全文获取类型
收费全文 | 97880篇 |
免费 | 5955篇 |
国内免费 | 12081篇 |
专业分类
化学 | 71016篇 |
晶体学 | 1165篇 |
力学 | 3315篇 |
综合类 | 1142篇 |
数学 | 18040篇 |
物理学 | 21238篇 |
出版年
2024年 | 102篇 |
2023年 | 709篇 |
2022年 | 1661篇 |
2021年 | 2030篇 |
2020年 | 2355篇 |
2019年 | 2317篇 |
2018年 | 2043篇 |
2017年 | 2995篇 |
2016年 | 3238篇 |
2015年 | 2629篇 |
2014年 | 3764篇 |
2013年 | 7129篇 |
2012年 | 6650篇 |
2011年 | 5447篇 |
2010年 | 4577篇 |
2009年 | 6269篇 |
2008年 | 6483篇 |
2007年 | 6715篇 |
2006年 | 6041篇 |
2005年 | 5128篇 |
2004年 | 4738篇 |
2003年 | 3919篇 |
2002年 | 5136篇 |
2001年 | 3025篇 |
2000年 | 2802篇 |
1999年 | 2619篇 |
1998年 | 2280篇 |
1997年 | 1820篇 |
1996年 | 1541篇 |
1995年 | 1449篇 |
1994年 | 1269篇 |
1993年 | 1076篇 |
1992年 | 1017篇 |
1991年 | 668篇 |
1990年 | 579篇 |
1989年 | 544篇 |
1988年 | 407篇 |
1987年 | 320篇 |
1986年 | 305篇 |
1985年 | 255篇 |
1984年 | 265篇 |
1983年 | 147篇 |
1982年 | 231篇 |
1981年 | 179篇 |
1980年 | 199篇 |
1979年 | 188篇 |
1978年 | 172篇 |
1977年 | 127篇 |
1976年 | 110篇 |
1973年 | 67篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Santanu Bhattacharya Basudeb Saha Amitava Dutta Pradyot Banerjee 《Coordination chemistry reviews》1998,170(1):47-74
This review narrates the electron transfer reactions of various nickel(III) and nickel(IV) complexes reported during the period 1981 until today. The reactions have been categorized mainly with respect to the type of nickel complexes. The reactivity of nickel(III) complexes of macrocycles, 2,2′-bipyridyl and 1,10-phenanthroline, peptides and oxime–imine, and of nickel(IV) complexes derived from oxime–imine, oxime and miscellaneous ligands with various organic and inorganic electron donors have been included. Kinetic and mechanistic features associated with such interactions have been duly analyzed. The relevance of Marcus cross-relation equations in the delineation of the electron transfer paths has also been critically discussed. 相似文献
992.
993.
Applying a Lindemann like criterion obtained previously by Kierfeld et al. [J. Kierfeld, T. Nattermann, T. Hwa, Phys. Rev. B 55 (1997) 626], we estimate the magnetic field and temperature for a high-Tc superconductor, at which a topologically ordered vortex glass phase becomes unstable with respect to a disorder-induced formation of dislocations. The employed criterion is shown to be equivalent to a conventional phenomenological Lindemann criterion including the values for the numerical factors, i.e., for the Lindemann number. The positional correlation length of the topologically ordered vortex glass is calculated. 相似文献
994.
Alexander I. Roshchin Sergey M. Kelchevski Nikolai A. Bumagin 《Journal of organometallic chemistry》1998,560(1-2)
Substituted 2-methylbenzofurans were obtained from 2-allylphenols via Pd2+-catalyzed oxidative cyclization using Cu(OAc)2–LiCl as a reoxidant and wet DMF as a solvent. 相似文献
995.
996.
Danch A. Lohner K. Ungerank M. Stelzer F. 《Journal of Thermal Analysis and Calorimetry》1998,54(1):161-170
Bis [(ω-(4′-cyanobiphenyl)-4-yl)oxy-n-alkyl]norborn-5-ene-2,3-dicarboxylate was polymerised via ring opening metathesis polymerisation
(ROMP). Two disubstituted polynorbornene derivatives both of cis configuration with different length of the side-chain were
studied. Differential scanning calorimetry (DSC) was used to study the effect of thermal history on the assignment of the
glass transition event associated with the biaxial orientation of a smectic phase. Glass transition temperatures, the change
of isobaric specific heats at Tg and the enthalpies of isotropisation were calculated. The DSC traces only show the classic step-wise change in Tg in some cases, giving the evidence that the amorphous domains are constrained and highly restricted in movement due to the
morphology developed as a result of the biaxial stretching. Based on the literature data of mono- and disubstituted polynorbornene
derivatives and our calorimetric experiments, the shape of Tg dependence on number of (CH2) units is interpreted. The origin of this shape is discussed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
997.
