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61.
Viscosimetric detection in size-exclusion chromatography (SEC/GPC): The Goldwasser method and beyond
Size-exclusion chromatography (SEC or GPC) is the most widely used separation method to characterize polymers. The high level of complexity of most polymeric materials necessitates the use of not only concentration-sensitive detection but also structure-sensitive detection. Viscometry is usually used in conjunction with a concentration-sensitive detector and universal calibration to determine molecular weights of polymers. Goldwasser proposed to use a viscometer as a single detector to determine number-average molecular weights, M(n) (ACS Symposium Series, 521, 143). The method is particularly of interest when concentration-sensitive detection is not available, because the sample is isorefractive or not UV-absorbing, or because composition is not constant (copolymers). It has known very little applications so far. It actually does not only allow determining M(n), but also the number hydrodynamic volume distribution. This opens a wider range of applications for the Goldwasser method. Size-exclusion chromatography only yields inaccurate molecular weight distributions for some complex branched polymers. Hydrodynamic volume distributions have then a strong potential for comparative studies owing to their far higher accuracy. Our experimental tests highlight the fact that the method is highly sensitive to noise and careful optimization of the injection concentration is needed, but number distribution can be obtained as well as M(n). 相似文献
62.
Wilhelmina H. A. de Jong Marianne H. L. I. Wilkens Elisabeth G. E. de Vries Ido P. Kema 《Analytical and bioanalytical chemistry》2010,396(7):2609-2616
Serotonin emerges as crucial neurotransmitter and hormone in a growing number of different physiologic processes. Besides
extensive serotonin production previously noted in patients with metastatic carcinoid tumors, serotonin now is implicated
in liver cell regeneration and bone formation. The aim was to develop a rapid, sensitive, and highly selective automated on-line
solid-phase extraction method coupled to high-performance liquid chromatography–tandem mass spectrometry (XLC-MS/MS) to quantify
low serotonin concentrations in matrices such as platelet-poor plasma and urine. Fifty microliters plasma or 2.5 μL urine
equivalent were pre-purified by automated on-line solid-phase extraction, using weak cation exchange. Chromatography of serotonin
and its deuterated internal standard was performed with hydrophilic interaction chromatography. Mass spectrometric detection
was operated in multiple reaction monitoring mode using a quadrupole tandem mass spectrometer with positive electrospray ionization.
Serotonin concentrations were determined in platelet-poor plasma of metastatic carcinoid patients (n = 23) and healthy controls (n = 22). Urinary reference intervals were set by analyzing 24-h urine collections of 120 healthy subjects. Total run-time was
6 min. Intra- and inter-assay analytical variation were <10%. Linearity in the 0–7300 μmol/L calibration range was excellent
(R2 > 0.99). Quantification limits were 30 and 0.9 nmol/L in urine and plasma, respectively. Platelet-poor serotonin concentrations
in metastatic carcinoid patients were significantly higher than in controls. The urinary reference interval was 10–78 μmol/mol
creatinine. Serotonin analysis with sensitive and specific XLC-MS/MS overcomes limitations of conventional HPLC. This enables
accurate quantification of serotonin for both routine diagnostic procedures and research in serotonin-related disorders. 相似文献
63.
Markus Albrecht Prof. Dr. Marcel Fiege Dr. Paul Kögerler Prof. Dr. Manfred Speldrich Dr. Roland Fröhlich Dr. Marianne Engeser Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(29):8797-8804
Based on chiral, enantiomerically pure 7‐[(S)‐phenylethylurea]‐8‐hydroxyquinoline ( 1 ‐H), trinuclear helicate‐type complexes 2 – 5 are formed with divalent transition‐metal cations. X‐ray structural analyses reveal the connection of two monomeric complex units [M( 1 )3]? (M=Zn, Mn, Co, Ni) by a central metal ion to form a “dimer”. Due to the enantiopurity of the ligand, the complexes are obtained as pure enantiomers, resulting in pronounced circular dichroism (CD) spectra. Single‐ion effects and intra‐ and intermolecular coupling are observed with dominating ferromagnetic coupling in the case of the cobalt(II) and nickel(II) and dominating antiferromagnetic coupling in the case of the manganese(II) complex. 相似文献
64.
65.
This paper presents an investigation on the enhancement of the barrier properties of paperboard and paper. Microfibrillar
cellulose (MFC) and shellac were deposited on the fibre based substrates using a bar coater or a spray coating technique.
The air, oxygen and water vapour permeability properties were measured to quantify the barrier effect of the applied coatings.
