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201.
Garramone G Pietrangeli D Ricciardi G Conoci S Guascito MR Malitesta C Cesari D Casilli S Giotta L Giancane G Valli L 《The journal of physical chemistry. B》2008,112(37):11517-11528
Thin films of a newly synthesized iron(III) porphyrazine, LFeOESPz ( L = ClEtO, OESPz = ethylsulfanylporphyrazine), have been deposited by the Langmuir-Schafer (LS) technique (horizontal lifting) on ITO or gold substrates. Before deposition, the floating films have been investigated at the air-water interface by pressure/area per molecule (pi/ A) experiments, Brewster angle microscopy (BAM) and UV-vis reflection spectroscopy (RefSpec). The complex reacts with water subphase (pH 6.2) forming the mu-oxo dimer, which becomes the predominant component of the LS films ( LS-Fe) as indicated by optical, IR, XPS, and electrochemical data. LS-Fe multilayers exhibit, between open circuit potential (OCP) and +0.90 V (vs SCE), two independent peak pairs with formal potentials, E surf (I) and E surf(II) of +0.56 V and +0.78 V, respectively. According to dynamic voltammetric and coulometric experiments the peak pair at +0.56 V is attributed to one-electron process at the iron(III) centers on the monomer, while the peak pair at +0.78 V is associated to a four-electron process involving mu-oxo-dimer oligomers. LS-Fe films prove to be quite stable electrochemically between OCP and +0.90 V. The electrochemical stability decreases, however, when the potential range is extended both anodically and cathodically outside these limits, due to formation of new species. Upon incubation with TCA solutions, LS-Fe films show remarkable changes in the UV-vis spectra, which are consistent with a significant mu-oxo dimer --> monomer conversion. Addition of TCA to the electrochemical cell using a LS-Fe film as working electrode, results in a linear increase of a cathodic current peak near -0.40 V as the TCA concentration varies in the 0.1-2.0 mM range. This behavior is interpreted in terms of TCA inducing a progressive change in the composition of the LS-Fe films in favor of the monomeric iron(III) porphyrazine, which is responsible for the observed increase in the cathodic current near -0.40 V. 相似文献
202.
Thayer MP McGuire C Stennett EM Lockhart MK Canache D Novak M Schmidtke SJ 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2011,84(1):227-232
The local environment dictates the structural and functional properties of many important chemical and biological systems. The impact of pH on the photophysical properties of a series of para-aminobenzoic acids is examined using a combination of experimental spectroscopy and quantum chemical calculations. Following photoexcitation, PABA derivatives may undergo an intramolecular charge transfer (ICT) resulting in the formation of a zwitterionic species. The thermodynamics of the excited state reaction and temperature-dependence of the radiative emission processes are evaluated through variable temperature fluorescence spectroscopy carried out in a range of aqueous buffers. Quantum chemical calculations are used to analyze structural changes with modifications at the amine position and different protonation states. The ICT is only observed in the tertiary amine, which calculations show has more sp(2) character than the primary or secondary amines. Thermodynamic analysis indicates the ICT reaction is driven by entropy. 相似文献
203.
Tarallo R Accardo A Falanga A Guarnieri D Vitiello G Netti P D'Errico G Morelli G Galdiero S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(45):12659-12668
Liposomes externally modified with the nineteen residues gH625 peptide, previously identified as a membrane‐perturbing domain in the gH glycoprotein of Herpes simplex virus type I, have been prepared in order to improve the intracellular uptake of an encapsulated drug. An easy and versatile synthetic strategy, based on click chemistry, has been used to bind, in a controlled way, several copies of the hydrophobic gH625 peptide on the external surface of 1,2‐dioleoyl‐sn‐glycero‐3‐phosphocholine (DOPG)‐based liposomes. Electron paramagnetic resonance studies, on liposomes derivatized with gH625 peptides, which are modified with the 2,2,6,6‐tetramethylpiperidine‐1‐oxyl‐4‐amino‐4‐carboxylic acid (TOAC) spin label in several peptide positions, confirm the positioning of the coupled peptides on the liposome external surface, whereas dynamic light scattering measurements indicate an increase of the diameter of the liposomes of approximately 30 % after peptide introduction. Liposomes have been loaded with the cytotoxic drug doxorubicin and their ability to penetrate inside cells has been evaluated by confocal microscopy experiments. Results suggest that liposomes functionalized with gH625 may act as promising intracellular targeting carriers for efficient delivery of drugs, such as chemotherapeutic agents, into tumor cells. 相似文献
204.
