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111.
Summary A reversed-phase HPLC method has been developed for the urinary determination of mutagenic 2,4- and 2,6-toluendiamines. These
amines are degradation products of polyurethane, a material used to cover textured silicone breast implants. FMOC-Cl was used
as fluorescent derivatising agent in order to obtain a limit of detection of 15 ng/ml in urine. Pre-treatment of urine samples
was by liquid/liquid extraction and urine specimens of patients after surgury were analysed. 相似文献
112.
The cure of a bismaleimide (BMI) neat resin modified with an aromatic diamine and a siloxane elastomer, has been studied by 13C solid state nuclear magnetic resonance. Two chemical reactions occur during the cure cycle; at a low temperature, Michael's reaction predominates, while at a high temperature the polymerization of the double bond maleimide creates the network. The degradation of this BMI material was characterized with isothermal and dynamic thermogravimetric analyses in air and in nitrogen. The BMI thermal stability is lower in nitrogen than in air. This behavior is an indication of oxygen participating in reactions at high temperatures. The activation energy (Ea) of thermal degradation was determined from isothermal data using an Arrhenius equation (In V vs. 1/T). The global Ea for the weight loss in air was found to be 91 kJ/mol. The nature and the evolution of the thermal degradation products were the combined analyzed by techniques of pyrolysis, gas chromatography and mass spectrometry. The major thermal decomposition products obtained in the temperature range of 300–700°C are identified as benzene, methyl formamide, aniline, toluene and isocyanate-derived products. 相似文献
113.
Laurence E. Strong Carter Van Waes Kenneth H. Doolittle II 《Journal of solution chemistry》1982,11(4):237-258
The three monofluorobenzoic acids together with 2,4-difluoro and 2,6-difluorobenzoic acids in aqueous solution are the subject of precision conductance measurements. The experimental data are analyzed to give ionization constants and limiting conductances at temperatures from 0 to 100°C. Walden products for the acid anions are derived from the limiting conductances while the ionization consatants are fitted by statistical methods to the function pK
a
(m)=A+B/T+ C logT+DT. Only the 2,6- acid requires the fourth term of the function to fit the data to a precision of better than 0.03%. Mathematical analysis of the pK function gives the standard changes in enthalpy, entropy, and heat capacity. All the acids studied are more acidic than the parent, benzoic acid, as well as more acidic than the isoelectronic methylbenzoic acids. In general the increased acidity is tied to decreases in enthalpy while entropy changes on ionization differn little from those found for the parent acid. 相似文献
114.
Zlatopolskiy BD Loscha K Alvermann P Kozhushkov SI Nikolaev SV Zeeck A de Meijere A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(19):4708-4717
The complete absolute configuration of hormaomycin 1 a has been established by HPLC and HPLC/MS experiments with appropriately derivatized 4-propylprolines, (2S,4S)-6 and (2R,4R)-6, as well as 4-(Z)-propenylprolines, cis-5 and trans-5, and also feeding experiments with enantiomerically pure samples of the deuterium-labeled 3-(2'-nitrocyclopropyl)alanine, (2S)-3,3-[D2]15 and (2S)-2,2'-[D2]15, and 4-(Z)-propenylproline 2',4-[D2]-(2S,4R)-5. The latter five amino acids were prepared for the first time and allowed one to unequivocally assign the hitherto unknown absolute configurations of the last four stereocenters in hormaomycin 1 a. As a bonus, some new information about the biosynthesis of this molecule has also been gathered. 相似文献
115.
V. N. Berezhnaya V. P. Vetchinov R. P. Shishkina V. I. Mamatyuk 《Russian Chemical Bulletin》1993,42(2):318-322
Using1H and13C NMR spectroscopy, naphthodihydroimidazolediols were identified as the primary products of photolysis of 2-dialkylamino-3-amino(alkylamino)-1,4-naphthoquinones. Their further non-photochemical (thermal) transformations depend on their structure and on the photolysis conditions.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 358–362, February, 1993. 相似文献
116.
Accurate, practical prediction of 13C NMR chemical shifts has been achieved with a new system, CAST/CNMR, taking account of stereochemistry. The CAST/CNMR system has solved the critical problem of the accurate distinction of differences and similarities in stereochemical structures around a specific carbon, which has not yet been achieved by any other database-oriented system for prediction of 13C NMR chemical shifts. CAST/CNMR uses a three-dimensional structural database together with a 13C NMR spectral database. Absolute/relative configurational and conformational structural information are described by the CAST (CAnonical-representation of STereochemistry) coding method. This paper provides an overview of the CAST/CNMR system, and describes its application to two natural products as examples. 相似文献
117.
