工业 | 250篇 |
原子能技术 | 11篇 |
自动化技术 | 88篇 |
出版年
2023年 | 11篇 |
2022年 | 32篇 |
2021年 | 35篇 |
2020年 | 21篇 |
2019年 | 17篇 |
2018年 | 19篇 |
2017年 | 16篇 |
2016年 | 23篇 |
2015年 | 43篇 |
2014年 | 39篇 |
2013年 | 55篇 |
2012年 | 55篇 |
2011年 | 65篇 |
2010年 | 38篇 |
2009年 | 36篇 |
2008年 | 48篇 |
2007年 | 28篇 |
2006年 | 34篇 |
2005年 | 30篇 |
2004年 | 19篇 |
2003年 | 23篇 |
2002年 | 19篇 |
2001年 | 14篇 |
2000年 | 8篇 |
1999年 | 18篇 |
1998年 | 38篇 |
1997年 | 28篇 |
1996年 | 25篇 |
1995年 | 8篇 |
1994年 | 17篇 |
1993年 | 17篇 |
1992年 | 10篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1986年 | 8篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 8篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1977年 | 7篇 |
1976年 | 17篇 |
1974年 | 6篇 |
1972年 | 3篇 |
1971年 | 4篇 |
1970年 | 6篇 |
排序方式: 共有1016条查询结果,搜索用时 31 毫秒
131.
The effect of structure on the deformation of as-quenched and tempered martensite in an Fe-0.2 pct C alloy 总被引:4,自引:0,他引:4
As-quenched and tempered martensite in an Fe-0.2 pct C alloy were subjected to tensile testing and structural characterization
by light and transmission electron microscopy. The light temper, 400°C-l min, did not change packet morphology, but did reduce
dislocation density, coarsen lath size and cause the precipitation of carbides of a variety of sizes. The yield strength of
the as-quenched martensite was strongly dependent upon packet size according to a Hall-Petch relationship, but tempering significantly
diminished the packet size dependency, a result attributed to packet boundary carbide precipitation and the attendant elimination
of carbon segregation present in the as-quenched martensite because of autotempering. Examination of thin foils from strained
tensile specimens showed that a well-defined cell structure developed in the as-quenched martensite, but that the random distribution
of jogged dislocations and carbide particles produced by tempering persisted on deformation of the tempered specimens.
The authors were formerly Research Assistant and Professor, respectively, at Lehigh University, Bethlehem, PA. 相似文献
132.
The effect of threat on the process of bargaining was investigated experimentally by asking Ss to imagine proceeding across a certain route on a map and having various experiences. Threat was seen to affect bargaining detrimentally. In that regard, cooperative ventures were seen to be safer than competitive ones. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
133.
Winkelmann S Schaeffter T Eggers H Doessel O 《IEEE transactions on medical imaging》2005,24(2):254-262
The steady-state free precessing (SSFP) sequences, widely used in MRI today, acquire data only during a short fraction of the repetition time (TR). Thus, they exhibit a poor scan efficiency. In this paper, a novel approach to extending the acquisition window for a given TR without considerably modifying the basic sequence is explored for radial SSFP sequences. The additional data are primarily employed to increase the signal-to-noise ratio, rather than to improve the temporal resolution of the imaging. The approach is analyzed regarding its effect on the image SNR (signal to noise ratio) and the reconstruction algorithm. Results are presented for phantom experiments and cardiac functions studies. The gain in SNR is most notable in rapid imaging, since SNR enhancement for a constant repetition time may be used to compensate for the increase in noise resulting from angular undersampling. 相似文献
134.
Gerhard?Sinn Herwig?MayerEmail author Stefanie?Stanzl-Tschegg 《Journal of Materials Science》2005,40(16):4325-4332
Surfaces created by ultrasonic-assisted cutting (UC) of beech and spruce and of medium density fibreboard (MDF) are compared to surfaces obtained by conventional linear cutting (CC) using a sharp tool. Topography is evaluated performing roughness measurements and scanning electron microscopy. No effect of UC procedure on mean roughness is found. The surface of MDF and large areas of the surfaces of the woods appear similar after UC and CC, whereas other regions show impact marks and microscopic reels produced by the periodic oscillation of the tool in UC. The wettability of surfaces produced with both wood processing techniques is similar. Surface free energy measurements indicate accelerated ageing caused by UC, probably due to heating. 相似文献
135.
