全文获取类型
收费全文 | 32292篇 |
免费 | 3661篇 |
国内免费 | 1964篇 |
专业分类
电工技术 | 1731篇 |
技术理论 | 3篇 |
综合类 | 3359篇 |
化学工业 | 3111篇 |
金属工艺 | 2306篇 |
机械仪表 | 2811篇 |
建筑科学 | 5471篇 |
矿业工程 | 1931篇 |
能源动力 | 1004篇 |
轻工业 | 1959篇 |
水利工程 | 1127篇 |
石油天然气 | 2214篇 |
武器工业 | 352篇 |
无线电 | 1759篇 |
一般工业技术 | 4214篇 |
冶金工业 | 1208篇 |
原子能技术 | 281篇 |
自动化技术 | 3076篇 |
出版年
2024年 | 89篇 |
2023年 | 562篇 |
2022年 | 962篇 |
2021年 | 1089篇 |
2020年 | 1203篇 |
2019年 | 1007篇 |
2018年 | 952篇 |
2017年 | 1125篇 |
2016年 | 1230篇 |
2015年 | 1307篇 |
2014年 | 2020篇 |
2013年 | 2150篇 |
2012年 | 2404篇 |
2011年 | 2504篇 |
2010年 | 2000篇 |
2009年 | 1938篇 |
2008年 | 1656篇 |
2007年 | 2220篇 |
2006年 | 1853篇 |
2005年 | 1546篇 |
2004年 | 1357篇 |
2003年 | 1092篇 |
2002年 | 881篇 |
2001年 | 830篇 |
2000年 | 715篇 |
1999年 | 552篇 |
1998年 | 402篇 |
1997年 | 423篇 |
1996年 | 343篇 |
1995年 | 289篇 |
1994年 | 224篇 |
1993年 | 181篇 |
1992年 | 154篇 |
1991年 | 108篇 |
1990年 | 114篇 |
1989年 | 102篇 |
1988年 | 59篇 |
1987年 | 42篇 |
1986年 | 37篇 |
1985年 | 41篇 |
1984年 | 33篇 |
1983年 | 35篇 |
1982年 | 24篇 |
1981年 | 7篇 |
1980年 | 26篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1975年 | 4篇 |
1964年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
1.
《Ceramics International》2021,47(19):27386-27394
In order to control the pore characteristics and macroscopical performance of porous ceramics, roles of the freeze casting parameters are the key points. Herein, aligned dendritic porous SiC was fabricated by freeze casting of PCS-camphene solutions with different solid loading, freeze front velocity, temperature gradient, and freezing temperature. Influence of these parameters on the microstructure and compressive strength of porous SiC was investigated. With increasing the PCS content, freeze temperature, freeze front velocity or temperature gradient, degree of undercooling of the camphene was increased, resulting in the formation of smaller pore size, decreased porosity and increased compressive strength. Compared to variables of freeze temperature and temperature gradient, increased freeze front velocity was more efficiency in improving the compressive strength of porous SiC, owing to the formation of smaller pore size and longer secondary dendritic crystals. Promising micron-sized porous SiC with high porosity (79.93 vol%) and satisfactory strength (15.84 MPa) was achieved for 10% PCS-camphene solution under optimized freezing conditions. 相似文献
2.
In the recent advancements in image and video analysis, the detection of salient regions in the image becomes the initial step. This plays a crucial role in deciding the performance of such algorithms. In this work, a Multi-Resolution Feature Extraction (MRFE) technique that makes use of Discrete Wavelet Convolutional Neural Network (DWCNN) for generating features is employed. An Enhanced Feature Extraction (EFE) module extracts additional features from the high level features of the DWCNN, which are used to frame both channel as well as spatial attention models for yielding contextual attention maps. A new hybrid loss function is also proposed, which is a combination of Balanced Cross Entropy (BCE) loss and Edge based Structural Similarity (ESSIM) loss that effectively identifies and segments the salient regions with clear boundaries. The method is tested exhaustively with five different benchmark datasets and is proved superior to the existing state-of-the-art methods with a minimum Mean Absolute error (MAE) of 0.03 and F-measure of 0.956. 相似文献
3.
《中国有色金属学会会刊》2021,31(8):2468-2478
An acoustic emission (AE) experiment was carried out to explore the AE location accuracy influenced by temperature. A hollow hemispherical specimen was used to simulate common underground structures. In the process of heating with the flame, the pulse signal of constant frequency was stimulated as an AE source. Then AE signals received by each sensor were collected and used for comparing localization accuracy at different temperatures. Results show that location errors of AE keep the same phenomenon in the early and middle heating stages. In the later stage of heating, location errors of AE increase sharply due to the appearance of cracks. This provides some beneficial suggestions on decreasing location errors of structural cracks caused by temperature and improves the ability of underground structure disaster prevention and control. 相似文献
4.
