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421.
Lee YA McGarrah JE Lachicotte RJ Eisenberg R 《Journal of the American Chemical Society》2002,124(36):10662-10663
The Au(I) dimers Au(2)[S(2)P(OR)(2)](2) for R = Me, Et are found to exhibit a structure in which aurophilic interactions yield one-dimensional Au...Au chains with intermolecular contacts (3.09-3.16 A) similar to the Au...Au distances within the dimers (3.10-3.18 A). The dimers are luminescent in the solid state and become brilliantly emissive at low temperatures. At 77 K, Au(2)[S(2)P(OMe)(2)](2) shows multiple emission bands. The two higher energy bands at 415 and 456 nm are assigned to (1)MC and (3)MC on the basis of lifetime measurements (20 ns and 2.16 micros, respectively) and concentration-related effects, while the lower energy band at 560 nm is attributed to a LMCT excited state. In frozen glasses of different solvents, Au(2)[S(2)P(OMe)(2)](2) as well as the Et and n-Pr derivatives exhibit a bright luminescence of different colors and striking thermochromism of the emission. 相似文献
422.
Electronically unsaturated three-coordinate chloride and methyl complexes of iron,cobalt, and nickel
Holland PL Cundari TR Perez LL Eckert NA Lachicotte RJ 《Journal of the American Chemical Society》2002,124(48):14416-14424
Three-coordinate organometallic complexes are rare, especially with the prototypical methyl ligand. Using a hindered, rigid bidentate ligand (L), it is possible to create 12-electron methyliron(II) and 13-electron methylcobalt(II) complexes. These complexes are thermally stable, and (1)H NMR spectra suggest that the low coordination number is maintained in solution. Attempts to create the 14-electron LNiCH(3) led instead to the three-coordinate nickel(I) complex LNi(THF). Single crystals of LMCH(3) are isomorphous with the new three-coordinate chloride complexes LNiCl and LCoCl. Along with the recently reported LFeCl (Smith, J. M.; Lachicotte, R. J.; Holland, P. L. Chem. Commun. 2001, 1542), these are the only examples of three-coordinate iron(II), cobalt(II), and nickel(II) complexes with terminal chloride ligands, enabling the systematic evaluation of the effect of coordination number and metal identity on M-Cl bond lengths. Electronic structure calculations predict the ground states of the trigonal complexes. 相似文献
423.
Rodrigo Caris Mauricio Valderrama Rene Rojas 《Journal of organometallic chemistry》2009,694(12):1795-8131
The synthesis of N-(1-(3,5-dimethylpyrazol-1-yl)ethylidene)-2,6-diisopropylaniline (1) and N-(1-(indazol-2-yl)ethylidene)-2,6-diisopropylaniline (2) allowed access to new transition metal complexes. When reacted with dibromo(2,2′-dimethoxyethylether)nickel(II) the complexes [NiBr2{N-(1-(3,5-dimethylpyrazol-1-yl)ethylidene)-2,6-diisopropylaniline}] (3) and [Ni2Br2(μ-Br)2{N-(1-(indazol-1-yl)ethylidene)-2,6-diisopropylaniline}2] (4) are yielded, respectively. The addition of MAO generates catalytically active species for the homopolymerization of ethylene. The polymer products were low molecular weight (3-6 K) and a monomodal molecular weight distribution, consistent with the presence of a single active site. In addition, the catalyst was found to efficiently oligomerize higher olefins to high molecular weights with narrow PDIs. 相似文献
424.
Ren Hommelsheim Yujing Guo Zhen Yang Claire Empel Rene M. Koenigs 《Angewandte Chemie (International ed. in English)》2019,58(4):1203-1207
Carbenes are very important reactive intermediates to access a variety of complex molecules and are applied widely in organic synthesis and drug discovery. Typically, their chemistry is accessed by the use of transition metal catalysts. Herein, we describe the application of low‐energy blue light for the photochemical generation of carbenes from donor–acceptor diazoalkanes. This catalyst‐free and operationally simple approach enables highly efficient cyclopropenation reactions with alkynes and the rearrangement of sulfides under mild reaction conditions, which can be utilized for both batch and continuous‐flow processes. 相似文献
425.
