全文获取类型
收费全文 | 9925篇 |
免费 | 1390篇 |
国内免费 | 1116篇 |
专业分类
化学 | 7227篇 |
晶体学 | 118篇 |
力学 | 546篇 |
综合类 | 119篇 |
数学 | 1323篇 |
物理学 | 3098篇 |
出版年
2024年 | 17篇 |
2023年 | 180篇 |
2022年 | 265篇 |
2021年 | 315篇 |
2020年 | 376篇 |
2019年 | 349篇 |
2018年 | 280篇 |
2017年 | 302篇 |
2016年 | 471篇 |
2015年 | 432篇 |
2014年 | 589篇 |
2013年 | 765篇 |
2012年 | 908篇 |
2011年 | 912篇 |
2010年 | 637篇 |
2009年 | 575篇 |
2008年 | 639篇 |
2007年 | 546篇 |
2006年 | 476篇 |
2005年 | 393篇 |
2004年 | 377篇 |
2003年 | 336篇 |
2002年 | 360篇 |
2001年 | 284篇 |
2000年 | 180篇 |
1999年 | 227篇 |
1998年 | 147篇 |
1997年 | 122篇 |
1996年 | 137篇 |
1995年 | 102篇 |
1994年 | 105篇 |
1993年 | 94篇 |
1992年 | 76篇 |
1991年 | 80篇 |
1990年 | 47篇 |
1989年 | 53篇 |
1988年 | 32篇 |
1987年 | 31篇 |
1986年 | 33篇 |
1985年 | 31篇 |
1984年 | 13篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1963年 | 7篇 |
1959年 | 12篇 |
1958年 | 11篇 |
1957年 | 15篇 |
1956年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
991.
Rapid-resolution liquid chromatography coupled with electrospray ion trap multistage mass spectrometry (ESI-MS n ) and electrospray quadrupole-time-of-flight mass spectrometry (ESI-Q-TOF) has been utilized to separate and characterize the phenolic components in Erigeron injections. After extensive separation on the column, each peaks’ potential structures were obtained based on their accurate mass supplied by ESI-Q-TOF and chemical database retrieval, and confirmed by ESI-MS n . A total of 44 compounds were identified or tentatively characterized and fifteen of them reported for the first time. In addition, the developed method was applied to monitor the elimination of phenolic compounds in rats after intravenous administration of 4 mL kg?1 Erigeron injection. The caffeoylquinic acids and flavonoids of the Erigeron injection were quickly degraded and most of them reached the low limit of detection (SNR < 3) at 2 h post-injection. 相似文献
992.
Mario Barbatti Jiří Pittner Marek Pederzoli Ute Werner Roland Mitrić Vlasta Bonačić-Koutecký Hans Lischka 《Chemical physics》2010
Non-adiabatic dynamics simulations were performed for pyrrole at time-dependent density functional theory level using the trajectory surface hopping approach. Initial conditions were prepared based on the UV-absorption spectrum so as to simulate monochromatic absorption in three distinct spectral regions. The results showed predominance of the NH-stretch mechanism for excited-state relaxation. With increasing initial energy, however, other mechanisms are activated as well, even though they still occurred for a minor fraction of the trajectories. Dynamics starting at the origin of the absorption spectrum exhibited internal conversion to the ground state with a time constant of 20 fs. In contrast, dynamics starting at higher energies gave rise to much longer time constants for internal conversion near 200 fs. 相似文献
993.
Hyeong Jin Yun Hyunjoo Lee Ji Bong Joo Nam Dong Kim Jongheop Yi 《Electrochemistry communications》2010,12(6):769-772
We describe a method tuning the band-gap energy (Eg) of visible light sensitive TiO2-xCx nanoparticle. Eg tends to become smaller with the increase in the amount of carbon dopant in TiO2-xCx nanoparticle due to the increase in excess electrons. Photo-catalytic oxidative activity, however, did not depend on only the value of Eg, but also the energy level of valence band. TiO1.96C0.04 nanoparticle having Eg of 2.6 eV showed outstanding performance in oxidative decomposition of phenol under the irradiation of visible light. 相似文献
994.
Hari Ji Singh Bhupesh Kumar Mishra Nand Kishor Gour 《Theoretical chemistry accounts》2010,125(1-2):57-64
The unimolecular decomposition reaction of CF3CCl2O radical has been investigated using theoretical methods. Two most important channels of decomposition occurring via C–C bond scission and Cl elimination have been considered during the present investigation. Ab initio quantum mechanical calculations are performed to get optimized structure and vibrational frequencies at DFT and MP2 levels of theory. Energetics are further refined by the application of a modified Gaussian-2 method, G2M(CC,MP2). The thermal rate constants for the decomposition reactions involved are evaluated using Canonical Transition State Theory (CTST) utilizing the ab initio data. Rate constants for C–C bond scission and Cl elimination are found to be 6.7 × 106 and 1.1 × 108 s?1, respectively, at 298 K and 1 atm pressure with an energy barrier of 8.6 and 6.5 kcal/mol, respectively. These values suggest that Cl elimination is the dominant process during the decomposition of the CF3CCl2O radical. Transition states are searched on the potential energy surface of the decomposition reactions involved and are characterized by the existence of only one imaginary frequency (NIMAG = 1) during frequency calculation. The existence of transition states on the corresponding potential energy surface is further ascertained by performing intrinsic reaction coordinate (IRC) calculation. 相似文献
995.
