全文获取类型
收费全文 | 2058篇 |
免费 | 81篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 40篇 |
综合类 | 17篇 |
化学工业 | 413篇 |
金属工艺 | 103篇 |
机械仪表 | 64篇 |
建筑科学 | 151篇 |
矿业工程 | 13篇 |
能源动力 | 81篇 |
轻工业 | 257篇 |
水利工程 | 12篇 |
石油天然气 | 11篇 |
武器工业 | 1篇 |
无线电 | 97篇 |
一般工业技术 | 391篇 |
冶金工业 | 142篇 |
原子能技术 | 23篇 |
自动化技术 | 332篇 |
出版年
2023年 | 11篇 |
2022年 | 20篇 |
2021年 | 37篇 |
2020年 | 25篇 |
2019年 | 32篇 |
2018年 | 37篇 |
2017年 | 55篇 |
2016年 | 60篇 |
2015年 | 46篇 |
2014年 | 71篇 |
2013年 | 139篇 |
2012年 | 96篇 |
2011年 | 135篇 |
2010年 | 92篇 |
2009年 | 111篇 |
2008年 | 110篇 |
2007年 | 112篇 |
2006年 | 89篇 |
2005年 | 74篇 |
2004年 | 63篇 |
2003年 | 68篇 |
2002年 | 79篇 |
2001年 | 63篇 |
2000年 | 41篇 |
1999年 | 29篇 |
1998年 | 47篇 |
1997年 | 34篇 |
1996年 | 27篇 |
1995年 | 20篇 |
1994年 | 19篇 |
1993年 | 18篇 |
1992年 | 14篇 |
1991年 | 15篇 |
1990年 | 15篇 |
1989年 | 14篇 |
1988年 | 19篇 |
1987年 | 14篇 |
1986年 | 16篇 |
1985年 | 20篇 |
1984年 | 15篇 |
1983年 | 18篇 |
1982年 | 7篇 |
1981年 | 11篇 |
1980年 | 15篇 |
1979年 | 15篇 |
1978年 | 11篇 |
1977年 | 10篇 |
1976年 | 11篇 |
1974年 | 12篇 |
1973年 | 8篇 |
排序方式: 共有2148条查询结果,搜索用时 15 毫秒
51.
Interaction of polymers and other organic admixtures on Portland cement hydration is reviewed. This has been compiled in a systematic way. First hydration of Portland cement is described in short. Later, interaction with 4 important components of Portland cement is discussed. Finally interphase effects in polymer modified hydraulic cement are discussed. It is concluded that polymers and organic admixtures interact with the components of Portland cement when they come in contact with water. This interaction is due to ionic binding, causing cross-links which inhibit the film formation property of polymers and influence considerably the crystallisation process during the hardening of concrete. Some low molecular weight organic substances also have a considerable influence on Portland cement during its reaction with water. 相似文献
52.
Achieving economic competitiveness as compared to LWRs and other Generation IV (Gen-IV) reactors is one of the major requirements to attract large-scale investment in commercial sodium cooled fast reactor (SFR) power plants. Advances in R&D for advanced SFR fuel and structural materials provide key long-term opportunities to improve SFR economics. In addition, other new opportunities are emerging to further improve SFR economics. This paper provides an overview on potential ideas from the perspective of thermal hydraulics to improve SFR economics. These include: (1) a new hybrid loop-pool reactor design to further optimize economics, safety, and reliability of SFRs with more flexibility, (2) a multiple-reheat and intercooling helium Brayton cycle to improve plant thermal efficiency and to reduce safety related overnight and operation costs, and (3) modern multi-physics thermal analysis methods to reduce analysis uncertainties and associated requirements for over-conservatism in reactor design. This paper reviews advances in all three areas and their potential beneficial impacts on SFR economics. 相似文献
53.
