全文获取类型
收费全文 | 39758篇 |
免费 | 4249篇 |
国内免费 | 3124篇 |
专业分类
电工技术 | 539篇 |
技术理论 | 1篇 |
综合类 | 3493篇 |
化学工业 | 8124篇 |
金属工艺 | 819篇 |
机械仪表 | 331篇 |
建筑科学 | 9766篇 |
矿业工程 | 1237篇 |
能源动力 | 791篇 |
轻工业 | 12538篇 |
水利工程 | 3246篇 |
石油天然气 | 990篇 |
武器工业 | 38篇 |
无线电 | 472篇 |
一般工业技术 | 1707篇 |
冶金工业 | 1228篇 |
原子能技术 | 382篇 |
自动化技术 | 1429篇 |
出版年
2024年 | 278篇 |
2023年 | 765篇 |
2022年 | 1482篇 |
2021年 | 1785篇 |
2020年 | 1657篇 |
2019年 | 1533篇 |
2018年 | 1485篇 |
2017年 | 1671篇 |
2016年 | 1761篇 |
2015年 | 1678篇 |
2014年 | 2529篇 |
2013年 | 2607篇 |
2012年 | 2967篇 |
2011年 | 3153篇 |
2010年 | 2325篇 |
2009年 | 2282篇 |
2008年 | 2000篇 |
2007年 | 2534篇 |
2006年 | 2175篇 |
2005年 | 1869篇 |
2004年 | 1561篇 |
2003年 | 1279篇 |
2002年 | 993篇 |
2001年 | 798篇 |
2000年 | 700篇 |
1999年 | 557篇 |
1998年 | 445篇 |
1997年 | 361篇 |
1996年 | 303篇 |
1995年 | 277篇 |
1994年 | 235篇 |
1993年 | 163篇 |
1992年 | 159篇 |
1991年 | 114篇 |
1990年 | 109篇 |
1989年 | 83篇 |
1988年 | 74篇 |
1987年 | 64篇 |
1986年 | 60篇 |
1985年 | 34篇 |
1984年 | 40篇 |
1983年 | 21篇 |
1982年 | 18篇 |
1981年 | 12篇 |
1980年 | 29篇 |
1979年 | 38篇 |
1959年 | 9篇 |
1958年 | 5篇 |
1956年 | 5篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
小剂量辐射对肿瘤细胞K_(562)及肿瘤病人天然杀伤细胞(NK)活性的影响 总被引:2,自引:0,他引:2
已知小剂量辐射可增强机体免疫功能。从对高本底地区的调查发现,该地区居民肿瘤死亡率及某些肿瘤发病率有所降低(1)。NK细胞能直接杀伤肿瘤细胞,在肿瘤免疫中起着重要的作用。本文观察小剂量辐射对肿瘤病人和正常人外周血淋巴细胞NK活性的相对效应以及对人红白血病细胞(K(562)细胞)的影响,以期从体外买验来探索较小剂量辐射对肿瘤治疗的影响 相似文献
12.
13.
粉喷桩处理软弱地基在祁临高速公路的应用 总被引:1,自引:1,他引:0
结合工程实例,介绍了粉喷桩的所属类型,粉喷桩对软弱地基加固的原因,所适应土质及加固特点,阐述了祁临十八合同段的粉喷桩施工过程及施工中应注意的若干问题,得出粉喷桩处理不良地基效果良好。 相似文献
14.
张鉴 《中国有色金属学会会刊》2002,12(1):120-126
Based on the principle of annexation and phase diagrams, the structural units of In-Pb-Sb and In-Bi-Pb melts were determined, and their calculating models of mass action concentrations were formulated. Calculated results agree well with practical values, which in turn show that the models deduced can reflect the structural realities of corresponding melts and the principle of annexation is applicable not only to some binary metallic melts, but also to ternary metallic melts. 相似文献
15.
16.
17.
