全文获取类型
收费全文 | 216203篇 |
免费 | 23890篇 |
国内免费 | 14955篇 |
专业分类
电工技术 | 18842篇 |
技术理论 | 4篇 |
综合类 | 19155篇 |
化学工业 | 29518篇 |
金属工艺 | 13639篇 |
机械仪表 | 14858篇 |
建筑科学 | 17674篇 |
矿业工程 | 7358篇 |
能源动力 | 6233篇 |
轻工业 | 18478篇 |
水利工程 | 6056篇 |
石油天然气 | 10170篇 |
武器工业 | 2774篇 |
无线电 | 25673篇 |
一般工业技术 | 20645篇 |
冶金工业 | 8507篇 |
原子能技术 | 3131篇 |
自动化技术 | 32333篇 |
出版年
2024年 | 1015篇 |
2023年 | 3430篇 |
2022年 | 7316篇 |
2021年 | 10043篇 |
2020年 | 7390篇 |
2019年 | 5548篇 |
2018年 | 6135篇 |
2017年 | 7050篇 |
2016年 | 6216篇 |
2015年 | 9643篇 |
2014年 | 12184篇 |
2013年 | 14451篇 |
2012年 | 17266篇 |
2011年 | 18039篇 |
2010年 | 16979篇 |
2009年 | 16184篇 |
2008年 | 16025篇 |
2007年 | 15298篇 |
2006年 | 13629篇 |
2005年 | 10819篇 |
2004年 | 7620篇 |
2003年 | 6016篇 |
2002年 | 5747篇 |
2001年 | 5230篇 |
2000年 | 4074篇 |
1999年 | 2838篇 |
1998年 | 1649篇 |
1997年 | 1372篇 |
1996年 | 1269篇 |
1995年 | 1078篇 |
1994年 | 871篇 |
1993年 | 552篇 |
1992年 | 443篇 |
1991年 | 319篇 |
1990年 | 263篇 |
1989年 | 239篇 |
1988年 | 157篇 |
1987年 | 108篇 |
1986年 | 104篇 |
1985年 | 37篇 |
1984年 | 41篇 |
1983年 | 34篇 |
1982年 | 32篇 |
1981年 | 52篇 |
1980年 | 51篇 |
1979年 | 33篇 |
1977年 | 9篇 |
1976年 | 10篇 |
1959年 | 16篇 |
1951年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
891.
UV-Vis spectroscopy was used to directly determine the concentration of Eu(Ⅱ) during electroreduction of Eu(Ⅲ) in hydrochloric acid medium. Electroreduction was carried out in a flow type electrolyzer with glassy carbon cathode at the constant potential of -800 mV vs. Ag/AgCl. The effects of oxygen and concentration of hydrochloric acid on the system were investigated. For 0.01 mol·L-1 hydrochloric acid, calibration curves for Eu(Ⅱ) absorption bands at 248 and 320 nm were constructed. Molar absorption coefficients were estimated to be 2016 and 648 L·mol-1·cm-1, respectively. The absorbance strongly decreased with decrease in pH of the solution, whereas concentration of chloride had only a negligible effect. 相似文献
892.
893.
894.
以籼型单季超级杂交稻中浙优1号为材料,研究水稻强化栽培氮肥管理对产量与氮素利用率的影响。结果表明:水稻强化栽培与常规栽培对照比较,增产达11.1%-15.2%,氮肥回收率比对照高5.3%~26.9%,农学利用率比对照高67.2%~92.2%,生理利用率比对照高6.0%~80.5%。因此,在水稻生产上应用水稻强化栽培可以提高氮肥的利用,降低氮肥在环境中积累及对环境造成污染。此外,本文对水稻强化栽培下氮肥管理的高产机理进行了探讨。 相似文献
895.
Computational models have been used widely in tissue engineering research and have proven to be powerful tools for bio-mechanical analysis (i.e., blood flow, growth models, drug delivery, etc). This paper focuses on developing higher-fidelity models for vascular structures and blood vessels that integrate computational shape representations with biomedical properties and features. Previous work in computer-aided vascular modeling comes from two communities. For those in biomedical imaging, the goal of past research has been to develop image understanding techniques for the interpretation of x-ray, magnetic resonance imaging (MRI), or other radiological data. These representations are predominantly discrete shape models that are not tied to physiological properties. The other corpus of existing work comes from those interested in developing physiological models for vascular growth and behavior based on bio-medical attributes. These models usually either have a highly simplified shape representation, or lack one entirely. Further, neither of these representations are suitable for the kind of interactive modeling required by tissue engineering applications.This paper aims to bridge these two approaches and develop a set of mathematical tools and algorithms for feature-based representation and computer-aided modeling of vascular trees for use in computer-aided tissue engineering applications. The paper offers a multi-scale representation based on swept volumes and a feature-based representation that can attribute the geometric representation with information about blood flow, pressure, and other biomedical properties. The paper shows how the resulting representation can be used as part of an overall approach for designing and visualizing vascular scaffolds. As a real-world example, we show how this computational model can be used to develop a tissue scaffold for liver tissue engineering. Such scaffolds may prove useful in a number of biomedical applications, including the growth of replacement tissue grafts and in vitro study of the pharmacological affects of new drugs on tissue cultures. 相似文献
896.
The recently developed high-order accurate multiple image approximation to the reaction field for a charge inside a dielectric sphere [J. Comput. Phys. 223 (2007) 846-864] is compared favorably to other commonly employed reaction field schemes. These methods are of particular interest because they are useful in the study of biological macromolecules by the Monte Carlo and Molecular Dynamics methods. 相似文献
897.
Xiaodan Zhang Wei Liu Dale Sun Youguo Li 《Metallurgical and Materials Transactions A》2007,38(3):499-505
The transformation of carbides with austenization time of a high speed steel (HSS) roll material, manufactured by a centrifugal
casting method, has been studied. The correlation between wear resistance and the type, morphology, volume fraction, and distribution
of the carbides has also been investigated. Microstructural observations, X-ray diffraction (XRD) analysis, hardness measurements,
and energy dispersive spectroscopy (EDS) have been used to characterize the carbides. The type and volume fraction of carbides
were found to change with austenizing time. During austenization, the transformation of the M3C carbides can be postulated as M3C + γ-Fe → M2C, with much finer nodular and rodlike MC carbides also forming through a solid-state transformation. The M2C carbide decomposes as M2C + γ-Fe → MC + M7C3 + M6C. The decomposed carbide substantially maintains a platelike shape until the end of decomposition. The most important finding
of this study is that austenization results in changes in the type, morphology, volume fraction, and distribution of carbides
and that it can be controlled to produced a homogeneous distribution of hard carbides, resulting in an improvement in the
wear resistance of HSS rolls. This finding may be of great use for the industrial production of HSS rolls. 相似文献
898.
主要介绍了土工布和膨润土防水毯(GCL)在垃圾卫生填埋场应用中的特点和作用,阐述了在卫生填埋场设计中选择土工布和GCL应注意的一些问题。 相似文献
899.
900.