全文获取类型
收费全文 | 465篇 |
免费 | 17篇 |
专业分类
化学 | 413篇 |
晶体学 | 1篇 |
力学 | 4篇 |
数学 | 24篇 |
物理学 | 40篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 11篇 |
2020年 | 8篇 |
2019年 | 21篇 |
2018年 | 13篇 |
2017年 | 9篇 |
2016年 | 15篇 |
2015年 | 15篇 |
2014年 | 14篇 |
2013年 | 45篇 |
2012年 | 30篇 |
2011年 | 31篇 |
2010年 | 30篇 |
2009年 | 20篇 |
2008年 | 30篇 |
2007年 | 21篇 |
2006年 | 21篇 |
2005年 | 23篇 |
2004年 | 21篇 |
2003年 | 19篇 |
2002年 | 18篇 |
2001年 | 18篇 |
2000年 | 6篇 |
1999年 | 4篇 |
1998年 | 5篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1976年 | 2篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1959年 | 2篇 |
1957年 | 1篇 |
1956年 | 1篇 |
1955年 | 1篇 |
1937年 | 1篇 |
1934年 | 2篇 |
1933年 | 2篇 |
排序方式: 共有482条查询结果,搜索用时 218 毫秒
71.
Alexander L. Rusanov Ludmila G. Komarova Tatyana S. Sheveleva Marina P. Prigozhina Svyatoslav A. Shevelev Michai L. D. Dutov Irina A. Vatsadze Olga V. Serushkina 《Macromolecular Symposia》1997,122(1):123-128
New aromatic diamines were obtained on the basis of available and inexpensive 2, 4, 6-trinitrotoluene (trotyl, TNT). Monomers obtained were used for the preparation of the new organo-soluble polyimides containing thiophenoxy and phenoxy side groups. 相似文献
72.
Alexander S. Lyakhov Pavel N. Gaponik Michail M. Degtyarik Ludmila S. Ivashkevich 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(6):m204-m206
In the polymeric title complex, [CuCl2(C3H6N4)2]n, there are two ligands in the asymmetric unit. The Cu atom adopts an elongated octahedral geometry, with two 2‐ethyltetrazole ligands [Cu—N = 2.0037 (16) and 2.0136 (16) Å] and two Cl atoms [Cu—Cl = 2.2595 (6) and 2.2796 (6) Å] in equatorial positions. A Cl atom and a symmetry‐related 2‐ethyltetrazole molecule [Cu—Cl = 2.8845 (8) Å and Cu—N = 2.851 (2) Å] lie in the axial positions of the octahedron. One of the two 2‐ethyltetrazole ligands of the asymmetric unit exhibits bidentate binding to two Cu atoms through two N atoms of the tetrazole ring, whereas the other ligand is coordinated in a monodentate fashion via one tetrazole N atom. The Cu‐atom octahedra form dimer entities by sharing edges with equatorial and axial Cl atoms. The dimers are linked together through the 2‐ethyltetrazole ligands to form one‐dimensional polymeric zigzag chains extending along the b axis. The chains are connected into infinite layers parallel to the (10) plane via the 2‐ethyltetrazole ligands. 相似文献
73.
Alexander D. Vasiliev Alexander M. Astachov Maxim S. Molokeev Ludmila A. Kruglyakova Rudolf S. Stepanov 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(9):o499-o501
The molecule of the title compound, C3H5N5O4, has a planar geometry. Due to the presence of a second nitro group, the lengths of the two conjugated C—N bonds are different. Nevertheless, the conjugation of the nitrimine group spreads to the nitramine group. Intermolecular N—H...O bonds connect molecules into dimers in the crystal structure. 相似文献
74.
Alexander D. Vasiliev Alexander M. Astachov Maxim S. Molokeev Ludmila A. Kruglyakova Rudolf S. Stepanov 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(10):o550-o552
The title compound, CH3N5O4, is almost planar, and the conformation is fixed by two intramolecular N—H⋯O hydrogen bonds. Owing to the delocalization of π‐electron density over the whole molecule, there is through‐conjugation, with the C—N, N—N and N—O bond lengths having values intermediate between those typical for the corresponding single and double bonds. 相似文献
75.
Carlos A. Crdoba Ludmila I. Ronco Celina E. Barrios Luis M. Gugliotta Roque J. Minari 《大分子反应工程》2019,13(2)
Miniemulsion polymerization is employed to produce high solid content (50%) acrylic/melamine latexes with varied crosslinking capability, for their potential application as waterborne crosslinkable coatings. This synthesis strategy allows the efficient incorporation of a hydrophobic crosslinker, iso‐butylated melamine (iBMF), into polymer particles, and to obtain latexes with different iBMF concentrations and acrylic polymer with varied content of hydroxylic groups (OH–). The involved crosslinking mechanisms and the physical transformations during film thermosetting of acrylic/iBMF nanocomposite are exhaustively investigated by combining thermal, spectroscopic, and thermo‐mechanical analyses. The influence of reactive groups concentration (iBMF and OH– content in the acrylic polymer) on the rate of curing, the crosslinking degree, and consequently onto the sensitive properties of cured films are discussed here. 相似文献
76.
