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991.
An improved pixel-based approach for analyzing 2-DE images is presented. The key feature of the method is to create a mask based on all gels in the experiment using image morphology, followed by multivariate analysis on the pixel level. The method reduces the impact of noise and background by identifying regions in the image where protein spots are present, but make no assumption on individual spot boundaries for isolated spots. This makes it possible to detect significant changes in complex regions, and visualize these changes over multiple gels in an easy way. False missing values and spot volumes caused by imposing erroneous spot boundaries are thus circumvented. The approach presented gives improved pixel-based information from the gels, and is also an alternative to existing methods for data-reduction, significance testing and visualization of 2-DE data. Results are compared with software using a common spot boundary approach on an experiment consisting of 35 full size gel images. Gel alignment is required before analysis. 相似文献
992.
Nørskov JK Bligaard T Hvolbaek B Abild-Pedersen F Chorkendorff I Christensen CH 《Chemical Society reviews》2008,37(10):2163-2171
This tutorial review, of relevance for the surface science and heterogeneous catalysis communities, provides a molecular-level discussion of the nature of the active sites in metal catalysis. Fundamental concepts such as "Br?nsted-Evans-Polanyi relations" and "volcano curves" are introduced, and are used to establish a strict partitioning between the so-called "electronic" and "geometrical" effects. This partitioning is subsequently employed as the basis for defining the concept "degree of structure sensitivity" which can be used when analyzing the structure sensitivity of catalytic reactions. 相似文献
993.
994.
Vinchurkar MS Bricarello DA Lagerstedt JO Buban JP Stahlberg H Oda MN Voss JC Parikh AN 《Journal of the American Chemical Society》2008,130(33):11164-11169
We show that a two-step process, involving spontaneous self-assembly of lipids and apolipoproteins and surface patterning, produces single, supported lipid bilayers over two discrete and independently adjustable length scales. Specifically, an aqueous phase incubation of DMPC vesicles with purified apolipoprotein A-I results in the reconstitution of high density lipoprotein (rHDL), wherein nanoscale clusters of single lipid bilayers are corralled by the protein. Adsorption of these discoidal particles to clean hydrophilic glass (or silicon) followed by direct exposure to a spatial pattern of short-wavelength UV radiation directly produces microscopic patterns of nanostructured bilayers. Alternatively, simple incubation of aqueous phase rHDL with a chemically patterned hydrophilic/hydrophobic surface produces a novel compositional pattern, caused by an increased affinity for adsorption onto hydrophilic regions relative to the surrounding hydrophobic regions. Further, by simple chemical denaturation of the boundary protein, nanoscale compartmentalization can be selectively erased, thus producing patterns of laterally fluid, lipid bilayers structured solely at the mesoscopic length scale. Since these aqueous phase microarrays of nanostructured lipid bilayers allow for membrane proteins to be embedded within single nanoscale bilayer compartments, they present a viable means of generating high-density membrane protein arrays. Such a system would permit in-depth elucidation of membrane protein structure-function relationships and the consequences of membrane compartmentalization on lipid dynamics. 相似文献
995.
Santambrogio G Janssens E Li S Siebert T Meijer G Asmis KR Döbler J Sierka M Sauer J 《Journal of the American Chemical Society》2008,130(45):15143-15149
The vibrational spectroscopy of the electronically closed-shell (Al 2O 3) n (AlO) (+) cations with n = 1-4 is studied in the 530-1200 cm (-1) range by infrared predissociation spectroscopy of the corresponding ion-He atom complexes in combination with quantum chemical calculations. In all cases we find, assisted by a genetic algorithm, global minimum structures that differ considerably from those derived from known modifications of bulk alumina. The n = 1 and n = 4 clusters exhibit an exceptionally stable conical structure of C 3 v symmetry, whereas for n = 2 and n = 3, multiple isomers of lower symmetry and similar energy may contribute to the recorded spectra. A blue shift of the highest energy absorption band is observed with increasing cluster size and attributed to a shortening of Al-O bonds in the larger clusters. This intense band is assigned to vibrational modes localized on the rim of the conical structures for n = 1 and n = 4 and may aid in identifying similar, highly symmetric structures in larger ions. 相似文献
996.
Bigmore HR Meyer J Krummenacher I Rüegger H Clot E Mountford P Breher F 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(19):5918-5934
Reactions of HC(Me2pz)3 with Grignard reagents, dialkyl magnesium compounds and dimethylzinc are reported, together with a DFT study on some of the aspects of this chemistry. Reactions of HC(Me2pz)3 with MeMgX (X=Cl or Br) gave the half-sandwich zwitterionic compounds [Mg((Me)Tpmd)X] (X=Cl (2) or Br (3); (Me)Tpmd(-)=[C(Me2pz)3](-)). Addition of HCl to 2 gave the structurally characterised half-sandwich compound [Mg{HC(Me2pz)3}Cl2(thf)] (4). The zwitterionic sandwich compound [Mg(MeTpmd)2] (5) formed in low yields in the reaction of MeMgX with HC(Me2pz)3 but was readily prepared from HC(Me2pz)3 and either MgnBu2 or MgPh2. The structurally characterised compound 5 contains two "naked" sp3-hybridised carbanions fully separated from the dicationic metal centre. Only by using MgPh2 as starting material could the half-sandwich compound [Mg(MeTpmd)Ph(thf)] (6) be isolated. The zwitterionic sandwich compound 5 reacted with HOTf (OTf(-)=[O3SCF3](-)) to form the dication [Mg{HC(Me2pz)3}2]2+ (7(2+)), which was structurally characterised. Pulsed field gradient spin-echo (PGSE) diffusion NMR spectroscopy revealed both compounds to be intact in solution. In contrast to the magnesium counterparts, HC(Me2pz)3 reacted only slowly with ZnMe2 (and not at all with ZnPh2) to form the half-sandwich zwitterion [Zn(MeTpmd)Me] (8), which contains a cationic methylzinc moiety separated from a single sp3-hybridised carbanion. Density functional calculations on the zwitterions [M(MeTpmd)Me] and [M(MeTpmd)2] (M=Mg, Zn) revealed that the HOMO in each case is a (Me)Tpmd-based carbanion lone pair. The kappa 1C isomers of [M(MeTpmd)Me] were calculated to be considerably less stable than their kappa 3N-bound counterparts, with the largest gain in energy for Mg due to the greater ease of electron transfer from metal to the (Me)Tpmd apical carbon atom on formation of the zwitterion. Moreover, the computed M-C bond dissociation enthalpies of the kappa 1C isomers of [M(MeTpmd)Me] are considerably higher than expected by simple extrapolation from the corresponding computed H-C bond dissociation enthalpy. 相似文献
997.
