全文获取类型
收费全文 | 655篇 |
免费 | 14篇 |
国内免费 | 1篇 |
专业分类
化学 | 474篇 |
晶体学 | 4篇 |
力学 | 4篇 |
数学 | 54篇 |
物理学 | 134篇 |
出版年
2022年 | 5篇 |
2021年 | 11篇 |
2020年 | 10篇 |
2019年 | 10篇 |
2018年 | 6篇 |
2017年 | 4篇 |
2016年 | 10篇 |
2015年 | 7篇 |
2014年 | 17篇 |
2013年 | 38篇 |
2012年 | 29篇 |
2011年 | 23篇 |
2010年 | 10篇 |
2009年 | 15篇 |
2008年 | 24篇 |
2007年 | 33篇 |
2006年 | 17篇 |
2005年 | 33篇 |
2004年 | 17篇 |
2003年 | 32篇 |
2002年 | 29篇 |
2001年 | 10篇 |
2000年 | 12篇 |
1999年 | 14篇 |
1998年 | 5篇 |
1997年 | 10篇 |
1996年 | 11篇 |
1995年 | 6篇 |
1994年 | 12篇 |
1993年 | 8篇 |
1992年 | 14篇 |
1991年 | 6篇 |
1990年 | 12篇 |
1989年 | 5篇 |
1988年 | 12篇 |
1987年 | 9篇 |
1986年 | 6篇 |
1985年 | 18篇 |
1984年 | 22篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 11篇 |
1980年 | 8篇 |
1979年 | 13篇 |
1978年 | 14篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1970年 | 3篇 |
1968年 | 3篇 |
排序方式: 共有670条查询结果,搜索用时 46 毫秒
51.
Yuta Suzuki Tetsuhiro NemotoShun-ichi Nakano Zengduo ZhaoYuta Yoshimatsu Yasumasa Hamada 《Tetrahedron letters》2014
A novel method for synthesizing 4,5-fused tricyclic quinoline derivatives based on an acid-promoted intramolecular Friedel–Crafts allenylation of anilines. Using aryl group-substituted propargyl alcohol derivatives with a meta-substituted N-Boc aniline unit as substrates, a four-step reaction sequence involving an acid-promoted intramolecular Friedel–Crafts allenylation of anilines, an acid-promoted intramolecular C–N bond formation, deprotection of the Boc group, and air oxidation proceeded in a single pot, producing the corresponding 4,5-fused tricyclic quinoline derivatives in 31–84% yield. 相似文献
52.
The reactions of 1,1-disubstituted alkenes with 4-hydroxyquinolin-2(1H)-ones under both Mn(III)-catalyzed aerobic oxidation conditions at room temperature and Mn(III)-mediated oxidation conditions at reflux temperature are described. The Mn(III)-catalyzed aerobic oxidation afforded bis(hydroperoxyethyl)quinolinones and azatrioxa[4.4.3]propellanes, while the oxidation with Mn(OAc)3·2H2O produced furo[3,2-c]quinolin-4-one analogues. The existence of a substituent at the 3-position of the 4-hydroxyquinolin-2(1H)-ones prevented a double reaction with the alkenes, and (endoperoxy)quinolinones and/or (hydroperoxyethyl)quinolinones were obtained under the Mn(III)-catalyzed aerobic conditions, while furo[3,2-c]quinolinone hemiacetals and vinylquinolinones were selectively produced under the Mn(III)-mediated oxidation conditions depending on the reaction temperature and times. Cyclic assembly of quinolinone-related 1,3-dicarbonyl compounds such as dihydropyridinones, pyranones, and dimedone derivatives was also examined under elevated temperature conditions. 相似文献
53.
Manabu Yamada Muniyappan Rajiv Gandhi Yoshihiko Kondo Fumio Hamada 《Supramolecular chemistry》2014,26(7-8):620-630
The ability of chloroform solutions of p-diethylaminomethylthiacalix[4]arene 1 to extract platinum from HCl media was tested. As an ion-pair extractant, compound 1 had the highest platinum extraction ability among all the thiacalix[n]arene derivatives tested in this study. Compound 1 was a highly specific extractant for Pt(IV) ions from single-metal solutions and platinum-group metal solutions from automotive catalyst residue. Various conditions such as contact time, pH, concentration of 1, effect of chloride ions, effect of acidity and Pt(IV) concentration were studied. The distribution ratio of platinum ions (D) was calculated. The platinum complex stoichiometry ratio was obtained using slope analysis. The 1–Pt(IV) complex was characterised using X-ray photoelectron spectroscopy, FT-IR and 1H NMR. Finally, the Pt(IV) extraction percentage of compound 1 was compared with that of previously reported thiacalix[n]arene-based extractants. 相似文献
54.
