全文获取类型
收费全文 | 275篇 |
免费 | 9篇 |
专业分类
电工技术 | 1篇 |
化学工业 | 85篇 |
金属工艺 | 3篇 |
机械仪表 | 2篇 |
建筑科学 | 9篇 |
能源动力 | 1篇 |
轻工业 | 18篇 |
无线电 | 36篇 |
一般工业技术 | 50篇 |
冶金工业 | 42篇 |
自动化技术 | 37篇 |
出版年
2022年 | 3篇 |
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 5篇 |
2018年 | 6篇 |
2017年 | 4篇 |
2016年 | 8篇 |
2015年 | 2篇 |
2014年 | 8篇 |
2013年 | 9篇 |
2012年 | 11篇 |
2011年 | 12篇 |
2010年 | 14篇 |
2009年 | 4篇 |
2008年 | 10篇 |
2007年 | 9篇 |
2006年 | 17篇 |
2005年 | 6篇 |
2004年 | 8篇 |
2003年 | 9篇 |
2002年 | 6篇 |
2001年 | 8篇 |
2000年 | 5篇 |
1999年 | 8篇 |
1998年 | 21篇 |
1997年 | 7篇 |
1996年 | 12篇 |
1995年 | 3篇 |
1994年 | 7篇 |
1993年 | 11篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 6篇 |
1984年 | 1篇 |
1983年 | 4篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1971年 | 3篇 |
1968年 | 1篇 |
排序方式: 共有284条查询结果,搜索用时 9 毫秒
1.
We fabricated nickel-shims including various types of structures with dimensions from hundreds of nanometers to several microns. The mastering process was made by electron-beam lithography, lift-off and reactive ion etching techniques. Then the structures were copied into a UV-curable ORMOCER-material and the Ni-shims were fabricated by electroforming using UV-copies as masters. The experiments showed that the use of UV-copying evades typical quartz master sticking and cracking problems. Furthermore, all features were replicated in the final Ni-shim as they existed in the quartz master proving the method suitable for the fabrication of the Ni-shims from the quartz masters with high precision. 相似文献
2.
3.
Microring resonator channel dropping filters 总被引:17,自引:0,他引:17
Little B.E. Chu S.T. Haus H.A. Foresi J. Laine J.-P. 《Lightwave Technology, Journal of》1997,15(6):998-1005
Microring resonators side coupled to signal waveguides provide compact, narrow band, and large free spectral range optical channel dropping filters. Higher order filters with improved passband characteristics and larger out-of-band signal rejection are realized through the coupling of multiple rings. The analysis of these devices is approached by the novel method of coupling of modes in time. The response of filters comprised of an arbitrarily large dumber of resonators may be written down by inspection, as a continued fraction. This approach simplifies both the analysis and filter synthesis aspects of these devices 相似文献
4.
The work reported here represents initial attempts to develop a complete kinetic and mechanistic understanding of the reaction chemistry of H2S under coal liquefaction conditions, using both model systems and coal. Hydrogen sulphide was found to promote/catalyse the transfer of hydrogen from tetralin to 2-hydroxyquinoline (2-HOQ). The presence of H2S can increase the rate of hydrogen transfer from tetralin to 2-HOQ by a factor of 10 compared with the same reaction run in the absence of H2S. The energy of activation for hydrogen transfer was found to decrease by ≈5 kcal mol−1 in the presence of H2S. The presence of H2S was also found to promote loss of oxygen from 2-HOQ to form small amounts of quinoline. No evidence of CC or CN bond cleavage in 2-HOQ was noted under any of the reaction conditions studied. These results suggest that the presence of H2S reduces the temperatures necessary to promote effective hydrogen transfer from tetralin by 50–75 °C. Moreover, they imply that similar effects occur in H2S-promoted coal liquefaction. 相似文献
5.
