全文获取类型
收费全文 | 1997篇 |
免费 | 71篇 |
国内免费 | 13篇 |
专业分类
化学 | 1320篇 |
晶体学 | 5篇 |
力学 | 78篇 |
数学 | 320篇 |
物理学 | 358篇 |
出版年
2023年 | 15篇 |
2022年 | 49篇 |
2021年 | 48篇 |
2020年 | 43篇 |
2019年 | 40篇 |
2018年 | 31篇 |
2017年 | 20篇 |
2016年 | 80篇 |
2015年 | 64篇 |
2014年 | 88篇 |
2013年 | 114篇 |
2012年 | 141篇 |
2011年 | 153篇 |
2010年 | 91篇 |
2009年 | 77篇 |
2008年 | 125篇 |
2007年 | 122篇 |
2006年 | 119篇 |
2005年 | 117篇 |
2004年 | 92篇 |
2003年 | 83篇 |
2002年 | 52篇 |
2001年 | 26篇 |
2000年 | 16篇 |
1999年 | 18篇 |
1998年 | 11篇 |
1997年 | 18篇 |
1996年 | 27篇 |
1995年 | 17篇 |
1994年 | 22篇 |
1993年 | 10篇 |
1992年 | 8篇 |
1991年 | 13篇 |
1990年 | 9篇 |
1989年 | 9篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1983年 | 10篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 10篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1975年 | 6篇 |
1973年 | 5篇 |
排序方式: 共有2081条查询结果,搜索用时 0 毫秒
991.
Searching for cyclin-dependent kinase inhibitors using a new variant of the cope elimination 总被引:1,自引:0,他引:1
Griffin RJ Henderson A Curtin NJ Echalier A Endicott JA Hardcastle IR Newell DR Noble ME Wang LZ Golding BT 《Journal of the American Chemical Society》2006,128(18):6012-6013
beta-Piperidinoethylsulfides are oxidized by m-chloroperbenzoic acid to intermediates containing both N-oxide and sulfone functions. These undergo a Cope-type elimination to a vinylsulfone that can be captured by amines to afford beta-aminoethylsulfones. When a beta-aminoethylsulfone group is linked to the 4-position of a phenyl group attached at N-2 of O6-cyclohexylmethylguanine, the resulting derivatives are inhibitors of the cyclin-dependent kinase CDK2. One of the most potent inhibitors (IC50 = 45 nM) contained a N-3-hydroxypropyl group on the aminoethylsulfonyl substituent. The crystal structure of this inhibitor bound to CDK2/cyclin A was determined and shows an unusual network of hydrogen bonds. The synthetic methodology developed can be utilized in multiple-parallel format and has numerous potential applications in medicinal chemistry. 相似文献
992.
Suarez-Moreira E Hannibal L Smith CA Chavez RA Jacobsen DW Brasch NE 《Dalton transactions (Cambridge, England : 2003)》2006,(44):5269-5277
Glutathionylcobalamin, nitrocobalamin and sulfitocobalamin are important cobalamin metabolites isolable from human tissues. Herein we demonstrate that a procedure used to synthesize and isolate gamma-glutamylcysteinylcobalamin and glutathionylcobalamin in aqueous solution in high yield and purity can be used to synthesize other novel, biologically relevant thiolatocobalamins, including d,l-homocysteinylcobalamin, N-acetyl-l-cysteinylcobalamin (Na(+) salt) and 2-N-acetylamino-2-carbomethoxy-l-ethanethiolatocobalamin, as well as other non-alkylcobalamins, such as sulfitocobalamin (Na(+) salt) and nitrocobalamin. This uncomplicated, general procedure will assist researchers in identifying unknown cobalamin metabolites isolated from biological samples, and researchers interested in studying the uptake and intracellular cobalamin processing mechanisms utilizing non-alkylcobalamin derivatives that are not yet commercially available. The X-ray structure and XAS spectrum of N-acetyl-l-cysteinylcobalamin are also presented. 相似文献
993.
Bianco A Bonadies F Romeo G Luisa Scarpati M Soriero A Uccella N 《Natural product research》2006,20(3):259-264
In this article, the phenolic composition of wastewaters prepared from different cultivars of Olea europaea have been described. The main aim is the recovery of these compounds for technological utilization. 相似文献
994.
995.
Nicola Ciccoli 《Advances in Mathematics》2006,199(1):104-135
We develop a quantum duality principle for coisotropic subgroups of a (formal) Poisson group and its dual: namely, starting from a quantum coisotropic subgroup (for a quantization of a given Poisson group) we provide functorial recipes to produce quantizations of the dual coisotropic subgroup (in the dual formal Poisson group). By the natural link between subgroups and homogeneous spaces, we argue a quantum duality principle for Poisson homogeneous spaces which are Poisson quotients, i.e. have at least one zero-dimensional symplectic leaf. As an application, we provide an explicit quantization of the homogeneous -space of Stokes matrices, with the Poisson structure given by Dubrovin and Ugaglia. 相似文献
996.
