全文获取类型
收费全文 | 14290篇 |
免费 | 1117篇 |
国内免费 | 805篇 |
专业分类
化学 | 7314篇 |
晶体学 | 295篇 |
力学 | 1139篇 |
综合类 | 67篇 |
数学 | 1537篇 |
物理学 | 5860篇 |
出版年
2024年 | 22篇 |
2023年 | 149篇 |
2022年 | 312篇 |
2021年 | 326篇 |
2020年 | 354篇 |
2019年 | 336篇 |
2018年 | 333篇 |
2017年 | 309篇 |
2016年 | 428篇 |
2015年 | 418篇 |
2014年 | 575篇 |
2013年 | 801篇 |
2012年 | 1060篇 |
2011年 | 1171篇 |
2010年 | 872篇 |
2009年 | 870篇 |
2008年 | 852篇 |
2007年 | 738篇 |
2006年 | 733篇 |
2005年 | 575篇 |
2004年 | 540篇 |
2003年 | 439篇 |
2002年 | 398篇 |
2001年 | 614篇 |
2000年 | 460篇 |
1999年 | 343篇 |
1998年 | 268篇 |
1997年 | 225篇 |
1996年 | 246篇 |
1995年 | 174篇 |
1994年 | 177篇 |
1993年 | 116篇 |
1992年 | 115篇 |
1991年 | 121篇 |
1990年 | 104篇 |
1989年 | 83篇 |
1988年 | 68篇 |
1987年 | 44篇 |
1986年 | 45篇 |
1985年 | 49篇 |
1984年 | 37篇 |
1983年 | 25篇 |
1982年 | 39篇 |
1981年 | 32篇 |
1980年 | 28篇 |
1979年 | 20篇 |
1978年 | 25篇 |
1977年 | 19篇 |
1976年 | 18篇 |
1975年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
171.
L.?S.?Roman R.?M.?Q.?Mello F.?Cunha I.?A.?HümmelgenEmail author 《Journal of Solid State Electrochemistry》2004,8(2):118-121
We report the use of sulfonated polyaniline, SPAN, as a positive charge transporting layer in organic electronic devices, demonstrating that it can be used to significantly improve injection into conjugated polymers. The introduction of an intermediate SPAN layer improves device rectification, even when low-work-function anode materials such as tin oxide are used. 相似文献
172.
A rapid, simple, and sensitive high-performance liquid chromatographic method for quantification of curcumin in dog plasma has been developed and validated. After addition of the internal standard (berberine), plasma was acidified and extracted with ethyl acetate. Analysis was performed on a C18 column. The mobile phase was acetonitrile–5% acetic acid, 52:48 (v/v) and the flow rate 1.0 mL min?1. The eluent was monitored at 425 nm. Chromatographic separation was achieved in less than 7 min and the calibration plot was linear over the concentration range 2–128 ng mL?1. Intra- and inter-assay variability were less than 7.3%. The accuracy ranged from 98.7 to 105.0%. The method was successfully applied to a pharmacokinetic study of curcumin in dogs. 相似文献
173.
174.
175.
Treatment of steroidal tertiary alcohols or olefins with N3H/BF3—éthérate/benzene gave 5-azido, 13-azido and 14-azido steroids. Reaction mechanism has been discussed. Chemical degradation and 13C NMR study confirmed structural assignments. 相似文献
176.
Bivas Mondal Rakesh Maiti Xing Yang Jun Xu Weiyi Tian Jia-Lei Yan Xiangyang Li Yonggui Robin Chi 《Chemical science》2021,12(25):8778
4,5-Dihydropyridazinones bearing an aryl substituent at the C6-position are important motifs in drug molecules. Herein, we developed an efficient protocol to access aryl-dihydropyridazinone molecules via carbene-catalyzed asymmetric annulation between dinucleophilic arylidene hydrazones and bromoenals. Key steps in this reaction include polarity-inversion of aryl aldehyde-derived hydrazones followed by chemo-selective reaction with enal-derived α,β-unsaturated acyl azolium intermediates. The aryl-dihydropyridazinone products accessed by our protocol can be readily transformed into drugs and bioactive molecules.Polarity inversion of arylidene hydrazones to react with bromoenals via carbene organic catalysis is disclosed. The reaction enantioselectively affords 6-aryl-4,5-dihydropyridazinones and related drugs with proven commercial applications. 相似文献
177.