Fluoroscopy-based 3-D reconstruction of femoral bone cement: a new approach for revision total hip replacement 总被引:1,自引:0,他引:1
de la Fuente M Ohnsorge JA Schkommodau E Jetzki S Wirtz DC Radermacher K 《IEEE transactions on bio-medical engineering》2005,52(4):664-675
In revision total hip replacement the removal of the distal femoral bone cement can be a time consuming and risky operation due to the difficulty in determining the three-dimensional (3-D) boundary of the cement. We present a new approach to reconstruct the bone cement volume by using just a small number of calibrated multiplanar X-ray images. The modular system design allows the surgeon to react intraoperatively to problems arising during the individual situation. When encountering problems during conventional cement removal, the system can be used on demand to acquire a few calibrated X-ray images. After a semi-automatic segmentation and 3-D reconstruction of the cement with a deformable model, the system guides the surgeon through a free-hand navigated or robot-assisted cement removal. The experimental evaluation using plastic test implants cemented into anatomic specimen of human femoral bone has shown the potential of this method with a maximal error of 1.2 mm (0.5 mm RMS) for the distal cement based on just 4-5 multiplanar X-ray images. A first test of the complete system, comparing the 3-D-reconstruction with a computed tompgraphy data set, confirmed these results with a mean error about 1 mm. 相似文献
136.
A single-blind randomized study was conducted on young (18–21 years, n = 16) and mature (25–35 years, n = 16) drivers to assess how age, combined with a modest dose of alcohol (0.7 g/kg for males and 0.6 g/kg for females), influenced performance on a driving simulator. The driving tasks included detecting the presence of a vehicle on the horizon as quickly as possible, estimating the point on the road that an approaching vehicle would have passed by the participants’ vehicle (time-to-collision) and overtaking another vehicle against a steady stream of oncoming traffic. The results of the vehicle detection task showed that detection times were significantly slower with maturity, alcohol consumption and lower approaching vehicle speeds (50 kph), particularly on curved sections of road. Approaching vehicle speed was also found to significantly influence time-to-collision (TTC) judgments, such that faster approach speeds led to less underestimated (and therefore riskier) judgments of TTC than slower speeds. In the overtaking task, mature participants demonstrated impaired discrimination skills with varying approaching vehicle speeds, while young participants recorded significantly slower speeds while overtaking a vehicle, thus increasing the time that they spent in the opposing lane. In conclusion, young and mature drivers demonstrated pivotal differences in behavior in this study. Young drivers showed a greater tendency to engage in risky driving, while experienced drivers appeared to be more susceptible to perceptual influences. Overall, alcohol consumption impaired a driver's ability to divide attention, but had little effect on decision-making processes. 相似文献
137.
Semiconductor quantum dots (QDs) have been used in a simple fluorometric assay to detect single cells of the pathogenic Escherichia coli O157:H7 serotype. Composed of CdSe/ZnS core/shell QDs conjugated to streptavidin, this system exhibits 2 orders of magnitude more sensitivity than a similar assay using a common organic dye. Selectivity for this pathogenic bacterial strain over a common lab strain (E. coli DH5alpha), which is gained from the use of specific biotinylated antibodies, is also demonstrated for QD labeling. Under continuous excitation, these QDs retain high fluorescence intensities for hours, whereas a typical organic dye bleaches within seconds, allowing for more rapid and accurate identification of E. coli O157:H7 in single-cell fluorescence-based assays. This indirect QD labeling method, based on antibody-antigen and streptavidin-biotin interactions, is flexible enough to expand to other systems and has great potential for use in simultaneous multicolor detection schemes. 相似文献
138.
Scanning transmission electron microscopy (STEM) coupled with electron energy loss spectroscopy (EELS) was used to determine the chemical distribution of semiconductor shell material around colloidal core-shell CdSe/ZnS quantum dots (QDs). EELS signals from positions around the QD indicate a well-defined shell of ZnS surrounding the CdSe core, but the distribution of the shell material is highly anisotropic. This nonuniformity may reflect the differences in chemical activity of the crystal faces of the core QD and implies a nonoptimal QD surface passivation. 相似文献
139.
Willets KA Nishimura SY Schuck PJ Twieg RJ Moerner WE 《Accounts of chemical research》2005,38(7):549-556
Fluorescence imaging of single molecules at room temperature is a powerful technique for studying complex condensed phase systems and revealing structure and dynamics hidden by ensemble measurements. Successful single-molecule spectroscopic experiments rely upon strong emitters that can be detected at the level of individual copies above the relevant background signals. This Account discusses a class of nonlinear optical chromophores that not only are well-suited for single-molecule imaging but also offer additional beneficial properties such as a significant ground-state dipole moment, moderate hyperpolarizability, and sensitivity to local environment. An overview of the photophysical properties of several members of this class of molecules as well as a mechanism to help understand the environmental sensitivity is presented. Some preliminary applications of the chromophores as single-molecule reporters in cellular and polymer systems are discussed, along with detection of the emitters by two-photon fluorescence. 相似文献
140.