全文获取类型
收费全文 | 13259篇 |
免费 | 353篇 |
国内免费 | 41篇 |
专业分类
化学 | 6894篇 |
晶体学 | 179篇 |
力学 | 317篇 |
数学 | 899篇 |
物理学 | 3567篇 |
无线电 | 1797篇 |
出版年
2023年 | 151篇 |
2022年 | 261篇 |
2021年 | 273篇 |
2020年 | 325篇 |
2019年 | 347篇 |
2018年 | 329篇 |
2017年 | 333篇 |
2016年 | 435篇 |
2015年 | 286篇 |
2014年 | 518篇 |
2013年 | 1004篇 |
2012年 | 733篇 |
2011年 | 827篇 |
2010年 | 534篇 |
2009年 | 529篇 |
2008年 | 607篇 |
2007年 | 598篇 |
2006年 | 469篇 |
2005年 | 422篇 |
2004年 | 320篇 |
2003年 | 252篇 |
2002年 | 241篇 |
2001年 | 167篇 |
2000年 | 175篇 |
1999年 | 130篇 |
1998年 | 92篇 |
1997年 | 96篇 |
1996年 | 136篇 |
1995年 | 144篇 |
1994年 | 150篇 |
1993年 | 135篇 |
1992年 | 166篇 |
1991年 | 127篇 |
1990年 | 108篇 |
1989年 | 119篇 |
1988年 | 115篇 |
1987年 | 115篇 |
1986年 | 87篇 |
1985年 | 143篇 |
1984年 | 153篇 |
1983年 | 116篇 |
1982年 | 124篇 |
1981年 | 119篇 |
1980年 | 132篇 |
1979年 | 106篇 |
1978年 | 113篇 |
1977年 | 89篇 |
1976年 | 69篇 |
1975年 | 73篇 |
1974年 | 88篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
CV Tomy D Pal SS Banerjee S Ramakrishnan AK Grover S Bhattacharya MJ Higgins G Balakrishnan McK Paul 《Pramana》2002,58(5-6):925-935
The weakly pinned single crystals of the hexagonal 2H-NbSe2 compound have emerged as prototypes for determining and characterizing the phase boundaries of the possible order-disorder
transformations in the vortex matter. We present here a status report based on the ac and dc magnetization measurements of
the peak effect phenomenon in three crystals of 2H-NbSe2, in which the critical current densities vary over two orders of magnitude. We sketch the generic vortex phase diagram of
a weakly pinned superconductor, which also utilizes theoretical proposals. We also establish the connection between the metastability
effects and pinning. 相似文献
32.
33.
R. G. Makitra G. G. Midyana E. Ya. Pal’chikova 《Russian Journal of Applied Chemistry》2006,79(1):43-49
The influence of physicochemical properties of organic solvents on the distribution constants of aromatic carboxylic acids between the organic and aqueous phases was examined. 相似文献
34.
35.
Synchronized whistlers recorded at Varanasi 总被引:1,自引:0,他引:1
Some interesting events of synchronized whistlers recorded at low latitude station Varanasi during magnetic storm period of
the year 1977 are presented. The dynamic spectrum analysis shows that the component whistlers are Eckersley whistlers having
dispersion 10 s1/2 and 30 s1/2. An attempt has been made to explain the dynamic spectra using lightning discharge generated from magnetospheric sources 相似文献
36.
Naber J.F. Singh H.P. Tanis W.J. Koshar A.J. Segalla G.L. 《Solid-State Circuits, IEEE Journal of》1992,27(10):1327-1331
An indirect, phase-locked-loop (PLL), GaAs-enhanced frequency synthesizer with 700 ns loop settling time has been developed. The two-chip GaAs insertion reduced the size of an existing synthesizer from 90 in3 to only 30 in3. The 6.0 in×5.5 in.×0.9 in module contains a 400 gate GaAs programmable divider and a sample and hold (S/H) which improved the settling time by 77% and reduced the size by 67% over the current state-of-the-art synthesizer. Furthermore, the divider reduced power dissipation by 9.7 W and the S/H reduced power dissipation by 1.3 W 相似文献
37.
Shyam K. Singh Oliver S. Fetzer John B. Hynes Thomas C. Williams 《Journal of heterocyclic chemistry》1991,28(5):1459-1461
Nitration of 2-amino-4-oxo-(3H)-5-trifluoromethylquinazoline is shown to occur exclusively at C6 as determined from an analysis of long range 1H and 19F scalar couplings to ring carbons. Nitration of 2-amino-4-oxo-(3H)-5-fluoroquinazoline is found to occur both at C6 and C8 as evident from an analysis of the 19F and 1H couplings of the ring protons. 相似文献
38.
Xie K. Zhao J.H. Flemish J.R. Burke T. Buchwald W.R. Lorenzo G. Singh H. 《Electron Device Letters, IEEE》1996,17(3):142-144
A 6H-SiC thyristor has been fabricated and characterized. A forward breakover voltage close to 100 V and a pulse switched current density of 5200 A/cm2 have been demonstrated. The thyristor is shown to operate under pulse gate triggering for turn-on and turn-off, with a rise time of 43 ns and a fall time of less than 100 ns. The forward breakover voltage is found to decrease by only 4% when the operating temperature is increased from room temperature to 300°C. It is found that anode ohmic contact resistance dominates the device forward drop at high current densities 相似文献
39.
An optoelectronic charge coupled device (OECCD) which is directly compatible with an incident optical signal is proposed. The nonlinear partial differential equation consisting of optical generation and recombination is solved in one dimension using the Crank-Nicolson finite-difference scheme. The charge transfer inefficiency is the main parameter considered for the calculation 相似文献
40.
The effect of interface-roughness-related disorder on the electronic and optoelectronic properties of a quantum wire structure are studied. It is seen that the disorder causes strong localization in the quasi-one-dimensional system. While the electronic states are seriously perturbed, the density of states is not affected drastically. Optoelectronic properties as reflected in the interband transition related phenomenon are not found to suffer significant deterioration as a result of the disorder. However, the results suggest that intraband relaxation processes may be seriously affected because of electron (hole) states being localized in different regions of the wire 相似文献