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71.
72.
Proper epidemiological, risk assessment and exposure analysis of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin) and related halogenated aromatic hydrocarbons (HAHs) requires accurate measurements of these chemicals both in the species of interest and in various exposure matrices (i.e. biological, environmental, food and feed). High-resolution instrumental analysis techniques are established for these chemicals, however, these procedures are very costly and time-consuming and as such, they are impractical for large scale sampling studies (i.e. for epidemiological studies and assessment of areas with widespread contamination). Accordingly, numerous bioanalytical methods have been developed for the detection of these chemicals in extracts from a variety of matrices, the majority of which take advantage of the ability of these chemicals to activate the aromatic hydrocarbon receptor (AhR) and the AhR signal transduction pathway. Here we review the currently available in vitro AhR-based cell bioassay systems with a focus on recent recombinant reporter gene cell lines that have been developed for detection and relative quantitation of TCDD and related HAHs. Comparison of the relative sensitivities of the various cell bioassays and examples of their use in screening and analysis of environmental, biological, and food and feed samples are presented. Currently available experimental results and validation studies demonstrate the utility of these cell bioassay systems to provide a relatively rapid, accurate, and cost effective screening approach for the detection of TCDD and related HAHs in a variety of environmental, biological, food and feed samples. The availability of these cell bioassay systems will not only facilitate the large scale sampling studies needed for accurate assessment of contamination and exposure to these environmental chemicals, but they provide avenues for the identification of novel classes of TCDD-like chemicals. 相似文献
73.
Reversed-phase liquid chromatographic (RP/LC) procedures are used to optimize the reaction conditions for the large scale preparation of 2,2-dimethyl-N-benzylmalonamide, 1. In acute studies using mice and rats, compound 1 is a very effective anticonvulsant agent. Large quantities of 1 (ca. 300 g) are needed for detailed studies of its chronic effects. LC monitoring of the synthesis of intermediate products and 1 result in the optimum use of reagents, increased product yields, and decreased reaction times. 相似文献
74.
High Performance Liquid Chromatographic Analysis of Pharmaceuticals Using Oil-In-Water Microemulsion Eluent and Monolithic Column 总被引:1,自引:0,他引:1
Novel and efficient separations of pharmaceutical substances were achieved using oil-in-water microemulsion eluent and a conventional
C18 packing with a flow rate of 1 mL/min−1. Attempts to decrease analysis time was limited due to the high viscosity of the microemulsion which generated relatively
high back-pressures. Monolithic columns gave 3-fold lower back-pressures and allowed flow rates of 4 mL/min−1. with the same microemulsion mobile phase which permitted rapid separations to be achieved. Separation of a test-mix of paraben
preservatives was achieved in both isocratic and gradient mode in less than 1 min. The monolith-microemulsion combination
was applied to rapidly quantitatively analyse two formulated products with excellent linearity, accuracy and repeatability.
Quantitative analysis times were under 90 seconds. Successful quantitation of both nicotine lozenges and naprosyn tablets
was performed using this approach. 相似文献
75.
The 1-(3,4-methylenedioxyphenyl)-3-butanamines (HMDAs) are prepared via reductive amination of the corresponding ketone with a series of low molecular weight alkylamines. These amines are homologues of the N-substituted 3,4-methylenedioxyamphetamines (MDAs). Compounds of the HMDA series have UV absorption properties similar to the MDAs because both series contain the same 3,4-methylenedioxyphenyl chromophore. The HMDAs are separated via reversed-phase liquid chromatographic methods using a C18 stationary phase and an acidic aqueous acetonitrile mobile phase. The mass spectra of these potential designer drugs are very similar to the spectra of the MDA homologues having the same N-substituent. 相似文献
76.
Peptidase-catalyzed formation of macrocyclic lactams on solid phase identifies ring systems that are favorably bound in the enzyme active site. We evaluated several cyclic peptide motifs linked by ester bonds between the P2 and P1' or the P1 and P2' side chains. The depsipeptide represented by structure 5 was readily generated by a variety of peptidases from precursor omega-amino acids or omega-amino esters. This strategy for identifying ring systems for potential macrocyclic transition state analogues was demonstrated with the serine peptidases trypsin and chymotrypsin, with the aspartic peptidase pepsin, and with the zinc peptidase thermolysin. 相似文献
77.
