全文获取类型
收费全文 | 78130篇 |
免费 | 339篇 |
国内免费 | 377篇 |
专业分类
化学 | 24274篇 |
晶体学 | 789篇 |
力学 | 6728篇 |
数学 | 31945篇 |
物理学 | 15110篇 |
出版年
2018年 | 10434篇 |
2017年 | 10264篇 |
2016年 | 6060篇 |
2015年 | 843篇 |
2014年 | 285篇 |
2013年 | 320篇 |
2012年 | 3769篇 |
2011年 | 10487篇 |
2010年 | 5622篇 |
2009年 | 6035篇 |
2008年 | 6592篇 |
2007年 | 8755篇 |
2006年 | 220篇 |
2005年 | 1311篇 |
2004年 | 1528篇 |
2003年 | 1976篇 |
2002年 | 1021篇 |
2001年 | 259篇 |
2000年 | 298篇 |
1999年 | 157篇 |
1998年 | 196篇 |
1997年 | 149篇 |
1996年 | 205篇 |
1995年 | 120篇 |
1994年 | 82篇 |
1993年 | 95篇 |
1992年 | 64篇 |
1991年 | 67篇 |
1990年 | 53篇 |
1989年 | 66篇 |
1988年 | 66篇 |
1987年 | 69篇 |
1986年 | 62篇 |
1985年 | 65篇 |
1984年 | 47篇 |
1983年 | 40篇 |
1982年 | 43篇 |
1981年 | 42篇 |
1980年 | 56篇 |
1979年 | 52篇 |
1978年 | 37篇 |
1977年 | 26篇 |
1973年 | 29篇 |
1914年 | 45篇 |
1913年 | 40篇 |
1912年 | 40篇 |
1909年 | 41篇 |
1908年 | 40篇 |
1907年 | 32篇 |
1904年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Wiesława Nocuń-Wczelik 《Journal of Thermal Analysis and Calorimetry》2007,88(1):291-294
The effect of PbO on cement hydration kinetics by calorimetric method
was evaluated as a first step in this project. Substantial retardation of
reaction with water at early stages with subsequent intensification of the
process was found. As the next step, the model systems covering pure cement
minerals and their mixtures of various composition as well as soluble Pb salts
were taken into account to elucidate the mechanism of delayed, by quite good
formation of products in the so-called post-induction period. The precipitation
of sulphate, forming very thin impermeable layer seems to be responsible for
this delaying effect in case of cement, however the other reactions of Pb
compounds in alkaline environment of hydrating calcium silicate are not out
of importance. In order to prove this, the studies of chemical composition
in small areas were also carried out. 相似文献
992.
S. V. Volkov S. V. Kutyakov A. N. Levov E. I. Polyakova Le Tuan An S. A. Soldatova P. B. Terentiev A. T. Soldatenkov 《Chemistry of Heterocyclic Compounds》2007,43(10):1260-1268
It has been established that on heating, 3-benzoyl-4-hydroxy-1-methyl-4-phenylpiperidine is ring-opened in the presence of
arylamines by a type of retroaldol reaction, with subsequent transamination of the intermediate Mannich base and the formation
of 3-arylamino-1-oxo-1-phenylpropanes. When using arylhydrazines this γ-piperidol is recyclized with the formation of 1,3-diarylpyrazoles
and their 4,5-dihydro derivatives. The mass spectral behavior of a series of 3-arylamino-substituted 1-phenylpropanones has
been studied.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1486–1495, October, 2007. 相似文献
993.
Attila R. Imre W. Alexander Van Hook Bong Ho Chang Young Chan Bae 《Monatshefte für Chemie / Chemical Monthly》2003,134(12):1529-1539
Summary. Upper critical solution temperatures (UCSTs) for liquid–liquid demixing in a set of mixtures of linear alkanes (pentane (N
1=5) to pentacontane (N
1=50)) with an oligostyrene (1241amu, N
2=12) are reported. We find strong correlation between the Hildebrand solubility parameters of the alkanes and the UCST. Correlations are developed which enable predictions concerning the miscibility of mixtures of compounds with longer chains. 相似文献
994.
Kamil Walczak 《Central European Journal of Chemistry》2004,2(3):524-533
An analytical approach to the electron transport phenomena in molecular devices is presented. The analyzed devices are composed
of various molecular bridges attached to two semi-infinite electrodes. Molecular system is described within the tight-binding
model, while the coupling to the electrodes is analyzed through the use of Newns-Anderson chemisorption theory. The current-voltage
(I-V) characteristics are calculated through the integration of transmission function in the standard Landauer formulation.
The essential question of quantum interference effect of electron waves is diseussed in three aspects: (i) the geometry of
a molecular bridge, (ii) the presence of an external magnetic field and (iii) the location of chemical substituent. 相似文献
995.
