全文获取类型
收费全文 | 6445篇 |
免费 | 213篇 |
国内免费 | 484篇 |
专业分类
化学 | 1432篇 |
晶体学 | 47篇 |
力学 | 24篇 |
综合类 | 2篇 |
数学 | 508篇 |
物理学 | 5129篇 |
出版年
2024年 | 10篇 |
2023年 | 64篇 |
2022年 | 72篇 |
2021年 | 82篇 |
2020年 | 156篇 |
2019年 | 175篇 |
2018年 | 186篇 |
2017年 | 151篇 |
2016年 | 272篇 |
2015年 | 251篇 |
2014年 | 362篇 |
2013年 | 378篇 |
2012年 | 338篇 |
2011年 | 558篇 |
2010年 | 376篇 |
2009年 | 474篇 |
2008年 | 478篇 |
2007年 | 384篇 |
2006年 | 416篇 |
2005年 | 283篇 |
2004年 | 280篇 |
2003年 | 220篇 |
2002年 | 177篇 |
2001年 | 162篇 |
2000年 | 161篇 |
1999年 | 111篇 |
1998年 | 154篇 |
1997年 | 53篇 |
1996年 | 52篇 |
1995年 | 48篇 |
1994年 | 37篇 |
1993年 | 23篇 |
1992年 | 33篇 |
1991年 | 33篇 |
1990年 | 20篇 |
1989年 | 16篇 |
1988年 | 23篇 |
1987年 | 9篇 |
1986年 | 19篇 |
1985年 | 11篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1973年 | 4篇 |
1966年 | 1篇 |
排序方式: 共有7142条查询结果,搜索用时 15 毫秒
131.
The unique optoelectronic properties of semiconductor quantum dots (QDs) make them well-suited as fluorescent bioprobes for use in various biological applications. Modification of CdSe/ZnS QDs with biologically relevant molecules provides for multipotent probes that can be used for cellular labeling, bioassays, and localized optical interrogation by means of fluorescence resonance energy transfer (FRET). Herein, we demonstrate the use of red-emitting streptavidin-coated QDs (QD605) as donors in FRET to introduce a competitive displacement-based assay for the detection of oligonucleotides. Various QD–DNA bioconjugates featuring 25-mer probe sequences diagnostic of Hsp23 were prepared. The single-stranded oligonucleotide probes were hybridized to dye-labeled (Alexa Fluor 647) reporter sequences, which were provided for a FRET-sensitized emission signal due to proximity of the QD and dye. The dye-labeled sequence was designed to be partially complementary and include base-pair mismatches to facilitate displacement by a more energetically favorable, fully complementary recognition motif embedded within a 98-mer displacer sequence. Overall, this study demonstrates proof-of-concept at the nM level for competitive displacement hybridization assays in vitro by reduction of fluorescence intensity that directly correlates to the presence of oligonucleotides of interest. This work demonstrates an analytical method that could potentially be implemented for monitoring of intracellular gene expression in the future. 相似文献
132.
On-vial immobilized CdSe quantum dots (QDs) are applied for the first time as chemiluminescent probes for the detection of trace metal ions. Among 17 metal ions tested, inhibition of the chemiluminescence when CdSe QDs are oxidized by H2O2 was observed for Sb, Se and Cu. Liquid–liquid–liquid microextraction was implemented in order to improve the selectivity and sensitivity of the chemiluminescent assay. 相似文献
133.
Yanlong He Jianniao TianJuanni Zhang Sheng ChenYixuan Jiang Yanchun ZhaoShulin Zhao 《Analytica chimica acta》2013
In this work, an ultrasensitive fluorescent polarization immunoassay (FPIA) method based on the quantum dot/aptamer/antibody/gold nanoparticles ensemble has been developed for the detection of adenosine triphosphate (ATP). DNA hybridization is formed when ATP is present in the PBS solution containing the DNA-conjugated quantum dots (QDs) and antibody-AuNPs. The substantial sensitivity improvement of the antibody-AuNPs-enhanced method is mainly attributed to the slower rotation of fluorescent unit when QDs-labeled oligonucleotides hybridize with antibody modified the gold nanoparticle. As a result, the fluorescent polarization (FP) values of the system increase significantly. Under the optimal conditions, a linear response with ATP concentration is ranged from 8 × 10−12 M to 2.40 × 10−4 M. The detection limit reached as low as 1.8 pM. The developed work provides a sensitive and selective immunoassay protocol for ATP detection, which could be applied in more bioanalytical systems. 相似文献
134.
