全文获取类型
收费全文 | 12628篇 |
免费 | 1110篇 |
国内免费 | 679篇 |
专业分类
化学 | 8550篇 |
晶体学 | 530篇 |
力学 | 114篇 |
综合类 | 20篇 |
数学 | 47篇 |
物理学 | 5156篇 |
出版年
2024年 | 19篇 |
2023年 | 113篇 |
2022年 | 226篇 |
2021年 | 298篇 |
2020年 | 347篇 |
2019年 | 272篇 |
2018年 | 230篇 |
2017年 | 256篇 |
2016年 | 438篇 |
2015年 | 272篇 |
2014年 | 367篇 |
2013年 | 936篇 |
2012年 | 769篇 |
2011年 | 741篇 |
2010年 | 642篇 |
2009年 | 804篇 |
2008年 | 828篇 |
2007年 | 1011篇 |
2006年 | 936篇 |
2005年 | 690篇 |
2004年 | 662篇 |
2003年 | 520篇 |
2002年 | 408篇 |
2001年 | 311篇 |
2000年 | 279篇 |
1999年 | 250篇 |
1998年 | 248篇 |
1997年 | 178篇 |
1996年 | 245篇 |
1995年 | 212篇 |
1994年 | 201篇 |
1993年 | 158篇 |
1992年 | 115篇 |
1991年 | 91篇 |
1990年 | 79篇 |
1989年 | 45篇 |
1988年 | 41篇 |
1987年 | 24篇 |
1986年 | 33篇 |
1985年 | 36篇 |
1984年 | 30篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 12篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1977年 | 3篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1972年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
911.
N. V. Kozak Yu. N. Nizel'skii L. F. Kosyanchuk S. D. Nesin 《Theoretical and Experimental Chemistry》2005,41(4):265-270
The influence of the nature of the central ion [Cu(2+), Cr(3+), Fe(3+)] of the chelate compound on the possibility of interaction
of the metal-containing modifier with one or both of the components of the incompatible PU/PMMA system was studied by the
ESR method. It was shown by low-angle X-ray diffraction that the change in the degree of microheterogeneity of the semi-IPN
correlated with the characteristics of complex forming metal and the polymer matrix.
__________
Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 41, No. 4, pp. 252–256, July–August, 2005. 相似文献
912.
D. P. Krutko M. V. Borzov E. N. Veksler A. V. Churakov 《Russian Chemical Bulletin》2005,54(1):117-123
The intracomplex conversion of (2-diphenylphosphanoethyl)cyclopentadienyl zirconium and titanium complexes into the corresponding 2-phosphinothioyl and 2-phosphinoyl derivatives, viz., (η5-C5H5)[η 5-C5H4CH2CH2P(S)Ph2]ZrCl2, [η5-C5H4CH2CH2P(S)Ph2]ZrCl3, [η5:η1C5H4CH2CH2P(O)Ph2]ZrCl3·THF, and [η5:η 1-C5H4CH2CH2P(O)Ph2]TiCl3 (7), was performed. The NMR spectroscopy data revealed the following order of the coordination ability of the functional groups with respect to the Zr center: Ph2P=O > Ph2P > Ph2P=S. An analogous order was found for the monodentate ligands (Ph3P=O > Ph3P > Ph3P=S) with respect to (η5-C5H5)ZrCl3. The molecular structure of complex 7 was established by X-ray diffraction analysis. Coordination of the Ph2P=O group to the titanium atom was found retained both in the crystalline state and solution.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 116–122, January, 2005. 相似文献
913.
914.
