全文获取类型
收费全文 | 1442篇 |
免费 | 18篇 |
国内免费 | 18篇 |
专业分类
化学 | 997篇 |
晶体学 | 25篇 |
力学 | 25篇 |
数学 | 245篇 |
物理学 | 186篇 |
出版年
2023年 | 8篇 |
2022年 | 8篇 |
2021年 | 10篇 |
2020年 | 18篇 |
2019年 | 8篇 |
2018年 | 6篇 |
2017年 | 8篇 |
2016年 | 22篇 |
2015年 | 18篇 |
2014年 | 20篇 |
2013年 | 66篇 |
2012年 | 62篇 |
2011年 | 86篇 |
2010年 | 46篇 |
2009年 | 51篇 |
2008年 | 101篇 |
2007年 | 104篇 |
2006年 | 88篇 |
2005年 | 67篇 |
2004年 | 70篇 |
2003年 | 77篇 |
2002年 | 81篇 |
2001年 | 27篇 |
2000年 | 33篇 |
1999年 | 23篇 |
1998年 | 21篇 |
1997年 | 18篇 |
1996年 | 34篇 |
1995年 | 12篇 |
1994年 | 17篇 |
1993年 | 11篇 |
1992年 | 19篇 |
1991年 | 9篇 |
1989年 | 12篇 |
1987年 | 6篇 |
1986年 | 11篇 |
1985年 | 17篇 |
1984年 | 13篇 |
1983年 | 7篇 |
1982年 | 18篇 |
1981年 | 26篇 |
1980年 | 13篇 |
1979年 | 19篇 |
1978年 | 18篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1975年 | 10篇 |
1974年 | 7篇 |
1973年 | 5篇 |
1972年 | 5篇 |
排序方式: 共有1478条查询结果,搜索用时 15 毫秒
991.
Stefan Köcher Gerard P.M. van Klink Gerard van Koten Heinrich Lang 《Journal of organometallic chemistry》2006,691(19):3955-3961
Ferrocene-bridged NCN pincer complexes of structural type Fe(η5-C5H4-4-NCN-1-MX)2 (X = I: 6, M = Pd; 7, M = Pt; X = Cl: 8, M = Pt; NCN = [4-C6H2(CH2NMe2)2-2,6]−) are accessible by the subsequent reaction of Fe(η5-C5H4-4-NCNH)2 (4) with nBuLi and [PtCl2(SEt2)2] (synthesis of 8) or treatment of Fe(η5-C5H4-4-NCN-1-I)2 (5) with [Pd2(dba)3] (synthesis of 6) or [Pt(tol)2(SEt2)]2 (synthesis of 7) (dba = dibenzylidene acetone, tol = 4-tolyl). In addition, the Sonogashira cross-coupling of Fe(η5-C5H4I)2 (1) with HCC-4-NCNH (2) gives Fe(η5-C5H4-CC-4-NCNH)2 (3). The reaction behavior of 3 towards tBuLi is reported as well.Cyclovoltammetric studies show that the ferrocene entity can be oxidized reversibly. The Fe(II)/Fe(III) potential decreases with increasing electron density at the NCN pincer units due to the presence of the M-halide moiety (M = Pd, Pt).The solid state structure of Fe(η5-C5H4-4-NCN-1-PdI)2 (6) is presented. In 6 the Fe(η5-C5H4)2 unit connects two NCN-PdI pincer entities with palladium in a square-planar environment. The cyclopentadienyl ligands show a staggered conformation. The C6H2 rings are tilted by 23.5(3)° towards the C5H4 entities and the C6H2 plane is almost coplanar with the coordination plane (10.3(3)°). 相似文献
992.
Paz Vaqueiro Gerard G. Sobany Kevin S. Knight 《Journal of solid state chemistry》2006,179(7):2047-2053
The skutterudite-related material CoGe1.5Te1.5 has been synthesised and structurally characterised by powder neutron diffraction. Analysis of the high-resolution powder neutron diffraction data indicates that the structure of CoGe1.5Te1.5 retains the a+a+a+ tilt system of the ideal skutterudite structure, while the anions are ordered in layers perpendicular to the [111] direction of the skutterudite unit cell. This anion ordering results in a lowering of the symmetry from cubic to rhombohedral (space group , a=12.3270(5) and c=15.102(1) Å at 293 K). The electrical transport properties have been investigated using four-probe resistivity and Seebeck coefficient measurements. The temperature dependence of the electrical resistivity and the magnitude of the Seebeck coefficient indicate that CoGe1.5Te1.5 is an n-type semiconductor. 相似文献
993.
994.
Hu X Spada S White S Hudson S Magner E Wall JG 《The journal of physical chemistry. B》2006,110(37):18703-18709
The adsorption of an anti-domoic acid single-chain Fv (scFv) antibody fragment onto a range of mesoporous silicate supports was investigated. The scFv fragment adsorbed to all materials investigated, and pI had an apparently large effect on coating, with the greatest-and fastest-adsorption found on the most negatively charged silicates. Maximal coating levels attainable did not reflect the pore diameters of the materials. The immobilized antibody was functional on all materials and bound its antigen, a naturally occurring neurotoxin produced by shellfish, in a rapidly saturating manner that suggested the antibody adsorbed in a multilayer on the mesoporous particles. The antigen:antibody ratio decreased from 1:1.3 to <1:10 with increasing concentration of immobilized antibody, and the immobilized scFv exhibited no detectable reduction in domoic acid binding over a 42-day incubation period. 相似文献
995.
