全文获取类型
收费全文 | 212168篇 |
免费 | 2880篇 |
国内免费 | 877篇 |
专业分类
化学 | 96964篇 |
晶体学 | 2531篇 |
力学 | 7861篇 |
综合类 | 7篇 |
数学 | 19295篇 |
物理学 | 55294篇 |
无线电 | 33973篇 |
出版年
2021年 | 1208篇 |
2020年 | 1323篇 |
2019年 | 1301篇 |
2018年 | 1373篇 |
2017年 | 1356篇 |
2016年 | 2735篇 |
2015年 | 2185篇 |
2014年 | 2914篇 |
2013年 | 8765篇 |
2012年 | 7008篇 |
2011年 | 8836篇 |
2010年 | 5708篇 |
2009年 | 6192篇 |
2008年 | 8904篇 |
2007年 | 9287篇 |
2006年 | 9035篇 |
2005年 | 8494篇 |
2004年 | 7585篇 |
2003年 | 6759篇 |
2002年 | 6543篇 |
2001年 | 7526篇 |
2000年 | 5904篇 |
1999年 | 4724篇 |
1998年 | 3849篇 |
1997年 | 3809篇 |
1996年 | 3708篇 |
1995年 | 3328篇 |
1994年 | 3262篇 |
1993年 | 3178篇 |
1992年 | 3404篇 |
1991年 | 3366篇 |
1990年 | 3005篇 |
1989年 | 2896篇 |
1988年 | 2787篇 |
1987年 | 2367篇 |
1986年 | 2267篇 |
1985年 | 3244篇 |
1984年 | 3186篇 |
1983年 | 2603篇 |
1982年 | 2787篇 |
1981年 | 2676篇 |
1980年 | 2621篇 |
1979年 | 2488篇 |
1978年 | 2580篇 |
1977年 | 2494篇 |
1976年 | 2428篇 |
1975年 | 2397篇 |
1974年 | 2277篇 |
1973年 | 2387篇 |
1972年 | 1427篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
851.
M.C. Gonzalez-Garcia M. Maltoni 《The European Physical Journal C - Particles and Fields》2003,26(3):417-428
We study the stability of the results of the three-neutrino oscillation analysis of atmospheric and reactor neutrino data
under departures of the one dominant mass scale approximation. In order to do so we perform the analysis of atmospheric and
reactor neutrino data in terms of three-neutrino oscillations where the effect of both mass differences is explicitly considered.
We study the allowed parameter space resulting from this analysis as a function of the mass splitting hierarchy parameter which parameterizes the departure from the one dominant mass scale approximation. We consider schemes with both direct and
inverted mass ordering. Our results show that in the analysis of the atmospheric data the derived range of the largest mass
splitting, , is stable, while the allowed ranges of mixing angles and are wider than those obtained in the one dominant mass scale approximation. Inclusion of the CHOOZ reactor data in the analysis
results in the reduction of the parameter space in particular for the mixing angles. As a consequence the final allowed ranges
of the parameters from the combined analysis are only slightly broader than when obtained in the one dominant mass scale approximation.
Received: 31 May 2002 / Revised version: 10 July 2002 / Published online: 31 October 2002 相似文献
852.
S. P. Ashburn M. C. Öztürk J. J. Wortman G. Harris J. Honeycutt D. M. Maher 《Journal of Electronic Materials》1992,21(1):81-86
Titanium and cobalt germanides have been formed on Si (100) substrates using rapid thermal processing. Germanium was deposited
by rapid thermal chemical vapor deposition prior to metal evaporation. Solid phase reactions were then performed using rapid
thermal annealing in either Ar or N2 ambients. Germanide formation has been found to occur in a manner similar to the formation of corresponding silicides. The
sheet resistance was found to be dependent on annealing ambient (Ar or N2) for titanium germanide formation, but not for cobalt germanide formation. The resistivities of titanium and cobalt germanides
were found to be 20 μΩ-cm and 35.3μΩ-cm, corresponding to TiGe2 and Co2Ge, respectively. During solid phase reactions of Ti with Ge, we have found that the Ti6Ge5 phase forms prior to TiGe2. The TiGe2 phase was found to form approximately at 800° C. Cobalt germanide formation was found to occur at relatively low temperatures
(425° C); however, the stability of the material is poor at elevated temperatures. 相似文献
853.
854.
855.
Ginsburg K.S. Lin J.C. O''Neill W.D. 《IEEE transactions on bio-medical engineering》1992,39(10):1011-1021
Excitable tissues have been reported to respond to weak microwave (MW) fields, possibly by nonlinear perturbation of a cellular process such as ion conduction across membranes. We sought effects of MW (continuous wave, 2.45 GHz, specific absorption rates 12.5 or 125 mW/g) on input resistances and action potential (AP) intervals of neurons in ganglia of snails (Helix aspersa), at 20.9 +/- 0.1 degrees C. At 12.5 mW/g, input resistance did not change during irradiation, but increased (p < 0.05) afterward. At 125 mW/g, input resistance during irradiation was lower than in unirradiated controls. Serial correlograms changed marginally more frequently in MW experiments than in controls, but the changes had no consistent pattern. The AP firing rate was affected by MW, but the direction was not consistent across cells. When AP generation was modeled as being due to a neuronal input current, MW did not affect its mean, standard deviation, or autocorrelation. Unlike MW, temperature changes caused neurons to respond robustly and reversibly. Threshold for changing input resistance was 0.63 degree C. The data suggest that MW may enhance degenerative effects such as metabolic rundown or loss of ion channel patency, but do not indicate a specific mechanism for MW interaction with neurons. 相似文献
856.
Emrys A. Jones Nicholas P. Lockyer John C. Vickerman 《International journal of mass spectrometry》2007,260(2-3):146
Recent developments in desorption/ionisation mass spectrometry techniques have made their application to biological analysis a realistic and successful proposition. Developments in primary ion source technology, mainly through the advent of polyatomic ion beams, have meant that the technique of secondary ion mass spectrometry (SIMS) can now access the depths of information required to allow biological imaging to be a viable option.Here the role of the primary ion C60+ is assessed with regard to molecular imaging of lipids and pharmaceuticals within tissue sections. High secondary ion yields and low surface damage accumulation are demonstrated on both model and real biological samples, indicating the high secondary ion efficiency afforded to the analyst by this primary ion when compared to other cluster ion beams used in imaging. The newly developed 40 keV C60+ ion source allows the beam to be focused such that high resolution imaging is demonstrated on a tissue sample, and the greater yields allow the molecular signal from the drug raclopride to be imaged within tissue section following in vivo dosing.The localisation shown for this drug alludes to issues regarding the chemical environment affecting the ionisation probability of the molecule; the importance of this effect is demonstrated with model systems and the possibility of using laser post-ionisation as a method for reducing this consequence of bio-sample complexity is demonstrated and discussed. 相似文献
857.
858.
859.
860.