全文获取类型
收费全文 | 2370篇 |
免费 | 77篇 |
国内免费 | 65篇 |
专业分类
化学 | 1501篇 |
晶体学 | 19篇 |
力学 | 109篇 |
综合类 | 1篇 |
数学 | 307篇 |
物理学 | 575篇 |
出版年
2023年 | 24篇 |
2022年 | 17篇 |
2021年 | 43篇 |
2020年 | 29篇 |
2019年 | 38篇 |
2018年 | 19篇 |
2017年 | 19篇 |
2016年 | 46篇 |
2015年 | 39篇 |
2014年 | 85篇 |
2013年 | 116篇 |
2012年 | 172篇 |
2011年 | 182篇 |
2010年 | 114篇 |
2009年 | 116篇 |
2008年 | 117篇 |
2007年 | 131篇 |
2006年 | 134篇 |
2005年 | 116篇 |
2004年 | 99篇 |
2003年 | 64篇 |
2002年 | 71篇 |
2001年 | 56篇 |
2000年 | 42篇 |
1999年 | 34篇 |
1998年 | 33篇 |
1997年 | 27篇 |
1996年 | 19篇 |
1995年 | 28篇 |
1994年 | 30篇 |
1993年 | 29篇 |
1992年 | 26篇 |
1991年 | 21篇 |
1990年 | 25篇 |
1989年 | 21篇 |
1988年 | 17篇 |
1987年 | 19篇 |
1985年 | 31篇 |
1984年 | 35篇 |
1983年 | 22篇 |
1982年 | 22篇 |
1981年 | 21篇 |
1980年 | 13篇 |
1979年 | 12篇 |
1978年 | 17篇 |
1977年 | 16篇 |
1976年 | 18篇 |
1975年 | 17篇 |
1974年 | 16篇 |
1973年 | 11篇 |
排序方式: 共有2512条查询结果,搜索用时 15 毫秒
141.
Kuei-Yi Chu Shiou-Ying Cheng Meng-Hsueh Chiang Yi-Jung Liu Chien-Chang Huang Tai-You Chen Chi-Shiang Hsu Wen-Chau Liu Wen-Yu Cheng Bin-Cian Lin 《Superlattices and Microstructures》2011,50(4):289-295
The characteristics of InGaP/InGaAs/GaAs dual channel pseudomorphic high electron mobility transistors (DCPHEMTs) with different graded triple delta-doped sheets are investigated and experimentally demonstrated. Based on a two-dimensional simulator of ATLAS, the band diagrams, electron densities and DC characteristics of studied devices are comprehensively analyzed. Due to the use of properly graded triple delta-doped sheets, good pinch-off and saturation characteristics, improved transport properties and wide current swing are obtained. For comparison, a practical DCPHEMT with good device performances is fabricated as well. It is found that the simulated data are in good agreement with experimental results. 相似文献
142.
Yi-Jung Liu Chih-Hung Yen Chia-Hao Hsu Kuo-Hui Yu Li-Yang Chen Tsung-Han Tsai Wen-Chau Liu 《Optical Review》2009,16(6):575-577
An interesting GaN-based light emitting diode (LED) using a 50 nm indium oxide (In2O3)/250 nm indium-tin oxide (ITO) mixed structure to replace the commonly used ITO (250 nm) current spreading layer is fabricated
and studied. Use of the In2O3 layer could reduce the contact resistance of p-GaN in LEDs. In addition, this highly-resistive In2O3 layer, below the ITO layer could improve the current spreading performance. Experimentally, at room temperature, using this
mixed structure, the luminous and EL intensities are enhanced by 17.7 and 17.1%, respectively. 相似文献
143.
Ao Yu Guoming Ma Jintian Jiang Yajing Hu Mingming Su Wangtao Long Shixin Gao Dr. Hsien-Yi Hsu Dr. Ping Peng Prof. Fang-Fang Li 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(40):10405-10412
Inspired by the spongy bone structures, three-dimensional (3D) sponge-like carbons with meso-microporous structures are synthesized through one-step electro-reduction of CO2 in molten carbonate Li2CO3−Na2CO3−K2CO3 at 580 °C. SPC4-0.5 (spongy porous carbon obtained by electrolysis of CO2 at 4 A for 0.5 h) is synthesized with the current efficiency of 96.9 %. SPC4-0.5 possesses large electrolyte ion accessible surface area, excellent wettability and electronical conductivity, ensuring the fast and effective mass and charge transfer, which make it an advcanced supercapacitor electrode material. SPC4-0.5 exhibits a specific capacitance as high as 373.7 F g−1 at 0.5 A g−1, excellent cycling stability (retaining 95.9 % of the initial capacitance after 10000 cycles at 10 A g−1), as well as high energy density. The applications of SPC4-0.5 in quasi-solid-state symmetric supercapacitor and all-solid-state flexible devices for energy storage and wearable piezoelectric sensor are investigated. Both devices show considerable capacitive performances. This work not only presents a controllable and facile synthetic route for the porous carbons but also provides a promising way for effective carbon reduction and green energy production. 相似文献
144.
