全文获取类型
收费全文 | 1919篇 |
免费 | 33篇 |
国内免费 | 3篇 |
专业分类
化学 | 1374篇 |
晶体学 | 26篇 |
力学 | 15篇 |
数学 | 162篇 |
物理学 | 378篇 |
出版年
2022年 | 9篇 |
2021年 | 13篇 |
2020年 | 12篇 |
2019年 | 16篇 |
2018年 | 12篇 |
2016年 | 20篇 |
2015年 | 19篇 |
2014年 | 33篇 |
2013年 | 78篇 |
2012年 | 86篇 |
2011年 | 78篇 |
2010年 | 50篇 |
2009年 | 55篇 |
2008年 | 120篇 |
2007年 | 94篇 |
2006年 | 83篇 |
2005年 | 96篇 |
2004年 | 78篇 |
2003年 | 84篇 |
2002年 | 107篇 |
2001年 | 48篇 |
2000年 | 29篇 |
1999年 | 24篇 |
1998年 | 24篇 |
1997年 | 30篇 |
1996年 | 30篇 |
1995年 | 24篇 |
1994年 | 25篇 |
1993年 | 18篇 |
1992年 | 32篇 |
1991年 | 19篇 |
1990年 | 16篇 |
1989年 | 15篇 |
1988年 | 19篇 |
1987年 | 26篇 |
1986年 | 28篇 |
1985年 | 30篇 |
1984年 | 39篇 |
1983年 | 25篇 |
1982年 | 39篇 |
1981年 | 32篇 |
1980年 | 28篇 |
1979年 | 26篇 |
1978年 | 22篇 |
1977年 | 22篇 |
1976年 | 26篇 |
1975年 | 31篇 |
1974年 | 14篇 |
1973年 | 18篇 |
1971年 | 11篇 |
排序方式: 共有1955条查询结果,搜索用时 828 毫秒
991.
Masao Kamiko Hiroyuki Mizuno Junhua Xu Ryoichi Yamamoto 《Solid State Communications》2005,134(12):803-808
This study was to investigate the surfactant effect of Bi on the heteroepitaxial growth of Fe/Cr(100) multilayers by reflection high-energy electron diffraction (RHEED) measurements. With predeposition of submonolayer Bi on Fe(100) prior to evaporation of Fe/Cr multilayer, more long-lasting RHEED intensity oscillations were observed. This implies that the layer-by-layer growth of Fe/Cr multilayer is enhanced. The observations of grazing incidence X-ray reflectivity confirmed that the interface structures of Fe/Cr multilayer with Bi were sharper than that of multilayer without Bi. The study was also to investigate the magnetotransport properties between Bi surfactant-mediated multilayers and normal ones. The magnetoresistance (MR) ratio of the multilayers was enhanced by predeposition of Bi. 相似文献
992.
993.
Toshiyasu Arai 《Archive for Mathematical Logic》1998,37(3):149-165
We show that the consistency of the first order arithmetic follows from the pointwise induction up to the Howard ordinal. Our proof differs from U. Schmerl [Sc]: We do not need Girard's
Hierarchy Comparison Theorem. A modification on the ordinal assignment to proofs by Gentzen and Takeuti [T] is made so that
one step reduction on proofs exactly corresponds to the stepping down in ordinals. Also a generalization to theories of finitely iterated inductive definitions is proved.
Received May 30, 1996 相似文献
994.
S. Kuribayashi T. Tomimasu S. Kawanishi S. Arai 《Applied physics. B, Lasers and optics》1997,65(3):393-398
2 . The laser generates an intense infrared macropulse with a duration of 17 μs; the macropulse consists of a train of 380 micropulses,
each of which has a duration of a few picoseconds. The fluence of a macropulse was estimated to be about 16 Jcm-2 at a beam waist. Peak wavelengths were set in the range of 9–10 μm. The macropulse induced the IRMPD of 1 and 5 Torr CHBrF2; most of molecules in the focal region seemed to decompose at a wavelength of 9.3 μm. The mechanism is the initial decomposition
of CHBrF2 to CF2 and HBr, followed by the dimerization of CF2 to form C2F4. The decomposition was found to be isotopically selective at 9.7 μm; the final product C2F4 had a 13C atomic fraction of 6%. Th
e addition of CO2 to CHBrF2 significantly decreased the yield of C2F4. vibrationally excited CHBrF2 molecules produced by laser pulses were efficiently deactivated by CO2 molecules.
