全文获取类型
收费全文 | 14231篇 |
免费 | 1248篇 |
国内免费 | 1032篇 |
专业分类
化学 | 7918篇 |
晶体学 | 95篇 |
力学 | 820篇 |
综合类 | 30篇 |
数学 | 443篇 |
物理学 | 5294篇 |
无线电 | 1911篇 |
出版年
2024年 | 16篇 |
2023年 | 175篇 |
2022年 | 243篇 |
2021年 | 276篇 |
2020年 | 342篇 |
2019年 | 319篇 |
2018年 | 287篇 |
2017年 | 364篇 |
2016年 | 533篇 |
2015年 | 491篇 |
2014年 | 734篇 |
2013年 | 1136篇 |
2012年 | 846篇 |
2011年 | 946篇 |
2010年 | 758篇 |
2009年 | 944篇 |
2008年 | 931篇 |
2007年 | 1022篇 |
2006年 | 960篇 |
2005年 | 612篇 |
2004年 | 602篇 |
2003年 | 557篇 |
2002年 | 441篇 |
2001年 | 348篇 |
2000年 | 358篇 |
1999年 | 282篇 |
1998年 | 301篇 |
1997年 | 198篇 |
1996年 | 184篇 |
1995年 | 153篇 |
1994年 | 179篇 |
1993年 | 129篇 |
1992年 | 123篇 |
1991年 | 115篇 |
1990年 | 79篇 |
1989年 | 94篇 |
1988年 | 61篇 |
1987年 | 50篇 |
1986年 | 31篇 |
1985年 | 34篇 |
1984年 | 55篇 |
1983年 | 16篇 |
1982年 | 34篇 |
1981年 | 28篇 |
1980年 | 20篇 |
1979年 | 27篇 |
1978年 | 18篇 |
1977年 | 8篇 |
1976年 | 14篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
自发参量下转换光场的实验研究进展综述 总被引:1,自引:0,他引:1
自发参量下转换(spontaneous parametric down-conversion,SPDC)光场是基于单色泵浦光子流和量子真空噪声对非线性晶体的综合作用而产生的,它固有的量子起源决定了在非经典光场研究中的重要地位和作用.对SPDC光场的相干特性和它在绝对测量光电探测器量子效率中的应用进行了深入而细致的研究和探讨. 相似文献
42.
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
43.
M. Dubé C. Daneault V. Vuorinen M. Alava M. Rost 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,56(1):15-26
We investigate the structure and dynamics of the interface between
two immiscible liquids in a three-dimensional disordered porous
medium. We apply a phase-field model that includes explicitly
disorder and discuss both spontaneous and forced imbibition.
The structure of the interface is dominated by a length scale
ξ× which arises from liquid conservation. We further show
that disorder in the capillary and permeability act on different
length scales and give rise to different scalings and
structures of the interface properties. We conclude with a
range of applications. 相似文献
44.
S Uma Sankar 《Pramana》2006,67(4):655-663
In this talk I review the physics possible at India-based Neutrino Observatory (INO). I discuss the improvement in the precision
of currently known quantities and the possibility measuring the presently unknown quantities. 相似文献
45.
46.
The thermal stability and measurement temperature dependence of Schottky contact characteristics on n-GaN using a W2B5/Ti/Au metallization scheme was studied using current-voltage (I-V), scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) measurements. The elemental profile obtained from samples annealed at 350 °C showed some titanium diffusion into the gold layer but little other difference from the as-deposited wafer. Annealing at 700 °C produced significant diffusion of titanium. The Schottky barrier height increased with anneal temperature up to 200 °C, reaching a maximum value of 0.65 eV, but decreased at higher annealing temperatures. The reverse breakdown voltage from diodes fabricated using the W2B5-based contacts showed a similar dependence. The reverse current magnitude was larger than predicted by thermionic emission alone. The barrier height showed only minor changes with measurement temperature up to 150 °C. 相似文献
47.
Munshi G. Mustafa 《Pramana》2006,66(4):669-687
We briefly introduce the thermal field theory within imaginary time formalism, the hard thermal loop perturbation theory and
some of its applications to the physics of the quark-gluon plasma, possibly created in relativistic heavy-ion collisions 相似文献
48.
J.E. Lorenzo H. Requardt 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(2):185-186
Eur. Phys. J. B 24, 315 (2001) Here we comment on a recently published paper on the presence of a phason contribution in the low temperature heat capacity data of the charge-density-wave compounds K0.3MoO3 and (TaSe4)2I. We have shown that the anomaly in the C
P
/
T
3
data reported by Odin et al. is straightforwardly interpreted in terms of low energy phonon modes resulting from the peculiar topology of these compounds.
Received 21 February 2002 Published online 19 July 2002 相似文献
49.
In this paper the effects of surface roughness and annealing temperature (T) of latex coating films on adhesion are discussed for the different stages of the film formation process. The surface free energy of latex films was assessed in terms of practical work of adhesion (W) (or adherence) using a custom-built adhesion-testing device (ATD), atomic force microscopy (AFM), and contact angle measurements. For preannealed latex films surface roughness averages (Ra) were determined from AFM height images and were related to the values of W obtained from ATD measurements at room temperature. The results obtained using these tests exhibiting surface behavior on different length scales indicate a dependence of the measured adhesion on surface roughness and temperature, as well as on the length scale of the measurements.First preannealed samples were studied, which were obtained by heat treatment above the respective glass transition temperatures (Tg). Increasing the temperature of preannealing resulted in a decrease of the adherence observed in ATD experiments at room temperature. However, on the nanoscale, using AFM, no significant variation of the adherence was observed. This observation can be explained by roughness arguments. Preannealing decreases roughness which results in lower adherence values measured by ATD while for essentially single asperity AFM experiments roughness has an insignificant effect. Specimens were also annealed over a constant period of time (90 min) at different temperatures. At the end of the heat treatment, adhesion was measured at the treatment temperature by ATD. The amplified effect of temperature observed in this case on adherence is attributed to the combination of roughness decrease and increasing test temperature. In a third set of experiments completely annealed samples were studied by ATD as well as by AFM as a function of temperature. With increasing T values ATD showed a decrease in adherence, which is attributed to a decreasing surface free energy of the annealed films at elevated T values. AFM, on the other hand, showed an opposite trend which is assigned to increasing penetration of the tip into the tip/wetting polymer samples versus increasing temperature. Finally, annealing isotherms as a function of time were investigated by ATD in situ at different temperatures. This last set of experiments allowed us to optimize annealing time and temperature to achieve complete curing. 相似文献
50.
A. M. Berezhkovskii Yu. A. Makhnovskii R. A. Suris 《Journal of statistical physics》1991,65(5-6):1025-1041
We review a novel approach to treating many-body effects in diffusion-limited kinetics. The derivation of the general expression for the survival probability of a Brownian particle in the presence of randomly distributed traps is given. The reduction of this expression to both the Smoluchowski solultion and the wellknown asymptotic behavior is demonstrated. It is shown that the Smoluchowski solution gives a lower bound for the particle survival probability. The correction to the Smoluchowski solution which takes into account the particle death slowdown in the initial process stage is described. The steady-state rate-constant concentration dependence and the reflection of many-body effects in it are discussed in detail. 相似文献