全文获取类型
收费全文 | 22043篇 |
免费 | 4104篇 |
国内免费 | 4618篇 |
专业分类
化学 | 16716篇 |
晶体学 | 348篇 |
力学 | 1454篇 |
综合类 | 327篇 |
数学 | 2687篇 |
物理学 | 9233篇 |
出版年
2024年 | 26篇 |
2023年 | 371篇 |
2022年 | 534篇 |
2021年 | 710篇 |
2020年 | 819篇 |
2019年 | 755篇 |
2018年 | 717篇 |
2017年 | 740篇 |
2016年 | 1019篇 |
2015年 | 1013篇 |
2014年 | 1233篇 |
2013年 | 1613篇 |
2012年 | 1947篇 |
2011年 | 1960篇 |
2010年 | 1480篇 |
2009年 | 1510篇 |
2008年 | 1751篇 |
2007年 | 1538篇 |
2006年 | 1418篇 |
2005年 | 1329篇 |
2004年 | 983篇 |
2003年 | 795篇 |
2002年 | 804篇 |
2001年 | 768篇 |
2000年 | 808篇 |
1999年 | 568篇 |
1998年 | 427篇 |
1997年 | 373篇 |
1996年 | 356篇 |
1995年 | 373篇 |
1994年 | 272篇 |
1993年 | 239篇 |
1992年 | 238篇 |
1991年 | 202篇 |
1990年 | 198篇 |
1989年 | 156篇 |
1988年 | 145篇 |
1987年 | 129篇 |
1986年 | 94篇 |
1985年 | 56篇 |
1984年 | 57篇 |
1983年 | 53篇 |
1982年 | 46篇 |
1981年 | 42篇 |
1980年 | 25篇 |
1979年 | 9篇 |
1978年 | 11篇 |
1965年 | 9篇 |
1964年 | 9篇 |
1959年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 390 毫秒
991.
Zhao Bin Chen Hao Gao Diankui Xu Lizhi Zhang Yuanyuan 《Journal of Thermal Analysis and Calorimetry》2021,143(4):3221-3232
Journal of Thermal Analysis and Calorimetry - In order to optimize structure of twin screw compressor, and improve the working efficiency of twin screw refrigeration compressor, the heat transfer... 相似文献
992.
Kevin W. Gao Xi Jiang Zach J. Hoffman Gurmukh K. Sethi Saheli Chakraborty Irune Villaluenga Nitash P. Balsara 《Journal of polymer science. Part A, Polymer chemistry》2020,58(2):363-371
Poly(ethylene oxide)-b-polyhedral oligomeric silsesquioxane (PEO–POSS) mixed with lithium bis(trifluoromethanesulfonyl)imide salt is a nanostructured hybrid organic–inorganic block copolymer electrolyte that may enable lithium metal batteries. The synthesis and characteristics of three PEO–POSS block copolymer electrolytes which only differ by their POSS silica cage substituents (ethyl, isobutyl, and isooctyl) is reported. Changing the POSS monomer structure results in differences in both thermodynamics and ion transport. All three neat polymers exhibit lamellar morphologies. Adding salt results in the formation of a disordered window which closes and gives way to lamellae at higher salt concentrations. The width of disordered window decreases with increasing length of the POSS alkyl chain substituent from ethyl to isobutyl and is absent in the isooctyl sample. Rheological measurements demonstrate good mechanical rigidity when compared with similar all-organic block copolymers. While salt diffusion coefficient and current ratio are unaffected by substituent length, ionic conductivity increases as the length of the alkyl chain substituent decreases: the ethyl substituent is optimal for ion transport. This is surprising because conventional wisdom suggests that ion transport occurs primarily in the PEO-rich domains, that is, ion transport should be unaffected by substituent length after accounting for the minor change in conducting phase volume fraction. © 2020 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2020 © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 363–371 相似文献
993.
Dr. Shuangyan Wu Dr. Mingchang Zhu Dr. Ying Zhang Prof. Marina Kosinova Prof. Vladimir P. Fedin Prof. Enjun Gao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(14):3137-3144
As a hot topic of global concern, the distinguishing and detecting of antibiotic pollution is crucial owing to its adverse effect on ecosystems and human health stemming from excessive use and poor management. Herein, a water-stable lanthanide coordination polymer sensor (Dy-TCPB) with multiple emitting centers is prepared. The versatile Dy-TCPB can conveniently differentiate various antibiotics, and displays a self-calibration luminescent response to nitrofurazone (NFZ) and furazolidone (FZD). Each antibiotic exhibits notable correlation to a unique combination of the two ligand-to-Dy ion emission intensity ratios, enabling two-dimensional fingerprint recognition. Furthermore, the novel self-calibration sensor demonstrates effective recognition of NFZ and FZD with excellent sensitivity and selectivity, and detection limits as low as 0.0476 and 0.0482 μm for NFZ and FZD, respectively. The synthetic approach for the fabrication of a singular coordination polymer exhibiting multiple emissions provides a promising strategy for the development of facile and effective ratiometric sensors. 相似文献
994.
