全文获取类型
收费全文 | 9337篇 |
免费 | 773篇 |
国内免费 | 419篇 |
专业分类
化学 | 4740篇 |
晶体学 | 61篇 |
力学 | 388篇 |
综合类 | 40篇 |
数学 | 1120篇 |
物理学 | 2378篇 |
无线电 | 1802篇 |
出版年
2024年 | 32篇 |
2023年 | 132篇 |
2022年 | 309篇 |
2021年 | 324篇 |
2020年 | 348篇 |
2019年 | 285篇 |
2018年 | 247篇 |
2017年 | 249篇 |
2016年 | 368篇 |
2015年 | 370篇 |
2014年 | 399篇 |
2013年 | 625篇 |
2012年 | 633篇 |
2011年 | 708篇 |
2010年 | 469篇 |
2009年 | 470篇 |
2008年 | 533篇 |
2007年 | 534篇 |
2006年 | 462篇 |
2005年 | 393篇 |
2004年 | 333篇 |
2003年 | 295篇 |
2002年 | 241篇 |
2001年 | 184篇 |
2000年 | 134篇 |
1999年 | 134篇 |
1998年 | 82篇 |
1997年 | 77篇 |
1996年 | 95篇 |
1995年 | 86篇 |
1994年 | 97篇 |
1993年 | 75篇 |
1992年 | 72篇 |
1991年 | 56篇 |
1990年 | 53篇 |
1989年 | 46篇 |
1988年 | 36篇 |
1987年 | 34篇 |
1986年 | 30篇 |
1985年 | 47篇 |
1984年 | 53篇 |
1983年 | 28篇 |
1982年 | 42篇 |
1981年 | 30篇 |
1980年 | 26篇 |
1979年 | 46篇 |
1978年 | 33篇 |
1977年 | 22篇 |
1976年 | 26篇 |
1974年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
提出了一种面向多级调制格式的先进高速光计算算法,利用高非线性光纤中超快简并和非简并四波混频(FWM),采用100Gb/s正交相位调制(DQPSK)信号,仿真实验实现了50Gbaud/s高速光计算,包括加法、双定向减法、补码、加倍等光计算功能。当比特误码率(BER)为10-9时,测得高速光计算的功率代价小于4dB。 相似文献
992.
Simeon Hubrich Meysam Joulaian Paolo Di Stolfo Andreas Schröder Alexander Düster 《PAMM》2016,16(1):201-202
The finite cell method is based on a fictitious domain approach, providing a simple and fast mesh generation of structures with complex geometries. However, this simplification leads to intersected cells where the standard Gauss quadrature does not perform well. To perform the numerical integration of these cells, we use the moment fitting approach that generates an individual quadrature rule for every broken cell. In this paper, we will perform a non-linear optimization approach to find the optimal position and number of the integration points. The findings show that the proposed method leads to efficient quadrature rules that require less integration points than other existing integration methods. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
993.
Hybrid Organic/Inorganic Nanostructures for Highly Sensitive Photoelectrochemical Detection of Dissolved Oxygen in Aqueous Media 下载免费PDF全文
Sebastiano Bellani Ali Ghadirzadeh Laura Meda Alberto Savoini Alessandra Tacca Gianluigi Marra Rui Meira Jorge Morgado Fabio Di Fonzo Maria Rosa Antognazza 《Advanced functional materials》2015,25(28):4531-4538
Precise, reliable, and remote measurement of dissolved oxygen in aqueous media is of great importance for many industrial, environmental, and biological applications. In particular, photoelectrochemical sensors working in differential mode have recently demonstrated promising properties, in terms of stability, sensitivity, and application potential. Here, a new approach is presented, combining visible light sensitivity, efficient photocurrent generation, and solution‐processed fabrication methods of conjugated polymers, with charge carriers selectivity, energetic alignment favorable to efficient interfacial charge transfer and high surface area achievable by using metal oxide nanostructures. Extensive characterization and optimization of the hybrid organic/inorganic system are carried out, leading to the realization of an oxygen sensor device, based on nanostructured palladium oxide/poly[(9,9‐dioctylfluorenyl‐2,7‐diyl)‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole]/[6,6]phenyl‐C61‐butyric acid methyl ester (PdO/APFO‐3:PCBM) as materials of choice. State‐of‐the‐art sensitivity, amounting at ?5.87 μA cm?2 ppm?1, low background signal, in the order of ?4.85 μA cm?2, good electrochemical stability for more than 2 h of continuous functioning and high reproducibility of the signal over the pH 1 to 10 range, are reported, making the hybrid device suitable for several practical uses. The results fully validate the mixed organic/inorganic approach for photoelectrochemical applications, and pave the way for its further exploitation in fields like waste water treatment, environmental monitoring, and water splitting. 相似文献
994.
995.
996.
997.
In this paper, the authors use the analytic methods and the properties of
character sums mod p to study the computational problem of one kind of mean value
involving the classical Dedekind sums and two-term exponential sums, and give an exact
computational formula for it. 相似文献
998.
999.
1000.
In the present study the correlation between the melting behaviour of poly(3-hydroxybutyrate) (PHB) original, non-reorganized crystals and the crystallinity increase during isothermal crystallization is presented and discussed. Since the reorganization processes modify the melting curve of original crystals, it is necessary to prevent and hinder all the processes that influence and increase the lamellar thickness. PHB exhibits melting/recrystallization on heating, the occurring of lamellar thickening in the solid state being excluded. The first step of the study was the identification of the scanning rate which inhibits PHB recrystallization at sufficiently high Tc. For the extrapolated onset and peak temperatures of the main melting endotherm, which is connected to fusion of dominant lamellae, a double dependence on the crystallization time was found. The crystallization time at which Tonset and Tpeak change their trends was found to correspond to the spherulite impingement time, so that the two different dependencies were put in relation with primary and secondary crystallizations respectively. The increase of both Tonset and Tpeak at high crystallization times after spherulite impingement was considered an effect due to crystal superheating and an indication of a stabilization process of the crystalline phase. Such stabilization, which produces an increase of the melting temperature, is probably connected with the volume filling that occurs after spherulite impingement. 相似文献