Squeglia F Marchetti R Ruggiero A Lanzetta R Marasco D Dworkin J Petoukhov M Molinaro A Berisio R Silipo A 《Journal of the American Chemical Society》2011,133(51):20676-20679
Bacterial Ser/Thr kinases modulate a wide number of cellular processes. In Bacillus subtilis , the Ser/Thr kinase PrkC has been shown to induce germination of bacterial spores in response to DAP-type but not Lys-type cell wall muropeptides. Muropeptides are a clear molecular signal that growing conditions are promising, since they are produced during cell wall peptidoglycan remodeling associated with cell growth and division of neighboring bacteria. However, whether muropeptides are able to bind the protein physically and how the extracellular region is able to distinguish the two types of muropeptides remains unclear. Here we tackled the important question of how the extracellular region of PrkC (EC-PrkC) senses muropeptides. By coupling NMR techniques and protein mutagenesis, we exploited the structural requirements necessary for recognition and binding and proved that muropeptides physically bind to EC-PrkC through DAP-moiety-mediated interactions with an arginine residue, Arg500, belonging to the protein C-terminal PASTA domain. Notably, mutation of this arginine completely suppresses muropeptide binding. Our data provide the first molecular clues into the mechanism of sensing of muropeptides by PrkC. 相似文献
205.
Analysis of essential oils from Scutellaria orientalis ssp. alpina and S. utriculata by GC and GC-MS
Formisano C Rigano D Senatore F Piozzi F Arnold NA 《Natural product communications》2011,6(9):1347-1350
The chemical composition of the essential oils obtained from aerial parts of Scutellaria orientalis L. ssp. alpina (Boiss.) O. Schwarz and S. utriculata Labill. growing wild in Lebanon, were analyzed by GC and GC-MS. In S. orientalis ssp. alpina, strongly characterized by sesquiterpenes (41.2%) and particularly sesquiterpene hydrocarbons (31.7%), hexahydrofarnesylacetone (11.7%) was recognized as the main constituent, together with hexadecanoic acid (7.6%), caryophyllene (7.4%), caryophyllene oxide (6.8%), 4-vinylguaiacol (5.4%) and germacrene D (5.4%). S. utriculata oil was instead constituted above all by monoterpenes (42.2%), particularly oxygen containing monoterpenes (39.9%), and in this oil the main compounds were linalool (20.1%), 4-vinyl guaiacol (15.5%), alpha-terpineol (8.9%), (E)-nerolidol (8.9%) and geraniol (8.2%). 相似文献
206.
Daniela Ž. Popović Jelena Miladinović Milica D. Todorović Milorad M. Zrilić Joseph A. Rard 《Journal of solution chemistry》2011,40(5):907-920
The osmotic coefficients of K2HPO4(aq) have been measured at T=298.15 K by the isopiestic vapor pressure method over the range of molalities from 1.3846 mol⋅kg−1 to 13.939 mol⋅kg−1 (oversaturation) with CaCl2(aq) as the reference solution. The molalities and osmotic coefficients of saturated solutions in equilibrium with K2HPO4⋅xH2O(cr) were measured simultaneously by the same method. Available literature osmotic coefficients of K2HPO4(aq) at T=298.15 K, and our new experimental data, were combined and modeled using an extended form of Pitzer’s equation and the Clegg-Pitzer-Brimblecombe
equation based on the mole-fraction-composition scale. These equations were used to calculate the activity coefficients of
K2HPO4(aq) at T=298.15 K. 相似文献
207.