Cosma P Catucci L Fini P Dentuto PL Agostiano A Angelini N Scolaro LM 《Photochemistry and photobiology》2006,82(2):563-569
The formation of inclusion complexes of hydroxypropyl-beta-cyclodextrin, heptakis(2,6-di-O-methyl)-beta-cyclodextrin and heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin with 5,10,15,20-tetrakis(4-pyridyl)porphyrin (TpyP) has been studied in aqueous buffer solution (phosphate buffer pH = 7 and I = 0.01 M) to give a structural and spectroscopic characterization of a new class of potential sensitizers for photodynamic therapy. The interaction was investigated by a combination of UV/Vis absorption, fluorescence anisotropy, time-resolved fluorescence and circular dichroism. The experimental results point to the presence of the pigment in water in a monomeric complexed form. The fluorescence anisotropy measurements suggest that TpyP forms 1:1 complexes with heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin and hydroxypropyl-beta-cyclodextrin, while 1:2 complexes are obtained with heptakis(2,6-di-O-methyl)-beta-cyclodextrin. 相似文献
997.
Bohl M Loeprecht B Wendt B Heritage T Richmond NJ Willett P 《Journal of chemical information and modeling》2006,46(5):1882-1890
Crystal structures taken from the Cambridge Structural Database were used to build a ring scaffold database containing 19 050 3D structures, with each such scaffold then being used to generate a centroid connecting path (CCP) representation. The CCP is a novel object that connects ring centroids, ring linker atoms, and other important points on the connection path between ring centroids. Unsupervised searching in the scaffold and CCP data sets was carried out using the atom-based LAMDA and RigFit search methods and the field-based similarity search method. The performance of these methods was tested with three different ring scaffold queries. These searches demonstrated that unsupervised 3D scaffold searching methods can find not only the types of ring systems that might be retrieved in carefully defined pharmacophore searches (supervised approach) but also additional, structurally diverse ring systems that could form the starting point for lead discovery programs or other scaffold-hopping applications. Not only are the methods effective but some are sufficiently rapid to permit scaffold searching in large chemical databases on a routine basis. 相似文献
998.
Raquel Caseiro Antonio De Nicola Joana M. Nunes da Costa 《Journal of Geometry and Physics》2010,60(6-8):951-961
We propose a definition of a Jacobi quasi-Nijenhuis algebroid and show that any such Jacobi algebroid has an associated quasi-Jacobi bialgebroid. Therefore, an associated Courant–Jacobi algebroid is also obtained. We introduce the notions of quasi-Jacobi bialgebroid morphism and Courant–Jacobi algebroid morphism, also providing some examples of Courant–Jacobi algebroid morphisms. 相似文献
999.
Savini I Santucci R Di Venere A Rosato N Strukul G Pinna F Avigliano L 《Applied biochemistry and biotechnology》1999,82(3):227-241
In this study, we investigated the optical features of the redox metal-dependent proteins cytochrome-c, horseradish peroxidase (HRP), and ascorbate oxidase embedded in a sol-gel-processed silica matrix as a function of gelation
time. Circular dichroism, absorbance, and fluorescence spectroscopies revealed that the sol-gel process affects the complex
structure of the dimeric ascorbate oxidase (although the prosthetic coppers still remain bound to the enzyme) but not that
of monomeric cytochrome-c and HRP. Any modifications in ascorbate oxidase occurred in the initial gelation phase; the drying process induced no further
alterations and the enzyme remained stable for months. Unfolding-refolding experiments on cytochrome-c revealed severely restricted motility in the protein moiety in the xerogel, the concentrated matrix that forms after drying. The diffusion time of the solvent within the matrix, which regulated the
enzyme-substrate reaction rate, depended on the thickness of the monolith, not on the dryness of the specimen. 相似文献
1000.
Dr. Daphné Stassen Dr. Nicola Demitri Prof. Dr. Davide Bonifazi 《Angewandte Chemie (International ed. in English)》2016,55(20):5947-5951
The synthesis of O‐doped benzorylenes, in which peripheral carbon atoms have been replaced by oxygen atoms, has been achieved for the first time. This includes key high‐yielding ring‐closure steps which, through intramolecular C?O bond formation, allow stepwise planarization of oligonaphthalenes. Single‐crystal X‐ray diffraction showed that the tetraoxa derivative forms remarkable face‐to‐face π–π stacks in the solid state, a favorable solid‐state arrangement for organic electronics. 相似文献