全文获取类型
收费全文 | 7558篇 |
免费 | 1392篇 |
国内免费 | 1201篇 |
专业分类
化学 | 6145篇 |
晶体学 | 81篇 |
力学 | 424篇 |
综合类 | 85篇 |
数学 | 794篇 |
物理学 | 2622篇 |
出版年
2024年 | 30篇 |
2023年 | 151篇 |
2022年 | 332篇 |
2021年 | 321篇 |
2020年 | 364篇 |
2019年 | 422篇 |
2018年 | 313篇 |
2017年 | 293篇 |
2016年 | 424篇 |
2015年 | 422篇 |
2014年 | 463篇 |
2013年 | 597篇 |
2012年 | 717篇 |
2011年 | 675篇 |
2010年 | 423篇 |
2009年 | 428篇 |
2008年 | 468篇 |
2007年 | 374篇 |
2006年 | 368篇 |
2005年 | 325篇 |
2004年 | 278篇 |
2003年 | 246篇 |
2002年 | 332篇 |
2001年 | 271篇 |
2000年 | 167篇 |
1999年 | 155篇 |
1998年 | 131篇 |
1997年 | 74篇 |
1996年 | 83篇 |
1995年 | 64篇 |
1994年 | 64篇 |
1993年 | 51篇 |
1992年 | 77篇 |
1991年 | 49篇 |
1990年 | 50篇 |
1989年 | 30篇 |
1988年 | 22篇 |
1987年 | 24篇 |
1986年 | 24篇 |
1985年 | 13篇 |
1984年 | 8篇 |
1983年 | 11篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1971年 | 1篇 |
1959年 | 2篇 |
1957年 | 3篇 |
1936年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
761.
在Su-Schrieffer-Heeger (SSH)原子链中,电子在胞内和胞间的跳跃依赖于其自旋时,即SSH原子链存在自旋轨道耦合作用时,存在不同缠绕数的非平庸拓扑边缘态.如何探测自旋轨道耦合SSH原子链不同缠绕数的边缘态是一个重要问题.本文在紧束缚近似下研究了自旋轨道耦合SSH原子链的非平庸拓扑边缘态性质及其零能附近的电子输运特性.研究发现四重和二重简并边缘态的缠绕数分别为2和1;并且仅当源极入射电子的自旋被极化(铁磁电极)时,自旋轨道耦合SSH原子链在零能附近的电子输运特性才能反映其边缘态的能谱特性.尤其是,随着自旋轨道耦合SSH原子链与左、右导线之间的耦合强度由弱到强改变,对于缠绕数为2的四重简并边缘态,入射电子在零能附近的透射峰数目将从4个变为0;而对于缠绕数为1的二重简并边缘态情形,其透射峰数目将从2个变为0.因此,在源极为铁磁电极的情形下,通过观察自旋轨道耦合SSH原子链在零能附近电子共振透射峰的数目随着其与左、右导线之间耦合强度的变化,来探测其不同缠绕数的边缘态.上述结果为基于电子输运特性探测自旋轨道耦合SSH原子链不同拓扑性质的边缘态提供了一种可选择的理论方案. 相似文献
762.
Synthesis,Structures, and Luminescent Properties of Lanthanide Complexes with Triphenylphospine Oxide 下载免费PDF全文
Yan Ma Shan Xu Xin Wang Min Liu Yue‐Xue Li Xiu‐Lan Xin Qiong‐Hua Jin 《无机化学与普通化学杂志》2017,643(12):780-788
Seven lanthanide complexes [Ln(OPPh3)3(NO3)3] ( 1 – 3 ) (OPPh3 = triphenylphosphine oxide, Ln = Nd, Sm, Gd), [Dy(OPPh3)4(NO3)2](NO3) ( 4 ), [Ln(OPPh3)3(NO3)3]2 ( 5 – 7 ) (Ln = Pr, Eu, Gd) were synthesized by the reactions of different lanthanide salts and OPPh3 ligand in the air. These complexes were characterized by single‐crystal X‐ray diffraction analysis, elemental analysis, IR and fluorescence spectra. Structure analysis shows that complexes 1 – 4 are mononuclear complexes formed by OPPh3 ligands and nitrates. The asymmetric units of complexes 5 – 7 consist of two crystallographic‐separate molecules. Complex 1 is self‐assembled to construct a 2D layer‐structure of (4,4) net topology by hydrogen bond interactions. The other complexes show a 1D chain‐like structure that was assembled by OPPh3 ligands and nitrate ions through C–H ··· O interactions. Solid emission spectra of compounds 4 and 6 are assigned to the characteristic fluorescence of Tb3+ (λem = 480, 574 nm) and Eu3+ (λem = 552, 593, 619, 668 nm). 相似文献
763.
