全文获取类型
收费全文 | 3146篇 |
免费 | 491篇 |
国内免费 | 426篇 |
专业分类
化学 | 2294篇 |
晶体学 | 30篇 |
力学 | 225篇 |
综合类 | 45篇 |
数学 | 311篇 |
物理学 | 1158篇 |
出版年
2024年 | 8篇 |
2023年 | 55篇 |
2022年 | 109篇 |
2021年 | 108篇 |
2020年 | 135篇 |
2019年 | 103篇 |
2018年 | 116篇 |
2017年 | 116篇 |
2016年 | 145篇 |
2015年 | 129篇 |
2014年 | 177篇 |
2013年 | 218篇 |
2012年 | 212篇 |
2011年 | 289篇 |
2010年 | 200篇 |
2009年 | 196篇 |
2008年 | 208篇 |
2007年 | 191篇 |
2006年 | 158篇 |
2005年 | 121篇 |
2004年 | 95篇 |
2003年 | 75篇 |
2002年 | 77篇 |
2001年 | 69篇 |
2000年 | 61篇 |
1999年 | 72篇 |
1998年 | 60篇 |
1997年 | 50篇 |
1996年 | 48篇 |
1995年 | 51篇 |
1994年 | 51篇 |
1993年 | 48篇 |
1992年 | 47篇 |
1991年 | 37篇 |
1990年 | 40篇 |
1989年 | 32篇 |
1988年 | 25篇 |
1987年 | 31篇 |
1986年 | 23篇 |
1985年 | 13篇 |
1984年 | 8篇 |
1983年 | 11篇 |
1982年 | 12篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1957年 | 4篇 |
排序方式: 共有4063条查询结果,搜索用时 15 毫秒
111.
Yi Song Jiang-Li Ni Zhang-Yin Wang Yan Lu Lian-Fang Han 《International Journal of Theoretical Physics》2017,56(10):3175-3187
We present a new scheme for deterministically realizing the mutual interchange of quantum information between two distant parties via selected quantum states as the shared entangled resource. We first show the symmetric bidirectional remote state preparation (BRSP), where two single-qubit quantum states will be simultaneously exchanged in a deterministic manner provided that each of the users performs single-qubit von Neumann measurements with proper measurement bases as well as appropriate unitary operations, depending essentially on the outcomes of the prior measurements. Then we consider to extend the symmetric protocol to an asymmetric case, in which BRSP of a general single-qubit state and an arbitrary two-qubit state is investigated successfully. The necessary quantum operations and the employed quantum resources are feasible according to the present technology, resulting in that this protocol may be realizable in the realm of current physical experiment. 相似文献
112.
Hydride generation atomic fluorescence spectrometry (HG-AFS) is used for the determination of hydride-forming elements due to its high sensitivity, simplicity, and low cost. A new HG-AFS method for the simultaneous determination of arsenic and lead in vegetable oil is reported. Vortex-assisted extraction with dilute nitric acid was used to isolate arsenic and lead from vegetable oil. The conditions influencing the fluorescence signal, including the carrier fluid, oxidizing agent, and reducing agent, were optimized. The interferences of coexisting ions were also evaluated. Under the optimized conditions, the limits of detection were 0.6 and 0.4?µg?kg?1 for arsenic and lead. The recoveries were from 84.4 to 105% for both metals in vegetable oil. The optimized method was used for the determination of arsenic and lead in commercial vegetable oil. The analytical results by this approach were in good agreement with values obtained by inductively coupled plasma mass spectrometry with microwave digestion. 相似文献
113.
114.
