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71.
The I-E response of the liquid membrane of the calcium selective electrode is studied under constant or linearly varying current and voltage. An increase in the membrane resistance, recorded when an electrical current crosses the membrane, is due to the outflow of Cl? ions initially present in the membrane. When calcium ions are replaced by alkaline ions inside the membrane at constant current, the decrease of the membrane resistance due to an ion exchange is in agreement with the conductivity measurements (Part II). When the applied voltage is imposed besides the ion exchange one must take into account the interfacial overpotential to explain the important rectification effect observed. The interfacial transfer constant rate of alkaline ions seems greater than that of Ca2+ ion. 相似文献
72.
Steric effects on proton transfer from, and to, hydroxylic oxygen have been studied in a series of seventeen α-methyl and a-benzyl cyclohexanols in anhydrous DMSO, under both acid and base catalysed conditions, using dynamic MNR techniques. The protonation rate constants (k1 ? 106 M-1 s-1 at 25°C) obey a Taft-Ingold relationship, containing only a steric contribution Es = EsOH + Esα, where: EsOH = 0 or 0.15 for an axial or equatorial hydroxyl respectively and Esα = ?0.070 (or ?0.115) for substituting an α-hydrogen by a methyl (or benzyl) group. An equatorial hydroxylic function is therefore 40% more reactive than its axial homologue. These kinetic data are fairly consistent with structural information resulting from IR spectroscopy (vco and vOH vibrations) and from NMR (hydroxylic chemical shifts and coupling constants). 相似文献
73.
Reaction of 1,6-enynes with a hydrosilane in the presence of immobilized cobalt/rhodium bimetallic nanoparticles gives 2-methyl-1-silylmethylidene-2-cyclopentanes in the absence of carbon monoxide and 2-formylmethyl-1-silylmethylidene-2-cyclopentanes under 1 atm of carbon monoxide, respectively. [reaction: see text] 相似文献
74.
A high-performance liquid chromatographic (HPLC) procedure has been evaluated to establish a routine test in the clinical laboratory for measuring the profiles of estrogen and progestin receptor isoforms in human breast and endometrial tumors. This procedure will be used to determine if there is a relationship between particular isoform profiles and response to various endocrine therapies. Evaluation of various HPLC modes has shown that high-performance ion-exchange chromatography (HPIEC) with silica-based anion exchangers offers a promising approach. In this paper, we have compared HPIEC columns of different lengths (10 and 25 cm) and pore sizes (300, 500 and 1,000 A) in order to obtain an optimal separation procedure. Because of receptor lability, all investigations were performed at 4 degrees C. The mobile phase consisted of 10-500 mM phosphate buffer, supplemented with the stabilizing agent, sodium molybdate at pH 7.4. Recoveries from each of the columns were between 70-100%. The length of the column did not influence significantly the retention time and salt concentration required for elution of receptor proteins. However, pore sizes appeared to alter these parameters. With a larger pore size (1,000 A), the retention of proteins was lower (elution with 50 mM phosphate) than that observed with the 500-A pore size column (elution with 100 mM phosphate) or of the 300-A pore size column (elution with 150 mM phosphate). Based solely on recovery patterns and peak shape, we conclude that separation of receptor isoforms on a 1,000-A, 25-cm column is best suited for clinical analysis. 相似文献
75.
Using reaction rate data collected in aprotic solvents, we have determined that the Baylis-Hillman rate-determining step is second order in aldehyde and first order in DABCO and acrylate. On the basis of these data, we have proposed a new mechanism involving a hemiacetal intermediate. The proposed mechanism was then supported using two different kinetic isotope experiments. 相似文献
76.
In this paper, adsorption characteristics of methyl mercaptan on virgin activated carbon and copper chloride impregnated activated carbons were studied by using a dynamic adsorption method in a fixed bed. The activated carbons were characterized by nitrogen adsorption, XRD, TGA and solubility tests. The impregnation of copper chloride on the activated carbon significantly enhanced the adsorption capacity of methyl mercaptan, despite a notable decrease in microporosity. It is likely that copper chloride may act as adsorption site for methyl mercaptan. Copper chloride on the activated carbon in a range of 3-20 wt% Cu content was present mostly in the amorphous form of CuCl(2), according to the results of the solubility, XRD and TGA tests. Starting at 10 wt% in Cu loading, the adsorption capacity for methyl mercaptan decreases gradually. It is likely that a decrease in the degree of copper chloride dispersion and an accessibility of small pores may lead to the decrease in the adsorption capacity of the activated carbon for methyl mercaptan. 相似文献
77.
Moonhor Ree Jong-Seong KimJae Jung Kim Byeang Hyean KimJuyoung Yoon Heesoo Kim 《Tetrahedron letters》2003,44(45):8211-8215
The synthesis of novel cavitands containing four fluorophores [tert-butoxycarbonyl protected 2,2′-bis(furyl)benzidine (t-BOC FurylBz) or 5,5′-bis(4-aminophenyl)-2,2′-bifuryl (t-BOC PFDA)] and ionophoric functional groups on the upper rim is reported. The cavitands bearing the four fluorophores emit blue light photoluminescence. In particular, the cavitand containing PFDA moieties exhibits a high photoluminescence quantum yield. 相似文献
78.
[Rb2(H2O)2][Re3(μ-Cl)3Br7(H2O)2]2 · H2O, a Mixed Halide-Hydrate with the Anionic Dimer {[Re3(μ-Cl)3Br7(H2O)2]2 · H2O}2? [Rb2(H2O)2][Re3(μ-Cl)3Br7(H2O)2]2 · H2O crystallizes as dark redbrown single crystals from an hydrobromic-acid solution of ReCl3 and RbBr at 0°C. An important feature of the crystal structure (monoclinic, C2/c; a = 1494.61(8); b = 835.71(4); c = 3079.96(19) pm; β = 97.801(4)°; Vm = 573.9(4) cm3mol?1; R = 0.060; Rw = 0.038) is the connection of two anions [Re3(μ-Cl)3Br7(H2O)2]? via a water molecule to dimers, {[Re3(μ-Cl)3Br7(H2O)2]2 · H2O}2?. These dimeric units are contained in slabs that are stacked in the [001] direction and held together by Rb+ cations and crystal water. 相似文献
79.
Cheng-Zhu Wu Xing Fu Cai Seong Su Hong Eun-Kyoung Seo Ji-Xing Nan Jung Joon Lee 《Tetrahedron letters》2007,48(50):8861-8864
Two novel dimeric meroterpenoids, bisbakuchiols A and B, along with (S)-bakuchiol were isolated from the seeds of Psoralea corylifolia L. (Fabaceae). Bisbakuchiols A and B contain an unprecedented dimeric meroterpenoid skeleton in which two meroterpenes are linked through a dioxane bridge. All compounds were evaluated for their potential to inhibit hypoxia-inducible factor-1 (HIF-1) activation induced by hypoxia in a HIF-1-mediated reporter gene assay in AGS human gastric cancer cells. (S)-Bakuchiol inhibited hypoxic activation of HIF-1 with an IC50 value of 6.1 μM. 相似文献
80.
Ring‐rearrangement metathesis (RRM) refers to the combination of several metathesis transformations into a domino process, in which an endocyclic double bond of a cycloolefin reacts with an exocyclic alkene. RRM has proven to be a powerful method for the rapid construction of complex structures. The extension of the basic ring‐opening–ring‐closing metathesis process by further metathesis steps as well as an examination of the driving forces, limits, scope, recent advantages, and future perspectives of these domino sequences is presented with various examples, thus reflecting the high efficiency and utility of RRM in organic synthesis. 相似文献