Modeling and assimilation of root zone soil moisture using remote sensing observations in Walnut Gulch Watershed during SMEX04 总被引:1,自引:0,他引:1
Soil moisture status in the root zone is an important component of the water cycle at all spatial scales (e.g., point, field, catchment, watershed, and region). In this study, the spatio-temporal evolution of root zone soil moisture of the Walnut Gulch Experimental Watershed (WGEW) in Arizona was investigated during the Soil Moisture Experiment 2004 (SMEX04). Root zone soil moisture was estimated via assimilation of aircraft-based remotely sensed surface soil moisture into a distributed Soil-Water-Atmosphere-Plant (SWAP) model. An ensemble square root filter (EnSRF) based on a Kalman filtering scheme was used for assimilating the aircraft-based soil moisture observations at a spatial resolution of 800 m × 800 m. The SWAP model inputs were derived from the SSURGO soil database, LAI (Leaf Area Index) data from SMEX04 database, and data from meteorological stations/rain gauges at the WGEW. Model predictions are presented in terms of temporal evolution of soil moisture probability density function at various depths across the WGEW. The assimilation of the remotely sensed surface soil moisture observations had limited influence on the profile soil moisture. More specifically, root zone soil moisture depended mostly on the soil type. Modeled soil moisture profile estimates were compared to field measurements made periodically during the experiment at the ground based soil moisture stations in the watershed. Comparisons showed that the ground-based soil moisture observations at various depths were within ± 1 standard deviation of the modeled profile soil moisture. Density plots of root zone soil moisture at various depths in the WGEW exhibited multi-modal variations due to the uneven distribution of precipitation and the heterogeneity of soil types and soil layers across the watershed. 相似文献
18.
The physicochemical and functional properties of convection oven- and freeze-dried gluten meals of two corn varieties were evaluated. The physicochemical properties (water solubility index, water absorption index, Hunter color parameters, and bulk density) and functional properties (water absorption, oil absorption, least gelation concentration, protein solubility, and emulsification properties) of convection-oven and freeze-dried corn gluten meals were compared with each other and soy flour. Freeze-dried corn gluten meals was observed to have lower bulk density (0.244-0.263 kg/m3) and was lighter in color (high L and ΔE) compared to their counterpart convection oven-dried gluten meals. Freeze-dried gluten meals from both corn varieties showed significantly higher oil absorption, water absorption, pH, emulsification, and protein solubility compared to oven-dried corn gluten meals. The gluten meals from both corn varieties had lower water absorption and bulk density but higher oil absorption than soy flour, suggesting the hydrophobic nature of corn proteins. Corn gluten meals formed thin (pourable) emulsions compared to soy flour emulsions, which were thick salad dressing type. Freeze- and convection oven-dried corn gluten meals showed significantly lower protein solubility measured at different pH than soy flour. 相似文献
19.
用化学还原法合成了FeBP非晶态合金超细微粒,用电感耦合等离子体光谱(ICP)、X射线粉末衍射(XRD)、透射电子显微镜(TEM)和差热分析(DSC)等手段对其进行了物性表征,并用微型催化反应装置考察了其对PH3分解的催化作用,结果表明,非晶态合金FeBP对PH3的分解具有良好的催化作用,能使PH3的分解温度从800℃以上降到500℃左右。490℃时分解率超过90%,540℃时达100%。 相似文献
20.
M. Loidl E. Leblanc T. Branger H. Rotzinger T. Daniyarov M. Linck A. Fleischmann C. Enss 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2004,520(1-3):73-75
We report on a feasibility study on precise determination of mass-specific activity of low-energy emitting radioisotopes. Conventional methods of activity measurement suffer from source self-absorption and a strong decrease in detection efficiency for low-energy electrons and photons. We propose a new method based on metallic magnetic microcalorimeters with the source embedded in the detector target in a 4π geometry. First results with a 55Fe source show that electrons and photons are detected with a detection efficiency close to unity and with little loss of energy for electrons. The aim of this study is to provide standards of activity with very low uncertainties in the framework of radiation metrology. 相似文献