全文获取类型
收费全文 | 10692篇 |
免费 | 1062篇 |
国内免费 | 246篇 |
学科分类
工业技术 | 12000篇 |
出版年
2024年 | 85篇 |
2023年 | 253篇 |
2022年 | 365篇 |
2021年 | 588篇 |
2020年 | 540篇 |
2019年 | 460篇 |
2018年 | 479篇 |
2017年 | 447篇 |
2016年 | 479篇 |
2015年 | 456篇 |
2014年 | 624篇 |
2013年 | 891篇 |
2012年 | 725篇 |
2011年 | 663篇 |
2010年 | 542篇 |
2009年 | 489篇 |
2008年 | 428篇 |
2007年 | 498篇 |
2006年 | 466篇 |
2005年 | 372篇 |
2004年 | 325篇 |
2003年 | 310篇 |
2002年 | 255篇 |
2001年 | 204篇 |
2000年 | 160篇 |
1999年 | 141篇 |
1998年 | 114篇 |
1997年 | 113篇 |
1996年 | 73篇 |
1995年 | 64篇 |
1994年 | 50篇 |
1993年 | 42篇 |
1992年 | 52篇 |
1991年 | 15篇 |
1990年 | 23篇 |
1989年 | 24篇 |
1988年 | 15篇 |
1987年 | 32篇 |
1986年 | 23篇 |
1985年 | 37篇 |
1984年 | 27篇 |
1983年 | 14篇 |
1982年 | 18篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1970年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
31.
The interaction of different metal oxides such as Co3O4, NiO, Al2O3, Cr2O3, Fe2O3 and SiO2 with Na2SO4 at a temperature of 1100 and 1200 K in flowing oxygen has been studied. The thermogravimetric studies for each system were
carried out as a function of Na2SO4 in the mixture. The presence of different constituents in the reaction products were identified by X-ray diffraction analysis
and the morphologies of the reaction products were characterized using metallography and scanning electron microscopy (SEM).
The formation of products was also investigated by thermodynamic computation of free energies of the reactions and the study
of relevant equilibrium phase diagrams. The soluble species in the aqueous solutions of the reaction products were determined
quantitatively using atomic absorption spectrophotometry.
The high temperature interaction products usually contain a 3-phase structure namely, Na2O·M2O
x
, M2O
x
and metal sulphide and/or metal sulphate. The formation of Na2O·M2O
x
depends upon the solid state solubility of metal oxide in the molten salt at high temperatures. Under limited solubility
conditions Na2O·M2O
x
is invariably formed, but as soon as this condition is relaxed the oxide. M2O
x
, precipitates and forms a separate phase. 相似文献
32.
简述江西省抚河流域的概况、水生态环境的现状及存在的问题.包括淤泥的堆积、水土的流失、水污染、沿岸圩堤的防洪标准普遍偏低等.并对这些问题提出了流域水生态环境恢复的目标,针对抚河流域水生态环境的恢复目标提出了水权分配、水土保持治理、水工程治理、水质治理等方面的一系列初步的措施与建议. 相似文献
33.
Tang Yuanyan 《Frontiers of Computer Science in China》2007,1(2):123-125
This paper gives an introduction and remarks on two review papers for Chinese character recognition. One review is made by
Chinese authors, another is from American scientists. They investigate Chinese character from different language environments;
they do the research from different points of view. Thus, a more comprehensive view on Chinese character recognition, which
is an important branch of pattern recognition, can be provided to the readers. Meantime, one article pays attention to online
process, and other paper deals with offline recognition, which complement each other.
The author is the Associate Editor-in-Chief of Frontiers of Computer Science in China 相似文献
34.
35.
36.
对照IS0 9001质量管理体系标推的要求,结合石化销售企业质量管理工作中存在的主要问题,提出质量管理工作创新的建议。 相似文献
37.
国际乳业的热点论题:蛋白质标准化 总被引:1,自引:0,他引:1
介绍了蛋白质的标准化这一国际乳品界正热的研究和讨论题目,综述了蛋白质标准化的必要性和世界上目前采用的方法,展望了膜技术在蛋白质标准化上的应用前景。 相似文献
38.
39.
40.
Air cleaning as a means of mitigating the risks arising from exposure to indoor radon progeny has been evaluated in a single-family house in the north eastem US. using an automated, semi-continuous activity-weighted size distribution measurement system. The measurements included radon concentration, condensation nuclei count, and activity-weighted size distribution of radon decay products. Measurements were made in the house with and without an operating air filtration system and with various particle sources common to normal indoor activities operating. Aerosols were generated by running water in a shower, candle burning, cigarette smoking, vacuuming, opening doors, and cooking. Using a room model, the changes in attachment rates, average attachment diameters, and deposition rates of the unattached fraction with and without the air cleaning system were calculated. In the presence of active aerosol sources, the air filtration unit typically reduced the concentration of particles within the hour following the end of particle generation. After candle burning, cigarette smoking, and vacuuming in the bedroom, the reductions of PAEC by air filtration are about 60% with the air filtration system operating in the bedroom. During cooking in the kitchen, the reductions of PAEC in the bedroom with the air filtration system were about 40%. However, for all cases the dose reductions were smaller than the particle and PAEC reductions. For those particles that were generated within the bedroom, there was a 20% to 50% reduction in dose. In the case of cooking where the door was open and particles infiltrated from the rest of the house, the dose reduction was only 5% on average and appears to be insignificant. Thus, the dose reductions were h e r than the reductions in activity concentration, but there were no cases where the estimated dose actually increased. 相似文献