全文获取类型
收费全文 | 30012篇 |
免费 | 1486篇 |
国内免费 | 143篇 |
专业分类
电工技术 | 572篇 |
综合类 | 240篇 |
化学工业 | 6555篇 |
金属工艺 | 574篇 |
机械仪表 | 654篇 |
建筑科学 | 1650篇 |
矿业工程 | 149篇 |
能源动力 | 922篇 |
轻工业 | 2335篇 |
水利工程 | 327篇 |
石油天然气 | 247篇 |
武器工业 | 4篇 |
无线电 | 2444篇 |
一般工业技术 | 5298篇 |
冶金工业 | 4877篇 |
原子能技术 | 216篇 |
自动化技术 | 4577篇 |
出版年
2023年 | 287篇 |
2022年 | 510篇 |
2021年 | 773篇 |
2020年 | 506篇 |
2019年 | 597篇 |
2018年 | 743篇 |
2017年 | 657篇 |
2016年 | 864篇 |
2015年 | 767篇 |
2014年 | 974篇 |
2013年 | 1840篇 |
2012年 | 1487篇 |
2011年 | 1922篇 |
2010年 | 1412篇 |
2009年 | 1350篇 |
2008年 | 1424篇 |
2007年 | 1320篇 |
2006年 | 1175篇 |
2005年 | 946篇 |
2004年 | 870篇 |
2003年 | 804篇 |
2002年 | 755篇 |
2001年 | 568篇 |
2000年 | 465篇 |
1999年 | 461篇 |
1998年 | 840篇 |
1997年 | 618篇 |
1996年 | 497篇 |
1995年 | 469篇 |
1994年 | 427篇 |
1993年 | 399篇 |
1992年 | 290篇 |
1991年 | 203篇 |
1990年 | 284篇 |
1989年 | 269篇 |
1988年 | 229篇 |
1987年 | 238篇 |
1986年 | 238篇 |
1985年 | 274篇 |
1984年 | 246篇 |
1983年 | 233篇 |
1982年 | 220篇 |
1981年 | 205篇 |
1980年 | 174篇 |
1979年 | 202篇 |
1978年 | 174篇 |
1977年 | 194篇 |
1976年 | 244篇 |
1975年 | 167篇 |
1974年 | 127篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Steven Y. Susswein Thomas C. Henderson Joseph L. Zachary Chuck Hansen Paul Hinker Gary C. Marsden 《International journal of parallel programming》1991,20(6):453-473
Filtering algorithms are well accepted as a means of speeding up the solution of the consistent labeling problem (CLP). Despite the fact that path consistency does a better job of filtering than arc consistency, AC is still the preferred technique because it has a much lower time complexity. We are implementing parallel path consistency algorithms on multiprocessors and comparing their performance to the best sequential and parallel arc consistency algorithms.(1,2) (See also work by Kerethoet al.
(3) and Kasif(4)) Preliminary work has shown linear performance increases for parallelized path consistency and also shown that in many cases performance is significantly better than the theoretical worst case. These two results lead us to believe that parallel path consistency may be a superior filtering technique. Finally, we have implemented path consistency as an outer product computation and have obtained good results (e.g., linear speedup on a 64K-node Connection Machine 2). 相似文献
72.
This communication shows an algorithm used in the drug infusion system discussed in a recent paper1 to be incorrect. The error is corrected, and a new algorithm is presented. 相似文献
73.
J Byrne S Kienzle D Johnson G Duke V Gannon B Selinger J Thomas 《Water science and technology》2006,53(10):327-334
Long-term trends in alpine and prairie snow pack accumulation and melt are affecting streamflow within the Oldman River Basin in southern Alberta, Canada. Unchecked rural and urban development also has contributed to changes in water quality, including enhanced microbial populations and increased waterborne pathogen occurrence. In this study we look at changing environment within the Oldman River Basin and its impact on water quality and quantity. The cumulative effects include a decline in net water supplies, and declining quality resulting in increased risk of disease. Our data indicates that decreases in the rate of flow of water can result in sedimentation of bacterial contaminants within the water column. Water for ecosystems, urban consumption, recreation and distribution through irrigation is often drawn from waterholding facilities such as dams and weirs, and concern must be expressed over the potential for contaminate build-up and disproportionate potential of these structures to pose a risk to human and animal health. With disruption of natural flow rates for water resulting from environmental change such as global warming and/or human intervention, increased attention needs to be paid to use of best management practices to protect source water supplies. 相似文献
74.
