全文获取类型
收费全文 | 12362篇 |
免费 | 1659篇 |
国内免费 | 1127篇 |
专业分类
化学 | 8948篇 |
晶体学 | 482篇 |
力学 | 1329篇 |
综合类 | 39篇 |
数学 | 290篇 |
物理学 | 4060篇 |
出版年
2024年 | 43篇 |
2023年 | 173篇 |
2022年 | 414篇 |
2021年 | 431篇 |
2020年 | 719篇 |
2019年 | 489篇 |
2018年 | 419篇 |
2017年 | 447篇 |
2016年 | 707篇 |
2015年 | 698篇 |
2014年 | 746篇 |
2013年 | 949篇 |
2012年 | 649篇 |
2011年 | 810篇 |
2010年 | 713篇 |
2009年 | 716篇 |
2008年 | 797篇 |
2007年 | 810篇 |
2006年 | 717篇 |
2005年 | 567篇 |
2004年 | 558篇 |
2003年 | 552篇 |
2002年 | 366篇 |
2001年 | 316篇 |
2000年 | 248篇 |
1999年 | 187篇 |
1998年 | 168篇 |
1997年 | 116篇 |
1996年 | 113篇 |
1995年 | 67篇 |
1994年 | 74篇 |
1993年 | 52篇 |
1992年 | 49篇 |
1991年 | 44篇 |
1990年 | 37篇 |
1989年 | 31篇 |
1988年 | 17篇 |
1987年 | 22篇 |
1986年 | 23篇 |
1985年 | 16篇 |
1984年 | 16篇 |
1983年 | 18篇 |
1982年 | 14篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 7篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1971年 | 6篇 |
1957年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Here, we will show photo-induced supramolecular chirality in thin films of achiral amorphous polymers with azo groups in their side-chain. A matter of particular interest is the effect of various film thicknesses on azimuthal rotation and ellipticity of incident/transmitted polarized light. Furthermore, we investigated the temporal stability of inscribed chirality. By polarimetric measurements, we found out that the azimuthal rotation gets higher with layer thickness. In this scope, we were able to measure a very high azimuthal rotation of /μm. The inscribed chirality was stable for several days. Furthermore, we investigated the time-resolved behavior of incident and transmitted polarization ellipticities for various thicknesses. The time dependency may be explained by a two-step process: (1) fast trans-cis-isomerization resulting in photo-orientation and (2) slow photo-induced mass flow. 相似文献
92.
《Surface and interface analysis : SIA》2003,35(3):263-267
The potential of a microline‐imaging laser‐induced plasma spectrometry (LIPS) system for surface and depth analysis of heterogeneous solid samples in air at atmospheric pressure has been demonstrated. A pulsed Nd : YAG laser beam operating at 532 nm, with a homogeneous energy distribution (flat top laser), was used to generate a microline plasma on the sample surface. Subsequent light from the microline plasma was resolved spectrally and spatially and detected with an imaging spectrograph and an intensified charged‐coupled device detector. A patterned metal sample was chosen as the most appropriate for this study. Three‐dimensional chemical maps of Ni and Cu from the edge connectors of a printed circuit board have been obtained. With this experimental configuration, the lateral resolution (limited by crater width) was 42 µm and the spatial resolution along the spectrometer slit was 17.4 µm. The results illustrate the capability of microline imaging for fast mapping of large‐area samples and for depth profiling purposes. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
93.
B. Roduit Ch. Borgeat B. Berger P. Folly B. Alonso J. N. Aebischer F. Stoessel 《Journal of Thermal Analysis and Calorimetry》2005,80(1):229-236
Summary An advanced kinetic study on the thermal behaviour of pyrotechnic ignition mixtures has been carried out by differential scanning calorimetry using different B/KNO3 mixtures (50:50, 30:70, 20:80) as a model reaction. The experimental conditions applied (isochoric conditions/closed crucibles and isobaric conditions/open crucibles) as well as the composition of the mixtures noticeably influences the relative thermal stabilities of the energetic materials. The kinetic study focused on the prediction of the thermal stability of the different mixtures both in extended temperature ranges and under temperature conditions at which ordinary investigation would be very difficult. Using advanced numerical tools [1], thermal ageing and influence of the complex thermal environment on the heat accumulation conditions were computed. This can be done for any surrounding temperature profile such as isothermal, non-isothermal, stepwise, modulated, shock, adiabatic conditions and additionally for temperature profiles reflecting real atmospheric temperature changes (yearly temperature profiles of different climates with daily minimal and maximal fluctuations). Applications of accurate decomposition kinetics enabled the determination of the time to maximum rate under adiabatic conditions (TMRad) with a precision given by the confidence interval of the predictions. This analysis can then be applied for the examination of the effects of the surrounding temperature for safe storage or transportation conditions (e.g. determination of the safe transport or storage temperatures). 相似文献
94.
