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101.
Qian-Feng Zhang Richard D. Adams Dieter Fenske 《Journal of inclusion phenomena and macrocyclic chemistry》2005,53(3):275-279
The self-assemblies of two pyrogallol[4]arenes held together by 48 intermolecular hydrogen bonds stably associate in the form of spherical hexameric capsules. The molecular structures of two hexameric capsules with large interior space were analyzed by single crystal X-ray crystallography. 相似文献
102.
Matrix isolation infrared studies of complexes formed between substituted phenols and trimethylamine
Infrared spectroscopy and matrix isolation technique have been used to study the 1 : 1 complexes formed between 2,4,5-trichlorophenol (TCP), pentachlorophenol (PCP) or 2-chloro-4,6-dinitrophenol (CNP) and trimethylamine (TMA) isolated in solid argon. The results were analyzed in relation to the type of complex formed. Depending on the proton-donor ability of the phenol three different types of hydrogen bonded complexes have been identified in argon matrices. The weakest phenol in the series, TCP (pKa = 6.72), forms a strong molecular hydrogen bonded complex with TMA as indicated by the broad ν(OHN) absorption with a maximum at 2490 cm−1 and a band at 811 cm−1 due to the νs(C3N) mode of the perturbed amine. The strongest phenol, CNP (pKa = 2.01), interacts with TMA in an argon matrix to form ionic complex with the proton transferred to the base molecule. This is evidenced by the presence of the ν(NH+---O−) absorption between 3000−1800 cm−1, by the νas(C3N+) and νs(C3N+) absorptions due to the protonated amine and by numerous product bands due to the relatively strongly perturbed modes of the phenol ring. The interaction between TMA and a phenol of intermediate strength, PCP (pKa = 4.74), in solid argon probably leads to the formation of two types of hydrogen bonded complexes: an ionic complex with the proton transferred to the amine molecule and a pseudosymmetric one with the proton more or less equally shared between the phenol and amine molecules. In this case the protonic absorption consists of two broad features situated in the 3000–1600 cm−1 and 950–400 cm−1 regions due to the ν(NH+O−) and ν(OHN) modes, respectively. 相似文献
103.
芳香二磺酸的配位化学研究化合物[Ni(cyclam)(1,5nds)]·1/3H_2O(1)和[Co(cyclam)(H_2O)_2](1,5nds)·2H_2O(2)的合成与结构(英文) 下载免费PDF全文
合成了两个二价的过渡金属磺酸化合物,并通过X-射线衍射单晶结构分析进行结构表征。化合物犤Ni(cyclam)(1,5nds)犦·1/3H2O(1)以P2(1)/c空间群结晶,晶胞参数为a=8.583(5),b=10.533(6),c=12.946(7)?,β=92.433(9)°。犤Ni(cyclam)犦2+与两个磺酸基团形成弱配位,从而构筑了一维的配聚物。犤Ni(cyclam)犦2+与磺酸基团之间的作用还通过O2S-O…H-N型氢键进一步被加强。化合物犤Co(cyclam)(H2O)2犦(1,5nds)·2H2O(2)以P1珔空间群结晶,晶胞参数为a=8.738(5),b=9.324(5),c=10.118(5)?,α=81.382(8),β=64.868(8),γ=62.999(8)°。在该化合物中,磺酸基团没有与Co2+形成配位键,而是以平衡离子的形式存在并与配离子形成氢键,构筑了有序的三维结构。 相似文献
104.
Katerina Liberkov Raymonde Touroude 《Journal of molecular catalysis. A, Chemical》2002,180(1-2):221-230
Selective hydrogenation of crotonaldehyde was performed on 5% Pt/SnO2 catalysts, in gaseous phase, at atmospheric pressure, at 353 K. Two types of catalyst were prepared using H2PtCl6 and Pt(NH3)4(NO3)2 as metallic precursors. Their performances were compared as a function of the reduction temperature and both catalysts were characterised by X-ray diffraction after different reduction treatments. Using the ex-chloride catalyst, the selectivity values to the unsaturated alcohol (UOL) resulted into a maximum of 45% while a selectivity as high as 70–77%, in 0–25% conversion range, was achieved by using ex-nitrate catalyst reduced at 443 K. The formation of Pt–Sn alloy on the metal particles of platinum was thought to be necessary to improve the activity and the selectivity on these catalysts. In the contrast, a presence of PtSn2 formed at a reduction temperature higher than 473 K led to a decrease of activity and selectivity. 相似文献
105.
