全文获取类型
收费全文 | 3733篇 |
免费 | 62篇 |
国内免费 | 42篇 |
专业分类
化学 | 2134篇 |
晶体学 | 62篇 |
力学 | 110篇 |
综合类 | 1篇 |
数学 | 789篇 |
物理学 | 741篇 |
出版年
2022年 | 42篇 |
2021年 | 76篇 |
2020年 | 40篇 |
2019年 | 42篇 |
2018年 | 63篇 |
2017年 | 73篇 |
2016年 | 92篇 |
2015年 | 89篇 |
2014年 | 118篇 |
2013年 | 255篇 |
2012年 | 179篇 |
2011年 | 214篇 |
2010年 | 138篇 |
2009年 | 151篇 |
2008年 | 223篇 |
2007年 | 191篇 |
2006年 | 182篇 |
2005年 | 161篇 |
2004年 | 172篇 |
2003年 | 125篇 |
2002年 | 122篇 |
2001年 | 58篇 |
2000年 | 53篇 |
1999年 | 47篇 |
1998年 | 49篇 |
1997年 | 57篇 |
1996年 | 65篇 |
1995年 | 34篇 |
1994年 | 39篇 |
1993年 | 44篇 |
1992年 | 31篇 |
1991年 | 36篇 |
1990年 | 35篇 |
1989年 | 33篇 |
1988年 | 29篇 |
1987年 | 27篇 |
1986年 | 20篇 |
1985年 | 40篇 |
1984年 | 49篇 |
1983年 | 27篇 |
1982年 | 27篇 |
1981年 | 34篇 |
1980年 | 30篇 |
1979年 | 28篇 |
1978年 | 25篇 |
1977年 | 33篇 |
1976年 | 18篇 |
1975年 | 21篇 |
1974年 | 17篇 |
1972年 | 14篇 |
排序方式: 共有3837条查询结果,搜索用时 15 毫秒
31.
Åse Støg»rd 《Chemical physics letters》1975,36(3):357-360
Ab initio as well as semi-empirical SCF MO calculations are presented for ClCN and ONCl. The relative intensities for Cl Kβ emission in the two molecules were calculated. The calculated spectra from the ab initio wavefunctions are in excellent agreement with experiments. 相似文献
32.
T. N. Srivastava R. C. Srivastava Mala Singh 《Journal of organometallic chemistry》1978,160(2):449-454
Iodine monohalides (ICl, IBr), cyanogen halides (CNBr, CNI) and thiocyanogen (SCN)2 add oxidatively to diaryltellurium(II), R2Te (R = Ph, p-Ch3OC6H4) under mild conditions (
°C). The resulting organotellurium(IV) derivatives react metathetically with silver pseudohalides to yield several new diaryltellurium(IV) pseudohalide derivatives. 相似文献
33.
A simple isotherm equation is derived for the adsorption of an organic component onto activated carbon in presence of water vapour. The theoretical results are compared with experimental data for toluene-water vapour-activated carbon, which were published byRipperger andGermerdonk [10].
Symbols a i adsorbate concentration in adsorbent, kg/kg of carbon - a 0i monolayer capacity, kg/kg of carbon - b i kinetic parameter of theLangmuir equation - E j adsorption energy in thej-th layer - i i-th component (1 — water vapour, 2 — organic compound) - j j-th layer - m number of layers - n number of adsorbed components - p partial pressure, Pa - p* saturation partial pressure, Pa - p C water vapour partial pressure at begining of capillary condensation, Pa - surface coverage 相似文献
Vorhersage der Adsorption einer organischen Komponente und Wasserdampf an Aktivkohle
Zusammenfassung Es wird eine einfache Adsorptionsisotherme abgeleitet, welche die gleichzeitige Adsorption eines organischen Stoffes und Wasser an Aktivkohle beschreibt. Die theoretischen Ergebnisse werden mit experimentellen Resultaten vonRipperger undGermerdonk [10] für Toluol-Wasser-Aktivkohle verglichen.
Symbols a i adsorbate concentration in adsorbent, kg/kg of carbon - a 0i monolayer capacity, kg/kg of carbon - b i kinetic parameter of theLangmuir equation - E j adsorption energy in thej-th layer - i i-th component (1 — water vapour, 2 — organic compound) - j j-th layer - m number of layers - n number of adsorbed components - p partial pressure, Pa - p* saturation partial pressure, Pa - p C water vapour partial pressure at begining of capillary condensation, Pa - surface coverage 相似文献
34.
The molecular electric dipole moments are reported for the series of tin-substituted tetracarbonyl cobalt compounds RnYm?nSn{Co(CO)4}4?m (m = 1–3; n ? m; R = alkyl, phenyl; Y = halogen). The effect of the substituents at the tin atom on the nature of the CoSn bond is established on calculating the (CO)4CoSn group dipole moments. It is shown that the charge transfer in the CoSn bond is mainly determined by the inductive properties of the ligands attached to tin. 相似文献
35.