《Ceramics International》2021,47(19):27351-27360
A series of xPbO–(45-x)CuO–55B2O3 glasses (5 ≤ x ≥ 40 mol %) were prepared by the melt-quenching technique. The X-ray diffraction (XRD) patterns of the prepared glasses are found to have amorphous structure. An extensive ultrasonic study has been made to explore the structural role of PbO and CuO in the borate network. Various elastic properties were calculated from the measured data of density and ultrasonic velocity. Ultrasonic velocity and elastic moduli revealed broad humps at about 20 mol % PbO, which are attributed to the borate anomaly. Below 20 mol % PbO, all Pb2+ ions are considered to be entering the borate network as a glass modifier. This results in the transforms the borate network from an open structure to a denser three-dimensional structure due to BO3 → BO4 conversion. Beyond 20 mol, addition of PbO results in the formation of metaborate, pyroborate, and orthoborate units with NBOs. This weakness the glass structure and decrease both ultrasonic velocity and elastic moduli. The elastic properties were predicted and quantitatively analyzed by taking into account the effect of boron coordination number on the compositional and structural parameters involved in Makishima–Mackenzie's theory, ring deformation model and bond compression model. An excellent agreement between the computed theoretical and experimental elastic moduli, micro-harness and Poisson's ratio was achieved for majority of samples. 相似文献
5.
During the service life of structural sealant glazing (SSG) facades, the load-bearing capacity of the silicone bonds needs to be guaranteed. Laboratory tests can assess the durability of SSG-systems based on mechanical characteristics of the bond after simultaneous exposure to both climatic and mechanical loads. This article studies how the material characteristics of two common structural sealants are affected by laboratory and field exposure. Dynamic mechanical analysis (DMA) confirms a reduction in the dynamic modulus of exposed silicone samples. Results from thermogravimetric analysis, Fourier-transform infrared spectroscopy, differential scanning calorimetry, and small-angle X-ray scattering/wide-angle X-ray scattering show differences between the two sealants and indicate no/minor changes in the composition and morphology of the laboratory and field exposed sealants. Mechanical characterization methods, such as DMA, and tensile and shear testing of the structural bond, are shown to be sensitive toward the combined climatic and mechanical loadings, and are hence suitable for studying degradation mechanisms of structural sealants. 相似文献
6.
7.
8.
《International Journal of Hydrogen Energy》2022,47(45):19758-19771
In this study, the effects of cell temperature and relative humidity on charge transport parameters are numerically analyzed. In order to perform this analysis, three-dimensional and anisotropic numerical models are developed. The numerical models are integrated into the experimental values for anisotropic electrical conductivities, as depending on cell temperature and relative humidity, that were obtained from our previous study. The achieved results indicate that the values of current densities in the in-plane direction increase with increasing cell temperature and relative humidity, while the current densities reach a maximum in the rib regions for both the numerical model at the through-plane direction. The behaviors of electrolyte potentials are similar with changes in the cell temperature and relative humidity. In addition, the cathode electrical potentials in both the in-plane direction and through-plane direction do not change to a considerable amount with increasing cell temperature and relative humidity. 相似文献
9.
Ewa Bczyska Katarzyna Karolina Pels Subhadip Basu Jakub Wodarczyk Baej Ruszczycki 《International journal of molecular sciences》2021,22(8)
Numerous brain diseases are associated with abnormalities in morphology and density of dendritic spines, small membranous protrusions whose structural geometry correlates with the strength of synaptic connections. Thus, the quantitative analysis of dendritic spines remodeling in microscopic images is one of the key elements towards understanding mechanisms of structural neuronal plasticity and bases of brain pathology. In the following article, we review experimental approaches designed to assess quantitative features of dendritic spines under physiological stimuli and in pathological conditions. We compare various methodological pipelines of biological models, sample preparation, data analysis, image acquisition, sample size, and statistical analysis. The methodology and results of relevant experiments are systematically summarized in a tabular form. In particular, we focus on quantitative data regarding the number of animals, cells, dendritic spines, types of studied parameters, size of observed changes, and their statistical significance. 相似文献
10.
Tilman Sauter Karl Kratz Samy Madbouly Frank Klein Matthias Heuchel Andreas Lendlein 《大分子材料与工程》2021,306(4):2000730
Isotropic and anisotropic shape-memory polymer foams are prepared by supercritical carbon dioxide foaming from a multiblock copolymer (PDLCL) consisting of poly(ω-pentadecalactone) and poly(ε-caprolactone) segments. Analysis by micro-computed tomography reveals for the anisotropic PDLCL foam cells a high shape anisotropy ratio of R = 1.72 ± 0.62 with a corresponding Young's compression moduli ratio between longitudinal and transversal direction of 4.3. The experimental compression data in the linear elastic range can be well described by the anisotropic open foam model of Gibson and Ashby. A micro-morphological analysis for single pores using scanning electron microscopy images permits the correlation between the macroscopic stress-compression behavior and microscale structural changes. 相似文献