全文获取类型
收费全文 | 1248篇 |
免费 | 40篇 |
国内免费 | 7篇 |
专业分类
化学 | 892篇 |
晶体学 | 13篇 |
力学 | 17篇 |
数学 | 153篇 |
物理学 | 220篇 |
出版年
2022年 | 6篇 |
2021年 | 5篇 |
2020年 | 9篇 |
2019年 | 10篇 |
2018年 | 5篇 |
2017年 | 18篇 |
2016年 | 26篇 |
2015年 | 18篇 |
2014年 | 26篇 |
2013年 | 64篇 |
2012年 | 46篇 |
2011年 | 78篇 |
2010年 | 37篇 |
2009年 | 50篇 |
2008年 | 68篇 |
2007年 | 88篇 |
2006年 | 82篇 |
2005年 | 93篇 |
2004年 | 78篇 |
2003年 | 58篇 |
2002年 | 64篇 |
2001年 | 17篇 |
2000年 | 22篇 |
1999年 | 20篇 |
1998年 | 13篇 |
1997年 | 18篇 |
1996年 | 14篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1992年 | 16篇 |
1991年 | 8篇 |
1990年 | 9篇 |
1989年 | 10篇 |
1988年 | 9篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 18篇 |
1984年 | 17篇 |
1983年 | 11篇 |
1982年 | 15篇 |
1981年 | 11篇 |
1980年 | 18篇 |
1979年 | 16篇 |
1978年 | 9篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1975年 | 14篇 |
1974年 | 9篇 |
1973年 | 8篇 |
1971年 | 4篇 |
排序方式: 共有1295条查询结果,搜索用时 85 毫秒
991.
From a MeOH extract of the aerial part of Piper futokadsura, the tetrahydrofuran lignans, futokadsurin A [(7S,8S,7'S,8'R)-3,4,3'-trimethoxy-4'-hydroxy-7,7'-epoxylignan], futokadsurin B [(7R,8R,7'R,8'S)-3,4-dimethoxy-3',4'-methylenedioxy-7,7'-epoxylignan], and futokadsurin C [(7R,8R,7'S,8'S)-3,4-methylenedioxy-3',4'-dimethoxy-7,7'-epoxylignan] were isolated, together with nine known neolignans. In addition, L-tryptophan, pellitorine, phytol, elemicin, and 1,2,4-trimethoxyphenyl-5-aldehyde were isolated. The structures of the new compounds were elucidated using spectroscopic methods. These lignans inhibited nitric oxide production by a murine macrophage-like cell line (RAW 264.7), which was activated by lipopolysaccharide and interferon-gamma. 相似文献
992.
Photoelectron emission and XPS studies of real iron surfaces subjected to scratching in air,water, and organic liquids 下载免费PDF全文
Yoshihiro Momose Keika Tsuruya Takao Sakurai Keiji Nakayama 《Surface and interface analysis : SIA》2016,48(4):202-211
The influence of temperature and surface overlayer on the photoelectron emission from scratched real iron surfaces was investigated using thermally assisted photoelectron emission (TAPE) and X‐ray photoelectron spectroscopy (XPS) measurements. The scratching was conducted with a diamond cutter in seven atmospheres. The intensity of TAPE as a function of temperature, called glow curve, was measured in the range 25–339 °C using a Geiger counter under ultraviolet irradiation at 210 nm. The temperature was scanned in two cycles (Up1 and Down1, and Up2 and Down2). The XPS measurements were carried out at 25 °C and after TAPE measurements at 200 and 339 °C. The photoelectron emission intensity at 40 °C in the Up1 scan increased in the order of air < water ≈ methanol ≈ cyclohexane < ethanol < benzene < acetone, and then each glow curve exhibited a gradual increase with temperature through a broad peak. It was found that the dependence of the emission intensity in the Up1 scan on the oxygen component ratio, ZO = O2?/(OH? + O2?) and the percentage of the Fe metal and FeOOH components of the Fe3p spectra for the atmospheres greatly differed. Additionally, the glow curve in the Up1 scan was completely different from that in the other scans. It was proposed that the photoelectron emission in the Up1 scan originates from not only the base metal but also the surface overlayer having trapped electrons and is strongly influenced by the acid–base interaction of the surface hydroxyl groups with the liquids molecules. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
993.
