全文获取类型
收费全文 | 5884篇 |
免费 | 167篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 84篇 |
综合类 | 5篇 |
化学工业 | 1113篇 |
金属工艺 | 115篇 |
机械仪表 | 80篇 |
建筑科学 | 333篇 |
矿业工程 | 8篇 |
能源动力 | 165篇 |
轻工业 | 388篇 |
水利工程 | 45篇 |
石油天然气 | 114篇 |
武器工业 | 1篇 |
无线电 | 402篇 |
一般工业技术 | 919篇 |
冶金工业 | 1466篇 |
原子能技术 | 54篇 |
自动化技术 | 769篇 |
出版年
2021年 | 63篇 |
2020年 | 60篇 |
2019年 | 62篇 |
2018年 | 72篇 |
2017年 | 64篇 |
2016年 | 82篇 |
2015年 | 83篇 |
2014年 | 89篇 |
2013年 | 365篇 |
2012年 | 204篇 |
2011年 | 235篇 |
2010年 | 168篇 |
2009年 | 185篇 |
2008年 | 226篇 |
2007年 | 231篇 |
2006年 | 198篇 |
2005年 | 189篇 |
2004年 | 171篇 |
2003年 | 158篇 |
2002年 | 166篇 |
2001年 | 92篇 |
2000年 | 100篇 |
1999年 | 114篇 |
1998年 | 99篇 |
1997年 | 94篇 |
1996年 | 120篇 |
1995年 | 82篇 |
1994年 | 82篇 |
1993年 | 92篇 |
1992年 | 85篇 |
1991年 | 64篇 |
1990年 | 77篇 |
1989年 | 91篇 |
1988年 | 80篇 |
1987年 | 89篇 |
1986年 | 82篇 |
1985年 | 105篇 |
1984年 | 113篇 |
1983年 | 84篇 |
1982年 | 77篇 |
1981年 | 86篇 |
1980年 | 63篇 |
1979年 | 99篇 |
1978年 | 73篇 |
1977年 | 79篇 |
1976年 | 58篇 |
1975年 | 67篇 |
1974年 | 60篇 |
1973年 | 76篇 |
1972年 | 55篇 |
排序方式: 共有6061条查询结果,搜索用时 231 毫秒
81.
In Starinshak et al. (J Comput Phys 262(1):1–16, 2014), we proposed a new level-set model for representing multimaterial flows in multiple space dimensions. Rather than associating each level-set function with the boundary of a material, the new model associates each level-set function with a pair of materials and the interface that separates them. In this paper, we extend the model to represent geometries with non-smooth boundaries. The model uses multiple level-set functions to describe the shape boundary, typically with one level-set function per smooth boundary segment. Sign information is collected from all level-set functions and a voting algorithm is used to determine the interior/exterior of the geometric shape. The model is well suited for representing boundaries with singularities; it offers significant improvement over standard level-set approaches, both in shape preservation and area conservation; and it eliminates the need for costly redistancing of the level-set function. Numerical examples illustrate the superior performance of the proposed model. 相似文献
82.
James N. K. Liu Yu-lin He Edward H. Y. Lim Xi-zhao Wang 《Neural computing & applications》2014,24(3-4):779-798
This paper proposes an ontology learning method which is used to generate a graphical ontology structure called ontology graph. The ontology graph defines the ontology and knowledge conceptualization model, and the ontology learning process defines the method of semiautomatic learning and generates ontology graphs from Chinese texts of different domains, the so-called domain ontology graph (DOG). Meanwhile, we also define two other ontological operations—document ontology graph generation and ontology graph-based text classification, which can be carried out with the generated DOG. This research focuses on Chinese text data, and furthermore, we conduct two experiments: the DOG generation and ontology graph-based text classification, with Chinese texts as the experimental data. The first experiment generates ten DOGs as the ontology graph instances to represent ten different domains of knowledge. The generated DOGs are then further used for the second experiment to provide performance evaluation. The ontology graph-based approach is able to achieve high text classification accuracy (with 92.3 % in f-measure) over other text classification approaches (such as 86.8 % in f-measure for tf–idf approach). The better performance in the comparative experiments reveals that the proposed ontology graph knowledge model, the ontology learning and generation process, and the ontological operations are feasible and effective. 相似文献
83.