Yung‐Chung Chen Chih‐Yu Hsu Jiann T. Lin 《Journal of polymer science. Part A, Polymer chemistry》2012,50(11):2121-2129
New conjugated copolymers, P1‐P3 , based on dithiafulvalene‐fused entity and different conjugated segments have been synthesized. Incorporation of electron‐deficient conjugated segments into the conjugated copolymers results in red shifting the absorption band and lowering the hole mobility. Bulk heterojunction solar cells using on these polymers as the donor and [6,6]‐phenyl‐C61 ‐butyric acid methyl ester (PC61BM) as the acceptor were fabricated by solution process. The cells based on the blend of P1‐P3 /PC61BM (1:1, w/w) have power conversion efficiencies (PCEs) ranging from 0.53 to 0.93%. Among these, the cell of P1 /PC61BM exhibited the highest open‐circuit voltage at 0.85 V, and the cell of P3/PC61BM exhibited the best PCE at 0.93% with the short‐circuit current (JSC) of 4.88 mA/cm2. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
145.
Tzu-Sheng Shane Hsu Timothy Fitzgerald Vincent Phuc Nguyen Trisha Patel Balakumar Balachandran 《Acta Mechanica Sinica》2017,33(2):327-340
Studies of fluid-structure interactions associated with flexible structures such as flapping wings require the capture and quantification of large motions of bodies that may be opaque. As a case study, motion capture of a free flying Manduca sexta, also known as hawkmoth, is con-sidered by using three synchronized high-speed cameras. A solid finite element (FE) representation is used as a reference body and successive snapshots in time of the displacement fields are reconstructed via an optimization procedure. One of the original aspects of this work is the formulation of an objective function and the use of shadow matching and strain-energy regularization. With this objective function, the authors penalize the projection differences between silhou-ettes of the captured images and the FE representation of the deformed body. The process and procedures undertaken to go from high-speed videography to motion estimation are dis-cussed, and snapshots of representative results are presented. Finally, the captured free-flight motion is also characterized and quantified. 相似文献
146.
The recently described pressure reaction in the presence of trithylamine with subsequent thermal (200°C) cyclization provided 13N‐pyridylcantharidinimides 4a‐4m from aminopyridines and cantharidin in yields of 15–83%. 2‐Amino‐3,5‐dichloropyridine failed to yield 4n . 相似文献
147.
Let be a compact immersed surface in the unit sphere with constant mean curvature . Denote by the linear map from into , , where is the linear map associated to the second fundamental form and is the identity map. Let denote the square of the length of . We prove that if , then is either totally umbilical or an -torus, where is a constant depending only on the mean curvature .
148.
Sodium borohydride regioselectively reduced various 3-sulfonyl glutarimides 1 to hydroxy piperidones 2, which were further dehydrated to 3,4-dihydro-5-sulfonylpyridin-2-ones 3 in the presence of boron trifluoride. Formal synthesis of 8a-epi-dendroprimine (4) possessing an indolizidine ring system has been accomplished via intramolecular radical cyclization of cyclic vinyl sulfone 5. 相似文献
149.
Hsu KF Chung DY Lal S Mrotzek A Kyratsi T Hogan T Kanatzidis MG 《Journal of the American Chemical Society》2002,124(11):2410-2411
The new materials CsPbBi(3)Te(6) and CsPb(2)Bi(3)Te(7) were discovered through reactions of CsBi(4)Te(6) with PbTe, whereas the isostructural materials CsSnBi(3)Te(6) and CsSn(2)Bi(3)Te(7) were discovered through corresponding reactions with SnTe. The compounds can also be prepared from stoichiometric mixtures of Cs(2)Te, Pb (Sn), Bi, and Te. The crystal structures show a layered architecture of NaCl-type slabs alternating with layers of Cs atoms. This group of compounds offers a new quaternary system, Cs-M-Bi-Te (M = Pb and Sn), available for thermoelectric investigations, including fine-tuning of compositions and doping. 相似文献
150.
A polymerized monolayer of 5,11,17,23,29,35-hexamercaptomethyl-37,38,40,41,42-hexakis-(1-n hexadecyloxy)calix[6]arene (1) has been synthesized on the surface of an ca. 15 mum-thick film derived from poly[1-(trimethylsilyl)-1-propyne] (PTMSP). This monolayer exhibits a permeation selectivity toward He and SF6 that exceeds Knudsen diffusion. Analogous membranes made from a calix[6]arene that contains amidoxime headgroups (i.e., 2) showed Knudsen diffusion characteristics. 相似文献