全文获取类型
收费全文 | 421篇 |
免费 | 25篇 |
国内免费 | 5篇 |
专业分类
化学 | 252篇 |
晶体学 | 6篇 |
力学 | 34篇 |
数学 | 30篇 |
物理学 | 80篇 |
无线电 | 49篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 7篇 |
2021年 | 14篇 |
2020年 | 22篇 |
2019年 | 13篇 |
2018年 | 15篇 |
2017年 | 13篇 |
2016年 | 20篇 |
2015年 | 13篇 |
2014年 | 23篇 |
2013年 | 48篇 |
2012年 | 42篇 |
2011年 | 49篇 |
2010年 | 26篇 |
2009年 | 14篇 |
2008年 | 17篇 |
2007年 | 16篇 |
2006年 | 8篇 |
2005年 | 7篇 |
2004年 | 5篇 |
2003年 | 12篇 |
2002年 | 12篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 1篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有451条查询结果,搜索用时 421 毫秒
371.
Faouzi Sebbak Farid Benhammadi Abdelghani Chibani Yacine Amirat Aicha Mokhtari 《电信纪事》2014,69(3-4):171-184
Context awareness and activity recognition are becoming a hot research topic in ambient intelligence (AmI) and ubiquitous robotics, due to the latest advances in wireless sensor network research which provides a richer set of context data and allows a wide coverage of AmI environments. However, using raw sensor data for activity recognition is subject to different constraints and makes activity recognition inaccurate and uncertain. The Dempster–Shafer evidence theory, known as belief functions, gives a convenient mathematical framework to handle uncertainty issues in sensor information fusion and facilitates decision making for the activity recognition process. Dempster–Shafer theory is more and more applied to represent and manipulate contextual information under uncertainty in a wide range of activity-aware systems. However, using this theory needs to solve the mapping issue of sensor data into high-level activity knowledge. The present paper contributes new ways to apply the Dempster–Shafer theory using binary discrete sensor information for activity recognition under uncertainty. We propose an efficient mapping technique that allows converting and aggregating the raw data captured, using a wireless senor network, into high-level activity knowledge. In addition, we propose a conflict resolution technique to optimize decision making in the presence of conflicting activities. For the validation of our approach, we have used a real dataset captured using sensors deployed in a smart home. Our results demonstrate that the improvement of activity recognition provided by our approaches is up to of 79 %. These results demonstrate also that the accuracy of activity recognition using the Dempster–Shafer theory with the proposed mappings outperforms both naïve Bayes classifier and J48 decision tree. 相似文献
372.
Crude oil reservoirs typically contain more water than oil, which is emulsified with the oil. During oil production, the emulsion is broken with demulsifiers. Most recently, based on methyl methacrylate, after which, the water, containing the methyl methacrylate, is discharged into surface waters. Significant health hazards have been associated with methyl methacrylate, and a limit of 30 ppm in ground waters has been established. This paper describes the preconcentration of methyl methacrylate from the separated water, using dispersive liquid–liquid microextraction, followed by freezing of the organic drop in an ice bath which facilitated separation of the phases (by centrifugation). In the optimized method, 15.0 μL of 2-dodecanol was rapidly injected into 5 mL water samples, followed by stirring, freezing, and decantation, then direct injection into the gas chromatograph equipped with a flame ionization detector. The method was optimized for: choice of extraction solvent, volume of extraction solvent, pH, ionic strength, temperature and extraction time. 相似文献
373.
The remedy for infected chronic wounds such as diabetic foot ulcers is more complicated particularly in the case of patients with an inefficient immune system. Also, fighting against microbial infections in the wound site by available antibiotics may not be effective because of emerging antibiotic resistance properties among pathogenic bacteria and fungi. Recently, applications of micro‐ and nanoformulations of biomaterials have demonstrated improved therapeutic abilities for wound dressings. In this way, carboxymethyl, dialdehyde, and 2,2,6,6‐tetramethylpiperidine‐1‐oxyl‐oxidized celluloses are common biomaterials having outstanding physicochemical and therapeutic properties compared to unmodified cellulose. Therefore, in this review, recent progress in the field of wound healing and antimicrobial activities of these derivatives are presented and discussed. 相似文献
374.
