全文获取类型
收费全文 | 8560篇 |
免费 | 163篇 |
国内免费 | 2篇 |
专业分类
化学 | 5144篇 |
晶体学 | 171篇 |
力学 | 158篇 |
数学 | 1187篇 |
物理学 | 2065篇 |
出版年
2023年 | 50篇 |
2022年 | 259篇 |
2021年 | 247篇 |
2020年 | 132篇 |
2019年 | 156篇 |
2018年 | 165篇 |
2017年 | 160篇 |
2016年 | 296篇 |
2015年 | 215篇 |
2014年 | 299篇 |
2013年 | 679篇 |
2012年 | 431篇 |
2011年 | 492篇 |
2010年 | 375篇 |
2009年 | 338篇 |
2008年 | 398篇 |
2007年 | 386篇 |
2006年 | 322篇 |
2005年 | 272篇 |
2004年 | 257篇 |
2003年 | 247篇 |
2002年 | 186篇 |
2001年 | 149篇 |
2000年 | 136篇 |
1999年 | 95篇 |
1998年 | 103篇 |
1997年 | 78篇 |
1996年 | 78篇 |
1995年 | 101篇 |
1994年 | 63篇 |
1992年 | 74篇 |
1991年 | 48篇 |
1990年 | 69篇 |
1989年 | 58篇 |
1988年 | 78篇 |
1987年 | 56篇 |
1986年 | 66篇 |
1985年 | 98篇 |
1984年 | 107篇 |
1983年 | 67篇 |
1982年 | 65篇 |
1981年 | 70篇 |
1980年 | 84篇 |
1979年 | 58篇 |
1978年 | 64篇 |
1977年 | 67篇 |
1976年 | 66篇 |
1975年 | 51篇 |
1974年 | 47篇 |
1973年 | 44篇 |
排序方式: 共有8725条查询结果,搜索用时 12 毫秒
801.
Joanna Szymańska-Cybulska Ewa Kamieńska-Piotrowicz 《Journal of solution chemistry》2006,35(12):1631-1643
The enthalpies of solution of Co(II) and Na(I) trifluoromethanesulfonates (triflates) in N,N-dimethylformamide (DMF)–methanol (MeOH) mixtures have been measured over the whole range of solvent composition. From these
data the enthalpies of transfer of Co(II) and triflate ions from methanol to the mixed solvent have been determined usingliterature
values of the enthalpies of transfer of the Na+ ion. The results have been analyzed by means of the theory of preferential solvation. The analysis revealed the preference
of DMF for solvating the Co(II) ion in the MeOH-rich region of solvent composition and the lack of preference of any component
in the DMF-rich region. Visible absorption spectra of the Co(II) ion in DMF–MeOH mixtures have been also measured in the whole
range of solvent composition and analyzed using the partial least-squares method. The mean composition of the solvation sphere
of the Co(II) ion versus solvent composition has been determined on the basis of both analyses. The results were found to be consistent with each
other and with those obtained previously from FT-IR spectra. 相似文献
802.
A. Birczyński Z.T. Lalowicz A.M. Szymocha M. Punkkinen E.E. Ylinen A.H. Vuorimäki 《Chemical physics》2006
Deuteron spin–lattice relaxation is studied in 5% and 100% deuterated ammonium hexachlorostannate and perchlorate. The relaxation rate is observed to be independent of deuteration down to temperatures slightly lower than that of the maximum. At lower temperatures the rate of the 5% deuterated sample exceeds that of the 100% deuterated sample by four and two orders of magnitude in ammonium hexachlorostannate and perchlorate, respectively. The angular dependence of the deuteron relaxation rate in 5% deuterated ammonium hexachlorostannate at 6 K is explained in terms of existing models on quadrupolar relaxation. In 5% ammonium perchlorate one hydrogen equilibrium position, which lies on the preferred axis for 120° rotations, has a larger probability to be occupied by the deuteron of NH3D+ ions. The deuterons at the other positions are still performing rotational jumps about the preferred C3 axis and also about the other threefold axes, although at a slower rate. Such observations require a reconsideration of the relaxation process. A somewhat more general expression is derived for the relaxation rate, which agrees with the experimentally observed angular dependence for 5% deuterated ammonium perchlorate at 60 K. At lower temperatures the quadrupole coupling of the deuterons at the preferred axis may become practically time-independent. Then a significant contribution to the relaxation rate can be provided by the deuteron–proton magnetic dipolar interaction, which is still fluctuating fast via the rotation of the three protons about the axis through the stationary deuteron. 相似文献
803.