Meccanica - Self-excited oscillation induced by the internal frictions of spline joints is a major cause of rotor system instability. In this study, the dynamic equations of spline-connected... 相似文献
995.
Yonghui Liu Huaying Gao Xiaoli Sheng Yuming Zhou Beibei Wang Xiao Sha Maolu Jin Jie Zhao Wenqi Liu 《应用有机金属化学》2019,33(11)
In this work, a series of novel acidic polymerized ionic liquids were used as heterogeneous catalyst for alkylation of o‐Xylene with styrene. And the effect of the amount of initiator and the type of acid used for ion exchange on catalyst structure and the catalytic performance of catalysts for alkylation were studied thoroughly. The experiment results show: when the percentage of the amount of initiator in the total material is 3%, the polymerized ionic liquid catalyst MPM‐SO3H‐[C3V][SO3CF3] has the most uniform with a specific surface area of 97.30 m2/g and a pore volume of 0.35 cm3/g. Benefiting from the unique structure features, MPM‐SO3H‐[C3V][SO3CF3] manifested an excellent catalytic performance for alkylation of o‐Xylene with styrene, along with the conversion of styrene was 96.8% and the yield of 1‐Phenyl‐1‐ortho‐xylene ethane was 94.7%. Therefore, this work provides a novel reference to the synthesis of polymerized ionic liquids and clearly explains the advantage of novel acidic polymerized ionic liquids on alkylation. 相似文献
996.
997.
Xiao-Yi Song Yu-Hang Zhang Ping-Ping Sun Prof. Dr. Jun Gao Prof. Dr. Fa-Nian Shi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(25):5654-5661
Novel lithium–lanthanide (Ln: cerium and praseodymium) bimetallic coordination polymers with formulas C10H2LnLiO8 (Ln: Ce (CeLipma) and Pr (PrLipma)) and C10H3CeO8 (Cepma) were prepared through a simple hydrothermal method. The three compounds were characterized by means of FTIR spectroscopy, X-ray diffraction, single-crystal X-ray diffraction, SEM, TEM, and X-ray photoelectron spectroscopy. The results of structural refinement show that they belong to triclinic symmetry and P space group with cerium (or praseodymium) and lithium cations, forming coordination bonds to oxygen atoms from different pyromellitic acid molecules, and leading to the construction of 3D structures. It is interesting to note that the frameworks exclude any coordination water and lattice water. As an electrode material for lithium-ion batteries, CeLipma exhibits a maximum capacity of 800.5 mAh g−1 and a retention of 91.4 % after 50 cycles at a current density of 100 mA g−1. The favorable electrochemical properties of the lanthanide coordination polymers show potential application prospects in the field of electrode materials. 相似文献
998.
Numerical Algorithms - Recently, continuous-stage Runge-Kutta-Nyström (CSRKN) methods for solving numerically second-order initial value problem $q^{\prime \prime }= f(q)$ have been proposed... 相似文献
999.
1000.
Sidra Jabeen Zhe Zeng Mohammednoor Altarawneh Xiangpeng Gao Anam Saeed Bogdan Z. Dlugogorski 《国际化学动力学杂志》2019,51(9):696-710
This contribution investigates thermal decomposition of leucine, as a representative model compound for amino acids in algal biomass. We map out potential energy surface for a wide array of unimolecular and self-condensation reactions operating in the decomposition of leucine. Decarboxylation and dehydration of leucine ensues by eliminating CO2 and –OH, respectively, from the –COOH group attached to the α-carbon. The molecular channel for deamination involves cleavage of NH2 from α-carbon of leucine. The activation energies for direct elimination of CO2, NH3, and H2O from a leucine molecule lie within 20.7 kJ/mol of each other. Activation energies for these decomposition pathways reside below the bond dissociation enthalpy of H–C(α) of 323.1 kJ/mol. The decarboxylation, deamination, and dehydration pathways, via radical-prompted pathways, systematically require lower energy barriers, in reference to closed-shell reaction corridors. Detailed computations at the CBS-QB3 level provide the Arrhenius rate parameters for the unimolecular and bimolecular reactions, and standard enthalpies of formation, standard entropies, and heat capacities for all the products and intermediates. A kinetic analysis of gas-phase reactions, within the context of a plug-flow reactor model, accounts qualitatively for the formation of major products observed experimentally in the thermal degradation of the condensed-phase leucine. Among notable N-containing species, the model predicts the prevailing of NH3 over HCN and HNCO, in addition to corresponding appreciable concentrations of amines, imines, and nitriles. Our detailed kinetic investigation illustrates a negligible contribution of the self-condensation reactions of leucine in the gas phase. 相似文献