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111.
The inter-zeolite conversion is a method to convert one meta-stable zeolite to a thermodynamically stable zeolite. Despite the enormous interest, this method is yet to be popularized or standardized in the zeolite community. Intending to provide more insights into hydrothermal conversions from one zeolite to another, this work developed a novel one-pot and flexible synthetic protocol to efficiently obtain the meta-stable *BEA topology and its derived MTW topology by varying the hydrothermal crystallization time. This inter-zeolite conversion process led to changes in the zeolite framework and modified physicochemical properties during the process. Such a transformation was feasible by forming hierarchical zeolite phases sharing a similar “mtw”-based common building units, possibly driving such conversion. The structure-reactivity relationship of four different zeolite materials, synthesized from this one-pot inter-zeolite conversion method, was established concerning their performance in the methanol-to-hydrocarbon (MTH) process, which has been well supported by operando UV-vis diffuse reflectance spectroscopic study coupled with online mass spectrometry and solid-state NMR spectroscopy. As a result, the pathway to synthesize various target zeolites from an identical initial synthesis gel with desired physicochemical properties has been scrutinized. 相似文献
112.
Abhishek Pandey Chandan Mazumdar R. Ranganathan 《Journal of magnetism and magnetic materials》2010,322(23):3765-3770
We report the magnetic and transport properties of the off-stoichiometric metallic perovskite like compounds GdPd3Bx (x=0.25, 0.50 and 0.75). Our results show that doping with boron in the lattice of parent binary-compound GdPd3 leads to lattice expansion. Which in turn manifests in contrasting magnetic and transport behaviors of the doped compounds in comparison with the undoped GdPd3. An attempt has been made to compare and correlate the results of magnetic and transport measurements of GdPd3Bx with that of stoichiometric compositions GdPd3BxC1−x. The comparative study of GdPd3Bx and GdPd3BxC1−x confirms that there is a strong correlations between the structural, magnetic and transport properties of these compounds. 相似文献
113.
Vinod Patidar N.K. Pareek K.K. Sud 《Communications in Nonlinear Science & Numerical Simulation》2009,14(7):3056-3075
In this paper, we propose a new loss-less symmetric image cipher based on the widely used substitution–diffusion architecture which utilizes chaotic standard and logistic maps. It is specifically designed for the coloured images, which are 3D arrays of data streams. The initial condition, system parameter of the chaotic standard map and number of iterations together constitute the secret key of the algorithm. The first round of substitution/confusion is achieved with the help of intermediate XORing keys calculated from the secret key. Then two rounds of diffusion namely the horizontal and vertical diffusions are completed by mixing the properties of horizontally and vertically adjacent pixels, respectively. In the fourth round, a robust substitution/confusion is accomplished by generating an intermediate chaotic key stream (CKS) image in a novel manner with the help of chaotic standard and logistic maps. The security and performance of the proposed image encryption technique has been analyzed thoroughly using various statistical analysis, key sensitivity analysis, differential analysis, key space analysis, speed analysis, etc. Results of the various types of analysis are encouraging and suggest that the proposed image encryption technique is able to manage the trade offs between the security and speed and hence suitable for the real-time secure image and video communication applications. 相似文献
114.
Chatterjee A Jurgenson CT Schroeder FC Ealick SE Begley TP 《Journal of the American Chemical Society》2006,128(22):7158-7159
The biosynthesis of thiamin pyrophosphate in eukaryotes is different from the prokaryotic biosynthesis and is poorly understood to date. Only one thiazole biosynthetic gene has been identified (Thi4 in Saccharomyces cerevisiae). Here we report the identification and characterization of a Thi4-bound metabolite that consists of the ADP adduct of 5-(2-hydroxyethyl)-4-methylthiazole-2-carboxylic acid. The unexpected structure of this compound yields the first insights into the mechanism of thiamin thiazole biosynthesis in eukaryotes. 相似文献
115.
Kitagawa T Dey A Lugo-Mas P Benedict JB Kaminsky W Solomon E Kovacs JA 《Journal of the American Chemical Society》2006,128(45):14448-14449
Superoxide reductases (SORs) are cysteine-ligated, non-heme iron enzymes that reduce toxic superoxide radicals (O2-). The functional role of the trans cysteinate, as well as the mechanism by which SOR reduces O2-, is unknown. Herein is described a rare example of a functional metalloenzyme analogue, which catalytically reduces superoxide in a proton-dependent mechanism, via a trans thiolate-ligated iron-peroxo intermediate, the first example of its type. Acetic-acid-promoted H2O2 release, followed by Cp2Co reduction, regenerates the active Fe(II) catalyst. The thiolate ligand and its trans positioning relative to the substrate are shown to contribute significantly to the catalyst's function, by lowering the redox potential, changing the spin state, and dramatically lowering the nuFe-O stretching frequency well-below that of any other reported iron-peroxo, while leaving nuO-O high, so as to favor superoxide reduction and Fe-O, as opposed to O-O, bond cleavage. Thus we provide critical insight into the relationship between the SOR structure and its function, as well as important benchmark parameters for characterizing highly unstable thiolate-ligated iron-peroxo intermediates. 相似文献
116.
Abhishek Banerjee 《Comptes Rendus Mathematique》2018,356(4):365-375
Let be the spectrum of a tensor-triangulated category . We show that there is a homeomorphism between the spectral space of radical thick tensor ideals in and the collection of open subsets of in inverse topology. In fact, we prove a more general result in terms of supports on and work by combining methods from commutative algebra, topology and tensor triangular geometry. 相似文献
117.