Received: 7 October 1996 相似文献
995.
Takahisa Omata Masao Kita Motomi Katada 《Journal of Physics and Chemistry of Solids》2005,66(1):53-62
Two cation-ordered phases were prepared by the oxidation of a pyrochlore phase as a precursor in the Sn-Nb-O system. One was a cation-ordered fluorite related phase, whose unit cell volume was eight times larger than that of the fluorite structure, similar to the κ-CeZrO4 phase. The other was a cation-ordered α-PbO2 phase, in which the ordered arrangement of cations was distinctly different from the well-known cation-ordered α-PbO2 structures such as wolflamite and columbite. The chemical compositions of the phases, including valence states of cations, local structure and electronic structure near the energy band gap were studied. The compositions of the precursor and its oxidized phases were evaluated, respectively, to be SnII1.62(NbV1.86SnIV0.14)O6.55 and SnIV0.81(NbV0.93SnIV0.07)O4.085, i.e. SnIV1.62(NbV1.86SnIV0.14)O8.17, by TG-DTA and ICP analyses, 119Sn Mössbauer spectroscopy and X-ray photoemission spectroscopy. It was ascertained using IR and Raman spectroscopies that the structural framework of the cation-ordered fluorite related phase was close to that of the precursor pyrochlore phase, and the structural framework of the cation-ordered α-PbO2 phase was distinct from that of the precursor pyrochlore. The Mössbauer parameters obtained showed a strong deviation of oxygen atoms contained in the SnO8 polyhedron in the cation-ordered fluorite related phase from the cubic arrangement for the ideal fluorite related structure, and a lower site symmetry of SnIV in the cation-ordered α-PbO2 than in rutile SnO2. An increase in the energy band gap from ∼2.5 eV for the precursor pyrochlore to ∼3.5 eV for the oxidized phases was attributed to the vanishing of Sn 5s2 lone-pair states upon oxidation of SnII in the precursor to SnIV in the oxidized phases. 相似文献
996.
Yukio Isozaki Jianxin Yao Tetsuo Matsuda Harutaka Sakai Zhansheng Ji Noriei Shimizu Noritada Kobayashi Hodaka Kawahata Hiroshi Nishi Masao Takano Tomomi Kubo 《Proceedings of the Japan Academy. Series B, Physical and biological sciences》2004,80(1):10
Precise stratigraphic analysis of Middle-Upper Permian and Lower Triassic sequence at Chaotian in northern Sichuan, China, identified two remarkable mass extinction horizons, one at the Middle-Upper Permian (Guadalupian-Lopingian; G-L) boundary and the other at the Upper Permian-Lower Triassic (P-T) boundary. Across each of the boundaries, biodiversity declined sharply in fusulinid, rugose coral, brachiopod, ammonite, conodont, and radiolaria. Both boundaries are characterized by two biohorizons, i.e., one marked by major extinction of pre-existing fauna and the other by the first appearance of younger fauna. It is noteworthy that a peculiar rhyo-dacitic tuff bed occurs at each of the extinction horizons. Thus the Late Permian biosphere was strongly affected twice by highly explosive, severe volcanism. Regional correlation of the G-L and P-T boundary tuff beds throughout South China, and partly to Japan, positively suggests a cause-effect link between large-scale explosive volcanism and mass extinction. 相似文献
997.
Binary crystal formed by 9,10-dihydro-9,10-[o]benzenoanthracene-1,4-dione (triptycenequinone, TPQ, yellow) and 9,10-dihydro-9,10-[o]benzenoanthracene-1,4-diol (triptycenehydroquinone, TPHQ, colorless) was found to be a substitutional solid solution of TPQ doped by TPHQ with concentration of TPHQ<ca. 0.2. The characteristic color (brown) of the solid solution may be ascribed to local intermolecular CT interaction between the p-benzoquinone and hydroquinone moieties of TPQ and TPHQ, respectively, enabled by a disorder in the binary crystal. It seemed appropriate to regard the solid solution as non-stoichiometric quinhydrone. Crystal structure of pure TPHQ is also reported. A common molecular arrangement in the crystals of pure TPQ and pure TPHQ, as well as the resemblance in the molecular structure, seems to be favorable for the formation of the solid solution. 相似文献
998.
