全文获取类型
收费全文 | 2911篇 |
免费 | 85篇 |
国内免费 | 10篇 |
专业分类
化学 | 1801篇 |
晶体学 | 57篇 |
力学 | 52篇 |
数学 | 422篇 |
物理学 | 674篇 |
出版年
2023年 | 17篇 |
2022年 | 18篇 |
2021年 | 74篇 |
2020年 | 66篇 |
2019年 | 87篇 |
2018年 | 86篇 |
2017年 | 45篇 |
2016年 | 100篇 |
2015年 | 66篇 |
2014年 | 99篇 |
2013年 | 148篇 |
2012年 | 164篇 |
2011年 | 184篇 |
2010年 | 106篇 |
2009年 | 117篇 |
2008年 | 129篇 |
2007年 | 121篇 |
2006年 | 115篇 |
2005年 | 114篇 |
2004年 | 87篇 |
2003年 | 75篇 |
2002年 | 74篇 |
2001年 | 33篇 |
2000年 | 30篇 |
1999年 | 43篇 |
1998年 | 23篇 |
1997年 | 27篇 |
1996年 | 27篇 |
1995年 | 35篇 |
1994年 | 18篇 |
1993年 | 32篇 |
1992年 | 23篇 |
1991年 | 25篇 |
1990年 | 17篇 |
1989年 | 23篇 |
1988年 | 12篇 |
1987年 | 13篇 |
1984年 | 17篇 |
1982年 | 13篇 |
1980年 | 12篇 |
1979年 | 24篇 |
1978年 | 14篇 |
1977年 | 19篇 |
1976年 | 22篇 |
1975年 | 20篇 |
1957年 | 13篇 |
1956年 | 17篇 |
1954年 | 14篇 |
1927年 | 11篇 |
1907年 | 11篇 |
排序方式: 共有3006条查询结果,搜索用时 78 毫秒
991.
Simakov A Sekiguchi O Bunkan AJ Uggerud E 《Journal of the American Chemical Society》2011,133(51):20816-20822
We report the unimolecular decomposition of protonated glyceraldehyde, [HOCH(2)CH(OH)CHO]H(+), and protonated dihydroxyacetone, [HOCH(2)C(O)CH(2)OH]H(+). On the basis of mass spectrometric experiments and computational quantum chemistry, we have found that these isomeric ions interconvert freely at energies below that required for their unimolecular decompositions. The losses of formaldehyde and water (the latter also followed by CO loss) are the dominating processes, with formaldehyde loss having the lower energetic threshold. The reverse of the formaldehyde loss, namely, the addition of formaldehyde to protonated glycolaldehyde, appears to be an inefficient reaction at low temperature and pressure in the gas phase, leading to dissociation products. The relevance of these findings to interstellar chemistry and prebiotic chemistry is discussed, and it is concluded that the suggestion made in the literature that successive addition of formaldehyde by proton-assisted reactions should account for interstellar carbohydrates most likely is incorrect. 相似文献
992.
Santoro A Prokhorov AM Kozhevnikov VN Whitwood AC Donnio B Williams JA Bruce DW 《Journal of the American Chemical Society》2011,133(14):5248-5251
Preparation of Ir(III) complexes using anisotropic 2,5-di(4-alkoxyphenyl)pyridine ligands leads to emissive, liquid-crystalline complexes containing bound Cl and dimethyl sulfoxide. Using analogous poly(alkoxy) ligands allows the preparation of bis(2-phenylpyridine)iridium(III) acac complexes, which are also mesomorphic. The observation of liquid crystallinity in octahedral complexes of this type is without precedent. 相似文献
993.
994.
Senkovskyy V Tkachov R Komber H Sommer M Heuken M Voit B Huck WT Kataev V Petr A Kiriy A 《Journal of the American Chemical Society》2011,133(49):19966-19970
Strongly electron-deficient (n-type) main-chain π-conjugated polymers are commonly prepared via well-established step-growth polycondensation protocols which enable limited control over polymerization. Here we demonstrate that activated Zn and electron-deficient brominated thiophene-naphthalene diimide oligomers form anion-radical complexes instead of conventional Zn-organic derivatives. These highly unusual zinc complexes undergo Ni-catalyzed chain-growth polymerization leading to n-type conjugated polymers with controlled molecular weight, relatively narrow polydispersities, and specific end-functions. 相似文献
995.
Fukin Georgy K. Baranov Evgeny V. Rumyantcev Roman V. Cherkasov Anton V. Maleeva Alevtina I. Gushchin Aleksey V. 《Structural chemistry》2020,31(5):1841-1849
996.
Arkhipova Ekaterina A. Strokova Natalia E. Tambovtseva Yulia A. Ivanov Anton S. Chernyak Sergei A. Maslakov Konstantin I. Egorova Tolganay B. Savilov Serguei V. Lunin Valery V. 《Journal of Thermal Analysis and Calorimetry》2020,140(6):2641-2648
Journal of Thermal Analysis and Calorimetry - Combustion heats of graphene nanoflakes (GNFs) of different thicknesses produced by chemical vapor deposition method were measured for the first time... 相似文献
997.
