全文获取类型
收费全文 | 1395篇 |
免费 | 34篇 |
国内免费 | 7篇 |
专业分类
化学 | 1141篇 |
晶体学 | 14篇 |
力学 | 12篇 |
数学 | 52篇 |
物理学 | 217篇 |
出版年
2023年 | 8篇 |
2022年 | 3篇 |
2021年 | 10篇 |
2020年 | 13篇 |
2019年 | 17篇 |
2018年 | 7篇 |
2017年 | 10篇 |
2016年 | 25篇 |
2015年 | 24篇 |
2014年 | 39篇 |
2013年 | 45篇 |
2012年 | 71篇 |
2011年 | 94篇 |
2010年 | 46篇 |
2009年 | 48篇 |
2008年 | 87篇 |
2007年 | 101篇 |
2006年 | 101篇 |
2005年 | 82篇 |
2004年 | 93篇 |
2003年 | 66篇 |
2002年 | 77篇 |
2001年 | 29篇 |
2000年 | 26篇 |
1999年 | 13篇 |
1998年 | 11篇 |
1997年 | 14篇 |
1996年 | 13篇 |
1995年 | 12篇 |
1994年 | 15篇 |
1993年 | 11篇 |
1992年 | 16篇 |
1991年 | 16篇 |
1990年 | 16篇 |
1989年 | 11篇 |
1988年 | 13篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 18篇 |
1984年 | 15篇 |
1983年 | 15篇 |
1982年 | 16篇 |
1981年 | 15篇 |
1980年 | 10篇 |
1979年 | 8篇 |
1978年 | 9篇 |
1977年 | 5篇 |
1976年 | 7篇 |
1975年 | 9篇 |
1968年 | 3篇 |
排序方式: 共有1436条查询结果,搜索用时 92 毫秒
101.
102.
Nakayama M Goto S Uchimoto Y Wakihara M Kitajima Y Miyanaga T Watanabe I 《The journal of physical chemistry. B》2005,109(22):11197-11203
Changes in the electronic structure of olivine Li(1-x)CoPO(4), 4.8 V positive electrode material for lithium ion batteries, were investigated using the X-ray absorption spectroscopy (XAS) technique. The threshold energy in the Co K-edge increased with electrochemical Li removal, indicating the oxidation of cobalt ions due to charge compensation. Moreover, P and O K-edge XAS showed a slight shift in threshold energy with Li removal. Although it is generally believed that the electrons of PO(4) polyanion do not contribute to the oxidation process, present experimental results indicate changes in the electronic structure around PO(4) units. Such results would be interpreted by the idea of the hybridization effect between the Co 3d and O 2p orbitals and of the polarization effect introduced by Li ions. 相似文献
103.
Yoshinori Sato 《Journal of organometallic chemistry》2004,689(4):744-750
A series of cobalt(II) complexes having terpyridine derivatives such as 2,2′:6′,2″-terpyridine (1), 4,4′,4″-tBu3-2,2′:6′,2″-terpyridine (2), 5,5″-Me2-2,2′:6′,2″-terpyridine (3), 6,6″-Me2-2,2′:6′,2″-terpyridine (4) and 6,6″-(3,5-Me2C6H3)2-2,2′:6′,2″-terpyridine (5) was synthesized. The structures of 1, 3, and 4 were confirmed by X-ray crystallography. The coordination sphere around the cobalt center in 1 can be described as pseudo square pyramidal. On the other hand, complex 4 has pseudo trigonal bipyramidal structure. Upon activation with d-MAO (dried-methylaluminoxane), these complexes showed high activities for the polymerization of norbornene (NBE). In particular, polymerization of NBE with 4/d-MAO system at room temperature resulted in quantitative yield within several hours to give the polymers with relatively narrow molecular weight distributions and controlled molecular weight. The polymerizations of NBE with these cobalt catalyst systems proceeded in vinyl addition polymerization, which was confirmed by 1H NMR spectra of the resulting polymers. 相似文献
104.