Silica xerogels with different structures and morphology, synthesized using a sol-gel procedure, were used as a carrier of vanadium catalysts (VOCl3/AlEt2Cl) for ethylene polymerization. Two techniques of catalyst synthesis were applied: slurry impregnation and gas-phase adsorption and the relevant polymerization methods were then employed. The effect of the carrier structure and morphology on the vanadium loading in the catalysts, the catalyst’s activity and kinetic stability were investigated. 相似文献
36.
A simple procedure to decompose the theoretical molecular charge distribution into cumulative atomic multipoles supplementing any population analysis scheme has been described and tested for a number of molecules in extended basis sets. This approach may be applied to describe local charge distributions in neutral as well as charged systems and also leads to a simplified point-charge model conserving the local anisotropy of the atomic charge distribution in molecules. Such an approach may be useful in estimating intermolecular interactions, representing the molecular environment in solvent effect or enzyme catalytic activity studies, evaluation of molecular electrostatic potentials or tracing the quality of basis set functions. 相似文献
37.
The resonanceRaman spectra of Fe(LC 12)3Cl2 and Fe(LC 18)3Cl2 (whereLC 12 andLC 18 denote 4,4′-didodecyloxy-2,2′-bipyridine and 4,4′-dioctadecyloxy-2,2′-bipyridine, respectively) have been measured along with their excitation profiles. The exciting lines of an Ar+ laser have been used. The bands appearing in theRR spectra within 1 200–1 600cm?1 (expected to arise from thebipy moiety C-N and C-C vibrations) suffer the greatest resonance enhancements. Both depolarization ratios of theRaman bands and excitation profiles reveal the interaction of the resonant electronic states. 相似文献
38.
Complex systems of paramagnetic centres existing in demineralised flame coal (71.4 wt% C), medium-rank coal (85.6 wt% C) and
anthracite (94.9 wt% C) were analysed by electron paramagnetic resonance spectroscopy (EPR). Different groups of paramagnetic
centres were searched in macerals (exinite, vitrinite, inertinite) of coals with carbon contents of 73.8 wt% C and 85.6 wt%
C. Experimental EPR spectra were fitted by different superposition of theoretical lines. Total concentration of paramagnetic
centres both in coal and macerals increases with carbon content in the sample. Total concentration of paramagnetic centres
in macerals increases from exinite to inertinite. Four groups of paramagnetic centres were found in medium-rank coal, and
only two groups exist in flame coal and anthracite. The EPR spectrum of medium-rank coal is a superposition of two broad and
two narrow lines. Both broad and narrow, and two narrow lines were measured in EPR spectra of flame coal and anthracite, respectively.
Two types of paramagnetic centres with broad lines and one group with narrow lines exist in exinite and vitrinite from medium-rank
coal. Two narrow components were observed in EPR spectra of its inertinite. Two different broad electron paramagnetic resonance
signals were detected for macerals from low-coalificated coal. Paramagnetic centres systems of medium-rank coal samples reveal
the most complex character. Broad EPR lines were not observed for the higher coalificated samples, i.e., anthracite and inertinite
from medium-rank coal. Narrow lines do not occur in EPR spectra of low-coalificated macerals. Strong dipolar interactions
and fast spin-lattice relaxation processes are characteristic for paramagnetic centres with broad lines. Strong exchange interactions
and short spin-lattice relaxation time were measured for paramagnetic centres with the narrowest EPR signals. 相似文献
39.
Kłonkowski Andrzej M. Widernik Teresa Grobelna Beata Jóźwiak Wojciech K. Proga Henryk Szubiakiewicz Ewa 《Journal of Sol-Gel Science and Technology》2001,20(2):161-180
The sol-gel process is a useful method for preparing two series of organically and co-ordinately modified xerogels of the types [CuN
n
]·N
5–n
·5xSiO4/2 (n < 4) and [Cu(N–N)n]·(N–N)2–n
·2x SiO4/2(n 2), where N = NH2(CH2)3 SiO3/2, N–N = NH2(CH2)2NH·(CH2)3SiO3/2 and x = [SiO4/2]/[N] or [SiO4/2]/[N–N]. The amino groups in the materials are coordinately active and participate partly in the coordination sphere of Cu(II) ions. The composition of the coordination sphere can be varied with the SiO4/2 content and also as a result of the thermal decomposition of the organic residues at higher temperatures.Because the xerogel materials are considered to be catalyst precursors, this study is focused on their coordination and thermal properties. The prepared xerogels, such as silica, aminated silicates with N and N–N, as well as those entities complexed with Cu(II), were characterised by FT-IR spectroscopy. During gelation and thermal decomposition the materials were analysed by electron paramagnetic resonance (EPR) spectroscopy. The xerogels were additionally studied by UV-Vis absorption spectroscopy. The gaseous products of the thermal decomposition of these materials in an Ar atmosphere were investigated by the use of FT-IR spectroscopy coupled with TG and DTG thermal analysis. These data were complemented by temperature-programmed decomposition (TPDec) in a 2% O2 + 98% Ar stream coupled with quadrupole mass spectroscopy. 相似文献
40.