全文获取类型
收费全文 | 361篇 |
免费 | 30篇 |
国内免费 | 1篇 |
专业分类
化学 | 261篇 |
晶体学 | 3篇 |
力学 | 16篇 |
数学 | 52篇 |
物理学 | 60篇 |
出版年
2023年 | 8篇 |
2022年 | 15篇 |
2021年 | 16篇 |
2020年 | 13篇 |
2019年 | 19篇 |
2018年 | 15篇 |
2017年 | 16篇 |
2016年 | 17篇 |
2015年 | 16篇 |
2014年 | 16篇 |
2013年 | 17篇 |
2012年 | 32篇 |
2011年 | 32篇 |
2010年 | 26篇 |
2009年 | 21篇 |
2008年 | 22篇 |
2007年 | 23篇 |
2006年 | 12篇 |
2005年 | 23篇 |
2004年 | 8篇 |
2003年 | 6篇 |
2002年 | 6篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1994年 | 1篇 |
1990年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有392条查询结果,搜索用时 15 毫秒
321.
Santanu Panda Aaron Coffin Q. Nhu Nguyen Dr. Dean J. Tantillo Prof. Joseph M. Ready 《Angewandte Chemie (International ed. in English)》2016,55(6):2205-2209
When activated by an acylating agent, pyridine boronic esters react with organometallic reagents to form a dihydropyridine boronic ester. This intermediate allows access to a number of valuable substituted pyridine, dihydropyridine, and piperidine products. 相似文献
322.
A Glimpse of Our Journey into the Design of Optical Probes in Self‐assembled Surfactant Aggregates 下载免费PDF全文
Dynamic self‐assembling amphiphilic surfactant molecules, popularly known as “micelles”, have received widespread attention, due to their ability to modulate the photophysical properties of various organic dyes upon encapsulation. Along with their well‐known use as cleaning agents, catalysts in organic reactions, and even for drug delivery purposes, these surfactant assemblies also show promising pertinence in the recognition of both ionic and nonionic targeted analytes. Low micropolarity and relatively hydrophobic environments promote their interaction with ionic analytes, whereas neutral species mostly affect the aggregation pattern of the probe molecules upon partitioning inside the micellar hydrophobic milieu. The environment‐sensitive nature of micelle‐based self‐assembled probes also prompts us to devise new sensor arrays for the recognition of multiple analytes. While this account will largely focus on our own work in developing surfactant‐triggered self‐assembled sensors, our findings have been placed in the context of the relevant contributions from others during their strategic evolution. 相似文献
323.
Mr. Subhajit Kar Dr. Kommula Bramhaiah Dr. Neena S. John Dr. Santanu Bhattacharyya 《化学:亚洲杂志》2021,16(9):1138-1149
Carbon dots (CDs) have become one of the most emerging materials as an alternative solar light-induced photocatalyst in contrast to traditional metal-based systems. However, one of the major challenges is the lack of visible light absorption. Herein, we have fabricated unique N, P-co-doped CDs with a self-assembled onion-like layered structure by using a bottom-up facile synthesis technique from chitosan gel and phosphoric acid as molecular precursors. This typical layered structure of N, P-co-doped carbon nano onions (N, P-CNOs), with an average size of 25–50 nm, displays an enhanced visible light absorption. Detailed structural and elemental characterizations confirm the extensive aromatic domain with P-containing surface functionalities, while electrochemical study clarifies the lowering of band gaps as well as the creation of new electronic states in comparison to the pristine N-CDs. Furthermore, the intrinsic structural features are correlated with the underpinning photophysical processes by steady-state and time-resolved fluorescence spectroscopy. In addition, steady-state polarized emission and thermo-responsive PL properties have been carried out to unveil further the structure-property correlation of N, P-CNOs, and their comparative study with pristine N-CDs at the different excitation wavelengths. Finally, N, P-CNOs exhibit efficient visible-light-induced photocatalysis, and the detailed mechanistic study is carried out by trapping the photogenerated species in an aqueous medium. The prepared N, P-CNOs displayed an excellent visible-light photocatalytic performance over MB dye with a degradation efficiency of 75.8% within 120 min along with a degradation rate constant of ∼0.0109 min−1. It is concluded that the easy to synthesize and low-cost N, P-CNOs with a unique morphology hold great potential for application in visible-light photocatalysis. 相似文献
324.
In the present work we investigate the behavior of all three components of persistent spin current in a quasi-periodic Fibonacci ring subjected to Rashba and Dresselhaus spin–orbit interactions. Analogous to persistent charge current in a conducting ring where electrons gain a Berry phase in presence of magnetic flux, spin Berry phase is associated during the motion of electrons in presence of a spin–orbit field which is responsible for the generation of spin current. The interplay between two spin–orbit fields along with quasi-periodic Fibonacci sequence on persistent spin current is described elaborately, and from our analysis, we can estimate the strength of any one of two spin–orbit couplings together with on-site energy, provided the other is known. 相似文献
325.