Katharina J. Hock Anja Knorrscheidt Ren Hommelsheim Junming Ho Martin J. Weissenborn Rene M. Koenigs 《Angewandte Chemie (International ed. in English)》2019,58(11):3630-3634
The functionalization of C?H bonds with non‐precious metal catalysts is an important research area for the development of efficient and sustainable processes. Herein, we describe the development of iron porphyrin catalyzed reactions of diazoacetonitrile with N‐heterocycles yielding important precursors of tryptamines, along with experimental mechanistic studies and proof‐of‐concept studies of an enzymatic process with YfeX enzyme. By using readily available FeTPPCl, we achieved the highly efficient C?H functionalization of indole and indazole heterocycles. These transformations feature mild reaction conditions, excellent yields with broad functional group tolerance, can be conducted on gram scale, and thus provide a unique streamlined access to tryptamines. 相似文献
426.
Bozena Hosnedlova Marta Kepinska Carlos Fernandez Qiuming Peng Branislav Ruttkay‐Nedecky Halina Milnerowicz Rene Kizek 《Chemical record (New York, N.Y.)》2019,19(2-3):502-522
Cancer represents one of the main causes of human death in developed countries. Most current therapies, unfortunately, carry a number of side effects, such as toxicity and damage to healthy cells, as well as the risk of resistance and recurrence. Therefore, cancer research is trying to develop therapeutic procedures with minimal negative consequences. The use of nanomaterial‐based systems appears to be one of them. In recent years, great progress has been made in the field using nanomaterials with high potential in biomedical applications. Carbon nanomaterials, thanks to their unique physicochemical properties, are gaining more and more popularity in cancer therapy. They are valued especially for their ability to deliver drugs or small therapeutic molecules to these cells. Through surface functionalization, they can specifically target tumor tissues, increasing the therapeutic potential and significantly reducing the adverse effects of therapy. Their potential future use could, therefore, be as vehicles for drug delivery. This review presents the latest findings of research studies using carbon nanomaterials in the treatment of various types of cancer. To carry out this study, different databases such as Web of Science, PubMed, MEDLINE and Google Scholar were employed. The findings of research studies chosen from more than 2000 viewed scientific publications from the last 15 years were compared. 相似文献
427.
Hector Rene Vega-Carrillo Antonio Baltazar-Raigosa 《Journal of Radioanalytical and Nuclear Chemistry》2011,287(1):323-327
Photoneutron spectra around an 18 MV LINAC were calculated in order to observe the effect produced by media around the accelerator.
Calculations were carried out with MCNP 4C code, three different cases were analyzed: Head model, Head and phantom model,
and Head, air, phantom and wall model. The spectra were calculated in five detectors located at the irradiation room at different
distances from the isocentre. A sixth detector, located near the entrance door was included to analyze how the maze change
the neutron spectrum. Neutrons are mainly produced in the LINAC head change the shape of evaporation neutrons from the source
term, some of these neutrons leak out the head with lesser energy, another neutrons goes with the treatment beam. At any site
near the isocentre neutron spectrum has evaporation and thermal neutrons joined by a set of epithermal neutrons. As the distance
from the isocentre increases evaporation neutrons tend to decrease while, epithermal and thermal neutrons tend to remain constant
regardless de distance due to room return produced by the walls. The maze contributes to reduce the neutron fluence, reducing
the evaporation neutrons; resulting spectrum is mainly the contribution of thermal and epithermal neutrons. Near the door
these neutrons can produce activation and prompt gamma rays. 相似文献
428.