Per Kreuger Rebecca Steinert Olof Görnerup Daniel Gillblad 《International Journal of Network Management》2018,28(2)
Managing and balancing load in distributed systems remains a challenging problem in resource management, especially in networked systems where scalability concerns favour distributed and dynamic approaches. Distributed methods can also integrate well with centralised control paradigms if they provide high‐level usage statistics and control interfaces for supporting and deploying centralised policy decisions. We present a general method to compute target values for an arbitrary metric on the local system state and show that autonomous rebalancing actions based on the target values can be used to reliably and robustly improve the balance for metrics based on probabilistic risk estimates. To balance the trade‐off between balancing efficiency and cost, we introduce 2 methods of deriving rebalancing actuations from the computed targets that depend on parameters that directly affects the trade‐off. This enables policy level control of the distributed mechanism based on collected metric statistics from network elements. Evaluation results based on cellular radio access network simulations indicate that load balancing based on probabilistic overload risk metrics provides more robust balancing solutions with fewer handovers compared to a baseline setting based on average load. 相似文献
54.
New CAMAC based data acquisition and beam control system for Lund nuclear microprobe 总被引:1,自引:0,他引:1
Mikael Elfman Per Kristiansson Klas Malmqvist Jan Pallon Anders Sjland Rogerio Utui Changyi Yang 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》1997,130(1-4):123-126
A new CAMAC based data acquisition system has been installed at the Lund Nuclear Microprobe facility. This paper reports on the development and present status of the data acquisition system. The system is a true multiparameter CAMAC based system with fast Fera bus readout and in crate memory buffer. The user interface is based on Sparrow Kmax software for a Power Macintosh platform. The system read out and tag the event data with position on-line, which make fast on-line monitoring of spectra or element maps possible.Simultaneously, all data can be saved event by event for off-line analysis. The beam scanning part is software controlled through a timed D/A converter, this allows fast scanning of the beam. With a CCD-camera and video card the area to be analysed could be defined directly from the image, and the sample position can be moved. Any kind of irregular scan patterns could be defined. 相似文献
55.
Serge Della Negra Yvon Le Beyec Per Håkansson 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》1985,9(1):103-106
A very simple time of flight mass spectrometer has been used to measure mass spectra for the negative ions of organic compounds in the mass range up to 3000 u. Desorbed ions were obtained by applying a constant negative voltage to a flat metallic surface, coated with a few micrograms of organic material. We show that electrons and negative ions are emitted simultaneously from the same point on the surface. Mass spectra obtained by this technique are compared to mass spectra for the same compounds, obtained with 252Cf fission fragment ionization. 相似文献
56.
57.
An effective wet digestion procedure for the determination of total iodine contents in milk powder samples was developed utilizing a high-pressure asher technique. The optimized method based on a two-stage digestion procedure. In the first stage, 500 mg samples were digested at 300 °C for 2 h using 15.2 mol L?1 HNO3 (5 mL) and 30 % H2O2 (3 mL). After the first digestion stage, digestion vessels were allowed to cool down and 1.2 mL of 20 % (w/v) Na2S2O8 solution was added as an additional oxidizing agent to the samples. After that, the vessels were closed, and they were heated at 100 °C for 30 min, resulting in clear and colorless sample solutions. Iodine concentrations in the digested samples were measured with inductively coupled plasma mass spectrometry. The accuracy of the optimized method was confirmed by analyzing milk powder reference material (BCR-151, milk powder). The obtained value for iodine (5.29?±?0.37 mg kg?1, n?=?6) was in good agreement with the certified value (5.35?±?0.14 mg kg?1). Furthermore, the results obtained for reference material showed that the developed method can be applied also for the determination of other elements, e.g., copper, iron, and lead in the digested milk powder samples. 相似文献
58.
