全文获取类型
收费全文 | 24501篇 |
免费 | 167篇 |
国内免费 | 632篇 |
专业分类
电工技术 | 347篇 |
综合类 | 140篇 |
化学工业 | 2320篇 |
金属工艺 | 680篇 |
机械仪表 | 1325篇 |
建筑科学 | 1291篇 |
矿业工程 | 590篇 |
能源动力 | 153篇 |
轻工业 | 6040篇 |
水利工程 | 363篇 |
石油天然气 | 387篇 |
武器工业 | 71篇 |
无线电 | 1488篇 |
一般工业技术 | 7953篇 |
冶金工业 | 544篇 |
原子能技术 | 289篇 |
自动化技术 | 1319篇 |
出版年
2023年 | 36篇 |
2022年 | 50篇 |
2021年 | 71篇 |
2020年 | 57篇 |
2019年 | 35篇 |
2018年 | 44篇 |
2017年 | 27篇 |
2016年 | 66篇 |
2015年 | 79篇 |
2014年 | 148篇 |
2013年 | 156篇 |
2012年 | 2288篇 |
2011年 | 2940篇 |
2010年 | 647篇 |
2009年 | 295篇 |
2008年 | 1975篇 |
2007年 | 1970篇 |
2006年 | 1600篇 |
2005年 | 1565篇 |
2004年 | 1361篇 |
2003年 | 1206篇 |
2002年 | 1047篇 |
2001年 | 1030篇 |
2000年 | 912篇 |
1999年 | 618篇 |
1998年 | 330篇 |
1997年 | 281篇 |
1996年 | 284篇 |
1995年 | 286篇 |
1994年 | 286篇 |
1993年 | 221篇 |
1992年 | 295篇 |
1991年 | 266篇 |
1990年 | 283篇 |
1989年 | 288篇 |
1988年 | 187篇 |
1987年 | 196篇 |
1986年 | 231篇 |
1985年 | 242篇 |
1984年 | 231篇 |
1983年 | 210篇 |
1982年 | 192篇 |
1981年 | 157篇 |
1980年 | 128篇 |
1979年 | 92篇 |
1978年 | 63篇 |
1977年 | 29篇 |
1976年 | 33篇 |
1975年 | 29篇 |
1974年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
A molecular structure viewer program, MOSBY has been developed for studies that use atomic coordinates to understand the structures of protein molecules. The program is designed to be portable with a comprehensive user interface by our high-throughput graphics library. In addition, it cooperates with extension modules customized for individual research topics and analysis. For example, an electron density module loads and displays electron density maps derived in X-ray crystallographic analysis superimposed to an atomic model. A molecular dynamics module reads a trajectory file of the results of molecular dynamics calculations and animates the structure. These plug-in modules are devised to function without modification to the MOSBY program. For variations of analysis and calculations with atomic coordinates, the portability and extensibility illustrated by MOSBY play an important rule in scientific computational tools with active software development. 相似文献
992.
993.
Mullett H O'Donnell T Felle P O'Rourke K FitzPatrick D 《Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine》2002,216(1):37-42
Several implant systems may be used to fuse the skull to the upper cervical spine (occipitocervical fusion). Current biomechanical evaluation is restricted by the limitations of human cadaveric specimens. This paper describes the design and validation of a synthetic testing model of the occipital bone. Data from thickness measurement and pull-out strength testing of a series of human cadaveric skulls was used in the design of a high-density rigid polyurethane foam model. The synthetic occipital model demonstrated repeatable and consistent morphological and biomechanical properties. The model provides a standardized environment for evaluation of occipital implants. 相似文献
994.
Organosilane self-assembled monolayers (SAMs) have been applied to resist materials for nanolithography based on scanning probe microscopy. An organosilane SAM was prepared on Si substrates from a precursor, that is octadecyltrimethoxysilane. Using an atomic force microscope with a conductive probe, current was injected from the probe into the SAM-covered Si substrate so that the SAM was locally degraded at the probe-contacting point. Nanoscale patterns drawn on the SAM was clearly imaged by lateral force microscopy. The patterning could be conducted in air while, in vacuum at the order of 10(-6) Torr, no detectable patterns were fabricated. The presence of adsorbed water at the probe/sample junction was confirmed to be crucial for the patterning of the SAM/Si. Its mechanism was, thus, ascribed to electrochemical reactions of both the SAM and Si with adsorbed water. 相似文献
995.
