全文获取类型
收费全文 | 2891篇 |
免费 | 87篇 |
国内免费 | 12篇 |
专业分类
化学 | 2260篇 |
晶体学 | 34篇 |
力学 | 24篇 |
数学 | 51篇 |
物理学 | 621篇 |
出版年
2021年 | 24篇 |
2020年 | 20篇 |
2019年 | 31篇 |
2018年 | 16篇 |
2017年 | 22篇 |
2016年 | 49篇 |
2015年 | 45篇 |
2014年 | 49篇 |
2013年 | 95篇 |
2012年 | 155篇 |
2011年 | 182篇 |
2010年 | 93篇 |
2009年 | 97篇 |
2008年 | 162篇 |
2007年 | 170篇 |
2006年 | 153篇 |
2005年 | 172篇 |
2004年 | 142篇 |
2003年 | 133篇 |
2002年 | 103篇 |
2001年 | 104篇 |
2000年 | 78篇 |
1999年 | 70篇 |
1998年 | 34篇 |
1997年 | 38篇 |
1996年 | 33篇 |
1995年 | 30篇 |
1994年 | 26篇 |
1993年 | 30篇 |
1992年 | 42篇 |
1991年 | 31篇 |
1990年 | 37篇 |
1989年 | 27篇 |
1988年 | 17篇 |
1987年 | 35篇 |
1986年 | 18篇 |
1985年 | 33篇 |
1984年 | 33篇 |
1983年 | 19篇 |
1982年 | 33篇 |
1981年 | 31篇 |
1980年 | 22篇 |
1979年 | 41篇 |
1978年 | 23篇 |
1977年 | 21篇 |
1976年 | 16篇 |
1975年 | 17篇 |
1974年 | 18篇 |
1973年 | 14篇 |
1968年 | 11篇 |
排序方式: 共有2990条查询结果,搜索用时 31 毫秒
151.
Takuo Kosuge Kuniro Tsuji Koichi Hirai Kentaro Yamaguchi Toshihiko Okamoto Yoichi Iitaka 《Tetrahedron letters》1981,22(35):3417-3420
A new toxin, named neosurugatoxin, was isolated from the toxic Japanese Ivory Shell and its structure was determined by X-ray crystallographic analysis. 相似文献
152.
Epoxidation of alpha,beta-unsaturated ketones using hydrogen peroxide in the presence of basic hydrotalcite catalysts 总被引:1,自引:0,他引:1
Yamaguchi K Mori K Mizugaki T Ebitani K Kaneda K 《The Journal of organic chemistry》2000,65(21):6897-6903
The basic layered hydrotalcites have been used as catalysts for the epoxidation of alpha,beta-unsaturated ketones in heterogeneous reaction media using hydrogen peroxide as an oxidant. A wide variety of alpha,beta-unsaturated ketones were oxidized to the corresponding epoxyketones in excellent yields under mild reaction conditions. For example, 2-cyclohexen-1-one gave 2,3-epoxycyclohexanone in 91% yield at 40 degrees C for 5 h with high efficiency in hydrogen peroxide. The catalytic activity of the hydrotalcites increased as the basicity of their surfaces increased. In the case of the epoxidation of less reactive substrates, adding a cationic surfactant such as n-dodecyltrimethylammonium bromide (DTMAB) to the above oxidation system accelerated the epoxidation reaction. These hydrotalcite catalysts were easily separated from the reaction mixture and were reusable. 相似文献
153.
Nakatani K Hagihara S Sando S Sakamoto S Yamaguchi K Maesawa C Saito I 《Journal of the American Chemical Society》2003,125(3):662-666
The binding of a dimeric form of the 2-amino-1,8-naphthyridine derivative (naphthyridine dimer) to a human telomeric sequence, TTAGGG, was investigated by UV melting, CD spectra, and CSI-MS measurements. Both the 9-mer d(TTAGGGTTA) and the 15-mer d(TTAGGGTTAGGGTTA) showed apparent melting temperatures (T(m)) of 45.6 and 63.6 degrees C, respectively, in the presence of naphthyridine dimer (30 microM) in sodium cacodylate buffer (50 mM, pH 7.0) containing 100 mM NaCl. The CD spectra at 235 and 255 nm of the 9-mer increased in intensity accompanied with strong induced CDs at 285 and 340 nm upon complex formation with naphthyridine dimer. UV titration of the binding of naphthyridine dimer to the 9-mer at 320 nm showed a hypochromism of the spectra. A Scatchard plot of the data showed the presence of multiple binding sites with different association constants. Cold spray ionization mass spectrometry of the complex between naphthyridine dimer and the 9-mer clearly showed that one to three molecules of the ligand bound to the dimer duplex of the 9-mer. Telomeric repeat elongation assay showed that the binding of naphthyridine dimer to the telomeric sequence inhibits the elongation of the sequence by telomerase. 相似文献
154.