75.
F Javier Benítez Ana I Leal Francisco J Real Juan L Acero Gloria Roldán 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(3):309-316
BACKGROUND: The first stage of the cork industrial process generates great volumes of wastewater with moderate to high organic pollutant content that must be purified using different procedures, such as filtration by membranes. RESULTS: The tangential filtration of these wastewaters was studied using two different laboratory equipments. In the first one, three ultrafiltration (UF) membranes were tested, with molecular weight cut‐off (MWCO) 100 kDa and 30 kDa, and two operating modes were used: total recycling of permeate and retentate streams, and in continuous mode, without recycling both streams. In the total recycling UF experiments, the influence of the operating variables on the permeate flux was first established. The effectiveness of the different membranes was determined by evaluating the rejection coefficients for several parameters that measure the global pollutant content of the effluent. The values found for these rejection coefficients were in the following order: ellagic acid and color > absorbance at 254 nm > tannic content > COD (chemical oxygen demand). In the continuous mode experiments, the fouling mechanism for each membrane was established by fitting the experimental data to various filtration fouling models given in the literature. The operating mode in the second equipment was batch concentration, and additional experiments were carried out with an UF membrane (2 kDa), and with a NF membrane (with MWCO in the range 150–300 Da). CONCLUSIONS: The three operating modes tested provided different rejection levels of organic matter; among them, the most effective procedure tested was batch concentration mode using a NF membrane. Copyright © 2007 Society of Chemical Industry 相似文献
76.
Thomas Kristenson 《Network Security》2003,2003(8):19
You may not know it, but some of your employees are installing vulnerable software — and you are silently accepting it, you may even encourage them to do so… 相似文献
77.
This paper presents data relating to the performance of sprinklers and detectors in real office fire situations. For sprinklers, these data are additional to that associated with the standardized testing used to determine the design delivery density and pressure requirements for various occupancy situations, and provide a useful insight into the effect of sprinklers on developing fires with various office situations. The data given in this paper include the times for activation of various types of sprinkler heads (normal and fast response), the efficacy of the systems as far as extinguishment is concerned, estimates of the maximum size of the fires prior to commencement of extinguishment and associated air temperatures at various locations within the office enclosures. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
78.
The non-uniformity of the air temperatures and the slow flow rate at the plane collector exit constitute the main cause of the limitations of the solar drying systems. In order to obtain an uniform and a variable flow rate for different uses, a hot air generator using concentrated solar radiation is proposed. To improve the thermal efficiency of the generator, a study of the influence of different shape parameters is realized. The generator is simulated in the laboratory while investigating the flow induced by a circular disc heated uniformly by Joule effect at constant temperature. This disc is placed at the entrance of an open ended vertical cylinder of a larger diameter. Thermal radiation emitted by the hot disc heats the cylinder wall. The heating of the fluid at the cylinder-inlet generates a thermosiphon flow around the one created by the hot disc. The comparison of the velocity and the temperature profiles of the resulting flow permits to determine the influence of the cylinder height, the vertical source-cylinder spacing and the radius ratio, on the resulting flow at the system exit. Thus, a judicious choice of the shape parameters entails an improvement of the flow rate as well as the thermal flux absorbed by the air and a good homogenization of the air temperature at the generator exit. 相似文献
79.
The cellulose solvent dimethyl sulfoxide (DMSO)/tetrabutylammonium fluoride trihydrate (TBAF) was
successfully applied as reaction medium for the synthesis of allyl cellulose by conversion of the polymer
with allyl chloride in the presence of solid NaOH. Samples with degree of substitution from 0.50 to 2.98
were accessible by varying the molar ratio anhydroglucose unit:allyl chloride:NaOH and reaction time. DMSO/TBAF
was found to be an efficient reaction medium for the preparation of highly functionalized samples from spruce
sulfite pulp with degree of polymerization of about 500 even in a scale of 50 g. The allyl cellulose samples
were characterized by means of FTIR- and NMR spectroscopy. Size exclusion chromatography revealed negligible
polymer degradation during synthesis and purification of the samples. 相似文献
80.