全文获取类型
收费全文 | 5335篇 |
免费 | 181篇 |
国内免费 | 12篇 |
专业分类
化学 | 4042篇 |
晶体学 | 51篇 |
力学 | 51篇 |
数学 | 778篇 |
物理学 | 606篇 |
出版年
2021年 | 49篇 |
2020年 | 61篇 |
2019年 | 55篇 |
2018年 | 33篇 |
2017年 | 39篇 |
2016年 | 108篇 |
2015年 | 117篇 |
2014年 | 126篇 |
2013年 | 202篇 |
2012年 | 261篇 |
2011年 | 285篇 |
2010年 | 190篇 |
2009年 | 192篇 |
2008年 | 283篇 |
2007年 | 219篇 |
2006年 | 248篇 |
2005年 | 215篇 |
2004年 | 226篇 |
2003年 | 174篇 |
2002年 | 158篇 |
2001年 | 89篇 |
2000年 | 79篇 |
1999年 | 78篇 |
1998年 | 72篇 |
1997年 | 77篇 |
1996年 | 83篇 |
1995年 | 73篇 |
1994年 | 76篇 |
1993年 | 65篇 |
1992年 | 66篇 |
1991年 | 72篇 |
1990年 | 55篇 |
1989年 | 57篇 |
1988年 | 56篇 |
1987年 | 56篇 |
1986年 | 66篇 |
1985年 | 87篇 |
1984年 | 94篇 |
1983年 | 52篇 |
1982年 | 73篇 |
1981年 | 89篇 |
1980年 | 74篇 |
1979年 | 66篇 |
1978年 | 77篇 |
1977年 | 46篇 |
1976年 | 68篇 |
1975年 | 53篇 |
1973年 | 51篇 |
1971年 | 41篇 |
1970年 | 34篇 |
排序方式: 共有5528条查询结果,搜索用时 12 毫秒
41.
42.
43.
Ulrich Dierkes 《manuscripta mathematica》1986,56(3):313-331
Plateau's problem for surfaces of prescribed mean curvature will be considered in regions which are not necessarily H-convex. 相似文献
44.
Ulrich Schafft 《manuscripta mathematica》1986,57(1):33-48
It is shown that the third Chern-number of a semistable Rk-3-vector bundle on a smooth hypersurface of degree 3 in 4 can be bounded by the first and the second Chern-number of the bundle. 相似文献
45.
Summary Coordination compounds of the S2N2 molecule including methods for their preparation, reactivities, i.r. data, structures, and aspects of chemical bonding are reviewed. Methods of synthesis include reactions of S2N2, S4N4 or (NSCl)3 with metal halides, metal complexes such as carbonyls, or even metals themselves. In all cases, the planar S2N2 ring is coordinated, usuallyvia both, of its nitrogen atoms so that S2N2 acts as a bridging ligand between two metal centres; short contact distances imply that halogen atoms linked to the metal atoms show some interaction with the sulphur atoms. The stability of S2N2 is greatly enhanced by coordination. In the i.r. spectra, two characteristic S2N2 vibrations assist identification of the S2N2 species, a ring stretching mode being observable atca. 850 cm–1 and the out-of-plane deformation at 450–490 cm–1. 相似文献
46.
Dr. Ulrich Mayer 《Monatshefte für Chemie / Chemical Monthly》1978,109(2):421-433
A model has been developed for calculating the enthalpy, entropy and free energy change associated with the creation of cavities in a liquid the size of which corresponds to the volume occupied by a solvent molecule. The molar enthalpy change H
cav equals the molar enthalpy of vaporization of the liquid, the free energy change G
cav is given by G
cav=–RT ln (V
m
·p
eq
/RT) (V
m
=molar volume,p
eq
=equilibrium vapor pressure) and is related to the standard free energy of vaporization. This relationship provides an estimate of the free energy of cavity formation required to accomodate a substrate in the liquid. It has been shown, that the free energy of solvation of a substrate can be dissected into different contributions accounting for (1) the concentration dependence of partial molar free energy quantities, (2) the formation of holes in the solvent, (3) the existence of specific, short range solute-solvent interactions and (4) the dielectric polarization of the medium. Application of this concept leads to an equation of the general form G
S
–G
R
=a(DN
S
–DN
R
)+b(AN
S
–AN
R
)+c(G
vp
oS
–G
vp
oR
), where G represents the free energy of reaction or activation,DN the donor number,AN the acceptor number and G
vp
o
the standard free energy of vaporization of a solventS and a reference solventR, resp.
