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101.
C.J. Weststrate J.W. Bakker C.P. Vinod S. Lizzit A. Baraldi B.E. Nieuwenhuys 《Surface science》2006,600(10):1991-2001
The interaction of NO with Pt(4 1 0) was studied using high-energy resolution fast XPS and temperature programmed desorption/reaction mass spectroscopy. LEED studies show that the surface in the clean state restructures, which results in the formation of some larger {1 0 0} terraces. STM measurements show, that most terraces are small, ∼1 nm. Two different binding energy (BE) components were observed in the N 1s region of the core level spectra, both assigned to molecular forms of NO. NO dissociation starts between 350 and 400 K. This is a significantly higher temperature than previous literature reports suggested. This difference is thought to be caused by the restructuring of the surface used in our experiments. The reaction of NO with H2, NH3 and CO was also studied. The onset of these NO reduction reactions is determined by the NOad dissociation temperature (between 350 and 400 K) and NOad dissociation is the rate limiting step for all the reactions that were studied. Reaction with H2 yields NH3 below 600 K, but the selectivity shifts towards N2 at higher temperatures. We did not find any indication that reaction between NOad and NH3 ad proceeds via a special NO-NH3 intermediate. A new surface species was detected during the reaction between NO and CO, both in the N 1s and the C 1s spectrum. It is tentatively assigned to either CN or CNO. The reactivity of NO on Pt(4 1 0) is compared with the reactivity that was observed for Pt(1 0 0) and other noble metal surfaces, such as Pd and Rh. 相似文献
102.
J.M. Lackner W. Waldhauser R. Ebner R.J. Bakker 《Applied Physics A: Materials Science & Processing》2004,79(4-6):1469-1471
The aim of the present work was the improvement of titanium-aluminium nitride (TiAlN) coatings by the solid-solution hardening with carbon atoms leading to titanium-aluminium carbon-nitride (Ti,Al)CxN1-x coatings with varying carbon (x) and nitrogen contents. The request of low deposition temperatures necessary for the coating of heat sensitive materials like tool steels of high hardness and polymers was reached by the application of the room temperature pulsed laser deposition (PLD) technique. A Nd:YAG laser of 1064 nm wavelength operated at two different laser pulse energies was used in the ablation experiments of pure TiAl targets (50 at.% Al) in various C2H2-Ar gas mixtures. Different pulse energies of the laser resulted in changes of the ratio of Ti/Al atoms in the grown coatings. Furthermore, the results reveal a strong proportionality of the gas mixture to the C and N content of the coatings. In the coatings deposited at low C2H2 gas flows the XRD investigations showed crystalline phases with fcc TiN type lattices, whereas high acetylene flows during deposition resulted in the formation of fully amorphous coatings and carbon precipitation or cluster boundaries found in Raman investigations. PACS 81.15.Fg; 46.55.+d 相似文献
103.
A large and robust selectivity improvement of ion-selective electrodes is presented for the measurement of abundant ions. An improvement in selectivity by more than two orders of magnitude has been attained for the hydrophilic chloride ions measured in a dilute background of the lipophilic ions perchlorate and salicylate in a pulsed chronopotentiometric measurement mode. This is attributed to a robust kinetic discrimination of the dilute lipophilic ions in this measuring mode, which is not possible to achieve in classical potentiometry. Maximum tolerable concentrations of the interfering ions are found to be on the order of 30 μM before causing substantial changes in potential. As an example of practical relevance, the robust detection of chloride in 72 μM salicylate (reflecting 1:10 diluted blood) with a detection limit of 0.5 mM chloride is demonstrated. Corresponding potentiometric sensors did not give a useful chloride response under these conditions. 相似文献
104.
K. D. Mooiman R. F. Maas‐Bakker H. Rosing J. H. Beijnen J. H. M. Schellens I. Meijerman 《Biomedical chromatography : BMC》2013,27(9):1107-1116
Complementary and alternative medicines (CAM) can affect the pharmacokinetics of anticancer drugs by interacting with the metabolizing enzyme cytochrome P450 (CYP) 3A4. To evaluate changes in the activity of CYP3A4 in patients, levels of 1‐hydroxymidazolam in plasma are often determined with liquid chromatography–quadrupole mass spectrometry (LC‐MS/MS). However, validated LC‐MS/MS methods to determine in vitro CYP3A4 inhibition in human liver microsomes are scarce and not optimized for evaluating CYP3A4 inhibition by CAM. The latter is necessary because CAM are often complex mixtures of numerous compounds that can interfere with the selective measurement of 1‐hydroxymidazolam. Therefore, the aim was to validate and optimize an LC‐MS/MS method for the adequate determination of CYP3A4 inhibition by CAM in human liver microsomes. After incubation of human liver microsomes with midazolam, liquid–liquid extraction with tert‐butyl methyl ether was applied and dried samples were reconstituted in 50% methanol. These samples were injected onto a reversed‐phase chromatography consisting of a Zorbax Extend‐C18 column (2.1 × 150 mm, 5.0 µm particle size), connected to a triple quadrupole mass spectrometer with electrospray ionization. The described LC‐MS/MS method was validated over linear range of 1.0–500 nm for 1‐hydroxymidazolam. The results revealed good inter‐assay accuracy (≥85% and ≤115%) and within‐day and between‐day precisions (coefficient of variation ≤ 4.43%). Furthermore, the applicability of this assay for the determination of CYP3A4 inhibition in complex matrix mixtures was successfully demonstrated in an in vitro experiment in which CYP3A4 inhibition by known CAM (β‐carotene, green tea, milk thistle and St. John's wort) was determined. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
105.
