全文获取类型
收费全文 | 1253篇 |
免费 | 55篇 |
国内免费 | 24篇 |
专业分类
化学 | 720篇 |
晶体学 | 9篇 |
力学 | 70篇 |
数学 | 114篇 |
物理学 | 419篇 |
出版年
2023年 | 13篇 |
2022年 | 12篇 |
2021年 | 10篇 |
2019年 | 20篇 |
2018年 | 8篇 |
2017年 | 7篇 |
2016年 | 26篇 |
2015年 | 27篇 |
2014年 | 39篇 |
2013年 | 41篇 |
2012年 | 86篇 |
2011年 | 98篇 |
2010年 | 64篇 |
2009年 | 64篇 |
2008年 | 77篇 |
2007年 | 78篇 |
2006年 | 70篇 |
2005年 | 60篇 |
2004年 | 40篇 |
2003年 | 38篇 |
2002年 | 31篇 |
2001年 | 26篇 |
2000年 | 28篇 |
1999年 | 12篇 |
1998年 | 11篇 |
1997年 | 17篇 |
1996年 | 19篇 |
1995年 | 9篇 |
1994年 | 14篇 |
1993年 | 28篇 |
1992年 | 19篇 |
1991年 | 23篇 |
1990年 | 20篇 |
1989年 | 10篇 |
1988年 | 11篇 |
1987年 | 12篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 13篇 |
1981年 | 11篇 |
1980年 | 12篇 |
1979年 | 15篇 |
1978年 | 11篇 |
1977年 | 9篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1972年 | 5篇 |
1970年 | 7篇 |
1969年 | 8篇 |
排序方式: 共有1332条查询结果,搜索用时 0 毫秒
91.
Observation of thermal-induced optical guiding and bistability in a mid-IR continuous-wave, singly resonant optical parametric oscillator 总被引:1,自引:0,他引:1
We report the observation of thermal-induced optical guiding and bistability in a mid-IR cw, singly resonant optical parametric oscillator (SRO) at approximately 3.2 microm. The SRO employs a MgO:PPLN crystal as the gain medium and a 1-nm-linewidth Yb-fiber laser at 1.064 microm as the pump source. As soon as the pump power reaches the thermal guiding threshold at 16.5 W, the SRO shows a step increase in the parametric efficiency by a factor of 2.5. At 25 W pump power, the SRO generated 5.3 and 1.2 W at 1.58 and 3.23 microm, respectively, with single-longitudinal-mode performance for the 3.23 microm radiation. 相似文献
92.
The effects of group-delay difference in an active nonlinear long-period fiber grating (LPFG) made in an erbium-doped amplifying fiber (EDF) are investigated by proposing a general model that include the effects of detuning, group-delay difference, gain saturation, gain bandwidth and Kerr nonlinearity. In particular, we observe a new feature caused by the interaction between the group-delay difference and the gain bandwidth: the pulse breakup effect due to the group-delay difference can be suppressed by the finite bandwidth of the linear gain. 相似文献
93.
M.F. Luo J.Y. Huang C.I. Chiang G.R. Hu C.C. Wang C.T. Wang C.W. Lin 《Surface science》2009,603(3):558-565
We present a self-organised approach for the synthesis of one-dimensional (1D) arrays of supported nanoclusters. By oxidising NiAl surfaces vicinal to the (1 0 0) plane tilted along the crystallographic direction [0 1 0], we produced ordered thin films of θ-Al2O3 that exhibit uniform protrusion stripes propagating uniquely along direction [0 0 1] of the NiAl. These protrusions are preferential centres for nucleation of metal deposited from a vapour; the nanoclusters grown from such metal are aligned and form massive 1D cluster arrays along direction [0 0 1]. The arrays of Co nanoclusters exhibit a diameter as small as 3 nm and length exceeding a micrometer. The results imply prospective applications for which a patterned assembly of nanoclusters is desired. 相似文献
94.
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
95.
