全文获取类型
收费全文 | 1008篇 |
免费 | 71篇 |
国内免费 | 12篇 |
专业分类
化学 | 581篇 |
晶体学 | 9篇 |
力学 | 33篇 |
数学 | 48篇 |
物理学 | 131篇 |
无线电 | 289篇 |
出版年
2023年 | 6篇 |
2022年 | 9篇 |
2021年 | 16篇 |
2020年 | 7篇 |
2019年 | 14篇 |
2018年 | 13篇 |
2017年 | 14篇 |
2016年 | 27篇 |
2015年 | 35篇 |
2014年 | 37篇 |
2013年 | 62篇 |
2012年 | 66篇 |
2011年 | 63篇 |
2010年 | 44篇 |
2009年 | 51篇 |
2008年 | 77篇 |
2007年 | 46篇 |
2006年 | 69篇 |
2005年 | 58篇 |
2004年 | 37篇 |
2003年 | 46篇 |
2002年 | 47篇 |
2001年 | 24篇 |
2000年 | 29篇 |
1999年 | 25篇 |
1998年 | 21篇 |
1997年 | 12篇 |
1996年 | 21篇 |
1995年 | 10篇 |
1994年 | 9篇 |
1993年 | 8篇 |
1992年 | 5篇 |
1991年 | 12篇 |
1990年 | 9篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 8篇 |
1985年 | 4篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 9篇 |
1977年 | 4篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1966年 | 1篇 |
1900年 | 1篇 |
排序方式: 共有1091条查询结果,搜索用时 234 毫秒
161.
C.Y. Liu S.F. Yoon J.H. Teng J.R. Dong S.J. Chua 《Applied Physics A: Materials Science & Processing》2008,91(3):435-439
GaInP/AlGaInP triple quantum well (TQW) lasers, grown by metalorganic chemical vapor deposition (MOCVD) using tertiarybutylarsine
(TBAs) and tertiarybutylphosphine (TBP), were fabricated with a pulsed anodic oxidation (PAO) process. The devices worked
at room temperature (RT) with the lowest threshold current density (Jth) of 1.5 kA/cm2 ever reported for GaInP/AlGaInP lasers grown using TBAs and TBP. Temperature dependent (35–250 K) electroluminescence (EL)
study of the GaInP/AlGaInP laser diode showed almost the same luminescence quenching behavior at a high temperature region
(120–250 K), independent of the injection current (100–150 mA). A model involving a nonradiative recombination mechanism was
presented to interpret the EL quenching behavior over the experimental temperature range. The nonradiative recombination centers
in the Al-containing barrier or cladding layer are believed to contribute to the loss of carriers via nonradiative recombination.
PACS 78.60.Fi; 71.20.Nr; 78.67.De; 81.15.Gh; 42.55.Px 相似文献
162.
A.S.W. Wong G.W. Ho S.L. Liew K.C. Chua D.Z. Chi 《Progress in Photovoltaics: Research and Applications》2011,19(4):464-472
The microstructure of β‐FeSi2 nanoparticles grown using magnetron sputtering on Si has been examined using various electron microscopy techniques. FeSi2 nanoparticles as small as ∼4 nm are found embedded in Si after growth using co‐sputtering of FeSi2 and Si, followed by rapid thermal annealing (RTA). The formation of nanoparticles and its variation in density with Fe content is discussed in terms of phase separation. Our study shows that the size and density of the nanoparticles as well as the extent of Fe diffusion into sputtered Si and substrate can be controlled by controlling the Fe content in the co‐sputtered film. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
163.
