全文获取类型
收费全文 | 1923篇 |
免费 | 57篇 |
国内免费 | 6篇 |
专业分类
化学 | 1274篇 |
晶体学 | 10篇 |
力学 | 99篇 |
数学 | 175篇 |
物理学 | 428篇 |
出版年
2021年 | 21篇 |
2020年 | 34篇 |
2019年 | 26篇 |
2018年 | 14篇 |
2017年 | 13篇 |
2016年 | 42篇 |
2015年 | 33篇 |
2014年 | 32篇 |
2013年 | 80篇 |
2012年 | 100篇 |
2011年 | 139篇 |
2010年 | 64篇 |
2009年 | 75篇 |
2008年 | 116篇 |
2007年 | 105篇 |
2006年 | 93篇 |
2005年 | 73篇 |
2004年 | 72篇 |
2003年 | 56篇 |
2002年 | 51篇 |
2001年 | 36篇 |
2000年 | 33篇 |
1999年 | 17篇 |
1998年 | 22篇 |
1997年 | 19篇 |
1996年 | 34篇 |
1995年 | 20篇 |
1994年 | 18篇 |
1993年 | 25篇 |
1992年 | 22篇 |
1991年 | 42篇 |
1990年 | 22篇 |
1989年 | 24篇 |
1988年 | 22篇 |
1987年 | 17篇 |
1986年 | 11篇 |
1985年 | 31篇 |
1984年 | 30篇 |
1983年 | 25篇 |
1982年 | 24篇 |
1981年 | 18篇 |
1980年 | 23篇 |
1979年 | 13篇 |
1978年 | 28篇 |
1977年 | 14篇 |
1976年 | 18篇 |
1975年 | 17篇 |
1974年 | 8篇 |
1972年 | 8篇 |
1968年 | 11篇 |
排序方式: 共有1986条查询结果,搜索用时 15 毫秒
101.
102.
Dr. Andreas Lerchen Dr. Narasimhulu Gandhamsetty Elliot H. E. Farrar Dr. Nils Winter Dr. Johannes Platzek Dr. Matthew N. Grayson Prof. Dr. Varinder K. Aggarwal 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(51):23307-23311
(−)-Finerenone is a nonsteroidal mineralocorticoid receptor antagonist currently in phase III clinical trials for the treatment of chronic kidney disease in type 2 diabetes. It contains an unusual dihydronaphthyridine core. We report a 6-step synthesis of (−)-finerenone, which features an enantioselective partial transfer hydrogenation of a naphthyridine using a chiral phosphoric acid catalyst with a Hantzsch ester. The process is complicated by the fact that the naphthyridine exists as a mixture of two atropisomers that react at different rates and with different selectivities. The intrinsic kinetic resolution was converted into a kinetic dynamic resolution at elevated temperature, which enabled us to obtain (−)-finerenone in both high yield and high enantioselectivity. DFT calculations have revealed the origin of selectivity. 相似文献
103.
Lenard Hanf Jonas Henschel Marcel Diehl Martin Winter Sascha Nowak 《Electrophoresis》2020,41(9):697-704
A new CE method with ultraviolet–visible detection was developed in this study to investigate manganese dissolution in lithium ion battery electrolytes. The aqueous running buffer based on diphosphate showed excellent stabilization of labile Mn3+, even under electrophoretic conditions. The method was optimized regarding the concentration of diphosphate and modifier to obtain suitable signals for quantification. Additionally, the finally obtained method was applied on carbonate-based electrolytes samples. Dissolution experiments of the cathode material LiNi0.5Mn1.5O4 (lithium nickel manganese oxide [LNMO]) in aqueous diphosphate buffer at defined pH were performed to investigate the effect of a transition metal-ion-scavenger on the oxidation state of dissolved manganese. Quantification of both Mn species revealed the formation of mainly Mn3+, which can be attributed to a comproportionation reaction of dissolved and complexed Mn2+ with Mn4+ at the surface of the LNMO structure. It was also shown that the formation of Mn3+ increased with lower pH. In contrast, dissolution experiments of LNMO in carbonate-based electrolytes containing LIPF6 showed only dissolution of Mn2+. 相似文献
104.
