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71.
The performance of mass spectrometric (MS) detection and UV detection in combination with reversed-phase liquid chromatography without and with the use of coupled column RPLC (LC-LC) has been compared for the trace analysis of phenylurea herbicides in environmental waters. The selected samples of this comparative study originated from an inter-laboratory study. For both detection modes, a 50 mm x 4.6 mm I.D. column and a 100 mm x 4.6 mm I.D. column packed with 3 microm C18 were used as the first (C-1) and second (C-2) column, respectively. Atmospheric pressure chemical ionization mass spectrometry was performed on a magnetic sector instrument. The LC-LC-MS analysis was carried out on-line by means of direct large volume (11.7 ml) injection (LVI). The performance of both on-line (LVI, 4 ml of sample) and off-line LC-LC-UV (244 nm) analysis was investigated. The latter procedure consisted of a solid-phase extraction (SPE) of 250 ml of water sample on a 500 mg C18 cartridge. The comparative study showed that LC-LC-MS is more selective then LC-LC-UV and, in most cases, more sensitive. The LVI-LC-LC-MS approach combines direct quantification and confirmation of most of the analytes down to a level of 0.01 microg/l in water samples in less then 30 min. As regards LC-LC-UV, the off-line method appeared to be a more viable approach in comparison with the on-line procedure. This method allows the screening of phenylurea's in various types of water samples down to a level of at least 0.05 microg/l. On-line analysis with LVI provided marginal sensitivity (limits of detection of about 0.1 microg/l) and selectivity was sometimes less in case of surface water samples. Both the on-line LVI-LC-LC-MS method and the LC-LC-UV method using off-line SPE were validated by analysing a series of real-life reference samples. These samples were part of an inter-laboratory test and contained residues of herbicides ranging from 0.02 to 0.8 microg/l. Beside good correlation between the methods the data agreed very well with the true values of the samples. 相似文献
72.
E. A. Hogendoorn G. R. van der Hoff P. van Zoonen 《Journal of separation science》1989,12(12):784-789
A method has been developed for the automated sample pretreatment of organochlorine pesticides (OCP's) and polychlorinated biphenyls (PCB's) in extracts of human milk. This work was part of a regular monitoring program presently carried out at our institute. In this program several hundreds of human milk samples have to be analyzed for the occurrence of PCB's and OCP's. With a normal bore straight phase HPLC system, utilizing column switching we are able to separate the fat from the compounds of interest and, moreover, complete separation of the PCB fraction from the OCP's can be achieved. Under the conditions used to separate the PCB fraction from intefering OCP's column-switching is essential since the retention times for the OCP's vary from 4 minutes for hexachlorobenzene (HCB) to more than 2 hours for dieldrin. 1 ml of an extract containing 45 mg of fat is injected on the first (pre)column, the fat is retained on this column and the early eluting HCB, the PCB fraction, and the DDT complex are transferred to the second (analytical) column. Compounds eluting later than p,p′-DDT are collected directly from the precolumn. Meanwhile, the PCB fraction is separated from the rest of the OCP's on the analytical column. Contrary to conventional gravity-controlled chromatography or solid phase extraction the clean-up process can be monitored on-line by UV-detection, thus rendering a fast and reliable optimization of the system. The OCP-fractions collected from the LC are pooled before they are transferred to a high resolution gas chromatograph equipped with a large volume option. The PCB-fraction is injected directly in a HRGC equipped with a concurrent solvent evaporation injection device. The limits of detection for the OCP's (HCB, α-,β- and γ-HCH, β-Hepo (heptachlorepoxide), dieldrin, p,p′-DDE, o,p′-DDT p,p′-DDT and TDE) and the PCB's investigated are at sub-ppb level (fat basis); the recoveries vary from 80 to 100%. 相似文献
73.
Gabeler EE Sluiter W van Hillegersberg R Edixhoven A Schoonderwoerd K Statius van Eps RG van Urk H 《Photochemistry and photobiology》2003,78(1):82-87
Photodynamic therapy (PDT) based on the photosensitive protoporphyrin IX (PpIX) may prevent restenosis after transluminal angioplasty. PpIX is synthesized in mitochondria, which differ in number and activity among various tissues. Therefore, we questioned whether the course of PpIX concentration after systemic aminolaevulinic acid (ALA) administration differed among various arteries. ALA was administered intravenously (200 mg/kg) to male Wistar rats (n = 21). At varying time intervals (0, 1, 2, 3, 6, 12 and 24 h) both central and peripheral arteries were isolated and homogenized, and the concentration of the various heme intermediates was determined by a fluorometric extraction method. The maximal PpIX concentration was more than two-fold higher in peripheral arteries (20.49 +/- 3.0 to 24.0 +/- 7.5 pmol/mg protein) than in central arteries (0-9.46 +/- 0.01 pmol/mg protein) (P < 0.004). However, the amount of citrate synthase, reflecting the mitochondrial mass, was lower (0.14-0.61 and 1.87-2.32 U/mg protein, respectively). Apparently, the level of PpIX cannot simply be explained by the mitochondrial content of the arteries. The time interval of maximal PpIX accumulation was similar in peripheral and central arteries (2 h and 27 min vs. 2 h and 8 min) (P = 0.13). Thus, if the efficacy of PDT in vivo is directly related to the tissue concentration of PpIX, more effect can be expected in peripheral arteries than in central arteries. 相似文献
74.
