全文获取类型
收费全文 | 5992篇 |
免费 | 294篇 |
国内免费 | 46篇 |
专业分类
电工技术 | 198篇 |
综合类 | 69篇 |
化学工业 | 1306篇 |
金属工艺 | 186篇 |
机械仪表 | 118篇 |
建筑科学 | 261篇 |
矿业工程 | 52篇 |
能源动力 | 178篇 |
轻工业 | 1185篇 |
水利工程 | 45篇 |
石油天然气 | 66篇 |
武器工业 | 12篇 |
无线电 | 296篇 |
一般工业技术 | 825篇 |
冶金工业 | 551篇 |
原子能技术 | 48篇 |
自动化技术 | 936篇 |
出版年
2023年 | 59篇 |
2022年 | 95篇 |
2021年 | 166篇 |
2020年 | 118篇 |
2019年 | 132篇 |
2018年 | 179篇 |
2017年 | 165篇 |
2016年 | 193篇 |
2015年 | 189篇 |
2014年 | 232篇 |
2013年 | 332篇 |
2012年 | 289篇 |
2011年 | 316篇 |
2010年 | 292篇 |
2009年 | 259篇 |
2008年 | 251篇 |
2007年 | 239篇 |
2006年 | 186篇 |
2005年 | 129篇 |
2004年 | 153篇 |
2003年 | 154篇 |
2002年 | 179篇 |
2001年 | 123篇 |
2000年 | 100篇 |
1999年 | 92篇 |
1998年 | 178篇 |
1997年 | 137篇 |
1996年 | 70篇 |
1995年 | 73篇 |
1994年 | 90篇 |
1993年 | 68篇 |
1992年 | 42篇 |
1991年 | 33篇 |
1990年 | 35篇 |
1989年 | 41篇 |
1988年 | 28篇 |
1987年 | 20篇 |
1985年 | 28篇 |
1984年 | 20篇 |
1983年 | 20篇 |
1982年 | 27篇 |
1981年 | 21篇 |
1977年 | 20篇 |
1976年 | 29篇 |
1924年 | 26篇 |
1923年 | 19篇 |
1918年 | 28篇 |
1917年 | 30篇 |
1916年 | 26篇 |
1915年 | 34篇 |
排序方式: 共有6332条查询结果,搜索用时 375 毫秒
1.
Lili Hou Axel Olesund Shameel Thurakkal Xiaoyan Zhang Bo Albinsson 《Advanced functional materials》2021,31(47):2106198
Developing high-performance visible-to-UV photon upconversion systems based on triplet–triplet annihilation photon upconversion (TTA-UC) is highly desired, as it provides a potential approach for UV light-induced photosynthesis and photocatalysis. However, the quantum yield and spectral range of visible-to-UV TTA-UC based on nanocrystals (NCs) are still far from satisfactory. Here, three different sized CdS NCs are systematically investigated with triplet energy transfer to four mediators and four annihilators, thus substantially expanding the available materials for visible-to-UV TTA-UC. By improving the quality of CdS NCs, introducing the mediator via a direct mixing fashion, and matching the energy levels, a high TTA-UC quantum yield of 10.4% (out of a 50% maximum) is achieved in one case, which represents a record performance in TTA-UC based on NCs without doping. In another case, TTA-UC photons approaching 4 eV are observed, which is on par with the highest energies observed in optimized organic systems. Importantly, the in-depth investigation reveals that the direct mixing approach to introduce the mediator is a key factor that leads to close to unity efficiencies of triplet energy transfer, which ultimately governs the performance of NC-based TTA-UC systems. These findings provide guidelines for the design of high-performance TTA-UC systems toward solar energy harvesting. 相似文献
2.
3.
A contact layer element for large deformations 总被引:1,自引:0,他引:1
4.
5.
6.
Breast cancer is the most frequently diagnosed cancer in women worldwide. The disease and its treatments exert profound effects on an individual’s physical and mental health. There are many factors that impact an individual’s risk of developing breast cancer, their response to treatments, and their risk of recurrence. The community of microorganisms inhabiting the gastrointestinal tract, the gut microbiota, affects human health through metabolic, neural, and endocrine signaling, and immune activity. It is through these mechanisms that the gut microbiota appears to influence breast cancer risk, response to treatment, and recurrence. A disrupted gut microbiota or state of ‘dysbiosis’ can contribute to a biological environment associated with higher risk for cancer development as well as contribute to negative treatment side-effects. Many cancer treatments have been shown to shift the gut microbiota toward dysbiosis; however, the microbiota can also be positively manipulated through diet, prebiotic and probiotic supplementation, and exercise. The objective of this review is to provide an overview of the current understanding of the relationship between the gut microbiota and breast cancer and to highlight potential strategies for modulation of the gut microbiota that could lead to improved clinical outcomes and overall health in this population. 相似文献
7.
8.
Ohne Zusammenfassung 相似文献
9.
The Determinants of Debt and (Private) Equity Financing: The Case of Young, Innovative SMEs from Germany 总被引:1,自引:0,他引:1
Financial theory creates a puzzle. Some authors argue that high-risk entrepreneurs choose debt contracts instead of equity contracts since risky but high returns are of relatively more value for a loan-financed firm. Conversely, authors who focus explicitly on start-up finance predict that entrepreneurs are the more likely to seek equity-like venture capital contracts, the more risky their projects are. Our paper is an initial step towards resolving this puzzle empirically. We present microeconometric evidence on the determinants of debt and equity financing in young and innovative SMEs. We pay special attention to the role of risk for the choice of the method of financing. Since risk is not directly observable we use different indicators for financial and project risk. It turns out that our data generally confirms the hypothesis that the probability that a young high-tech firm receives equity financing is an increasing function of the financial risk. With regard to the intrinsic project risk, our results are less conclusive, as some of our indicators of a risky project are found to have a negative effect on the likelihood to be financed by private equity. 相似文献
10.
Semi‐Markovian processes (SMP) serve as a versatile means to model various traffic types generated by sources or superposed
from links in ATM networks. An efficient discrete time analysis method is proposed for SMP/G/1 queueing systems to evaluate
ATM switches with non‐renewal input. Some basic results are derived for the autocorrelation function of semi‐Markovian processes
and for the effect of state space reduction on autocorrelation, which show how to represent correlated traffic with given
characteristic by an adequate SMP model of limited size.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献