全文获取类型
收费全文 | 10143篇 |
免费 | 430篇 |
国内免费 | 88篇 |
专业分类
化学 | 6937篇 |
晶体学 | 91篇 |
力学 | 265篇 |
综合类 | 1篇 |
数学 | 1738篇 |
物理学 | 1629篇 |
出版年
2023年 | 77篇 |
2022年 | 56篇 |
2021年 | 184篇 |
2020年 | 209篇 |
2019年 | 250篇 |
2018年 | 158篇 |
2017年 | 159篇 |
2016年 | 384篇 |
2015年 | 288篇 |
2014年 | 320篇 |
2013年 | 603篇 |
2012年 | 607篇 |
2011年 | 653篇 |
2010年 | 453篇 |
2009年 | 405篇 |
2008年 | 586篇 |
2007年 | 631篇 |
2006年 | 497篇 |
2005年 | 547篇 |
2004年 | 440篇 |
2003年 | 351篇 |
2002年 | 338篇 |
2001年 | 162篇 |
2000年 | 142篇 |
1999年 | 68篇 |
1998年 | 72篇 |
1997年 | 89篇 |
1996年 | 99篇 |
1995年 | 90篇 |
1994年 | 80篇 |
1993年 | 95篇 |
1992年 | 74篇 |
1991年 | 76篇 |
1990年 | 69篇 |
1989年 | 65篇 |
1988年 | 48篇 |
1987年 | 55篇 |
1986年 | 64篇 |
1985年 | 103篇 |
1984年 | 99篇 |
1983年 | 77篇 |
1982年 | 68篇 |
1981年 | 70篇 |
1980年 | 64篇 |
1979年 | 65篇 |
1978年 | 67篇 |
1977年 | 41篇 |
1976年 | 40篇 |
1975年 | 50篇 |
1974年 | 54篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
Szymon Szufa Piotr Piersa ukasz Adrian Justyna Czerwiska Artur Lewandowski Wiktoria Lewandowska Jan Sielski Maria Dziku Marek Wrbel Marcin Jewiarz Adrian Knapczyk 《Molecules (Basel, Switzerland)》2021,26(4)
Miscanthus is resistant to dry, frosty winters in Poland and most European Union countries. Miscanthus gives higher yields compared to native species. Farmers can produce Miscanthus pellets after drying it for their own heating purposes. From the third year, the most efficient plant development begins, resulting in a yield of 25–30 tons of dry matter from an area of 1 hectare. Laboratory scale tests were carried out on the processes of drying, compacting, and torrefaction of this biomass type. The analysis of the drying process was conducted at three temperature levels of the drying agent (60, 100, and 140 °C). Compaction on a hydraulic press was carried out in the pressure range characteristic of a pressure agglomeration (130.8–457.8 MPa) at different moisture contents of the raw material (0.5% and 10%). The main interest in this part was to assess the influence of drying temperature, moisture content, and compaction pressure on the specific densities (DE) and the mechanical durability of the pellets (DU). In the next step, laboratory analyses of the torrefaction process were carried out, initially using the Thermogravimetric Analysis TGA and Differential Scaning Calorimeter DSC techniques (to assess activation energy (EA)), followed by a flow reactor operating at five temperature levels (225, 250, 275, 300, and 525 °C). A SEM analysis of Miscanthus after torrefaction processes at three different temperatures was performed. Both the parameters of biochar (proximate and ultimate analysis) and the quality of the torgas (volatile organic content (VOC)) were analyzed. The results show that both drying temperature and moisture level will affect the quality of the pellets. Analysis of the torrefaction process shows clearly that the optimum process temperature would be around 300–340 °C from a mass loss ratio and economical perspective. 相似文献
43.
Pekárek Stanislav Mikeš Jan Červenka Milan Hanuš Ondřej 《Plasma Chemistry and Plasma Processing》2021,41(3):779-792
Plasma Chemistry and Plasma Processing - We investigated the air supply mode effects on ozone production of the surface dielectric barrier discharge in the cylindrical configuration. The air into... 相似文献
44.
Designs, Codes and Cryptography - In this article we generalize the concepts that were used in the PhD thesis of Drudge to classify Cameron–Liebler line classes in PG $$(n,q), n\ge 3$$ , to... 相似文献
45.
46.
Evaluation of Fe and Ru Pincer‐Type Complexes as Catalysts for the Racemization of Secondary Benzylic Alcohols 下载免费PDF全文
Dr. Oscar Verho Prof. Dr. Matthias Beller Prof. Dr. Jan‐E. Bäckvall 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(33):11583-11586
Fe and Ru pincer‐type catalysts are used for the racemization of benzylic alcohols. Racemization with the Fe catalyst was achieved within 30 minutes under mild reaction conditions, with a catalyst loading as low as 2 mol %. This reaction constitutes the first example of an iron‐catalyzed racemization of an alcohol. The efficiency for racemization of the Fe catalyst and its Ru analogue was evaluated for a wide range of sec‐benzylic alcohols. The commercially available Ru complex proved to be highly robust and even tolerated the presence of water in the reaction mixture. 相似文献
47.
“Grafting through” polymerization represents copolymerization of free monomers in solution and polymerizable units bound to a substrate. Free polymer chains are formed initially in solution and can incorporate the surface-bound monomers, and thereby, get covalently bonded to the surface during the polymerization process. As more growing chains attach to the surface-bound monomers, an immobilized polymer layer is formed on the surface. We use a combination of computer simulation and experiments to comprehend this process for monomers bound to a flat impenetrable substrate. We concentrate specifically on addressing the effect of spatial density of the surface-bound monomers on the formation of the surface-attached polymers. We employ a lattice-based Monte Carlo model utilizing the bond fluctuation model scheme to provide molecular-level insight into the grafting process. For experimental validation, we create gradients of density of bound methacrylate units on flat silicon wafers using organosilane chemistry and carry out “grafting through” free radical polymerization initiated in bulk. We report that the proximity of the surface-bound polymerizable units promotes the “grafting through” process but prevents more free growing chains to “graft through'' the polymerizable units. The “grafting through” process is self-limiting in nature and does not affect the overall density of the surface-bound polymer layer, except in case of the highest theoretical packing density of surface-bound monomers. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 263–274 相似文献
48.
Jan Dereziński 《Annales Henri Poincare》2014,15(8):1569-1653
The paper is devoted to a systematic and unified discussion of various classes of hypergeometric type equations: the hypergeometric equation, the confluent equation, the F 1 equation (equivalent to the Bessel equation), the Gegenbauer equation and the Hermite equation. In particular, recurrence relations of their solutions, their integral representations and discrete symmetries are discussed. 相似文献
49.
Analyse von Protease‐Inhibitor‐Interaktionen unter Nutzung evolvierbarer tricyclischer Microviridine
50.