Boone CM Manetto G Tagliaro F Waterval JC Underberg WJ Franke JP de Zeeuw RA Ensing K 《Electrophoresis》2002,23(1):67-73
An interlaboratory pilot study was performed to determine the reproducibility of mobility parameters in capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC). The study was performed by an intended small number of laboratories (three) that used different brands of instruments (two). The effective mobility was corrected using standards by a method that was recently introduced to obtain a more reproducible migration parameter. A test set of 20 acidic test compounds and 5 reference compounds were analyzed during five days in each laboratory using CZE and MEKC. Buffers used consisted of 90 mM borate set at pH 8.4 (CZE) and 20 mM phosphate, 50 mM sodium dodecyl sulfate set at pH 7.5 (MEKC). Analyses were carried out using fused-silica capillaries at an electric field strength of either 52.6 kV/m or 37.5 kV/m. The interlaboratory reproducibility (mean RSD) of the effective mobility was 3.0% for CZE and 6.7% for MEKC. After applying the correction method, these values became 3.0% for CZE and 3.3% for MEKC, which is adequate for systematic toxicological analysis (STA) applications. A significant improvement of reproducibility for the calculated corrected effective mobility mu(eff)c was observed when variations are high. Therefore, it is recommended to use the correction method in interlaboratory situations, especially when instruments and capillaries from different manufacturers are used. 相似文献
75.
Blomgren A Berggren C Holmberg A Larsson F Sellergren B Ensing K 《Journal of chromatography. A》2002,975(1):157-164
A method for the extraction of clenbuterol from calf urine samples using a molecularly imprinted polymer (MIP) has been developed. The aim was that the final extracts from the MIP should allow quantitation of clenbuterol down to 0.5 ng/mL urine using HPLC with UV detection. The MIP was produced using brombuterol as a template and the selectivity of the MIP, for clenbuterol, was tested against a non-imprinted polymer (produced without template) and was found to be high. After loading of 5 mL diluted centrifuged urine, selective binding was established in acetonitrile-acetic acid (98:2). For further elution of interferences, 0.5 M ammonium acetate buffer pH 5 and 70% acetonitrile in water was used. Clenbuterol was eluted using 1% trifluoroacetic acid in methanol, which was evaporated and reconstituted in buffer. Results from the HPLC analyses showed that the extraction of clenbuterol using MIP is linear in the range 0.5-100 ng/mL with good precision (4.3% for 0.6 ng/mL and 2.1% for 6.0 ng/mL) and accuracy (96.7% for 0.6 ng/mL and 96.7% for 6.0 ng/mL). The recoveries were 75%. The results show that the method offers a selectivity and sensitivity that make the quantitation of 0.5 ng clenbuterol/mL urine by HPLC-UV possible and a competitive alternative to state-of-the-art routine analytical methods. 相似文献
76.
C. Molins E. A. Hogendoorn H. A. G. Heusinkveld A. C. van Beuzekom P. van Zoonen R. A. Baumann 《Chromatographia》1998,48(5-6):450-456
Summary Recent work demonstrated that the combination of microwave assisted solvent extraction (MASE) and capillary gas chromatography
with selective nitrogen detection (GC-NPD) is a viable approach for the efficient determination of triazine herbicides in
soils. However, for soils with a high organic matter content or the injection of more concentrated extracts to obtain lower
LOD's the performance of gas chromatographic analysis of uncleaned extracts is hampered. This results in both a decrease of
the chromatographic response of analytes and a decrease in the life time of the column due to coextracted matrix substances.
The effect of various types of soils on the chromatographic analysis of triazine herbicides was studied. It appeared that
for the investigated samples with an organic matter content below 5% processing of uncleaned extracts is possible. Samples
with a higher organic matter content required a cleanup step. A rapid procedure on 100 mg silica cartridges has been developed
using solvents compatible with the MASE extracts and the instrumental analysis. Beside the testing with different standard
soils, about 120 samples of an ongoing monitoring program involving three different types of soil (organic matter content:
3–37%) were analysed. The selected compounds atrazine, desethylatrazine, desisopropyl-atrazine and simazine could be assayed
in the various soil types to a level of at least 2 μg kg−1. For soil samples with a high organic matter content (>5%), the rapid cleanup procedure allowed the trace analysis of the
triazines and considerably increased the life time of the capillary column. Recoveries at levels from 2 to 50 μg kg−1 ranged from 70 to 100% with RSDs ranging from 5.1 to 9.5%. Confirmation of positive samples was carried out by gas chromatography
mass spectrometry. 相似文献
77.
