全文获取类型
收费全文 | 14711篇 |
免费 | 1141篇 |
国内免费 | 146篇 |
专业分类
电工技术 | 259篇 |
综合类 | 54篇 |
化学工业 | 3669篇 |
金属工艺 | 338篇 |
机械仪表 | 558篇 |
建筑科学 | 466篇 |
矿业工程 | 48篇 |
能源动力 | 926篇 |
轻工业 | 1348篇 |
水利工程 | 246篇 |
石油天然气 | 182篇 |
武器工业 | 5篇 |
无线电 | 1607篇 |
一般工业技术 | 2842篇 |
冶金工业 | 755篇 |
原子能技术 | 131篇 |
自动化技术 | 2564篇 |
出版年
2024年 | 55篇 |
2023年 | 294篇 |
2022年 | 571篇 |
2021年 | 1026篇 |
2020年 | 814篇 |
2019年 | 966篇 |
2018年 | 1072篇 |
2017年 | 986篇 |
2016年 | 974篇 |
2015年 | 606篇 |
2014年 | 934篇 |
2013年 | 1458篇 |
2012年 | 903篇 |
2011年 | 1010篇 |
2010年 | 664篇 |
2009年 | 563篇 |
2008年 | 389篇 |
2007年 | 312篇 |
2006年 | 263篇 |
2005年 | 185篇 |
2004年 | 163篇 |
2003年 | 138篇 |
2002年 | 116篇 |
2001年 | 80篇 |
2000年 | 73篇 |
1999年 | 87篇 |
1998年 | 178篇 |
1997年 | 150篇 |
1996年 | 121篇 |
1995年 | 93篇 |
1994年 | 72篇 |
1993年 | 68篇 |
1992年 | 47篇 |
1991年 | 61篇 |
1990年 | 50篇 |
1989年 | 43篇 |
1988年 | 33篇 |
1987年 | 37篇 |
1986年 | 41篇 |
1985年 | 39篇 |
1984年 | 39篇 |
1983年 | 41篇 |
1982年 | 17篇 |
1981年 | 16篇 |
1980年 | 13篇 |
1979年 | 14篇 |
1978年 | 19篇 |
1977年 | 19篇 |
1976年 | 24篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 326 毫秒
991.
Ali Babaei Balal Khalilzadeh Mohammad Afrasiabi 《Journal of Applied Electrochemistry》2010,40(8):1537-1543
A new chemically modified electrode is constructed based on a copper(II) doped zeolite modified carbon paste electrode (Cu2+Y/ZMCPE). It is demonstrated that this novel sensor could be used for the simultaneous determination of the pharmaceutically
important compounds paracetamol (PAR) and mefenamic acid (MEF). The measurements were carried out using the differential pulse
voltammetry (DPV) method. The prepared modified electrode shows voltammetric responses of high sensitivity, selectivity and
stability for PAR and MEF under optimal conditions, which makes it a suitable sensor for simultaneous submicromolar detection
of PAR and MEF in solution. The oxidation peak current for PAR in Briton Robinson buffer (pH = 10) was measured at various
concentrations between 0.25 and 900 μM. (The detection limit was 0.1 μM and S/N was 3.) It proved linear (the correlation
coefficient was 0.9987). For the MEF a linear correlation between oxidation peak current and concentration of MEF over the
range 0.3–100 μM, with a correlation coefficient of 0.9991 and a detection limit of 0.04 μM, was obtained. The analytical
performance of this sensor has been evaluated for the detection of PAR and MEF in human serum, human urine and a pharmaceutical
preparation. 相似文献
992.
