全文获取类型
收费全文 | 750篇 |
免费 | 57篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 9篇 |
综合类 | 1篇 |
化学工业 | 193篇 |
金属工艺 | 10篇 |
机械仪表 | 28篇 |
建筑科学 | 86篇 |
矿业工程 | 2篇 |
能源动力 | 21篇 |
轻工业 | 84篇 |
水利工程 | 7篇 |
无线电 | 51篇 |
一般工业技术 | 156篇 |
冶金工业 | 34篇 |
原子能技术 | 2篇 |
自动化技术 | 125篇 |
出版年
2023年 | 9篇 |
2022年 | 17篇 |
2021年 | 24篇 |
2020年 | 18篇 |
2019年 | 23篇 |
2018年 | 19篇 |
2017年 | 25篇 |
2016年 | 34篇 |
2015年 | 31篇 |
2014年 | 33篇 |
2013年 | 60篇 |
2012年 | 42篇 |
2011年 | 44篇 |
2010年 | 39篇 |
2009年 | 31篇 |
2008年 | 45篇 |
2007年 | 40篇 |
2006年 | 29篇 |
2005年 | 30篇 |
2004年 | 23篇 |
2003年 | 17篇 |
2002年 | 23篇 |
2001年 | 7篇 |
2000年 | 19篇 |
1999年 | 17篇 |
1998年 | 22篇 |
1997年 | 12篇 |
1996年 | 14篇 |
1995年 | 5篇 |
1994年 | 10篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 5篇 |
1989年 | 3篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1972年 | 1篇 |
1971年 | 4篇 |
1970年 | 1篇 |
排序方式: 共有809条查询结果,搜索用时 31 毫秒
101.
Marc Daniel Heinemann Karsten von Maydell Folker Zutz Joanna Kolny‐Olesiak Holgert Borchert Ingo Riedel Jürgen Parisi 《Advanced functional materials》2009,19(23):3788-3795
The photo‐induced charge transfer and the dynamics of persistent charge carriers in blends of semiconducting polymers and nanocrystals are investigated. Regioregular poly(3‐hexylthiophene) (P3HT) is used as the electron donor material, while the acceptor moiety is established by CdSe nanocrystals (nc‐CdSe) prepared via colloidal synthesis. As a reference system, organic blends of P3HT and [6,6]‐phenyl C61‐butyric acid methyl ester (PCBM) are studied as well. The light‐induced charge transfer between P3HT and the acceptor materials is studied by photoluminescence (PL), photo‐induced absorption (PIA) and light‐induced electron spin resonance spectroscopy (LESR). Compared to neat P3HT samples, both systems show an intensified formation of polarons in the polymer upon photo‐excitation, pointing out successful separation of photogenerated charge carriers. Additionally, relaxation of the persistent charge carriers is investigated, and significant differences are found between the hybrid composite and the purely organic system. While relaxation, reflected in the transient signal decay of the polaron signal, is fast in the organic system, the hybrid blends exhibit long‐term persistence. The appearance of a second, slow recombination channel indicates the existence of deep trap states in the hybrid system, which leads to the capture of a large fraction of charge carriers. A change of polymer conformation due to the presence of nc‐CdSe is revealed by low temperature LESR measurements and microwave saturation techniques. The impact of the different recombination behavior on the photovoltaic efficiency of both systems is discussed. 相似文献
102.
103.
From a top-down to a bottom-up urban discourse: (re) constructing the city in a family-inclusive way
Lia Karsten 《Journal of Housing and the Built Environment》2009,24(3):317-329
This paper focuses on urban discourses as powerful instruments intertwined with the dialectic of inclusion and exclusion.
First, three dominant contemporary urban discourses developed in the field of urban planning are scrutinized on their inclusiveness
of families and daily family life. The attractive city, the creative city and the city as an emancipation machine are examples
of urban discourses communicated top-down via reports, debates and media attention. It is argued that these three discourses
do not address families as urban citizens nor the very notion of reproduction and its daily manifestation. The exclusionary
character of contemporary urban discourses does not only result in a neglect of urban families, it also legitimates non-intervention
when it comes to family issues. This conclusion activated the search for an alternative discourse as expanded in the second
part of the paper. This alternative discourse is constructed from the bottom-up and is rooted in the day-to-day experiences
of urban families themselves. It is a refined discourse, with interrelated geographical scales including the city as a whole,
the neighbourhood, the street and the home. This is a city that integrates—as families themselves do—the different domains
of life. The city is appreciated for its qualities of proximity, the neighbourhood for its ethnically mixed children’s domains,
the street as an urban haven and the house as the place that accommodates private life for each member of the family. This
alternative discourse is called the balanced city. The empirical basis is drawn from middle-class urban families in Rotterdam, The Netherlands. 相似文献
104.
