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991.
I. Sajó 《Journal of Thermal Analysis and Calorimetry》1969,1(2):221-225
According to the direct reading thermometric method the concentration of the component to be determined is established from the temperature variation of the sample solution obtained on adding to it an excess of a reagent which reacts selectively with the respective component. Under suitably chosen experimental conditions the concentration of the respective component is determined from a single measured value. Since the established measurement technique requires little manual work and the respective components may be determined from the sample solution directly without any separations, the method in its present form is chiefly suitable for rapid serial analyses.
Zusammenfassung Bei der thermometrischen Methode mit Direktablesung wird die Konzentration der gesuchten Komponente aus der Temperaturänderung der Probelösung bestimmt, die nach Zugabe eines Überschusses von einem selektiv reagierenden Reagens wahrnehmbar ist.Unter geeigneten Versuchsbedingungen kann man die Konzentration der gesuchten Komponente aus einem einzigen Meßwert, nämlich der Temperaturänderung der Probelösung bestimmen. Da die ausgearbeitete Meßtechnologie wenig Arbeit erfordert und die gesuchten Komponenten ohne jede Trennung direkt bestimmt werden können, ist die Methode in ihrer jetzigen Ausführungsart hauptsächlich zu betriebsmäßigen Serien-Schnellanalysen geeignet.
Résumé Selon la méthode thermométrique à lecture directe, on détermine la concentration du constituant cherché d'après la variation de température de la solution échantillon que l'on additionne d'un excès de réactif sélectif de celui-ci. Dans les conditions expérimentales appropriées, une seule mesure suffit pour déterminer la concentration du constituant cherché. Comme la technique de mesure qui a été mise au point demande peu de travail et comme on peut doser sans aucune séparation les constituants étudiés, la méthode dans sa forme actuelle se prête en premier lieu aux dosages en séries industriels.
, , . . . , . .相似文献
992.
Federico Moscardó Miguel Paniagua Emilio San-Fabián 《Theoretical chemistry accounts》1979,53(4):377-381
Anab initio study of the relative stability for the states2
A
1g
and2
E
g of C2H
6
+
has been carried out. The results of the Open Shell Restricted Hartree-Fock calculations lead to assign the2
A
1
g
as the ground state of the molecule in agreement with previous SCF calculations.The correlation energy associated to both states has been calculated within the correlation hole model and the results, contrary to those obtained from Configuration Interaction calculations, do not alter qualitatively the conclusions from SCF. 相似文献
993.
Jenny?ZevallosEmail author Alejandro?Toro-Labbé Otilia?Mó Manuel?Yá?ez 《Structural chemistry》2005,16(3):295-303
High level ab initio and density functional theory calculations have been carried out to investigate the relative stability of the different conformers of hyponitrous acid and its mono- and dithio-derivatives. Geometries and vibrational frequencies were obtained at the B3LYP/6-311+G(d,p) level and final energies through B3LYP/6-311++G(3df,2pd) single point calculations. The reliability of this theoretical scheme has been assessed by comparing these DFT results with those obtained at the G3 level of theory, for some suitable cases. The cis conformers of hyponitrous acid and its mono- and dithio-derivatives are systematically more stable than the
trans ones because in the cis conformation a dative interaction between the nitrogen-lone pairs and the σNX^* antibonding orbital is significantly favored. Quite interestingly, in general, the conformers presenting an intramolecular hydrogen bond (IHB) are not the global minima of the corresponding potential energy surfaces and only for hyponitrous acid the conformer with a OH ⋅s O IHB is slightly more stable than the cis conformer without IHB. The low stability of the tautomers with IHB is closely related with another weak intramolecular interaction which involves the lone-pairs of the chalcogen atoms and the πNN* antibondig orbital, and which is significantly perturbed when the IHB is formed. 相似文献
994.
The cationization of poly(ethylene glycol)s, PEG 4000 and PEG 6000, under matrix-assisted laser desorption/ionization conditions was studied by using different concentration ratios of the sodium ion, as the reference ion, and another alkali metal ion (Li(+), K(+), Rb(+), Cs(+)). A linear correlation was found between the intensity ratio of the sodiated PEGs and PEGs cationized with alkali metal ions versus the initial concentration ratio of sodium and alkali metal ions. The slopes of these straight lines are proposed as a novel selectivity ratio for the ionization process. The intensity distribution of the cationized PEGs was also investigated. It was found that the cationized oligomers follow Poisson statistics. The M(n) and M(w) values were also evaluated. An explanation for the observed effects is given. 相似文献
995.
