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71.
AbstractFive thienylnicotinamidine derivatives 5a–e were prepared from their corresponding nicotinonitriles 3a–e on treatment with lithium trimethylsilylamide [LiN(TMS)2] followed by hydrolysis using ethanolic/HCl (gas). The nicotinonitriles 3a–e were prepared via Suzuki coupling reaction of bromothienyl derivative 1 with the appropriate phenylboronic acids 2a–e. The DFT calculation was used to optimize the geometric structure of the newly synthesized nicotinamidines. The comparison of DFT/B3LYP calculated spectral data (1H-NMR and 13C-NMR) with the experimental data showed acceptable agreement. Mass fragmentation patterns of 3,4-dimethoxyphenyl, 3,5-dimethoxyphenyl, and 3,4,5-trimethoxyphenyl thienylnicotinamidine derivatives were investigated. 相似文献
72.
Synthesis and derivatization of daptomycin: a chemoenzymatic route to acidic lipopeptide antibiotics
Grünewald J Sieber SA Mahlert C Linne U Marahiel MA 《Journal of the American Chemical Society》2004,126(51):17025-17031
Daptomycin is a branched cyclic nonribosomally assembled acidic lipopeptide, which is the first clinically approved antibiotic of this class. Here we show that the recombinant cyclization domain of the Streptomyces coelicolor calcium-dependent antibiotic (CDA) nonribosomal peptide synthetase (NRPS) is a versatile tool for the chemoenzymatic generation of daptomycin derivatives. Linear CDA undecapeptide thioesters with single exchanges at six daptomycin-specific residues were successfully cyclized by CDA cyclase. Simultaneous incorporation of all six of these residues into the peptide backbone and elongation of the N-terminus of CDA by two residues yielded a daptomycin derivative that lacked only the beta-methyl group of l-3-methylglutamate. Bioactivity studies with several substrate analogues revealed a significant role of nonproteinogenic constituents for antibacterial potency. In accordance with acidic lipopeptides, the bioactivity of the chemoenzymatic assembled daptomycin analogue is dependent on the concentration of calcium ions. Single deletions of the four acidic residues in the peptide backbone suggest that only two aspartic acid residues are essential for antimicrobial potency. These two residues are strictly conserved among other nonribosomal acidic lipopeptides and the EF-motif of ribosomally assembled calmodulin. Based on these findings CDA cyclase is a versatile catalyst that can be used to generate novel daptomycin derivatives that are otherwise difficult to obtain by chemical modification of the parental tridecapeptide to improve further its therapeutic activity. 相似文献
73.
Anwar Usman Ibrahim Abdul Razak Suchada Chantrapromma Hoong‐Kun Fun Varughese Philip A. Sreekanth M. R. Prathapachandra Kurup 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(11):o652-o654
The title compound, C16H17N5S, is in the thione form and crystallizes with two independent molecules in the asymmetric unit. In both molecules, the pentamethyleneimine five‐membered ring adopts an envelope conformation, and in one of the molecules this ring shows positional disorder. The thione S and hydrazine N atoms are in the Z configuration with respect to the C—N bond. 相似文献
74.
5-Amino-3-(3-methyl-5-oxo-1-phenyl-2-pyrazolin-4-yl)-7-phenyl-7H-thiazolo[3,2-a]pyrimidine-6-carbonitrile was synthesized via the reaction of 4-(2-aminothiazol-4-yl)-3-methyl-1-phenyl-2-pyrazolin-5-one with benzylidene malononitrile and was then transformed
to related fused heterocyclic systems. The antifungal and antibacterial studies revealed in some cases excellent biocidal
properties. 相似文献
75.
Mohamed R. Mahran Wafaa M. Abdou Maha D. Khidre 《Monatshefte für Chemie / Chemical Monthly》1990,121(1):51-58
Summary The reaction of furil (1) with trialkyl phosphites2 yielded caged phosphorane derivatives of types3a-c. Dry hydrogen chloride gas converted3a-c into the respectivea-hydroxyvinyl-phosphates8a-c which are equally produced by reacting furil with the appropriate dialkyl phosphite7. The reaction of furil with ylide-phosphoranes10 proceeded according to the Wittig reaction mechanism to give the respective ethylenes11a-c. The new compounds have been characterized by their spectroscopic data (IR, PMR,31P-NMR, MS) and elementary analyses.Dedicated to Prof. M. Sidky on the occasion of his 60th birthday 相似文献
76.
