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排序方式: 共有646条查询结果,搜索用时 15 毫秒
631.
Andrew Baker Birgit Richter Markus Szymik 《Journal of Pure and Applied Algebra》2012,216(11):2361-2376
We investigate a notion of Azumaya algebras in the context of structured ring spectra and give a definition of Brauer groups. We investigate their Galois theoretic properties, and discuss examples of Azumaya algebras arising from Galois descent and cyclic algebras. We construct examples that are related to topological Hochschild cohomology of group ring spectra and we present a -local variant of the notion of Brauer groups. 相似文献
632.
Herbert Schumann Yilmaz Aksu Stefan Schutte Birgit C. Wassermann Stefan H. Mühle 《Journal of organometallic chemistry》2006,691(22):4717-4724
A series of novel first-generation silicon-centred tin dendrimers Si(CH2CH2SnR3)4 [R = CH3 (3), iBu (4), CCCH3 (5), C6H4CH3-4 (6), C6H4OCH3-4 (7), (CH2)4OCH2CH2OCH3 (8), CH2SiMe3 (9)] was prepared by the reaction of Si(CH2CH2SnBr3)4 (2) with the appropriate Grignard reagent or LiCH2SiMe3 in tetrahydrofuran. The new compounds were characterized by multinuclear NMR studies (1H, 13C, 119Sn), mass spectrometry (MALDI-TOF, EI) and elemental analyses. The molecular structure of Si[CH2CH2SnBr3(THF)2]2[CH2-CH2SnBr3(THF)]2 (2a) was determined by single-crystal X-ray diffraction. 相似文献
633.
Reduction of primary freeze-drying time by electric field induced ice nucleus formation 总被引:1,自引:0,他引:1
The potential of a high electric field was utilized to induce ice nucleus formation in aqueous solutions. Using this technique it was possible to reduce the primary drying time during lyophilization. Samples of 10% (w/v) hydroxyethylstarch (HES) solution were frozen at a constant rate of −1 K/min, while nucleation was initiated at temperatures of −1.5, −4.5 and −8.5°C. In contrast, spontaneous nucleation was observed in a range between −11.5 and −17.1°C. Electrically induced nucleus formation has proved to be a reliable method to start crystallization at a desired temperature. Continuous measurement of the weight allowed to determine the drying rate and to detect at which time primary drying was completed. The drying time and the drying rate were found to be strongly dependent on the nucleation temperature during freezing. A relation between the nucleation temperature, the structure of the frozen samples and the drying times could be established.
相似文献
Ansgar PetersenEmail: |
634.
Birgit Birkmann Andreas W. Ehlers Dr. Roland Fröhlich Dr. Koop Lammertsma Prof. Dr. F. Ekkehardt Hahn Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(17):4301-4311
Meso complex versus helicate : A naphthalene‐bridged bis(benzene‐o‐dithiol) ligand reacts with Ti4+ to give both dinuclear triple‐stranded meso complexes and helicates, depending on the counterion employed during synthesis. DFT calculations performed with a simplified complex revealed that the interconversion of Λ to its Δ enantiomer proceeds via a C3h‐symmetric transition state (see figure).
635.
Lutz F. Tietze Birgit Krewer Holm Frauendorf 《Analytical and bioanalytical chemistry》2009,395(2):437-448
One of the main problems of anti-cancer therapy is an insufficient differentiation between normal and malignant cells by the
known anti-proliferant agents. The antibody-directed enzyme prodrug therapy is a promising approach for a selective treatment
of cancer, in which a non-toxic prodrug is enzymatically converted into a highly cytotoxic drug at the surface of malignant
cells by a targeted antibody–enzyme conjugate. The transformations and the stability of a very promising novel prodrug and
its corresponding cytotoxic derivative were now investigated in detail by high-performance liquid chromatography (HPLC)–mass
spectrometry (MS). In order to determine the time-dependent DNA alkylation efficiency and the sequence selectivity of the
novel compounds, DNA binding studies using direct electrospray–Fourier transform ion cyclotron resonance–MS (ESI–FTICR–MS)
have been performed. These measurements were accompanied by HPLC analyses followed by MS of the separated species to confirm
the results of the direct ESI–FTICR–MS measurements. The sites of DNA alkylation could be identified unambiguously by the
mass spectrometric fragmentation pattern of the alkylated oligodeoxynucleotides as well as by the results of HPLC followed
by MS. A combination of all techniques applied led to a better understanding of the mode of action of the new therapeutics
and might be used for an estimation of the cytotoxicity of different prodrugs and drugs since the alkylation efficiency correlates
with the bioactivity of the compounds in cell culture investigations.
After enzymatic cleavage of the sugar moiety, the untoxic prodrug is converted rapidly into the corresponding highly cytotoxic
drug that alkylates DNA with high efficiency
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
相似文献
Lutz F. TietzeEmail: |
636.
