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141.
Claire Jabot Maëva Fieu Barbara Giroud Audrey Buleté Hervé Casabianca 《International journal of environmental analytical chemistry》2015,95(3):240-257
The aim of the work was to develop an analytical procedure able to quantify traces of 13 neonicotinoids and pyrethroids as well as carboxamide in beeswax at low levels (ng g?1) to evaluate the contamination. For this purpose, an efficient sample preparation procedure was developed based on solid–liquid extraction using dispersive diatomaceous earth and acetonitrile. This step was followed by a selective and sensitive analysis based on ultra-high-performance liquid chromatography coupled to tandem mass spectrometry (ESI-MS/MS). This analytical procedure was validated based on International Conference on Harmonization guidelines. The limits of quantification ranged from 1 ng g?1 (thiamethoxam, clothianidin, imidacloprid, acetamiprid, thiacloprid and boscalid) to 40 ng g?1 (lambda-cyhalothrin). The method was then successfully applied to 60 samples of beeswax collected in several areas of France. The presence of thiacloprid, boscalid, imidacloprid and deltamethrin in beeswax was confirmed. The most frequently quantified pesticide was boscalid. 相似文献
142.
The presence of antibiotics in the environment is of increased interest and, as modern mass spectrometers become more efficient, we are increasingly aware of traces of pharmaceuticals appearing in a wide range of environmental and biological matrices. The Q-Exactive mass spectrometer is part of these innovative hybrid high-resolution mass spectrometers (HRMS) which is often associated with peptide sequencing or metabolomics but with a limited number of studies focusing on its application to the quantification of small molecules in environmental and biological matrices. It combines the high resolving power (RP) performance of the Orbitrap with the high performance selectivity of the quadrupole. Tetracyclines (TCs) are a family comprising some of the most widely used antibiotics in veterinary medicine. This study presents the quantitative performances of the Q-Exactive by illustrating a new approach to quantify TCs using liquid chromatography coupled to a HRMS in a complex matrix, i.e., swine manure. The Q-Exactive was used at high-resolution in both full scan (FS) and targeted ion fragmentation (tMS2) modes. These two modes were optimized and compared to determine the most reliable and efficient approach to quantify TCs with good accuracy. The proposed method was optimized to obtain the best selectivity and sensitivity, thus eliminating false positive and allowing the detection of trace levels of analyte. The TCs were extracted from the matrix by sonication using McIlvaine buffer followed by an off-line solid phase extraction method to concentrate and clean the extracts. Both FS and tMS2 modes presented good linearity (R2 > 0.991) and repeatability (RSD < 15%). Mass accuracy was acceptable with values below 2 ppm. The method detection limits (MLD) calculated from the calibration curves ranged from 2.0 to 12 ng g−1 for FS mode and from 1.5 to 3.6 ng g−1 for tMS2 mode. Accuracy and interday/intraday relative standard deviations were below 21% for both modes studied. TCs were quantified in real samples of swine manure with concentrations ranging from 29 to 75 ng g−1. This study showed the possibility of using hybrid HRMS for trace detection and quantification of TCs in a complex matrix, thus avoiding false positive while achieving good selectivity and sensitivity. 相似文献
143.
Absolute photoionization cross sections of furanic fuels: 2‐ethylfuran, 2‐acetylfuran and furfural 下载免费PDF全文
Absolute photoionization cross sections of the molecules 2‐ethylfuran, 2‐acetylfuran and furfural, including partial ionization cross sections for the dissociative ionized fragments, are measured for the first time. These measurements are important because they allow fuel quantification via photoionization mass spectrometry and the development of quantitative kinetic modeling for the complex combustion of potential fuels. The experiments are carried out using synchrotron photoionization mass spectrometry with an orthogonal time‐of‐flight spectrometer used for mass analysis at the Advanced Light Source of Lawrence Berkeley National Laboratory. The CBS‐QB3 calculations of adiabatic ionization energies and appearance energies agree well with the experimental results. Several bond dissociation energies are also derived and presented. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
144.
D. Aussel R. Correa M. Marechal 《Journal of Optimization Theory and Applications》2011,151(3):474-488
The gap function (or merit function) is a classic tool for reformulating a Stampacchia variational inequality as an optimization
problem. In this paper, we adapt this technique for quasivariational inequalities, that is, variational inequalities in which
the constraint set depends on the current point. Following Fukushima (J. Ind. Manag. Optim. 3:165–171, 2007), an axiomatic approach is proposed. Error bounds for quasivariational inequalities are provided and an application to generalized
Nash equilibrium problems is also considered. 相似文献
145.