Xiangyang Tai Guozhang Wu Yoichi Tominaga Shigeo Asai Masao Sumita 《Journal of Polymer Science.Polymer Physics》2005,43(2):184-189
A substantial approach to one‐dimensional (1D) electrically conductive composites was proposed which was based on the thermodynamic analysis of electric‐field‐induced particle alignment in a nonpolar thermoplastic polymer matrix. The process condition window was based on the real‐time exploration of dynamic percolation under different electric fields with carbon black (CB)‐filled polyethylene as a model. The CB content was the main factor of the process condition. Its upper limit was set as the critical percolation concentration at the thermodynamic equilibrium state without an electric field to eliminate the possibility of conductive network formation perpendicular to the electric‐field direction, whereas its lower limit the critical percolation concentration at the thermodynamic equilibrium state under a critical electric field (E*). A composite with CB content in this window, isothermally treated in an electric field not less than E*, showed conductivity in the electric‐field direction about 105 times larger than that in the perpendicular direction. A 1D cluster structure in the direction of the electric filed was confirmed with scanning electron microscopy morphology observations. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 184–189, 2005 相似文献
999.
Extension of accompanying coordinate expansion and recurrence relation method for general‐contraction basis sets 下载免费PDF全文
An algorithm of the accompanying coordinate expansion and recurrence relation (ACE‐RR), which is used for the rapid evaluation of the electron repulsion integral (ERI), has been extended to the general‐contraction (GC) scheme. The present algorithm, denoted by GC‐ACE‐RR, is designed for molecular calculations including heavy elements, whose orbitals consist of many primitive functions with and without higher angular momentum such as d‐ and f‐orbitals. The performance of GC‐ACE‐RR was assessed for ‐, ‐, ‐, and ‐type ERIs in terms of contraction length and the number of GC orbitals. The present algorithm was found to reduce the central processing unit time compared with the ACE‐RR algorithm, especially for higher angular momentum and highly contracted orbitals. Compared with HONDOPLUS and GAMESS program packages, GC‐ACE‐RR computations for ERIs of three‐dimensional gold clusters Aun (n = 1, 2, …, 10, 15, 20, and 25) are more than 10 times faster. © 2014 Wiley Periodicals, Inc. 相似文献
1000.
Rycce S. Pratikha Takahiro Inoue Yuka Arai Tatsuhiro Kojima Nobuto Yoshinari Takumi Konno 《中国化学会会志》2020,67(12):2189-2197
The reaction of Na[CoIII(d -ebp)] (d -H4ebp = N,N′-ethylenebis[d -penicillamine]) with [(AuICl)2(dppe)] (dppe = 1,2-bis[diphenylphosphino]ethane) gave a cationic AuI4CoIII2 hexanuclear complex, [CoIII2(LAu4)]2+ ([ 1 ]2+), where [LAu4]4− is a cyclic tetragold(I) metalloligand with a 32-membered ring, [AuI4(dppe)2(d -ebp)2]4−. Complex [ 1 ]2+ crystallized with NO3− to produce a charge-separation (CS)-type ionic solid of [ 1 ](NO3)2. In [ 1 ](NO3)2, the complex cations are assembled to form cationic supramolecular hexamers of {[ 1 ]2+}6, which are closely packed in a face-centered cubic (fcc) lattice structure. The nitrate anions of [ 1 ](NO3)2 were accommodated in hydrophilic and hydrophobic tetrahedral interstices of the fcc structure to form tetrameric and hexameric nitrate clusters of {NO3−}4 and {NO3−}6, respectively. An analogous CS-type ionic solid formulated as [NiIICoIII(LAu4)](NO3) ([ 2 ](NO3)) was obtained when a 1:1 mixture of Na[CoIII(d -ebp)] and [NiII(d -H2ebp)] was reacted with [(AuICl)2(dppe)], accompanied by the conversion of the diamagnetic, square-planar [NiII(d -H2ebp)] to the paramagnetic, octahedral [NiII(d -ebp)]2−. While the overall fcc structure in [ 2 ](NO3) was similar to that of [ 1 ](NO3)2, none of the nitrate anions were accommodated in any hydrophobic tetrahedral interstice, reflecting the difference in the complex charges between [ 1 ]2+ and [ 2 ]+. 相似文献