Zian Tang Dr. Antony George Dr. Andreas Winter David Kaiser Christof Neumann Dr. Thomas Weimann Prof. Dr. Andrey Turchanin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(29):6473-6478
Field effect transistors (FETs) based on 2D materials are of great interest for applications in ultrathin electronic and sensing devices. Here we demonstrate the possibility to add optical switchability to graphene FETs (GFET) by functionalizing the graphene channel with optically switchable azobenzene molecules. The azobenzene molecules were incorporated to the GFET channel by building a van der Waals heterostructure with a carbon nanomembrane (CNM), which is used as a molecular interposer to attach the azobenzene molecules. Under exposure with 365 nm and 455 nm light, azobenzene molecules transition between cis and trans molecular conformations, respectively, resulting in a switching of the molecular dipole moment. Thus, the effective electric field acting on the GFET channel is tuned by optical stimulation and the carrier density is modulated. 相似文献
105.
Marlon Winter Niklas Limberg Dr. Mathias A. Ellwanger Dr. Alberto Pérez-Bitrián Dr. Karsten Sonnenberg Dr. Simon Steinhauer Prof. Dr. Sebastian Riedel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(68):16089-16097
Trifluoromethylation of [AuF3(SIMes)] with the Ruppert–Prakash reagent TMSCF3 in the presence of CsF yields the product series [Au(CF3)xF3−x(SIMes)] (x=1–3). The degree of trifluoromethylation is solvent dependent and the ratio of the species can be controlled by varying the stoichiometry of the reaction, as evidenced from the 19F NMR spectra of the corresponding reaction mixtures. The molecular structures in the solid state of trans-[Au(CF3)F2(SIMes)] and [Au(CF3)3(SIMes)] are presented, together with a selective route for the synthesis of the latter complex. Correlation of the calculated SIMes affinity with the carbene carbon chemical shift in the 13C NMR spectrum reveals that trans-[Au(CF3)F2(SIMes)] and [Au(CF3)3(SIMes)] nicely follow the trend in Lewis acidities of related organo gold(III) complexes. Furthermore, a new correlation between the Au−Ccarbene bond length of the molecular structure in the solid state and the chemical shift of the carbene carbon in the 13C NMR spectrum is presented. 相似文献
106.
107.
Benedikt Nowak Oskar Karlström Peter Backman Anders Brink Maria Zevenhoven Severin Voglsam Franz Winter Mikko Hupa 《Journal of Thermal Analysis and Calorimetry》2013,111(1):183-192
In order to determine the intrinsic reactivity behavior from thermogravimetry studies, the experimental conditions should be such that the reactions are not mass transfer limited. Biomass char usually has a higher reactivity than coal chars. Therefore, mass transfer limitations may be more problematic when studying biomass char reactivity. Chemical reaction kinetics and mass transfer processes present in thermogravimetry are used for modeling the overall reaction rate for spruce bark CO2 gasification. Thermogravimetric experiments are carried out between 700 and 900 °C, and the CO2 concentration is varied between 10 and 90 vol%. The intrinsic activation energy is found to be 120 kJ mol?1. The transition temperature between regimes I and II is here defined when the fraction apparent to true activation energy equals 0.75. Higher external mass transfer (e.g., by decreasing the diffusion path through the crucible’s freeboard), decreasing the sample amounts, and higher CO2 partial pressures for the Langmuir–Hinshelwood reaction type increase the transition temperature. The results show that the transition temperature between regimes I and II conditions is approx. 1,030 °C for 90 vol% CO2. 相似文献
108.
Stable [C5H5Ni(NN)]BF4 complexes are formed by treatment of [C5H5Ni(SR2)2]BF4 (R = CH3) with some 1,2-diaminoalkylidenes NN; Chemical and spectroscopic properties are reported. 相似文献
109.
110.