全文获取类型
收费全文 | 4615篇 |
免费 | 244篇 |
国内免费 | 87篇 |
专业分类
化学 | 3150篇 |
晶体学 | 26篇 |
力学 | 151篇 |
综合类 | 10篇 |
数学 | 555篇 |
物理学 | 1054篇 |
出版年
2023年 | 21篇 |
2022年 | 36篇 |
2021年 | 63篇 |
2020年 | 80篇 |
2019年 | 72篇 |
2018年 | 69篇 |
2017年 | 65篇 |
2016年 | 125篇 |
2015年 | 120篇 |
2014年 | 163篇 |
2013年 | 263篇 |
2012年 | 305篇 |
2011年 | 351篇 |
2010年 | 207篇 |
2009年 | 161篇 |
2008年 | 286篇 |
2007年 | 271篇 |
2006年 | 265篇 |
2005年 | 267篇 |
2004年 | 210篇 |
2003年 | 180篇 |
2002年 | 159篇 |
2001年 | 100篇 |
2000年 | 117篇 |
1999年 | 59篇 |
1998年 | 46篇 |
1997年 | 44篇 |
1996年 | 44篇 |
1995年 | 59篇 |
1994年 | 58篇 |
1993年 | 57篇 |
1992年 | 46篇 |
1991年 | 32篇 |
1990年 | 30篇 |
1989年 | 27篇 |
1988年 | 30篇 |
1987年 | 32篇 |
1986年 | 21篇 |
1985年 | 28篇 |
1984年 | 30篇 |
1982年 | 30篇 |
1981年 | 29篇 |
1980年 | 22篇 |
1979年 | 40篇 |
1978年 | 34篇 |
1977年 | 33篇 |
1976年 | 27篇 |
1975年 | 22篇 |
1974年 | 24篇 |
1973年 | 14篇 |
排序方式: 共有4946条查询结果,搜索用时 15 毫秒
961.
Jong Won NamKwang-Dae Kim Dong Wun KimHyun Ook Seo Young Dok Kim Dong Chan Lim 《Current Applied Physics》2012,12(2):429-433
CO oxidation reactivity of bare and TiO2-coated nanoparticles consisting of both NiO and Ni(OH)2 surfaces was studied. For the deposition of TiO2, atomic layer deposition was used, and formation of three-dimensional domains of TiO2 on NiO-Ni(OH)2 could be identified. Based on the data of X-ray Photoelectron Spectroscopy, we suggest that upon TiO2 deposition only Ni(OH)2 was remained on the surface, whereas NiO surface disappeared. Both CO adsorption and CO oxidation took place on NiO-Ni(OH)2 surfaces under our experimental conditions. CO adsorption was almost completely suppressed after TiO2 deposition, whereas CO oxidation activity was maintained to large extent. It is proposed that bare NiO cannot be active for CO oxidation, and can only uptake CO under our experimental condition, whereas hydroxylated surface of NiO can be active for CO oxidation. 相似文献
962.
An alternative all-fiber sensor for simultaneous strain and temperature measurement based on a photonic crystal fiber (PCF) spliced between single-mode fibers cascaded with a long period grating (LPG) is proposed. By collapsing the air holes at two splicing regions along the PCF, a simple but effective modal-interference (MI) is occurred between the core and cladding modes of the PCF. Due to the different responses on the changes of strain and temperature on the MI and the cascaded LPG, the strain and temperature can be measured simultaneously. Experimental results show that the sensing resolution of 9.1 με in strain measurement is experimentally achieved over a range of 2640 με, while the temperature sensing resolution is 0.27 °C within a range of 30-100 °C. 相似文献
963.
This paper proposes an integrated roughness measurement system that is based on adaptive optics (AO) and binary analysis of speckle pattern images. The aim of this study was to demonstrate the necessity for AO compensation in regions containing both heat and fluid flow turbulences. A speckle image was obtained by projecting a laser beam onto the specimen surface, and the laser pattern image reflected from the surface was binarized to experimentally correlate the intensity with the surface roughness. In the absence of the AO correction scheme, induced turbulences can severely increase the residual rms error from 0.14 to 1.4 μm. After a real-time closed-loop AO correction, we can reduce the wavefront root mean square (rms) error to 0.12 μm, which not only compensates for the aberration error from induced disturbances but also improves the overall performance of the optical system. In addition, an AO system having different gains was investigated, and a threshold gain value was found to be able to steadily compensate for the wavefront errors in less than 2 s. Measurement results of five steel samples having roughness ranging from 0.2 to 3.125 μm (0.3λ and 5λ, where λ is the diode laser wavelength) demonstrate an excellent correlation between the intensity distribution of binary images and average roughness with a correlation coefficient of 0.9982. Furthermore, the proposed AO-assisted system is in good agreement with the stylus method and less than 9.73% error values can be consistently obtained. 相似文献
964.