Kumar Rohit Raj Abhishek Kardam Jyoti Kumar Arora Shalini Srivastava 《Journal of Radioanalytical and Nuclear Chemistry》2010,283(3):797-801
The tendency of selenium to interact with heavy metals in presence of naturally occurring species has been exploited for the
development of green bioremediation of toxic metals from soil using Artificial Neural Network (ANN) modeling. The cross validation
of the data for the reduction in uptake of Hg(II) ions in the plant R. sativus grown in soil and sand culture in presence of selenium has been used for ANN modeling. ANN model based on the combination
of back propagation and principal component analysis was able to predict the reduction in Hg uptake with a sigmoid axon transfer
function. The data of fifty laboratory experimental sets were used for structuring single layer ANN model. Series of experiments
resulted into the performance evaluation based on considering 20% data for testing and 20% data for cross validation at 1,500
Epoch with 0.70 momentums The Levenberg–Marquardt algorithm (LMA) was found as the best of BP algorithms with a minimum mean
squared error at the eighth place of the decimal for training (MSE) and cross validation. 相似文献
118.
Attention has shifted from the treatment of colorectal cancer (CRC) to chemoprevention using aspirin and folic acid as agents capable of preventing the onset of colon cancer. However, no sensitive analytical method exists to simultaneously quantify the two drugs when released from polymer‐based nanoparticles. Thus, a rapid, highly sensitive method of high‐performance liquid chromatography analysis to simultaneously detect low quantities of aspirin (hydrolyzed to salicylic acid, the active moiety) and folic acid released from biodegradable polylactide‐co‐glycolide (PLGA) copolymer nanoparticles was developed. Analysis was done on a reversed‐phase C18 column using a photodiode array detector at wavelengths of 233 nm (salicylic acid) and 277 nm (folic acid). The mobile phase consisted of acetonitrile–0.1% trifluoroacetic acid mixture programmed for a 30 min gradient elution analysis. In the range of 0.1–100 μg/mL, the assay showed good linearity for salicylic acid (R2 = 0.9996) and folic acid (R2 = 0.9998). The method demonstrated good reproducibility, intra‐ and inter‐day precision and accuracy (99.67, 100.1%) and low values of detection (0.03, 0.01 μg/mL) and quantitation (0.1 and 0.05 μg/mL) for salicylic acid and folic acid, respectively. The suitability of the method was demonstrated by simultaneously determining salicylic acid and folic acid released from PLGA nanoparticles. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
119.
Ewout De Geyter Eirini Antonatou Dimitris Kalaitzakis Sabina Smolen Abhishek Iyer Laure Tack Emiel Ongenae Georgios Vassilikogiannakis Annemieke Madder 《Chemical science》2021,12(14):5246
Recent dramatic expansion in potential uses of protein conjugates has fueled the development of a wide range of protein modification methods; however, the desirable single-site multi-functionalization of proteins has remained a particularly intransigent challenge. Herein, we present the application of 5-hydroxy-1,5-dihydro-2H-pyrrol-2-ones (5HP2Os) as advantageous alternatives to widely used maleimides for the chemo- and site-selective labeling of cysteine residues within proteins. A variety of 5HP2O building blocks have been synthesized using a one-pot photooxidation reaction starting from simple and readily accessible furans and using visible light and oxygen. These novel reagents display excellent cysteine selectivity and also yield thiol conjugates with superior stability. 5HP2O building blocks offer a unique opportunity to introduce multiple new functionalities into a protein at a single site and in a single step, thus, significantly enhancing the resultant conjugate''s properties.Recent expansion in potential uses of protein conjugates has fueled the development of a range of protein modification methods; however, the desirable single-site multi-functionalization of proteins has remained a particularly intransigent challenge. 相似文献
120.
Dey A Glaser T Moura JJ Holm RH Hedman B Hodgson KO Solomon EI 《Journal of the American Chemical Society》2004,126(51):16868-16878
Ligand K-edge XAS of an [Fe3S4]0 model complex is reported. The pre-edge can be resolved into contributions from the mu(2)S(sulfide), mu(3)S(sulfide), and S(thiolate) ligands. The average ligand-metal bond covalencies obtained from these pre-edges are further distributed between Fe(3+) and Fe(2.5+) components using DFT calculations. The bridging ligand covalency in the [Fe2S2]+ subsite of the [Fe3S4]0 cluster is found to be significantly lower than its value in a reduced [Fe2S2] cluster (38% vs 61%, respectively). This lowered bridging ligand covalency reduces the superexchange coupling parameter J relative to its value in a reduced [Fe2S2]+ site (-146 cm(-1) vs -360 cm(-1), respectively). This decrease in J, along with estimates of the double exchange parameter B and vibronic coupling parameter lambda2/k(-), leads to an S = 2 delocalized ground state in the [Fe3S4]0 cluster. The S K-edge XAS of the protein ferredoxin II (Fd II) from the D. gigas active site shows a decrease in covalency compared to the model complex, in the same oxidation state, which correlates with the number of H-bonding interactions to specific sulfur ligands present in the active site. The changes in ligand-metal bond covalencies upon redox compared with DFT calculations indicate that the redox reaction involves a two-electron change (one-electron ionization plus a spin change of a second electron) with significant electronic relaxation. The presence of the redox inactive Fe(3+) center is found to decrease the barrier of the redox process in the [Fe3S4] cluster due to its strong antiferromagnetic coupling with the redox active Fe2S2 subsite. 相似文献