Graphitic anode materials for lithium ion batteries processed under high humidity conditions show severe performance losses. The sensitivity of these materials towards humidity can be significantly reduced by adsorbing metal ions like silver or copper ions, with subsequent heat treatment of these composites. Results of X-ray photoelectron spectroscopy, high-resolution electron microscopy, thermogravimetry, and differential thermal analysis indicate that the deposited metals exist in metallic and carbide, MxC (M=Cu or Ag), forms. They remove or cover (i.e. deactivate) active hydrophilic sites at the surface of the graphite. These composites absorb less water during processing. The electrochemical performance, including reversible capacity, coulombic efficiency in the first cycle, and cycling behavior, is markedly improved. This approach provides a potentially powerful method to manufacture lithium ion batteries under less demanding conditions.Presented at the 3rd International Meeting on Advanced Batteries and Accumulators, 16–20 June 2002, Brno, Czech Republic 相似文献
95.
V.G. Kessler A.N. Panov N.Ya. Turova A.Yu. Borissevitch 《Journal of Sol-Gel Science and Technology》1997,8(1-3):1049-1051
The hydrolysis of solutions, containing either LiMo2O4(OPr
i
)5(
i
PrOH) and “La(OPr
i
)3” or LiOPr
i
and La2Mo4O8(OPr
i
)14 in 1∶1 ratio, in toluene or
i
PrOH, by water solutions in isopropanol, leads to formation of monolythic gels. The latter can be converted by drying and
heat treatment at 600°C into a fine powder of pure α-LiLaMo2O8 phase, which is transformed into β-LiLaMo2O8 powder by annealing at 800°C. The sintering of the pellets pressed under 4 bar pressure of α-LiLaMo2O8 powder at 800°C for 2 h converts them into pieces of β-LiLaMo2O8 transparent ceramics, thus providing a route to LiLnMo2O8 laser waveguide materials. 相似文献
96.
Tao Miao 《Tetrahedron letters》2007,48(1):95-99
The immobilization of copper in organic-inorganic hybrid materials catalyzing the Ullmann reaction has been described. Phenols reacted with aryl iodides, aryl bromides and aryl chlorides smoothly in the presence of a 3-(2-aminoethylamino)propyl functionalized silica gel immobilized copper catalyst. The protocol involved the use of DMSO as the solvent, and potassium fluoride as the base. The reactions generated the corresponding cross-coupling products in good to excellent yields. Furthermore, the silica-supported copper could be recovered and recycled by a simple filtration of the reaction solution and used for 10 consecutive trials without loss of its reactivity. 相似文献
97.
F. C. Adams 《Accreditation and quality assurance》1998,3(8):308-316
The basic concepts of traceability as they are defined by the Comité Consultatif pour la Cluantité de Matière are contrasted
with the practical exploitation in chemical analysis. The applicability of traceability concepts are tested for their practical
applicability on four different analytical methodologies, neutron activation analysis, plasma mass spectrometry, beam microscopical
analysis and speciation analysis of organometallic compounds.
Received: 31 March 1998 · Accepted: 6 June 1998 相似文献
98.
The interlaboratory variability in the quantification of adsorbable organically bound halogens (AOX) in industrially contaminated
soil is presented. Three consecutive rounds of a proficiency testing scheme, in which between 88 and 119 routine laboratories
participated, yielded relative reproducibility standard deviations between 7 and 20% at AOX contents between 10.9 and 268 mg
kg−1. Nineteen laboratories with established proficiency were invited to participate in the certification of the AOX content in
three soil reference materials meant for the internal quality control in analytical laboratories. The certified values are
(1349 ± 59) mg kg−1, (80 ± 7) mg kg−1 and (102 ± 8) mg kg−1, respectively. 相似文献
99.
Cimpeanu V Parvulescu VI Amorós P Beltrán D Thompson JM Hardacre C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(18):4640-4646
Heterogeneous catalytic oxidation of a series of thioethers (2-thiomethylpyrimidine, 2-thiomethyl-4,6-dimethyl-pyrimidine, 2-thiobenzylpyrimidine, 2-thiobenzyl-4,6-dimethylpyrimidine, thioanisole, and n-heptyl methyl sulfide) was performed in ionic liquids by using MCM-41 and UVM-type mesoporous catalysts containing Ti, or Ti and Ge. A range of triflate, tetrafluoroborate, trifluoroacetate, lactate and bis(trifluoromethanesulfonyl)imide-based ionic liquids were used. The oxidations were carried out by using anhydrous hydrogen peroxide or the urea-hydrogen peroxide adduct and showed that ionic liquids are very effective solvents, achieving greater reactivity and selectivity than reactions performed in dioxane. The effects of halide and acid impurities on the reactions were also investigated. Recycling experiments on catalysts were carried out in order to evaluate Ti leaching and its effect on activity and selectivity. 相似文献
100.
A. A. Vedenyapin M. D. Baturova G. I. Ioseliani G. Kh. Areshidze 《Russian Chemical Bulletin》1997,46(1):76-80
The anodic oxidation of the carbon felt Carbonetcalon results in the formation of surface defects which serve as centers of
strong adsorption of PdII, NiII, and CuII ions. The electrochemical reduction of adsorbed ions makes it possible to obtain metallic catalysts, which undergo multiple
redox cycles without loss of metal. The catalysts are characterized by high dispersity of the reduced phase, high adsorption
capacity with respect to hydrogen, and 100% selectivity in hydrogenation of acetophenone.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 81–85, January 1997 相似文献