Aladdin Riad Sarah B. Gitto Hwan Lee Harrison D. Winters Paul M. Martorano Chia-Ju Hsieh Kuiying Xu Dalia K. Omran Daniel J. Powell Jr. Robert H. Mach Mehran Makvandi 《Molecules (Basel, Switzerland)》2020,25(24)
Theranostics are emerging as a pillar of cancer therapy that enable the use of single molecule constructs for diagnostic and therapeutic application. As poly adenosine diphosphate (ADP)-ribose polymerase 1 (PARP-1) is overexpressed in various cancer types, and is localized to the nucleus, PARP-1 can be safely targeted with Auger emitters to induce DNA damage in tumors. Here, we investigated a radioiodinated PARP inhibitor, [125I]KX1, and show drug target specific DNA damage and subsequent killing of BRCA1 and non-BRCA mutant ovarian cancer cells at sub-pharmacological concentrations several orders of magnitude lower than traditional PARP inhibitors. Furthermore, we demonstrated that viable tumor tissue from ovarian cancer patients can be used to screen tumor radiosensitivity ex-vivo, enabling the direct assessment of therapeutic efficacy. Finally, we showed tumors can be imaged by single-photon computed tomography (SPECT) with PARP theranostic, [123I]KX1, in a human ovarian cancer xenograft mouse model. These data support the utility of PARP-1 targeted radiopharmaceutical therapy as a theranostic option for PARP-1 overexpressing ovarian cancers. 相似文献
375.
Jens Moons Francisco de Azambuja Jelena Mihailovic Karoly Kozma Katarina Smiljanic Mehran Amiri Tanja Cirkovic Velickovic May Nyman Tatjana N. Parac‐Vogt 《Angewandte Chemie (International ed. in English)》2020,59(23):9094-9101
The selective hydrolysis of proteins by non‐enzymatic catalysis is difficult to achieve, yet it is crucial for applications in biotechnology and proteomics. Herein, we report that discrete hafnium metal‐oxo cluster [Hf18O10(OH)26(SO4)13?(H2O)33] ( Hf18 ), which is centred by the same hexamer motif found in many MOFs, acts as a heterogeneous catalyst for the efficient hydrolysis of horse heart myoglobin (HHM) in low buffer concentrations. Among 154 amino acids present in the sequence of HHM, strictly selective cleavage at only 6 solvent accessible aspartate residues was observed. Mechanistic experiments suggest that the hydrolytic activity is likely derived from the actuation of HfIV Lewis acidic sites and the Brønsted acidic surface of Hf18 . X‐ray scattering and ESI‐MS revealed that Hf18 is completely insoluble in these conditions, confirming the HHM hydrolysis is caused by a heterogeneous reaction of the solid Hf18 cluster, and not from smaller, soluble Hf species that could leach into solution. 相似文献
376.
Robabeh Ghafouri Ali Movaghar Mehran Mohsenzadeh 《Wireless Personal Communications》2018,103(3):2035-2070
Cloud Computing enables delivery of IT resources over the Internet and follows the pay-as-you-go billing model. The cloud infrastructures can be used as an appropriate environment for executing of workflow applications. To execute workflow applications in this environment, it is necessary to develop the workflow scheduling algorithms that consider different QoS parameters such as execution time and cost. Therefore, in this paper we focus on two criteria: total completion time (makespan) and execution cost of workflow, and propose two heuristic algorithms: MTDC (Minimum Time and Decreased Cost) which aims to create a schedule that minimizes the makespan and decreases execution cost, and CTDC (Constrained Time and Decreased Cost) which is based on the first algorithm (MTDC) and aims to create a schedule that decreases the execution cost while satisfying the deadline constraint of the workflow application. The proposed algorithms are evaluated by a simulation process using WorkflowSim. To evaluate the proposed algorithms, the results of MTDC are compared with the results of HEFT (Heterogeneous Earliest Finish Time), and the results of CTDC are compared with the results of heuristic based algorithms [such as IC-PCP (IaaS Cloud Partial Critical Paths), IC-PCPD2 (Deadline Distribution) and BDHEFT (Budget and Deadline HEFT)] and meta-heuristic based algorithms [such as PSO (Particle Swarm Optimization) and CGA2 (Coevolutionary Genetic Algorithm with Adaptive penalty function)]. The results show that the proposed algorithms perform better than the mentioned algorithms in most cases. 相似文献
377.