RC4 is one of the most popular stream cipher with wide industrial applications, it has received serious attention in cryptology literature in the last 2 decades. In 1995, Roos pointed out that the elements \(S_N[y]\) of the permutation \(S_N\) after the key scheduling algorithm for the first few values of y are biased to certain combinations of secret key bytes. These correlations were theoretically studied by Paul and Maitra (SAC, 2007). The formula for the correlation probabilities provided by them gives a wrong impression that the probabilities decrease as the value of y becomes larger, which is not true. In this paper, we point out some gaps in their analysis and present a detailed analysis of Roos bias. We provide a more accurate formula for the correlation probabilities. We further study nested Roos type biases and present comparison results. These types of biases are used to reconstruct key from the permutation \(S_N\) for better success probability. 相似文献
326.
Mixed-integer quadratic programming is the problem of optimizing a quadratic function over points in a polyhedral set where some of the components are restricted to be integral. In this paper, we prove that the decision version of mixed-integer quadratic programming is in NP, thereby showing that it is NP-complete. This is established by showing that if the decision version of mixed-integer quadratic programming is feasible, then there exists a solution of polynomial size. This result generalizes and unifies classical results that quadratic programming is in NP (Vavasis in Inf Process Lett 36(2):73–77 [17]) and integer linear programming is in NP (Borosh and Treybig in Proc Am Math Soc 55:299–304 [1], von zur Gathen and Sieveking in Proc Am Math Soc 72:155–158 [18], Kannan and Monma in Lecture Notes in Economics and Mathematical Systems, vol. 157, pp. 161–172. Springer [9], Papadimitriou in J Assoc Comput Mach 28:765–768 [15]). 相似文献
327.
Tailoring membrane properties for biomedical applications, e.g., hemodialysis, have been a challenge which material scientists have been addressing for last few decades. The fundamental challenge lies in identifying and controlling the parameters which are responsible for yielding cytocompatibility and hemocompatibility to the material. The present article is an attempt to understand the physical parameters which are responsible for the biological manifestations of a polymer membrane. Two types of dialysis membranes, viz., high performance membrane and high cutoff, have been synthesized. Membrane surfaces were modified via dry and wet annealing, and conditions of annealing were optimized. Subsequently, physical and surface properties of the membranes after annealing were investigated. In‐depth investigation of biological and blood response has been undertaken on the basis of fundamental parameters like polarizability and surface rigidity. Cell adhesion, proliferation, protein adsorption, hemolysis, platelet adhesion, thrombus formation, and complement activation tests were performed on the membranes. It was observed that dry heating increases surface smoothness but in the process develops cracks on membrane surface as well as increases work of adhesion for blood contact. On the other hand, wet heating of membrane surface not only improves biological performance but it is also easy to retrofit with existing spinning technologies for spinning dialysis membranes. In‐house spinning technology was used to synthesize hemodialysis membranes which were annealed at the optimized conditions, and their surfaces were compared with commercial fibers to ascertain the rationale of annealing as a facile method to lend desired surface properties to membranes. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
328.
Naphthalene and pyrrole substituted guanidine 1 has been designed and synthesised. Compound 1 efficiently distinguishes Cu2+, Hg2+ and Pb2+ ions by exhibiting different responses in fluorescence. While compound 1 exhibited turn-on emission selectively in the presence of Hg2+ and Pb2+ ions in CH3CN and CH3CN–H2O (1:1, v/v), respectively, it showed decrease in emission upon interaction with Cu2+ ion in CH3CN. Furthermore, the Cu-1 ensemble has been established as a potential probe for selective detection of CN? ion over a series of other anions involving colour change (in ordinary light: colourless to light yellow and under UV light: colourless to sky blue). Theoretical insight has been invoked to understand the mode of metal–ligand interaction. 相似文献
329.
Cholesterol-based Schiff base 1 has been designed and synthesised. The Schiff base 1 forms yellow coloured gel in DMF:H2O (2:1, v/v) and the gel is anion responsive. Among different anions, the gel phase of 1 is selectively transformed into sol in the presence of CN– ions and validates its visual sensing. 1H NMR, FTIR and HRMS spectroscopic techniques were adopted to study the gelation of 1 and its responsive behaviour towards anions. 相似文献
330.
Multichromophoric Organic Molecules Encapsulated in Polymer Nanoparticles for Artificial Light Harvesting 下载免费PDF全文
We designed a self‐assembled multichromophoric organic molecular arrangement inside polymer nanoparticles for light‐harvesting antenna materials. The self‐assembled molecular arrangement of quaterthiophene molecules was found to be an efficient light‐absorbing antenna material, followed by energy transfer to Nile red (NR) dye molecules, which was confined in polymer nanoparticles. The efficiency of the antenna effect was found to be 3.2 and the effective molar extinction coefficient of acceptor dye molecules was found to be enhanced, which indicates an efficient light‐harvesting system. Based on this energy‐transfer process, tunable photo emission and white light emission has been generated with 14 % quantum yield. Such self‐assembled oligothiophene–NR systems encapsulated in polymer nanoparticles may open up new possibilities for fabrication of artificial light harvesting system. 相似文献