全文获取类型
收费全文 | 924篇 |
免费 | 29篇 |
国内免费 | 7篇 |
专业分类
化学 | 678篇 |
晶体学 | 8篇 |
力学 | 20篇 |
数学 | 138篇 |
物理学 | 116篇 |
出版年
2023年 | 6篇 |
2022年 | 11篇 |
2021年 | 13篇 |
2020年 | 18篇 |
2019年 | 13篇 |
2018年 | 12篇 |
2017年 | 14篇 |
2016年 | 14篇 |
2015年 | 19篇 |
2014年 | 24篇 |
2013年 | 57篇 |
2012年 | 70篇 |
2011年 | 61篇 |
2010年 | 38篇 |
2009年 | 12篇 |
2008年 | 47篇 |
2007年 | 58篇 |
2006年 | 50篇 |
2005年 | 42篇 |
2004年 | 46篇 |
2003年 | 47篇 |
2002年 | 31篇 |
2001年 | 11篇 |
2000年 | 13篇 |
1998年 | 5篇 |
1997年 | 10篇 |
1996年 | 12篇 |
1995年 | 13篇 |
1994年 | 12篇 |
1993年 | 4篇 |
1992年 | 11篇 |
1991年 | 11篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 7篇 |
1985年 | 4篇 |
1984年 | 9篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 13篇 |
1977年 | 8篇 |
1976年 | 12篇 |
1975年 | 9篇 |
1974年 | 7篇 |
1973年 | 8篇 |
1972年 | 6篇 |
1970年 | 7篇 |
排序方式: 共有960条查询结果,搜索用时 296 毫秒
61.
Jensen TW Hu BH Delatore SM Garcia AS Messersmith PB Miller WM 《Journal of the American Chemical Society》2004,126(46):15223-15230
The ability to present cell adhesion molecule (CAM) ligands in controlled amounts on a culture surface would greatly facilitate the control of cell growth and differentiation. Supported lipid monolayer/bilayer systems have previously been developed that allow for presentation of CAM ligands for cell interaction; however, these systems have employed peptide loadings much higher than those used in poly(ethylene glycol) (PEG)-based immobilization systems. We report the development of synthetic methods that can be used for the efficient and versatile creation of many linear and cyclic lipid-linked peptide moieties. Using RGD-based peptides for the alpha5beta1 integrin as a model system, we have demonstrated that these lipopeptides support efficient cell binding and spreading at CAM ligand loadings as low as 0.1 mol %, which is well below that previously reported for supported lipid systems. Engineered lipopeptide-based surfaces offer unique presentation options not possible with other immobilization systems, and the high activity at low loadings we have shown here may be extremely useful in presenting multiple CAM ligands for studying cell growth, differentiation, and signaling. 相似文献
62.
Dean M. Philipp William A. Goddard Michael J. Mullins Phillip S. Athey 《Tetrahedron letters》2004,45(28):5441-5444
We have been engaged in a search for coordination catalysts for the copolymerization of polar monomers (such as vinyl chloride and vinyl acetate) with ethylene. We have been investigating complexes of late transition metals with heterocyclic ligands. In this report we describe the synthesis of a symmetrical bis-thiadiazole. We have characterized one of the intermediates using single crystal X-ray diffraction. Several unsuccessful approaches toward 1 are also described, which shed light on some of the unique chemistry of thiadiazoles. 相似文献
63.
Hodge theory for a smooth algebraic curve includes both theHodge structure (period matrix) on cohomology and the use ofthat Hodge structure to study the geometry of the curve, viathe Jacobian variety. Hodge extended the theory of the periodmatrix to smooth algebraic varieties of any dimension, definingin general a Hodge structure on the cohomology of the variety.He gave a few applications to the geometry of the variety, butthese did not attain the richness of the Jacobian variety. Inrecent years, Hodge theory has been successfully extended toarbitrary varieties, and to families of varieties. In this expositorypaper, some of these developments are reviewed, with specialemphasis on instances where these extensions can be used tostudy the geometry especially the algebraic cycles on the variety. 2000 Mathematics Subject Classification 14CDFJ. 相似文献
64.
