全文获取类型
收费全文 | 3779篇 |
免费 | 104篇 |
国内免费 | 4篇 |
专业分类
化学 | 2445篇 |
晶体学 | 40篇 |
力学 | 99篇 |
数学 | 448篇 |
物理学 | 855篇 |
出版年
2023年 | 20篇 |
2022年 | 61篇 |
2021年 | 130篇 |
2020年 | 75篇 |
2019年 | 86篇 |
2018年 | 84篇 |
2017年 | 88篇 |
2016年 | 158篇 |
2015年 | 113篇 |
2014年 | 167篇 |
2013年 | 220篇 |
2012年 | 244篇 |
2011年 | 301篇 |
2010年 | 187篇 |
2009年 | 214篇 |
2008年 | 254篇 |
2007年 | 232篇 |
2006年 | 187篇 |
2005年 | 147篇 |
2004年 | 137篇 |
2003年 | 86篇 |
2002年 | 85篇 |
2001年 | 58篇 |
2000年 | 61篇 |
1999年 | 30篇 |
1998年 | 47篇 |
1997年 | 25篇 |
1996年 | 35篇 |
1995年 | 44篇 |
1994年 | 31篇 |
1993年 | 24篇 |
1992年 | 23篇 |
1991年 | 30篇 |
1990年 | 18篇 |
1989年 | 18篇 |
1988年 | 14篇 |
1987年 | 13篇 |
1986年 | 14篇 |
1985年 | 20篇 |
1984年 | 8篇 |
1983年 | 11篇 |
1982年 | 7篇 |
1981年 | 17篇 |
1980年 | 10篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1976年 | 9篇 |
1975年 | 4篇 |
1974年 | 4篇 |
排序方式: 共有3887条查询结果,搜索用时 93 毫秒
41.
D. S. Gouveia R. Rosenhaim M. A. M. A. de Maurera S. J. G. Lima C. A. Paskocimas E. Longo A. G. Souza I. M. G. Santos 《Journal of Thermal Analysis and Calorimetry》2004,75(2):453-460
With the aim of obtaining materials with applications in pigments, CoxZn7-xSb2O12 spinels were synthesized using the Pechini method. This method consists in the formation of a polymeric net, where the metallic
cations are homogeneously distributed. In this work, two types of alcohol (ethyl glycol and ethylene glycol) were used for
the synthesis of a zinc antimoniate spinel, CoxZn7-xSb2O12 (x=0-7). The materials were characterized by termogravimetry (TG) and differential thermal analysis (DTA). TG results indicated
a decrease in total mass loss when cobalt was added to the solution substituting zinc, for samples prepared using the two
different alcohols. Decomposition temperatures, obtained by TG and DTA, presented a decreasing behavior as cobalt was added
to the material. In relation to the alcohols, all results indicated a better polymerization of the resin when ethylene glycol
was used, being the most indicated one for cation immobilization. X-ray diffraction did not show differences between the two
alcohols - both presented the spinel phase (Co, Zn)2.33Sb0.67O4. Samples with higher quantity of cobalt also presented ilmenite phase (Co, Zn)Sb2O6.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
42.
O. N. Oliveira Jr. G. F. Leal Ferreira 《Applied Physics A: Materials Science & Processing》1987,42(3):213-217
Surface-potential measurements carried out in negatively corona charged 12 m samples of fluorethylenepropylene (Teflon FEP) showed the following characteristics: 1) with a constant charging current, the potential initially rises linearly, and then sublinearly; 2) the potential saturates irrespectively of the charging process and 3) practically no potential decay is observed after switching off the corona. These results have been interpreted in terms of an usual model (field-independent trapping time) for charge transport in insulators, with saturable deep traps in both surface and bulk of the sample and a relatively high electron mobility in order to prevent free-space charge accumulation. The partial differential equations derived from the model are numerically solved and it was found that only the product of the mobility with the trapping time is relevant to the fitting of experimental results, provided that >10–8 cm2/Vs. A field-dependent trapping time model leads to poorer fittings. 相似文献
43.
Sokoloff MD Anjos JC Appel JA Bracker SB Browder TE Cremaldi LM Elliott JR Escobar CO Estabrooks P Gibney MC Hartner GF Karchin PE Kumar BR Losty MJ Luste GJ Mantsch PM Martin JF McHugh S Menary SR Morrison RJ Nash T Ong P Pinfold J Purohit MV Raab JR Santoro AF Sidhu JS Sliwa K Souza MH Spalding WJ Streetman ME Stundia AB Witherell MS 《Physical review letters》1986,57(24):3003-3006
44.
Summary Electron microscope examination of thixotropic aluminium and thorium molybdate gels shows that one hour after formation they are constituted by short fibrils of small axial ratio. The fibrils of the aluminium molybdate gels, with ageing at room temperature or with boiling, increase in diameter and length; the fibrous shape of the particles is maintained after two and a half years of ageing; all fibrils are crystalline by electron diffraction. The fibrils of the thorium molybdate gels, except in the gels containing hydrochloric acid, change with ageing at room temperature or with boiling, into plates of hexagonal, elliptical or rectangular profile; the fibrils and plates are crystalline and have the same electron diffraction pattern as the fibrils.This work was aided, in part, by grants from Conselho Nacional de Pesquisas and the Rockefeller Foundation. 相似文献
45.
