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131.
A versatile nonaqueous emulsion polyaddition process for the one-step fabrication of spherical polyurethane nanoparticles
is presented. Three different emulsion systems were used consisting of N,N′-dimethylformamide (DMF) dispersed in n-hexane, acetonitrile dispersed in cyclohexane, and acetonitrile dispersed in tetradecane. After successful stabilization
of the emulsion systems by using a poly(isoprene)-poly(methylmethacrylate) block copolymer, the fabrication of the polyurethanes
was carried out within the dispersed polar phase. The polyurethane particles showed average diameters as small as 35 nm. Additionally,
infrared (IR) characterization revealed that the formation of any urea, which decreases the mechanical properties of the polyurethanes,
was prevented during the polyaddition. This was attributed to the anhydrous reaction conditions. Gel permeation chromatography
(GPC) analysis demonstrated the average molecular weights (M
n) of the polyurethanes to be as high as 16,500 g/mol, corresponding to conversions of 0.98. Comparable molecular weights and
conversions have not previously been achieved without the formation of urea. 相似文献
132.
Yang J Okuyama K Morris K Arp Z Laane J 《The journal of physical chemistry. A》2005,109(37):8290-8292
With the aid of a reported inversion splitting value, the far-infrared spectrum resulting from the ring-puckering vibration of coumaran has been reassigned and the one-dimensional potential energy function has been determined. The barrier to planarity is 155 +/- 4 cm(-1) and the dihedral angle is 25 degrees . These results agree well with the millimeter wave spectra values of 152 cm(-1) and 23 degrees , which utilized different data and a different type of potential function for the calculations. The MP2/cc-pvtz ab initio values of 238 cm(-1) and 26.5 degrees agree more poorly. If the benzene ring is assumed to remain rigid, the calculated barrier drops to 204 cm(-1). The puckering potential functions for the ring-flapping and ring-twisting vibrationally excited states were also determined and the barriers were found to be 149 and 156 cm(-1), respectively. 相似文献
133.
Saleh N Sarbu T Sirk K Lowry GV Matyjaszewski K Tilton RD 《Langmuir : the ACS journal of surfaces and colloids》2005,21(22):9873-9878
Fully sulfonated poly(styrenesulfonate) brushes were grown from the surface of colloidal silica particles and used to prepare stable trichloroethylene-in-water and heptane-in-water Pickering emulsions. These particles were highly charged and colloidally stable in water but could not be dispersed in trichloroethylene or heptane. Both two-phase (emulsion plus neat water) and three-phase (emulsion separating neat oil and water phases) systems were observed, with water-continuous emulsion phases in all cases. Emulsion phases containing as much as 83% (v/v) oil were stable for over six months. Poly(styrenesulfonate)-grafted particles were very efficient emulsifiers; stable emulsion phases were prepared when using as little as 0.04 wt% particles. The emulsifying effectiveness of the poly(styrenesulfonate)-grafted silica particles can be attributed to the hydrophobicity of the vinylic polymer backbone that makes this highly charged polyelectrolyte unusually surface active at the oil/water interface. 相似文献
134.
Olefin cross-metathesis (CM) is potentially an attractive method for generating dynamic combinatorial libraries (DCLs). In order for the CM reaction to be useful for DCL production, the course of the reaction and product distribution must be relatively insensitive to functionality remote from the reacting centers. We report on the CM of a series of allyl- and homoallylamides that are strongly dependent on remote functionality. This includes an unusual example of a cis-selective CM. [Reaction: see text] 相似文献
135.
Ethylene tetramerization: a new route to produce 1-octene in exceptionally high selectivities 总被引:11,自引:0,他引:11
Bollmann A Blann K Dixon JT Hess FM Killian E Maumela H McGuinness DS Morgan DH Neveling A Otto S Overett M Slawin AM Wasserscheid P Kuhlmann S 《Journal of the American Chemical Society》2004,126(45):14712-14713
Linear alpha-olefins, such as 1-hexene and 1-octene, are important comonomers in the production of linear low-density polyethylene (LLDPE). The conventional method of producing 1-hexene and 1-octene is by oligomerization of ethylene, which yields a wide spectrum of linear alpha-olefins (LAOs). While there exists several processes for producing 1-hexene via ethylene trimerization, a similar route for the selective production of 1-octene has so far been elusive. We now, for the first time, report an unprecedented ethylene tetramerization reaction that produces 1-octene in selectivities exceeding 70%, using an aluminoxane-activated chromium/((R2)2P)2NR1 catalyst system. 相似文献
136.
James KJ Crowley J Hamilton B Lehane M Skulberg O Furey A 《Rapid communications in mass spectrometry : RCM》2005,19(9):1167-1175
The potent neurotoxins from cyanobacteria, anatoxin-a (AN), its methyl analogue, homoanatoxin-a (HMAN), and their degradation products, have been studied using nano-electrospray hybrid quadrupole time-of-flight mass spectrometry (QqTOF-MS). The anatoxin degradation products, which are readily produced in vivo by either reduction or epoxidation, were also examined in this study. The high mass accuracy QqTOF-MS data was used to confirm formula assignments for major product ions and quadrupole ion-trap (QIT)-MS was used to construct fragmentation pathways for anatoxins. Significant differences between these fragmentation pathways were observed. Comparisons between the spectra of compounds that differ in side-chain length (the AN and HMAN series) were used to identify ions that are characteristic of the homologues. The application to forensic samples in which the principal neurotoxin had undergone rapid biodegradation has been demonstrated and used to confirm anatoxin poisoning of dogs. 相似文献
137.