Preparation of core–shell structure Fe3O4@SiO2 superparamagnetic microspheres immoblized with iminodiacetic acid as immobilized metal ion affinity adsorbents for His‐tag protein purification 下载免费PDF全文
Qian Ni Bing Chen Shaohua Dong Lei Tian Quan Bai 《Biomedical chromatography : BMC》2016,30(4):566-573
The core–shell structure Fe3O4/SiO2 magnetic microspheres were prepared by a sol–gel method, and immobiled with iminodiacetic acid (IDA) as metal ion affinity ligands for protein adsorption. The size, morphology, magnetic properties and surface modification of magnetic silica nanospheres were characterized by various modern analytical instruments. It was shown that the magnetic silica nanospheres exhibited superparamagnetism with saturation magnetization values of up to 58.1 emu/g. Three divalent metal ions, Cu2+, Ni2+ and Zn2+, were chelated on the Fe3O4@SiO2–IDA magnetic microspheres to adsorb lysozyme. The results indicated that Ni2+‐chelating magnetic microspheres had the maximum adsorption capacity for lysozyme of 51.0 mg/g, adsorption equilibrium could be achieved within 60 min and the adsorbed protein could be easily eluted. Furthermore, the synthesized Fe3O4@SiO2–IDA–Ni2+ magnetic microspheres were successfully applied for selective enrichment lysozyme from egg white and His‐tag recombinant Homer 1a from the inclusion extraction expressed in Escherichia coli. The result indicated that the magnetic microspheres showed unique characteristics of high selective separation behavior of protein mixture, low nonspecific adsorption, and easy handling. This demonstrates that the magnetic silica microspheres can be used efficiently in protein separation or purification and show great potential in the pretreatment of the biological sample. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
115.
116.
117.
First-principles study of structural stability and elastic property of pre-perovskite PbTiO3 下载免费PDF全文
The structural stability and the elastic properties of a novel structure of lead titanate,which is named preperovskite PbTiO3 (PP-PTO) and is constructed with TiO6 octahedral columns arranged in a one-dimensional manner,are investigated by using first-principles calculations.PP-PTO is energetically unstable compared with conventional perovskite phases,however it is mechanically stable.The equilibrium transition pressures for changing from preperovskite to cubic and tetragonal phases are 0.5 GPa and 1.4 GPa,respectively,with first-order characteristics.Further,the differences in elastic properties between pre-perovskite and conventional perovskite phases are discussed for the covalent bonding network,which shows a highly anisotropic character in PP-PTO.This study provides a crucial insight into the structural stabilities of PP-PTO and conventional perovskite. 相似文献
118.
119.
120.
Liyong Chen Mingzu Zhang Zhuang Liu Zixu Gu Yingfeng Tu Peihong Ni 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(11):862-871
A biocompatible complex has been prepared as gene carrier via electrostatic interaction, which is composed of a polycation, that is, poly[(dimethylamino)ethyl methacrylate] end-capped with cholesterol moiety (Chol-PDMAEMA30), along with a polyanion named poly(aspartic acid)-grafted-poly(ethylene glycol) (PASP-g-PEG). The complexes have less cytotoxicity compared to the case of alone Chol-PDMAEMA30 or branched polyethylenimine (PEI) system. In the present study, biocompatible complexes have been prepared as gene carrier via electrostatic interaction, which is composed of a polycation, that is, poly[(dimethylamino)ethyl methacrylate] end-capped with cholesterol moiety (Chol-PDMAEMA30), along with a polyanion named poly(aspartic acid)-grafted-poly(ethylene glycol) (PASP-g-PEG). We first synthesized polysuccinimide (PSI) via condensation polymerization of aspartic acid, and then used PEG-NH2 to react with the partial pentacyclic rings of PSI to yield a kind of graft copolymer polysuccinimide-grafted-poly(ethylene glycol) (PSI-g-PEG). After hydrolysis of the residual succinimide units, a new biodegradable and biocompatible graft copolymer PASP-g-PEG was prepared successfully. Chol-PDMAEMA30 was synthesized via oxyanion-initiated polymerization, as reported in our previous literature. We investigated the interactions between every pair among calf thymus DNA, Chol-PDMAEMA30, and PASP-g-PEG by agarose gel retardation assay. The results indicate that the prepared complexes could completely bind DNA and may become more stable during systemic circulation. The complexes have less cytotoxicity compared to the case of alone Chol-PDMAEMA30 or branched polyethylenimine (PEI) system. Furthermore, the physicochemical properties of the complexes were also investigated by zeta potential, transmission electron microscopy (TEM) and dynamic light scattering (DLS) measurements. These biodegradable and biocompatible polymeric carriers have potential applications in gene delivery. 相似文献