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51.
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   
52.
[reaction: see text] The nature of a linker used for preparing glycoconjugate vaccines is of utmost importance as it may lead to immunogenic biomolecules. We report the conjugation of carbohydrate haptens to protein carriers leading to potential vaccines using the traceless Staudinger ligation. The ligation relies on the selective transfer of a phosphane substituent to an azide to form a native amide bond in the final product upon release of an oxidized phosphane byproduct. We designed new phosphino-functionalized cross-linkers suitable for protein carrier derivatization. We evaluated their utility in preparing conjugates using both synthetic and purified bacterial carbohydrates. The use of a borane-protected phosphane which is deprotected at the time of the ligation reaction led to the best results observed thus far in terms of stability toward oxidation and reactivity.  相似文献   
53.
β-(trichloromethyl)-β-propiolactone (CCl3-PL), β-(trifluoromethyl,methyl)-β-propiolactone (CF3, Me-PL) and β-(trifluoromethyl,ethyl)-β-propiolactone (CF3,Et-PL) have been obtained by the reaction of ketene with chloral, 1,1,1-trifluoroacetone and 1,1,1-trifluorobutanone, respectively. Chiral catalysis lead to optically active monomers. The enantiomeric excess of the lactones has been measured by 1H-NMR spectroscopy, in the presence of 2,2,2-trifluoro-1-(9-anthryl)ethanol or an europium chiral shift reagent. Polymerizations have been carried out in bulk or in toluene, at 60°C or 80°C, using mainly organometallic initiators. The Polymers become insoluble and crystalline at enantiomeric excesses over 80% for CCl3-PL and 70% for CF3,Me-PL. Melting temperatures were recorded from 238 to 268°C for poly(CCl3-PL) and from 78 to 100°C for poly(CF3,Me-PL), depending upon the molecular weight and the enantiomeric excess. The 13C-NMR specroscopy of poly(CCL3-PL) indicates that the polymerization of the corresponding lactone leads to polymers of increasing degrees of isotacticity with the enantiomeric excess of the monomer.  相似文献   
54.
Manicoline B, isolated from the root bark of Dulacia guianensis (Olacaceae), was shown by X-ray analysis to be an equimolecular mixture of two diastereoisomers of a new alkaloid and to have structure (3).  相似文献   
55.
A new and general synthesis of 2,5-dioxopiperazine condensed with the thiazolidine ring is described. The synthesis involves the use of N-ethoxy carbonyl-2-ethoxy-1-2-dihydroquinoleine (EEDQ) as activating agent to form the 2,5-diketopiperazine (EEDQ) as activating agent to form the 2,5-diketopiperazine ring. By this method 9-carbobutoxy-7,7-dimethyl-2,5-dioxo-8-this-1,4-diazabicyclo[4.3.0] nonane (6) and 9-carboxy-8,8 dimethyl-2,5-dioxo-7-thia-1,4-diazabicy clo [4.3.0] nonane (8) were obtained, with near quantitative yield, from 4-carboxy-2-carbobutoxy-5,5 dimethylthiazolidine (4). The former was transformed into acid 7 by hydrolysis with barium bydroxyde and the latter was esterified with diazornethane thus producing a methylester 9. The use of the ethy lester of N-(2-cabobutoxy-4-carboxy-5,5-dimethyl-thiazolidine)glycine (10) for synthesis of 6 was also successful. The spectromethric data were interpreted and confirm the proposed structure of the new compounds.  相似文献   
56.
