全文获取类型
收费全文 | 3479篇 |
免费 | 224篇 |
国内免费 | 19篇 |
专业分类
化学 | 2654篇 |
晶体学 | 36篇 |
力学 | 51篇 |
数学 | 266篇 |
物理学 | 715篇 |
出版年
2023年 | 14篇 |
2022年 | 68篇 |
2021年 | 80篇 |
2020年 | 66篇 |
2019年 | 73篇 |
2018年 | 50篇 |
2017年 | 49篇 |
2016年 | 142篇 |
2015年 | 107篇 |
2014年 | 154篇 |
2013年 | 222篇 |
2012年 | 285篇 |
2011年 | 302篇 |
2010年 | 181篇 |
2009年 | 167篇 |
2008年 | 224篇 |
2007年 | 219篇 |
2006年 | 181篇 |
2005年 | 167篇 |
2004年 | 186篇 |
2003年 | 126篇 |
2002年 | 140篇 |
2001年 | 61篇 |
2000年 | 81篇 |
1999年 | 40篇 |
1998年 | 21篇 |
1997年 | 17篇 |
1996年 | 28篇 |
1995年 | 27篇 |
1994年 | 17篇 |
1993年 | 20篇 |
1992年 | 38篇 |
1991年 | 20篇 |
1990年 | 6篇 |
1989年 | 9篇 |
1988年 | 6篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 17篇 |
1984年 | 7篇 |
1982年 | 6篇 |
1981年 | 11篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 10篇 |
1976年 | 5篇 |
1975年 | 7篇 |
1974年 | 11篇 |
1973年 | 4篇 |
排序方式: 共有3722条查询结果,搜索用时 15 毫秒
991.
Young-Hyun Shin 《Applied Surface Science》2007,253(16):6872-6877
A carbon nanotube (CNT) tip, which assembled on the sharp end of a Si tip by dielectrophoresis, was structurally modified using focused ion beam (FIB). We described the imaging characterization of the FIB-modified CNT tip in noncontact AFM mode in terms of wear, deep trench accessibility, and imaging resolution. Compared to a conventional Si tip, the FIB-modified CNT tip was superior, especially for prolonged scanning over 10 h. We conclude that modified CNT tips have the potential to obtain high-quality images of nanoscale structures. 相似文献
992.
Shien-Kuei Liaw Kuan-Luen Hung Yi-Tseng Lin Chia-Chin Chiang Chow-Shing Shin 《Optics & Laser Technology》2007,39(6):1214-1217
We report the development of a ring tunable fiber laser based on tunable fiber Bragg gratings (TFBG) integrated with an optical circulator. The TFBG is embedded inside a 3-piont bending device for wavelength tuning. The tunable laser operating in the C-band has power variation, tuning resolution, tuning range and laser line width of ±0.5 dB, 0.5 nm, 25.0 nm and less than 0.05 nm, respectively. As 40 mW of pump power is used, the ring tunable laser has a side mode suppression ratio of 60 dB and a power conversion efficiency of 25%. These specifications ensure the high-quality operation of a tunable laser. 相似文献
993.
We propose and demonstrate a simple technique to stabilize the frequencies of multiple semiconductor lasers simultaneously using a Fabry-Perot etalon filter and a digital signal processing. Unlike other stabilization techniques, the proposed technique could stabilize DFB lasers using only one digital feedback control loop. The result shows that the proposed technique could maintain the frequency stability of 16 DFB lasers within ±150 MHz. 相似文献
994.
Hyunkwon Shin 《Optics Communications》2007,269(2):299-303
We have investigated angle multiplexing combined with peristrophic (rotational) multiplexing in a photorefractive LiNbO3 crystal of cylindrical shape. The peristrophic multiplexing was achieved by rotating the recording medium while the angle multiplexing, by varying the incident angle of the reference beam. Angle multiplexing in synchronization with rotation of the sample made it possible to continuously record and retrieve holograms. In the combined multiplexing, holograms were stored at different peristrophic positions and thus their angular selectivity could be much improved in comparison to that of only angle-multiplexed holograms. The theoretical angular selectivity was derived, along with its dependence on the sample rotation. The experimentally measured selectivity was in agreement with the theoretical one. The angular selectivity of angle-multiplexed holograms was measured to be 0.03° in the absence of sample rotation and it became less than 0.0075° with a sample rotation by 5.4°. 相似文献
995.
