全文获取类型
收费全文 | 2681篇 |
免费 | 128篇 |
国内免费 | 9篇 |
专业分类
化学 | 2276篇 |
晶体学 | 23篇 |
力学 | 26篇 |
数学 | 259篇 |
物理学 | 234篇 |
出版年
2023年 | 18篇 |
2022年 | 30篇 |
2021年 | 36篇 |
2020年 | 55篇 |
2019年 | 51篇 |
2018年 | 28篇 |
2017年 | 31篇 |
2016年 | 75篇 |
2015年 | 80篇 |
2014年 | 90篇 |
2013年 | 117篇 |
2012年 | 199篇 |
2011年 | 248篇 |
2010年 | 113篇 |
2009年 | 99篇 |
2008年 | 211篇 |
2007年 | 206篇 |
2006年 | 196篇 |
2005年 | 195篇 |
2004年 | 173篇 |
2003年 | 132篇 |
2002年 | 119篇 |
2001年 | 35篇 |
2000年 | 25篇 |
1999年 | 24篇 |
1998年 | 20篇 |
1997年 | 16篇 |
1996年 | 27篇 |
1995年 | 13篇 |
1994年 | 8篇 |
1993年 | 18篇 |
1992年 | 18篇 |
1991年 | 9篇 |
1988年 | 5篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1975年 | 6篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1969年 | 5篇 |
1968年 | 3篇 |
排序方式: 共有2818条查询结果,搜索用时 93 毫秒
951.
Two phosphonated hexaaza-macrocycles with 24- and 26-membered rings have been synthesized via a Mannich reaction and characterized. The novel crystal structures of the macrocyclic ligands show the extended 3-D hydrogen bonded structure in their solid states. These ligands have unusual ring conformations with two or four pendent arms wrapping around the macrocycle with alternating up and down orders. Strong hydrogen bonding between the protonated phosphonate groups and the deprotonated phosphonated groups was observed in those structures together with the complicated solvent hydrogen bonding networks. 相似文献
952.
Conditional glycosylation in eukaryotic cells using a biocompatible chemical inducer of dimerization
Czlapinski JL Schelle MW Miller LW Laughlin ST Kohler JJ Cornish VW Bertozzi CR 《Journal of the American Chemical Society》2008,130(40):13186-13187
Chemical inducers of dimerization (CIDs) are cell-permeable small molecules capable of dimerizing two protein targets. The most widely used CID, the natural product rapamycin and its relatives, is immunosuppressive due to interactions with endogenous targets and thus has limited utility in vivo. Here we report a new biocompatible CID, Tmp-SLF, which dimerizes E. coli DHFR and FKBP and has no endogenous mammalian targets that would lead to unwanted in vivo side effects. We employed Tmp-SLF to modulate gene expression in a yeast three-hybrid assay. Finally, we engineered the Golgi-resident glycosyltransferase FucT7 for tunable control by Tmp-SLF in mammalian cells. 相似文献
953.
Photochemistry of adsorbed nitrate 总被引:2,自引:0,他引:2
Schuttlefield J Rubasinghege G El-Maazawi M Bone J Grassian VH 《Journal of the American Chemical Society》2008,130(37):12210-12211
In the atmosphere, gas-phase nitrogen oxides including nitric acid react with particle surfaces (e.g., mineral dust and sea salt aerosol) to yield adsorbed nitrate, yet little is known about the photochemistry of nitrate on the surface of these particles. In this study, nitrate adsorbed on alumina surfaces, a surrogate for mineral dust aerosol, is irradiated with broadband light (lambda > 300 nm) in the absence and presence of coadsorbed water, at <1% and 45 +/- 2% relative humidity (%RH), respectively, and molecular oxygen. Upon irradiation, the nitrate ion readily undergoes photolysis to yield nitrogen-containing gas-phase products, NO2, NO, and N2O. Although NO2, NO, and N2O form under the different conditions investigated, both coadsorbed water and molecular oxygen change the gas-phase product distribution, with NO being the major product under dry and humid conditions in the absence of molecular oxygen and NO2 the major product in the presence of molecular oxygen. To the best of our knowledge, this is the first study to investigate the role of solvation by coadsorbed water in the photochemistry of adsorbates at solid interfaces and the roles that molecular oxygen, adsorbed water, and relative humidity may have in photochemical processes on aerosol surfaces that have the potential to alter the chemical balance of the atmosphere. 相似文献
954.
Pentelute BL Gates ZP Dashnau JL Vanderkooi JM Kent SB 《Journal of the American Chemical Society》2008,130(30):9702-9707
The recently discovered glycine-rich snow flea antifreeze protein (sfAFP) has no sequence homology with any known proteins. No experimental structure has been reported for this interesting protein molecule. Here we report the total chemical synthesis of the mirror image forms of sfAFP (i.e., L-sfAFP, the native protein, and D-sfAFP, the native protein's enantiomer). The predicted 81 amino acid residue polypeptide chain of sfAFP contains Cys residues at positions 1, 13, 28, and 43 and was prepared from four synthetic peptide segments by sequential native chemical ligation. After purification, the full-length synthetic polypeptide was folded at 4 degrees C to form the sfAFP protein containing two disulfides. Chemically synthesized sfAFP had the expected antifreeze activity in an ice recrystallization inhibition assay. Mirror image D-sfAFP protein was prepared by the same synthetic strategy, using peptide segments made from d-amino acids, and had an identical but opposite-sign CD spectrum. As expected, D-sfAFP displays the same antifreeze properties as L-sfAFP, because ice presents an achiral surface for sfAFP binding. Facile synthetic access to sfAFP will enable determination of its molecular structure and systematic elucidation of the molecular basis of the antifreeze properties of this unique protein. 相似文献
955.
