全文获取类型
收费全文 | 2621篇 |
免费 | 73篇 |
国内免费 | 19篇 |
专业分类
化学 | 1920篇 |
晶体学 | 26篇 |
力学 | 26篇 |
数学 | 257篇 |
物理学 | 484篇 |
出版年
2023年 | 18篇 |
2021年 | 29篇 |
2020年 | 32篇 |
2019年 | 35篇 |
2018年 | 22篇 |
2017年 | 20篇 |
2016年 | 28篇 |
2015年 | 48篇 |
2014年 | 56篇 |
2013年 | 146篇 |
2012年 | 109篇 |
2011年 | 144篇 |
2010年 | 82篇 |
2009年 | 72篇 |
2008年 | 142篇 |
2007年 | 153篇 |
2006年 | 134篇 |
2005年 | 149篇 |
2004年 | 144篇 |
2003年 | 127篇 |
2002年 | 116篇 |
2001年 | 64篇 |
2000年 | 55篇 |
1999年 | 48篇 |
1998年 | 42篇 |
1997年 | 31篇 |
1996年 | 38篇 |
1995年 | 22篇 |
1994年 | 24篇 |
1993年 | 32篇 |
1992年 | 36篇 |
1991年 | 32篇 |
1990年 | 25篇 |
1989年 | 29篇 |
1988年 | 17篇 |
1987年 | 14篇 |
1986年 | 22篇 |
1985年 | 32篇 |
1984年 | 38篇 |
1983年 | 24篇 |
1982年 | 30篇 |
1981年 | 24篇 |
1980年 | 26篇 |
1979年 | 33篇 |
1978年 | 17篇 |
1977年 | 15篇 |
1976年 | 16篇 |
1975年 | 14篇 |
1974年 | 35篇 |
1973年 | 18篇 |
排序方式: 共有2713条查询结果,搜索用时 343 毫秒
71.
Kinoshita M Murakami E Oda Y Funakubo T Kawakami D Kakehi K Kawasaki N Morimoto K Hayakawa T 《Journal of chromatography. A》2000,890(2):261-271
Frontal affinity chromatography is a method for quantitative analysis of biomolecular interactions. We reinforced it by incorporating various merits of a contemporary liquid chromatography system. As a model study, the interaction between an immobilized Caenorhabditis elegans galectin (LEC-6) and fluorescently labeled oligosaccharides (pyridylaminated sugars) was analyzed. LEC-6 was coupled to N-hydroxysuccinimide-activated Sepharose 4 Fast Flow (100 μm diameter), and packed into a miniature column (e.g., 10×4.0 mm, 0.126 ml). Twelve pyridylaminated oligosaccharides were applied to the column through a 2-ml sample loop, and their elution patterns were monitored by fluorescence. The volume of the elution front (V) determined graphically for each sample was compared with that obtained in the presence of an excess amount of hapten saccharide, lactose (V0); and the dissociation constant, Kd, was calculated according to the literature [K. Kasai, Y. Oda, M. Nishikawa, S. Ishii, J. Chromatogr. 376 (1986) 33]. This system also proved to be useful for an inverse confirmation; that is, application of galectins to an immobilized glycan column (in the present case, asialofetuin was immobilized on Sepharose 4 Fast Flow), and the elution profiles were monitored by fluorescence based on tryptophan. The relative affinity of various galectins for asialofetuin could be easily compared in terms of the extent of retardation. The newly constructed system proved to be extremely versatile. It enabled rapid (analysis time 12 min/cycle) and sensitive (20 nM for pyridylaminated derivatives, and 1 μg/ml for protein) analyses of lectin–carbohydrate interactions. It should become a powerful tool for elucidation of biomolecular interactions, in particular for functional analysis of a large number of proteins that should be the essential issues of post-genome projects. 相似文献
72.
73.
74.
The separation of daughter nuclides in the carrier-free state from90Sr?90Y and140Ba?140La aqueous solution systems was performed by thin-layer chromatographic methods. (1) When a silica gel adsorbent and a developer of 1N NaCl, KCl, NH4Cl, CaCl2, SrCl2 or BaCl2 solutions was employed,90Y and140La were retained at the origin, while90Sr and140Ba advanced with the developer front. Addition of gypsum as binder to the silica gel prevented the separation of the140Ba?140La system, retaining both components at the origin. (2) When the140Ba?140La system was developed with water on a silica gel adsorbent containing 5% of gypsum, which was treated with various concentrations of nitric acid, the Rf value of140La increased with the concentration of nitric acid used, reaching a maximum of 0.98 at 0.1 N. The Rf value then decreased on the further increase of the concentration of nitric acid. When the same process was applied to the90Sr?90Y system, there was no separation. The radiochemical purities of90Y and140La obtained in the above two ways were more than 99%. 相似文献
75.
