全文获取类型
收费全文 | 1591篇 |
免费 | 33篇 |
国内免费 | 7篇 |
专业分类
化学 | 1111篇 |
晶体学 | 6篇 |
力学 | 13篇 |
数学 | 270篇 |
物理学 | 231篇 |
出版年
2021年 | 13篇 |
2020年 | 17篇 |
2019年 | 15篇 |
2016年 | 24篇 |
2015年 | 33篇 |
2014年 | 32篇 |
2013年 | 62篇 |
2012年 | 29篇 |
2011年 | 37篇 |
2010年 | 37篇 |
2009年 | 38篇 |
2008年 | 76篇 |
2007年 | 53篇 |
2006年 | 71篇 |
2005年 | 54篇 |
2004年 | 46篇 |
2003年 | 57篇 |
2002年 | 55篇 |
2001年 | 40篇 |
2000年 | 32篇 |
1999年 | 30篇 |
1998年 | 27篇 |
1997年 | 25篇 |
1996年 | 29篇 |
1995年 | 28篇 |
1994年 | 45篇 |
1993年 | 39篇 |
1992年 | 52篇 |
1991年 | 22篇 |
1990年 | 16篇 |
1989年 | 21篇 |
1988年 | 23篇 |
1987年 | 34篇 |
1986年 | 27篇 |
1985年 | 25篇 |
1984年 | 24篇 |
1983年 | 29篇 |
1982年 | 24篇 |
1981年 | 16篇 |
1980年 | 21篇 |
1979年 | 22篇 |
1978年 | 29篇 |
1977年 | 17篇 |
1976年 | 12篇 |
1975年 | 17篇 |
1974年 | 25篇 |
1973年 | 20篇 |
1972年 | 16篇 |
1971年 | 21篇 |
1970年 | 12篇 |
排序方式: 共有1631条查询结果,搜索用时 15 毫秒
121.
122.
Matthes J Pery T Gründemann S Buntkowsky G Sabo-Etienne S Chaudret B Limbach HH 《Journal of the American Chemical Society》2004,126(27):8366-8367
Some transition metal complexes are known to catalyze ortho/para hydrogen conversion, hydrogen isotope scrambling, and hydrogenation reactions in liquid solution. Using the example of Vaska's complex, we present here evidence by NMR that the solvent is not necessary for these reactions to occur. Thus, solid frozen solutions or polycrystalline powdered samples of homogeneous catalysts may become heterogeneous catalysts. Comparative liquid- and solid-state studies provide novel insight into the reaction mechanisms. 相似文献
123.
Caesium heptaiodo‐dititanate(III), CsTi2I7, is obtained from CsI, Ti and TiI4 at 250 °C in a sealed tantalum ampoule as dark red single crystals. The crystal structure (trigonal, R‐3, a = 1706.6(3), c = 2088.3(5) pm, Z = 12, R1 = 0.0619) contains [TiI4] tetrahedra sharing common vertices (with Ti—I—Ti angles of 180°) to isolated ditetrahedra [Ti2I7]—. It may also be described as a cubic closest packing of alternating CsI3 and I4 layers between which neighbouring tetrahedra are occupied in a way that [Ti2I7]— ditetrahedra are achieved. http://www.gerdmeyer.de 相似文献
124.
From a range of preparative methods, three geometric isomers of bis(diphenylarsino)methane‐dichloroplatinum(II) have been isolated, viz. cis‐PtCl2(dpam), trans, trans‐Pt2Cl4(dpam)2 and cis, trans‐Pt2Cl4(dpam)2. Their structures were determined by single‐crystal X‐ray diffraction. 相似文献
125.
Colourless single crystals of the caffeine adduct of mercurous perchlorate dihydrate, [Hg2(Caf)2](ClO4)2(H2O)2, were grown from aqueous solutions of mercurous perchlorate and caffeine by isothermal evaporation at ambient temperature. The crystal structure (monoclinic, P21/n, Z = 4, a = 1628.0(2), b = 780.4(1), c = 2229.6(3) pm, β = 99.84(1)°, R1(all data) = 0.0894) contains [trans‐Caf‐Hg‐Hg‐Caf]2+ cations with a Hg‐Hg distance of 250.88(6) pm, Hg‐N (bond) distances of 214.4(6) and 215.1(6) pm and Hg‐Hg‐N angles of 176.9(2) and 165.1(2)°, respectively. These cations are attached via weak Hg‐O contacts to dimers which are further arranged to leave large channels into which one crystal water molecule is included. The second water molecule and the two perchlorate anions are weakly attracted to one Hg atom. 相似文献
126.