Summary Ten heterocyclic aromatic amines (HAA) (1)–(10) were analyzed in commercially available meat products and fish. After sample preparation by Extrelut treatment and subsequent
solid phase extraction applying propylsulphonic and C18 silica cartridges, HPLC-ESI-MS-MS using selected reaction monitoring (SRM) and d3-PhIP and d3-MeIQx as internal and external standards, respectively, revealed the widely distributed presence of PhIP (8) and MeIQx (4), ranging from 0.1 to 5.3 ng g−1 and 0.1 to 5.2 ng g−1, respectively. Lower amounts were found for 4,8-DiMeIQx (5) and 7,8-DiMeIQx (6), ranging from 0.2 to 2.0 ng g−1 and 0.1 to 0.2 ng g−1, respectively. The other HAA under study, i.e. IQ, MeIQ, 4,7,8-TriMeIQx, Glu-P-1, and Glu-P-2 were not determinable under
the experimental conditions used (determination limit 0.1 ng g−1). 相似文献
118.
Georgia Gatidou Nikolaos S. Thomaidis Themistokles D. Lekkas 《Analytica chimica acta》2005,528(1):89-99
A method for the simultaneous determination of two antifouling booster biocides, diuron (1-(3,4 dichlorophenyl) 3,3 dimethyl urea) and irgarol 1051 (2-methylthio-4-tert-butylamino-6-cyclopropylamino-s-triazine), and their metabolites, DCPMU (1-(3,4 dichlorophenyl)-3 methyl urea), DCPU (1-(3,4 dichlorophenyl) urea), DCA (3,4 dichloroaniline) and M1 (2-methylthio-4-tert-butylamino-s-triazine) in seawater by high performance liquid chromatography-diode array detector (HPLC-DAD) was developed. The optimization of the extraction procedure included the type of sorbent and the type of the organic solvent for the elution. Optimization of the liquid chromatography (LC) separation was also performed and the robustness of the developed separation was tested, in respect to the effect of three factors (column temperature, flow rate and initial strength of acetonitrile) on the retention times, peak resolution and peak area of the six compounds. The optimized procedure included off-line extraction of these compounds from seawater samples using C18 solid phase extraction (SPE) cartridges. The inter-day precision of the developed procedure was less than 14% (as R.S.D.s) for all the tested compounds. Satisfactory recoveries (higher than 82%) were obtained for all substances, except for DCA, for which low recovery was obtained (30.5%). The limits of detection (LODs) of the substances varied between 0.005 (DCPMU) and 0.026 (M1) μg L−1. 相似文献
119.
Summary High pressure liquid chromatographic methods for the determination of diphenylmethane-4,4-diisocyanate (MDI) and toluene diisocyanate (TDI) in chemical products are described. The MDI- and TDI monomers were determined as their urea derivative formed by the reaction with 9-(methyl aminomethyl)-anthracene. Using these methods MDI- and TDI monomer concentrations have been determined in 55 chemical products: sealing waxes, insulating- and adhesive foam, hardener, primer, adhesives and surface coatings. The recovery of both MDI and TDI monomers from various types of chemical product was found to be 92–97%, and the relative standard deviations of the methods was <5% for all types of products. 相似文献
120.
Dissociative and nondissociative electron attachment in the electron impact energy range 0–14 eV are reported for SOF2 SOF4, SO2F2, SF4, SO2, and SiF4 compounds which can be formed by electrical discharges in SF6. The electron energy dependences of the mass-identified negative ions were determined in a time-of-flight mass spectrometer. The ions studied include F– and SOF
2
–*
from SOF2; SOF
3
–
and F– from SOF4; SO2F
2
–*
, SO2F–, F
2
–
, and F– from SO2F2; SF
4
–*
and F– from SF4; O–, SO–, and S– from SO2; and SiF
3
–
and F– from SiF4. Thermochemical data have been determined from the threshold energies of some of the fragment negative ions. Lifetimes of the anions SOF
2
–*
, SO2F
2
–*
, and SF
4
–*
are also reported. 相似文献