135.
《Journal of Dispersion Science and Technology》2013,34(3-4):453-464
Abstract Inorganic nanostructures that interface with biological systems have recently attracted widespread interest in biology and medicine. Nanoparticles are thought to have potential as novel luminescent probes for both diagnostic (e.g., imaging) and therapeutic (e.g., drug delivery) purposes because of their size comparable to biomolecules and their novel optical, electronic, and magnetic properties. Critical issues for successful nanoparticle delivery include the ability to target specific tissues and cell types and escape from the biological particulate filter known as reticuloendothelial system. Three distinct types of luminescent nanoparticles have been identified which show promise in bioanalysis, namely dye‐doped nanoparticles, semiconductor and metal nanoparticles. In this article we examine the recent advances in the development of dye‐doped nanoparticles, metal and semiconductor nanoparticles, bioconjugation schemes to attach these nanoparticles to biomolecules and a few biological applications. 相似文献
136.
A fluctuating charge interaction potential function for alanine-water was constructed in the spirit of newly developed ABEEMσπ/MM(atom-bond electronegativity equalization method at the σπ level fused into molecular mechanics). The properties of gaseous neutral alanine-(H2O)n(n=1-7) clusters were systematically investigated by quantum mechanics(QM) and the constructed ABEEMσπ/MM potential, such as conformations, hydrogen bonds (H-bonds), interaction energies, charge distributions, and so on. The results of ABEEMσπ/MM model are in fair agreement with those of QM and available experimental data. For isolated alanine, compared with those of experimental structure, the average absolute deviations(AAD) of bond length and bond angle are 0.002 nm and 1.4°, respectively. For alanine-water clusters, the AAD of interaction energies and H-bond lengths are only 3.77 kJ/mol and 0.012 nm, respectively, compared to the results of MP2/aug-cc-pVDZ//MP2/6-311+G** method. The ABEEMσπ charges fluctuate with the changing conformation of the system, and can accurately and reasonably reflect the interpolarization between water and alanine. The presented alanine-water potential function may provide a basis for further simulations on related aqueous solutions of biomolecules. 相似文献
137.
以3-巯基丙酸为稳定剂在水相中合成了Cu掺杂的ZnSe量子点(QDs), 并利用硫脲(CH4N2S)对其进行表面修饰, 制备出核壳结构的ZnSe:Cu/ZnS 量子点. 制得的量子点呈闪锌矿结构, 尺寸约为5 nm, 有较好的分散性, 其荧光发射峰在460 nm左右. 经CH4N2S修饰后, 量子点表面形成了宽禁带的ZnS包覆层, 将电子和空穴限域在了ZnSe:Cu 核内, 减少了表面发生非辐射复合的载流子, 显著提高了量子点的荧光强度. 与Na2S、硫代乙酰胺(TAA)等常用硫源相比, 以CH4N2S为硫源制得的ZnSe:Cu/ZnS 量子点壳层厚度可控, 表面钝化效果更好, 显示出更佳的荧光效率和稳定性. ZnSe:Cu/ZnS 量子点经过紫外线照射后消除了表面的悬空键, 进一步提高了其量子产率, 最终获到了具有较好荧光性质的ZnSe:Cu/ZnS量子点. 相似文献
138.