I. P. Romanova S. G. Fattakhov A. A. Nafikova I. I. Vandyukova R. R. Shagidullin N. M. Azancheev V. S. Reznik O. G. Sinyáshin 《Russian Chemical Bulletin》1998,47(9):1812-1819
The reactions of phosphine derivatives of diallyl isocyanurates with palladium(ii) dichloride lead to the formation of complexes, whose structure, composition, and stability depend on the length of the methylene
chain between the isocyanurate and diphenylphosphine fragments in the ligand. 1,3-Diallyl-5-[5′-(diphenylphosphino)pentyl
and 10′-(diphenyl-phosphino)decyl] isocyanurates with PdCl2 form monomeric L2PdCl2
trans-complexes in which P atoms of the ligands participate in coordination with the metal. 1,3-Diallyl-5-[2′-(diphenylphosphino)ethyl]
isocyanurate with PdCl2 forms a dimeric (LPdCl2)2 complex, which decomposes in a solution to the monomer including solvent molecule into the coordination sphere of the metal.
The reactions of 1,3-diallyl-5-[4′-(diphenylphosphino)butyl] isocyanurate and 1,3-diallyl-5-[6′-(diphenylphosphino)hexyl]
isocyanurate with PdCl2 give monomeric chelate LPdCl2 complexes in which one of the allyl groups of the isocyanurate cycle participates in coordination with the central ion along
with the phosphorus atom.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1859–1865, September, 1998. 相似文献
998.
Jon Samseth Richard J. Spontak Kell Mortensen 《Journal of Polymer Science.Polymer Physics》1993,31(4):467-474
Poly(siloxaneimide) (PSI) segmented copolymers exhibit organized microdomains if the blocks are sufficiently incompatible. As with neat diblock and triblock copolymers, the processing route employed to prepare films of PSI materials is expected to influence the dimensions and/or morphology of the resultant microstructure. In this work, small-angle neutron scattering (SANS) is utilized to characterize the disordered microstructure found in films of a series of PSI copolymers which are subjected to solvent casting and various thermal treatments. Microstructural dimensions such as the periodicity and correlation length are deduced from the Teubner-Strey (TS) model for disordered microemulsions. The scattering intensity of each copolymer up to q = 5.0 nm?1, where q is the scattering vector, is found to scale as q?2.8+?0.1. Results indicate that processing the materials as cast films or as melt-pressed films allowed to cool slowly has a small, but discernible, effect on microstructural characteristics. SANS profiles of films quenched from elevated temperatures reveal a clear transition in microdomain periodicity, which correlates well with the glass transition temperature of the imide microphase in these and other materials of similar chemical structure. © 1993 John Wiley & Sons, Inc. 相似文献
999.
Triorganotin(IV) and triorganolead(IV) derivatives of the types Me3Sn(SCZ) and Ph3Pb(SCZ) (where SCZ? is the anion of a semicarbanzone ligand) have been synthesized by substitution reactions of trimethyltin chloride and triphenyl-lead chloride with semicarbazones derived from heterocyclic ketones. The resulting complexes have been characterized by elemental analyses, molecualr weight determinations and conductivity measurements. The mode of bonding has been established on the basis of infrared and 1H, 13C and 119Sn NMR spectroscopic studies. Some respresentative complexes have also been evaluated for their antimicrobial effects on different species of pathogenic fungi and bacteria; the results of these investigations have been reported in the present paper. 相似文献
1000.
A series of chain-extended PET samples were obtained by the use of different amounts of a diepoxide as chain extender, which
was prepared for this purpose. These samples exhibited different intrinsic viscosities and degrees of branching or cross-linking.
The effects of this differentiation on the thermal properties were studied by differential scanning calorimetry. The thermal
parameters studied were the glass transition temperature (Tg), the cold-crystallization temperature (Tcc), the melting temperature (Tm), the enthalpy (ΔHm) and the degree of crystallinity. The data revealed that, the higher the quantity of chain extender or the chain extension
time, the higher Tgand Tcc, but the lower Tmand ΔHm, i.e. the more amorphous the chain-extended samples, as also shown by density measurements.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献