全文获取类型
收费全文 | 20606篇 |
免费 | 3944篇 |
国内免费 | 5955篇 |
专业分类
化学 | 16722篇 |
晶体学 | 676篇 |
力学 | 1300篇 |
综合类 | 611篇 |
数学 | 2399篇 |
物理学 | 8797篇 |
出版年
2024年 | 59篇 |
2023年 | 350篇 |
2022年 | 824篇 |
2021年 | 796篇 |
2020年 | 837篇 |
2019年 | 903篇 |
2018年 | 765篇 |
2017年 | 920篇 |
2016年 | 909篇 |
2015年 | 1059篇 |
2014年 | 1305篇 |
2013年 | 1628篇 |
2012年 | 1726篇 |
2011年 | 1847篇 |
2010年 | 1600篇 |
2009年 | 1620篇 |
2008年 | 1765篇 |
2007年 | 1507篇 |
2006年 | 1495篇 |
2005年 | 1344篇 |
2004年 | 1062篇 |
2003年 | 844篇 |
2002年 | 909篇 |
2001年 | 864篇 |
2000年 | 833篇 |
1999年 | 509篇 |
1998年 | 283篇 |
1997年 | 184篇 |
1996年 | 214篇 |
1995年 | 185篇 |
1994年 | 195篇 |
1993年 | 197篇 |
1992年 | 169篇 |
1991年 | 125篇 |
1990年 | 128篇 |
1989年 | 104篇 |
1988年 | 96篇 |
1987年 | 74篇 |
1986年 | 54篇 |
1985年 | 37篇 |
1984年 | 35篇 |
1983年 | 43篇 |
1982年 | 11篇 |
1981年 | 19篇 |
1980年 | 18篇 |
1979年 | 16篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1974年 | 5篇 |
1971年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Joseph Israel Gurti Prof. Xun-Lei Ding Ya-Ya Wang Yan Chen Dr. Wei Li Dr. Xin Wang 《Chemphyschem》2022,23(14):e202200124
The reaction of N2 with trinuclear niobium and tungsten sulfide clusters Nb3Sn and W3Sn (n=0–3) was systematically studied by density functional theory calculations with TPSS functional and Def2-TZVP basis sets. Dissociations of N−N bonds on these clusters are all thermodynamically allowed but with different reactivity in kinetics. The reactivity of Nb3Sn is generally higher than that of W3Sn. In the favorite reaction pathways, the adsorbed N2 changes the adsorption sites from one metal atom to the bridge site of two metal atoms, then on the hollow site of three metal atoms, and at that place, the N−N bond dissociates. As the number of ligand S atoms increases, the reactivity of Nb3Sn decreases because of the hindering effect of S atoms, while W3S and W3S2 have the highest reactivity among four W3Sn clusters. The Mayer bond order, bond length, vibrational frequency, and electronic charges of the adsorbed N2 are analyzed along the reaction pathways to show the activation process of the N−N bond in reactions. The charge transfer from the clusters to the N2 antibonding orbitals plays an essential role in N−N bond activation, which is more significant in Nb3Sn than in W3Sn, leading to the higher reactivity of Nb3Sn. The reaction mechanisms found in this work may provide important theoretical guidance for the further rational design of related catalytic systems for nitrogen reduction reactions (NRR). 相似文献
972.
973.
Highly selective, sensitive, and stable biosensors are essential for the molecular level understanding of many physiological activities and diseases. Electrochemical aptamer-based (E-AB) sensor is an appealing platform for measurement in biological system, attributing to the combined advantages of high selectivity of the aptamer and high sensitivity of electrochemical analysis. This review summarizes the latest development of E-AB sensors, focuses on the modification strategies used in the fabrication of sensors and the sensing strategies for analytes of different sizes in biological system, and then looks forward to the challenges and prospects of the future development of electrochemical aptamer-based sensors. 相似文献
974.
Membrane technology is of particular significance for the sustainable development of society owing to its potential capacity to tackle the energy shortage and environmental pollution. Membrane materials are the core part of membrane technology. Researchers have always been pursuing predictable structures of advanced membrane materials, which provides a possibility to fully unlock the potential of membranes. Covalent organic frameworks(COFs), with the advantage of controllable pore microenvironment, are considered to be promising candidates to achieve this design concept. The customizable function of COF membranes through pore engineering does well in the enhancement of selective permeability performance, which offers COF membranes with great application potentials in separation and transportation fields. In this context, COF-based membranes have been developed rapidly in recent years. Herein, we present a brief overview on the strategies developed for pore engineering of COF membranes in recent years, including skeleton engineering, pore surface engineering, host-guest chemistry and membrane fabrication. Moreover, the features of transmission or separation of molecules/ions based on COF membranes and corresponding applications are also introduced. In the last part, the challenges and prospects of the development of COF membranes are discussed. 相似文献
976.