Summary The thiolato-bridged dinuclear compounds [Rh(-SR)-(COD)]2, where R=p-C6HF4 (1),p-C6H4F (2) and CF3 (3), are obtained from the chloro-bridged analogue by ligand exchange.Compound (1) crystallizes in the space group P1 with a=9.740(3)Å, b=11.642(4)Å, c=13.997(6)Å, =103.87(3)°, =106.98(3)° and =105.10(2)°; z=2. In this dinuclear molecule both Rh atoms have a square planar coordination sharing one edge, namely the two sulphur bridging atoms. The Rh—Rh separation of 2.96 Å is consistent with at most a very weak metal-metal interaction. Upon addition of CO the dimeric [Rh(-SR)(CO)2]2 (4), (5) and (6) are obtained, but addition of PPh3 affords the monomeric species [Rh(SR)(PPh3)-(COD)] (7), (8) and (9). Reactions of the dimeric tetracarbonyl derivatives with PPh3 vary with the nature of R; [Rh(-SR)(PPh3)(CO)]2 is obtained when R=p-C6H4F (10) and CF3 (11) but monomeric [Rh(SR)-(PPh3)(CO)2] (12) is produced when R=p-C6HF4. The latter mononuclear compounds, with R=p-C6H4F (13) and CF3 (14), are also formed by reaction of [Rh(SR)-(PPh3)(COD)] with CO.  相似文献   
57.
A method combining surface plasmon resonance and epitope mapping was developed to study the protein conformation at the oil/water interface of an emulsion. The conformation of beta-lactoglobulin stabilizing dodecane/water and miglyol/water interfaces was investigated using five anti-beta-lactoglobulin monoclonal antibodies. The developed method allows us to specifically recognize the emulsified beta-lactoglobulin at the surface of a sensor chip with good repeatability; i.e., standard deviations range between 0.7 and 3.6%. Considering that the monoclonal antibodies, recognizing conformational epitopes, still bind to beta-lactoglobulin at oil/water interfaces, it is concluded that the protein retains a globular conformation. It is shown that the inhibition-binding values of two pairs of Mabs are different for beta-lactoglobulin stabilizing dodecane/water and miglyol/water interfaces. This indicates that the conformations of emulsified beta-lactoglobulin are slightly different according to the nature of the oil phase. Copyright 2000 Academic Press.  相似文献   
58.
From the study of the CuCuBrCu2?εSC solid cell in the range of cubic digenite and “high temperature” hexagonal chalcocite we have deduced the laws of variation of the deviation from stoichiometry and the holes concentration with the equilibrium partial pressure of sulfur (δ and p are found to be proportional to p14S2). The electronic model corresponding to the formation of associations (V×CuVCu) in the presence of neutral vacancies V×Cu allows one to explain these laws. In the low temperature range (range of “low temperature” hexagonal chalcocite and orthorhombic chalcocite) the study of thermal variations of Hall coefficient permits us to propose the following models: (a) the deviation from stoichiometry of the “low temperature” hexagonal chalcocite is due to the simple ionized vacancies VCu; (b) the deviation from stoichiometry of the orthorhombic chalcocite is due to the vacancies VCu and to the associations (V×CuV×Cu).  相似文献   
59.
A stereoselective approach has been developed for the synthesis of cis- and trans-2-methyl-4-arylpiperidines from a common intermediate. The Ni-catalyzed hydrogenolysis of N-Boc-2-methyl-4-aryl-4-piperidinols, obtained by addition of organometallic reagents on N-Boc-2-methyl-4-piperidone, afforded the trans derivatives with up to 95% selectivity whereas the corresponding cis isomers were obtained in the presence of palladium catalysts.  相似文献   
60.
Syntheses of new sulfinylcinnolines, quinoxalines, quinazolines and phtalazines have been investigated starting from the appropriate halogenobenzodiazine derivatives. The latter were converted in one step to the corresponding sulfanyl benzodiazines which upon oxidation with m-CPBA led to the corresponding sulfoxide derivatives of benzodiazines in moderate to good yields. In parallel to this study, an improved method for the synthesis of 2-methylsulfinylquinoxaline starting from 2-sulfanylquinoxaline is also described and in the quinazoline series a synthetic route has been developed to prepare 2-tert-butyl-5-phenylsulfinylquinazoline with satisfactory yield as well as 2-tert-butyl-5-tert-butylsulfinyl-4(3H)-quinazolinone and 2-tert-butyl-8-tert-butylsulfinyl-4(3H)-quinazolinone.  相似文献   
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