Hiroshi Hata Dr. Shigeru Yamaguchi Goro Mori Satomi Nakazono Taisuke Katoh Keishi Takatsu Satoru Hiroto Hiroshi Shinokubo Prof. Dr. Atsuhiro Osuka Prof. Dr. 《化学:亚洲杂志》2007,2(7):849-859
Highly regioselective and efficient borylation of a variety of porphyrins has been achieved by reaction with bis(pinacolato)diboron through C? H bond activation under iridium catalysis on the basis of the synthetic protocol developed by Miyaura, Hartwig, and Smith. A boryl group can be selectively introduced at sterically uncongested positions in the peripheral aryl groups of porphyrin substrates whose peripheral β‐positions are sterically hindered. Curiously, β substituents adjacent to the aryl group to be borylated have unexpectedly large effects on the regioselectivity, because the iridium catalyst can discriminate between subtle steric differences. Chemoselective borylation was also achieved for several functionalized porphyrins. This borylation protocol can be applied to various monomeric and oligomeric functional porphyrins, hence offering an efficient route to elaborate multiporphyrin‐based molecular constructs. 相似文献
155.
H. Okamoto K. Yamaguchi M. Haraguchi T. Okamoto 《Applied physics. B, Lasers and optics》2012,108(1):149-152
We fabricated and investigated a plasmonic racetrack resonator with a trench structure. Trench channel plasmon polaritons excited by end-fire coupling at a wavelength of 633 nm are observed in the fabricated racetrack resonator. The racetrack resonator also worked as a plasmonic racetrack resonator. The experimental and simulation results of the electric field distributions are in good agreement. 相似文献
156.
157.
Koichiro Shirota Ichirou Yamaguchi Kiyoshi Kanie Tomiki Ikeda Tamejiro Hiyama Ichiro Kobayashi 《Liquid crystals》2013,40(5):555-558
The optical properties of two kinds of photochromic antiferroelectric liquid crystal (AFLC) containing an azo group have been examined. Depending on the substituting group at the chiral centre, these AFLCs showed different photoinduced phase transitions by Ar+ laser light irradiation. This phase transition has led to a new form of optical switching controlled by a bias voltage. In addition, it was found that these AFLCs caused an azimuthal photoalignment effect regulated by linearly polarized Ar+ laser light irradiation. These phenomena were applied to image storage. 相似文献
158.
Shoichi Kutsumizu Koushi Morita Tatsuya Ichikawa Shinichi Yano Shuichi Nojima Takanari Yamaguchi 《Liquid crystals》2013,40(11):1447-1458
The structure of the thermotropic cubic phases of 4′- n -alkoxy-3′-nitrobiphenyl-4-carboxylic acids (ANBC- n , where n indicates the number of carbon atoms in the alkoxy group) was studied by X-ray diffraction. For the homologues with n = 15, 16, 17, and 18, the cubic phase was of an Ia 3 d type, whereas the homologues with n = 19, 20, and 21 exhibited an Im 3 m cubic structure; for these seven homologues the same type of cubic structure was observed both on heating and cooling. Further lengthening of the alkoxy chain to n = 22 and 26, however, gave two types of cubic structure in the cubic phase region on heating, one with Im 3 m symmetry in the low temperature region and the other with Ia 3 d symmetry in the high temperature region. On cooling, the two homologues exhibited the Ia 3 d cubic structure only. This is the first example in the cubic phase region of a series of homologues containing two types of structure, dependent on temperature and n . Such a complicated phase diagram in the cubic region is clearly understood qualitatively in terms of Gibbs free energy-temperature diagrams. The dependence of structural parameters such as the cubic lattice constant on the alkoxy chain length n are also presented and discussed. 相似文献
159.
160.
Seiichi Ohta Susumu Inasawa Yukio Yamaguchi 《Journal of Polymer Science.Polymer Physics》2012,50(12):863-869
When a mixture of liquid crystal (LC) and photo reactive monomer is irradiated by UV light, polymerization occurs and LC droplets form through phase separation, producing polymer dispersed LCs (PDLCs). Although size control of LC droplets and reduced amounts of LC in PDLC films are important in applications, precise size control of LC droplets at a low LC fraction has not yet been accomplished. In this study, the phase diagrams of the LC/initial monomer and the LC/polymer during polymerization were used to control LC droplet size at various LC fractions. Both the relative position of the sample in the initial phase diagram and the shift of the phase separation line during polymerization were shown to be important in determining the size of LC droplets. Our results are expected to provide a new strategy for precise size control of LC droplets especially at a low LC fraction range, which would be a great help for PDLC applications. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012 相似文献