The reactivity of [rac-(C2H4(1-indenyl)2)Zr(n-butyl)][MeB(C6F5)3] (4), [rac-(C2H4(1-indenyl)2)Zr(sec-butyl)][MeB(C6F5)3] (5), and [rac-(C2H4(1-indenyl)2)Zr(polypropenyl)][MeB(C6F5)3] with propene, ethene, and hydrogen was studied by low-temperature (<-40 degrees C) 1H and 13C NMR spectroscopy in toluene solutions. In contrast with previous suggestions that 2 degrees zirconium alkyl species such as 5 are dormant sites, these measurements demonstrate reactivity of 2 degrees zirconium alkyls with propene and ethene comparable to the 1 degrees zirconium alkyl species 4 and [rac-(C2H4(1-indenyl)2)Zr(polypropenyl)][MeB(C6F5)3]. Because 2,1-insertion of propene is an infrequent event, these results preclude significant accumulation of catalyst in the form of 2 degrees zirconium alkyls for this metallocene and counterion. The reactivity of 5 with hydrogen is at least 2 orders of magnitude faster than other 1 degrees zirconium alkyls. Such high reactivity accounts for the puzzlingly high fraction of butyl end groups in prior hydrooligomerization studies and implies that catalyst responsivity to H2 as a molecular weight control agent correlates with the regioselectivity of the catalyst. 相似文献
78.
79.
A. J. A. Clark R. S. Lenk 《Journal of polymer science. Part A, Polymer chemistry》1985,23(9):2461-2479
This paper further investigates imide formation in amidation reactions involving Bischloride A2 and suitably selected mono- and difunctional analogues on the one hand, and primary aromatic mono- and diamines on the other. It also investigates the reaction of these acid chlorides with secondary mono- and diamines. If, say, N,N′ dimethyl p-phenylene diamine and hydroquinone dioxyacetyl chloride or bischloride A2 were to react quantitatively, then a linear unbranched polyamide would be expected to be the result which, in the absence of any hydrogen remaining at the amide link, would no longer present a site for further electrophilic attack on the part of the exceptionally reactive aroxyacetyl chloride. There also arises the possibility that a monoamine such as aniline could conceivably act as a difunctional reagent in the presence of aroxyacetyl chlorides. In the event of this reaction proceeding quantitatively one would expect to obtain a linear polyimide in which each imide–nitrogen atom carries a phenyl group. In carrying out the experimental preparative work which is required to elucidate these points we used both monofunctional reactants as model compounds and difunctional reactants in order to assess the polymeric resultants. The products were characterized by means of 1H-NMR, 13C-NMR, IR spectroscopy, TLC, and Tg determinations. The conclusions drawn on the basis of the experimental work provided a satisfactory interpretation of the complex reactions which occur during the polyamidation of bischloride A2. They also point to interesting possibilities for the use of difunctional aroxyacetyl chlorides as modifying comonomers in minor amounts in the preparation of copolyaramides with reduced crystallinity. Such copolyaramides would be expected to have better solubility in common solvents and to be more easily processable than the rather specialized and extremely high-melting polyaramides currently commercially available and could therefore extend the range of useful applications for this class of polymers. The experimental section is preceded by an introduction which briefly reviews the “state of the art,” especially as far as bischloride A2-based polyamidation reactions are concerned. It is followed by a discussion of the results, by the conclusions, and a brief summary. 相似文献
80.
Clark SB Turnipseed SB Nandrea GJ Madson MR Hurlbut JA Sofos JN 《Journal of AOAC International》2002,85(5):1009-1014
A confirmatory method is described for phenylbutazone (PB) residues in bovine kidney tissue. Ground kidney tissue is diluted with water, and the mixture is made basic with 25% ammonium hydroxide in water; the lipids are extracted with ethyl and petroleum ethers. The ether layer is discarded, and the tissue is acidified with 6N HCl. PB residues are extracted with tetrahydrofuranhexane (1 + 4). The extract is passed through a silica solid-phase extraction column, and the eluate is evaporated to dryness. The residue is dissolved in acidified acetonitrile-water-acetic acid (50 + 49.4 + 0.6). A single quadrupole mass spectrometer coupled to a liquid chromatograph with an electrospray interface is used to confirm the identity of the PB residues in the kidney extract. Negative-ion detection with selected-ion monitoring of 4 ions is used. Sets of control and fortified-control kidney tissues (at 50, 100, and 200 ppb PB) and several kidney tissue field samples were analyzed for method validation. The method was tested further during the course of a survey to determine the incidence of PB residues in bovine kidney samples obtained from slaughterhouses across the country. In addition, the method was tested for use with an ion-trap mass spectrometer coupled to a liquid chromatograph, which allowed confirmation of PB at lower levels (5-10 ppb) in kidney tissue. 相似文献