全文获取类型
收费全文 | 33773篇 |
免费 | 3894篇 |
国内免费 | 3201篇 |
专业分类
化学 | 23427篇 |
晶体学 | 316篇 |
力学 | 1502篇 |
综合类 | 254篇 |
数学 | 4295篇 |
物理学 | 11074篇 |
出版年
2023年 | 425篇 |
2022年 | 517篇 |
2021年 | 782篇 |
2020年 | 990篇 |
2019年 | 1071篇 |
2018年 | 835篇 |
2017年 | 778篇 |
2016年 | 1302篇 |
2015年 | 1328篇 |
2014年 | 1569篇 |
2013年 | 2333篇 |
2012年 | 2405篇 |
2011年 | 2516篇 |
2010年 | 1882篇 |
2009年 | 1811篇 |
2008年 | 2110篇 |
2007年 | 1912篇 |
2006年 | 1689篇 |
2005年 | 1545篇 |
2004年 | 1375篇 |
2003年 | 1196篇 |
2002年 | 1189篇 |
2001年 | 953篇 |
2000年 | 764篇 |
1999年 | 683篇 |
1998年 | 515篇 |
1997年 | 452篇 |
1996年 | 436篇 |
1995年 | 443篇 |
1994年 | 390篇 |
1993年 | 367篇 |
1992年 | 305篇 |
1991年 | 306篇 |
1990年 | 286篇 |
1989年 | 247篇 |
1988年 | 217篇 |
1987年 | 184篇 |
1986年 | 173篇 |
1985年 | 274篇 |
1984年 | 265篇 |
1983年 | 180篇 |
1982年 | 206篇 |
1981年 | 159篇 |
1980年 | 156篇 |
1979年 | 146篇 |
1978年 | 121篇 |
1977年 | 169篇 |
1976年 | 146篇 |
1975年 | 121篇 |
1973年 | 118篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
Yu‐Fei Song De‐Liang Long Chris Ritchie Leroy Cronin 《Chemical record (New York, N.Y.)》2011,11(3):158-171
The latest advances in the area of polyoxometalate (POM)‐based inorganic/organic hybrid materials prepared by self‐assembly, covalent modification, and supramolecular interactions are presented. This Review is composed of five sections and documents the effect of organic cations on the formation of novel POMs, surfactant encapsulated POM‐based hybrids, polymeric POM/organic hybrid materials, POMs‐containing ionic crystals, and covalently functionalized POMs. In addition to their role in the charge‐balancing, of anionic POMs, the crucial role of organic cations in the formation and functionalization of POM‐based hybrid materials is discussed. DOI 10.1002/tcr.201100002 相似文献
992.
993.
Yidan Liu Yizhong Yuan Xiaohui Tian Jinyu Sun 《International journal of quantum chemistry》2020,120(23):e26399
Nowadays, blue fluorescent organic light-emitting diodes (FOLEDs) have attracted considerable attention from both academia and industry. According to spin statistics, electrical excitation results in the formation of ∼25% singlet excitons and ∼75% triplet excitons (signifying ~75% energy loss), which triggered wide-ranging efforts to harvest as many triplet excitons as possible. The materials that can convert triplet excitons into singlet excitons from the high-lying excited triplet states (referred as “hot exciton” channel) to realize high efficiency were reported, which can also efficaciously avoid the accumulation of triplet excitons in T1 state. In this study, by means of density functional theory (DFT) and time-dependent DFT, we have theoretically investigated the electronic and photophysical properties of 16 newly designed molecules with donor-bridge-acceptor framework to search for the blue FOLED materials exploiting the “hot exciton” path. Important properties, such as singlet-triplet energy gaps, absorption and emission parameters, and reverse intersystem crossing rates (kRISC), of five target molecules were studied. The calculated results demonstrate that thiophene-diphenylamine (kRISC up to 1.03 × 108 seconds−1) may have promising potential as blue FOLED materials by virtue of the “hot exciton” effect. 相似文献
994.
Arnab Bagchi Yu‐Hsuan Huang Z. F. Xu P. Raghunath Yuan T. Lee Chi‐Kung Ni M. C. Lin Yuan‐Pern Lee 《化学:亚洲杂志》2011,6(11):2961-2976
The photodissociation of gaseous benzaldehyde (C6H5CHO) at 193, 248, and 266 nm using multimass ion imaging and step‐scan time‐resolved Fourier‐transform infrared emission techniques is investigated. We also characterize the potential energies with the CCSD(T)/6‐311+G(3df,2p) method and predict the branching ratios for various channels of dissociation. Upon photolysis at 248 and 266 nm, two major channels for formation of HCO and CO, with relative branching of 0.37:0.63 and 0.20:0.80, respectively, are observed. The C6H5+HCO channel has two components with large and small recoil velocities; the rapid component with average translational energy of approximately 25 kJ mol?1 dominates. The C6H6+CO channel has a similar distribution of translational energy for these two components. IR emission from internally excited C6H5CHO, ν3 (v=1) of HCO, and levels v≤2, J≤43 of CO are observed; the latter has an average rotational energy of approximately 13 kJ mol?1 and vibrational energy of approximately 6 kJ mol?1. Upon photolysis at 193 nm, similar distributions of energy are observed, except that the C6H5+HCO channel becomes the only major channel with a branching ratio of 0.82±0.10 and an increased proportion of the slow component; IR emission from levels ν1 (v=1) and ν3 (v=1 and 2) of HCO and v≤2, J≤43 of CO are observed; the latter has an average energy similar to that observed in photolysis at 248 nm. The observed product yields at different dissociation energies are compared to statistical‐theory predicted results based on the computed singlet and triplet potential‐energy surfaces. 相似文献
995.
