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61.
Volmer DA Brombacher S Whitehead B 《Rapid communications in mass spectrometry : RCM》2002,16(24):2298-2305
In this study, the performance of monolithic columns was evaluated for ultrafast liquid chromatography/mass spectrometry (LC/MS) analyses and for high-resolution separations of several azaspiracid biotoxin analogs. Because of their high permeability, monolithic columns offer a number of advantages over conventional packed columns; viz., very low backpressures and relatively flat van Deemter curves at high flow rates. That is, very high flow rates can be used for ultrafast analyses or, by using longer than normal columns, high-resolution separations are possible. In a series of experiments, we varied the mobile phase flow rates between 1 and 8 mL/min, and studied their impact on chromatographic parameters such as retention time, resolution, number of plates and pressure. The chromatographic run times could be reduced to ca. 30 s without a significant change in the separation efficiency. A signal intensity comparison revealed interesting differences between atmospheric-pressure chemical ionization (APCI) and electrospray ionization (ESI) in their flow-rate dependency. An explanation with respect to the behavior as of a mass-flow or a concentration-dependent device is given in the paper. Additionally, the column length was varied between 10 and 70 cm. As a result, the number of theoretical plates increased substantially. In the example shown in the report, an increase from 13 000 plates for a 10-cm column to 80 000 for a 70-cm column is demonstrated. In addition, the potential of the monolithic columns for high-resolution LC/MS separations is shown for a complex biotoxin mixture, which was separated on a 40-cm-long column. 相似文献
62.
Thomas F Schulz S Nieger M Nättinen K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(8):1915-1924
Bimetallic, pentel-bridged complexes of the type [(dmap)Me2M-E(SiMe3)2-M'(CO)n] (M=Al, Ga; E=P, As, Sb; M'=Cr, Fe, Ni; DMAP=4-(dimethylamino)pyridine) are formed by reactions of DMAP-coordinated monomeric Group 13/15 compounds [(dmap)Me2M-E(SiMe3)2] with the transition metal complexes [(Me3N)Cr(CO)5], [Fe3(CO)12], and [Ni(CO)4]. For the first time, this reaction offers a general pathway to compounds containing a Group 13 metal and a transition metal bridged by a pentel atom. Complexes prepared in this way were characterized by IR and multinuclear NMR spectroscopy and by single-crystal X-ray structure analysis. Their electronic and structural properties are discussed in detail. The Group 13/15 ligands are very weak acceptors, which is likely to be due to the electropositive Group 13 metal, and the complexes feature comparatively long pentel-transition metal bonds. In addition, the synthesis and structural characterization of the parent DMAP-coordinated gallanes [(dmap)Me2Ga-E(SiMe3)2] (E=P, As) are reported. 相似文献
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65.
The determination of carbonyl compounds in gaseous samples is usually accomplished by enrichment methods, in which 2,4-dinitrophenyl-hydrazine (DNPH) as a derivatization reagent has become established to a large extent. However, the conventional methods of DNPH-impingers and of DNPH-cartridges are applicable to emission measurements in a limited way only, depending on the NO2-concentration in the exhaust gas. It could be proved that DNPH-derivatives, as well as DNPH, are also decomposed by NO2 at a different speed, in which the hydrazones of unsaturated carbonyl compounds are probably more sensitive than those of the saturated carbonyl compounds. In view of this fact, the collecting methods had to be modified to avoid losses with the enrichment. The analysis of the compounds is carried out by HPLC with an effective gradient-system which is able to separate and detect the carbonyl compounds in exhaust gas within 16 min. Furthermore, a simple working-up procedure is presented which facilitates a parallel analysis by GC. 相似文献
66.
The reaction of primary alkyl bromides or chlorides with diethylzinc in the presence of Ni(acac)(2) (5 mol %) furnishes the corresponding alkylzinc halides (X = Br, Cl) via a halogen-zinc exchange reaction. The treatment of terminal alkenes with diethylzinc (neat, 25-60 degrees C) in the presence of Ni(acac)(2) as a catalyst (1-5 mol %) and 1,5-cyclooctadiene (COD) affords the corresponding dialkylzincs via a hydrozincation reaction. Whereas the conversion for simple alkenes bearing a remote functionality reaches 40 to 63%, the hydrozincation of allylic, homoallylic alcohols and allylic amines proceeds very efficiently (85-95% conversion). All the zinc organometallics obtained react with various electrophiles (allylic halides, enones, acid chlorides, alkynyl halides, ethyl propiolate) after transmetalation with CuCN.2LiCl. In the presence of the chiral catalyst 12, the dialkylzincs prepared add to aldehydes with high enantioselectivity. 相似文献
67.