Structural Evolution and Electronic Properties of Au2Gen-/0 (n=1-8) Clusters: Anion Photoelectron Spectroscopy and Theoretical Calculations 下载免费PDF全文
Investigating the structures and properties of Au-Ge mixed clusters can give insight into the microscopic mechanisms in gold-catalyzed Ge films and can also provide valuable information for the production of germanium-based functional materials. In this work, size-selected anion photoelectron spectroscopy and theoretical calculations were used to explore the structural evolution and electronic properties of Au2Gen-/0 (n=1-8) clusters. It is found that the two Au atoms in Au2Gen-/0 (n=1-8) showed high coordination numbers and weak aurophilic interactions. The global minima of Au2Gen- anions and Au2Gen neutrals are in spin doublet and singlet states, respectively. Au2Gen- anions and Au2Gen neutrals showed similar structural features, except for Au2Ge4-/0 and Au2Ge5-/0. The C2v symmetric V-shaped structure is observed for Au2Ge1-/0, while Au2Ge2-/0 has a C2v symmetric dibridged structure. Au2Ge3-/0 can be viewed as the two Au atoms attached to different Ge-Ge bonds of Ge3 triangle. Au2Ge4- has two Au atoms edge-capping Ge4 tetrahedron, while Au2Ge4 neutral adopts a C2v symmetric double Au atoms face-capping Ge4 rhombus. Au2Ge5-8-/0 show triangular, tetragonal, and pentagonal prism-based geometries. Au2Ge6 adopts a C2v symmetric tetragonal prism structure and exhibits σ plus π double bonding characters. 相似文献
139.
Marketa Ryvolova Kristyna Smerkova Jana Chomoucka Jaromir Hubalek Vojtech Adam Rene Kizek 《Electrophoresis》2013,34(6):801-808
Cisplatin, carboplatin, and oxaliplatin represent three generations of platinum based drugs applied successfully for cancer treatment. As a consequence of the employment of platinum based cytostatics in the cancer treatment, it became necessary to study the mechanism of their action. Current accepted opinion is the formation of Pt‐DNA adducts, but the mechanism of their formation is still unclear. Nanomaterials, as a progressively developing branch, can offer a tool for studying the interactions of these drugs with DNA. In this study, fluorescent CdTe quantum dots (QDs, λem = 525 nm) were employed to investigate the interactions of platinum cytostatics (cisplatin, carboplatin, and oxaliplatin) with DNA fragment (500 bp, c = 25 μg/mL). Primarily, the fluorescent behavior of QDs in the presence of platinum cytostatics was monitored and major differences in the interaction of QDs with tested drugs were observed. It was found that the presence of carboplatin (c = 0.25 mg/mL) had no significant influence on QDs fluorescence; however cisplatin and oxaliplatin quenched the fluorescence significantly (average decrease of 20%) at the same concentration. Subsequently, the amount of platinum incorporated in DNA was determined by QDs fluorescence quenching. Best results were reached using oxaliplatin (9.4% quenching). Linear trend (R2 = 0.9811) was observed for DNA platinated by three different concentrations of oxaliplatin (0.250, 0.125, and 0.063 mg/mL). Correlation with differential pulse voltammetric measurements provided linear trend (R2 = 0.9511). As a conclusion, especially in the case of oxaliplatin‐DNA adducts, the quenching was the most significant compared to cisplatin and nonquenching carboplatin. 相似文献
140.
Georgiana Surpateanu Jean-François Soulé Jean-Marie Beau Stéphanie Norsikian Bogdan I. Iorga 《Journal of carbohydrate chemistry》2013,32(2):114-129
The conformational flexibility of two glycal-type neuraminidase inhibitors has been studied, using several molecular modeling techniques. In agreement with the experimental data available, an intramolecular hydrogen bond, representing a key structural feature that controls the conformer distribution in solution, has been identified. The contribution of each substituent to the overall equilibrium was evaluated using simplified derivatives. Additionally, four methods for estimating NMR coupling constants from dihedral angles were evaluated and the Haasnoot method was found to be appropriate for this class of sugars. These results should allow a better understanding of the structural parameters governing physico-chemical properties of glycal-like compounds. Supplemental materials are available for this article. Go to the publisher's online edition of Journal of Carbohydrate Chemistry to view the free supplemental file. 相似文献