Several metallocomplexes of tetrakis-carboxyphenylporphyrin (TCPP) were separated on fused-silica capillary using CZE with UV-VIS detection. Metalloporphyrins of Co(II), Cu(II), Mn(II), Ni(II), and Zn(II) were formed directly in TCPP solution with addition of Cd(II) to increase the formation reaction rate. The composition of BGE, its concentration, and pH were optimized to ensure the stability of complexes and proper resolution. In particular, the problem of signals' shape was investigated and discussed. The presence of beta-CD in borate buffer significantly improved separation efficiency and signal shapes due to formation of inclusion complexes. Under the best separation conditions (50 mM borate running buffer at pH 9 with addition of 2 mM beta-CD, 30 kV applied voltage) a separation of metal complexes with TCPP was accomplished in 16 min. 相似文献
804.
SARS-CoV-2 Mpro is one of the enzymes essential for the replication process of the virus responsible for the COVID-19 pandemic. This work is focused on exploring its proteolysis reaction by means of QM/MM methods. The resulting free energy landscape of the process provides valuable information on the species appearing along the reaction path and suggests that the mechanism of action of this enzyme, taking place in four steps, slightly differs from that of other cysteine proteases. Our predictions, which are in agreement with some recently published experimental data, can be used to guide the design of COVID-19 antiviral compounds with clinical potential.The molecular mechanism of the proteolysis reaction catalyzed by SARS-CoV-2 Mpro, one of the enzymes essential for the replication process of the virus responsible for the COVID-19 pandemic, is described using computational QM/MM methods. 相似文献
805.
Xinghui Qi Dr. Sébastien Pillet Dr. Coen de Graaf Michał Magott Dr. El-Eulmi Bendeif Dr. Philippe Guionneau Dr. Mathieu Rouzières Dr. Valérie Marvaud Dr. Olaf Stefańczyk Dr. Dawid Pinkowicz Dr. Corine Mathonière 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(8):3141-3145
The photoinduced properties of the octacoordinated complex K4MoIV(CN)8⋅2 H2O were studied by theoretical calculations, crystallography, and optical and magnetic measurements. The crystal structure recorded at 10 K after blue light irradiation reveals an heptacoordinated Mo(CN)7 species originating from the light-induced cleavage of one Mo−CN bond, concomitant with the photoinduced formation of a paramagnetic signal. When this complex is heated to 70 K, it returns to its original diamagnetic ground state, demonstrating full reversibility. The photomagnetic properties show a partial conversion into a triplet state possessing significant magnetic anisotropy, which is in agreement with theoretical studies. Inspired by these results, we isolated the new compound [K(crypt-222)]3[MoIV(CN)7]⋅3 CH3CN using a photochemical pathway, confirming that photodissociation leads to a stable heptacyanomolybdate(IV) species in solution. 相似文献
806.
Natalia CZUMA Wojciech FRANUS Pawe BARAN WIK Agnieszka Katarzyna ZARBSKA 《Turkish Journal of Chemistry》2020,44(1):155
In the presented study, the sulfur dioxide sorption properties of fly ash zeolite X were investigated. Sorption tests were performed on fly ash zeolite samples that were not prepared specially for sorption, in addition to dried samples and samples in the presence of water vapor. The samples saturated with water vapor showed the highest sorption capacity. The sorption capacity of the samples additionally dried prior to the sorption experiment was higher than that of the samples that were not specially prepared for the sorption test. Regeneration tests indicated relatively good regeneration properties. The obtained results were described with the use of Langmuir, Sips, and Dubinin–Astakhov models, with the Dubinin–Astakhov model providing the best fit. 相似文献
807.