Lukas Fischer Alexander K. Strzelczyk Nils Wedler Christian Kropf Stephan Schmidt Laura Hartmann 《Chemical science》2020,11(36):9919
Catechol and amine residues, both abundantly present in mussel adhesion proteins, are known to act cooperatively by displacing hydration barriers before binding to mineral surfaces. In spite of synthetic efforts toward mussel-inspired adhesives, the effect of positioning of the involved functional groups along a polymer chain is not well understood. By using sequence-defined oligomers grafted to soft hydrogel particles as adhesion probes, we study the effect of catechol–amine spacing, as well as positioning relative to the oligomer terminus. We demonstrate that the catechol–amine spacing has a significant effect on adhesion, while shifting their position has a small effect. Notably, combinations of non-charged amides and catechols can achieve similar cooperative effects on adhesion when compared to amine and catechol residues. Thus, these findings provide a blueprint for the design of next generation mussel-inspired adhesives.The catechol driven adhesion of precision macromolecules on glass surfaces is quantified by soft colloidal probe readout. Catechol moieties are shown to synergize with amine and amide residues depending on residue spacing and residue order. 相似文献
68.
Convenient high-yield syntheses of the primary and di-primary heteroaryl-phosphines R-PH2 and H2P-R'-PH2(with R = 2-thienyl, 2-furyl, and R'= 2,5-thiophenediyl, 2,5-furandiyl, respectively) are presented. The products and a set of precursor molecules have been characterized by analytical and spectral data, and the crystal structures of selected molecules have been determined: 2-C4H3O-PCl2, 2,5-(Cl2P)2C4H2O, 2,5-[(Et2N)2P]2C4H2E (with E = O, S). In the crystals, the two molecules with -PCl2 substituents adopt trans conformations, while the other two have the -P(NEt2)2 groups rotated into a twist conformation. The reaction of the thienyl compounds with tris[(tert-phosphine)gold]oxonium tetrafluoroborates gave almost quantitative yields of the tri- and hexanuclear gold complexes, respectively: {2-C4H3S-P[Au(PR3)]3}+BF4- and [2,5-{[(R3P)Au]3P}2C4H2S]2+(BF4(-)2, (R =tBu, Ph). The structures of the compounds with R3P =tBu3P ligands have been determined. In both cases the [2-C4H3/2S-P] units cap triangles of gold atoms in an array that can be described as three [Au(PR3)]+ cations bridged by a phosphido dianion (RP)2-. 相似文献
69.
Low water vapor and air permeability is a persistent challenge in wearable and on-skin electronics, as it reduces wearing comfort, and leads to skin irritation and inflammation in the long term. To tackle this issue, Zheng and coworkers designed a stretchable conductor based on an elastomeric fiber mat coated by liquid metal. After simple activation via stretching, the flexible conductor was endowed with excellent permeability, good stretchability, exceptional electrical stability, and good biocompatibility, ascribed to the mesh-like structure and the vertically buckled structure of the liquid metal. Based on the intriguing properties of the material, it was employed in a multi-functional wearable device, able to detect the heartbeat and sweat while serving as a heating device. The corresponding research has been published in Nature Materials and can be accessed at https://doi.org/10.1038/s41563-020-00902-3. 相似文献
70.
Quentin Coquerel Claire Legendre Jacinthe Frangieh Stephan De Waard Jrme Montnach Leos Cmarko Joseph Khoury Charifat Said Hassane Dimitri Brard Benjamin Siegler Ziad Fajloun Harold De Pomyers Kamel Mabrouk Norbert Weiss Daniel Henrion Pascal Richomme Csar Mattei Michel De Waard Anne-Marie Le Ray Christian Legros 《Molecules (Basel, Switzerland)》2022,27(13)
Voltage-gated Na+ (NaV) channels are significant therapeutic targets for the treatment of cardiac and neurological disorders, thus promoting the search for novel NaV channel ligands. With the objective of discovering new blockers of NaV channel ligands, we screened an In-House vegetal alkaloid library using fluorescence cell-based assays. We screened 62 isoquinoline alkaloids (IA) for their ability to decrease the FRET signal of voltage sensor probes (VSP), which were induced by the activation of NaV channels with batrachotoxin (BTX) in GH3b6 cells. This led to the selection of five IA: liriodenine, oxostephanine, thalmiculine, protopine, and bebeerine, inhibiting the BTX-induced VSP signal with micromolar IC50. These five alkaloids were then assayed using the Na+ fluorescent probe ANG-2 and the patch-clamp technique. Only oxostephanine and liriodenine were able to inhibit the BTX-induced ANG-2 signal in HEK293-hNaV1.3 cells. Indeed, liriodenine and oxostephanine decreased the effects of BTX on Na+ currents elicited by the hNaV1.3 channel, suggesting that conformation change induced by BTX binding could induce a bias in fluorescent assays. However, among the five IA selected in the VSP assay, only bebeerine exhibited strong inhibitory effects against Na+ currents elicited by the hNav1.2 and hNav1.6 channels, with IC50 values below 10 µM. So far, bebeerine is the first BBIQ to have been reported to block NaV channels, with promising therapeutical applications. 相似文献