A chemical inhibitor reveals the role of Raf kinase inhibitor protein in cell migration 总被引:7,自引:0,他引:7
Raf kinase inhibitor protein (RKIP) is a modulator of cell signaling that functions as an endogenous inhibitor of multiple kinases. We demonstrate here a positive role for RKIP in the regulation of cell locomotion. We discovered that RKIP is the relevant cellular target of locostatin, a cell migration inhibitor. Locostatin abrogates RKIP's ability to bind and inhibit Raf-1 kinase, and it acts by disrupting a protein-protein interaction, an uncommon mode of action for a small molecule. Small interfering RNA-mediated silencing of RKIP expression also reduces cell migration rate. Overexpression of RKIP converts epithelial cells to a highly migratory fibroblast-like phenotype, with dramatic reduction in the sensitivity of cells to locostatin. RKIP is therefore the compound's valid target and a key regulator of cell motility. 相似文献
138.
Dhanpat Rai Dean A. Moore Nancy J. Hess Kevin M. Rosso Linfeng Rao Steve M. Heald 《Journal of solution chemistry》2007,36(10):1261-1285
Chromium(III)-carbonate reactions are expected to be important in managing high-level radioactive wastes. Extensive studies
on the solubility of amorphous Cr(III) hydroxide solid in a wide range of pH (3–13) at two different fixed partial pressures
of CO2(g) (0.003 or 0.03 atm.), and as functions of K2CO3 concentrations (0.01 to 5.8 mol⋅kg−1) in the presence of 0.01 mol⋅dm−3 KOH and KHCO3 concentrations (0.001 to 0.826 mol⋅kg−1) at room temperature (22±2 °C) were carried out to obtain reliable thermodynamic data for important Cr(III)-carbonate reactions.
A combination of techniques (XRD, XANES, EXAFS, UV-Vis-NIR spectroscopy, thermodynamic analyses of solubility data, and quantum
mechanical calculations) was used to characterize the solid and aqueous species. The Pitzer ion-interaction approach was used
to interpret the solubility data. Only two aqueous species [Cr(OH)(CO3)22− and Cr(OH)4CO33−] are required to explain Cr(III)-carbonate reactions in a wide range of pH, CO2(g) partial pressures, and bicarbonate and carbonate concentrations. Calculations based on density functional theory support
the existence of these species. The log 10
K° values of reactions involving these species [{Cr(OH)3(am) + 2CO2(g)⇌Cr(OH)(CO3)22−+2H+} and {Cr(OH)3(am) + OH−+CO32−
⇌Cr(OH)4CO33−}] were found to be −(19.07±0.41) and −(4.19±0.19), respectively. No other data on any Cr(III)-carbonato complexes are available
for comparisons. 相似文献
139.
Gervais C Dupree R Pike KJ Bonhomme C Profeta M Pickard CJ Mauri F 《The journal of physical chemistry. A》2005,109(31):6960-6969
13C, 14N, 15N, 17O, and 35Cl NMR parameters, including chemical shift tensors and quadrupolar tensors for 14N, 17O, and 35Cl, are calculated for the crystalline forms of various amino acids under periodic boundary conditions and complemented by experiment where necessary. The 13C shift tensors and 14N electric field gradient (EFG) tensors are in excellent agreement with experiment. Similarly, static 17O NMR spectra could be precisely simulated using the calculation of the full chemical shift (CS) tensors and their relative orientation with the EFG tensors. This study allows correlations to be found between hydrogen bonding in the crystal structures and the 17O NMR shielding parameters and the 35Cl quadrupolar parameters, respectively. Calculations using the two experimental structures for L-alanine have shown that, while the calculated isotropic chemical shift values of 13C and 15N are relatively insensitive to small differences in the experimental structure, the 17O shift is markedly affected. 相似文献
140.
Raha K van der Vaart AJ Riley KE Peters MB Westerhoff LM Kim H Merz KM 《Journal of the American Chemical Society》2005,127(18):6583-6594
Pairwise decomposition of the interaction energy between molecules is shown to be a powerful tool that can increase our understanding of macromolecular recognition processes. Herein we calculate the pairwise decomposition of the interaction energy between the protein human carbonic anhydrase II (HCAII) and the fluorine-substituted ligand N-(4-sulfamylbenzoyl)benzylamine (SBB) using semiempirical quantum mechanics based methods. We dissect the interaction between the ligand and the protein by dividing the ligand and the protein into subsystems to understand the structure-activity relationships as a result of fluorine substitution. In particular, the off-diagonal elements of the Fock matrix that is composed of the interaction between the ionic core and the valence electrons and the exchange energy between the subsystems or atoms of interest is examined in detail. Our analysis reveals that the fluorine-substituted benzylamine group of SBB does not directly affect the binding energy. Rather, we find that the strength of the interaction between Thr199 of HCAII and the sulfamylbenzoyl group of SBB affects the binding affinity between the protein and the ligand. These observations underline the importance of the sulfonamide group in binding affinity as shown by previous experiments (Maren, T. H.; Wiley: C. E. J. Med. Chem. 1968, 11, 228-232). Moreover, our calculations qualitatively agree with the structural aspects of these protein-ligand complexes as determined by X-ray crystallography. 相似文献