Mohammad Reza Ganjali Farhang Mizani Masoud Salavati-Niasari Mehran Javanbakht 《Analytical sciences》2003,19(2):235-238
A plasticized Cr3+ ion sensor by incorporating 2,3,8,9-tetraphenyl-1,4,7,10-tetraazacyclododeca-1,3,7,9-tetraene (TTCT) ionophore exhibits a good potentiometric response for Cr3+ over a wide concentration range (1.0 x 10(-6)-1.0 x 10(-1) M) with a slope of 19.5 mV per decade. The sensor response is stable for at least three months. Good selectivity for Cr3+ in comparison with alkali, alkaline earth, transition and heavy metal ions, and minimal interference are caused by Li+, Na+, K+, Co2+, Hg2+, Ca2+, Pb2+ and Zn2+ ions, which are known to interfere with other chromium membrane sensors. The TTCT-based electrode shows a fast response time (15 s), and can be used in aqueous solutions of pH 3-5.5. The proposed sensor was used for the potentiometric titration of Cr3+ with EDTA and for a direct potentiometric determination of Cr3+ content in environmental samples. 相似文献
378.
Mohammad Reza Ganjali Mohammad Yousefi Mehran Javanbakht Tahereh Poursaberi Masoud Salavati-Niasari Leila Hajiagha-Babaei Elnaz Latifi Mojtaba Shamsipur 《Analytical sciences》2002,18(8):887-892
The construction, performance characteristics, and application of a novel polymeric membrane coated on a graphite electrode with unique selectivity towards SCN- are reported. The electrode was prepared by incorporating Ni(II)-2,2,4,9,9,11-hexamethyltetraazacyclotetradecanediene perchlorate into a plasticized poly(vinyl chloride) membrane. The influences of membrane composition, pH and foreign ions were investigated. The electrode displays a near Nernstian slope (-57.8 mV decade-1) over a wide concentration range of 1 x 10(-7)-1 x 10(-1) M of SCN- ion. The electrode has a detection limit of 4.8 x 10(-8) M (2.8 ng/cm3) SCN- and shows response times of about 15 s and 120 s for low to high and high to low concentration sequences, respectively. The proposed sensor shows high selectivity towards SCN- over several common organic and inorganic anions. The electrode revealed a great enhancement in selectivity coefficients and detection limit for SCN-, in comparison with the previously reported electrodes. It was successfully applied to the direct determination of SCN- in milk and biological samples, and as an indicator electrode in titration of Ag+ ions with thiocyanate. 相似文献
379.
Mojtaba Shamsipur Armen Avanes Mehran Javanbakht Mohammad Reza Ganjali Hashem Sharghi 《Analytical sciences》2002,18(8):875-879
New polymeric membrane (PME) and coated graphite (CGE) copper(II)-selective electrodes based on 1-hydroxy-2-(prop-2'-enyl)-4-(prop-2'-enyloxy)-9,10-anthraquinone were prepared. The electrodes reveal linear emf-pCu2+ responses over wide concentration ranges (1.0 x 10(-5)-1.0 x 10(-1) M with a slope of 27.3 mV decade-1 for PME and 8.0 x 10(-8)-5.0 x 10(-2) M with a slope of 29.1 mV decade-1 for CGE) and very low limits of detection (8.0 x 10(-6) M for PME and 5.0 x 10(-8) M for CGE). The potentiometric response is independent of the pH of the test solution in the pH range 3.0-6.0. The proposed electrodes possess very good selectivities over a wide variety of other cations, including alkali, alkaline earth, transition and heavy metal ions, the selectivity coefficients for the CGE being much improved over those for the PME. The electrodes were used as indicator electrodes in the potentiometric titration of Cu2+ and in the recovery of copper ions from wastewater. 相似文献
380.
We study the statistical prediction of a continuous time stochastic process admitting a functional autoregressive representation. We construct an approximation of Parzen's optimal predictor in reproducing kernel spaces framework. To cite this article: F. Mokhtari, T. Mourid, C. R. Acad. Sci. Paris, Ser. I 334 (2002) 65–70 相似文献