Recently an electromagnetic hexapole system for the correction of the spherical aberration of the objective lens of a 200 kV transmission electron microscope has been constructed by Haider and coworkers. By appropriately exciting the hexapole elements it is possible to adjust specific values of the spherical aberration coefficient ranging from the value of the original uncorrected instrument over zero even to negative values. In the first part of the paper the consequences of the tunable spherical aberration are investigated. New imaging modes are available: By adjustment of an optimum value for the spherical-aberration coefficient, the point resolution of phase-contrast imaging can be extended to the information limit. Phase-contrast imaging can be improved by a reduced level of contrast delocalisation. For zero aberration contrast delocalisation does not occur. In this case high-resolution investigations are carried out under amplitude-contrast conditions, where the local image intensity of crystalline objects is controlled by electron diffraction channelling. The defocus and spherical aberration values related to the new imaging modes are given. In the second part novel applications of the instrument to semiconductor heterostructures and ceramic grain boundaries are examined. 相似文献
996.
997.
998.
Tanaka M Yoshimura M Suto M Yokota A Asano K Sukara E Tomita F 《Journal of Bioscience and Bioengineering》2002,93(6):531-536
A highly potent allelopathic factor, lepidimoide, was initially extracted from mucilage of germinated cress seeds. Polysaccharide extracted from okra (Abelmoschus esculentum Moench) is considered to have a similar structure to lepidimoide as its repeating unit. We therefore initiated the screening of enzymes capable of degrading okra polysaccharide into lepidimoide from endophytes. We discovered an endophytic fungal strain AHU9748 isolated from Coleus galeatus, which produced an oligosaccharide having similar properties to lepidimoide on thin layer chromatography. The physico-chemical data from ESI-MS, NMR spectra and other analyses also showed the purified product to be identical to lepidimoide. The strain AHU9748 was identified as a fungus belonging to the coelomycetes, closely related to the genus Colletotrichum, based on morphological characteristics and sequence analysis of the 18S rDNA and ITS region. 相似文献
999.
Characterization of the microbial community in an anaerobic ammonium-oxidizing biofilm cultured on a nonwoven biomass carrier 总被引:7,自引:0,他引:7
The enrichment and characterization of anaerobic ammonium-oxidizing biofilm cultures are ongoing in our laboratories. Biomass, with a predominately red color, demonstrating simultaneous removal of ammonium and nitrite under autotrophic and anoxic conditions, which is characteristic of anaerobic ammonium-oxidizing planctomycetes, was enriched and maintained for an extended period on a polyester nonwoven carrier. To investigate the bacterial composition of the mature biofilm community, 16S rDNA sequences were amplified by PCR and comparative analyses using DNA databases were conducted. Only one sequence had a notable similarity (92.2%) to that of the first discovered anaerobic ammonium-oxidizing planctomycete and lesser, yet significant, similarities to the 16S rDNA sequences of other recently reported anaerobic ammonium-oxidizing strains. The newly discovered strain (designated KSU-1) reported here was dominant among detectable members of the biofilm community. By fluorescence imaging, KSU-1 was shown to form spherical clusters wrapped in a thin layer of Zoogloea sp. Possible interactions and interdependencies of these two species are discussed with regard to the putative unculturability of the anaerobic ammonium-oxidizing planctomycetes. 相似文献
1000.
Kim YJ Yoshizawa M Takenaka S Murakami S Aoki K 《Journal of Bioscience and Bioengineering》2002,93(6):584-588
The two ammonia-assimilating enzymes glutamate dehydrogenase (GDH; EC 1.4.1.4) and glutamine synthetase (GS; EC 6.3.1.2) were synthesized steadily during the cell growth of Klebsiella pneumoniae F-5-2 that can utilize NH4+ and NO3- simultaneously under aerobic conditions. The enzymes were purified to homogeneity from cell extracts and characterized. The molecular mass of the purified GDH was 300 kDa with six identical 52-kDa subunits. GDH showed its maximal activity (aminating) at pH 8.0 and was stable between pHs 5.5 and 11.5. The enzyme was NADP-specific and strongly inhibited by Ag+. It catalyzed the amination of 2-ketovalerate, 2-ketoadipate, and 2-ketobutyrate, in addition to 2-ketoglutarate. The purified GS has a molecular mass of 470 kDa with eight identical 60-kDa subunits. GS showed its maximal activity at pH 8.0 and was stable between pHs 6.0 and 7.0. The enzyme was strongly inhibited by Fe3+, Hg2+, and Cu2+. 相似文献