We demonstrate the use of a nonlinear photonic crystal to generate a harmonic comb and an ultrabroad-band acousto-optic modulator for the field amplitudes and phases of the comb to succeed in synthesizing femtosecond and subfemtosecond optical field waveforms. Nonsinusoidal fields of various shapes are synthesized and verified using shaper-assisted linear cross-correlation. The compact all-solid-state system could lead to the realization of a portable arbitrary optical waveform synthesizer that is analogous in many aspects to an RF function generator. 相似文献
965.
Chan KW 《Optics letters》2012,37(13):2739-2741
The theory of ghost imaging is examined by taking into account the quantum state of the light source explicitly. It is proved that ghost images can be obtained by any light source that is non-Poissonian. It is also shown that ghost images with unity visibility can be achieved with either quantum or classical correlation. 相似文献
966.
Phytochemical studies of the leaves and rhizomes of Paraboea pa niculata (Gesneriaceae) are reported for the first time. Three phenylethanoid glycosides were isolated and characterized as 3,4-dihydroxyphenethyl-(3"-O-beta-D-apiofuranosyl)-beta-D-glucopyranoside, calceoralarioside E, and acteoside. These isolates exhibited weak cytotoxic activity against the K-562 cell line with a 50% of cell killing rate of 40.18 microM, 27.05 microM, and 27.24 microM, respectively. In the DPPH free radical scavenging assay, their IC50 values were determined as 75.89 microM, 25.00 microM, and 26.04 microM, respectively. 相似文献
967.
968.
Ye F Wu C Jin Y Wang M Chan YH Yu J Sun W Hayden S Chiu DT 《Chemical communications (Cambridge, England)》2012,48(12):1778-1780
We demonstrate a new compact CN-PPV dot, which emits in the orange wavelength range with high brightness. The small particle size, high brightness, and the ability to highly specifically target subcellular structures make the CN-PPV dots promising probes for biological imaging and bioanalytical applications. 相似文献
969.
Yubo ChenDengjie Chen Ran RanHee Jung Park Chan KwakSung Jin Ahn Kyeong Suk MoonZongping Shao 《Electrochemistry communications》2012,14(1):36-38
Nickel oxide was introduced as a grain growth inhibitor into Ba0.5Sr0.5Co0.8Fe0.2O3 − δ (BSCF) electrode to increase its activity for oxygen reduction reaction. Small amount of NiO can effectively suppress the grain growth of BSCF by spinning the grain boundary and thus increase the electrode surface area, while the particle connection is not obviously affected. Electrochemical impedance spectra of symmetric cells indicate that the electrode activity for oxygen reduction is indeed effectively improved by introducing NiO additive. At 600 °C, area specific resistance of BSCF+5wt.% NiO is about 36.5% lower than that of pure BSCF electrode. Single cell tests also demonstrate an improved cell power output by introducing NiO additive. It implies that the adoption of a sintering inhibitor may be a facile and practical way to increase electrode activity for oxygen reduction. 相似文献
970.
So LC Liu CC Chan MC Lo JC Sze KH Zhu N 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(2):565-573
The nature and importance of C-H···F-C interactions is a topical yet controversial issue, and the development of spectroscopic methods to probe such contacts is therefore warranted. A series of Group 4 bis(benzyl) complexes supported by (σ-aryl)-2-phenolate-6-pyridyl [O,C,N-R(1)] ligands bearing a fluorinated R(1) group (CF(3) or F) in the vicinity of the metal has been prepared. The X-ray crystal structure of the CF(3)-substituted Hf derivative features intramolecular C-H···F-C and Hf···F-C contacts. All complexes have been characterized by multinuclear NMR spectroscopy. The (1)H and (13)C NMR spectra of [M(O,C,N-CF(3))(CH(2)Ph)(2)] derivatives display coupling (assigned to (1h)J(HF) and (2h)J(CF) for Ti; (3)J(HF) and (2)J(CF) (through M···F) for Hf and Zr) between the benzyl CH(2) and CF(3) moieties. [(1)H,(19)F]-HMBC NMR experiments have been performed for the M-[O,C,N-R(1)] complexes and their [O,N,C] counterparts, revealing significant scalar coupling across the C-H···F-C interactions for Ti-[O,C,N] and [O,N,C] species. 相似文献