Johann T. B. H. Jastrzebski Johannes M. Klerks Gerard van Koten Kees Vrieze 《Journal of organometallic chemistry》1981,210(3):C49-C53
Whereas p-Tol2Zn reacts with t-BuN=CHCH=N-t-Bu (t-BuDAB) to give a stable
complex [p-Tol2Zn(t-BuDAB)], Et2Zn gives EtZ
-(t-Bu) via intramolecular ethyl transfer in the unstable Et2Zn(t-BuDAB) complex. In solution the stable persistent organozinc radical EtZn(t-BuDAB), which is formed in trace amounts in the Et2Zn/t-BuDAB reaction, is in equilibrium with its stable C---C coupled dimer [EtZn-t-BuN=CH(t-BuN)CH]2. The dimer can be prepared in quantitative yield by the reaction of (EtZnCl)4 with K(t-BuDAB). 相似文献
78.
Aihara H Alston-Garnjost M Avery RE Barbaro-Galtieri A Barker AR Barnes AV Barnett BA Bauer DA Bengtsson H Bintinger DL Blumenfeld BJ Bobbink GJ Bross AD Buchanan CD Buijs A Cain MP Caldwell DO Chamberlain O Chien C Clark AR Cowan GD Crane DA Dahl OI Derby KA Eastman JJ Eberhard PH Eisner AM Enomoto R Erne FC Fujii T Gabioud B Gary JW Gorn W Hauptman JM Hofmann W Huth JE Hylen J Joshi UP Kamae T Kaye HS Kees KH Kenney RW Kerth LT Ko W Koda RI Kofler RR Kwong KK Lander RL Langeveld WG Layter JG 《Physical review letters》1986,57(1):51-54
79.
Jan Keijsper Henk Van Der Poel Louis H. Polm Gerard Van Koten Kees Vrieze Paul F.A.B. Seignette Ronald Varenhorst Caspar Stam 《Polyhedron》1983,2(11):1111-1116
The crystal and molecular structures of c-Hex-DAB (c-hexyl-NC(H)C(H)N-c-hexyl; DAB = 1,4-diaza-1,3-butadiene) and of trans-[PdCl2(PPh3)(t-Bu-DAB)] are reported. Crystals of c-Hex-DAB are monoclinic with space group C2/c and cell constants: a = 24.70(1), b = 4.660(2), c = 12.268(3)Å, β = 107.66(4)°, Z = 4. The molecule has a flat E-s-trans-E structure with bond lengths of 1.258(3)Å for the CN double bond and 1.457(3)Å for the central CC′ bond. These bond lengths and the NC-C′ angle of 120.8(2)° indicate that the C- and N-atoms are purely sp2-hybridized and that there is little or no conjugation within the central DAB skeleton. Crystals of trans-[PdCl2(PPh3)(t-Bu-DAB)] are triclinic with space group P-1 and cell constants: a = 17.122(3), b = 18.279(3), c = 10.008(5)Å, α = 96.77(2), β = 95.29(3), γ = 109.79(2). Z = 4. The t-Bu-DAB ligand is coordinated to the metal via one lone pair only. In this 2e; σ-N coordination mode the E-s-trans-E conformation of the free DAB-ligand is still present and the bonding distances within the DAB-ligand are hardly affected. [CN: 1.261(10)Å; CC′: 1.479(10)Å (mean).] The PdN-, NC- and central CC′-bond lengths are compared with those found in other metal -R-DAB complexes. 相似文献
80.
Summary The platinum-platinum bonded [PtR2(OAc)L1]2 complexes (R = Ph, L1 = Et2S, n-Pr2S; R =p-tolyl, L1 = Et2S), have been prepared by oxidising [PrR2L1 ]2 with AgOAc or Tl(OAc)3. The sulphide ligand is replaced by weak ligands to give [PtR2(OAc)L2]2 (L2 = PhNH2, 4-picoline, CI–) whereas PEt3 or P(OMe)3 react to give Pt2R4(OAc)2(PR3)(R = Et, OMe). The methyl platinum analogues could also be prepared. Similar complexes Pt2Me4(O2CCF3)2L3 (L3 = Et2S1 4-picoline) were obtained by the reaction of Hg(O2CCF3)2 with [PtMe2(O2CCF3)L3]2.31p,1H and13C n.m.r. of the complexes are reported. 相似文献