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101.
Acid-Catalyzed Rearrangement of 9-Hydroxyfuranoeremophilanes to Eremophilanlactones 9-Hydroxyfuranoeremophilanes 1–3 are the main components of freshly harvested rhizomes of P. hybridus (furanopetasin chemovar, Table, Fig. 1). They easily and quantitatively rearrange in the presence of traces of acid to give an epimeric mixture of 8-H-eremophilanlactones 4–6 (eremophilenolides, Table, Figs. 4 and 5). Besides subsequent oxidation (see 4 → 7 ), this is the most important reaction occuring during drying and storage of rhizomes of P. hybridus (Figs. 1 and 3). A reasonable mechanism of the rearrangement is presented, and spectroscopic structure elucidation of 8-H-eremophilanlactones is discussed. 相似文献
102.
The new [2 + 2] Schiff-base macrocyclic ligand L2, containing pyridazine head units and pyridine pendant arms, was synthesised as [Ba(II)2L2(ClO4)4(OH2)] 1 from the barium(II) ion templated condensation reaction of 3,6-diformylpyridazine and N1-(2-aminoethyl)-N1-(methylene-2-pyridyl)-ethane-1,2-diamine. Subsequent transmetallation reactions of 1 with copper(II), iron(II) and manganese(II) perchlorates led to the formation of [Cu(II)2L2](ClO4)4.2MeCN 2, [Fe(II)2L2(MeCN)2](ClO4)4 3 and two manganese complexes, 4 and 5, with the same formula, [Mn(II)2L2(MeCN)(OH2)](ClO4)4, but slightly different crystal structures, respectively. Single-crystal X-ray structural analyses reveal the variety of structures which can be supported by L2 in order to meet the coordination environment preferences of the incorporated metal ions. The barium(II) ions in 1 have an irregular ten-coordinate geometry whereas the copper(II) ions in 2 have a square pyramidal geometry and the iron(II) ions in 3 have an octahedral geometry, while in 4 and 5 every manganese(II) ion is seven-coordinate and the environment can be best described as distorted pentagonal bipyramidal. In 1, 4 and 5 the pyridazine moieties bridge the metal centres [Ba(1)...Ba(2) 4.9557(3)A 1; Mn(1)...Mn(2) 4.520(1)A 4; Mn(1)[dot dot dot]Mn(2) 4.3707(8)A 5] but this is not observed in the copper(II) and iron(II) complexes, 2 and 3, in which the metal ions are well separated [Cu(1)...Cu(2) 5.9378(6)A 2; Fe(1)...Fe(2) 5.7407(12)A 3]. In the cyclic voltammogram of [Cu2(II)L2](ClO4)4.2MeCN 2 in MeCN vs. Ag/AgCl two separate reversible one-electron transfer steps are observed [E(1/2)=0.04 V, DeltaE= 0.12 V and E(1/2)= 0.20 V, DeltaE=0.12 V; K(c)=510; in this system E(1/2)(Fc+/Fc)=0.42 V and DeltaE(Fc+/Fc)=0.08 V]. The other complexes cannot be reversibly reduced/oxidised. 相似文献
103.
We present relativistic configuration interaction calculations with the spin-free no-pair hamiltonian on the gold hydride molecule, treating the ground state as well as the eleven lowest excited states. The calculations provide a picture of the bonding in theX 1Σ+ ground state consistent with previous work on this species using four-component spinors: compared to non-relativistic calculations, the dipole moment is reduced by a factor of two, hybridization (and thus participation ofd orbitals at the bonding) is greatly enhanced, the bond length is shortened by 20 pm, and the dissociation energy is increased by 50%. Comparison of the spin-averaged potential curves of the excited states with experiment suggests a reinterpretation of theC 1Σ+ as the 0+ fine structure component of 23Π and the prediction of a weakly bound3Σ+ state with weak transitions to the ground state in the range of 2.9–3.1 eV. 相似文献
104.
水相中金属铜表面生成亚铜—邻菲罗啉配合物的反应 总被引:1,自引:0,他引:1
本文研究了零价铜在邻菲罗啉水溶液中的反应。当溶液敞露于空气并存在有机阴离子X-时,例如苯甲酸盐(Bz)、对甲基苯磺酸盐(Ts)等,铜的表面生成了致密的反应产物的薄层,经IR、UV/VIS、MS和元素分析证明了该薄层为相当纯的亚铜的邻菲罗啉配位化合物,结构为[Cu(phen)2]+X-。在乙醇/甲苯混合溶剂中得到了表面反应产物的晶体[Cu(phen)2](CH3C4H6SO3)C2H5OH,并用X-ray测得了结构。本工作表明溶液中的CuⅡ离子抑制Cu0氧化成CuⅠ而影响反应层的形成,同时又促进CuⅠ氧化成CuⅡ的过程 相似文献
105.
