全文获取类型
收费全文 | 1719篇 |
免费 | 91篇 |
国内免费 | 278篇 |
专业分类
化学 | 1475篇 |
晶体学 | 2篇 |
力学 | 76篇 |
综合类 | 15篇 |
数学 | 37篇 |
物理学 | 483篇 |
出版年
2024年 | 5篇 |
2023年 | 10篇 |
2022年 | 30篇 |
2021年 | 34篇 |
2020年 | 47篇 |
2019年 | 48篇 |
2018年 | 41篇 |
2017年 | 44篇 |
2016年 | 48篇 |
2015年 | 60篇 |
2014年 | 83篇 |
2013年 | 219篇 |
2012年 | 63篇 |
2011年 | 108篇 |
2010年 | 76篇 |
2009年 | 80篇 |
2008年 | 95篇 |
2007年 | 127篇 |
2006年 | 94篇 |
2005年 | 84篇 |
2004年 | 87篇 |
2003年 | 93篇 |
2002年 | 82篇 |
2001年 | 66篇 |
2000年 | 57篇 |
1999年 | 49篇 |
1998年 | 44篇 |
1997年 | 37篇 |
1996年 | 26篇 |
1995年 | 21篇 |
1994年 | 27篇 |
1993年 | 25篇 |
1992年 | 19篇 |
1991年 | 10篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 3篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1970年 | 2篇 |
排序方式: 共有2088条查询结果,搜索用时 15 毫秒
31.
32.
Qingmin Wang Runqiu Huang 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):173-179
Abstract 1-Oxo-4-chlorocarbony1-1-phospha-2,6,7-trioxabicyclo[2.2.2]octane (5) was obtained from phosphorus oxychloride. Benzyl chloroformate was synthesized by the reaction of benzyl alcohol and triphosgene in good yield for the first time. N-r-Butyl-N-benzoylhydrazine(II) was prepared in a new and convenivent procedure with good yield. The reaction of 5 and II proceeded smoothly in the presence of sodium carbonate and afforded the desired compound 13 in good yield, while in the presence of triethylamine, the elimination of butyl was observed and afforded the compound 12. 相似文献
33.
The Knoevenagel condensation of Meldrum's acid with aromatic aldehydes proceeded efficiently in a reusable ionic liquid, ethylammonium nitrate, at room temperature in the absence of any catalyst with high yields. 相似文献
34.
Nora M. Rateb 《合成通讯》2013,43(15):2789-2794
An improved Claisen–Schmidt condensation reaction of methyl ketones and aromatic aldehydes can be achieved by grinding at room temperature in the absence of solvents. This process is simple, efficient, economical, and environmentally benign compared to classical reactions. 相似文献
35.
36.
A convenient three‐step route toward a functionalized pyrrole building block for novel anti‐inflammatory agents is reported. In contrast to previous strategies, the present approach focuses on inexpensive starting materials and application on a multigram scale. A high degree of functional diversity is demonstrated in various derivatives, and the scope and limitations of this route are discussed. Complementary to the described tetrasubstituted pyrroles, a novel ring‐closure protocol based on the Feist–Benary condensation affords trisubstituted analogues. 相似文献
37.
In current paper we study the so-called “complete condensation” of zero range process on the fitness network. It is found that under the high temperature limit, the condensation behavior on the fitness model converges to that of the scale-free network, as expected. However, at some temperatures below the critical temprature of Bose- Einstein condensate phase on the fitness network, the complete condensation occurs as well for some values of δ> δc, which is impossible on scale-free network according to the criterion. 相似文献
38.
In the framework of relativistic mean field theory, the condensations of K- and \bar{K}0 in neutron star matter including baryon octet and Δ quartet are studied. We find that in this case K- and \bar{K}0 condensations canoccur at relative shallow optical potential depth of \bar{K} from -80 MeV to -160 MeV. Both K- and \bar{K}0 condensations favor the appearances of Δ resonances. With \bar{K} condensations all the Δ quartet can appear well inside the maximum mass stars. The appearances of Δ resonances change the composition and distribution of particles at high densities. The populations ofΔ resonances can enhance K- condensation. It is found that in the core of massive neutron stars, neutron star matter includes rich particle species, such as antikaons, baryon octet, and Δ quartet. In the presence of Δ resonances and \bar{K} condensation, the EOS becomes softer and results in smaller maximum mass stars. Furthermore the impact of antikaon condensations,hyperons, and Δ resonances on direct Urca process with nucleons is also discussed briefly. 相似文献
39.
The Superstable Weakly Imperfect Bose-Gas (Sup-WIBG) was originally proposed to solve some inconsistencies of the Bogoliubov theory based on the WIBG. The grand-canonical
thermodynamics of the Sup-WIBG has been recently studied in details but only out of the point of the (first order) phase transition.
The present paper closes this gap. The key technical tools are the Large Deviations (LD) formalism and in particular the analysis
of the Kac distribution function. It turns out that the condensate fraction discontinuity as a function of the chemical potential
(that occurs at the phase transition point) disappears if one considers it as a function of the total particle density. We
prove that at this point the equilibrium state of the Sup-WIBG is a mixture of two (low- and high-density) pure phases related
to two critical particle densities. Non-zero Bose-Einstein condensate starts at the smaller critical density and continuously
grows (for a constant chemical potential) until the second critical density. For higher particle densities, the Bose condensate
fraction as well as the chemical potential both increase monotonously. 相似文献
40.
LIUGuang-Zhou LIUWei ZHAOEn-Guang 《理论物理通讯》2004,42(1):99-102
In this paper a new phase structure of neutron star matter including nucleons and delta isobars is presented. Particle fractions populated and pion condensations in neutron star matter are investigated in this model. The existence of the pion condensations can postpone the appearance of delta isobars. We found that both the pion condensation and reduce of the ratio of delta isobar to nucleons couplings can soften the corresponding equation of state. The maximum masses and their corresponding radii of neutron stars are calculated, and the obtained values are in observational region. 相似文献