全文获取类型
收费全文 | 1928篇 |
免费 | 151篇 |
国内免费 | 172篇 |
专业分类
化学 | 1380篇 |
晶体学 | 33篇 |
力学 | 81篇 |
综合类 | 1篇 |
数学 | 44篇 |
物理学 | 712篇 |
出版年
2024年 | 1篇 |
2023年 | 32篇 |
2022年 | 32篇 |
2021年 | 34篇 |
2020年 | 36篇 |
2019年 | 40篇 |
2018年 | 31篇 |
2017年 | 31篇 |
2016年 | 44篇 |
2015年 | 72篇 |
2014年 | 77篇 |
2013年 | 158篇 |
2012年 | 153篇 |
2011年 | 159篇 |
2010年 | 182篇 |
2009年 | 221篇 |
2008年 | 183篇 |
2007年 | 152篇 |
2006年 | 162篇 |
2005年 | 95篇 |
2004年 | 66篇 |
2003年 | 57篇 |
2002年 | 37篇 |
2001年 | 37篇 |
2000年 | 17篇 |
1999年 | 17篇 |
1998年 | 18篇 |
1997年 | 6篇 |
1996年 | 6篇 |
1995年 | 7篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 7篇 |
1989年 | 4篇 |
1988年 | 44篇 |
1987年 | 21篇 |
排序方式: 共有2251条查询结果,搜索用时 437 毫秒
911.
Lian Chun Zou Tong Fei Zhu Shu Cai Gan Da Cheng Wang Yu Zhang Xu Ming Deng 《中国化学快报》2008,19(10):1224-1227
From the roots ofPicrorhiza scrophulariiflora, two new secoifidoid glycosides, named picrosecosides Ⅰ and Ⅱ (1, 2) have been isolated. Their structures were elucidated on the basis of chemical and spectropic evidences. 相似文献
912.
The substituted phenanthrene-9-carboxyaldehydes are very important intermediates for the syntheses of phenanthroindolizidine and phenanthroquinolizidine alkaloids. The novel title compound was prepared from the reaction of 5 steps starting from the condensation of 3-methoxyl-4-methyl-phenylacetic acid and 4-(benzyloxy)-2-iodobenzaldehyde, followed by esterification, cyclization, reduction, and oxidation. A new method for the preparation of phenanthrene ring via palladium-catalyzed intramolecular Heck reaction was described. The title compound was characterized by IR, ^1H NMR, ^13C NMR, elemental analysis, and MS. 相似文献
913.
Y. Wang L. Y. Duan G. Q. Wang M. S. Shan Y. C. Liu J. Y. Shi Y. Lan 《Russian Journal of Coordination Chemistry》2008,34(9):683-687
A novel chiral 2-D layer coordination polymer [Co(Pydc)(H2O)2] · H2O (Pydc = Pyridine-2,5-dicarboxylate) was hydrothermally synthesized and characterized by elemental analysis, IR spectra and
TG analysis. Single-crystal X-ray diffraction shows that Co(1) was connected by the oxygen atom and nitrogen atom of different
carboxyls and form a helical-shaped {O(3)-Co-N}
n
chain along 21 helical axes. The adjacent 1-D {O(3)-Co-N}
n
helical-shaped chains are developing along 21 helical axes with the same direction and are connected by O(4) to form an ordered 2-D layer. All the molecules exist in the
same optical activity that imparts the chiral nature to the whole compound.
The text was submitted by the authors in English. 相似文献
914.
The magnetocaloric effect in the MnFeP0.35As0.65−xSix intermetallic compounds, prepared via solid-state sintering was studied. Adiabatic temperature and magnetic entropy changes were obtained in order to characterize these compounds. The substitution of silicon for arsenic leads to a significant enhancement of the magnetocaloric effect for silicon amount x = 0.11. The adiabatic temperature change increased from 2.3 to 3.3 K for the magnetic field change from 0 to 1.7 T. This improvement has been correlated with the increase of crystalline cell volume and change of lattice constants. Additionally, the structure of pure MnFeP0.33As0.67 has been modeled in order to check the spin alignment within the framework of ferromagnetic collinear model. 相似文献
915.