E. T. Denisov 《Russian Chemical Bulletin》2005,54(4):914-923
Interatomic distances in the reaction centers of the addition reactions of (i) H· to the C=C, C=O, N≡C, and C≡C bonds, (ii) ·CH3 radical to the C=C, C=O, and C≡C bonds, and (iii) alkyl, aminyl, and alkoxyl radicals to olefin C=C bonds were determined
using a new semiempirical method for calculating transition-state geometries of radical reactions. For all reactions of the
type X· + Y=Z → X— Y—Z· the r
#
X...Y distance in the transition state is a linear function of the enthalpy of reaction. Parameters of this dependence were determined
for seventeen classes of radical addition reactions. The bond elongation, Δr
#
X...Y, in the transition state decreases as the triplet repulsion, electronegativity difference between the atoms X and Y in the
reaction center, and the force constant of the attacked multiple bond increase.
__________
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 894–902, April, 2005. 相似文献
106.
Hoebbel Dagobert Nacken Manfred Schmidt Helmut 《Journal of Sol-Gel Science and Technology》1998,13(1-3):37-43
Heterometal materials based on glycidoxypropyltrialkoxysilane and titaniumalkoxide are used for optical applications and require a high homogeneity on the molecular level. The presence of heterometal titanosiloxanes, their distribution and hydrolytic stability should influence the homogeneity of these materials. 29Si and 17O NMR spectroscopy has been used to investigate sols with molar ratios Si : Ti = 1 and H2O : OR (H) = 0.5 – 2.0 and their gels after heat treatment at 130°C. The presence of Si—O—Ti bonds in sols with a low water content (H < 0.2) and in the corresponding gels was identified by the high-field shift of the 29Si NMR signals of T1 and T2 units of up to 2–3 ppm compared to corresponding signals of homo-condensed Si—O—Si bonds. The existence of Si—O—Ti bonds in the sols is supported by 17O NMR spectra which show a characteristic signal around 340 ppm. A cleavage of the Si—O—Ti bonds occurs with increasing water/OR ratio in the sols. The cleavage of the heterometal bonds and the building up of homo-condensed species leads to a separation into areas with predominantly Ti—O—Ti and Si—O—Si bonds resulting in a decreased molecular homogeneity of the materials. 相似文献
107.
Xiu-Lin Zeng Wang-Hua Chen Jia-Cong Liu Jin-Lin Kan 《Journal of Molecular Structure》2007,810(1-3):47-51
Three density-functional methods (B3P86, B3PW91, and B3LYP) are employed to investigate the O–NO2 bond lengths, frontier orbital energies, and O–NO2 bond dissociation energies (BDEs) of n-propyl nitrate (NPN), isopropyl nitrate (IPN), 2-ethylhexyl nitrate (EHN), triethylene glycol dinitrate (Tri-EGDN), and tetraethylene glycol dinitrate (Tetra-EGDN). It is found that the O–NO2 bond lengthens (destabilizes) in the order of IPN, NPN, EHN, Tetra-EGDN, and Tri-EGDN. From the data of frontier orbital energies (EHOMO, ELUMO), and energy gaps (ΔE), we estimate the relative thermal stability ordering of five nitrates and their corresponding radicals. The predicted BDEs of O–NO2 bond in NPN, IPN, EHN, Tri-EGDN, and Tetra-EGDN, are 176.6, 174.5, 168.1, 156.1, and 159.3 kJ mol−1, respectively. Based on the finding that the present results of BDEs are well coincident with the experimental results of apparent activation energies from the literature, we can draw a conclusion that the experimental thermolysis of five nitrates is only unimolecular homolytical cleavage of the O–NO2 bonds. 相似文献
108.