John Mommers Jeroen Knooren Ynze Mengerink Arno Wilbers Rene Vreuls Sjoerd van der Wal 《Journal of chromatography. A》2011,1218(21):3159-3165
In gas chromatography (GC) reproducible retention times are in many cases highly favorable or in some cases even required. In one-dimensional GC, retention time shifts can be eliminated or minimized using a procedure called retention time locking (RTL). This procedure is based on adjusting the (constant) column head pressure. Unfortunately, this RTL procedure cannot be used in comprehensive two-dimensional gas chromatography (GC × GC) given the fact that peaks will shift in both dimensions. Adjusting the column head pressure in GC × GC will only minimize or eliminate the primary retention time shifts. In this paper, a fast and easy to perform, two-step retention time locking procedure for two-dimensional gas chromatography (2D-RTL) is proposed and its feasibility is demonstrated. This 2D-RTL procedure involves adjustment of the column head pressure or constant column flow, followed by the adjustment of the so-called effective secondary column length. The secondary column length is increased or decreased, simply by moving it stepwise through the modulator. It is demonstrated that retention time shifts in both the primary- and secondary-dimension, which may occur after e.g. replacing the column set, can be minimized to less than half peak base width. The proposed 2D-RTL procedure is used successfully for approximately 1 year in our laboratory. 相似文献
429.
Hector Rene Vega-Carrillo Berenice Hernández-Almaraz Victor Martin Hernández-Dávila Arturo Ortíz-Hernández 《Journal of Radioanalytical and Nuclear Chemistry》2010,283(1):261-265
Bonner sphere spectrometer with TLDs pairs has been utilized to measure the neutron spectrum 100 cm from isocenter of a 18
MV LINAC, simultaneously the ambient dose equivalent due to neutrons and photons was measured in the control room area with
neutron and gamma-ray area monitors. Measurements were carried out when the LINAC was delivering a dose of 600 MU at the isocentre
that was located at 5 cm depth of a head phantom. Undesired neutron field in the treatment room produce activation reactions
with nuclei in different materials of LINAC, couch, air, and phantom. To determine the dose due to decay of activation nuclei
the ambient dose due to gamma-rays was measured inside the treatment room immediately after dose was delivered. Measured spectrum
has two peaks, one between 0.1–1 MeV and other in the thermal region, the ambient dose equivalent in the control room are
3.1 and 0.93 μSv h−1 for photons and neutrons, respectively. In the treatment room the ambient dose equivalent due to photons produced during
decay of activation nuclei varies from 6 to 26.1 μSv h−1. 相似文献
430.
Endlicher E Rümmele P Hausmann F Rath HC Knüchel R Krieg RC Schölmerich J Messmann H 《Photochemistry and photobiology》2004,79(2):189-192
5-Aminolevulinic acid (ALA) and ALA ester-induced protoporphyrin IX (PPIX) fluorescence are used for photodynamic diagnosis and therapy with promising results. The aim of the present study was to investigate the detection of dysplastic lesions by fluorescence after topical application of ALA and different esterified derivatives in a model of chronic colitis in rats. In female CD rats chronic colitis was induced by oral application of 5% dextrane sulfate sodium. ALA was used at different concentrations (0.072 and 0.036 mol/L). ALA-methylester (m-ALA), ALA-hexylester (h-ALA) and ALA-benzylester (b-ALA) were used at a concentration of 0.003, 0.002 and 0.002 mol/L, respectively. Fluorescence was examined under blue light, and histological findings of fluorescent and nonfluorescent biopsy specimens were recorded. Using ALA at a concentration of 0.072 mol/L, all dysplastic lesions (8/8) showed fluorescence (sensitivity 100%). Specificity was low at 57%. Reducing the concentration to 0.036 mol/L resulted in a sensitivity of only 56% (5/9) with an increase in specificity to 76%. On using h-ALA, sensitivity was 60% (3/5) with a specificity of 51%. Using m-ALA and b-ALA, sensitivity values were 25% and 33%, and values for specificity were 62% and 63%, respectively. Despite a low number of dysplastic lesions, the results of this study indicate that ALA ester-induced PPIX fluorescence has the potential for the detection of premaligant lesions but was not superior to ALA. ALA esters were used in 18- to 36-fold lower concentrations compared with ALA. 相似文献