The purpose of the present study was to determine the tropane alkaloid content of genetically transformed hairy root cultures of Atropa belladonna L. Determination of alkaloids was performed by HPLC method. Samples were extracted with chloroform – methanol - cc. ammonia 15:5:1 (v/v/v). Crude extracts were purified on Extrelut columns. HPLC separation was performed on Luna C8 reversed phase column. An isocratic mixture of acetonitrile – 30 mM phosphate buffer - methanol 12.2:79.7:8.1(v/v/v) was used as eluent. Peaks were identified by addition of standards and diode-array detection. Hyoscyamine, scopolamine and apoatropine were determined by external standard method at 210 nm. We measured the alkaloid content of genetically transformed in vitro cultures (hairy roots and reorganised plants) cultivated on Gamborg B5 basic media. The highest hyoscyamine and scopolamine content was found in hairy root clone #K5 (0,223 m/m%) and in hairy root clone #K4 (0,018 m/m%) respectively. Alkaloid contents were higher in the hairy roots than in the reorganised plants. 相似文献
996.
María L. López-Rodríguez María José Morcillo Bellinda Benhamú María Luisa Rosado 《Journal of computer-aided molecular design》1997,11(6):589-599
The clinical use of currently available drugs acting at the5-HT4 receptor has been hampered by their lack of selectivityover 5-HT3 binding sites. For this reason, there is considerableinterest in the medicinal chemistry of these serotonin receptor subtypes, andsignificant effort has been made towards the discovery of potent and selectiveligands. Computer-aided conformational analysis was used to characterizeserotoninergic 5-HT3 and 5-HT4 receptorrecognition. On the basis of the generally accepted model of the5-HT3 antagonist pharmacophore, we have performed a receptormapping of this receptor binding site, following the active analog approach(AAA) defined by Marshall. The receptor excluded volume was calculated as theunion of the van der Waals density maps of nine active ligands(pKi 8.9), superimposed in pharmacophoric conformations.Six inactive analogs (pKi < 7.0) were subsequently used todefine the essential volume, which in its turn can be used to define theregions of steric intolerance of the 5-HT3 receptor. Five activeligands (pKi 9.3) at 5-HT4 receptors wereused to construct an antagonist pharmacophore for this receptor, and todetermine its excluded volume by superimposition of pharmacophoricconformations. The volume defined by the superimposition of five inactive5-HT4 receptor analogs that possess the pharmacophoric elements(pKi 6.6) did not exceed the excluded volume calculated forthis receptor. In this case, the inactivity may be due to the lack of positiveinteraction of the amino moiety with a hypothetical hydrophobic pocket, whichwould interact with the voluminous substituents of the basic nitrogen ofactive ligands. The difference between the excluded volumes of both receptorshas confirmed that the main difference is indeed in the basic moiety. Thus,the 5-HT3 receptor can only accommodate small substituents inthe position of the nitrogen atom, whereas the 5-HT4 receptorrequires more voluminous groups. Also, the basic nitrogen is located at ca.8.0 Å from the aromatic moiety in the 5-HT4 antagonistpharmacophore, whereas this distance is ca. 7.5 Å in the5-HT3 antagonist model. The comparative mapping of bothserotoninergic receptors has allowed us to confirm the three-componentpharmacophore accepted for the 5-HT3 receptor, as well as topropose a steric model for the 5-HT4 receptor binding site. Thisstudy offers structural insights to aid the design of new selective ligands,and the resulting models have received some support from the synthesis of twonew active and selective ligands: 24 (Ki(5-HT3)= 3.7 nM; Ki(5-HT4) > 1000 nM) and 25(Ki(5-HT4) = 13.7 nM;Ki(5-HT3) > 10 000 nM). 相似文献
997.