The structure, stability, and paths of formation of 11 (HF)m(DMF)n heterocomplexes (m = 1–4, n = 1, 2) were studied in terms of the B3LYP/6-31++G(d, p) density functional calculation. The results of this calculation suggest that: a) addition of hydrogen fluoride molecules to the (HF)mDMF cyclic fragment is the basic tendency in complex formation in the HF-DMF system; b) data about the structure and properties of stable molecular forms that prevail in N,N-dimethylformamide solutions of hydrogen fluoride can be obtained by quantum chemical calculations for (HF)mDMF complexes (m = 5–10). 相似文献
109.
Joel T. Mague 《Journal of Cluster Science》1995,6(2):217-269
The short-bite ligands CH2(PR
2)2 or CH(PR
2)3 (R = Me, Ph),RN(PX
2)2 (R=H, Me, Et;X = F, OR (R= Me, Et, i-Pr, Ph), Ph),RE(CH2
ER2)2 (E = P, As;R = Me, Ph ), Ph2 P(2-C5H4N) and related species are particularly versatile for the synthesis of di- and polynuclear complexes which frequently possess metal-metal bonds. In addition to homometallic products, these ligands often permit the directed synthesis of heterometallic complexes. Selected aspects of the chemistry of these complexes are also reviewed. 相似文献
110.
Jurij V. Brenčič Boris Čeh Ivan Leban 《Monatshefte für Chemie / Chemical Monthly》1981,112(12):1359-1368
Trans-[Cr(NH3)4F2]I·H2O (A) has monoclinic P2l/m (No. 11) space group witha=5.033 (3),b=16.333 (10),c=5.539 (3) Å and =98.47 (3)°,Z=2.Cis-[Cr(NH3)4F2]ClO4 (B) has tetragonal space group I4lmd (No. 109) witha=7.417 (1),c=16.610 (2) Å,Z=4. Cr–F and Cr–N bonding distances are 1.894 (3); 2.087 and 2.083 (5) Å for A and 1.887 (6); 2.062 (5) and 2.051 (7) Å for B. Octahedral angles within the cations are close to 90° for both compounds. Cr–N bondtrans to Cr–F bond in thecis compound is shorter. Structures were refined toR
2 values of 0.072 (A) and 0.058 (B).Trans-[Cr(NH3)4F2]I·H2O has weak N–H–F hydrogen bonds between the cations. None such interactions were found incis-[Cr(NH3)4F2]ClO4.
Fluorhältige Komplexe des Cr(III), 2. Mitt.: Kristall- und Molekülstruktur von trans-[Cr(NH3)4F2]I·H2O und cis-[Cr(NH3)4F2]ClO4
Zusammenfassung Trans-[Cr(NH3)4F2]I·H2O (A) kristallisiert in der Raumgruppe P2l/m (No. 11) mitZ=2 unda=5,033 (3),b=16,333 (10),c=5,539 (3) Å und =98,47 (3)°.Cis-[Cr(NH3)4F2]ClO4 (B) kristallisiert in der Raumgruppe I4lmd (No. 109) mitZ=4,a=7,417 (1) undc=16,610 (2) Å. Die Cr–F- und Cr–N-Abstände sind 1,894 (3); 2,087 (6), 2,083 (5) Å für A und 1,887 (6); 2,062 (5), 2,051 (7) Å für B. Die octaedrischen Bindungswinkel innerhalb der Kationen weichen nicht viel von 90° ab. Der Cr–N-Abstand intrans-Position der Cr–F-Bindung ist kürzer. Die Strukturen wurden bis zu GütefaktorenR 2 0,072 (A) und 0,058 (B) verfeinert. Bei der Verbindung A wurden schwache N–H ... F-Wasserstoff-Bindungen zwischen verschiedenen Kationen beobachtet, während bei der Verbindung B keine Wasserstoff-Bindungen vorhanden sind.相似文献