全文获取类型
收费全文 | 32131篇 |
免费 | 1420篇 |
国内免费 | 91篇 |
专业分类
电工技术 | 473篇 |
综合类 | 67篇 |
化学工业 | 7620篇 |
金属工艺 | 736篇 |
机械仪表 | 616篇 |
建筑科学 | 2338篇 |
矿业工程 | 251篇 |
能源动力 | 982篇 |
轻工业 | 2955篇 |
水利工程 | 233篇 |
石油天然气 | 81篇 |
武器工业 | 2篇 |
无线电 | 2200篇 |
一般工业技术 | 5982篇 |
冶金工业 | 3448篇 |
原子能技术 | 188篇 |
自动化技术 | 5470篇 |
出版年
2023年 | 274篇 |
2022年 | 516篇 |
2021年 | 867篇 |
2020年 | 519篇 |
2019年 | 536篇 |
2018年 | 734篇 |
2017年 | 705篇 |
2016年 | 892篇 |
2015年 | 776篇 |
2014年 | 1075篇 |
2013年 | 2120篇 |
2012年 | 1623篇 |
2011年 | 2260篇 |
2010年 | 1601篇 |
2009年 | 1533篇 |
2008年 | 1770篇 |
2007年 | 1553篇 |
2006年 | 1331篇 |
2005年 | 1196篇 |
2004年 | 1041篇 |
2003年 | 894篇 |
2002年 | 850篇 |
2001年 | 506篇 |
2000年 | 489篇 |
1999年 | 536篇 |
1998年 | 575篇 |
1997年 | 493篇 |
1996年 | 456篇 |
1995年 | 372篇 |
1994年 | 382篇 |
1993年 | 351篇 |
1992年 | 320篇 |
1991年 | 252篇 |
1990年 | 259篇 |
1989年 | 268篇 |
1988年 | 229篇 |
1987年 | 220篇 |
1986年 | 203篇 |
1985年 | 277篇 |
1984年 | 259篇 |
1983年 | 212篇 |
1982年 | 199篇 |
1981年 | 223篇 |
1980年 | 155篇 |
1979年 | 164篇 |
1978年 | 168篇 |
1977年 | 156篇 |
1976年 | 182篇 |
1975年 | 145篇 |
1974年 | 133篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
1.
2.
3.
Golam Haider Krishna Sampathkumar Tim Verhagen Lukáš Nádvorník Farjana J. Sonia Václav Valeš Jan Sýkora Peter Kapusta Petr Němec Martin Hof Otakar Frank Yang-Fang Chen Jana Vejpravová Martin Kalbáč 《Advanced functional materials》2021,31(29):2102196
Recent advancements in isolation and stacking of layered van der Waals materials have created an unprecedented paradigm for demonstrating varieties of 2D quantum materials. Rationally designed van der Waals heterostructures composed of monolayer transition-metal dichalcogenides (TMDs) and few-layer hBN show several unique optoelectronic features driven by correlations. However, entangled superradiant excitonic species in such systems have not been observed before. In this report, it is demonstrated that strong suppression of phonon population at low temperature results in a formation of a coherent excitonic-dipoles ensemble in the heterostructure, and the collective oscillation of those dipoles stimulates a robust phase synchronized ultra-narrow band superradiant emission even at extremely low pumping intensity. Such emitters are in high demand for a multitude of applications, including fundamental research on many-body correlations and other state-of-the-art technologies. This timely demonstration paves the way for further exploration of ultralow-threshold quantum-emitting devices with unmatched design freedom and spectral tunability. 相似文献
4.
Michael Lommel Vera Froese Moritz Sieber Marvin Jentzsch Tim Bierewirtz Ümit Hasirci Tim Rese Josef Seefeldt Sebastian Schimek Ulrich Kertzscher Christian Oliver Paschereit 《Indoor air》2021,31(6):1860-1873
The SARS-CoV-2 pandemic has created a great demand for a better understanding of the spread of viruses in indoor environments. A novel measurement system consisting of one portable aerosol-emitting mannequin (emitter) and a number of portable aerosol-absorbing mannequins (recipients) was developed that can measure the spread of aerosols and droplets that potentially contain infectious viruses. The emission of the virus from a human is simulated by using tracer particles solved in water. The recipients inhale the aerosols and droplets and quantify the level of solved tracer particles in their artificial lungs simultaneously over time. The mobile system can be arranged in a large variety of spreading scenarios in indoor environments and allows for quantification of the infection probability due to airborne virus spreading. This study shows the accuracy of the new measurement system and its ability to compare aerosol reduction measures such as regular ventilation or the use of a room air purifier. 相似文献
5.