This paper describes a validation study performed by comparing the Climate-SAF Surface Albedo Product (SAL) to ground truth observations over Greenland and the ice-covered Arctic Ocean. We compare Advanced Very High Resolution Radiometer (AVHRR)-based albedo retrievals to data from the Greenland Climate Network (GCN) weather stations and the floating ice station Tara for polar summer 2007. The AVHRR dataset consists of 2755 overpasses. The overpasses are matched to in situ observations spatially and temporally. The SAL algorithm presented here derives the surface broadband albedo from AVHRR channels 1 and 2 using an atmospheric correction, temporal sampling of an empirical Bidirectional Reflectance Distribution Function (BRDF), and a narrow-to-broadband conversion algorithm. The satellite product contains algorithms for snow, sea ice, vegetation, bare soil, and water albedo. At the Summit and DYE-2 stations on the Greenland ice sheet, instantaneous SAL RMSE is 0.073. The heterogeneous surface conditions at satellite pixel scale over the stations near the Greenland west coast increase RMSE to > 0.12. Over Tara, the instantaneous SAL RMSE is 0.069. The BRDF sampling approach reduces RMSE over the ice sheet to 0.053, and to 0.045 over Tara. Taking into account various sources of uncertainty for both satellite retrievals and in situ observations, we conclude that SAL agrees with in situ observations within their limits of accuracy and spatial representativeness. 相似文献
6.
John Wiens Robert Sutter Jon Blanchard Naikoa Aguilar-Amuchastegui Stephen Laine 《Remote sensing of environment》2009,113(7):1370-73
A major focus of conservation is on protecting areas to ensure the persistence of biological diversity. Because such areas may be large, not easily accessible, subject to change, and sensitive to the surrounding landscape, remote sensing can be a valuable tool in establishing and managing protected areas. We describe three case studies to illustrate how remote sensing can contribute to setting priorities for conservation actions, monitoring the status of conservation targets, and evaluating the effectiveness of conservation strategies. In the Connecticut River watershed, remote sensing has been used to assess flood regimes and identify key areas of floodplain forests and their context for conservation planning. At Eglin Air Force Base in Florida, remote sensing has provided information to assess the effectiveness of management strategies to restore fire to the longleaf pine sandhills ecosystem, control invasive species, and prioritize annual prescribed burns. In eastern US forests, remote sensing is being used to evaluate the ecological condition and changes at properties where direct access would be difficult.As the resolution and capacities of remote-sensing technology continue to develop, however, several issues are becoming increasingly important. It is essential that the spatial and temporal resolution of remote-sensing data be matched to the relevant scales of biodiversity, major threats, and management actions. Data layers must be compatible, both in scale and in measurement properties, and key patterns must be distinguished from irrelevant detail, especially at the finer scales of application in local management. Combining remote sensing with ground surveys can expand the array of information used in management and contribute to the ecological interpretation of remote-sensing data. Because conservation funds are always limited, remote sensing also must be cost effective. This requires balancing the wealth of detail afforded by ever-finer resolution of remote-sensing data with what is actually needed to implement sound conservation and management. Remote sensing is a valuable tool, but it is not a panacea for all of the challenges of conservation monitoring and management. 相似文献
7.
In this paper, we examine the possibilities of using voxel representations as a generic way for expressing complex and feature-rich geometry on current and future GPUs. We present in detail a compact data structure for storing voxels and an efficient algorithm for performing ray casts using this structure. We augment the voxel data with novel contour information that increases geometric resolution, allows more compact encoding of smooth surfaces, and accelerates ray casts. We also employ a novel normal compression format for storing high-precision object-space normals. Finally, we present a variable-radius postprocess filtering technique for smoothing out blockiness caused by discrete sampling of shading attributes. Based on benchmark results, we show that our voxel representation is competitive with triangle-based representations in terms of ray casting performance, while allowing tremendously greater geometric detail and unique shading information for every voxel. Our voxel codebase is open sourced and available at http://code.google.com/p/efficient-sparse-voxel-octrees/. 相似文献
8.
