全文获取类型
收费全文 | 2705篇 |
免费 | 84篇 |
国内免费 | 17篇 |
专业分类
化学 | 1550篇 |
晶体学 | 27篇 |
力学 | 150篇 |
数学 | 327篇 |
物理学 | 752篇 |
出版年
2023年 | 8篇 |
2022年 | 43篇 |
2021年 | 54篇 |
2020年 | 42篇 |
2019年 | 45篇 |
2018年 | 20篇 |
2017年 | 25篇 |
2016年 | 51篇 |
2015年 | 67篇 |
2014年 | 90篇 |
2013年 | 140篇 |
2012年 | 176篇 |
2011年 | 203篇 |
2010年 | 126篇 |
2009年 | 114篇 |
2008年 | 201篇 |
2007年 | 139篇 |
2006年 | 152篇 |
2005年 | 131篇 |
2004年 | 108篇 |
2003年 | 82篇 |
2002年 | 92篇 |
2001年 | 66篇 |
2000年 | 66篇 |
1999年 | 39篇 |
1998年 | 35篇 |
1997年 | 22篇 |
1996年 | 42篇 |
1995年 | 36篇 |
1994年 | 35篇 |
1993年 | 40篇 |
1992年 | 30篇 |
1991年 | 36篇 |
1990年 | 22篇 |
1989年 | 20篇 |
1988年 | 24篇 |
1987年 | 16篇 |
1986年 | 15篇 |
1985年 | 19篇 |
1984年 | 19篇 |
1983年 | 21篇 |
1982年 | 16篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1979年 | 10篇 |
1978年 | 11篇 |
1977年 | 11篇 |
1976年 | 7篇 |
1974年 | 4篇 |
1972年 | 4篇 |
排序方式: 共有2806条查询结果,搜索用时 9 毫秒
941.
We use the natural bond orbital (NBO) method to decompose a MO wavefunction into the intuitive valence bond (VB) structures. At least two natural orbital type MO are required to describe the essential binding of the H2 molecule at all inter nuclear distances. At first the MO wavefunction is transformed into an unrestricted Hartree-Fock wave-function consisted of non-orthogonal localized orbitals u' and v', and then the NBO method is used to decompose u' and v' into the physical meaningful orthogonal localized orbitals. Our results show that the orbitals u' and v' are decomposed into an atomic and an overlap parts. The latter part gives rise to the conventional ionic structure in the VB picture. 相似文献
942.
Hee‐Jeong Cha Se‐Yeun Hwang Da‐Som Lee Akula Ravi Kumar Yong‐Uk Kwon Moritz Voß Eva Schuiten Uwe T. Bornscheuer Frank Hollmann Deok‐Kun Oh Jin‐Byung Park 《Angewandte Chemie (International ed. in English)》2020,59(18):7024-7028
Long‐chain aliphatic amines such as (S,Z)‐heptadec‐9‐en‐7‐amine and 9‐aminoheptadecane were synthesized from ricinoleic acid and oleic acid, respectively, by whole‐cell cascade reactions using the combination of an alcohol dehydrogenase (ADH) from Micrococcus luteus, an engineered amine transaminase from Vibrio fluvialis (Vf‐ATA), and a photoactivated decarboxylase from Chlorella variabilis NC64A (Cv‐FAP) in a one‐pot process. In addition, long chain aliphatic esters such as 10‐(heptanoyloxy)dec‐8‐ene and octylnonanoate were prepared from ricinoleic acid and oleic acid, respectively, by using the combination of the ADH, a Baeyer–Villiger monooxygenase variant from Pseudomonas putida KT2440, and the Cv‐FAP. The target compounds were produced at rates of up to 37 U g?1 dry cells with conversions up to 90 %. Therefore, this study contributes to the preparation of industrially relevant long‐chain aliphatic chiral amines and esters from renewable fatty acid resources. 相似文献
943.
Chol‐Won Koh U‐Hwang Lee Dr. June‐Kyu Song Hae‐Rim Lee Min‐Hye Kim Myungkoo Suh Dr. Young‐Uk Kwon Prof. Dr. 《化学:亚洲杂志》2008,3(5):862-867
We report the preparation of mesoporous titania thin films with the R m pore structure derived from the Im m self‐assembled ordering of the titania species and an EO106PO70EO106 triblock copolymer. The films were spin‐cast and then aged at 18 °C at a relative humidity of 70 %, which led to the orientation of the Im m structure with the [111] direction perpendicular to the substrates. The [111] body‐diagonal channels became vertical channels upon calcination at 400 °C, thus leading to thin films with vertical channels. The pores are ordered over a large area of up to 1 μm2. The titania films can be formed on various types of substrates. By using a titania film formed on a Pt‐coated Si wafer as a template, we produced by an electrochemical‐deposition technique arrays of gold nanowires, whose morphology suggests that most of the pores of the titania thin films are accessible. The pore structure of vertical channels is stable up to 600 °C, at which temperature the wall materials crystallize into anatase. 相似文献
944.