A simple quantum-mechanics/molecular-mechanics (QM/MM) approach for calculating NMR shielding tensors (sigma) is presented. The method involves capping the QM region with quantum capping potentials (QCPs) and representing the MM region with point charges. Test calculations on simple systems without MM charges show that calculated sigma values improve relative to the full QM results with increasing distance between the capped bond and chromophore. Calculations on the histidine amino acid and cytosine monophosphate (CMP) nucleic acid show that the use of QCPs with point charges result in mean errors in the isotropic component of sigma that are less than 1.6 ppm. The results also reveal that, contrary to previous work, the explicit effect of point charges on sigma through coupling with gauge factors, as in the gauge including atomic orbital approach, is minimal for the CMP molecule. The present QM/MM approach for calculating sigma is easy to apply and requires no code modification. 相似文献
65.
Carter EB Culver SL Fox PA Goode RD Ntai I Tickell MD Traylor RK Hoffman NW Davis JH 《Chemical communications (Cambridge, England)》2004,(6):630-631
The anions of the sweeteners saccharin and acesulfame form ionic liquids when paired with a variety of organic cations. 相似文献
66.
Costa PR Sun B Griffin RG 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2003,164(1):92-103
The solid state NMR technique of rotational resonance (R2) has been used extensively to measure distances approaching 5-6 A between 13C nuclei in a variety of compounds including amyloidogenic peptides and membrane proteins. The accuracy of the distance information extracted from the time-dependent spin dynamics at R2 is often limited by the accuracy with which the relevant zero-quantum lineshape parameters are estimated. Here we demonstrate that measurement of spinning frequency dependent magnetization exchange dynamics provides data from which both distance and zero-quantum relaxation parameters can be extracted independently. In addition to providing more accurate distance information, this technique allows examination of the zero-quantum lineshape, which can indicate the presence of correlated relaxation or chemical shift distributions between dipolar-coupled sites. With this approach we have separated the contribution of dipolar couplings and zero quantum relaxation to R2 exchange curves. Thus, we have significantly improved the accuracy of the measurement of the intramolecular, internuclear distances between a pair of 13C's in two model compounds (N-acetyl-D,L-valine and glycylglycine.HCl) that lie in the distance range 4.6-4.7 A. 相似文献
67.
68.
Novel PI analogues selectively block activation of the pro-survival serine/threonine kinase Akt 总被引:8,自引:0,他引:8
Kozikowski AP Sun H Brognard J Dennis PA 《Journal of the American Chemical Society》2003,125(5):1144-1145
The synthesis from l-quebrachitol of a series of 3-deoxygenated ether lipid-type phosphatidylinositol (PI) analogues is reported, that selectively block activation of Akt and downstream substrates without affecting activation of the upstream kinase, PDK-1, or other kinases downstream of ras such as MAPK in H157 and H1703 lung cancer cells that have high levels of constitutively active Akt. The 2-hydroxyl in these compounds was deleted or alkylated with the intent to preclude metabolic degradation of these compounds by PI-specific phospholipase C (PI-PLC). PI analogues with phosphate linkers are more effective than those with carbonate linkers. Specific inhibition of Akt by these compounds validates ligand design targeted to the PH domains of crucial signaling proteins, thus providing a unique class of possible cancer therapeutics. 相似文献
69.
Alexander I. Nosich Elena I. Smotrova Svetlana V. Boriskina Trevor M. Benson Phillip Sewell 《Optical and Quantum Electronics》2007,39(15):1253-1272
Research into microdisk lasers demonstrates new achievements both in the technology and in the associated physical effects
and applications. Melting and rounding of the disk edge boosts the Q-factors due to improved surface smoothness. In-plane
cavity shape is widely used as a design instrument. Optimal shaping of pumped area lowers the threshold power. Photonic molecules
made of several microdisks as “photonic atoms” show lasing at several closely spaced frequencies. A microdisk with a single
quantum dot as an active region is considered as the most promising system for realisation of a single photon emitter necessary
for quantum computing. These new effects and devices can be simulated with accurate numerical techniques, developed recently
for “warm-cavity” linear modelling, that are able to bring a new vision of the physics of lasing. 相似文献