Beaussart A Mierczynska-Vasilev AM Harmer SL Beattie DA 《Journal of colloid and interface science》2011,357(2):510-520
The adsorption of two modified dextrins (phenyl succinate dextrin--PS Dextrin; styrene oxide dextrin--SO Dextrin) on four different mineral surfaces has been studied using X-ray photoelectron spectroscopy (XPS), in situ atomic force microscopy (AFM) imaging, and captive bubble contact angle measurements. The four surfaces include highly orientated pyrolytic graphite (HOPG), freshly cleaved synthetic sphalerite (ZnS), and two surfaces produced through surface reactions of sphalerite: one oxidized in alkaline solution (pH 9, 1 h immersion); and one subjected to metal ion exchange between copper and zinc (i.e. copper activation: exposed to 1×10(-3) M CuSO(4) solution for 1 h). XPS measurements indicate that the different sphalerite surfaces contain varying amounts of sulfur, zinc, oxygen, and copper, producing substrates for polymer adsorption with a range of possible binding sites. AFM imaging has shown that the two polymers adsorb to a similar extent on HOPG, and that the two polymers display very different propensities for adsorption on the three sphalerite surface types, with freshly cleaved sphalerite encouraging the least adsorption, and copper activated and oxidized sphalerite encouraging significantly more adsorption. Contact angle measurements of the four surfaces indicate that synthetic sphalerite has a low contact angle upon fracture, and that oxidation on the timescale of one hour substantially alters the hydrophobicity. HOPG and copper-activated sphalerite were the most hydrophobic, as expected due to the carbon and di/poly-sulfide rich surfaces of the two samples, respectively. SO Dextrin is seen to have a significant impact on the wettability of HOPG and the surface reacted sphalerite samples, highlighting the difficulty in selectively separating sphalerite from carbonaceous unwanted minerals in flotation. PS Dextrin has the least effect on the hydrophobicity of the reacted sphalerite surfaces, whilst still significantly increasing the wettability of graphite, and thus has more potential for use as a polymer depressant in this separation. 相似文献
146.
Nasr G Guerlin A Dumur F Beouch L Dumas E Clavier G Miomandre F Goubard F Gigmes D Bertin D Wantz G Mayer CR 《Chemical communications (Cambridge, England)》2011,47(38):10698-10700
Two iridium(III) soft salts based on ion-paired dinuclear cationic and mononuclear anionic complexes were designed and investigated as phosphorescent emitters for solution processed OLEDs. New dinuclear cationic complexes were prepared with two different bridging ligands, a carbazole and a phenylene spacer. Best devices were designed with the soft salt bearing a carbazole moiety. 相似文献
147.
Catalytic intramolecular alkene aziridination of sulfamate is an emerging methodology for the asymmetric synthesis of chiral functionalized amines involving the formation of bicyclic aziridines. This study demonstrates the ability of the latter to undergo ring-opening with various carbon nucleophiles: Grignard reagents, lithium salts of terminal alkynes, dithiane, malonate. These S(N)2-type reactions occur with high levels of regio- and chemoselectivity to generally afford seven-membered cyclic sulfamidates in good yields. Carbon nucleophiles have also been found to react with these sulfamidates provided that the sulfamate ester has been previously activated by introduction of a tosyl substituent on the NH group. The versatility of this strategy has been illustrated with the syntheses of spisulosine and its fluoro analogue. 相似文献
148.
Ayers S Graf TN Adcock AF Kroll DJ Shen Q Swanson SM Wani MC Darveaux BA Pearce CJ Oberlies NH 《Tetrahedron letters》2011,52(40):5128-5130
A fungal extract (MSX 63619), from the Mycosynthetix library of over 50,000 fungi, displayed promising cytotoxicity against a human tumor cell panel. Bioactivity-directed fractionation led to the isolation of an o-pyranonaphthoquinone decaketide, which we termed obionin B (1). The structure of 1 was deduced via spectroscopic and spectrometric techniques. The IC50 value of 1 was moderate, ranging from 3 to 13 μM, depending on the cell line tested. 相似文献
149.
Audrey MartinezJimmy Sélambarom 《Tetrahedron letters》2011,52(13):1444-1447
A convenient and general one-pot, two-step protocol to prepare both N-acyl-1,3-thiazolidines and N-acyl-1,3-oxazolidines from formaldehyde, fatty acyl chlorides, and natural α-amino acids has been performed for the peculiar case of formaldehyde. In the presence of triethylamine to promote both the ring-forming process and the amide bond formation, subsequent addition of the acyl donor proved to be efficient to trap the preformed stable formaldehyde-derived 1,3-thiazolidine or the transient 1,3-oxazolidine using an appropriate ratio of formaldehyde. 相似文献
150.