Substituted μ3-carbido-capped tricobalt carbonyl clusters have been synthesised by reaction of [Co3(μ3-C(O)OCH2CHCH2)(CO)9] with a range of monodentate and chelating phosphane ligands. The products have been characterised by microanalysis, IR and NMR spectroscopy, mass spectrometry and, in the case of [Co3(μ3-CR)(CO)7(dppe)], [Co3(μ3-CR)(CO)7(dppm)], [Co3(μ3-CR)(CO)7(PPh3)2], [Co3(μ3-CR)(CO)7(PMe3)2] and [Co3(μ3-CR)(CO)6(PEt3)3] (R=C(O)OCH2CHCH2), single crystal X-ray diffraction. 相似文献
915.
Hieronim Maciejewski Agnieszka Sydor Maciej Kubicki 《Journal of organometallic chemistry》2004,689(19):3075-3081
Reactions of the nickel(0) complexes [Ni(cod)2] (in the presence of PP or [Ni(PPh3)2C2H4] with vinyl-siloxanes, -silanes or -silazanes yield, by displacement of alkene ligand, the new nickel π-complexes [Ni(PPh3)2(η-CH2CHSi(OSiMe3)3)] (2), [{Ni(PPh3)}2{μ-(η-{(CH2CH)2SiMe}2O})] (4), [Ni(PPh3){η4-CH2CHSi(Me)(μ-O)}3] (5), [{Ni(η-CH2CHSiMe2)2O}(η-CH2CHSiMe3)] (7) and the known complexes [Ni(PPh3)2(η-CH2CHSiMe3)] (1), [{Ni(PPh3)}2{μ-(η-(CH2CH)4Si})] (3), [{Ni(PPh3)(η-CH2CHSiMe2)2NH}] (6) obtained by a simple one pot synthesis, more efficiently than in hitherto published reports. The X-ray crystal structure of (1) shows a trigonal planar environment around the nickel atom. 相似文献
916.
The vesicle system consisting of 80 mol% dipalmitoylphosphatidylethanolamine (DPPE) and 20 mol% dipalmitoylphosphatidylglycerol (DPPG) undergoes to structural changes caused by various concentrations of Salmonella minnesota R595 lipopolysaccharide (LPS). The phenomenon was investigated by methods applying small- and wide-angle X-ray scattering (SAXS and WAXS), calorimetry (DSC) and freeze-fracture. In the low LPS concentration regime (investigated at 0.02 LPS/DPPE–DPPG molar ratio) a phase separation was observed. Two kind of domains are formed which are rich and poor in DPPE and in these domains cubic and lamellar structures are present, respectively. Increasing the LPS concentration up to 0.1 LPS/DPPE–DPPG molar ratio the phase separation is more expressed and the temperature domains of the phase transitions are more different. Increasing the temperature chain melting of the lamellar phase occurs first and destruction of the cubic phase is observed later. At high LPS concentration (equimolar ratio of LPS/DPPE–DPPG), where this amphiphilic molecule cannot be considered any more a guest molecule, the cubic structure dominates the phase behaviour of the LPS molecules. 相似文献
917.
I. L. Fedushkin A. N. Lukoyanov G. K. Fukin M. Hummert H. Schumann 《Russian Chemical Bulletin》2006,55(7):1177-1183
Reduction of benzophenone and 4,4′-bis(methoxy)benzophenone with the aluminum complex (dpp-BIAN)AlI(Et2O) (1) containing the dianionic dpp-BIAN ligand (dpp-BIAN is 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) affords the pinacolate
complexes [(dpp-BIAN)AlI]2[μ-O2C2Ph4] (2) and [(dpp-BIAN)AlI]2[μ-O2C2(C6H4OMe)4] (3), respectively, which undergo the pinacolone rearrangement upon prolonged storage in diethyl ether to form [(dpp-BIAN)AlI]2O (4). The reaction of 1 with fluoren-9-one produces stable pinacolate (dpp-BIAN)Al[μ-O2(C13H8)2] (7) and the (dpp-BIAN)AlI2 complex (8). Compounds 2—4, 7, and 8 were characterized by ESR spectroscopy. Hydrolysis products of compounds 2 and 3 were characterized by 1H NMR spectroscopy. The structures of complexes 4 and 7 were established by X-ray diffraction.
dpp-BIAN is 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1134–1140, July, 2006. 相似文献
918.
