全文获取类型
收费全文 | 792篇 |
免费 | 34篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 18篇 |
综合类 | 1篇 |
化学工业 | 172篇 |
金属工艺 | 19篇 |
机械仪表 | 20篇 |
建筑科学 | 13篇 |
矿业工程 | 1篇 |
能源动力 | 70篇 |
轻工业 | 43篇 |
水利工程 | 6篇 |
石油天然气 | 13篇 |
无线电 | 108篇 |
一般工业技术 | 160篇 |
冶金工业 | 46篇 |
原子能技术 | 4篇 |
自动化技术 | 138篇 |
出版年
2023年 | 10篇 |
2022年 | 19篇 |
2021年 | 35篇 |
2020年 | 19篇 |
2019年 | 17篇 |
2018年 | 46篇 |
2017年 | 30篇 |
2016年 | 41篇 |
2015年 | 27篇 |
2014年 | 40篇 |
2013年 | 76篇 |
2012年 | 48篇 |
2011年 | 53篇 |
2010年 | 39篇 |
2009年 | 42篇 |
2008年 | 24篇 |
2007年 | 24篇 |
2006年 | 20篇 |
2005年 | 16篇 |
2004年 | 15篇 |
2003年 | 11篇 |
2002年 | 14篇 |
2001年 | 7篇 |
2000年 | 9篇 |
1999年 | 11篇 |
1998年 | 19篇 |
1997年 | 9篇 |
1996年 | 7篇 |
1995年 | 8篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1987年 | 6篇 |
1984年 | 4篇 |
1983年 | 7篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1972年 | 3篇 |
1971年 | 3篇 |
1959年 | 2篇 |
排序方式: 共有832条查询结果,搜索用时 578 毫秒
91.
92.
Sparsity-motivated automatic target recognition 总被引:1,自引:0,他引:1
We present an automatic target recognition algorithm using the recently developed theory of sparse representations and compressive sensing. We show how sparsity can be helpful for efficient utilization of data for target recognition. We verify the efficacy of the proposed algorithm in terms of the recognition rate and confusion matrices on the well known Comanche (Boeing-Sikorsky, USA) forward-looking IR data set consisting of ten different military targets at different orientations. 相似文献
93.
This paper deals with the estimation of the reliability function and parameters of a doubly truncated Weibull distribution using point and credible/highest posterior density intervals. Bayesian estimates, which obtained, compared with their corresponding classical counterparts. 相似文献
94.
The degradation pattern of the synthetic absorbable polyester is thought to occur from the center of the material outward, and the bulk degradation is therefore attributed largely to the chemical composition of the material. It was hypothesized that this pattern might be altered by changing the morphology of the material, i.e., by introducing molecular orientation into the system. A new solid state uniaxial orientation (SS-UO) process was used to orient two types of lactide polymer films. The films were exposed to a phosphate buffered solution, then chemically, mechanically, and visually analyzed after predetermined times. This paper explores the results of flexural testing which will be later correlated with microscopic degradation events, as part of the larger degradation study. The results show that, while orientation does not have an overall significant effect on the flexural modulus, there is a significant material/orientation interaction. 相似文献
95.
Sand Control Measures and Sand Drift Fences 总被引:1,自引:0,他引:1
Sand drift and sand dune movements are typical logistic problems facing civilian and industrial cities in arid and semiarid countries like Saudi Arabia. Some of these countries are considered active when it comes to sand drift and sand dune movement, due to the high annual sand drift rate. Urban cities have extensive facilities in the middle of these active areas that require good protection and innovative solutions?to this problem. This paper briefly reviews sand movement control measures and highlights sand drift fence design guidelines for the first time. 相似文献
96.
A Castillo W Nasser G Condemine S Reverchon 《Canadian Metallurgical Quarterly》1998,1442(2-3):148-160
Erwinia chrysanthemi is a broad host range phytopathogenic enterobacterium responsible for soft-rot disease of many plant species. The pecT gene encodes a repressor that negatively regulates the expression of virulence factors, such as pectinases, motility or exopolysaccharide synthesis. The cloned pecT gene was overexpressed using a phage T7 system. The purification of PecT involved the use of a TSK-heparin column and delivered the PecT protein that was purified to near homogeneity. The purified repressor displayed a 34 kDa apparent molecular mass. Gel-filtration experiments revealed that the PecT protein is a dimer. Band-shift assays demonstrated that the tetramer of the PecT protein could specifically bind in vitro to the regulatory regions of the pectate lyase genes with variable affinities. In addition, we demonstrated that PecT represses its own synthesis by interacting independently with two 200 bp regions, R1 and R2, located from -382 to -632 and -17 to -234, respectively, from the distal P1 promoter and from -465 to -715 and -100 to -317 from the P2 proximal promoter. We propose a model that explains the regulation exerted by PecT on its target genes and that integrates the phenotype obtained with a PecT overproducing pec-1 mutant or a pecT mutant. 相似文献
97.