Transition metal catalysed C−H bond activation chemistry has emerged as an exciting and promising approach in organic synthesis. This allows us to synthesize a wider range of functional molecules and conjugated polymers in a more convenient and more atom economical way. The formation of C−C bonds in the construction of pi-conjugated systems, particularly for conjugated polymers, has benefited much from the advances in C−H bond activation chemistry. Compared to conventional transition-metal catalysed cross-coupling polymerization such as Suzuki and Stille cross-coupling, pre-functionalization of aromatic monomers, such as halogenation, borylation and stannylation, is no longer required for direct arylation polymerization (DArP), which involve C−H/C−X cross-coupling, and oxidative direct arylation polymerization (Ox-DArP), which involves C−H/C−H cross-coupling protocols driven by the activation of monomers’ C(sp2)−H bonds. Furthermore, poly(annulation) via C−H bond activation chemistry leads to the formation of unique pi-conjugated moieties as part of the polymeric backbone. This review thus summarises advances to date in the synthesis of conjugated polymers utilizing transition metal catalysed C−H bond activation chemistry. A variety of conjugated polymers via DArP including poly(thiophene), thieno[3,4-c]pyrrole-4,6-dione)-containing, fluorenyl-containing, benzothiadiazole-containing and diketopyrrolopyrrole-containing copolymers, were summarized. Conjugated polymers obtained through Ox-DArP were outlined and compared. Furthermore, poly(annulation) using transition metal catalysed C−H bond activation chemistry was also reviewed. In the last part of this review, difficulties and perspective to make use of transition metal catalysed C−H activation polymerization to prepare conjugated polymers were discussed and commented. 相似文献
164.
S.T. Tan X.W. Sun X.H. Zhang B.J. Chen S.J. Chua Anna Yong Z.L. Dong X. Hu 《Journal of Crystal Growth》2006,290(2):518-522
Zinc oxide (ZnO) quantum dots (QDs) were fabricated on silicon substrates by metal organic chemical vapor deposition. Formation of QDs is due to the vigorous reaction of the precursors when a large amount of precursors was introduced during the growth. The size of the QDs ranged from 3 to 12 nm, which was estimated by high-resolution transmission electron microscopy. The photoluminescence measured at 80 K showed that the emission of QDs embedded film ranged from 3.0 to 3.6 eV. The broad near-band-edge emission was due to the quantum confinement effect of the QDs. 相似文献
165.
The iridium complex [Cp1IrCl2]2 is a good catalyst for the directed oxidative coupling of arenes with alkenes; a wide range of carbonyl functionalities (NHCOR, CONH2 and COR) can be employed as the directing group. 相似文献
166.
Cathleen Teh Purnima Naresh Manghnani Grace Ng Hwee Boon Terrence You De Cheng Wan‐Teck Lim Elaine Hsuen Lim Boon Tin Chua Bin Liu 《Advanced functional materials》2019,29(25)
Cancer prognosis will benefit from a scoring system that could grade malignant traits of patient‐derived cells by assessing their growth and metastasis in a living system. Specific tracking of patient‐derived cells requires labeling by contrast agents with good signal‐to‐noise ratio and no specific stain of host tissues. Towards this aim, aggregation‐induced emission (AIE) dots are developed for in vivo cancer tracking with emphasis on reproducible optimized formulation and specific fluorescent labeling of cells that enable enhanced spatial temporal resolution in vivo. The importance of energy‐dependent AIE dots uptake for patient‐derived cell labeling is emphasized to reveal their specific uptake by viable cancer cells. Using optically transparent zebrafish embryo, the ability is demonstrated to follow the engraftment of transplanted AIE dot labeled cells in zebrafish brains over one week. Cells detected outside the brain after 7 d are quantified as metastatic cells. Results from seven clinical samples demonstrate the utility of this methodology to differentiate low engraftment level of benign neoplasms from higher engraftment level and metastasis detected in malignant ovarian cancer specimens. Achieving clinically validated results supports the use of AIE dot labeled patient derived cells in zebrafish xenografts for future cancer prognosis. 相似文献
167.
