全文获取类型
收费全文 | 87017篇 |
免费 | 827篇 |
国内免费 | 501篇 |
专业分类
化学 | 30704篇 |
晶体学 | 859篇 |
力学 | 7133篇 |
综合类 | 3篇 |
数学 | 33033篇 |
物理学 | 16613篇 |
出版年
2023年 | 85篇 |
2022年 | 340篇 |
2021年 | 433篇 |
2020年 | 359篇 |
2019年 | 445篇 |
2018年 | 10691篇 |
2017年 | 10445篇 |
2016年 | 6560篇 |
2015年 | 1241篇 |
2014年 | 851篇 |
2013年 | 1359篇 |
2012年 | 4511篇 |
2011年 | 11146篇 |
2010年 | 6127篇 |
2009年 | 6437篇 |
2008年 | 7010篇 |
2007年 | 9127篇 |
2006年 | 507篇 |
2005年 | 1588篇 |
2004年 | 1695篇 |
2003年 | 2141篇 |
2002年 | 1152篇 |
2001年 | 322篇 |
2000年 | 339篇 |
1999年 | 213篇 |
1998年 | 229篇 |
1997年 | 194篇 |
1996年 | 241篇 |
1995年 | 148篇 |
1994年 | 113篇 |
1993年 | 112篇 |
1992年 | 88篇 |
1991年 | 95篇 |
1990年 | 79篇 |
1989年 | 94篇 |
1988年 | 91篇 |
1987年 | 91篇 |
1986年 | 87篇 |
1985年 | 83篇 |
1984年 | 77篇 |
1983年 | 57篇 |
1982年 | 69篇 |
1981年 | 57篇 |
1980年 | 69篇 |
1979年 | 64篇 |
1978年 | 52篇 |
1914年 | 45篇 |
1912年 | 40篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Dusanka Ž. Obadović Anikó Vajda Maya Garić A. Bubnov Vera Hamplová M. Kašpar Katalin Fodor-Csorba 《Journal of Thermal Analysis and Calorimetry》2005,80(2):519-523
Summary Thermal properties of a homologous series of ferroelectric liquid crystals S-(-)-[4-(2-n-alkoxy-propionyloxy)]biphenyl-4'-[n-alkoxy-(3,5-dimethyl)]benzoate have been investigated by polarizing optical microscopy and differential scanning calorimetry.
The mesophases were identified and confirmed by X-ray too. Three binary mixtures were prepared from the individual homologues.
In one of the mixtures (Mix1), the ferroelectric SmC* phase has broadened and became enantiotropic. This mesophase remained
monotropic in the other two mixtures (Mix2, Mix3). The chiral nematic N* phase did not appear in Mix1, but remained monotropic
for the other two mixtures. Two molecular parameters, the layer spacing and the average intermolecular distance have been
calculated from the X-ray results for the homologues and their mixtures. An intercalated tail-to-tail packing of molecules
was found both in the single compounds and their mixtures resulting in the layer spacing about half of the molecular length
of the single compounds. 相似文献
992.
Miniaturizing all dimensions of apparatus, such as electronics and computers, is the current trend followed by scientists
in various fields. The idea of Lab-on-a-Chip has significantly expanded and found its broad applications in analytical chemistry.
Microplasmas can act as a sample excitation source and are the miniaturized versions of full-sized plasmas. These can be created
in various forms, such as direct current, microwave induced, capacitively coupled and inductively coupled plasmas. Scaling
down the size would reduce the amount of gases, liquids and consumables required, as well as the sample analysis time, which
in turn would decrease the operating costs. Therefore, several research groups are involved in the development of microplasmas
for utilisation in analytical instruments. 相似文献
993.
The redox behaviour of adsorbed species of 2,4,6-tri(2-pyridyl)-1,3-5-triazine (TPTZ) at the surface of a mercury electrode was examined using cycling voltammetry. Based on the adsorption and accumulation of TPTZ at the charged mercury surface cathodic adsorptive stripping voltammetry (CSV) is applied for the trace determination of TPTZ using a differential pulse (DP) technique. Experimental and operational parameters for the quantitative analysis of TPTZ are optimized and the detection limit was found to be 3×10–9 mol/l. The effect of some interferences, e.g. organic compounds, cations and anions, are investigated. 相似文献
994.
Bocquet ML Michaelides A Loffreda D Sautet P Alavi A King DA 《Journal of the American Chemical Society》2003,125(19):5620-5621
Reaction mechanisms and activation energies for the complete conversion of ethene to ethene epoxide on two recently characterized oxidized Ag{111} surfaces have been determined from density functional theory. On both surfaces, epoxidation proceeds through a two-step nonconcerted mechanism via an oxametallacycle intermediate. The key implications are that both surfaces are active and that epoxidation can take place over a wide O coverage regime. 相似文献
995.
996.
997.
Danielle Giron S. Monnier M. Mutz P. Piechon T. Buser F. Stowasser K. Schulze M. Bellus 《Journal of Thermal Analysis and Calorimetry》2007,89(3):729-743
Adequate very sensitive quantification methods are needed for the development and are also now required for the monitoring
of undesirable solid form(s) as routine tests. The pre-requisite for quantitation are selectivity, sensitivity and most important
the purity of standards and their proper storage, what is a challenge for metastable forms.
Several analytical techniques are available such as X-ray diffraction, spectroscopy, thermal analysis and microcalorimetry.
The different steps of the validation of the analytical methods and problems to be solved are discussed. Examples illustrate
the different techniques and compare their possible advantages and limits. The relative standard deviation of measurements
should allow for checking the homogenization procedure of mixtures for calibration. The validation should be carried out following
ICH guidelines for validation of analytical methods. Comparison of different techniques in adequate concentration range add
confidence in the analytical results. 相似文献
998.
999.
Andrzej Czerwiński Iwona Kiersztyn Michał Grdeń 《Journal of Solid State Electrochemistry》2003,7(6):321-326
The effect of temperature on hydrogen and deuterium electrosorption into a palladium LVE (limited-volume electrode) has been
investigated. A decrease in hydrogen capacity (H/Pd ratio) with increasing temperature has been observed. Temperature strongly
influences the plots of measured H(D)/Pd values vs. potential scan rate. In addition, hydrogen absorption was found to be
dependent on the composition of the surrounding electrolyte solution. These results have confirmed the hypothesis that two
different mechanisms of hydrogen desorption from the palladium electrode take place, namely electrochemical oxidation and
non-electrochemical recombination. Further, the ratio between the rate constants for these two processes has been found to
change with temperature.
Electronic Publication 相似文献
1000.
Summary The thermal behavior of KH2PO4, NaH2PO4 and Na2HPO4 under non-isothermal conditions using TG method with different heating rates was studied. The values of the reaction rate were processed by means of Friedmans differential-isoconversional method. A dependence of the activation energy vs. conversion was observed. Therefore a procedure based on the compensation effect (suggested by Budrugeac and Segal) was applied. A less speculative data processing protocol was offered by the non-parametric kinetics method suggested by Serra, Nomen and Sempere. Three steps were observed by non-isothermal heating: a dehydration, a dimerization and a polycondensation. The differences in the intimate reaction mechanism are determined by the initial number of water molecules. 相似文献