Ana Dolores Santiago de Freitas Everardo Valadares Sá Barretto de Sampaio Bárbara Laine Ribeiro da Silva Jarcilene Silva de Almeida Cortez R?mulo Sim?es Cezar Menezes 《Nutrient Cycling in Agroecosystems》2012,94(2-3):181-192
Although biological nitrogen fixation (BNF) is considered the main input of N in mature and regenerating native tropical vegetation, it has seldom been quantified. Biomass and N accumulation and fixation were determined for spontaneously occurring herbaceous species in caatinga areas in four regeneration stages (2, 17, 39 and >50?years after abandonment from agricultural use). BNF was estimated using the 15N natural-abundance method. The 2-year regeneration area had the highest total herb (6,355?kg?ha?1) and legume (262?kg?ha?1) biomass production, N stocks (82?kg?ha?1) and fixed N (5.0?kg?ha?1). N2-fixing legumes (nine species in the sampled area) contributed over 97?% of legume biomass in all areas. Macroptilium gracile added the largest amount of N (3.9?kg?ha?1 in the 2-year regeneration area) because of its large biomass production (205?kg?ha?1), although it was not the species with the highest proportion of fixed N (76?%). All of the N2-fixing species obtained large proportions of their N from symbiosis, most of them more than 50?%.However, the amounts of fixed N per unit area were relatively low (0.22?C5.00?kg?ha?1) because the biomass of N2-fixing species was always less than 5?% of the total herb biomass. 相似文献
9.
Jerome Kluza Victoriane Peugnet Blanche Daunou William Laine Gwenola Kervoaze Gaëlle Rmy Anne Loyens Patrice Maboudou Quentin Fovez Corinne Grangette Isabelle Wolowczuk Philippe Gosset Guillaume Garon Philippe Marchetti Florence Pinet Muriel Pichavant Emilie Dubois-Deruy 《International journal of molecular sciences》2022,23(1)
Mitochondrial dysfunctions are implicated in several pathologies, such as metabolic, cardiovascular, respiratory, and neurological diseases, as well as in cancer and aging. These metabolic alterations are usually assessed in human or murine samples by mitochondrial respiratory chain enzymatic assays, by measuring the oxygen consumption of intact mitochondria isolated from tissues, or from cells obtained after physical or enzymatic disruption of the tissues. However, these methodologies do not maintain tissue multicellular organization and cell-cell interactions, known to influence mitochondrial metabolism. Here, we develop an optimal model to measure mitochondrial oxygen consumption in heart and lung tissue samples using the XF24 Extracellular Flux Analyzer (Seahorse) and discuss the advantages and limitations of this technological approach. Our results demonstrate that tissue organization, as well as mitochondrial ultrastructure and respiratory function, are preserved in heart and lung tissues freshly processed or after overnight conservation at 4 °C. Using this method, we confirmed the repeatedly reported obesity-associated mitochondrial dysfunction in the heart and extended it to the lungs. We set up and validated a new strategy to optimally assess mitochondrial function in murine tissues. As such, this method is of great potential interest for monitoring mitochondrial function in cohort samples. 相似文献
10.
Samuli Leppälä 《Papers in Regional Science》2018,97(3):467-484
Empirical evidence shows that innovation is geographically concentrated, but whether localized knowledge spillovers provide a logically valid explanation for this phenomenon is unclear. I show that in the context of cost‐reducing R&D spillovers between Cournot oligopolists the explanation is plausible: localized knowledge spillovers encourage agglomeration, but whether this leads to higher levels of effective R&D depends on the extent of the spillovers, the number of firms, and the industry's R&D efficiency. Contrary to the earlier theoretical work, this illustrates a context, in which the localized knowledge spillover explanation is actualized, and provides necessary conditions, which can be empirically tested. 相似文献