Chen Y Vela J Htoon H Casson JL Werder DJ Bussian DA Klimov VI Hollingsworth JA 《Journal of the American Chemical Society》2008,130(15):5026-5027
Semiconductor nanocrystal quantum dots (NQDs) comprise an important class of inorganic fluorophores for applications from optoelectronics to biology. Unfortunately, to date, NQD optical properties (e.g., their efficient and particle-size-tunable photoluminescence) have been susceptible to instabilities at the bulk and single-particle levels. Specifically, ensemble quantum yields (QYs) in emission are dependent upon NQD surface chemistry and chemical environment, while at the single-particle level, NQDs are characterized by significant fluorescence intermittency (blinking) that hinders applications as single-photon light sources for quantum informatics and biolabels for real-time monitoring of single biomolecules. Furthermore, while NQDs are significantly more photostable than their organic dye counterparts, traditional NQDs photobleach over periods of seconds to many minutes. Here, we demonstrate for the first time that by encapsulating the NQD core in a sufficiently thick inorganic shell, we are able to divorce NQD function from NQD surface chemistry and chemical environment. We show that our "giant" NQDs (g-NQDs) are functionally distinct from standard core-only, core/shell and even core/multishell NQDs. g-NQDs are substantially less sensitive to changes in surface chemistry. They do not photobleach under continuous laser excitation over periods of several hours repeated over several days, and they exhibit markedly different blinking behavior; >20% of the g-NQDs do not blink, while >40% have on-time fractions of >80%. All of these observations are in stark contrast with control samples comprising core-only and standard, thinner core/multishell NQDs. 相似文献
956.
957.
Mann JE Xie Z Savee JD Braams BJ Bowman JM Continetti RE 《Journal of the American Chemical Society》2008,130(12):3730-3731
Dissociative charge exchange of CH5+ with Cs, coupled with quasiclassical trajectory calculations on an ab initio PES for CH5, has been used to probe the structure of the CH5+ cation. Product kinetic energy release distributions and branching ratios for CH5 --> CH4 + H and CH5 --> CH3 + H2 have been compared. The agreement of the product branching ratios provides evidence for the fluxional nature of CH5+. 相似文献
958.
Herein we report nano-molding proteins for the fabrication of protein PRINT particles of monodisperse size and shape. Lyophilized protein particles are generally highly dispersed in particle size, aggregated, and often made through costly and complicated processes. Attempts to engineer monodisperse, discrete protein particles using wet-milling, spray-freeze-drying, microemulsion, or super critical fluid methods have realized little success. The PRINT technology enables a gentle, facile route to monodisperse particles of 100% protein as small as 200 nm cylinders. Protein PRINT particles of any shape and size are effortlessly achievable. Our research efforts include making PRINT particles composed of albumin and albumin 0.5 wt % siRNA, and Abraxane, the gold standard therapeutic used in metastatic breast cancer. 相似文献
959.
Tam-Chang SW Helbley J Iverson IK 《Langmuir : the ACS journal of surfaces and colloids》2008,24(5):2133-2139
Ionic perylenebis(dicarboximide)s 1-5 were synthesized. The aggregation and liquid-crystalline properties of these compounds in aqueous solutions were investigated. In the concentration range of approximately 5 x 10-7-5 x 10-4 M, the structures of the ammonium side chains and counterions did not have a significant effect on the electronic transition properties and H-aggregate formation of these compounds. However, the liquid-crystalline phase properties varied with the structure of the side chains and the counterions. Ionic perylenebis(dicarboximide)s 1, 3, and 5 with chloride ions formed nematic (N) phases from the isotropic (I) phase, while 2 and 4 with p-methylbenzenesulfonate ions formed chromonic ribbons from the I phase. Studies by polarized light microscopy and 2H NMR spectroscopy indicated that the N phase of 5 (with gem dimethyl groups) formed at higher concentrations than those observed for 1 and 3 at the same temperature. Furthermore, the N phase of 5 was less ordered compared to those of 1 and 3 at a similar concentration and temperature, presumably due to the bulkiness of the side chains of 5 that hindered the stacking and pi-interactions of the aromatic rings. 相似文献
960.
We investigate the structure and flow behavior of colloidal gels in microchannels using confocal microscopy. Silica particles are first coated with a cationic polyelectrolyte and then flocculated by the addition of an anionic polyelectrolyte. In the quiescent state, the suspension is an isotropic and homogeneous gel. Under shear flow, the suspension contains dense clusters that yield at intercluster boundaries, resulting in network breakup at high shear rates. These structural changes coincide with a transition from pluglike flow at low pressures to fluidlike flow at high pressures. 相似文献