A new fluorescent calix crown ether: synthesis and complex formation with alkali metal ions 总被引:1,自引:0,他引:1
Stoll I Eberhard J Brodbeck R Eisfeld W Mattay J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(4):1155-1163
We synthesised a new N-benzylaza-21-crown-7 ether 5 with a dihydroxy coumarin as a fluorescence sensor and investigated the binding behaviour towards alkali metal cations in methanol by fluorescence titrations. The association constants are within one order of magnitude, with the exception of sodium. Potassium is the preferred binding partner (K(Na)=330 M(-1); K(K)=8600 M(-1); K(Rb)=8200 M(-1); K(Cs)=4400 M(-1)). The corresponding aza-21-crown-7 ether (6) was attached by a methylene unit to a resorcarene to give fluorescent calix crown ether 12. The binding abilities of the calix crown ether towards alkali metal ions in methanol have also been investigated, and an increasing complex stability, distinct for potassium and rubidium in comparison with 5, was found: K(Na)=440 M(-1); K(K)=110,000 M(-1); K(Rb)=63,000 M(-1); K(Cs)=20,000 M(-1). Like bis(crown ether)s, a cooperative complexation of the crown ether and the cavitand scaffold can be assumed. The proposed complex geometry is supported by Kohn-Sham DFT calculations for the potassium and caesium complexes. 相似文献
998.
Soltwisch J Berkenkamp S Dreisewerd K 《Rapid communications in mass spectrometry : RCM》2008,22(1):59-66
We introduce a two-component matrix for ultraviolet matrix-assisted laser desorption/ionization mass spectrometry (UV-MALDI-MS) that consists of 2,5-dihydroxybenzoic acid (DHB) and glycerol. Upon slow evaporation of residual water/methanol solvents in a pre-vacuum chamber sample preparations are obtained that exhibit a homogeneous morphology with analyte-matrix crystals evenly distributed over the whole sample spot. At a molar DHB/glycerol ratio of approximately 1:5, the crystals range in length from approximately 100 to 300 microm and are about 15-30 microm wide. Mass spectra of peptides, proteins, and an oligosaccharide are presented and compared with those recorded from standard dried-droplet DHB matrix. The ion signals show a reproducibility of the order of 10-15% when scanning the surface of an individual sample or even different samples that contain the same amount of peptide, A close to linear relationship between peptide concentration and the corresponding peptide ion signal is found over three orders of magnitude of sample prepared. However, when a fixed position is irradiated with a large number of laser pulses, a monotonous decay of peptide ion signal with time is observed. Potentially, the binary matrix will be especially useful for the analysis of samples that are stabilized in buffered aqueous glycerol solution and preliminary results addressing this aspect are shown. 相似文献
999.
Henze A Rohn S Gericke B Raila J Schweigert FJ 《Rapid communications in mass spectrometry : RCM》2008,22(20):3270-3274
Transthyretin (TTR) is a sensitive marker of protein-energy malnutrition and changes in serum and expression levels during protein and energy deficiency are well described. However, little is known about structural modifications of TTR during protein and/or energy deprivation. Therefore, the aim of this study was to determine the effects of protein inadequacies on post-translational modifications of TTR. For this purpose, male Wistar rats were fed a diet with either casein or gelatine as sole protein source subsequent to a protein wash-out period. Changes in TTR serum levels as well as other markers of nutritional status as body weight, food consumption, total serum protein and serum RBP4 levels as well as antioxidative capacity were determined. Post-translational modifications of TTR were examined by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOFMS) analysis. The rats from the gelatine group revealed a marked change in the post-translational modification pattern of TTR which was reflected by a significant elevation of sulfonated TTR and which was inversely correlated to the antioxidative capacity. Additionally, the elevation of sulfonated TTR was accompanied by a decrease in body weight and food consumption, low antioxidative capacity as well as a deprivation of serum TTR, RBP4 and total serum protein levels in the animals of the gelatine group. Protein-energy malnutrition leads therefore next to changes in TTR serum concentration, also to changes in the post-translational modification pattern of TTR. Such changes are probably induced by protein-energy malnutrition-driven oxidative stress and might be linked to alterations in protein function and stability. 相似文献
1000.
Enghoff MB Pedersen JO Bondo T Johnson MS Paling S Svensmark H 《The journal of physical chemistry. A》2008,112(41):10305-10309
Aerosol nucleation has been studied experimentally in purified, atmospheric air, containing trace amounts of water vapor, ozone, and sulfur dioxide. The results are compared with model calculations. It is found that an increase in ionization by a factor of 10 increases the production rate of stable clusters by a factor of approximately 3, probably due to ion-induced nucleation. 相似文献