Lim BK Shin JO Choe SC Choi SW Jeong JO Seong IW Kim DK Jeon ES 《Experimental & molecular medicine》2005,37(1):51-57
Endomyocardial biopsy often fails to show myocardial inflammation for patients with clinically suspected myocarditis. The serum isoforms of troponin T (cTnT) level is a very sensitive marker of myocardial injury and it is elevated even in the absence of myocardial inflammation. We investigated the correlations for myocardial injury, virus titers and inflammation in acute viral infection. Using the murine coxsackievirus group B3 (CVB3) myocarditis model, the histopathologic findings and virus titers in mouse hearts were compared with the serum cTnT levels measured by ELISA at various time points. Viable virus titers in the hearts peaked at 3 days after infection (8.22 +/- 0.13 log10 PFU/100 mg of heart); they decreased at day 7 and no viable virus was detected from day 14. Myocardial inflammation was minimal at day 3, peaked at day 7 and markedly decreased at day 14. The individual serum TnT levels were significantly increased at day 3 (7.37 +/- 1.46 ng/ml), persisted to day 7 (0.73 +/- 0.08 ng/ml), and normalized at day 14. Serum cTnT levels were correlatable with virus titers in the heart (r = 0.744, P <0.01), but the serum cTnT levels were not correlated with the degrees of inflammation. Using the less myocarditic strain of CVB3, similar relationships were observed between the changes for the serum cTnT levels and the heart virus titers. During the course of viral infection, myocardial injury precedes the pathologic evidence of inflammation, and the elevated cTnT levels provide evidence of myocardial injury even in the absence of any histologic findings of myocarditis. 相似文献
996.
Shin Y Saba M Pasquini TA Ketterle W Pritchard DE Leanhardt AE 《Physical review letters》2004,92(5):050405
A trapped-atom interferometer was demonstrated using gaseous Bose-Einstein condensates coherently split by deforming an optical single-well potential into a double-well potential. The relative phase between the two condensates was determined from the spatial phase of the matter wave interference pattern formed upon releasing the condensates from the separated potential wells. Coherent phase evolution was observed for condensates held separated by 13 microm for up to 5 ms and was controlled by applying ac Stark shift potentials to either of the two separated condensates. 相似文献
997.
Kitagawa Y Sentoku Y Akamatsu S Sakamoto W Kodama R Tanaka KA Azumi K Norimatsu T Matsuoka T Fujita H Yoshida H 《Physical review letters》2004,92(20):205002
An ultraintense laser injected a 10 J of power at 1.053 microm in 0.5 ps into a glass capillary of 1 cm long and 60 microm in diameter and accelerated plasma electrons to 100 MeV. One- and two-dimensional particle codes describe wakefields with 10 GV/m gradient excited behind the laser pulse, which are guided by a plasma density channel far beyond the Rayleigh range. The blueshift of the laser spectrum supports that a plasma of 10(16) cm(-3) is inside the capillary. A bump at the high energy tail suggests the electron trapping in the wakefield. 相似文献
998.
We present a new technique for measuring the temperature profiles of visible LED chips by use of a nematic liquid crystal with IR laser illumination. The LEDs studied have a multi-quantum-well InGaN/GaN/sapphire structure. New features in this technique are the use of a high-power IR laser beam as the sensing light and the insertion of a color filter in the optical path to block the high-intensity LED light. For the LEDs measured, the conversion efficiency decreases by 70% when the junction temperature rises from 25 to 107 degrees C. This technique is a valuable tool for studying the performance of LEDs as a function of junction temperature. 相似文献
999.
K.W.?KwokEmail author C.W.?Tsang F.G.?Shin H.L.W.?Chan C.L.?Choy 《Applied Physics A: Materials Science & Processing》2004,79(8):1931-1934
In this paper, we demonstrate that a sol-gel-derived lead zirconate titanate film can be depolarized by the application of ac fields of diminishing amplitude, and we explain the phenomenon based on the concept of the Preisach model. The amplitude of the ac fields is decreased from 19.5 MV/m to 0.2 MV/m in eight steps. The observed piezoelectric coefficient of the film decreases after each step and finishes with almost the same value as that of an as-deposited film. Our results also reveal the existence of a distribution of coercive fields in the microdomains (Preisach dipolar units), and that the P–E loop of each microdomain is shifted by interaction fields so that the magnitudes of its switch-up and switch-down fields are not necessarily the same. PACS 77.22.Ej; 77.70.+a; 77.90.+k 相似文献
1000.
We report direct full-field magneto-optical observations of Barkhausen avalanches in Co polycrystalline thin films at criticality. We provide experimental evidence for the validity of a phenomenological model of the Barkhausen avalanche originally proposed by Cizeau, Zapperi, Durin, and Stanley [Phys. Rev. Lett. 79, 4669 (1997)]], where the model describes a 180 degrees -type flexible domain wall deformed by a localized defect with consideration of long-range dipolar interaction. The Barkhausen jump areas show a power-law scaling distribution with critical exponent tau approximately 1.33 for all the samples having different thickness from 5 to 50 nm, which is in accord with the two-dimensional prediction of the model. 相似文献