Siegfried L Comparone A Neuburger M Kaden TA 《Dalton transactions (Cambridge, England : 2003)》2005,(1):30-36
The metal promoted hydrolysis of nitrile groups in the side chains of tetraazamacrocyclic Cu2+ complexes has been studied by stopped-flow techniques. It is shown that the reaction proceeds by an intramolecular attack of an axially coordinated OH- onto the nitrile group to give the corresponding amide. In alkaline solution the amide then deprotonates and binds to the axial position of the Cu2+ thus preventing further coordination of an OH-. This explains mechanistically that in the Cu2+ complexes of macrocycles carrying two nitrile functions only one is selectively hydrolysed. The nitrile hydrolysis has also been used on a preparative scale to synthesize tetraazamacrocycles with two different side chains. X-Ray diffractions of several products are presented to confirm the structures and the results from the kinetics and equilibria measurements. 相似文献
106.
107.
Thoma G Streiff MB Katopodis AG Duthaler RO Voelcker NH Ehrhardt C Masson C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,12(1):99-117
Polyvalent carbohydrate-protein interactions occur frequently in biology, particularly in recognition events on cellular membranes. Collectively, they can be much stronger than corresponding monovalent interactions, rendering it difficult to control them with individual small molecules. Artificial macromolecules have been used as polyvalent ligands to inhibit polyvalent processes; however, both reproducible synthesis and appropriate characterization of such complex entities is demanding. Herein, we present an alternative concept avoiding conventional macromolecules. Small glycodendrimers which fulfill single molecule entity criteria self-assemble to form non-covalent nanoparticles. These particles-not the individual molecules-function as polyvalent ligands, efficiently inhibiting polyvalent processes both in vitro and in vivo. The synthesis and characterization of these glycodendrimers is described in detail. Furthermore, we report on the characterization of the non-covalent nanoparticles formed and on their biological evaluation. 相似文献
108.
E. Anklam Maria Rosa Bassani Thomas Eiberger Stefan Kriebel Markus Lipp Reinhard Matissek 《Analytical and bioanalytical chemistry》1997,357(7):981-984
Pyrolysis Mass Spectrometry (Py-MS) was used for the discrimination of cocoa butters from other vegetable fats. Mass spectra
ranging from 50 amu to 250 amu were analyzed by principal component analysis (PCA) and with neural nets. The application of
neural nets leads to a good discrimination between the two classes. Detailed analysis of the nets revealed that only the first
60 masses were used within the net. The use of PCA requires a careful selection of the number of masses included in the calculation.
Canonical variance analysis was applied to determine the significant masses. Optimal performance of PCA was observed only
using the first 22 significant masses. Most of these masses were different from the ones used by the neural net. It seems
that the mass spectra obtained by Py-MS contain sufficient information for the discrimination of pure cocoa butter from other
vegetable fats, but none of the methods seems to be able to extract all information available. Neural net provides a very
robust method for this task and no prior data selection was necessary.
Received: 13 May 1996 / Revised: 7 August 1996 / Accepted: 7 August 1996 相似文献
109.
110.
水热合成CdS纳米晶体的形貌控制研究 总被引:4,自引:0,他引:4
研究了水热合成CdS纳米晶体形貌的化学控制,选择不同的络合试剂为模板,研究其对水热合成CdS纳米晶体形貌的影响.实验发现若以络合试剂乙二胺、甲胺为模板时,产品CdS晶体的形貌分别为(20~30) nm×(200~600) nm和(40~50) nm×(200~600) nm尺寸的纳米棒;而以络合试剂吡啶、 氨为模板时,产品CdS晶体的形貌分别为平均尺寸约30 nm和20 nm的纳米颗粒.用XRD、TEM、XPS、PL和Raman光谱等技术对所得CdS纳米棒进行了表征.同时对水热合成CdS纳米晶体形貌的模板控制机制进行了探讨,提出了一种水热合成CdS纳米棒的络合物结构诱导生长机理. 相似文献