Mohammad Hosein NaeeniYadollah Yamini Mohammad Rezaee 《The Journal of Supercritical Fluids》2011,57(3):219-226
Supercritical fluid extraction (SFE) coupled with dispersive liquid-liquid microextraction (DLLME) and followed by gas chromatography-flame ionization detection (GC-FID) was applied for extraction and determination of ultra-trace amounts of seven organophosphorus pesticides (OPPs) (o,o,o-triethyl phosphorothioate, thionazin, sulfotepp, disulfoton, methyl parathion, parathion, and famphur) in soil and marine sediment samples. Supercritical CO2 at 150 bar, 60 °C, 10 min static and 30 min dynamic extraction times was used to extract the pesticides. The extracts were collected in 1.0 mL of acetonitrile. Seventeen μL of carbon tetrachloride was dissolved in the collecting solvent and the mixture was then injected rapidly into 5.0 mL of aqueous solution. About (5.0 ± 0.2 μL) of sediment phase was collected after centrifuging and finally 2.0 μL of it was injected into gas chromatography (GC) injection port for analyses. The extraction recoveries for the target analytes were in the range of 44.4% and 95.4% and relative standard deviation (RSD%) for four-replicate measurements was below 7.5%. The limit detections of the method for determining the pesticides were in the range of 0.001-0.009 mg kg−1. The method was successfully applied for analysis of OPPs in real soil and marine sediment samples and satisfactory results were obtained. 相似文献
993.
Mohammad Mohammadi 《The International Journal of Advanced Manufacturing Technology》2010,50(9-12):1165-1174
Presenting an integrated lotsizing, loading, and scheduling model for the capacitated flexible flow shops with sequence-dependent setups is the main contribution of this paper. An exact formulation of the problem is provided as a mixed integer program. To solve this problem, mixed integer programming-based heuristics based on iterative procedures are provided. To test the accuracy of heuristics, two lower bounds are developed and compared against the optimal solution. The trade-offs between solution quality and computational time of heuristics are also provided. 相似文献
994.
Abbas Ramezani Mohammad Masoud Mohebi Alireza Souri 《Journal of Materials Engineering and Performance》2013,22(4):1010-1017
In this study, four types of castables as calcium-aluminate cement (CAC)-bonded and nano-silica (NS)-bonded castables based on tabular-alumina and bauxite aggregates were prepared to investigate the replacement of the calcium-aluminate cement by NS. All samples were allowed to dry at 110 °C then fired at 800 and 1200 °C. Bulk density and apparent porosity of samples were measured. The molten aluminum static corrosion test (cup test) results showed that NS-bonded specimens had higher resistance to corrosion compared to CAC-bonded samples (based on the measured average aluminum penetration depth into the refractory texture). However no penetration was observed in bauxite NS-bonded samples. The results were consistent with dynamic corrosion test in aluminum melt carried out at 800 °C for 100 h. The small pore size in NS-bonded castables was found to be the main cause for high corrosion resistance as micro-pores prevented the melt to penetrate into the refractory. 相似文献
995.
This study reports on the formulation of doxycycline HCL in an ion activated in situ gelling delivery system and its implications for the treatment of periodontal disease. The system is based on the use of alginate as the gelling agent and hydroxypropyl methylcellulose (HPMC) as a viscosity enhancing agent. The ion activated gelling mechanism in this system is based on the concept of interaction with the divalent calcium ions present in the gingival crevicular fluid (GCF). The gelling capacity of the prepared formulations was assessed visually and by investigating their rheological behavior upon mixing with human blood serum since it has the same composition as the GCF. The rheological behavior of all formulations was not affected by incorporation of the drug. In vitro release studies showed that the alginate/HPMC mixture, upon gelling after mixing with serum, can sustain the release of doxycycline HCL for an extended period of time which was more than 12 days. These results indicated that this system can be used as an in situ gelling local delivery system for the treatment of periodontal disease. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
996.
997.
Wireless sensor networks (WSNs) are known to be highly energy-constrained and consequently lifetime is a critical metric in their design and implementation. Range assignment by adjusting the transmission powers of nodes create a energy-efficient topology for such networks while preserving other network issues, however, it may effect on the performance of other techniques such as network coding. This paper addresses the problem of lifetime optimization for WSNs where the network employs both range assignment and network-coding-based multicast. We formulate the problem and then reformulated it as convex optimization that offer a numerous theoretical or conceptual advantages. The proposed programming leads to efficient or distributed algorithms for solving the problem. Simulation results show that the proposed optimized mechanism decreases end-to-end delay and improve lifetime as compared by other conventional ones. 相似文献
998.