Ko YJ Shakya A Wang H Grubisic A Zheng W Götz M Ganteför G Bowen KH Jena P Kiran B 《The Journal of chemical physics》2010,133(12):124308
The equilibrium structure, stability, and electronic properties of the Al(13)X (X=H,Au,Li,Na,K,Rb,Cs) clusters have been studied using a combination of photoelectron spectroscopy experiment and density functional theory. All these clusters constitute 40 electron systems with 39 electrons contributed by the 13 Al atoms and 1 electron contributed by each of the X (X=H,Au,Li,Na,K,Rb,Cs) atom. A systematic study allows us to investigate whether all electrons contributed by the X atoms are alike and whether the structure, stability, and properties of all the magic clusters are similar. Furthermore, quantitative agreement between the calculated and the measured electron affinities and vertical detachment energies enable us to identify the ground state geometries of these clusters both in neutral and anionic configurations. 相似文献
127.
Anna Grünberg Dr. Xu Yeping Dr. Hergen Breitzke Dr. Gerd Buntkowsky Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(23):6993-6998
The Wilkinson’s catalyst [RhCl(PPh3)3] has been immobilized inside the pores of amine functionalized mesoporous silica material SBA‐3 and The structure of the modified silica surface and the immobilized rhodium complex was determined by a combination of different solid‐state NMR methods. The successful modification of the silica surface was confirmed by 29Si CP‐MAS NMR experiments. The presence of the Tn peaks confirms the successful functionalization of the support and shows the way of binding the organic groups to the surface of the mesopores. 31P‐31P J‐resolved 2D MAS NMR experiments were conducted in order to characterize the binding of the immobilized catalyst to the amine groups of the linkers attached to the silica surface. The pure catalyst exhibits a considerable 31P‐31P J‐coupling, well resolvable in 2D MAS NMR experiments. This J‐coupling was utilized to determine the binding mode of the catalyst to the linkers on the silica surface and the number of triphenylphosphine ligands that are replaced by coordination bonds to the amine groups. From the absence of any resolvable 31P‐31P J‐coupling in off‐magic‐angle‐spinning experiments, as well as slow‐spinning MAS experiments, it is concluded, that two triphenylphosphine ligands are replaced and that the catalyst is bonded to the silica surface through two linker molecules. 相似文献
128.
Thomas Schwarze Wulfhard Mickler Dr. Carsten Dosche Dr. Roman Flehr Tillmann Klamroth Dr. Hans‐Gerd Löhmannsröben Prof. Dr. Peter Saalfrank Prof. Dr. Hans‐Jürgen Holdt Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(6):1819-1825
Fluoroionophores of fluorophore–spacer–receptor format were prepared for detection of PdCl2 by fluorescence enhancement. The fluorescent probes 1 – 13 consist of a fluorophore group, an alkyl spacer and a dithiomaleonitrile PdCl2 receptor. First, varying the length of the alkylene spacer (compounds 1 – 3 ) revealed a dominant through‐space pathway for oxidative photoinduced electron transfer (PET) in CH2‐bridged dithiomaleonitrile fluoroionophores. Second, fluorescent probes 4 – 9 containing two anthracene or pyrene fragments connected through CH2 bridges to the dithiomaleonitrile unit were synthesized. Modulation of the oxidation potential (EOx) through electron‐withdrawing or ‐donating groups on the anthracene moiety regulates the thermodynamic driving force for oxidative PET (ΔGPET) in bis(anthrylmethylthio)maleonitriles and therefore the fluorescence quantum yields (Φf), too. The new concept was confirmed and transferred to pyrenyl ligands, and fluorescence enhancements (FE) greater than 3.2 in the presence of PdCl2 were achieved by 7 and 8 (FE=5.4 and 5.2). Finally, for comparison, monofluorophore ligands 10 – 13 were synthesized. 相似文献
129.
130.
Koen Sandra Alberto dos Santos Pereira Gerd Vanhoenacker Frank David Pat Sandra 《Journal of chromatography. A》2010,1217(25):4087-4099
A lipidomics strategy, combining high resolution reversed-phase liquid chromatography (RPLC) with high resolution quadrupole time-of-flight mass spectrometry (QqTOF), is described. The method has carefully been assessed in both a qualitative and a quantitative fashion utilizing human blood plasma. The inherent low technical variability associated with the lipidomics method allows to measure 65% of the features with an intensity RSD value below 10%. Blood plasma lipid spike-in experiments demonstrate that relative concentration differences smaller than 25% can readily be revealed by means of a t-test. Utilizing an advanced identification strategy, it is shown that the detected features mainly originate from (lyso-)phospholipids, sphingolipids, mono-, di- and triacylglycerols and cholesterol esters. The high resolution offered by the up-front RPLC step further allows to discriminate various isomeric species associated with the different lipid classes. The added value of utilizing a Jetstream electrospray ionization (ESI) source over a regular ESI source in lipidomics is for the first time demonstrated. In addition, the application of ultra high performance LC (UHPLC) up to 1200 bar to extend the peak capacity or increase productivity is discussed. 相似文献