Usefulness of Mesoporous Silica as a Template for the Preparation of Bundles of Bi Nanowires with Precisely Controlled Diameter Below 10 nm 下载免费PDF全文
Masaki Kitahara Hasbuna Kamila Prof. Dr. Atsushi Shimojima Prof. Dr. Hiroaki Wada Prof. Dr. Takao Mori Prof. Dr. Ichiro Terasaki Prof. Dr. Kazuyuki Kuroda 《化学:亚洲杂志》2016,11(6):900-905
The reduction of the diameter of Bi nanowires below 10 nm has been an important target because of the theoretical prediction with regard to significant enhancement in thermoelectric performance by size reduction. In this study, we have demonstrated the usefulness of mesoporous silica with tunable pore size as a template for the preparation of thin Bi nanowires with diameters below 10 nm. Bi was deposited within the templates through a liquid phase deposition using hexane and 1,1,3,3‐tetramethyldisiloxane as a solvent and reducing agent, respectively. Bundles of thin Bi nanowires with non‐crystalline frameworks were successfully obtained after the template removal. The diameter was precisely controlled between about 6 nm and 9 nm. The judicious choices of mesoporous silica and deposition conditions are critical for the successful preparation. The reliable formation of such thin Bi nanowires reported here opens up exciting new possibilities. 相似文献
994.
The gonality sequence \({(d_{r})_{r}}\) of a curve X of genus g which doubly covers a curve of genus h satisfies \({d_{r} = 2(r + h)}\) for all \({r = h, h + 1, \ldots, g - 3h}\) provided that \({g \gg h}\). In this paper we explore if this striking feature of \({(d_{r})_{r}}\) actually characterizes such a covering. 相似文献
995.
Preparation and Characterization of Nano-structured Ceramic Powders Synthesized by Emulsion Combustion Method 总被引:7,自引:0,他引:7
Takatori Kazumasa Tani Takao Watanabe Naoyoshi Kamiya Nobuo 《Journal of nanoparticle research》1999,1(2):197-204
The emulsion combustion method (ECM), a novel powder production process, was originally developed to synthesize nano-structured metal-oxide powders. Metal ions in the aqueous droplets were rapidly oxidized by the combustion of the surrounding flammable liquid. The ECM achieved a small reaction field and a short reaction period to fabricate the submicron-sized hollow ceramic particles with extremely thin wall and chemically homogeneous ceramic powder. Alumina, zirconia, zirconia–ceria solid solutions and barium titanate were synthesized by the ECM process. Alumina and zirconia powders were characterized to be metastable in crystalline phase and hollow structure. The wall thickness of alumina was about 10nm. The zirconia–ceria powders were found to be single-phase solid solutions for a wide composition range. These powders were characterized as equiaxed-shape, submicron-sized chemically homogeneous materials. The powder formation mechanism was investigated through the synthesis of barium titanate powder with different metal sources. 相似文献
996.
Yuzuki Eda Tomoyo Manaka Takao Hanawa Peng Chen Maki Ashida Kazuhiko Noda 《Surface and interface analysis : SIA》2022,54(8):892-898
Titanium (Ti) is always covered by thin passive films. Thus, valence band (VB) spectra, obtained using X-ray photoelectron spectroscopy (XPS), are superpositions of the VB spectra of passive films and that of the metallic Ti substrate. In this study, to obtain the VB spectra only of passive films, angular resolution (for eliminating the substrate Ti contribution) and argon ion sputtering (for removing passive films) were used along with XPS. The passive film on Ti was determined to consist of a very thin TiO2layer with small amounts of Ti2O3, TiO, hydroxyl groups, and water with a thickness of 5.9 nm. The VB spectra of Ti were deconvoluted into four peak components: a peak at ~1 eV, attributed to the Ti metal substrate; a broad peak in the 3–10 eV range, mainly attributed to O 2p (~6 eV) and O 2p-Ti 3d hybridized states (~8 eV), owing to the π (non-bonding) and σ (bonding) orbitals in the passive oxide film; and a peak at ~13 eV, attributed to the 3σ orbital of O 2p as OH−or H2O. The VB region spectrum between approximately 3 and 14 eV from Ti is originating from the passive film on Ti. In particular, characterization of VB spectrum obtained with a takeoff angle of less than 24° is effective to obtain VB spectrum only from the passive film on Ti. The property as n-type semiconductor of the passive film on Ti is probably higher than that of rutile TiO2ceramics. 相似文献
997.
