全文获取类型
收费全文 | 78770篇 |
免费 | 5619篇 |
国内免费 | 5503篇 |
专业分类
化学 | 39995篇 |
晶体学 | 631篇 |
力学 | 4177篇 |
综合类 | 1134篇 |
数学 | 16725篇 |
物理学 | 27230篇 |
出版年
2024年 | 102篇 |
2023年 | 625篇 |
2022年 | 1286篇 |
2021年 | 2436篇 |
2020年 | 1760篇 |
2019年 | 1815篇 |
2018年 | 1584篇 |
2017年 | 1821篇 |
2016年 | 2130篇 |
2015年 | 1887篇 |
2014年 | 2798篇 |
2013年 | 5180篇 |
2012年 | 3337篇 |
2011年 | 3612篇 |
2010年 | 3110篇 |
2009年 | 4379篇 |
2008年 | 4675篇 |
2007年 | 5081篇 |
2006年 | 4057篇 |
2005年 | 3136篇 |
2004年 | 2742篇 |
2003年 | 2871篇 |
2002年 | 5325篇 |
2001年 | 2739篇 |
2000年 | 2423篇 |
1999年 | 2033篇 |
1998年 | 2008篇 |
1997年 | 1253篇 |
1996年 | 1269篇 |
1995年 | 1107篇 |
1994年 | 1149篇 |
1993年 | 997篇 |
1992年 | 1043篇 |
1991年 | 700篇 |
1990年 | 664篇 |
1989年 | 538篇 |
1988年 | 527篇 |
1987年 | 439篇 |
1986年 | 420篇 |
1985年 | 485篇 |
1984年 | 424篇 |
1983年 | 253篇 |
1982年 | 426篇 |
1981年 | 618篇 |
1980年 | 508篇 |
1979年 | 545篇 |
1978年 | 439篇 |
1977年 | 353篇 |
1976年 | 273篇 |
1973年 | 182篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
The thermodynamic model of inorganic arsenic was validated by comparing the predicted As(III) concentration with the experimentally determined one in several river waters samples of the Basque Country (Spain) collected in two sampling campaigns: spring and autumn 2000. This model takes into account the acid-base equilibria of As(III) and As(V) together with the redox equilibria between the H3AsO3 and H3AsO4 species. A correct prediction of As(III) concentration requires the knowledge of the total concentration of arsenic, pH, redox potential (referred to hydrogen electrode), and ionic strength values of the solution. The estimation of the activity coefficients of the arsenic species was performed by means of the Modified Bromley’s Methodology (MBM).In order to perform the experimental As(III) determination, an analytical method was implemented by using an ion exchange separation of As(III)/As(V) on a continuous FIA-IE-HG-AAS system. The total arsenic concentration was determined together with total concentration of the main alkaline or alkaline-earth metals and anions in the natural waters. Temperature compensated measurements of the pH and redox potentials were made in-situ at the sampling sites.For both seasonal campaigns, the agreement between predicted and experimental As(III) is really high for those samples belonging to non polluted river waters. 相似文献
992.
C. AutretC. Martin A. MaignanM. Hervieu B. RaveauG. André F. Bourée 《Journal of solid state chemistry》2002,165(1):65-73
The Ho0.5Sr0.5MnO3 perovskite, synthesized in air, has been studied by combining neutron powder and electron diffraction techniques. The Pnma-type structure exhibits a strong tilting of the MnO6 octahedra. This octahedra tilting and microtwinning involve a complex strained structure. No structural transition is observed down to 1.4 K, but short-range A-type antiferromagnetism running over only a few perovskite subcells is evidenced below ≈90 K. The different behavior of this perovskite compared to other Ln0.5Sr0.5MnO3 perovskites is discussed in terms of A-site cationic mismatch. 相似文献
993.
Stability constants of the ternary complexes [CuAL] whereA = 5-Nitro-1,10-phenanthroline, bis(2-pyridyl) ketone (DPK) orbis(2-pyridyl)amine (DPA) andL is the dianion of catechol, tiron, protocatechic acid, pyrogallol, 1,8-dihydroxynaphthalene, catecholaldehyde, 2,3-dihydroxynaphthalene,
dopamine or adrenaline have been determined by potentiometric titration in dioxane water (1:1 v/v) medium using a SCOGS computer
programme. The observed trend of stability is explained on the basis of the nature of substitution over the ligands, chelate
ring size and also the composition of mixed solvent in case of DPK. Structural changes in DPK have also been discussed as
a function of pH, composition of medium and coordinating mode of the secondary ligand in the ternary complexes. 相似文献
994.
The ultraviolet photoelectron spectra of mono and binuclear cyclooctatetraene (COT) complexes (CO)3FeCOT (I) [(CO)3Fe]2COT (II), CpCrCOT (Cp: 1,3 cyclopentadienyl) (III) and (CpCr)2COT (IV) are reported. The interpretation of the low energy part of the spectra is followed by a discussion concerning the metal–ligand (COT) and metal–metal interactions. The calculated gas phase structure of CpCrCOT is presented and its main features are discussed. 相似文献
995.
Yu. V. Fedorov O. A. Fedorova N. E. Shepel’ S. P. Gromov M. V. Alfimov L. G. Kuz’mina J. A. K. Howard J. Saltiel 《Russian Chemical Bulletin》2005,54(9):2119-2128
Benzobisthiazole-based bis(crown ether) was synthesized and its complexation with alkali and alkaline earth cations was studied.
Photochemical transformations of the free ligand and its complexes with alkaline earth cations involve E,Z-photoisomerization and [2+2] photocycloaddition.
Dedicated to Academician N. S. Zefirov on the occasion of his 70th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2056–2065, September, 2005. 相似文献
996.
A. A. Toropov V. O. Kudyshkin N. L. Voropaeva I. N. Ruban S. Sh. Rashidova 《Journal of Structural Chemistry》2004,45(6):945-950
For a series of monomers, QSPR test analysis is performed by optimizing the correlation weights of the local invariants of molecular graphs representing monomer structures in order to construct models of the reactivity parameters of monomers Q and e. This approach may be used as a tool in reactivity predictions for monomers for which no experimental data on Q and e are available.Original Russian Text Copyright © 2004 by A. A. Toropov, V. O. Kudyshkin, N. L. Voropaeva, I. N. Ruban, and S. Sh. Rashidova__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 6, pp. 994–998, November–December, 2004. 相似文献
998.
999.
Minkin V. I. Gribanova T. N. Starikov A. G. Minyaev R. M. 《Russian Chemical Bulletin》2003,52(3):519-525
The electronic and molecular structure of planar (cyclic and linear) tetra- and hexaatomic clusters (XY)
n
(XY = CC, BN, BeO, LiF; n = 2, 3) was studied using the ab initio CCD(full)/6-311+G** method and density functional approach (B3LYP/6-311+G**). The stability of cyclic clusters C6, B3N3, and Be3O3 with D3h
symmetry is mainly determined by the aromaticity of their -electron systems. 相似文献
1000.