A mixed-ligand Zn(II) complex formulated as [Zn(aldtc)2(bipy)] (aldtc=diallyldithiocarbamate; bipy=2,2′-bipyridine) was synthesized and characterized by IR, 1H and 13C NMR spectral measurements and X-ray crystallography. The crystal structure of this complex indicates that Zn has a distorted octahedral geometry. The Zn—N distances are invariant (2.168(2) Å), while those of the Zn—S are slightly different (2.5408(9) and 2.5440(9) Å). The N—Zn—N, S—Zn—S and N—Zn—S bond angles are in the range 75.35(13)–99.75(7)°, 70.48(3)–161.02(5)° and 95.26(7)–160.32(7)°, respectively. The crystal packing of the complex shows different motifs of supramolecularity resulting from both hydrophilic ((π)C—H···S) and hydrophobic ((allyl)C—H···C(π)) intermolecular interactions. These interactions result in a chain arrangement of molecules along crystallographic c axis and the chains are further connected via π···π stacking along with ((π)C—H···S along b axis leading to an overall crystal packing that can be regarded as layers of complexes along bc plane, which are held together through nonconventional hydrogen bonding and π···π stacking. 相似文献
919.
Nanosize nickel-substituted cobalt ferrites were prepared using aerosol route and characterized by TEM, XRD, magnetic and Mössbauer spectroscopy. The particle size of as obtained samples was found to be ∼10 nm which increases upto ∼80 nm on annealing at 1200 °C. The unit cell parameter ‘a’ decreases linearly with the nickel concentration due to smaller ionic radius of nickel. The saturation magnetization for all the samples after annealing at 1200 °C lies in the range 47.6-84.5 emu/g. Room temperature Mössbauer spectra of as obtained samples exhibit a broad doublet, suggesting super paramagnetic nature of the sample. The broad doublet is further resolved into two doublets corresponding to the iron atoms residing at the surface and internal regions of the particle. The samples annealed at 1200 °C showed broad sextet, which is resolved into two sextets, corresponding to tetrahedrally and octahedrally coordinated Fe cations. Cation distribution calculated using XRD and Mössbauer data indicates a decrease in Fe3+(oct.)/Fe3+(tet.) ratio with increasing nickel concentration. 相似文献
920.
M. Gdaniec B. T. Ibragimov S. A. Talipov 《Journal of inclusion phenomena and macrocyclic chemistry》1990,8(4):431-438
The crystal structure of the 2: 1 inclusion complex of gossypol with amyl acrylate has been determined by X-ray structure analysis. The crystals of (C30H30O8)2C8H14O2 are triclinic, space group P
,a = 14.425(2),b = 15.519(1),c = 16.409(2) Å, =97.89(1), = 117.80(1), =67.01(1)° (reduced cell:a = 14.425(2),b = 15.519(2),c = 16.017(2)Å, = 92.19(1), = 115.01(l), =67.01(1)°],V = 2986.7(5) Å3,Z = 2,D
x = 1.31 g cm–3, (CuK
) = 7.40 cm–1,T = 292 K. The structure has been solved by direct methods and refined to the final R value of 0.059 for 5155 observed reflections. The gossypol molecules bonded via several hydrogen bonds form centrosymmetric tetramers. The two independent gossypol molecules, A and B, are related within the tetramer by a local noncrystallographic 2-fold axis. The host molecules in the crystal form cavities in which two guest molecules are placed. The ester molecule interacts via a pair of C-...H-O hydrogen bonds with two gossypol molecules of the same chirality and belonging to the same tetramer unit. The amyloxy group of the ester molecule shows a very large thermal motion. It adopts a non-extended conformation in which it can be fitted into the cavity formed by the host molecules. 相似文献