996.
Xiao‐Chi Ma Xiulan Xin Bao‐jing Zhang Sha Deng Ji‐hong Yao Chang‐yuan Wang Jian Cui Yan Tian Ke‐xin Liu 《Journal of separation science》2010,33(15):2272-2277
An efficient separation method of using high‐speed counter‐current chromatography was successfully established to directly purify cytotoxic transformed products of cinobufagin by Cordyceps militaris. The two‐phase solvent system composed of n‐hexane–ethyl acetate–methanol–water (4:6:3:4, v/v) was used in high‐speed counter‐current chromatography. A total of 9 mg of 4β,12α‐dihydroxyl‐cinobufagin ( 1 ), 15 mg of 12β‐hydroxyl‐cinobufagin ( 2 ), 8 mg of 5β‐hydroxyl‐cinobufagin ( 3 ), 12 mg of deacetylcinobufagin ( 4 ) and 6 mg of 3‐keto‐cinobufagin ( 5 ) were obtained in a one‐step separation from 400 mg of the crude extract with purity of 98.7, 97.2, 90.6, 99.1 and 99.4%, respectively, as determined by HPLC. Their chemical structures were identified on the basis of 1H‐NMR and 13C‐NMR technology. All products ( 1 – 5 ) showed the potent activities against human carcinoma cervicis (Hela) and malignant melanoma (A375) cells in vitro. 相似文献
997.
Jakub Plášil Elena Buixaderas Jiří Čejka Jiří Sejkora Jan Jehlička Milan Novák 《Analytical and bioanalytical chemistry》2010,397(7):2703-2715
The uranyl sulphate mineral zippeite was studied by Raman spectroscopy. The phase purity of the sample was initially checked
by X-ray powder diffraction and its chemical composition was defined by electron microprobe (wavelength dispersive spectroscopy,
WDS) analysis. The Raman spectroscopy research focused on the low wavenumber and uranyl stretching vibration regions. Vibration
bands down to 50 cm–1 were tentatively assigned. The U–O bond lengths were calculated based on empirical relations. Inferred values are consistent
with those obtained from the crystal structure analysis of synthetic zippeite. Number of bands was interpreted on the basis
of factor group analysis. 相似文献
998.
Sonia Herranz Markéta Bocková María Dolores Marazuela Ji?í Homola María Cruz Moreno-Bondi 《Analytical and bioanalytical chemistry》2010,398(6):2625-2634
A surface plasmon resonance (SPR) biosensor for the detection of microcystins (MCs) in drinking water has been developed.
Several assay formats have been evaluated. The selected format is based on a competitive inhibition assay, in which microcystin-LR
(MCLR) has been covalently immobilized onto the surface of an SPR chip functionalized with a self-assembled monolayer. The
influence of several factors affecting sensor performance, such as the nature and concentration of the antibody, the composition
of the carrier buffer, and the blocking and regeneration solutions, has been evaluated. The optimized SPR biosensor provides
an IC50 0.67 ± 0.09 μg L−1, a detection limit of 73 ± 8 ng L−1, and a dynamic range from 0.2 to 2.0 μg L−1 for MCLR. Cross-reactivity to other related MCs, such as microcystin-RR (88%) and microcystin-YR (94%), has also been measured.
The SPR biosensor can perform four simultaneous determinations in 60 min, and each SPR chip can be reused for at least 40
assay–regeneration cycles without significant binding capacity loss. The biosensor has been successfully applied to the direct
analysis of MCLR in drinking water samples, below the provisional guideline value of 1 μg L−1 established by the World Health Organization for drinking water. 相似文献
999.
HUANG Yu LIU JunLiang ZHANG Ji LIU Qiang HOU JiTing ZHANG Yu ZHANG DaWei LU QiaoSen CHEN ShanYong LIN HongHui & YU XiaoQi Key Laboratory of Green Chemistry Technology Ministry of Education College of Chemistry Sichuan University Chengdu China Key Laboratory of Bio-resources Eco-environment College of Life Sciences China. 《中国科学:化学》2010,(1)
A series of novel molecules with a cyclen(1,4,7,10-tetraazacyclododecane) moiety appended on and bearing different aromatic fragments in the structures were synthesized and characterized.The binding activities of these compounds towards DNA were systematically studied by spectroscopic,viscometric and gel electrophoresis methods.The results suggest that the stacking interaction plays an important role in improving the DNA binding ability of the compounds.The binding modes of the compounds towards DNA are als... 相似文献
1000.
Yue Zhu Min Pu De-Cai Fang Yong-Qiang Ji Jing He David G. Evans 《Structural chemistry》2010,21(4):817-825