The reaction of enynals 1, including o-alkynylbenzaldehydes, and carbonyl compounds 2 in the presence of a catalytic amount of AuBr3 in 1,4-dioxane at 100 degrees C gave the functionalized aromatic compounds 3 in high yields. The AuBr3-catalyzed formal [4 + 2] benzannulation proceeds most probably through the coordination of the triple bond of 1 to AuBr3, the formation of a pyrylium auric ate complex via the nucleophilic addition of the carbonyl oxygen atom, the reverse electron demand-type Diels-Alder addition of the enols, derived from 2, to the auric ate complex, and subsequent dehydration and bond rearrangement. Similarly, the AuBr3-catalyzed reactions of 1 with acetal compounds afforded the corresponding aromatic compounds in good yields. 相似文献
105.
106.
Hitoshi Watarai Hideaki Monjushiro Satoshi Tsukahara Masayori Suwa Yoshinori Iiguni 《Analytical sciences》2004,20(3):423-434
The recent development of new migration methods of micro-particles in liquids using various external fields is reviewed. The combination of a laser scattering force and a photothermal effect produced photothermal-conversion laser-photophoresis. A dielectric field generated in a planer or a capillary quadrupole electrode realized dielectrophoresis. Using a micrometer-scaled magnetic field gradient, the "Magnetophoretic velocimetry" of micro-particles was invented. Furthermore, the Lorentz force generated by combining an electric field and a magnetic field was utilized for electromagnetophoresis. These new methods were overlooked and the advantages in analytical use were discussed. 相似文献
107.
A new aromadendrane-type sesquiterpenoid, 4(15)-aromadendren-12,5alpha-olide and an aromadendrane-guaianolide dimer have been isolated from the New Zealand liverwort Chiloscyphus subporosus. Their structures were established by extensive NMR techniques and X-ray crystallographic analysis. 相似文献
108.
Yoshinori Miyazaki Nobuyoshi Asai Yasushi Kikuchi DongSheng Cai Yasuhiko Ikebe. 《Mathematics of Computation》2004,73(246):719-730
In this paper, it is first given as a necessary and sufficient condition that infinite matrices of a certain type have double eigenvalues. The computation of such double eigenvalues is enabled by the Newton method of two variables. The three-term recurrence relations obtained from its eigenvalue problem (EVP) subsume the well-known relations of (A) the zeros of ; (B) the zeros of ; (C) the EVP of the Mathieu differential equation; and (D) the EVP of the spheroidal wave equation. The results of experiments are shown for the three cases (A)-(C) for the computation of their ``double pairs'.
109.
Abe S Fujishima T Tsubone T Fujimura R Ono H Matoba O Oda K Shimura T Kuroda K 《Optics letters》2003,28(6):420-422
The photorefractive effect in a nominally undoped 0.91Pb(Zn1/3Nb2/3)O3-0.09PbTiO3 single crystal is measured. We report what is, to our knowledge, the first observation of the photorefractive effect in Pb-based relaxor ferroelectric crystals. The crystal is grown by the flux solution method. Then it is cut into a 2 mm x 4 mm x 8 mm piece and electrically poled along the [111] direction. The coupling constant of the two-wave mixing is 17 cm(-1), and the normalized time constant under 1-W/cm(2) illumination is 12 s at a wave-length of 476 nm. The effective trap density is calculated as 5 x 10(16) cm(-3) from the Debye screening length under the assumption of Kukhtarev's band-transport model. The dominant carrier is identified to be holes from the direction of two-wave mixing energy transfer. 相似文献
110.
Zegers RG Sumihama M Ahn DS Ahn JK Akimune H Asano Y Chang WC Daté S Ejiri H Fujimura H Fujiwara M Hicks K Hotta T Imai K Ishikawa T Iwata T Kawai H Kim ZY Kino K Kohri H Kumagai N Makino S Matsumura T Matsuoka N Mibe T Miwa K Miyabe M Miyachi Y Morita M Muramatsu N Nakano T Niiyama M Nomachi M Ohashi Y Ooba T Ohkuma H Oshuev DS Rangacharyulu C Sakaguchi A Sasaki T Shagin PM Shiino Y Shimizu H Sugaya Y Toyokawa H Wakai A Wang CW Wang SC Yonehara K Yorita T Yoshimura M Yosoi M 《Physical review letters》2003,91(9):092001
Beam polarization asymmetries for the p(gamma-->,K+)Lambda and p(gamma-->,K+)Sigma(0) reactions are measured for the first time for E(gamma)=1.5-2.4 GeV and 0.6相似文献