Mette Schmedes Asker Daniel Brejnrod Eli Kristin Aadland Pia Kiilerich Karsten Kristiansen Hlne Jacques Charles Lavigne Ingvild Eide Graff
yvin Eng Asle Holthe Gunnar Mellgren Jette Feveile Young Ulrik Krmer Sundekilde Bjrn Liaset Hanne Christine Bertram 《Molecular nutrition & food research》2019,63(1)
105.
Karsten Müller 《化学,工程师,技术》2019,91(4):383-392
The efficient and dense storage of hydrogen still is a challenge for research and development. Next to compression and liquefaction, there are a number of alternative approaches, which try to enhance storage density by bonding hydrogen to another substance. Physisorbing as well as chemisorbing organic and inorganic carrier systems are possible. Many of these technologies have not yet exceeded the technology readiness level of lab‐scale tests. However, some of the technologies have already reached significantly higher technological levels. The first part of this study discusses storage approaches with recovery of elemental hydrogen. 相似文献
106.
Tanja Gärtner Erhard Gernand Jutta Gottschalk Karsten Donat 《Journal of dairy science》2019,102(10):9187-9199
In the transition period from late gestation to early lactation, dairy cows undergo tremendous metabolic changes. Insulin is a relevant antilipolytic factor. Decreasing serum concentrations of insulin and glucose, increasing serum concentrations of nonesterified fatty acids (NEFA) and β-hydroxybutyrate (BHB), and changes in body condition score (BCS) reflect the negative energy balance around calving. This study investigated peripartum metabolic adaptation in 359 primiparous and 235 multiparous German Holstein cows from a commercial dairy herd under field conditions. Body condition score was recorded and blood samples were taken 10 to 1 d prepartum, 2 to 4 d postpartum, and 12 to 20 d postpartum. Generalized mixed models and generalized estimation equations were applied to assess associations between prepartum BCS; BCS changes during the transition period; insulin, glucose, NEFA, and BHB serum concentrations; and milk yield, which was taken from an electronic milk meter from d 6 of lactation. Serum insulin concentrations of multiparous postpartum cows were lower compared with prepartum, and compared with primiparous cows. In general, primiparous cows had lower postpartum NEFA and BHB concentrations than multiparous cows. In primiparous cows, we identified a positive association between prepartum BCS and prepartum serum insulin concentration. Prepartum obese multiparous cows, but not primiparous cows, were characterized by higher postpartum serum NEFA and BHB concentrations and lower milk yield than other cows in the same parity class. Primiparous cows with a smaller degree of BCS loss during the transition period had higher postpartum insulin and lower NEFA concentrations and lower milk yield than other primiparous cows. In conclusion, primiparous cows had less lipolysis and lower milk yield than multiparous cows, associated with higher insulin concentrations. Avoiding high body condition loss during the transition period is a main factor in preventing peripartal metabolic imbalances of glucose and fat metabolism. 相似文献
107.
108.
109.
110.
Identifying the mechanisms by which diseases spread among populations is important for understanding and forecasting patterns of epidemics and pandemics. Estimating transmission coupling among populations is challenging because transmission events are difficult to observe in practice, and connectivity among populations is often obscured by local disease dynamics. We consider the common situation in which an epidemic is seeded in one population and later spreads to a second population. We present a method for estimating transmission coupling between the two populations, assuming they can be modelled as susceptible–infected–removed (SIR) systems. We show that the strength of coupling between the two populations can be estimated from the time taken for the disease to invade the second population. Confidence in the estimate is low if only a single invasion event has been observed, but is substantially improved if numerous independent invasion events are observed. Our analysis of this simplest, idealized scenario represents a first step toward developing and verifying methods for estimating epidemic coupling among populations in an ever-more-connected global human population. 相似文献