全文获取类型
收费全文 | 1994篇 |
免费 | 386篇 |
国内免费 | 51篇 |
专业分类
化学 | 99篇 |
晶体学 | 1篇 |
力学 | 23篇 |
综合类 | 12篇 |
数学 | 18篇 |
物理学 | 1402篇 |
综合类 | 876篇 |
出版年
2024年 | 4篇 |
2023年 | 7篇 |
2022年 | 16篇 |
2021年 | 24篇 |
2020年 | 14篇 |
2019年 | 18篇 |
2018年 | 22篇 |
2017年 | 44篇 |
2016年 | 43篇 |
2015年 | 38篇 |
2014年 | 132篇 |
2013年 | 80篇 |
2012年 | 94篇 |
2011年 | 151篇 |
2010年 | 79篇 |
2009年 | 128篇 |
2008年 | 164篇 |
2007年 | 154篇 |
2006年 | 163篇 |
2005年 | 122篇 |
2004年 | 124篇 |
2003年 | 105篇 |
2002年 | 113篇 |
2001年 | 78篇 |
2000年 | 83篇 |
1999年 | 69篇 |
1998年 | 46篇 |
1997年 | 45篇 |
1996年 | 35篇 |
1995年 | 51篇 |
1994年 | 20篇 |
1993年 | 29篇 |
1992年 | 26篇 |
1991年 | 22篇 |
1990年 | 16篇 |
1989年 | 13篇 |
1988年 | 16篇 |
1987年 | 14篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 5篇 |
1979年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有2431条查询结果,搜索用时 15 毫秒
31.
32.
Sulaiman Wadi Harun Nizam Tamchek Mohd Kamil Abd-Rahman Prabakaran Poopalan Harith Ahmad 《Optical Review》2003,10(3):133-135
A multiwavelength Brillouin/erbium fibre laser (BEFL) which operates in the long wavelength (L-band) region is demonstrated for potential applications in an L-band wavelength division multiplexing (WDM) communication system. The laser configuration consists of a long erbium-doped fibre to enable L-band amplification where two 3-dB couplers take a portion of the generated BEFL signal and re-inject it into the single mode fibre to seed a cascaded BEFL line in the same direction as the first BEFL line. A stable and strong laser comb of up to five lines with 10-GHz spacing has been obtained with a Brillouin pump (BP) of 9.2 mW and a 980 nm pump of 92 mW. The BEFL has shown a broad tuning range with a tuning characteristic for line #1 which is flat over a range greater than 9.9 nm. 相似文献
33.
34.
35.
提出了一种采用现代控制理论中的状态空间表达式的系统方块图直接实现了OTA-C滤波器的方法,SPICE程序模拟结果验证了设计方法的正确。 相似文献
36.
在无氧条件下,生物染料亚甲基蓝可以作为生物新陈代谢过程中体内脱氢酶催化反应的电子受体,亚甲基蓝与细菌悬液共存时,其退色速度标志着细菌脱氢酶活性的大小。脱氢酶的活性大小在一定程度上能够反映出微生物新代谢的能力,微生物所处的水环境中毒物的存在会引起微生物脱氢酶活性变化,毒物的毒性与脱氢酶的活性相关。本文以动力学比色法测定亚甲基蓝的退色速度为基础设计并制造了一台水质综合毒性相关。本文以动力学比色法测定亚 相似文献
37.
Zeng -Gui Chen 《International Journal of Infrared and Millimeter Waves》1993,14(2):197-211
A cylindrical waveguide gyro-peniotron amplifier is analysed theoretically in this paper. By a ballistic method and directly using the energy conservation in the beam-wave system, a set of interaction equations for the cylindrical waveguide gyro-peniotron amplifier is derived. Computer simulation shows that under defined conditions an interaction efficiency of 47%, an output power of 240kW at a gain of 22. 5 dB and a 3 dB-instantaneous bandwidth of 1. 9% for a central frequency of 35GHz, TE03 mode gyro-peniotron amplifier could be achieved. The influence of the operation parameters on the amplifier performance is also presented. 相似文献
38.
With a set of equations for the self-consistent large-signal interaction derived in this paper, the bandwidth characteristics of a non-reflection-type gyrotron-TWA using a tapered waveguide and tapered magnetic field system have been analysed. Numerical calculations indicate that under defined conditions an instantaneous bandwidth of nearly 10 % at a center frequency of 35 GHz with a length of the order of only8 cm of the rf interaction region could be achieved. 相似文献
39.
Marcos Mandaji Tiago Buckup Rafael Rech Ricardo Rego Bordalo Correia Tarso Ledur Kist 《Talanta》2007,71(5):1998-2002
The performance of fluorescence detectors in capillary electrophoresis is maximized when the excitation light intensity is modulated in time with optimal frequencies. This is especially true when photomultiplier tubes are used to detect the fluorescent light. The photomultiplier tube amplified raw output signal can in principle be captured directly by a personal computer sound card (PCSC) and processed by a lock-in emulated by software. This possibility is demonstrated in the present work and the performance of this new setup is compared with a traditional data acquisition system. The results obtained with this “PCSC and lock-in emulated by software” were of the same quality or even better compared to that obtained by conventional time integrators (Boxcars) and data acquisition boards. With PCSC the limits of detection (LOD) found for both naphthalene-2,3-dicarboxaldehyde-derivatized tyrosine and alanine were 3.3 and 3.5 fmol (injection of 5 nL of samples at 0.66 and 0.70 μmol/L), respectively. This is at least three times better compared to conventional systems when light emitting diodes (LEDs) are used as the excitation source in fluorescence detectors. The PCSC linear response range was also larger compared to conventional data acquisition boards. This scheme showed to be a practical and convenient alternative of data acquisition and signal processing for detection systems used in capillary electrophoresis. 相似文献
40.
Determination of trace elements in seawater samples by on-line column extraction/graphite furnace atomic absorption spectrometry 总被引:2,自引:0,他引:2
An innovative procedure for the on-line coupling of ion chromatography with graphite furnace atomic absorption spectrometry is described, which is particularly effective for the determination of trace metals in seawater samples. The Capillary Injection Device (CID) is used as an interface which allows the eluent to be transferred from the chromatographic column into the graphite tube at a flow rate of as high as 2 ml/min. The analytical procedure is based on the metal complex formation with 8-hydroxyquinoline in the sample solution, followed by the preconcentration of the complexes in a chromatographic column packed with XAD-2 resin. The complexes were then eluted from the column with methanol, and quantitatively injected into the furnace. The procedure was validated by determining cadmium and lead in certified reference seawater samples at a level of 30–40 pg/g, with a typical reproducibility of 10% and an accuracy of better than 5%. Finally, it was tested on a real sample of seawater. Due to the high reproducibility, a pg/g concentration level can be measured. 相似文献