Anton Korban Siarhei Charapitsa Radomír abala Sobolenko Lidia Svetlana Sytova 《Journal of mass spectrometry : JMS》2020,55(3)
The potential use of ethanol as an internal standard (IS) for GC‐MS analysis was studied. The paper describes the analysis of spirit drinks and other alcoholic products which consist of a mixture of water, ethanol, and volatile compounds. In the suggested method, ethanol was employed as an IS for the common procedure of volatile compounds quantification. A number of standard solutions of nine compounds with different concentrations was prepared in a water‐ethanol matrix and measured with GC‐MS in the SIM mode. Two possible approaches were suggested to avoid detector saturation during ethanol detection. The first one consisted in using less abundant m/z 47 as quantifiers. These ions mainly correspond to unfragmented heavy ethanol molecules containing one 13C isotope. The second method consisted in reduction of the voltage of MS electron multiplier. The experiment also included the preparation and subsequent dilution of the standard solution and ethanol with water, which determined the linearity of the modified MS response relative to the ethanol content. Analysis of the obtained results revealed that volatile compounds can be successfully accurately determined with GC‐MS by employing ethanol as an IS. Application of the suggested method is not limited to the reported volatile compounds and alcoholic products. 相似文献
998.
Sergey V. Ovsyannikov Maxim Bykov Sergey A. Medvedev Pavel G. Naumov Anton Jesche Alexander A. Tsirlin Elena Bykova Irina Chuvashova Alexander E. Karkin Vadim Dyadkin Dmitry Chernyshov Leonid S. Dubrovinsky 《Angewandte Chemie (International ed. in English)》2020,59(14):5632-5636
Functional oxides whose physicochemical properties may be reversibly changed at standard conditions are potential candidates for the use in next‐generation nanoelectronic devices. To date, vanadium dioxide (VO2) is the only known simple transition‐metal oxide that demonstrates a near‐room‐temperature metal–insulator transition that may be used in such appliances. In this work, we synthesized and investigated the crystals of a novel mixed‐valent iron oxide with an unconventional Fe5O6 stoichiometry. Near 275 K, Fe5O6 undergoes a Verwey‐type charge‐ordering transition that is concurrent with a dimerization in the iron chains and a following formation of new Fe?Fe chemical bonds. This unique feature highlights Fe5O6 as a promising candidate for the use in innovative applications. We established that the minimal Fe?Fe distance in the octahedral chains is a key parameter that determines the type and temperature of charge ordering. This model provides new insights into charge‐ordering phenomena in transition‐metal oxides in general. 相似文献
999.
Rudolf Podoba Igor Štubňa Viera Trnovcová Anton Trník 《Journal of Thermal Analysis and Calorimetry》2014,118(2):597-601
The samples from kaolin Sedlec were investigated by the help of DTA, TG, and temperature dependences of DC conductivity using Pt wire electrodes and linear heating up to 1,050 °C. After drying, the samples contained ~1.5 mass% of the physically bound water. DTA and TG reflected generally known facts about a release of the physically bound water, dehydroxylation, and metakaolinite → Si–Al spinel transformation. The results of electrical measurements showed the electric current passed over the maximum at 60 °C. The self-ionization of water results in the process H2O → H+ + OH? in the water layers on the crystal surfaces; consequently, OH? and H+ are the main charge carriers in the low-temperature region. The water molecules simultaneously evaporate from the sample which decreases the number of the charge carriers. When the physically bound water evaporates, the current is carried mostly by K+ and Na+ ions. During dehydroxylation, the hydroxyls OH? split into H+ and O2?. The ions H+ jump to the neighboring OH? groups creating the water molecules. The ions O2?remain bounded to the newly created metakaolinite lattice. Therefore, mobile protons contribute to the electric current. At the same time, this contribution gradually decreases because of the escape of H2O from the sample. The sharp current peak and DTA peak at 970 °C imply relatively fast metakaolinite → Si–Al spinel transformation. This DC current peak results from the shift of Al3+ and O2? ions into new positions. 相似文献
1000.
Nina V. Kosova Evgeniya T. Devyatkina Arseny B. Slobodyuk Anton K. Gutakovskii 《Journal of Solid State Electrochemistry》2014,18(5):1389-1399
Single-phase LiVPO4F and LiVPO4F/Li3V2(PO4)3 nanostructured composite cathode materials were prepared by heating of the VPO4?+?LiF mechanochemically activated mixture to 700 °C and subsequent quick or slow cooling to room temperature, respectively. The formation of the composites was proved by a combination of different physico-chemical methods, including XRD, FTIR, 6Li and 31P NMR, SEM, TEM, and HRTEM. It has been shown that in the composites LiVPO4F and Li3V2(PO4)3 nanocrystals well inset into each other resulting in the nanodomain composite formation. Charge–discharge curves of the composites have a sloping profile both in the high-voltage (3.0–4.5 V) and in the low-voltage (1.3–2.5 V) ranges, noticeably different from plateaus for a phase-pure LiVPO4F, thus indicating a probable change of a two-phase regime of lithium intercalation for a single-phase one. Enhanced rate capability of the LiVPO4F/Li3V2(PO4)3 composites is associated with their microstructure and high ionic conductivity of Li3V2(PO4)3. 相似文献