全文获取类型
收费全文 | 219722篇 |
免费 | 5152篇 |
国内免费 | 3527篇 |
专业分类
化学 | 115231篇 |
晶体学 | 2940篇 |
力学 | 10107篇 |
综合类 | 296篇 |
数学 | 24461篇 |
物理学 | 75366篇 |
出版年
2021年 | 2172篇 |
2020年 | 2547篇 |
2019年 | 2769篇 |
2018年 | 3341篇 |
2017年 | 3193篇 |
2016年 | 4668篇 |
2015年 | 3261篇 |
2014年 | 4619篇 |
2013年 | 10488篇 |
2012年 | 8771篇 |
2011年 | 10375篇 |
2010年 | 7218篇 |
2009年 | 7111篇 |
2008年 | 9208篇 |
2007年 | 9193篇 |
2006年 | 8817篇 |
2005年 | 7895篇 |
2004年 | 7236篇 |
2003年 | 6337篇 |
2002年 | 6207篇 |
2001年 | 6975篇 |
2000年 | 5442篇 |
1999年 | 4199篇 |
1998年 | 3288篇 |
1997年 | 3098篇 |
1996年 | 2798篇 |
1995年 | 2746篇 |
1994年 | 2581篇 |
1993年 | 2408篇 |
1992年 | 2725篇 |
1991年 | 2668篇 |
1990年 | 2604篇 |
1989年 | 2382篇 |
1988年 | 2434篇 |
1987年 | 2433篇 |
1986年 | 2262篇 |
1985年 | 2953篇 |
1984年 | 3200篇 |
1983年 | 2601篇 |
1982年 | 2769篇 |
1981年 | 2731篇 |
1980年 | 2603篇 |
1979年 | 2701篇 |
1978年 | 2789篇 |
1977年 | 2806篇 |
1976年 | 2864篇 |
1975年 | 2653篇 |
1974年 | 2628篇 |
1973年 | 2762篇 |
1972年 | 1745篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Inas A. Abdallah Sherin F. Hammad Alaa Bedair Mohamed A. Abdelaziz Neil D. Danielson Ahmed H. Elshafeey Fotouh R. Mansour 《Biomedical chromatography : BMC》2022,36(6):e5365
Favipiravir is a potential antiviral medication that has been recently licensed for Covid-19 treatment. In this work, a gadolinium-based magnetic ionic liquid was prepared and used as an extractant in dispersive liquid–liquid microextraction (DLLME) of favipiravir in human plasma. The high enriching ability of DLLME allowed the determination of favipiravir in real samples using HPLC/UV with sufficient sensitivity. The effects of several variables on extraction efficiency were investigated, including type of extractant, amount of extractant, type of disperser and disperser volume. The maximum enrichment was attained using 50 mg of the Gd-magnetic ionic liquid (MIL) and 150 μl of tetrahydrofuran. The Gd-based MIL could form a supramolecular assembly in the presence of tetrahydrofuran, which enhanced the extraction efficiency of favipiravir. The developed method was validated according to US Food and Drug Administration bioanalytical method validation guidelines. The coefficient of determination was 0.9999, for a linear concentration range of 25 to 1.0 × 105 ng/ml. The percentage recovery (accuracy) varied from 99.83 to 104.2%, with RSD values (precision) ranging from 4.07 to 11.84%. The total extraction time was about 12 min and the HPLC analysis time was 5 min. The method was simple, selective and sensitive for the determination of favipiravir in real human plasma. 相似文献
2.
Rastsvetaeva R. K. Chukanov N. V. Pekov I. V. Varlamov D. A. Kazheva O. N. 《Crystallography Reports》2022,67(2):166-171
Crystallography Reports - The crystal structure and crystallochemical features of a Fe-deficient zirconium-rich analog of eudialyte from the Lovozero alkaline massif (Kola peninsula) have been... 相似文献
3.
Qianqian Fan Zirui Liu Feng Qiu Prof. Yong Mao Prof. Qingju Liu Prof. Longzhou Zhang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(63):e202202700
The artificially accurate design of nonmetal electrocatalysts’ active site has been a huge challenge because no pure active species with the specific structure could be strictly controlled by traditional synthetic methods. Species with a multiconfiguration in the catalyst hinder identification of the active site and the subsequent comprehension of the reaction mechanism. We have developed a novel electro-assisted molecular assembly strategy to obtain a pure pentagon ring on perfect graphene avoiding other reconstructed structures. More importantly, the active atom was confirmed by the subtle passivation process as the topmost carbon atom. Recognition of the carbon-defect electrocatalysis reaction mechanism was first downsized to the single-atom scale from the experimental perspective. It is expected that this innovative electro-assisted molecular assembly strategy could be extensively applied in the active structure-controlled synthesis of nonmetal electrocatalysts and verification of the exact active atom. 相似文献
4.
Gaineev A. M. Galkina I. V. Davletshin R. R. Davletshina N. V. Kuznetsov N. O. Grishaev D. Yu. Shulayeva M. P. Pozdeev O. K. 《Russian Journal of General Chemistry》2022,92(7):1208-1213
Russian Journal of General Chemistry - Aminophosphabetaines, i.e., isobutyl {[alkyl(dimethyl)ammonio]methyl}phosphonates with higher alkyl substituents at the nitrogen atom, were obtained by a... 相似文献
5.
6.
7.
Filatova S. M. Guseva M. K. Bodrova T. G. Parshina D. V. Budanova U. A. Sebyakin Yu. L. 《Russian Journal of General Chemistry》2022,91(1):S13-S23
Russian Journal of General Chemistry - The review article traces the main trends of the synthetic approach to the solution of the problem of overcoming the resistance of pathogenic bacterial... 相似文献
8.
Varfolomeev S. D. Panin A. A. Semenova N. A. Ublinskiy M. V. Akhadov T. A. Bykov V. I. Tsybenova S. B. 《Russian Chemical Bulletin》2022,71(3):591-594
A kinetic study of the effect of thermoheliox (inhalation of a helium and oxygen mixture, 70 °C) on the functional hemodynamics of the human brain by functional magnetic resonance imaging was carried out. The dynamic responses of the BOLD signal were found to be biphasic. An empirical equation describing the first phase of the hemodynamic response to visual stimulus was proposed. It was shown that preliminary inhalation of thermoheliox stimulates the hemodynamic responses by slowing down the vasoconstriction.
相似文献9.
为提高煤与瓦斯突出矿井瓦斯抽放效果,建立了3个一级指标、14个二级指标的突出矿井瓦斯抽放限制影响因素评价指标体系,利用AHP和熵权法分别确定指标因子主、客观权重.通过实地调研分析和反馈验证了AHP-熵权法的可行性和正确性,利用加权平均法确定评价模型的综合权重.研究表明:封孔方式、钻孔半径、抽放时间、煤体裂隙发育程度和抽放负压是目前影响煤矿瓦斯抽放效果的主控因素. 相似文献
10.
Theoretical and Mathematical Physics - Dynamic systems acting on the plane and possessing the Wada property have been observed. There exist only two topological types, symmetric and antisymmetric,... 相似文献