The present work is an attempt to assess racemization in stepwise solid-phase peptide synthesis at elevated temperatures (SPPS-ET), a high-speed approach in which peptide elongation occurs at 55-75 °C. This attempt was based on the notion that a high propensity for this side reaction would hamper employment of this alternative approach and would dampen interest in its further development. Simple peptide models were synthesized using customized protocols for classical SPPS or SPPS-ET. Systematic analyses of the resulting crude peptides by reversed-phase HPLC, ion-exchange HPLC, capillary electrophoresis and electrospray ionization mass spectrometry revealed low diastereomeric byproduct contents. These results indicate that, from the standpoint of racemization, classical SPPS and SPPS-ET protocols were equivalent. Therefore, further studies employing SPPS-ET protocols are justified. 相似文献
46.
G. Gousset M. Touzeau M. Vialle C. M. Ferreira 《Plasma Chemistry and Plasma Processing》1989,9(2):189-206
A simple kinetic model predicting the concentration of oxygen atoms, metastable singlet molecules O2(a
1) and negative ions O — in the positive column of a DC glow discharge is developed. The calculated O and O2(a
1) concentrations are compared to previously reported measurements for pressuresp=0.2–2 Torr and discharge currentsI=10–80 mA. The electron density calculated from the continuity equationj=n
e
e v
d agrees well with experiment. The rate coefficients for electron impact processes used in the balance equations of O, O2(a
1), and O– were taken from the literature as a function of the reduced electric fieldE/N forE/N=40–80 Td. A reasonable agreement is obtained between the model and the experiment with a set of 10 reactions for the production and destruction of the above-mentioned species 相似文献
47.
María?Belén?Sierra Marcela?A.?Morini Pablo?C.?SchulzEmail author María?Luján?Ferreira 《Colloid and polymer science》2005,283(9):1016-1024
Following the studies on the effect of double bonds in the surfactant hydrophobic tail on the formation of mixed surfactant aggregates, we studied the viscosity and density of the system Sodium 10-undecenoate (SUD)–decyltrimethylammonium bromide (DTAB)–water. We found that the partial molar volume (pmv) and intrinsic viscosity of both, micellised and unmicellised mixtures, are non-ideal, dependent on the mixture composition and related to structural changes in micelles. These phenomena are caused by the presence of the double bond at the distal extreme of the SUD molecule, which has some affinity with water by formation of hydrogen bonds. In particular, as far as we know, this is the first report on non-ideal behavior of the pmv in mixed micelles. 相似文献
48.
This work focuses on the optimization of the rheological behavior of suspensions considering different solvent compositions. The effects of methyl ethyl ketone (MEK)/ethanol (E) solvent mixtures on reaction sialon suspensions were investigated by measuring sedimentation behavior, adsorption of dispersant, and flow behavior. It was shown that both the flow behavior and the sedimentation behavior strongly depended on selection of solvent composition. Using 3 wt% KD1 as dispersant, well-dispersed colloidal suspensions could be obtained in MEK-rich solvents. The suspensions with 60 vol% MEK/40 vol% E as solvent could be fitted to the Bingham model with very low yield stress, while suspensions with pure MEK or ethanol-rich mixtures as solvent showed pseudo plastic behavior with relatively high yield stress values. A model was proposed to explain the different flow behaviors of suspensions considering the different configurations of dispersant at particles' surfaces. 相似文献
49.
Marta M.?Conceio V. J.?Fernandes Jr. F. S. M.?Sinfrnio J. C. O.?Santos M. C. D.?Silva V. M.?Fonseca A. G.?Souza 《Journal of Thermal Analysis and Calorimetry》2005,79(2):263-266
Summary Sulfonylureas are widely used for the treatment of non-insulin dependent diabetes mellitus. Glibenclamide belongs to the group of substituted arylsulfonylureas. Many representative of this group shows polymorphism. The purpose of this work was to investigate the thermal behaviour and compatibility between glibenclamide and some excipients using thermoanalytical techniques (TG-DTG/DSC). The thermal and isothermal kinetics data showed incompatibility between glibenclamide and magnesium stearate. 相似文献
50.
M. Zampieri S. R. Lazaro C. A. Paskocimas A. G. Ferreira E. Longo J. A. Varela 《Journal of Sol-Gel Science and Technology》2006,37(1):9-17
Titanium citrate and lead and titanium citrate were prepared by polymeric precursor method in aqueous solution. This citrate
was analyzed by 1H, 13C NMR and gHMBC–NMR (Hetero-nuclear multiple-bond correlation) to investigate the formation of the citrate complexs and influence
of the Pb2+ ion in this complex. These complexs were characterized by interaction between Ti4+ ion and citric acid carboxyls. Quantum mechanic simulations in level ab initio were used to study the electronic structure and natural charges (NBO) to both the complexs. Such techniques indicated the
formation of an octahedral complex with an arrangement similar to Ti atom in the crystalline structure of the PbTiO3. A study using the technique FT-Raman made possible the confirmation of the interaction among the Ti4+ and Pb2+ ions with the citric acid carboxyls. 相似文献