Sugato Hajra Manisha Sahu Aneeta Manjari Padhan In Sang Lee Dong Kee Yi Perumal Alagarsamy Sitansu Sekhar Nanda Hoe Joon Kim 《Advanced functional materials》2021,31(28):2101829
The naturally available cyclodextrin has opened up a wide range of research avenues because of its superior characteristics such as being non-toxic, biocompatible, and edible. The cyclodextrin is the green multifunctional material that can add to the triboelectric series and extend its self-powered applications. The ultrasonic synthesized cyclodextrin metal–organic framework (CD-MOF) designed using sodium as a metal ion and cyclodextrin as a ligand for the triboelectric nanogenerator is reported. The various detailed characterizations of the CD-MOFs give an insight into the properties of the synthesized material. The Kelvin probe force microscopy suggests three types of CD-MOFs, exhibiting a positive potential. As per the surface potential, the output of the various CD-MOF based TENG is varied as alpha CD MOF/Teflon > gamma CD-MOF/Teflon > beta CD-MOF/Teflon. The alpha CD MOF/Teflon TENG produces an electrical output of 152 V, 1.2 μA, and 14.3 nC, respectively. The fabricated device output is utilized for powering numerous low-power electronics through a capacitor and bridge rectifier circuit. The multiunit Z-shaped TENG device is attached to various surfaces such as the shoe heel and the backside of the school bag, and the corresponding energy harvesting response is demonstrated. 相似文献
168.
Shuyu Bao Yue Wang Khaw Lina Li Zhang Bing Wang Wardhana Aji Sasangka Kenneth Eng Kian Lee Soo Jin Chua Jurgen Michel Eugene Fitzgerald Chuan Seng Tan Kwang Hong Lee 《半导体学报》2021,42(2):83-102
The heterogeneous integration of Ⅲ-Ⅴ devices with Si-CMOS on a common Si platform has shown great promise in the new generations of electrical and optical systems for novel applications,such as HEMT or LED with integrated control cir-cuitry.For heterogeneous integration,direct wafer bonding(DWB)techniques can overcome the materials and thermal mis-match issues by directly bonding dissimilar materials systems and device structures together.In addition,DWB can perform at wafer-level,which eases the requirements for integration alignment and increases the scalability for volume production.In this paper,a brief review of the different bonding technologies is discussed.After that,three main DWB techniques of single-,double-and multi-bonding are presented with the demonstrations of various heterogeneous integration applications.Mean-while,the integration challenges,such as micro-defects,surface roughness and bonding yield are discussed in detail. 相似文献
169.
Chan Cheong Loong Lee Sheng Chyan Yeong Kee Choon Tan Su Wei 《Wireless Personal Communications》2018,103(2):1677-1697
Wireless Personal Communications - The dependence on broadband to enhance the economy and environment sustainability is imposing immense urgency to provide ubiquitous wireless broadband access... 相似文献
170.
Clara L. Hedegaard Estelle C. Collin Carlos Redondo‐Gómez Luong T. H. Nguyen Kee Woei Ng Alfonso A. Castrejón‐Pita J. Rafael Castrejón‐Pita Alvaro Mata 《Advanced functional materials》2018,28(16)
Effective integration of molecular self‐assembly and additive manufacturing would provide a technological leap in bioprinting. This article reports on a biofabrication system based on the hydrodynamically guided co‐assembly of peptide amphiphiles (PAs) with naturally occurring biomolecules and proteins to generate hierarchical constructs with tuneable molecular composition and structural control. The system takes advantage of droplet‐on‐demand inkjet printing to exploit interfacial fluid forces and guide molecular self‐assembly into aligned or disordered nanofibers, hydrogel structures of different geometries and sizes, surface topographies, and higher‐ordered constructs bound by molecular diffusion. PAs are designed to co‐assemble during printing in cell diluent conditions with a range of extracellular matrix (ECM) proteins and biomolecules including fibronectin, collagen, keratin, elastin‐like proteins, and hyaluronic acid. Using combinations of these molecules, NIH‐3T3 and adipose derived stem cells are bioprinted within complex structures while exhibiting high cell viability (>88%). By integrating self‐assembly with 3D‐bioprinting, the study introduces a novel biofabrication platform capable of encapsulating and spatially distributing multiple cell types within tuneable pericellular environments. In this way, the work demonstrates the potential of the approach to generate complex bioactive scaffolds for applications such as tissue engineering, in vitro models, and drug screening. 相似文献