Jony Javorski Eckert Fabio Mazzariol Santiciolli Elvis Bertoti Eduardo dos Santos Costa Fernanda Cristina Corrêa Ludmila Corrêa de Alkmin e Silva 《基于设计的结构力学与机械力学》2018,46(2):238-253
In the present work, the Adaptive-Weight Genetic Algorithm was employed in order to determine the gear shifting strategies that allow an automobile to work in the best compromise among fuel consumption, engine emissions, and vehicle performance. For the assessment of each of the three objective functions, a simulation model based on engine data and on the well-established equations of the longitudinal dynamics was developed. The driving cycle chosen for the calculations was the FTP-75, which takes into account both cold and hot starts, meaning that the transient operation during the warm-up of the catalyst is also considered. 相似文献
77.
Didier Gastmans Vinícius Santos Juliana Aparecida Galhardi João Felipe Gromboni Ludmila Vianna Batista Konrad Miotlinski 《Isotopes in environmental and health studies》2017,53(5):518-538
Based on Global Network Isotopes in Precipitation (GNIP) isotopic data set, a review of the spatial and temporal variability of δ18O and δ2H in precipitation was conducted throughout central and eastern Brazil, indicating that dynamic interactions between Intertropical and South Atlantic Convergence Zones, Amazon rainforest, and Atlantic Ocean determine the variations on the isotopic composition of precipitation over this area. Despite the seasonality and latitude effects observed, a fair correlation with precipitation amount was found. In addition, Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) air mass back trajectories were used to quantify the factors controlling daily variability in stable isotopes in precipitation. Through a linear multiple regression analysis, it was observed that temporal variations were consistent with the meteorological parameters derived from HYSPLIT, particularly precipitation amount along the trajectory and mix depth, but are not dependent on vapour residence time in the atmosphere. These findings also indicate the importance of convective systems to control the isotopic composition of precipitation in tropical and subtropical regions. 相似文献
78.
Mikhail A. Matsko Ludmila G. Echevskaya Vladimir A. Zakharov Marina I. Nikolaeva Tatyana B. Mikenas Marina P. Vanina 《Macromolecular Symposia》2009,282(1):157-166
Summary: Heterogeneity of active centers (AC) of titanium-magnesium catalysts (TMC) and vanadium-magnesium catalyst (VMC) in ethylene-hexene-1 copolymerization has been studied on the base of data of polymer molecular weight distribution (MWD) deconvolution technique and copolymer fractionation onto narrow fractions. It was found that 3 and 4 Flory components (groups of active centers) are required to describe experimental MWD curves of copolymers produced over TMC with different Ti content. In the case of VMC MWD of homopolymer and copolymer are characterized by set of 5 Flory components (5 groups of AC). Different character of inter-relationship between MW and short chain branching (SCB) was found for ethylene-hexene-1 copolymers produced over different catalysts: heterogeneous type in the case of TMC and more uniform for copolymer prepared over VMC. The content of Ti affects on the slope of that profile in copolymers produced over TMC. The results indicated that TMC and VMC are different greatly on the heterogeneity of active centers to the formation of polymers with different molecular weights and to formation of copolymers with different inter-relationship between MW and short chain branching. TMC produces polymers with more narrow MWD but it contains highly heterogeneous centers regarding comonomer reactivity ratios. VMC produces polymers with broad and bimodal MWD but it contains more homogeneous centers regarding comonomer reactivity ratios. 相似文献
79.
Ludmila Hejtmánková Josef Jirman Miloš Sedlák 《Research on Chemical Intermediates》2009,35(5):615-623
The paper deals with a simple and sufficient synthesis of key precursor of Lasofoxifene. The 1-(4-benzyloxyphenyl)-6-methoxy-2-phenyl-3,4-dihydronaphthalene was prepared by a sequence of five reactions steps: first 1-(4-benzyloxyphenyl)-6-methoxy-3,4-dihydronaphthalene
was prepared (70%), and this was quantitatively epoxidized to 7b-[4-(benzyloxy)phenyl]-5-methoxy-1a,2,3,7b-tetrahydronaphtho[1,2-b]oxirene. Catalytic (ZnI2) isomerization of the epoxide gave 1-(4-benzyloxyphenyl)-6-methoxy-1,2,3,4-tetrahydronaphthalen-2-one (75%). Its subsequent
reaction with phenylmagnesium bromide gave 1-(4-benzyloxyphenyl)-6-methoxy-2-phenyl-1,2,3,4-tetrahydro-2-naphthol (87%). Acid-catalysed
dehydration of this alcohol by polyphosphoric acid (25°C) provides 1-(4-benzyloxyphenyl)-6-methoxy-2-phenyl-1,4-dihydronaphthalene (80%). Dehydration in the system of acetic anhydride/polyphosphoric acid gives 1-(4-benzyloxyphenyl)-6-methoxy-2-phenyl-3,4-dihydronaphthalene (66%). 相似文献
80.
Semi-Lagrangian semi-implicit (SLSI) method is currently one of the most efficient approaches for numerical solution of the atmosphere dynamics equations. In this research we apply splitting techniques in the context of a two-time-level SLSI scheme in order to simplify the treatment of the slow physical modes and optimize the solution of the elliptic equations related to implicit part of the scheme. The performed numerical experiments show the accuracy and computational efficiency of the scheme. 相似文献