Quantitative structure-activity/property relationships (QSAR/QSPR) studies have been exploited extensively in the designs of drugs and pesticides, but few such studies have been applied to the design of colour reagents. In this work, the topological indices A(x1) - A(x3) suggested in this laboratory were applied to multivariate analysis in structure-property studies. The topological indices of 43 phosphone bisazo derivatives of chromotropic acid were calculated. The structure-property relationships between colour reagents and their colour reactions with cerium were studied using A (x1 a (x)3) indices with satisfactory results. The purpose of this work was to establish whether QSAR can be used to predict the contrasts of colour reactions and in the longer term to be a helpful tool in colour reagent design. 相似文献
178.
Zhen-Qiang Yu Xiaodong Li Wei Wan Xin-Shun Li Kuo Fu Yue Wu Alexander D. Q. Li 《Chemical science》2021,12(9):3146
Balancing the rigidity of a π-conjugated structure for strong emission and the flexibility of liquid crystals for self-assembly is the key to realizing highly emissive liquid crystals (HELCs). Here we show that (1) integrating organization-induced emission into dual molecular cooperatively-assembled liquid crystals, (2) amplifying mesogens, and (3) elongating the spacer linking the emitter and the mesogen create advanced materials with desired thermal–optical properties. Impressively, assembling the fluorescent acceptor Nile red into its host donor designed according to the aforementioned strategies results in a temperature-controlled Förster resonance energy transfer (FRET) system. Indeed, FRET exhibits strong S-curve dependence as temperature sweeps through the liquid crystal phase transformation. Such thermochromic materials, suitable for dynamic thermo-optical sensing and modulation, are anticipated to unlock new and smart approaches for controlling and directing light in stimuli-responsive devices.A temperature-sensitive Förster resonance energy transfer system was constructed using a highly emissive liquid crystal co-assembled with Nile red, enabling thermo-optical modulation for controlling and directing light in stimuli-responsive devices. 相似文献
179.
Y Masuo H Wang D Pélaprat Z Q Chi W Rostène 《Chemical & pharmaceutical bulletin》1992,40(9):2520-2524
We have recently demonstrated that [3H]ohmefentanyl, a non-peptidergic opioid ligand which was suggested to cross the blood brain barrier in contrast to other peptidergic opioid ligands, bound not only to mu opioid receptor sites but also to sigma sites. In order to examine whether [3H]ohmefentanyl can be used as a marker for mu sites, we investigated the effects of brain lesions on [3H]ohmefentanyl binding site densities, as compared with [3H][D-Ala2, MePhe4, Gly-ol5]enkephalin ([3H]DAGO), a selective mu ligand. These binding site densities were measured by quantitative autoradiography in the rat striatum and substantia nigra, two brain structures known to contain a high density of mu receptors, following lesions of the nigro-striatal dopaminergic pathway and striatal intrinsic neurons. Following unilateral nigral lesion with 6-hydroxydopamine, [3H]ohmefentanyl binding site densities were decreased in the patches (-35%) and matrix (-20%) of the ipsilateral striatum and in the lesioned substantia nigra pars compacta (-49%). Unilateral striatal lesion with quinolinic acid induced 72%, 61% and 50% decreases in [3H]ohmefentanyl binding in the patches and matrix of the lesioned striatum and in the ipsilateral substantia nigra pars reticulata, respectively. Similar results were obtained in the binding of [3H]DAGO. Indeed, a significant linear correlation was observed between [3H]ohmefentanyl and [3H]DAGO binding site densities. Therefore, mu opioid receptors may be mainly located on intrinsic neurons in the striatum, dopaminergic cell bodies in the substantia nigra pars compacta and nerve terminals of striatal efferents in the substantia nigra pars reticulata.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
180.
A comprehensive study has been conducted to compare the adsorptions of alkali metals (including Li, Na, and K) on the basal plane of graphite by using molecular orbital theory calculations. All three metal atoms prefer to be adsorbed on the "middle hollow site" above a hexagonal aromatic ring. A novel phenomenon was observed, that is, Na, instead of Li or K, is the weakest among the three types of metal atoms in adsorption. The reason is that the SOMO (single occupied molecular orbital) of the Na atom is exactly at the middle point between the HOMO and the LUMO of the graphite layer in energy level. As a result, the SOMO of Na cannot form a stable interaction with either the HOMO or the LUMO of the graphite. On the other hand, the SOMO of Li and K can form a relatively stable interaction with either the HOMO or the LUMO of graphite. Why Li has a relatively stronger adsorption than K on graphite has also been interpreted on the basis of their molecular-orbital energy levels. 相似文献