Ashish Rawson Mohammad B. Hossain Ankit Patras Maria Tuohy Nigel Brunton 《Food research international (Ottawa, Ont.)》2013,50(2):513-518
Fennel (Foeniculum vulgare cv dulce.) is a hardy, perennial, umbelliferous (Apiaceae) plant as a source of the secondary metabolites group's polyacetylenes and polyphenols.The present study investigated the effect of boiling (100 ° C for 30 min) and roasting (160 °C for 15 min) on the levels of these phytochemicals. Boiling resulted in a significant decrease in the levels of polyacetylenes (falcarinol, falcarindiol, falcarindiol- 3- acetate) and polyphenols (caffeic acid, gallic acid, apigenin-7-o-glucoside, ferulic acid, syringic acid, isovitexin, phloridzin). The loss of polyphenols from the boiled bulbs may be in part due to leaching of these components in the water. Roasting resulted in a significant decrease in falcarindiol, falcarindiol-3-acetate, and falcarinol by 81%, 78%, and 66% when compared to raw unprocessed fennel bulbs. In general, levels of all polyphenols decreased in roasted samples. The exceptions were ferulic acid which showed an increase and gallic acid which did not show any decrease. In line with results for polyphenol levels, antioxidant activity decreased following thermal processing, and the presence of hydroxymethylfurfural was confirmed in roasted samples of fennel. 相似文献
999.
Javed Syed Rahmath Ulla Baig Salem Algarni Y.V.V. Satyanarayana Murthy Mohammad Masood Mohammed Inamurrahman 《International Journal of Hydrogen Energy》2017,42(21):14750-14774
The rapid growth of vehicular pollution; mostly running on the diesel engine, emissions emerging are the concerns of the day. Owing to clean burn characteristics features, Hydrogen (H2) as a fuel is the paradigm of the researcher. Extensive research presented in the literature on H2 dual fueled diesel engine reveals, the significant role of H2 in reducing emissions and enhancing the performance of a dual fueled diesel engine. With meager qualitative experiment data, the feasibility to develop an efficient Artificial Neural Network (ANN) model is investigated, the developed model can be utilized as a tool to investigate the H2 dual fueled diesel engine further. In the process of developing an ANN model, engine load and H2 flow rate are varied to register performance and emission characteristics. The creditability of the experiment is ascertained with uncertainty analysis of measurable and computed parameters. Leave-out-one method is adopted with 16 data sets; seven training algorithms are explored with eight transfer function combinations to evolve a competent ANN model. The efficacy of the developed model is adjudged with standard benchmark statistic indices. ANN model trained with Broyden, Fletcher, Goldfarb, & Shanno (BFGS) quasi-Newton backpropagation (trainbfg) stand out the best among other algorithms with regression coefficient ranging between 0.9869 and 0.9996. 相似文献
1000.
Lei Yao Khan R. Chodavarapu V.P. Tripathi V.S. Bright F.V. 《IEEE transactions on biomedical circuits and systems》2009,3(5):304-311
We present the design and implementation of a phase luminometry sensor system with improved and tunable detection sensitivity achieved using a complementary metal-oxide semiconductor (CMOS) integrated circuit. We use sol-gel derived xerogel thin films as an immobilization media to house oxygen (O2) responsive luminescent molecules. The sensor operates on the principal of phase luminometry wherein a sinusoidal modulation signal is used to excite the luminophores encapsulated in the porous xerogel films and the corresponding phase shift of the emission signals is monitored. The phase shift is directly related to excited state lifetimes of the luminophores which in turn are related to the concentration of the target analyte species present in the vicinity of the luminophores. The CMOS IC, which consists of a 16 times 16 high-gain phototransistor array, current-to-voltage converter, amplifier and tunable phase shift detector, consumes an average power of 14 mW with 5-V power supply operating at a 38-kHz modulation frequency. The output of the IC is a dc voltage that corresponds to the detected luminescence phase shift with respect to the excitation signal. As a prototype, we demonstrate an oxygen sensor system by encapsulating the luminophore tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) within the xerogel matrices. The sensor system showed a fast response on the order of few seconds and we obtained a detection sensitivity of 118 mV per 1% change in O2 concentration. The system demonstrates a novel concept to tune and improve the detection sensitivity for specific concentrations of the target analyte in many biomedical monitoring applications. 相似文献