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101.
This report describes the use of Pd(II)/bis-sulfoxide 1 catalyzed intra- and intermolecular allylic C-H amination reactions to rapidly diversify structures containing a sensitive β-lactam core similar to that found in the monobactam antibiotic Aztreonam. Pharmacologically interesting oxazolidinone, oxazinanone, and linear amine motifs are rapidly installed with predictable and high selectivities under conditions that use limiting amounts of substrate. Additionally, we demonstrate for the first time that intramolecular C-H amination processes may be accelerated using catalytic amounts of a Lewis acid co-catalyst [Cr(III)(salen)Cl 2]. 相似文献
102.
Clio Dessinioti Christina Antoniou Andreas Katsambas Alexander J. Stratigos 《Photochemistry and photobiology》2010,86(3):481-491
Basal cell carcinoma (BCC) is the most common skin cancer in white populations with an increasing incidence worldwide, thereby imposing an important public health problem. Its etiology is still unclear, but existing data indicate that the risk for BCC development is of multifactorial origin and results from the interplay of both constitutional and environmental factors. Yet, UV radiation (UVR) is believed to be the predominant causative risk factor in the pathogenesis of BCC. For years, BCC and squamous cell carcinoma (SCC) have been grouped together as “nonmelanoma skin cancer.” However, it seems that there are considerable biologic differences between BCC and SCC, and thus each type of epithelial cancer should be addressed separately. The present review provides an overview of the intriguing etiologic link of BCC with UVR and attempts a comprehensive review of recent epidemiologic and molecular evidence that supports this association. 相似文献
103.
Christina M. Gonzalez Jeffrey Hernandez Jason G. Parsons Jorge L. Gardea-Torresdey 《Microchemical Journal》2010,96(2):324-329
Selenium (Se) is naturally occurring in the environment and is an essential nutrient in mammals. However, environmental Se can be increased to toxic levels through different industrial practices. The potential adsorption of the Se oxoanions, selenite and selenate, from aqueous solutions onto nanosynthesized MnFe2O4 was investigated using batch techniques and DRC-ICP-MS spectroscopy. The nanomaterial (NM) was laboratory synthesized through slow titration of a mixture of Fe2+ and Mn2+ ions. X-ray diffraction and Scherrer's equation were used to determine the phase of the material and crystallite size, respectively. The effects of pH, reaction time, competitive anions, and the adsorption capacity of the synthesized NM to bind selenite and selenate were investigated. The Langmuir isotherm was used to determine the binding capacity of the NM. Results showed that the phase of the nanomaterial was similar to Jacobsite with a size of 27.5 nm. Results also showed that the sorption of either 100 ppb of selenite or selenate was pH independent in the pH range 2 to 6 and occurred within 5 min of contact time. The introduction of Cl− and NO3− anions individually added to solution had no significant effect on the sorption of either selenite or selenate. However, it was found that the addition of SO42− had a competitive effect only on the sorption of selenate, first seen at 10 ppm and more pronounced at 100 ppm of SO42−. In the presence of 100 ppm of PO43−, the adsorption of selenate decreased to 87% while selenite sorption decreased to 20%. From the Langmuir isotherm equation it was determined that the nano-Jacobsite had a selenite and selenate binding capacity of 6573.76 and 769.23 mg Se/kg of NM, respectively. 相似文献
104.
Qiu P Jensen C Charity N Towner R Mao C 《Journal of the American Chemical Society》2010,132(50):17724-17732
We report a general method for preparing nanoparticle clusters (NPCs) in an oil-in-water emulsion system mediated by cetyl trimethylammonium bromide (CTAB), where previously only individual nanoparticles were obtained. NPCs of magnetic, metallic, and semiconductor nanoparticles have been prepared to demonstrate the generality of the method. The NPCs were spherical and composed of densely packed individual nanoparticles. The number density of nanoparticles in the oil phase was found to be critical for the formation, morphology, and yield of NPCs. The method developed here is scalable and can produce NPCs in nearly 100% yield at a concentration of 5 mg/mL in water, which is approximately 5 times higher than the highest value reported in the literature. The surface chemistry of NPCs can also be controlled by replacing CTAB with polymers containing different functional groups via a similar procedure. The reproducible production of NPCs with well-defined shapes has allowed us to compare the properties of individual and clustered iron oxide nanoparticles, including magnetization, magnetic moments, and contrast enhancement in magnetic resonance imaging (MRI). We found that, due to their collective properties, NPCs are more responsive to an external magnetic field and can potentially serve as better contrast enhancement agents than individually dispersed magnetic NPs in MRI. 相似文献
105.