The treatment of ReOCl3(OPPh3)(SMe2) with an appropriate amount of [1,3]- and [1,4]-diaza heterocyclic ligands N N (were N N = pyrimidine (pym) and pyrazine (pyz)) in boiling acetonitrile under different reaction conditions yielded either the mononuclear ReOCl3(OPPh3)(pym) (1), ReOCl3(OPPh3)(pyz) (2) or dinuclear compounds [ReOCl3(OPPh3)]2(μ-pym) (3), [ReOCl3(OPPh3)]2(μ-pyz) (4). The new complexes were characterized in solution by means of NMR, IR, FIR, and UV–Vis spectroscopic methods. The molecular and crystal structures of 1, 3 and 4 were also determined by X-ray crystallography. All complexes adopt distorted octahedral geometries, with similar donor atoms arrangement, were axial positions are taken by terminal oxygen and triphenylphosphine oxide molecules. The equatorial planes are occupied by three chloride ligands and one nitrogen atom of the diaza ligand. The dinuclear complexes 3 and 4 comprise two equivalent six-coordinated monomeric units. Two halves of the dimer molecule are rotated about the Re–N N–Re fragment: thus, an N-heterocyclic ring is stacked with two adjacent phenyl rings belonging to two triphenylphosphine oxide ligands. The preliminary results concerning the reactivity of the dimeric complexes point to their relative inertness in attempted further substitution towards synthesis of polynuclear complexes. 相似文献
808.
W. Ferenc A. Dziewulska-Kułaczkowska J. Sarzyński B. Paszkowska 《Journal of Thermal Analysis and Calorimetry》2008,91(1):285-292
4-Chloro-2-methoxybenzoates of heavy lanthanides(III) and yttrium(III) were obtained as mono-, di-, tri-or tetrahydrates with
metal to ligand ratio of 1:3 and general formula Ln(C8H6ClO3)3·nH2O, where n=1 for Ln=Er, n=2 for Ln=Tb, Dy, Tm, Y, n=3 for Ln=Ho and n=4 for Yb and Lu. The complexes were characterized by elemental analysis, FTIR spectra, TG, DTA and DSC curves, X-ray diffraction
and magnetic measurements.
The carboxylate group appears to be a symmetrical bidentate chelating ligand. All complexes are polycrystalline compounds.
The values of enthalpy, ΔH, of the dehydration process for analysed complexes were also determined. The solubilities of heavy lanthanide(III) 4-chloro-2-methoxybenzoates
in water at 293 K are of the order of 10−4 mol dm−3. The magnetic moments were determined over the range of 76–303 K. The results indicate that there is no influence of the
ligand field of 4f electrons on lanthanide ions and the metal ligand bonding is mainly electrostatic in nature. 相似文献
809.
W. W. Sułkowski S. Mistarz T. Borecki M. Moczyński A. Danch J. Borek M. Maciążek Anna Sułkowska 《Journal of Thermal Analysis and Calorimetry》2006,84(1):91-97
From the TG data of rubber
granulates, different polyurethane and composites it can be seen that the
thermal decomposition for the rubber granulate and all of the composites start
above 520 K. Two major mass losses for the rubber granulates and majority
of the composites were observed and thermal decomposition is essentially complete
by ~820 K. The changes of activation energies of lower and higher temperature
decomposition, calculated according to the different equations were observed
for a priori assumed first-order reaction for devolatilisation. Differences
between determined and calculated results could suggest a possible reaction
between polyurethane agents and rubber granulate during the composites formations. 相似文献
810.
Krzysztof Staliński Zofia Urbańczyk-Lipkowska Leszek Rupnicki 《Journal of organometallic chemistry》2006,691(11):2394-2402
A series of tri- and tetraorganotin compounds containing the optically active 2-(4-isopropyl-2-oxazolinyl)-5-phenyl ligand and tert-butyl, methyl and/or phenyl groups on the tin has been synthesized. All the novel compounds have been characterized, especially by means of the multinuclear NMR investigation, the results of which are discussed. The tin halides, as pairs of diastereoisomers in solution, crystallize in the form of one diastereoisomer. The single-crystal X-ray analysis of tin iodide 10a revealed pseudo-equatorial position of the tert-butyl group opposite to the isopropyl group. In the corresponding diastereomeric tin hydrides values of 1J(1H-117/119Sn) differ significantly, suggesting a different pseudo-axial/equatorial position of the hydrogen atom. 相似文献