Two isomorphic organically templated zinc/cobalt oxalates, (dmdabco)[Zn2(C2O4)3]·4H2O (1), and (dmdabco)[Co2(C2O4)3]·4H2O (2) (C2O42? = oxalate; dmdabco = N,N′-dimethyl-1,4-diazabicyclo[2,2,2]octane), have been prepared under solvothermal conditions and characterized by X-ray structural analyses. The dmdabco2+ templating agent was derived from simple in situ N-alkylation between methanol and 1,4-diazabicyclo[2,2,2]octane (dabco). Distinct from conventional Eschweiler-Clarke methylation containing excess formic acid and formaldehyde, such one-step methylation from methanol molecules is convenient. Both 1 and 2 exhibit a uninodal 3-connected 3-D interrupted open-framework, in which oxalate ligands have in-plane and out-of-plane connection modes. 相似文献
764.
Wang Jia Liu Yuan Deng Xiling Zhao Na Ying Xue Ye Bang-Ce Li Yingchun 《Mikrochimica acta》2017,184(10):3893-3900
Microchimica Acta - The authors describe an electrochemical sensor for ultrasensitive voltammetric of histamine (HA) by using a gold electrode that was modified with a film consisting of... 相似文献
765.
A pyrene-based dual chemosensor for colorimetric detection of Cu2+ and fluorescent detection of Fe3+
Yuxin Guo Lei Wang Jiezhen Zhuo Bo Xu Xue Li Jianyu Zhang Zhiqiang Zhang Haijun Chi Yan Dong Gonghao Lu 《Tetrahedron letters》2017,58(42):3951-3956
A pyrene based chemosensor was designed and synthesized. The pyrene fluorophore was connected with a pyridine unit through a Schiff base structure to give the sensor (L). L was tested with a variety of metal ions and exhibited high colorimetric selectivities for Cu2+ and Fe3+ over other ions. Upon binding with Cu2+ or Fe3+, L showed an obvious optical color change from colorless to pink for Cu2+ or orange for Fe3+ over a wide pH range from 3 to 12. Moreover, the fluorescence of L at 370 nm decreased sharply after bonding with Fe3+, while other metal ions including Cu2+ had no apparent interference. Thus, using such single chemosensor, Cu2+ and Fe3+ can be detected independently with high selectivity and sensitivity. The limits of detection toward Cu2+ and Fe3+ were 8.5 and 2.0 μM, respectively. DFT calculation results also proved the formation of stable coordination complexes and the phenomenon of fluorescence quenching by Fe3+. Furthermore, L was also successfully used as a bioimaging reagent for detection of Fe3+ in living cells. 相似文献
766.
Immobilization of silver nanoparticles into POEGMA polymer brushes as SERS‐active substrates 下载免费PDF全文
Qian Zhang Jun‐Jiao Yin Feng Liu Xue‐Na Zou Li‐Qiang Chu 《Surface and interface analysis : SIA》2017,49(4):316-322
Surface‐enhanced Raman scattering (SERS) has attracted a great deal of interest during the past four decades and emerged as an ultrasensitive optical technique for chemical and biomedical analysis. It is widely accepted that the facile fabrication of SERS substrates with high activity and good reproducibility is of crucial importance for their applications. Herein, we report on a fast and robust method for the synthesis and immobilization of silver nanoparticles (AgNPs) into poly(oligo(ethylene glycol) methacrylate) (POEGMA) brushes under mild conditions without using any reducing agents. POEGMA brushes of different chain lengths were synthesized directly on silicon wafers by surface‐initiated atom transfer radical polymerization with various reaction time. X‐ray photoelectron spectroscopy and field emission scanning electron microscope measurements indicated that the AgNPs were firmly and homogeneously embedded into POEGMA brushes. The resulting POEGMA–AgNP hybrid films were employed as SERS substrates for the detection of 4‐aminothiophenol, giving rise to an enhancement factor of up to 1.9 × 106. The influence of the POEGMA's chain length on SERS performance was also investigated. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
767.