916.
Tongchao Liu Huanming Ren Cong Li Guohua Chen Maosheng Cheng Dongmei Zhao Jingkang Shen Jia Li Yubo Zhou Bing Xiong Yue-Lei Chen 《Tetrahedron letters》2018,59(4):415-417
From adenosine and 2′-C-Me adenosine, a 3-step route towards nucleoside DOT1L inhibitors, including pinometostat, EPZ5677, and FED1, was established. With useful structural-activity relationship information, the newly prepared 2′-C-Me adenosine derivatives contribute to the limited repertoire of ribose-modified nucleoside DOT1L inhibitors. In general, this new synthetic method will facilitate not only the study of nucleoside DOT1L inhibitors, but also the synthetic and medicinal chemistry research of 5′-deoxy-5′-amino adenosine derivatives. 相似文献
917.
《Particuology》2015
Widely used bioaerosol generators like Collison nebulizer probably produce electrostatically charged particles, but the electrical charges carried by laboratory-generated airborne microorganisms using bubbling aerosolizers are poorly understood. In this study, we measured the fraction of neutral particles and number of elementary charges per particle as a function of the aerodynamic diameter of airborne bacteria (Escherichia coli and Enterococcus hirae). Bioaerosols were produced by a liquid sparging aerosolizer-type bubbling generator, with particle sizes ranging from roughly 0.6 to 2 μm. The experimental setup included an electrostatic precipitator and real-time devices including an electrometer, aerodynamic particle sizer, and electrical low-pressure impactor. Experimental results obtained for various operating conditions showed that aerosols produced with a higher bubbling airflow contained a larger proportion of neutral particles (from around 30% to 50%) and that bacteria carried a greater average absolute number of elementary charges (from around –10 to –60 elementary units) than those under lower airflow. Under the investigated conditions, a neutralization step is unnecessary because it may have a negative effect on the viability of sensitive microorganisms. Our results suggest that the neutral fraction can be used downstream of an electrostatic precipitator, and that this setup may have advantages over bipolar neutralizers. 相似文献
918.
Liuyuan Chen Yinghui Duan Chang Li Yu Wang Xupeng Tong Yi Dai Xinsheng Yao 《Magnetic resonance in chemistry : MRC》2013,51(12):842-846
Four new prenylated flavonoids, cudraflavanones E‐F (1–2) and cudraflavones F‐G (6–7), together with eight known compounds were isolated from the roots of Cudrania tricuspidata. The structures of new compounds were elucidated on the basis of extensive spectroscopic analyses, including 1D and 2D NMR, HRESIMS and CD. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
919.
A series of thiourea derivatives have been synthesized. Their structures were confirmed by MS and 1H NMR. Several compounds showed potent activities as antagonists of CCR4 receptor. 相似文献
920.
Rong Lu Jin SunYongjun Wang Haiyan LiJianfang Liu Liang FangZhonggui He 《Journal of chromatography. A》2009,1216(27):5190-5198
The linear solvation energy relationship (LSER) was applied to characterize biopartitioning micellar chromatography (BMC) system using monolithic column, and was utilized to compare the above system with other physicochemical and biological processes in this study. The solute volume and HB basicity had the maximum influence on the retention of the solutes, and an increase in the dipolarity/polarizability, HB basicity, HB acidity or excess molar refraction of the solutes decreased the retention. Principal component analysis of LSER coefficients showed that the system had certain similarity to drug biomembrane transport processes, such as blood–brain barrier penetration, transdermal and oral absorption. The quantitative retention–activity relationship (QRAR) of drug penetration across blood–brain barrier was established and its predictive capability for this biological process was evaluated. With the aid of the high flow rate, the monolithic column significantly facilitated the high-throughput analysis of large compounds’ bank without changing the mechanism of the retention in BMC and without impairing good predictive capability of the biological processes. Accordingly, the BMC system, together with monolithic column, allows for high-throughput profiling the biological processes, such as blood–brain barrier penetration. 相似文献