Declan Williams Suzanne Ackloo Peihong Zhu Peter Bowden Kenneth R. Evans Christina L. Addison Chris Lock John G. Marshall 《Analytical and bioanalytical chemistry》2010,396(3):1223-1247
The endogenous peptides of human serum may have regulatory functions, have been associated with physiological states, and
their modifications may reveal some mechanisms of disease. In order to correlate levels of specific peptides with disease
alongside internal standards, the polypeptides must first be reliably extracted and identified. Endogenous blood peptides
can be effectively enriched by precipitation of the serum with organic solvents followed by selective extraction of peptides
using aqueous solutions modified with organic solvents. Polypeptides on filter paper were assayed with Coomasie brilliant
blue binding. The polypeptides were resolved by detergent tricine polyacrylamide electrophoresis and visualized by diamine
silver staining. Peptides in the extracts were collected by C18 and analyzed by matrix-assisted laser desorption/ionization
and liquid chromatography–electrospray ionization–tandem mass spectrometry (MS/MS) quadrupole time-of-flight MS/MS. Peptides
were resolved as multiple isotopic peaks in MS mode with mass deviation of 0.1 Da or less and similar accuracy for fragments.
The sensitivity of MS and MS/MS analysis was estimated to be in the picomolar range or less. The peptide composition of the
extracts was dependent on solvent formulation. Multiple peptides from apolipoproteins, complement proteins, coagulation factors,
and many others were identified by X!Tandem with high mass accuracy of peptide ions and fragments from collision-induced dissociation.
Many previously unreported posttranslational modifications of peptides including phosphorylations, oxidations, glycosylations,
and others were detected with high mass accuracy and may be of clinical importance. About 4,630 redundant peptides were identified
with 99% confidence separately, and together some 1,251 distinct proteins were identified with 99% confidence or greater using
the Paragon algorithm. 相似文献
106.
107.
R. Andrew Sims Christina C.C. Willis Timothy S. McComb Vikas Sudesh Menelaos K. Poutous Martin Richardson 《Optics Communications》2011,284(7):1988-739
Output beams from three independently frequency-stabilized thulium master-oscillator power-amplifier fiber laser systems were spectrally combined using a plane-ruled metal diffraction grating. Two laser channels were frequency-stabilized with guided mode resonance filters and the third was stabilized using a plane-ruled metal diffraction grating. The systems had output wavelengths between 1984 and 2015 nm, each with a spectral width of 100-450 pm and output powers between 40-120 W. The combined beam had powers up to 49 W and was 32% efficient with respect to the launched pump power. 相似文献
108.
Kummerlöwe G Grage SL Thiele CM Kuprov I Ulrich AS Luy B 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2011,209(1):19-30
The successful measurement of anisotropic NMR parameters like residual dipolar couplings (RDCs), residual quadrupolar couplings (RQCs), or residual chemical shift anisotropy (RCSA) involves the partial alignment of solute molecules in an alignment medium. To avoid any influence of the change of environment from the isotropic to the anisotropic sample, the measurement of both datasets with a single sample is highly desirable. Here, we introduce the scaling of alignment for mechanically stretched polymer gels by varying the angle of the director of alignment relative to the static magnetic field, which we call variable angle NMR spectroscopy (VA-NMR). The technique is closely related to variable angle sample spinning NMR spectroscopy (VASS-NMR) of liquid crystalline samples, but due to the mechanical fixation of the director of alignment no sample spinning is necessary. Also, in contrast to VASS-NMR, VA-NMR works for the full range of sample inclinations between 0° and 90°. Isotropic spectra are obtained at the magic angle. As a demonstration of the approach we measure 13C-RCSA values for strychnine in a stretched PDMS/CDCl? gel and show their usefulness for assignment purposes. In this context special care has been taken with respect to the exact calibration of chemical shift data, for which three approaches have been derived and tested. 相似文献
109.
Computer-generated holograms displayed by phase-modulating spatial light modulators have become a well-established tool for beam shaping purposes in holographic optical tweezers. Still, the generation of light intensity patterns with high spatial symmetry and simultaneously without interfering ghost traps is a challenge. We have implemented an iterative Fourier transform algorithm that is capable of controlling these ghost traps and demonstrate the benefit of this approach in the experiment. 相似文献
110.
Christina Knöfel Hsiang-Jen WangKarl T.S. Thydén Mogens Mogensen 《Solid State Ionics》2011,195(1):36-42
A porous composite electrode LSM-YSZ (lanthanum strontium manganite and yttria stabilized zirconia) was impregnated with different amounts of SDC (samarium substituted ceria) nanoparticles. The materials were investigated with X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy to determine the microstructure, the interface chemistry and the surface chemistry of the various impregnated samples. The SDC nanoparticles cover the surface of the LSM-YSZ backbone to a large extent; they are approximately 5-20 nm in diameter and have a cubic crystal structure. Low concentrations of lanthanum and manganese originating from LSM were detected within SDC particles. It was also observed that the relative atomic concentration of strontium increased on the LSM-YSZ surface with increasing amount of SDC nanoparticles. These findings are related to the applied nanoparticle impregnation method. It is indicated that interactions between surfactant, nanoparticles, impregnation solution and the LSM-YSZ composite take place which can locally affect the surface and interface chemistry of the investigated materials. 相似文献