K. H. Park D. H. Jang J. K. Lee H. S. Cho J. S. Kim J. H. Han H. T. Lee N. Hwang H. M. Kim H. M. Park S. -C. Park 《Optical and Quantum Electronics》1995,27(5):547-552
A distributed feedback (DFB) laser module has been developed for 2.5 Gbs-1 optical transmission systems. The DFB laser has a multiple-quantum-well (MQW) active layer and a planar buried heterostructure (PBH) for a low threshold current and stable singlemode operation with low chirping. A PBH DFB laser module with a single-mode fibre pigtail and an optical isolator was designed and fabricated by employing a single lens and a laser welding method. The fabricated MQW PBH DFB laser module is shown to be a suitable light source for 2.5 Gb s-1 optical transmission systems with a minimum received power of-33 dBm after 47 km conventional optical fibre transmission. 相似文献
945.
Woojin Jeon Sang Ho Rha Woongkyu Lee Cheol Hyun An Min Jung Chung Sang Hyun Kim Cheol Jin Cho Seong Keun Kim Cheol Seong Hwang 《固体物理学:研究快报》2015,9(7):410-413
The energy diagram of RuO2/Al‐doped TiO2/RuO2 structures was estimated from the capacitance–voltage and leakage current density–voltage curves. The Al‐doping profile in TiO2 film was varied by changing position of the atomic layer deposition cycle of Al2O3 during the atomic layer deposition of 9 nm‐thick TiO2 film. The interface between the TiO2 film and the RuO2 electrode containing Al‐doping layer showed a higher Schottky barrier by 0.1 eV compared with the opposite interface without the doping layer. The evolution of various leakage current profiles upon increasing the bias with opposite polarity could be well explained by the asymmetric Schottky barrier. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
946.
Tan YW Zhang Y Bolotin K Zhao Y Adam S Hwang EH Das Sarma S Stormer HL Kim P 《Physical review letters》2007,99(24):246803
The conductivity of graphene samples with various levels of disorder is investigated for a set of specimens with mobility in the range of 1-20x10(3) cm2/V sec. Comparing the experimental data with the theoretical transport calculations based on charged impurity scattering, we estimate that the impurity concentration in the samples varies from 2-15x10(11) cm(-2). In the low carrier density limit, the conductivity exhibits values in the range of 2-12e2/h, which can be related to the residual density induced by the inhomogeneous charge distribution in the samples. The shape of the conductivity curves indicates that high mobility samples contain some short-range disorder whereas low mobility samples are dominated by long-range scatterers. 相似文献
947.
W.?-Y.?P.?Hwang Bo-Qiang?MaEmail author 《The European Physical Journal A - Hadrons and Nuclei》2005,25(3):467-471
The neutron fraction in the very high-energy cosmic rays near the Greisen-Zatsepin-Kuzmin (GZK) cutoff energy is analyzed
by taking into account the time dilation effect of the neutron decays and also the pion photoproduction behaviors above the
GZK cutoff. We predict a non-trivial neutron fraction above the GZK cutoff and a negligibly small neutron fraction below.
However, there should be a large antiproton fraction in the high-energy cosmic rays below the GZK cutoff in several existing
models for the observed cosmic-ray events above and near the GZK cutoff. Such a large antiproton fraction can manifest itself
by the muon charge ratio μ+/μ- in the collisions of the primary nucleon cosmic rays with the atmosphere, if there is no neutron contribution. We suggest
to use the muon charge ratio as one of the information to detect the composition of the primary cosmic rays near or below
the GZK cutoff. 相似文献
948.
Diffusion, coalescence, and reconstruction of vacancy defects in graphene layers are investigated by tight-binding molecular dynamics (TBMD) simulations and by first principles total energy calculations. It is observed in the TBMD simulations that two single vacancies coalesce into a 5-8-5 double vacancy at the temperature of 3000 K, and it is further reconstructed into a new defect structure, the 555-777 defect, by the Stone-Wales type transformation at higher temperatures. First principles calculations confirm that the 555-777 defect is energetically much more stable than two separated single vacancies, and the energy of the 555-777 defect is also slightly lower than that of the 5-8-5 double vacancy. In TBMD simulation, it is also found that the four single vacancies reconstruct into two collective 555-777 defects which is the unit for the hexagonal haeckelite structure proposed by Terrones et al. [Phys. Rev. Lett. 84, 1716 (2000)]. 相似文献
949.
Sae‐Jin Kim Joohwi Lee Seung‐Cheol Lee Chan Park Cheol Seong Hwang Jung‐Hae Choi 《固体物理学:研究快报》2012,6(3):108-110
The migration barrier energies of the nitrogen atom and N2 molecule, and the activation barriers for the dissociation and formation of N2 in Ge2Sb2Te5 were calculated by ab‐initio methods. Various transition and metastable states were found along the migration pathway. Migration barrier energies up to 1.19 eV for the nitrogen atom suggest that it is difficult for it to move from one site to any other site or diffuse out from Ge2Sb2Te5 although doped nitrogen is energetically less stable with respect to N2 in vacuum. N2 in Ge2Sb2Te5 was hardly expected to dissociate into nitrogen atoms and vice versa. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
950.