The Sn-Cu eutectic alloy has been produced by rapid solidification using the melt-spinning technique, and both Zn and Bi have
been added individually to it, in the ratio 0.5 wt.%. X-ray diffraction (XRD) analysis and differential thermal analysis (DTA)
have been carried out. Resistivity, Vickers microhardness (HV), and yield stress (σy) have been measured. Also a new method for measuring creep has been described using a HV tester. The creep measured by this
method is termed “microcreep.” It is a quick, nondestructive method and requires a small sample, about 1 cm2, with thickness 1 mm or less. The results show that formation of Cu39Sn11 occurs due to the addition of both Zn and Bi. The addition of Zn increases HV and σy, but slightly lowers the creep resistance; however, the addition of Bi deteriorates the creep resistance. Also, it is found
that the creep rate of as-quenched melt-spun alloys is high. 相似文献
98.
H. H. Afify S. A. Nasser S. E. Demian 《Journal of Materials Science: Materials in Electronics》1991,2(3):152-156
The influence of substrate temperature on the structural, optical and electrical properties of ZnO films prepared by the spray pyrolysis method using aqueous solution of zinc acetate has been investigated. The films are polycrystalline and X-ray diffraction measurements show a strong preferred orientation along the [002] plane which is strongly dependent on the substrate temperature. Optical absorption spectra, show high transparency of the film (90–95% transmission) in the visible range, with a sharp absorption edge around 375 nm wavelength of light which closely corresponds to the intrinsic band gap of ZnO (3.3 eV). ZnO films with the lowest resistivity, which is due to the increased mobility resulting from the improvement of the crystallinity of the films, can be prepared at a substrate temperature of 490 °C. 相似文献
99.
The recirculation of naive lymphocytes from blood to lymph that is initiated in high endothelial venules (HEV) of secondary lymphoid organs such as lymph nodes and Peyer's patches (PP) is regulated by multiple interactions of adhesion receptor/counter-receptor pairs involving both selectins and integrins. We showed previously that blocking of only L-selectin is sufficient to ablate trafficking of naive CD4 cells and the development of their responses in peripheral lymph nodes but not in PP where alpha4beta7 integrins are thought to primarily regulate entry. However, although antibody to alpha4 integrins partially inhibited homing of naive CD4 cells to PP and not to lymph nodes, there was no effect on the development primary responses in these tissues or spleens. Since previous studies indicate that both alpha4beta7 integrins and L-selectin regulate adhesion of naive cells to PP HEV, we examined the effect a blockade of both adhesion pathways on the recirculation of naive CD4 cells. There was no detectable homing of naive CD4 cells to PP or lymph nodes when interactions with both receptors were inhibited, resulting in a profound depletion of naive CD4 cells and loss of antigen responses in these sites. In contrast, increased numbers of naive CD4 cells and responses of higher magnitude were found in the spleen. The results demonstrate recirculation of naive CD4 cells through tissues where entry is controlled through HEV is essential for the local generation of primary responses. 相似文献
100.
Composite materials are being utilized in a multitude of industrial and commercial applications. This is due to their desirable features such as light weight, durability and strength. This presents quite a challenge to the field of nondestructive testing and evaluation (NDT&E). Due to the material complexity associated with these materials, many techniques have been shown to be ineffective when inspecting these materials. The ability of microwaves to penetrate deeply inside such dielectric materials and composites makes microwave NDT techniques very attractive for interrogating such materials. Microwaves are also sensitive to the presence of dissimilar layers in these materials which allows for accurate thickness variation measurement in the range of a few micrometers at frequencies as low as 10 GHz. Near-field microwave inspection techniques were successfully used for detecting and locating defects and voids of different sizes and shapes in composites. For optimal detection, the standoff distance between the sensor and the composite and frequency of operation were used as optimization parameters to improve the detection capability. Carbon-loaded composites present a challenge to microwave NDT because of the lossy nature of carbon, especially at high microwave frequencies. Lower frequencies penetrate more (deeper) in carbon-loaded composites, however, the size of the waveguide sensor increases drastically at lower frequencies and consequently the resolution degrades rapidly as well. To overcome this dilemma, open-ended rectangular waveguides loaded with a dielectric material will be used to inspect carbon-loaded composites. The loading of the waveguide reduces the frequency of operation and keeps the small size of the waveguide (i.e. increases the penetration depth and maintains the resolution). Carbon-loaded composites with disbonds will be inspected and the ability of utilizing loaded rectangular waveguides for carbon-loaded composites inspection will be assessed. 相似文献