The synthesis of goethite by oxidation of Fe2+in presence of metallic iron was undertaken in an aqueous medium containing indifferent salts such as Na2SO4, (NH4)2SO4, NaCl, and NH4Cl. Temperature and bubbling air rate were maintained, respectively, at 70°C and 1 L/min. The influence of anions and cations on the kinetics of each step of the process has been followed distinctly, the iron dissolution rate has been determined by the variation of the medium acidity, and the precipitation of goethite has been determined by gravimetric measurements. With respect to Cl−, the SO42−anion decreases the rate of the two reactions. NH4+acts as an inhibitor when it is present at low concentrations and as an accelerator for higher concentrations; the limit corresponding to the change of NH4+behavior depends on the nature of the counter ion. The reaction product is composed of pure goethite in the presence of sulfate salts, whereas a mixture of goethite and lepidocrocite, respectively, 60–70 and 40–30%, was observed in the presence of chloride salts. 相似文献
77.
Adenier A Chehimi MM Gallardo I Pinson J Vilà N 《Langmuir : the ACS journal of surfaces and colloids》2004,20(19):8243-8253
The electrochemical oxidation of aliphatic amines (primary, secondary, and tertiary) has been investigated by cyclic voltammetry and preparative electrolysis. The oxidation mechanisms have been established, and the lifetimes of the radical cations have been measured for secondary and tertiary amines. These results have been put in parallel with the attachment of amines to glassy carbon, Au, and Pt electrodes by cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), and infrared reflection-absorption spectroscopy (IRRAS). It is then possible to show that it is not the radical cation but the radical obtained after the deprotonation which reacts with the electrode surface. XPS results also point to the existence of a covalent bond between Au or Pt and the organic moiety. 相似文献
78.
Benoit Bachand Mohamed Atfani Bita Samim Sophie Lévesque Daniel Simard Xianqi Kong 《Tetrahedron letters》2007,48(49):8587-8589
A practical synthetic route to various 2-alkylpropane-1,3-sultones, the key intermediates for the preparation of 2-substituted homotaurines as analogs of tramiprosate, was developed. 相似文献
79.
Ibrahim El-Sayed El-Kholy Morcos Michael Mishrikey Hassan Mostafa Feid-Allah 《Journal of heterocyclic chemistry》1981,18(1):105-110
The reaction of piperidine, morpholine, piperazine or dimethylamine with several coumarins, 3-bromocoumarin, 4,6-diaryl-2H-pyran-2-ones and 3-bromo-4,6-diaryl-2H-thiopyran-2-ones gave o-hydroxycinnamic acid amides, benzofurans, open-chain δ-oxoamides and thiophene derivatives, respectively. 相似文献
80.
Mangelings D Tanret I Matthijs N Maftouh M Massart DL Vander Heyden Y 《Electrophoresis》2005,26(4-5):818-832
The effect of five factors on the capillary electrochromatographic enantioseparation of acidic compounds was studied using an experimental design. The studied factors were pH, acetonitrile content in the mobile phase, temperature, buffer concentration, and applied voltage. These experiments allowed defining a generic separation strategy applicable on acidic compounds with chemical and structural diversity. The starting screening conditions consist of a 45 mM ammonium formate electrolyte at pH 2.9 mixed with 65% acetonitrile, an applied voltage of 15 kV, and a temperature of 25 degrees C. The screening phase occasionally can be followed by an optimization procedure. Evaluation of the proposed strategy pointed out that it allows achieving baseline resolution within a relatively short time when a beginning of separation is obtained at the starting conditions. This strategy revealed enantioselectivity for 11 compounds out of 15, of which 10 could be baseline-separated after the proposed optimization steps. 相似文献