Martin Berkheij Claudia Sewing Jan Willem Terpstra Wouter I. Iwema Bakker Jan H. van Maarseveen 《Tetrahedron letters》2005,46(14):2369-2371
A novel efficient synthetic route towards the pharmaceutically relevant 2-substituted piperazine class is described. The key step involves α-lithiation of N-Boc piperazines, followed by reaction with several electrophiles. To obtain high yields, in some cases transmetallation to copper after the lithiation step is required. 相似文献
106.
Anne Bakker Matthias Freitag Elena Kolodzeiski Peter Bellotti Alexander Timmer Jindong Ren Bertram Schulze Lammers Daniel Moock Herbert W. Roesky Harry Mnig Saeed Amirjalayer Harald Fuchs Frank Glorius 《Angewandte Chemie (International ed. in English)》2020,59(32):13643-13646
The structural properties and binding motif of a strongly σ‐electron‐donating N‐heterocyclic carbene have been investigated on different transition‐metal surfaces. The examined cyclic (alkyl)(amino)carbene (CAAC) was found to be mobile on surfaces, and molecular islands with short‐range order could be found at high coverage. A combination of scanning tunneling microscopy (STM), X‐ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations highlights how CAACs bind to the surface, which is of tremendous importance to gain an understanding of heterogeneous catalysts bearing CAACs as ligands. 相似文献
107.
Dr. Mikhail V. Butovskii Dr. Benjamin Oelkers Dr. Tobias Bauer Dr. Jacinta M. Bakker Dr. Viktor Bezugly Dr. Frank R. Wagner Prof. Dr. Rhett Kempe 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(10):2804-2811
Bismetallocenes [Cp2LuReCp2] and [Cp*2LaReCp2] (Cp=cyclopentadienyl; Cp*=pentamethylcyclopentadienyl) were prepared using different synthetic strategies. Salt metathesis—performed in aromatic hydrocarbons to avoid degradation pathways caused by THF—were identified as an attractive alternative to alkane elimination. Although alkane elimination is more attractive in the sense of its less elaborate workup, the rate of the reaction shows a strong dependence on the ionic radius of Ln3+ (Ln=lanthanide) within a given ligand set. Steric hindrance can cause a dramatic decrease in the reaction rate of alkane elimination. In this case, salt metathesis should be considered the better alternative. Covalent bonding interactions between the Ln and transition‐metal (TM) cations has been quantified on the basis of the delocalization index. Its magnitude lies within the range characteristic for bonds between transition metals. Secondary interactions were identified between carbon atoms of the Cp ligand of the transition metal and the Ln cation. Model calculations clearly indicated that the size of these interactions depends on the capability of the TM atom to act as an electron donor (i.e., a Lewis base). The consequences can even be derived from structural details. The observed clear dependency of the Lu?Ru and interfragment Lu?C bonding on the THF coordination of the Lu atom points to a tunable Lewis acidity at the Ln site, which provides a method of significantly influencing the structure and the interfragment bonding. 相似文献
108.
Bastien Néel Majid Ghahraman Asfhar Gastón A. Crespo Marcin Pawlak Denis Dorokhin Eric Bakker 《Electroanalysis》2014,26(3):473-480
A series of polymeric nitrite‐selective electrodes containing a new lipophilic ionophore Co(II) tert‐butyl‐salophen is reported. The stability of Co(II) ionophores within a PVC‐based membrane was investigated by leaching experiments. Different membrane compositions were explored in order to reach the lowest possible limit of detection for a PVC‐based nitrite selective polymeric membrane electrode containing this ionophore. The optimal electrode showed a limit of detection of 2×10?6 M and exhibited four orders of magnitude of discrimination over nitrate, chloride and bromide. The electrodes were evaluated in undiluted human urine and attest to the robustness of the ionophore. 相似文献
109.
Szigeti Z Malon A Vigassy T Csokai V Grün A Wygladacz K Ye N Xu C Chebny VJ Bitter I Rathore R Bakker E Pretsch E 《Analytica chimica acta》2006,572(1):1-10
Ten Ag+-selective ionophores have been characterized in terms of their potentiometric selectivities and complex formation constants in solvent polymeric membranes. The compounds with π-coordination show much weaker interactions than those with thioether or thiocarbamate groups as the coordinating sites. Long-term studies with the best ionophores show that the lower detection limit of the best Ag+ sensors can be maintained in the subnanomolar range for at least 1 month. The best ionophores have also been characterized in fluorescent microspheres. The so far best lower detection limits of 3 × 10−11 M (potentiometrically) and 2 × 10−11 M Ag+ (optically) are found with bridged thiacalixarenes. 相似文献
110.