Danlu Xue Chunyi Liu Xiaomin Li Jie Tang Lihua Cao Yi Liu Zhengping Chen 《Journal of Radioanalytical and Nuclear Chemistry》2017,313(2):419-428
We studied on the structural requirement of C11b chirality of tetrabenazine (TBZ) analogs as vesicular monoamine transporter 2 (VMAT2) ligands. TBZ analogs (2, 6a, 6b) and 18F-radiolabeled [18F]6a and [18F]6b with eliminated C11b chirality were synthesized and characterized. Competition studies demonstrated that 2, 6a and 6b displayed much lower in vivo VMAT2 bindings than TBZ. MicroPET imaging studies of [18F]6a and [18F]6b showed negligible accumulation in VMAT2-enriched regions as compared with the known VMAT2 ligand 18F-FP-(+)-DTBZ. These results suggest that C11b chirality of TBZ analogs is essential for in vivo VMAT2 binding bioactivity. 相似文献
768.
Molecular bulks are favorable for the thermal and morphological stability in organic wide-bandgap semiconducting polymers with potential applications in both information and energy electronics. In this review, we present our progress in the design of fluorene-based bulky semiconductors with a fractal four-element pattern. Firstly, we established one-pot methods to spirofluorenes, especially spiro[fluorene-9,9′-xanthene](SFX) serving as the next-generation spiro-based semiconductors. Secondly, we observed the supramolecular forces at the bulky groups and discovered the supramolecular steric hindrance(SSH) effect on polymorphisms, nanocrystals as well as device performance. Thus, a synergistically molecular attractor-repulsor theory(SMART) was proposed for the control of nanocrystal morphology, thin film phase and morphology. Thirdly, the third possible type of defects has been identified to generate green band(g-band) emission in widebandgap semiconductors by the introduction of molecular strain design of cyclofluorene. Finally, the first bulky polydiarylfluorene with highly crystalline and β conformation was achieved by an attractor-repulsor design of tadpole-shape monomer, which offered an effective platform to fabricate stable wide-bandgap semiconducting devices. All the discoveries offer the solid basis to break through bottlenecks of organic/polymer wide-bandgap semiconductors by the improvements of overall performances. 相似文献
769.
In this work,the effect of dioctadecyl dimethyl ammonium chloride(DDAC,a kind of alkyl ammonium salt) on polar β phase content and the diameter of electrospun PVDF nanofibers was investigated for the first time.Our experimental results show that the diameter of the electrospun PVDF nanofiber could be largely reduced and the content of polar β phase also become dominant immediately by just adding a little amount of DDAC.When the mass fraction of DDAC reached 4%,the content of polar β phase increased by about 39.1% compared with PVDF nanofibers without DDAC.Besides,the crystallinity of PVDF nanofibers also increased with the addition of DDAC.Based on the results,the possible mechanism of cooperative effect between electrospinning and DDAC on fiber diameter and formation of β phase in PVDF was discussed. 相似文献
770.
Song Li Xupeng Cao Yan Wang Zhen Zhu Haowei Zhang Song Xue Jing Tian 《Applied biochemistry and biotechnology》2017,183(3):923-930
With the fast development of microalgal biofuel researches, the proteomics studies of microalgae increased quickly. A filter-aided sample preparation (FASP) method is widely used proteomics sample preparation method since 2009. Here, a method of microalgae proteomics analysis based on modified filter-aided sample preparation (mFASP) was described to meet the characteristics of microalgae cells and eliminate the error caused by over-alkylation. Using Chlamydomonas reinhardtii as the model, the prepared sample was tested by standard LC-MS/MS and compared with the previous reports. The results showed mFASP is suitable for most of occasions of microalgae proteomics studies. 相似文献