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991.
Aromatic aminocatalysis refers to transformations that employ aromatic amines, such as anilines or aminopyridines, as catalysts. Owing to the conjugation of the amine moiety with the aromatic ring, aromatic amines demonstrate distinctive features in aminocatalysis compared with their aliphatic counterparts. For example, aromatic aminocatalysis typically proceeds with slower turnover, but is more active and conformationally rigid as a result of the stabilized aromatic imine or iminium species. In fact, the advent of aromatic aminocatalysis can be traced back to before the renaissance of organocatalysis in the early 2000s. So far, aromatic aminocatalysis has been widely applied in bioconjugation reactions through transamination; in asymmetric organocatalysis through imine/enamine tautomerization; and in cooperative catalysis with transition metals through C?H/C?C activation and functionalization. This Focus Review summarizes the advent of and major advances in the use of aromatic aminocatalysis in bioconjugation reactions and organic synthesis.  相似文献   
992.
993.
Graphdiyne oxide (GDO), the oxidized form of graphdiyne (GDY), exhibits an ultrafast humidity response with an unprecedented response speed (ca. 7 ms), which is three times faster than that of graphene oxide (GO) with the same thickness and O/C ratio. The ultrafast humidity response of GDO is considered to benefit from the unique carbon hybridization of GDO, which contains acetylenic bonds that are more electron‐withdrawing than ethylenic bonds in GO, consequently giving rise to a faster binding rate with water. This distinctive structure‐based property enables the fabrication of a novel GDO‐based humidity sensor with an ultrafast response speed and good selectivity against other kinds of gas molecules as well as high sensitivity. These properties allow the sensor to accurately monitor the respiration rate change of human and hypoxic rats.  相似文献   
994.
A new Er(III)–Na(I) coordination polymer of stoichiometry [NaEr2L5(H2O)6(NO3)](NO3)·3.5H2O (HL = picolinic acid N-oxide) has been synthesized and characterized by single-crystal X-ray analysis. Crystals are triclinic, P with a = 9.823(2), b = 12.453(2), c = 20.643(4) Å; = 98.49(3), ( = 101.40(3), = 108.69(3)°; V = 2284(1) Å3; Z = 2. Of the two independent eight-coordinate erbium(III) ions in this complex, one is surrounded by four bidentate chelating L ligands, and the other by one bidentate chelating L ligand, four aqua ligands and two anti-carboxylate oxygen atoms from two neighboring [ErL4] units. The sodium(I) ion is in a distorted octahedral environment, being coordinated by a unidentate nitrate anion, three aqua ligands and two anti-carboxylate oxygen atoms from two adjacent [ErL4] units. The complex is built from zigzag chains of syn-anti carboxylate-bridged erbium(III) moieties directed in the a direction, which are cross-linked pairwise by aqua-bridgeddimericsodium(I) units. The resulting composite polymeric chains are further connected by hydrogen bonds to form a three-dimensional network.  相似文献   
995.
A general and efficient synthesis of 5-aryl imidazo[1,5- a]pyrazines by palladium-catalyzed coupling of the corresponding 8-substituted derivatives with aryl halides is described. The scope of this new reaction for the imidazo[1,5- a]pyrazine ring system was explored using three readily available 8-substituted precursors, X = NH2, NMe2, and OMe, as well as 8-aryl derivatives, X = Ar'. On the basis of these results as well as studies using a deuterated derivative, a Heck-like mechanism is proposed for this transformation.  相似文献   
996.
A new method for the determination of sulfur forms in wine, i.e., free SO2, total SO2, bound SO2, total S, and sulfate, is presented. The method is based on the measurement of the carbon monosulfide (CS) molecular absorption produced in a conventional air–acetylene flame using high-resolution continuum source absorption spectrometry. Individual sulfur forms can be distinguished because of the different sensitivities of the corresponding CS molecular absorption. The sensitivity of free SO2 is about three times higher than the value for bound SO2 and sulfate. The method makes use of procedures similar to those used in classic reference methods. Its performance is verified by analyzing six wine samples. Relative standard deviations are between 5 and 13% for free SO2 and between 1 and 3% for total SO2. For the validation of the accuracy of the new method, the results are compared with those of reference methods. The agreement of the values for total SO2 with values of the classic method is satisfactory: five out of six samples show deviations less than 16%. Due to the instability of free SO2 in wine and the known problems of the used reference method, serious deviations of the free SO2 results are found for three samples. The evaluation of the limits of detection focuses on the value for free SO2, which is the sulfur form having by far the lowest concentration in wine. Here, the achievable limit of detection is 1.8 mg L−1. Figure Detection of non-metal elements using continuum source flame absorption spectrometry  相似文献   
997.
A new electrochemical sensor was demonstrated for selective sensing of 3,4-dihydroxyphenylacetic acid (DOPAC) through a non-oxidative mechanism by using single-walled carbon nanotubes (SWNTs) as the electronic transducer and a synthetic cyclophane electron acceptor as the recognition element.  相似文献   
998.
Some research has reported interaction between polyamidoamine dendrimers or polyethylenimine and quantum dots causing a quantum yield decrease of quantum dots. In this work, however, polyethylenimines of different molecular weight that were used to modify CdS quantum dots gave rise to the enhancement of CdS quantum yield to nearly 100%. Herein, we present the synthesis of a kind of easily prepared high-quantum-yield CdS quantum dot in aqueous solution and the study of the interaction between CdS and polyethylenimine.  相似文献   
999.
A novel one-step method for preparing C-5-substituted Omicron(6),5'-cyclopyrimidine nucleoside analogues is reported. This method employs molecular iodine to mediate the cyclization from the 5'-Omicron-hydroxyl group of the sugar ring and C-6 at the position of the nitrogen base in ammonia water under mild conditions without any other aprotic organic solvent.  相似文献   
1000.
Two new quaternary strontium selenium(IV) and tellurium(IV) oxychlorides, namely, Sr3(SeO3)(Se2O5)Cl2 and Sr4(Te3O8)Cl4, have been prepared by solid-state reaction. Sr3(SeO3)(Se2O5)Cl2 features a three-dimensional (3D) network structure constructed from strontium(II) interconnected by Cl, SeO32− as well as Se2O52− anions. The structure of Sr4(Te3O8)Cl4 features a 3D network in which the strontium tellurium oxide slabs are interconnected by bridging Cl anions. The diffuse reflectance spectrum measurements and results of the electronic band structure calculations indicate that both compounds are wide band-gap semiconductors.  相似文献   
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