Jérémy Vuilleumier Geoffrey Gaulier Raphaël De Matos Yannick Mugnier Gabriel Campargue Jean-Pierre Wolf Luigi Bonacina Sandrine Gerber-Lemaire 《Helvetica chimica acta》2020,103(1):e1900251
While chemotherapy is one of the most used treatments in oncology, the systemic administration of chemotherapeutics generally results in undesired damages to healthy tissues and cells, side effects such as severe nausea and leukopenia, and reduced efficacy due to multidrug resistance and poor target accessibility. The limitations of conventional chemotherapy formulation have prompted the development of alternative nanomaterials-based strategies to achieve targeted and stimuli sensitive payload delivery to reach optimal local drug concentration at tumor sites. In this study, the anticancer drug chlorambucil (Clb) was conjugated to the surface of silica coated lithium niobate (LNO) harmonic nanoparticles (HNPs) using a photocaging tether based on coumarin-4-yl methyl derivative. Upon laser pulsed femtosecond irradiation at 790 nm, the second harmonic emission from the metal oxide core induced the efficient release of Clb, with concomitant contribution from the nonlinear absorption of the coumarin (CM)-based moiety. 相似文献
996.
A newly developed electrochemical sensor for determination of hydrogen peroxide (H2O2) in beverages using a water‐insoluble picket‐fence porphyrin (FeTpivPP) functionalized multiwalled carbon nanotubes (MWNTs) is demonstrated. Introduction of FeTpivPP on MWNTs led to enhanced electron transfer. As a new platform in electrochemical analysis, the resultant sensor showed excellent electrocatalytic activity toward the reduction of H2O2 due to the synergic effect between MWNTs and FeTpivPP, thus leading to highly sensitive amperometric sensing of H2O2 with a detection limit of 0.05 µmol L?1. The developed method is successfully used to detect H2O2 in beverages and shows great promise for routine sensing applications. 相似文献
997.
Yong Tang Jinfeng Zhuge Jihua Gou Ruey‐Hung Chen Christopher Ibeh Yuan Hu 《先进技术聚合物》2011,22(10):1403-1413
In this study, a hybrid nanopaper consisting of carbon nanofiber (CNF) and polyhedral oligomeric silsequioxane (POSS) or cloisite Na+ clay, has been fabricated through the papermaking process. The hybrid nanopaper was then coated on the surface of glass fiber (GF) reinforced polymer matrix composites through resin transfer molding (RTM) process. The morphologies of the hybrid nanopaper and resulting nanocomposites were characterized with scanning electron microscopy (SEM). It can be seen that the nanopaper had a porous structure with highly entangled carbon nanofibers and the polyester resin completely penetrated the nanopaper throughout the thickness. The thermal decomposition behavior of the hybrid nanopapers and nanocomposites was studied with the real‐time thermogravimetric analysis/ flourier transform infrared spectrometry (TGA/FTIR). The test results indicate that the addition of pristine nanoclay increased the thermal stability of the nanopaper, whereas the POSS particles decreased the thermal stability of the nanopaper. The fire retardant performance of composite laminates coated with the hybrid nanopaper was evaluated with cone calorimeter tests using a radiated heat flux of 50 kW/m2. The cone calorimeter test results indicate that the peak heat release rate (PHRR) decreased dramatically in composite laminates coated with the CNF‐clay nanopaper. However, the PHRRs of the CNF‐POSS nanopaper coated composite laminates increased. The formation of compact char materials was observed on the surface of the residues of the CNF‐clay nanopaper after cone calorimeter test. The flame retardant mechanisms of the hybrid nanopaper in the composite laminates are discussed. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
998.
999.
1000.
Zhihua Qiao Qilong Tai Lei Song Yuan Hu Pin Lv Ganxin Jie Wei Huang Yi Fu Deqing Zhang 《先进技术聚合物》2011,22(12):2602-2608
An intumescent flame retardant system composed of ammonium polyphosphate (APP) and pentaerythritol (PER) was used for flame retarding ethylene–propylene–diene‐modified elastomer (EPDM)/polypropylene (PP) blends. Cerium phosphate (CeP) was synthesized and the effect on flame retardancy and thermal stability of EPDM/PP composites based on intumescent flame retardant (IFR) were studied by limiting oxygen index (LOI), UL‐94, and thermogravimetic analysis (TGA), respectively. Scanning electron microscopy (SEM) and Fourier transform infrared spectrometry (FTIR) were used to analyze the morphological structure and the component of the residue chars formed from the EPDM/PP composites, and the mechanical properties of the materials were also studied. The addition of CeP to the EPDM/PP/APP/PER composites gives better flame retardancy than that of EPDM/PP/APP/PER composites. TGA and RT‐FTIR studies indicated that an interaction occurs among APP, PER, and EPDM/PP. The incorporation of CeP improved the mechanical properties of the materials. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献