Yasumasa Hamada 《Chemical record (New York, N.Y.)》2014,14(2):235-250
This review describes our recent works on the diastereo‐ and enantioselective synthesis of anti‐β‐hydroxy‐α‐amino acid esters using transition‐metal–chiral‐bisphosphine catalysts. A variety of transition metals, namely ruthenium (Ru), rhodium (Rh),iridium (Ir), and nickel (Ni), in combination with chiral bisphosphines, worked well as catalysts for the direct anti‐selective asymmetric hydrogenation of α‐amino‐β‐keto ester hydrochlorides, yielding anti‐β‐hydroxy‐α‐amino acid esters via dynamic kinetic resolution (DKR) in excellent yields and diastereo‐ and enantioselectivities. The Ru‐catalyzed asymmetric hydrogenation of α‐amino‐β‐ketoesters via DKR is the first example of generating anti‐β‐hydroxy‐α‐amino acids. Complexes of iridium and axially chiral bisphosphines catalyze an efficient asymmetric hydrogenation of α‐amino‐β‐keto ester hydrochlorides via dynamic kinetic resolution. A homogeneous Ni–chiral‐bisphosphine complex also catalyzes an efficient asymmetric hydrogenation of α‐amino‐β‐keto ester hydrochlorides in an anti‐selective manner. As a related process, the asymmetric hydrogenation of the configurationally stable substituted α‐aminoketones using a Ni catalyst via DKR is also described. 相似文献
55.
Lung cancer is the leading type of cancer worldwide in terms of the number of new cases and is responsible for the largest number of deaths due to poor prognosis and difficult early detection. Due to its ability to detect numerous small molecular metabolites simultaneously, metabolomics has been widely used for the assessment of global metabolic changes in a living organism to discover candidate biomarkers for cancer diagnosis, investigate the development of cancer, and provide insights into the underlying pathophysiology. This review will mainly describe recent developments in lung cancer metabolomics in terms of early‐stage detection, biomarker discovery and mechanism exploration by using nuclear magnetic resonance, liquid chromatography–mass spectrometry, gas chromatography–mass spectrometry, and capillary electrophoresis–mass spectrometry in the last 10 years. The sample collection and metabolite extraction methods are also summarized. 相似文献
56.
The fast potential change near the separatrix is measured directly at the L-H transition by a heavy-ion-beam probe. The potential changes with two different time scales at the L-H transition triggered by a sawtooth crash: it drops at first with the time scale of 10--100 mus just after the arrival of the heat pulse due to the sawtooth crash. Then, it decreases again at a few 100 mus after the first drop at a time scale of about 200 mus. 相似文献
57.
Hashi K Shimizu T Goto A Kiyoshi T Matsumoto S Wada H Fujito T Hasegawa K Yoshikawa M Miki T Ito S Hamada M Hayashi S 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2002,156(2):318-321
We have developed a 920-MHz NMR system and performed the proton NMR measurement of H(2)O and ethylbenzene using the superconducting magnet operating at 21.6 T (920 MHz for proton), which is the highest field produced by a superconducting NMR magnet in the persistent mode. From the NMR measurements, it is verified that both homogeneity and stability of the magnet have a specification sufficient for a high resolution NMR. 相似文献
58.
T.R. Hamada 《Journal of sound and vibration》1981,74(2):221-233
The response problem of a simply supported and damped Bernoulli-Euler uniform beam of finite length traversed by a constant force moving at a uniform speed is solved by applying the double Laplace transformation with respect both to time and to the length co-ordinate along the beam. This leads to obtaining the sum of the Fourier series which represents the forced vibration part of the transient response in closed form. The solution thus obtained is effective for computing beam stresses. It is also shown that the forced vibration part can be expanded in a double power series, and that the coefficients of the series at the point of application of the moving force can be readily obtained by making use of Bernoulli polynomials. As a numerical example, simple approximate formulae obtained from the series are used to compute the forced vibration parts of the deflection and the beam stresses at the mid-span of the beam when a moving load is exactly at the mid-point of the beam, and their truncation errors are calculated. 相似文献
59.
A fluorimetric assay for lecithin-cholesterol acyltransferase in human plasma (normal and pathological) is described. The lowered cholesterol concentration in the enzyme reaction is determined fluorimetrically by using the cholesterol oxidase—peroxidase —tyramine system. The assay requires only 10 μl of plasma. 相似文献
60.
Tomoshige Morita Takeshi Hamada Koji Ishida 《Fresenius' Journal of Analytical Chemistry》1981,309(5):377-379
Summary The TLC behaviour of Rh(III), Ir(III) and Ir(IV) has been investigated in the two systems consisting of DEAE-cellulose or ECTEOLA-cellulose and 5 M HCl media containing H2O2. These systems, especially in combination with a simple chemical pretreatment of samples (with LiCl, HCl and H2O2), can effectively be applied to the complete separation of mixtures of Rh(III) and Ir(III) or Ir(IV) in a wide range of ratios and amounts (Rh: Ir=1100 to 1001).
Dünnschicht-chromatographische Trennung von Rhodium(III) und Iridium(III, IV) durch Anionenaustausch
Zusammenfassung Das dünnschicht-chromatographische Verhalten von Rh(III), Ir(III) und Ir(IV) wurde in H2O2-haltiger 5 M salzsaurer Lösung auf DEAE-sowie ECTEOLA-Cellulose untersucht. In Kombination mit einer einfachen chemischen Vorbehandlung der Probe (mit LiCl, HCl, H2O2) kann eine wirkungsvolle Trennung von Rh(III) und Ir(III) oder Ir(IV) über einen weiten Konzentrationsbereich erzielt werden (Rh: Ir=1100 bis 1001).相似文献