Concetta?De?Stefano Antonio?GianguzzaEmail author Alberto?Pettignano Daniela?Piazzese Silvio?Sammartano 《Journal of Radioanalytical and Nuclear Chemistry》2011,289(3):689-697
Stability data on the formation of dioxouranium(VI) species with polyacrylic (PAA) and fulvic acids (FA) are reported with
the aim to define quantitatively the sequestering capacity of these high molecular weight synthetic and naturally occurring
ligands toward uranium(VI), in aqueous solution. Investigations were carried out at t = 25 °C in NaCl medium at different ionic strengths and in absence of supporting electrolyte for uranyl–fulvate (
\textUO22+ {{\text{UO}}_{2}}^{2+} –FA) and uranyl–polyacrylate (
\textUO 2 2+ {{\text{UO}}_{ 2}}^{ 2+ } –PAA, PAA MW 2 kDa) systems, respectively. The experimental data are consistent with the following speciation models for the
two systems investigated: (i) UO2(FA1), UO2(FA1)(FA2), UO2(FA1)(FA2)(H) for
\textUO 2 2+ {{\text{UO}}_{ 2}}^{ 2+ } –fulvate (where FA1 and FA2 represent the carboxylic and phenolic fractions, respectively, both present in the structure of FA), and (ii) UO2(PAA), UO2(PAA)(OH), (UO2)2(PAA)(OH)2 for
\textUO 2 2+ {{\text{UO}}_{ 2}}^{ 2+ } –polyacrylate. By using the stability data obtained for all the complex species formed, the uranium(VI) sequestration by PAA
and FA was expressed by the pL50 parameter [i.e. the −log(total ligand concentration) necessary to bind 50% of uranyl ion] at different pH values. A comparison
between pL50 values of FA and PAA and some low molecular weight carboxylic ligands toward uranyl ion is also given. 相似文献
208.
Wissenbach DK Meyer MR Remane D Philipp AA Weber AA Maurer HH 《Analytical and bioanalytical chemistry》2011,400(10):3481-3489
Today, immunoassays and several chromatographic methods are in use for drug screening in clinical and forensic toxicology
and in doping control. For further proof of the authors’ new metabolite-based liquid chromatography-mass spectrometry (LC-MSn) screening concept, the detectability of drugs of abuse and their metabolites using this screening approach was studied.
As previously reported, the corresponding reference library was built up with MS2 and MS3 wideband spectra using a LXQ linear ion trap with electrospray ionization in the positive mode and full scan information-dependent
acquisition. In addition to the parent drug spectra recorded in methanolic solution, metabolite spectra were identified after
protein precipitation of urine from rats after administration of the corresponding drugs and added to the library. This consists
now of data of over 900 parent compounds, including 87 drugs of abuse, and of over 2,300 metabolites and artifacts, among
them 436 of drugs of abuse. Recovery, process efficiency, matrix effects, and limits of detection for selected drugs of abuse
were determined using spiked human urine, and the resulting data have been acceptable. Using two automatic data evaluation
tools (ToxID and SmileMS), the intake of 54 of the studied drugs of abuse could be confirmed in urine samples of drug users
after protein precipitation and LC separation. The following drugs classes were covered: stimulants, designer drugs, hallucinogens,
(synthetic) cannabinoids, opioids, and selected benzodiazepines. The presented LC-MSn method complements the well-established gas chromatography-mass spectroscopy procedure in the authors’ laboratory. 相似文献
209.
210.
Seven new microcystin variants discovered from a native Microcystis aeruginosa strain – unambiguous assignment of product ions by tandem mass spectrometry 下载免费PDF全文