Mit 3 Abbildungen 相似文献
Mit 3 Abbildungen 相似文献
47.
Different transformations of the functions fixed on a heterocyclic molecule were made. It is thus possible to quickly determine the number of functions of each type present in the molecule: e.g. (i) all the functions are silylated and (ii) the alcohols are acetylated whilst the sulfates and acids are silylated. Mass spectra of atractylate, apoatractylate and gummiferine have been studied and the substituents are counted and enumerated. 相似文献
48.
Ulrich Häussermann Magnus BoströmPer Viklund Östen RappTherese Björnängen 《Journal of solid state chemistry》2002,165(1):94-99
The intermetallic compounds FeGa3 and RuGa3 were prepared from the elements using a Ga flux and their structures were refined from single-crystal X-ray data. Both compounds crystallize with the FeGa3 structure type (tetragonal, space group P42/mnm, Z=4). Electrical resistivity measurements revealed a semiconducting behavior for FeGa3 and RuGa3, which is in contrast to the good metallic conductivity observed for the isotypic compound CoGa3. The origin of the different electronic properties of these materials was investigated by first-principle calculations. It was found that in compounds adopting the FeGa3 structure type the transition metal atoms and Ga atoms interact strongly. This opens a d-p hybridization bandgap with a size of about 0.31 eV in the density of states at the Fermi level for 17-electron compounds (i.e., FeGa3 and RuGa3). The electronic structure of CoGa3 (an 18-electron compound) displays rigid band behavior with respect to FeGa3. As a consequence, the Fermi level in CoGa3 becomes located above the d-p hybridization gap which explains its metallic conductivity. 相似文献
49.
Two protocols for functionalization of glass supports with hexaethylene glycol (HEG)-linked oligonucleotides were developed.
The first method (standard amidite protocol) made use of the 2-cyanoethyl-phosphoramidite derivative of 4,4′-dimethoxytrityl-protected
HEG. This was first coupled to the support by standard solid-phase phosphoramidite chemistry followed by extension with a
thymidylic acid icosanucleotide. Stepwise addition of the linker phosphoramidite graduated at 1% (relative to the total sites
available) perstep at 50°C resulted in an optimal yield of immobilized oligonucleotides at a density of 2.24 × 1010 strands/mm2. This observed loading maximum lies well below the theoretical maximum loading owing to nonspecific adsorption of HEG on
the glass and subsequent blocking of reactive sites. Surface loadings as high as 3.73 × 1010/mm2 and of excellent sequence quality were achieved with a reverse amidite protocol. The support was first modified into a 2-cyanoethyl-N,N-diisopropylphosphoramidite analog followed by coupling with 4,4′-dimethoxytrityl-protected HEG. This protocol is conveniently
available when using a conventional DNA synthesizer. The reverse amidite protocol allowed for control of the surface loading
at values suitable for subsequent analytical applications that make use of immobilized oligonucleotides as probes for selective
hybridization of sample nucleic acids of unknown sequence and concentration. 相似文献
50.
Ulrich Schubert 《Journal of Sol-Gel Science and Technology》2003,26(1-3):47-55
Organically substituted metal alkoxides can be prepared by reaction of the parent alkoxides with complexing organic compounds. The chemical and structural consequences of such substitutions are discussed in this article. Examples are given showing how functional organic moieties, such as polymerizable groups, can be incorporated into sol-gel materials via the complexing ligands. Major structural differences between silica-based and metal-based hybrid materials originate from the different charge/coordination number ratios of silicon and most metals. This results in a high tendency for the molecular building blocks to aggregate. In many cases, metal oxide clusters are formed which are capped by the organic ligands. Such surface-modified clusters are themselves very valuable condensed matter units for materials syntheses. 相似文献