全文获取类型
收费全文 | 1985篇 |
免费 | 5篇 |
专业分类
化学 | 990篇 |
晶体学 | 27篇 |
力学 | 86篇 |
综合类 | 1篇 |
数学 | 176篇 |
物理学 | 710篇 |
出版年
2021年 | 19篇 |
2020年 | 33篇 |
2019年 | 31篇 |
2018年 | 60篇 |
2017年 | 58篇 |
2016年 | 66篇 |
2015年 | 23篇 |
2014年 | 60篇 |
2013年 | 74篇 |
2012年 | 57篇 |
2011年 | 75篇 |
2010年 | 63篇 |
2009年 | 64篇 |
2008年 | 62篇 |
2007年 | 70篇 |
2006年 | 56篇 |
2005年 | 34篇 |
2004年 | 40篇 |
2003年 | 51篇 |
2002年 | 45篇 |
2001年 | 37篇 |
2000年 | 41篇 |
1999年 | 26篇 |
1998年 | 25篇 |
1997年 | 22篇 |
1994年 | 17篇 |
1990年 | 16篇 |
1989年 | 20篇 |
1988年 | 23篇 |
1986年 | 19篇 |
1985年 | 28篇 |
1984年 | 33篇 |
1983年 | 16篇 |
1981年 | 30篇 |
1980年 | 29篇 |
1979年 | 25篇 |
1978年 | 30篇 |
1977年 | 36篇 |
1976年 | 24篇 |
1975年 | 23篇 |
1972年 | 22篇 |
1971年 | 19篇 |
1970年 | 23篇 |
1969年 | 15篇 |
1968年 | 33篇 |
1967年 | 22篇 |
1965年 | 25篇 |
1964年 | 20篇 |
1960年 | 21篇 |
1959年 | 16篇 |
排序方式: 共有1990条查询结果,搜索用时 15 毫秒
41.
The complexing processes in the triple cobalt(II)–dithiooxamide-formaldehyde and cobalt(II)–dithiooxamide-glyoxal systems taking place in the cobalt(II)hexacyanoferrate(II) gelatin-immobilized matrix in contact with aqueous alkaline solutions (pH ca. 12) containing (dithiooxamide+formaldehyde) and (dithiooxamide+glyoxal), have been studied. Template synthesis leading to macrocyclic coordination compounds with tetradentate N,N,S,S-donor ligands-(2,8-dithio-3,7-diaza-5-oxanonan-dithioamide-1,9) and (2,7-dithio-3,6-diazaoctadien-3,5-dithioamide-1,8) with CoII–CoIII redox-process occurs under these specific conditions where dithiooxamide, formaldehyde and glyoxal are the ligand synthons. 相似文献
42.
J. Kvasil I. N. Mikhailov R. Ch. Safarov B. Choriev 《Czechoslovak Journal of Physics》1978,28(8):843-856
Some generalizations of the model for odd nuclei suggested by Kerman are considered. The effects of phonon admixtures on matrix elements of Coriolis interaction are studied. Several schemes are considered for studying the role of non-adiabatic effects in the even-even core.One of the authors B. Ch. thanks L. A.Malov and V. O.Nesterenko for many discussions of some questions connected with the determination of the phonon-quasiparticle admixtures. 相似文献
43.
Low-temperature radiolysis and photolysis of crystalline 2,4,6-triazido-3,5-dichloropyridine (TAP) were studied by means of the ESR technique. It was found that the long-term irradiation of TAP at 77 K leads to the appearance of characteristic signals of quintet 2,6-dinitreno-4-azido-3,5-dichloropyridine and 2,4-dinitreno-6-azido-3,5-dichloropyridine; their radiation-chemical yield was 0.035 and 0.012 molecule/100 eV, respectively. The photolysis of crystalline 2,4,6-triazido-3,5-dichloropyridine proceeded less effectively, producing only quintet 2,6 dinitrene with a quantum yield of ~4.5 × 10?4. The study showed that the generation of high-spin nitrenes via radiolysis of crystalline azides is much superior to the photochemical technique in efficiency and may be of practical importance for the preparation of magnetically active organic materials. 相似文献
44.
Lisachenko A. A. Kuznetsov V. N. Zakharov M. N. Mikhailov R. V. 《Kinetics and Catalysis》2004,45(2):189-197
A combined study of intrinsic structural defects in reduced TiO2 was performed using mass spectrometry, optical diffuse-reflectance spectroscopy, and UV photoelectron spectroscopy (UPS). It was found that the reduction of TiO2 resulted in the appearance of absorption in the region 0.50 h 3.50 eV (400 2500 nm), which is formed by absorption due to free electrons (a continuum at h 1.50 eV), local centers—Ti3+ ions (a band at 2.00 eV), and oxygen vacancies (bands at 1.17, 2.81, and 2.55 eV). The spectrum of induced occupied electronic states in the forbidden gap and the position of oxygen vacancy levels with respect to the Fermi level were determined by UPS. The absorption of reduced TiO2 was stable on the sample to T = 800 K in a vacuum; however, it weakened in contact with O2, NO, and N2O molecules beginning at T = 300 K (surface sites) and T 400 K (subsurface sites) as a result of filling oxygen vacancies with atomic oxygen in the course of dissociative adsorption. The adsorption complexes formed by the interaction of O2, NO, and N2O with defects were analyzed by temperature-programmed desorption. The distribution of sites over the energies of oxygen binding was found with the use of a nonuniform surface model, and specific oxygen adsorption species were revealed. It was found that the irradiation of TiO2 activates the formation and decay of sites and results in the formation of specific O2 and N2O adsorption species. 相似文献
45.