Fiora Rosati Arnold J. Boersma Jaap E. Klijn Dr. Auke Meetsma Ben L. Feringa Prof. Gerard Roelfes Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(37):9596-9605
The recently developed concept of DNA‐based asymmetric catalysis involves the transfer of chirality from the DNA double helix in reactions using a noncovalently bound catalyst. To date, two generations of DNA‐based catalysts have been reported that differ in the design of the ligand for the metal. Herein we present a study of the first generation of DNA‐based catalysts, which contain ligands comprising a metal‐binding domain linked through a spacer to a 9‐aminoacridine moiety. Particular emphasis has been placed on determining the effect of DNA on the structure of the CuII complex and the catalyzed Diels–Alder reaction. The most important findings are that the role of DNA is limited to being a chiral scaffold; no rate acceleration was observed in the presence of DNA. Furthermore, the optimal DNA sequence for obtaining high enantioselectivities proved to contain alternating GC nucleotides. Finally, DNA has been shown to interact with the CuII complex to give a chiral structure. Comparison with the second generation of DNA‐based catalysts, which bear bipyridine‐type ligands, revealed marked differences, which are believed to be related to the DNA microenvironment in which the catalyst resides and where the reaction takes place. 相似文献
996.
Lucy Rutten Dr. Birgit Wieczorek Jean‐Paul B. A. Mannie Cornelis A. Kruithof Dr. Harm P. Dijkstra Dr. Maarten R. Egmond Prof. Martin Lutz Dr. Robertus J. M. Klein Gebbink Prof. Piet Gros Prof. Gerard van Koten Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(17):4270-4280
Crystal‐clear structures : The first crystal structures of organometallic pincer–cutinase hybrids (see figure) provide insight into the 3D structural arrangement of both the protein and the organometallic pincer moiety, and reveal different binding modes for different pincers.
997.
Let j≥k≥0 be integers. An ?-L(j,k)-labelling of a graph G=(V,E) is a mapping ?:V→{0,1,2,…,?} such that |?(u)−?(v)|≥j if u,v are adjacent and |?(u)−?(v)|≥k if they are distance two apart. Let λj,k(G) be the smallest integer ? such that G admits an ?-L(j,k)-labelling. Define to be the smallest ? if G admits an ?-L(j,k)-labelling with ?(V)={0,1,2,…,?} and ∞ otherwise. An ?-cyclic L(j,k)-labelling is a mapping ?:V→Z? such that |?(u)−?(v)|?≥j if u,v are adjacent and |?(u)−?(v)|?≥k if they are distance two apart, where |x|?=min{x,?−x} for x between 0 and ?. Let σj,k(G) be the smallest ?−1 of such a labelling, and define similarly to . We determine λ2,0, , σ2,0 and for all Hamming graphs Kq1□Kq2□?□Kqd (d≥2, q1≥q2≥?≥qd≥2) and give optimal labellings, with the only exception being for q≥4. We also prove the following “sandwich theorem”: If q1 is sufficiently large then for any graph G between Kq1□Kq2 and Kq1□Kq2□?□Kqd, and moreover we give a labelling which is optimal for these eight invariants simultaneously. 相似文献
998.
Zieger PC van de Meerakker SY Heiner CE Bethlem HL van Roij AJ Meijer G 《Physical review letters》2010,105(17):173001
The level of control that one has over neutral molecules in beams dictates their possible applications. Here we experimentally demonstrate that state-selected, neutral molecules can be kept together in a few mm long packet for a distance of over one mile. This is accomplished in a circular arrangement of 40 straight electrostatic hexapoles through which the molecules propagate over 1000 times. Up to 19 packets of molecules have simultaneously been stored in this ring structure. This brings the realization of a molecular low-energy collider within reach. 相似文献
999.
Twenty-three relapsing remitting multiple sclerosis (RRMS) patients and 14 controls were imaged to produce normal-appearing white and grey matter T1 histograms. These were used to assess whether histogram measures from principal component analysis (PCA) and linear discriminant analysis (LDA) out-perform traditional histogram metrics in classification of T1 histograms into control and RRMS subject groups and in correlation with the expanded disability status score (EDSS). The histograms were classified into one of two groups using a leave-one-out analysis. In addition, the patients were scanned serially, and the calculated parameters correlated with the EDSS. The classification results showed that the more complex techniques were at least as good at classifying the subjects as histogram mean, peak height and peak location, with PCA/LDA having success rates of 76% for white matter and 68%/65% for grey matter. No significant correlations were found with EDSS for any histogram parameter. These results indicate that there is much information contained within the grey matter as well as the white matter histograms. Although in these histograms PCA and LDA did not add greatly to the discriminatory power of traditional histogram parameters, they provide marginally better performance, while relying only on data-driven feature selection. 相似文献
1000.
Maxime A. Siegler Sylvestre Bonnet Antoine M. M. Schreurs Robertus J. M. Klein Gebbink Gerard van Koten Anthony L. Spek 《Journal of chemical crystallography》2010,40(9):753-760