Sorption equilibrium of methanol on new composite sorbents “CaCl<Subscript>2</Subscript>/silica gel”
Yuri I. Aristov Larissa G. Gordeeva Yuri D. Pankratiev Ludmila M. Plyasova I. V. Bikova Angelo Freni Giovanni Restuccia 《Adsorption》2007,13(2):121-127
This paper presents experimental data on methanol sorption on new composite sorbents which consist of mesoporous silica gels
and calcium chloride confined to their pores. Sorption isobars and XRD analysis showed the formation of a solid crystalline
solvate CaCl2⋅2MeOH at low methanol uptake, while at higher uptake the formation of the CaCl2–methanol solution occurred. The solution confined to the silica pores showed the sorption properties similar to those of
the CaCl2–methanol bulk solution. Calorimetric and isosteric analyses showed that the heat of methanol sorption depends on the methanol
uptake, ranging from 38±2 kJ/mol for the solution to 81±4 kJ/mol for the solid crystalline phase CaCl2⋅2MeOH. The above mentioned characterizations allowed the evaluation of the methanol sorption and the energy storage capacities,
clearly showing that the optimal applications of these new composite sorbents are the methanol removal from gaseous mixtures,
heat storage and sorption cooling driven by low temperature heat. 相似文献
996.
Tatjana Topalovic Vincent A. Nierstrasz Lorenzo Bautista Dragan Jocic Antonio Navarro Marijn M. C. G. Warmoeskerken 《Cellulose (London, England)》2007,14(4):385-400
Hydrogen peroxide can be catalyzed to bleach cotton fibers at temperatures as low as 30°C by incorporating dinuclear tri-μ-oxo
bridged manganese(IV) complex of the ligand 1,4,7-trimethyl-1,4,7-triazacyclononane (MnTACN) as the catalyst in the bleaching
solution. The catalytic system was found to be more selective under the conditions applied than the non-catalytic H2O2 system, showing better bleaching performance while causing slightly lower decrease in degree of polymerization (DP) of cellulose.
In order to gain fundamental knowledge of the bleach effect on cotton fibers and cellulose as its main component, especially
after catalytic bleaching, X-ray Photoelectron Spectroscopy (XPS) was used to study surface chemical effects. The Washburn
method was applied to investigate wetting properties, and liquid porosity was used to obtain pore volume distribution (PVD)
plots. Parallel analyzes performed on model cotton fabric, i.e. “clean” cotton fabric stained with morin - a pigment regularly
found in native cotton fiber, helped to differentiate between pigment oxidation and other bleaching effects produced on the
(regular) industrially scoured cotton fabric. Bleaching was not limited to the chemical action but also affected cotton fiber
capillary parameters most likely due to the removal of non-cellulosic materials as well as chain-shortened cellulose. 相似文献
997.
The adsorption of a basic dye (Methylene Blue; MB) and an acidic dye (Acid Orange; AO) has been studied on three activated carbons (ACs; FAS, SKD, and BAU) significantly differing in their porous structures and surface concentrations of ion-exchange groups and on graphitic thermal carbon black (GTCB). The effective specific surface area of FAS, SKD, and BAU determined by dye adsorption is, respectively, 60, 50, and 40% of the BET nitrogen adsorption surface area. The MB uptake on ACs and GTCB increases with rising pH, while the AO uptake decreases. Addition of an electrolyte (0.3 M NaCl) virtually does not effect the adsorption of dyes on ACs and GTCB. It is suggested that hydrophobic interactions, and not ionic ones, are the major contributors to the adsorption of dyes on ACs. 相似文献
998.
In this paper we, present some MATLAB and GAP programs and use them to find the automorphism group of the Euclidean graph
of the C80 fullerence with connectivity and geometry of I
h
symmetry point group. It is proved that this group has order 120 and is isomorphic to I
h
≊Z2×A5, where Z2 is, a cyclic group of order 2 and A5 is the alternating group on five symbols. 相似文献
999.
The effectiveness of applying a pulsed corona discharge to the destruction of olfactory pollution in air was investigated.
This paper presents a comparative study of the decomposition of three representative sulfide compounds in diluted concentrations:
hydrogen sulfide (H2S), dimethyl sulfide (DMS), and ethanethiol (C2H5SH), which could be completely removed when a sufficient but reasonable energy density was deposited in the gas. DMS showed
the lowest energy cost (around 30 eV/molecules); C2H5SH and H2S had an EC of respectively 45 eV and 115 eV. The efficiency of the non-thermal plasma process increased with decreasing the
initial concentration of sulfide compounds, while the energy yield remained almost unchanged. SO2 was the only identified byproduct of H2S decomposition, but the sulfur balance suggests the formation of undetected SO3. The byproducts analyzed during the degradation of DMS and C2H5SH enabled to propose a reaction mechanism, starting with radical attack and breaking of C–S bonds. 相似文献
1000.
Koichiro Fukuda Tomoyuki Iwata Takashi Orito 《Journal of solid state chemistry》2005,178(12):3662-3666
The structural disorder in Ba0.6Sr0.4Al2O4 (space group P6322) was investigated by X-ray powder diffraction and selected-area electron diffraction (SAED). The initial structural model was determined using direct methods, and it was further modified by the combined use of Rietveld method and maximum-entropy method (MEM). MEM-based pattern fitting method was subsequently applied, resulting in the final reliability indices of Rwp=9.61%, Rp=6.96%, RB=1.40% and S=1.25. The electron density distribution was satisfactorily expressed by the split-atom model in which the strontium/barium and oxygen atoms were split to occupy the lower symmetry sites. The diffuse scattering in SAED was mainly attributable to the positional disorder of oxygen atoms. 相似文献