977.
The precise release of drugs is essential to improve cancer therapeutic efficacy. In this work, a tandem responsive strategy was developed based on a triple-layered metal-organic framework (MOF) hybrid. The MOF nanoprobe was stepwise fabricated with a telomerase-responsive inner, a pH-sensitive MOF filling and H2O2-responsive coordination complex shell of Fe3+ and eigallocatechin gallate (EGCG). In the tumor microenvironment, the shell was dissociated by endogenous H2O2 and simultaneously produced highly reactive hydroxyl radicals by a Fenton reaction. Meanwhile, the released EGCG could downregulate the expression of P-glycoprotein responsible for drug resistance. After the dissociation of the framework by protons, telomerase could trigger the release of the drug from the DNA duplex on the exposed inner shell. By integrating confined drug release, inhibited efflux pump and chemodynamic therapy, the all-in-one chemotherapy strategy was identified with enhanced therapeutic efficacy in drug-resistant cancer cells. 相似文献
978.
Cheng Tang Xiaoming Chen Hua Yao Haiyan Yin Xiaoping Ma Mingji Jin Xin Lu Quntao Wang Kun Meng Qipeng Yuan 《Molecules (Basel, Switzerland)》2021,26(11)
The purpose of this study was to develop mixed polymeric micelles with high drug loading capacity to improve the oral bioavailability of icaritin with Soluplus® and Poloxamer 407 using a creative acid-base shift (ABS) method, which exhibits the advantages of exclusion of organic solvents, high drug loading and ease of scaling-up. The feasibility of the ABS method was successfully demonstrated by studies of icaritin-loaded polymeric micelles (IPMs). The prepared IPMs were characterized to have a spherical shape with a size of 72.74 ± 0.51 nm, and 13.18% drug loading content. In vitro release tests confirmed the faster release of icaritin from IPMs compared to an oil suspension. Furthermore, bioavailability of icaritin in IPMs in beagle dogs displayed a 14.9-fold increase when compared with the oil suspension. Transcellular transport studies of IPMs across Caco-2 cell monolayers confirmed that the IPMs were endocytosed in their intact forms through macropinocytosis, clathrin-, and caveolae-mediated pathways. In conclusion, the results suggested that the mixed micelles of Soluplus® and Poloxamer 407 could be a feasible drug delivery system to enhance oral bioavailability of icaritin, and the ABS method might be a promising technology for the preparation of polymeric micelles to encapsulate poorly water-soluble weakly acidic and alkaline drugs. 相似文献
979.
Electrostatic drag in the intramolecular Schmidt reactions of azidopropylcyclohexanones is characterized using density functional theory (DFT) calculations and direct dynamics simulations. Despite resulting from enthalpically favorable interactions, electrostatic drag slows down N2 loss during formation of bridged lactam products, an effect with implications for controlling product selectivity. 相似文献
980.
The synergism/inhibition level, solubilization sites and the total solubility (St) of co-solubilization systems of phenanthrene, anthracene and pyrene in Tween 80 and sodium dodecyl sulfate (SDS) are studied by 1H-NMR, 2D nuclear overhauser effect spectroscopy (NOESY) and rotating frame overhauser effect spectroscopy (ROESY). In Tween 80, inhibition for phenanthrene, anthracene and pyrene is observed in most binary and ternary systems. However, in SDS, synergism is predominant. After analysis, we find that the different synergism or inhibition situation between Tween 80 and SDS is related to the different types of surfactants used and the resulting different co-solubilization mechanisms. In addition, we also find that three polycyclic aromatic hydrocarbons (PAHs) have similar solubilization sites in both Tween 80 and SDS, which are almost unchanged in co-solubilization systems. Due to the similar solubilization sites, the chemical shift changes of surfactant and PAH protons follow the same pattern in all solubilization systems, and the order of chemical shift changes is consistent with the order of changes in the St of PAHs. In this case, it is feasible to evaluate St of PAHs by chemical shift. In both Tween 80 and SDS solutions, the ternary solubilization system has relatively high St rankings. Therefore, in practical applications, a good overall solubilization effect can be expected. 相似文献