Saito T Nihei H Otani T Suyama T Furukawa N Saito M 《Chemical communications (Cambridge, England)》2008,(2):172-174
The first examples of C[double bond, length as m-dash]S induced Pauson-Khand type reactions are described; 2-alkynylphenyl isothiocyanates were converted to 3-substituted-2H-thieno[2,3-b]indol-2-ones in the presence of a stoichiometric amount of Mo(CO)(6) or Co(2)(CO)(8), or a catalytic amount of Rh catalyst under an atmospheric pressure of carbon monoxide. 相似文献
998.
999.
Reaction of [ArN(2)][BF(4)] salts immobilized in [BMIM][PF(6)] ionic liquid (IL) with TMSX (X = I, Br) and TMSN(3) represents an efficient method for the preparation of iodo-, bromo-, and azido-derivatives via dediazoniation. The reactions can also be effected starting with ArNH(2) by in situ diazotization with [NO][BF(4)] followed by reaction with TMSX or TMSN(3). Depending on the substituents on the benzenediazonium cation, competing fluorodediazoniation (ArF formation) and hydrodediazoniation (ArH formation) were observed. Dediazoniation with TMSN(3) and with TMSI generally gave the highest chemoselectivity toward ArN(3) and ArI formation. The IL was recycled and reused up to 5 times with no appreciable decrease in the conversions. Multinuclear NMR monitoring of the interaction of [ArN(2)][BF(4)]/TMSX, [BMIM][PF6]/TMSX, and [BMIM][PF(6)]/TMSX/[ArN(2)][BF(4)] indicated that TMSF is formed primarily via [ArN(2)][BF(4)]/TMSX, generating [ArN(2)][X] in situ, which gives ArX on dediazoniation. Competing formation of ArF in Sandmeyer-type bromodediazoniation of [ArN(2)][BF(4)] with Cu(I)Br immobilized in the IL points to significant involvement of heterolytic dediazoniation. 相似文献
1000.
Hiroyuki Kudo Teruyoshi Goto Takao Saito Hirokazu Saito Kimio Otsuka Kohji Mitsubayashi 《Mikrochimica acta》2008,160(4):421-426
An enzyme-based gas sensor (bio-sniffer) for choline vapour was fabricated and tested. The bio-sniffer was constructed using
a Clark-type dissolved oxygen electrode and an enzyme (choline oxidase) immobilized membrane. This bioelectronic device measures
choline concentration by the oxygen consumption induced by an enzyme reaction of choline oxidase. As the assessment of sensor
performances, the calibration curves for choline in the liquid and gas phases were investigated, respectively. The responses
of the bioelectronic device to choline solutions of various concentrations were related within a range from 5.00 to 700 μmol·L−1 with a correlation coefficient of 0.999. On the other hand, the bio-sniffer for choline vapour was placed into a gas-measuring
chamber and calibrated using gas detection tubes. The calibration range was 1.00–30.0 ppm (correlation coefficient: 0.996).
The response time for choline vapour was approximately 15% slower than that of biosensor for choline solution. These results
indicate that the bio-sniffer is useful to monitor colourless and odourless choline gas released from coating compositions
including choline.
Correspondence: Kohji Mitsubayashi, Department of Biomedical Devices and Instrumentation, Institute of Biomaterials and Bioengineering,
Tokyo Medical and Dental University, 2-3-10 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-0062, Japan 相似文献