Hirai A Matsui A Komatsu K Tanino K Miyashita M 《Chemical communications (Cambridge, England)》2002,(17):1970-1971
A highly regio- and stereoselective alpha-methylation reaction of gamma,delta-epoxy-alpha,beta-unsaturated esters was achieved by using a Me2Zn-CuCN reagent. 相似文献
76.
Highly efficient methods for synthesizing metacyclophanes such as 2,6-bridged pyrones and pyridines are described. 4-Hydroxy-2-pyrone derivative 3 bridged at the 3 and 6-positions is readily available. This compound was transformed into 2,6-bridged 4-pyrone 4 on heating in ethanol or in hydrochloric acid. Heating 4 with ammonia or methylamine afforded the corresponding 2,6-bridged 4-pyrone 7 or 8. These pyridones were synthesized directly from 3 by treatment with ammonia or methylamine. These methods have a wide applicability to the bridge length of metacyclophane; compounds with a short bridge (n=8) as well as long bridge (n=18) are synthesized in satisfactory yields. 相似文献
77.
Akhtaruzzaman M Kamata N Nishida J Ando S Tada H Tomura M Yamashita Y 《Chemical communications (Cambridge, England)》2005,(25):3183-3185
Dithiazolylbenzothiadiazoles easily obtained have high electron affinity and the FET device of a trifluoromethylphenyl derivative exhibited a good n-type performance with high electron mobility. 相似文献
78.
Sub-Doppler high-resolution excitation spectra and the Zeeman effects of the 6(0)(1), 1(0)(1)6(0)(1), and 1(0)(2)6(0)(1) bands of the S1(1)B2u<--S(0)(1)A1g transition of benzene were measured by crossing laser beam perpendicular to a collimated molecular beam. 1593 rotational lines of the 1(0) (1)6(0) (1) band and 928 lines of the 1(0)(2)6(0)(1) band were assigned, and the molecular constants of the excited states were determined. Energy shifts were observed for the S1(1)B2u(v1=1,v6=1,J,Kl=-11) levels, and those were identified as originating from a perpendicular Coriolis interaction. Many energy shifts were observed for the S1(1)B2u(v1=2,v6=1,J,Kl) levels. The Zeeman splitting of a given J level was observed to increase with K and reach the maximum at K=J, which demonstrates that the magnetic moment lies perpendicular to the molecular plane. The Zeeman splittings of the K=J levels were observed to increase linearly with J. From the analysis, the magnetic moment is shown to be originating mostly from mixing of the S1(1)B2u and S2(1)B1u states by the J-L coupling (electronic Coriolis interaction). The number of perturbations was observed to increase as the excess energy increases, and all the perturbing levels were found to be a singlet state from the Zeeman spectra. 相似文献
79.
Murakami M Usui I Hasegawa M Matsuda T 《Journal of the American Chemical Society》2005,127(5):1366-1367
Cyclobutene, having a pinacolatoboryl group at the 3-position, was prepared by the reaction of trimethyl borate with a cyclobutenyl anion, which was generated by reductive lithiation of 3-(phenylselenyl)cyclobutene. Its thermal ring-opening reaction provided (Z)-1-borylbuta-1,3-diene selectively despite the arising steric congestion. The contrasteric behavior was accounted for by assuming an electron-accepting interaction of the vacant boron p orbital with the distorted breaking sigma orbital in the inward transition state. 相似文献
80.
Tsuda M Izui N Shimbo K Sato M Fukushi E Kawabata J Katsumata K Horiguchi T Kobayashi J 《The Journal of organic chemistry》2003,68(13):5339-5345
A novel cytotoxic 16-membered macrodiolide, amphidinolide X (1), has been isolated from a marine dinoflagellate Amphidinium sp. (strain Y-42). The gross structure of 1 was elucidated on the basis of spectroscopic data including one-bond and long-range (13)C-(13)C correlations. The relative and absolute stereochemistries were determined by combined analyses of NOESY data and (1)H-(1)H and (1)H-(13)C coupling constants of 1 and NMR data of the degradation products. Amphidinolide X (1) is the first macrodiolide consisting of polyketide-derived diacid and diol units from natural sources. The biosynthetic origins of 1 were investigated by means of feeding experiments with (13)C-labeled acetates. 相似文献