Luis Adrio Gemma Alberdi Adriana Amoedo Darío Lata Alberto Fernndez Javier Martínez M. Teresa Pereira Jos M. Vila 《无机化学与普通化学杂志》2005,631(11):2197-2203
Reaction of the thiosemicarbazone ligands C4H4NC(H)=NN(H)C(S)NHR (R = Me, a ; Et, b ) with Li2[PdCl4] gave the dinuclear complexes [Pd{C4H4NC(H)=NNC(S)NHR}(μ‐Cl)]2 (R = Me, 1a ; Et, 1b ) with a central Pd2Cl2 core and with deprotonation of the thiosemicarbazones at the hydrazinic nitrogen atom. Treatment of 1a and 1b with triphenylphosphine gave the mononuclear compounds [Pd{C4H4C(H)=NNC(S)NHR}(Cl)(PPh3)] (R = Me, 2a ; Et, 2b ), whereas reaction of 1a and 1b with tertiary diphosphines gave mono‐ and dinuclear compounds, as appropriate, with the corresponding diphosphine acting as a monodentate ( 6b ), chelating ( 3a ) and bridging ligand ( 4a, 5a , 4b, 5b ). Treatment of 1a and 1b with (Ph2PCH2CH2PPh2)W(CO)5 gave the new heterobimetallic complexes 7a and 7b . The crystal structures of complexes 3a and 4a are described. 相似文献
998.
S. A. Amitina I. V. El’tsov T. V. Rybalova Yu. V. Gatilov I. A. Grigor’v 《Russian Chemical Bulletin》2004,53(8):1700-1703
Reactions of alicyclic 2-hydroxyamino oximes with pentafluorophenylglyoxal afford mixtures of annelated derivatives of 2-pentafluorophenylpyrazine 1,4-dioxide and tetrafluoro- 10H-imidazo[1,2-b][1,2]benzooxazin-10-one. The structures of the latter were established by X-ray diffraction analysis.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1636–1639, August, 2004. 相似文献
999.
Rebeka Nádasdi István Szilágyi Gergely Kovács Sándor Dóbé Tibor Bérces Ferenc Márta 《Reaction Kinetics and Catalysis Letters》2006,89(1):193-199
Summary The fast flow technique with OH resonance fluorescence detection has been applied at T = 298 ± 2 K to study the kinetics of the overall reaction: H + CH3C(O)Cl → products (1) A rate constant value of k1 = (1.02 ± 0.12) x 1010 cm3 mol-1 s-1 has been determined which is the first direct kinetic parameter reported for reaction (1) in the literature (the error given
refers to 2σ accuracy). 相似文献
1000.
J. Zsakó 《Journal of Thermal Analysis and Calorimetry》1979,15(2):369-377
Shape and position parameters and are proposed for the characterization of TG curves and are defined by Eqs (6), (7) and (8), respectively. These parameters being reduced to the standard conditionsn=0 andq=1/6 K sec–1, the nomogram given in Fig. 1 can be constructed by means fo Eqs (9), (11) and (12). An iteration method is proposed, allowing derivation of the kinetic parametersn, E andZ of simple thermal decomposition reactions, from the parameters n,E andZ, by using the empirica formulae (9), (10), (11) and (12) and the nomogram. Table 3 contains data necessary to construct this nomogram.
Zusammenfassung Die Gestalts- und Positionsparameter , und werden zur Charakterisierung von TG-Kurven vorgeschlagen, bzw. durch die Gleichungen (6), (7) und (8) definiert. Durch Reduktion dieser Parameter auf die Standardbedingungenn=0 undq=1/6 K sec–1 mit Hilfe der Gleichungen (9), (11) und (12) kann das Nomogramm in Abb. 1 konstruiert werden. Eine Iterationsmethode wird vorgeschlagen, welche die Ableitung der kinetischen Parameter,n, E undZ einfacher thermischer Zersetzungsreaktionen aus den Parametern and unter Anwendung der empirischen Formeln (9), (10), (11) und (12) sowie des Nomogramms ermöglicht. Tabelle 3 enthält die zur Konstruktion des Nomogramms nötigen Angaben.
Résumé Pour caractériser les courbes TG, on propose les paramètres de forme et de position , et définis par les équations (6), (7) et (8). En réduisant ces paramètres aux conditions standardsn=0 etq=1/6 K sec–1, à l'aide des équations (9), (11) et (12), le nomogramme donné dans la figure 1 peut être construit. On propose une méthode d'itération pour déduire les paramètres cinétiquesn, E etZ à partir des paramètres , et dans le cas des réactions simples de décomposition thermique, en utilisant les formules empiriques (9), (10), (11) et (12) ainsi que le nomogramme. Le tableau 3 contient les données nécessaires pour construire ce nomogramme.
G , , (6), (7) (8). « » =0 q=1/6 –1 , . 1, (9), (11) (12). , , E Z , (9), (10), (11) (12) . 3 , .相似文献