ABSTRACT: Wheat and rye bread artificially inoculated with molds were packed in modified atmospheres of 0%, 50%, 75%, or 100% CO2 balanced with N2 , and 3 levels of residual O2 , 1%, 0.03%, or <0.01%/O2 -absorber, and stored for 30 to 35 d. Modified atmosphere packaging (MAP) was quantitatively more effective for rye bread because fewer mold species grew at elevated CO2 . However, the major rye bread contaminant, Penicillium roqueforti , was the overall most CO2 -resistant mold and only the use of O2 -absorber could prevent growth of this species. On wheat bread, the most CO2 -tolerant mold was Penicillium commune , growing in 99% CO2 (with high residual O2 ), and Aspergillus flavus was the mold species that grew at lowest O2 in 75% CO2 treatment. The spoilage yeast/"chalk mold" Endomyces fibuliger was less affected by the different O2 levels than the true filamentous molds, and none of the tested MAP treatments could prevent growth, but lag-phase was increased with O2 -absorber on wheat bread and decreased with 1% residual O2 on rye bread. Experiments with volatile mustard oil showed that A. flavus and Eurotium repens were the most mustard oil-resistant species on wheat and rye bread, respectively. A combination strategy with MAP and mustard oil proved most optimal, and total inhibition was achieved with 2 μL mustard oil/rye bread slice and between 2 and 3 μL/wheat bread. Results indicated that the nature and surface area of the product influences effectiveness of active packaging with mustard oil. 相似文献
59.
Atmospheric transport of polybrominated diphenyl ethers and polychlorinated biphenyls to the Baltic Sea 总被引:5,自引:0,他引:5
The atmospheric transport of polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) was compared by measuring concentrations in air and deposition on an island located in the central basin of the Baltic Sea. Median sigmaPBDE and sigmaPCB concentrations (gaseous + particle) were 8.6 and 7.4 pg m(-3), respectively. Airborne PCBs were mainly found in the gaseous phase, while most of the PBDEs were detected on particles, which agrees with predicted particle/gas distributions. SigmaPBDE levels were dominated by the decabrominated BDE209 followed bythe tetrabrominated BDE47 and pentabrominated BDE99. BDE209 is a marker for the environmental distribution of the commercial deca-BDE formulation (>99.5% BDE209), whereas BDE47 and BDE99 are markers for the commercial penta-BDE mixture. General correlations between PBDEs and PCBs suggested similarities in sources and transport mechanism, while more detailed examination of the data identified notable behaviors and exceptions. Differences in regression slopes among tetra-, penta-, and decabrominated PBDEs may reflect different transport processes and the change in usage pattern. Tetra- and pentabrominated PBDEs may originate from secondary sources such as air surface exchange in a manner similar to that of the PCBs, while the deca-BDE209 formulation still has primary sources. The tribrominated BDE17 was also detected and is proposed to be a breakdown product due to atmospheric debromination processes. PBDEs had higher washout ratios than PCBs, explaining their higher concentrations compared to PCBs in precipitation (median of 6.0 and 0.5 ng L(-1) for sigmaBDE and sigmaPCB concentrations ("dissolved" + particle), respectively) than in air. The calculated yearly deposition of PBDEs and PCBs indicated that the atmospheric input of PBDEs to the Baltic Proper is currently exceeding that of the PCBs by a factor of 40, while that of the PCBs is decreasing. 相似文献
60.
Helle Lindberg Madsen Lotte Andersen Luise Christiansen Per Brockhoff Grete Bertelsen 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1996,203(4):333-338
The sensory intensity measured as theabsolute threshold value of spice andrecognition of spice was evaluated for summer savory and rosemary in meat balls. The values forabsolute threshold value of spice were found to be significantly lower for rosemary than for summer savory. The antioxidative activity of the spices was analysed in two accelerated model systems and in a storage experiment. In one of the model systems, oxidation was accelerated by heat and by an elevated pressure of oxygen. Both spices significantly improved the oxidative stability of the meat balls in this model system. In the second model system metal catalyst oxidation in a meat slurry was used and a reduction in the oxidative processes in samples containing the spices was again shown. In both model systems a slightly higher antioxidative activity was seen for rosemary compared to summer savory. In the storage experiment, the spices were added at a sensorially acceptable level and the heat-treated meat balls were stored at 5°C. A significant reduction in the development of warmed-over flavour (WOF) caused by the addition of spices was measured by a reduction in 2-thiobarbituricacid-reactivesubstances (TBARS) and in hexanal. A reduction in TBARS of approximately 30% in meat balls containing added spices was seen independently of packaging in 1% oxygen or in atmospheric air and the reduction (30%) was constant throughout the storage period. 相似文献