Nanoscale artificial oil bodies (NOBs) could be assembled from plant oil, phospholipids (PLs), and oleosin (Ole) as previously
reported. NOBs have a lipid-based structure that contains a central oil space enclosed by a monolayer of Ole-bound PLs. As
an oil structural protein, Ole functions to maintain the integrity of NOBs. Like Ole, caleosin (Cal) is a plant oil-associated
protein. In this study, we investigated the feasibility of NOBs assembled by Cal for targeted delivery of drugs. Cal was first
fused with anti-HER2/neu affibody (ZH2), and the resulting fusion gene (Cal–ZH2) was then expressed in Escherichia coli. Consequently, NOBs assembled with the fusion protein were selectively internalized by HER2/neu-positive tumor cells. The internalization efficiency could reach as high as 90%. Furthermore, a hydrophobic anticancer drug,
Camptothecin (CPT), was encapsulated into Cal-based NOBs. These CPT-loaded NOBs had a size around 200 nm and were resistant
to hemolysis. Release of CPT from NOBs at the non-permissive condition followed a sustained and prolonged profile. After administration
of the CPT formulation, Cal–ZH2-displayed NOBs exhibited a strong antitumor activity toward HER2/neu-positive cells both in vitro and in vivo. The result indicates the potential of Cal-based NOBs for targeted delivery of hydrophobic drugs. 相似文献
96.
97.
Shih-Feng Tseng Wen-Tse HsiaoDonyau Chiang Kuo-Cheng HuangChang-Pin Chou 《Applied Surface Science》2011,257(16):7204-7209
The fluorine-doped tin oxide (FTO) thin film deposited on a soda-lime glass substrate was annealed by a defocus ultraviolet (UV) laser irradiation at ambient temperature. The mechanical and optoelectric properties of FTO films annealed by using the various laser processing parameters were reported. After the FTO films were subjected to laser post-annealing, the microhardness were slightly less but the reduced modulus values were larger than that of unannealed FTO films, respectively. The average optical transmittance in the visible waveband slightly increased with increasing the laser annealing energy and scan speed. Moreover, all the sheet resistance of laser annealed films was less than that of the unannealed ones. We found that the sheet resistance decrease was obviously influenced by annealing. The suitable annealing conditions could maintain the film thickness and relief the internal stress generated in the film preparation process to improve the electrical conductivity via decreasing laser energy or increasing scan speed. 相似文献
98.
Angle-resolved photoemission is employed to measure the band structure of TiSe2 in order to clarify the nature of the ( 2 x 2 x 2) charge density wave transition. The results show a very small indirect gap in the normal phase transforming into a larger indirect gap at a different location in the Brillouin zone. Fermi surface topology is irrelevant in this case. Instead, electron-hole coupling together with a novel indirect Jahn-Teller effect drives the transition. 相似文献
99.
We report a demonstration of distributed-feedback (DFB) optical parametric oscillation (OPO) by writing photorefractive gratings in periodically poled lithium niobate (PPLN). The photorefractive DFB structures were fabricated by illumination of PPLN with UV light through a photomask and by writing of PPLN with UV-light gated interfering laser beams at 532 nm. Evidence of OPO was observed from the spectral narrowing at the 1438.8- and the 619.3-nm signal wavelengths from 1064- and 532-nm-pumped PPLN crystals with the DFB grating periods phase matched to the 4084.5- and 3774-nm idler wavelengths, respectively. 相似文献
100.
Scattering by a cylindrical cavity in a porous solid is studied by the boundary layer approximation of Mei and Foda. Quantitative results will be presented for two cases: (1) vacuum cavity and (2) cavity filled with fluid. In each case both P and SV incident waves will be studied. Focus will be on the stress distribution near the cavity surface and contrast to the non-porous case will be pointed out. The effect of fluid compressibility due to possible entrainment of air will be discussed. These results should be of interest to the design of long tunnels subject to earthquakes. 相似文献