Pumping Yb:YAG or Yb:LuAG into the zero-phonon line at 969?nm instead of using the common pump wavelength of 940?nm reduces the heat generation by 32%. In addition to the 3% increase of the Stokes efficiency, this significantly reduces the diffraction losses caused by the thermally induced phase distortions leading to a remarkable increase of the overall efficiency especially of fundamental-mode thin-disk lasers. Using this pumping scheme in an Yb:LuAG thin-disk laser, we achieved 742?W of nearly diffraction limited (M2≈1.5) output power at an unprecedented high optical efficiency of 58.5%. For multimode operation (M2≈15) the maximum optical efficiency of an Yb:YAG thin-disk laser was increased to 72%. 相似文献
637.
Birgit Kosan Frank Meister Tim Liebert Thomas Heinze 《Cellulose (London, England)》2006,13(1):105-113
The application of starch in tailored materials is limited because of the high hydrophilicity of the polysaccharide. Thus,
simple and efficient paths for the hydrophobic modification of native, cationic or thermoplastic starches by means of a radical
grafting process using bifunctional fatty acid oxazoline derivatives were investigated. The modified starches can be manufactured
by means of an extrusion process showing high grafting yields at adjustable grafting contents from 2.5 to 30%. Resulting starch
materials are distinguished by modified water absorption properties and solubility, which is a prerequisite for their application
in the paper or painting industry. Moreover the structure of the oxazoline derivative supplies the opportunity for reactive
blending of different polymers carrying carboxyl, amino, mercapto or epoxy groups. This is exemplarily shown for the conversion
with biodegradable polyesters, which contain carboxylic acid functions. Film forming properties of the new starch-based materials
were studied. Results of the examination of manufactured shouldered test bars of starches coupled with biodegradable polyesters
are presented as well. 相似文献
638.
Birgit Stubbe Arn Mignon Heidi Declercq Sandra Van Vlierberghe Peter Dubruel 《Macromolecular bioscience》2019,19(8)
Hydrogels are interesting as wound dressing for burn wounds to maintain a moist environment. Especially gelatin and alginate based wound dressings show strong potential. Both polymers are modified by introducing photocrosslinkable functionalities and combined to hydrogel films (gel‐MA/alg‐MA). In one protocol gel‐MA films are incubated in alg‐MA solutions and crosslinked afterward into double networks. Another protocol involves blending both and subsequent photocrosslinking. The introduction of alginate into the gelatin matrix results in phase separation with polysaccharide microdomains in a protein matrix. Addition of alg(‐MA) to gel‐MA leads to an increased swelling compared to 100% gelatin and similar to the commercial Aquacel Ag dressing. In vitro tests show better cell adhesion for films which have a lower alginate content and also have superior mechanical properties. The hydrogel dressings exhibit good biocompatibility with adaptable cell attachment properties. An adequate gelatin‐alginate ratio should allow application of the materials as wound dressings for several days without tissue ingrowth. 相似文献
639.
Ina Reiche Stefan R?hrs Joseph Salomon Birgit Kanngie?er Yvonne H?hn Wolfgang Malzer Friederike Voigt 《Analytical and bioanalytical chemistry》2009,393(3):1025-1041
The paper presents an analytical method developed for the nondestructive study of nineteenth-century Persian polychrome underglaze
painted tiles. As an example, 9 tiles from French and German museum collections were investigated. Before this work was undertaken
little was known about the materials used in pottery at that time, although the broad range of colors and shades, together
with their brilliant glazes, made these objects stand out when compared with Iranian ceramics of the preceding periods and
suggested the use of new pigments, colorants, and glaze compositions. These materials are thought to be related to provenance
and as such appropriate criteria for art-historical attribution. The analytical method is based on the combination of different
nondestructive spectroscopic techniques using microfocused beams such as proton-induced X-ray emission/proton-induced γ-ray
emission, X-ray fluorescence, 3D X-ray absorption near edge structure, and confocal Raman spectroscopy and also visible spectroscopy.
It was established to address the specific difficulties these objects and the technique of underglaze painting raise. The
exact definition of the colors observed on the tiles using the Natural Color System?? helped to attribute them to different colorants. It was possible to establish the presence of Cr- and U-based colorants as
new materials in nineteenth-century Persian tilemaking. The difference in glaze composition (Pb, Sn, Na, and K contents) as
well as the use of B and Sn were identified as a potential marker for different workshops.
Figure UV fluorescence and visible spectroscopy are two of the non-destructive analytical methods used to investigate the coloring
agents of underglaze painted tiles. Imaging of the uranium-containing areas was carried out by UV photography and identification
of the chemical species by visible spectroscopy.
相似文献
Ina ReicheEmail: |
640.
In this paper, the controllability and admissibility of perturbed semigroup systems are studied, using tools from the theory of interpolation and Carleson measures. In addition, there are new results on the perturbation of Carleson measures and on the weighted interpolation of functions and their derivatives in Hardy spaces, which are of interest in their own right. 相似文献