Aleksandar Miletić Peter Panjan Miha Čekada Lazar Kovačević Pal Terek Janez Kovač Goran Dražič Branko Škorić 《Ceramics International》2021,47(2):2022-2033
With the goal to produce a hard and tough coating intended for tribological applications, CrAlN/TiSiN nanolayer coating was prepared by alternative deposition of CrAlN and TiSiN layers. In the first part of the article, a detailed study of phase composition, microstructure, and layer structure of CrAlN/TiSiN coating is presented. In the second part, its mechanical properties, fracture and tribological behavior are compared to the nanocomposite TiSiN coating. An industrial magnetron sputtering unit was used for coating deposition. X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy were used for compositional and microstructural analysis. Mechanical properties and fracture behavior were studied by instrumented indentation and focused ion beam techniques. Tribological properties were evaluated by ball-on-disk test in a linear reciprocal mode. A complex layer structure was found in the nanolayer coating. The TiSiN layers were epitaxially stabilized inside the coating which led to formation of dislocations at interfaces, to introduction of disturbances in the coating growth, and as a result, to development of fine-grained columnar microstructure. Indentation load required for the onset of fracture was twice lower for the nanolayer CrAlN/TiSiN, compared to the nanocomposite TiSiN coating. This agrees very well with their mechanical properties, with H3/E2 being twice higher for the TiSiN coating. However, the nanolayer coating experienced less severe damage, which had a strong impact on tribological behavior. A magnitude of order lower wear rate and four times lower steady state friction coefficient were found for the nanolayer coating. 相似文献
6.
Jens Mller Anne Busch Christian Berens Helmut Hotzel Andreas Burkovski 《International journal of molecular sciences》2021,22(7)
Corynebacterium silvaticum is a newly identified animal pathogen of forest animals such as roe deer and wild boars. The species is closely related to the emerging human pathogen Corynebacterium ulcerans and the widely distributed animal pathogen Corynebacterium pseudotuberculosis. In this study, Corynebacterium silvaticum strain W25 was characterized with respect to its interaction with human cell lines. Microscopy, measurement of transepithelial electric resistance and cytotoxicity assays revealed detrimental effects of C. silvaticum to different human epithelial cell lines and to an invertebrate animal model, Galleria mellonella larvae, comparable to diphtheria toxin-secreting C. ulcerans. Furthermore, the results obtained may indicate a considerable zoonotic potential of this newly identified species. 相似文献
7.
Dr. Timo Broese Dr. Peter Ehlers Dr. Peter Langer Dr. Jan von Langermann 《Chembiochem : a European journal of chemical biology》2021,22(23):3314-3318
Fluoro-substituted and heteroaromatic compounds are valuable intermediates for a variety of applications in pharma- and agrochemistry and synthetic chemistry. This study investigates the chemoenzymatic preparation of chiral alcohols bearing a heteroaromatic ring with an increasing degree of fluorination in α-position. Starting from readily available picoline derivatives prochiral α-halogenated acyl moieties were introduced with excellent selectivity and 64–95 % yield. The formed carbonyl group was subsequently reduced to the corresponding alcohols using the alcohol dehydrogenase from Lactobacillus kefir, yielding an enantiomeric excess of 95–>99 % and up to 98 % yield. 相似文献
8.
Katja F. Hellendahl Felix Kaspar Dr. Xinrui Zhou Zhaoyi Yang Prof. Dr. Zhen Huang Prof. Dr. Peter Neubauer Dr. Anke Kurreck 《Chembiochem : a European journal of chemical biology》2021,22(11):2002-2009
Selenium-modified nucleosides are powerful tools to study the structure and function of nucleic acids and their protein interactions. The widespread application of 2-selenopyrimidine nucleosides is currently limited by low yields in established synthetic routes. Herein, we describe the optimization of the synthesis of 2-Se-uridine and 2-Se-thymidine derivatives by thermostable nucleoside phosphorylases in transglycosylation reactions using natural uridine or thymidine as sugar donors. Reactions were performed at 60 or 80 °C and at pH 9 under hypoxic conditions to improve the solubility and stability of the 2-Se-nucleobases in aqueous media. To optimize the conversion, the reaction equilibria in analytical transglycosylation reactions were studied. The equilibrium constants of phosphorolysis of the 2-Se-pyrimidines were between 5 and 10, and therefore differ by an order of magnitude from the equilibrium constants of any other known case. Hence, the thermodynamic properties of the target nucleosides are inherently unfavorable, and this complicates their synthesis significantly. A tenfold excess of sugar donor was needed to achieve 40−48 % conversion to the target nucleoside. Scale-up of the optimized conditions provided four Se-containing nucleosides in 6–40 % isolated yield, which compares favorably to established chemical routes. 相似文献
9.
10.