In addition, the mechanical properties were determined and image analysis of the structure was performed to examine the coating
adhesion. The air permeance of the paperboard and papers was substantially decreased with a multilayer coating of MFC and
shellac. Furthermore, for the MFC and shellac coated papers, the oxygen transmission rate decreased several logarithmic units
and the water vapour transmission rate reached values considered as high barrier in food packaging (6.5 g/m2 24 h). The analysis of mechanical and morphological properties indicated good adhesion between the coating and the base substrate. 相似文献
66.
Marianne Akian St��phane Gaubert Bas Lemmens 《Journal of Fixed Point Theory and Applications》2011,9(2):295-325
We study the stable behaviour of discrete dynamical systems where the map is convex and monotone with respect to the standard
positive cone. The notion of tangential stability for fixed points and periodic points is introduced, which is weaker than
Lyapunov stability. Among others we show that the set of tangentially stable fixed points is isomorphic to a convex inf-semilattice,
and a criterion is given for the existence of a unique tangentially stable fixed point. We also show that periods of tangentially
stable periodic points are orders of permutations on n letters, where n is the dimension of the underlying space, and a sufficient condition for global convergence to periodic orbits is presented. 相似文献
67.
Wolfgang G. Kreyling Pratim Biswas Maria E. Messing Neil Gibson Marianne Geiser Alexander Wenk Manoranjan Sahu Knut Deppert Izabela Cydzik Christoph Wigge Otmar Schmid Manuela Semmler-Behnke 《Journal of nanoparticle research》2011,13(2):511-524
The intensive use of nano-sized titanium dioxide (TiO2) particles in many different applications necessitates studies on their risk assessment as there are still open questions on their safe handling and utilization. For reliable risk assessment, the interaction of TiO2 nanoparticles (NP) with biological systems ideally needs to be investigated using physico-chemically uniform and well-characterized NP. In this article, we describe the reproducible production of TiO2 NP aerosols using spark ignition technology. Because currently no data are available on inhaled NP in the 10?C50 nm diameter range, the emphasis was to generate NP as small as 20 nm for inhalation studies in rodents. For anticipated in vivo dosimetry analyses, TiO2 NP were radiolabeled with 48V by proton irradiation of the titanium electrodes of the spark generator. The dissolution rate of the 48V label was about 1% within the first day. The highly concentrated, polydisperse TiO2 NP aerosol (3?C6 × 106 cm?3) proved to be constant over several hours in terms of its count median mobility diameter, its geometric standard deviation, and number concentration. Extensive characterization of NP chemical composition, physical structure, morphology, and specific surface area was performed. The originally generated amorphous TiO2 NP were converted into crystalline anatase TiO2 NP by thermal annealing at 950 °C. Both crystalline and amorphous 20-nm TiO2 NP were chain agglomerated/aggregated, consisting of primary particles in the range of 5 nm. Disintegration of the deposited TiO2 NP in lung tissue was not detectable within 24 h. 相似文献
68.
69.
Muriel De Bock Marie-Alice Meuwis Tran Quang Minh Jean-Paul Chapelle Michel Malaise Marianne Fillet 《Talanta》2010,82(1):245-594
In most diseases, the clinical need for serum/plasma markers has never been so crucial, not only for diagnosis, but also for the selection of the most efficient therapies, as well as exclusion of ineffective or toxic treatment. Due to the high sample complexity, prefractionation is essential for exploring the deep proteome and finding specific markers.In this study, three different sample preparation methods (i.e., highly abundant protein precipitation, restricted access materials (RAM) combined with IMAC chromatography and peptide ligand affinity beads) were investigated in order to select the best fractionation step for further differential proteomic experiments focusing on the LMW proteome (MW inferior to 40,000 Da). Indeed, the aim was not to cover the entire plasma/serum proteome, but to enrich potentially interesting tissue leakage proteins. These three methods were evaluated on their reproducibility, on the SELDI-TOF-MS peptide/protein peaks generated after fractionation and on the information supplied.The studied methods appeared to give complementary information and presented good reproducibility (below 20%). Peptide ligand affinity beads were found to provide efficient depletion of HMW proteins and peak enrichment in protein/peptide profiles. 相似文献
70.
The thermotropic liquid crystalline behaviour of two N-alkylpyridinium tetrahalocuprates was investigated. The n-pentadecyl tetrachloro and tetrabromo derivatives (CU15-CL and CU15-BR, respectively) exhibit very similar behaviour on cooling, and specifically, a high temperature smectic phase followed by a cubic phase. We fully elucidated the Ia3¯d space group for the cubic phase from X-ray diffraction on single crystals. The type of cubic phase is still under discussion, but we suggest that it is a direct type of structure based on the known phase sequence of lower and higher homologues. A model for the local organization of CU15-CL and CU15-BR in the cubic and smectic mesophases is also proposed. 相似文献