I. Kiricsi S. Kh. Akopyan A. V. Mikhailov H. F?rster 《Reaction Kinetics and Catalysis Letters》1990,42(1):145-150
Formation of alkenylcarbenium ions has been proved during transformation of allyl alcohol on zeolite HZSM-5.
HZSM-5.相似文献
46.
Oleg V. Mikhailov Marina A. Kazymova Tatyana A. Shumilova Galina A. Chmutova Svetlana E. Solovieva 《Transition Metal Chemistry》2005,30(1):18-21
The complexing processes in the M
II
-dithiomalonamide-diacetyl triple system (M=Ni, Cu) occuring in the nickel(II)- and copper(II)hexacyanoferrate(II) gelatin-immobilized matrix in contact with aqueous alkaline solutions (pH~12) containing dithiomalonamide and diacetyl at room temperature, and between MCl2, dithiomalonamide
and
diacetyl
in
EtOH
solutions
upon
heating
to$80°C, have been studied. In the Ni
II
-dithiomalonamide-diacetyl system, template synthesis occurs in EtOH solution but does not occur in the gelatin-immobilized matrix, whereas in the Cu
II
-dithiomalonamide-diacetyl system, template synthesis occurs in the gelatin-immobilized matrix but not in EtOH solution. Dithiomalonamide and diacetyl are the ligand synthons in the processes indicated. 相似文献
47.
V. I. Minkin I. E. Mikhailov G. A. Dushenko O. E. Kompan A. Zschunke 《Russian Chemical Bulletin》1998,47(5):884-894
The kinetics and mechanism of circumambulatory rearrangements of N-centered (NCS) and S-centered (SPh, SC3Ph3, SC(OEt)=S) groups in corresponding derivatives of 1,2,3-triphenylcyclopropene and cycloheptatriene were studied by dynamic1H and13C NMR spectroscopy. Migrations of the isothiocyanate group occur by the dissociation-recombination mechanism with intermediate formation of a tight ionic pair. Migrations of the phenylthio group around the perimeter of cyclopropene and cycloheptatriene rings occur by the 1,2-shift mechanism. It was found that rearrangements of theO-ethyl dithiocarbonate group inS-(1,2,3-triphenylcyclopropen-3-yl)-O-ethyl dithiocarbonate occur by the 3,3-sigmatropic shift mechanism. The molecular and crystal structure ofO-ethylS-(1,2,3-triphenylcyclopropen-3-yl) dithiocarbonate was studied by X-ray analysis. 相似文献
48.
Udovenko A. A. Zemnukhova L. A. Gorbunova Yu. E. Mikhailov Yu. N. Davidovich R. L. 《Russian Journal of Coordination Chemistry》2002,28(1):12-14
The crystal structure of a novel antimony(III) fluoride complex, ammonium undecafluorotriantimonate(III) (NH4)2Sb3F11, was determined. The crystals are triclinic: a = 7.780(2) Å, b = 8.370(2) Å, c = 10.620(1) Å, = 71.06(1)°, = 89.03(1)°, = 63.58(1)°, V = 579.1(2) Å3, Z = 2, (calcd) = 3.500 g/cm3, (exp) = 3.51 g/cm3, F(000) = 548.0, space group P
. The structure consists of anionic [Sb3F11]2– chains and ammonium cations combined into a framework by the N–H···F hydrogen bonds. 相似文献
49.
50.
Highly reactive allyl(dialkyl)-, crotyl(dialkyl)-, 3,3-dimethylallyl(dialkyl)-(= prenyl(dialkyl), and diallyl(alkyl)-boranes were prepared by allylation of esters R2BOR′, RB(OR′)2 or thioesters R2BSR′ (R = alkyl) using allylic derivatives of aluminium, magnesium or boron in exchange reactions.The titled compounds are stable up to 100°C and do not symmetrize even on heating at 100°C for a long time. PMR spectroscopy data show that the characteristic feature of these compounds is a permanent allyl rearrangement, the rate of which increases with an increase in temperature. For allyl(diethyl)-borane at 100°C and 125°C the rates are equal to 2500 and 5000 sec?1 respectively; activation energy of the rearrangement amounts to 11.8±0.2 kcal mol?1.The boronallyl bonds in unsymmetrical allyl(alkyl)boranes readily split under the action of water and alcohols, protonolysis being accompanied by allyl rearrangement, crotyl and prenyl compounds are converted into 1-butene or 3-methyl-1-butene, respectively. 相似文献