84.
Effect of alkali and alkaline earth metals on nitrogen release during temperature programmed pyrolysis of coal 总被引:3,自引:0,他引:3
Formation of HCN, NH3, and N2 during fixed-bed pyrolysis at 10K min−1 has been studied using coal samples after partial demineralization followed by addition of metal hydroxides from aqueous systems. Without additives, NH3 is the predominant product at ≤ 700°C, showing the two peaks in the formation rate profile, whereas N2 is the only product at ≥ 800°C. The presence of NaOH, KOH and Ca(OH)2 promotes considerable NH3 formation between 450 and 600°C, but in contrast suppresses HCN formation in this region. The Ca shows the largest effect on both the promotion and suppression. It is likely that the NH3 increased by Ca addition arises partly from HCN, but mainly from secondary reactions of tar-N. These hydroxides affect N2 formation in quite different manners: the Na decreases the rate between 700 and 950°C, and the K changes it less significantly than the Na, but the Ca remarkably increases the rate in a low temperature region of 550–700°C. These different features are discussed in terms of solid-phase reactions of alkali metal carbonates with char-N and secondary decomposition reactions of tar-N on CaO particles. As a result, total conversion of coal-N to HCN, NH3 and N2 up to 1000°C increases in the sequence of Na < none < K < Ca. 相似文献
85.
86.
Robert A. Gibson Mark A. Neumann Sharon L. Burnard Josephine A. Rinaldi Glen S. Patten Edward J. McMurchie 《Lipids》1992,27(3):169-176
Adult male marmoset monkeys were fed eicosapentaenoic acid (20∶5n−3) as the ethyl ester in diets containing either 32% (reference
diet, no added cholesterol) or 7% (atherogenic diet with 0.2% added cholesterol) linoleic acid (18∶2n−6) for 30 wk. No changes
were seen in the level of phosphatidylcholine (PC) or phosphatidylethanolamine (PE) but minor changes were observed in both
the sphingomyelin (SPM) and phosphatidylinositol plus phosphatidylserine (PI+PS) fractions of erythrocyte lipids. The extent
of total n−3 fatty acid incorporation into membrane lipids was higher in atherogenic diets (polyunsaturated/monounsaturated/saturated
(P/M/S) ratio 0.2∶0.6∶1.0) than reference diets (P/M/S ratio 1∶1∶1) and this was true for both PE (33.4±1.0%vs 24.3±1.1%) and PC (9.3±0.5%vs 4.9±0.3%). Although suitable controls for cholesterol effects were not included in the study, earlier results obtained with
marmosets lead us to believe such effects were probably small. Regardless of basic diet (atherogenic, reference), 20∶5n−3
was preferentially incorporated into PE (10.8±0.2%, 6.0±0.02%) while smaller amounts were incorporated into PC (6.9±0.4%,
3.2±0.2%). The major n−3 polyunsaturated fatty acid found in PE in response to dietary 20∶5n−3 was the elongation metabolite
22∶5n−3 in both the atherogenic (17.7±0.7%) and reference (14.3±1.0%) dietary groups; 22∶6n−3 levels were less affected by
diet (4.7±0.3% and 3.9±0.2%, respectively). The results can be interpreted to indicate an inverse relationship between the
amount of dietary 18∶2n−6 and incorporation of 20∶5n−3 into erythrocyte membrane phospholipids regardless of whether the major
dietary n−3 fatty acid was α-linolenate (18∶3n−3) or 20∶5n−3. This interpretation is supported by theoretical calculations. 相似文献
87.
These investigations are concerned with water-polymer interactions in polymer latices. It is known that water can act as a plasticizer for many solid polymers and cause a reduction in the glass transition temperature, Tg, of the amorphous regions. Experiments were carried out to determine whether pulsed n.m.r. techniques could be used to study the Tg of a polymer suspension and hence the influence of water and electrolyte on it. From T1 and T2 proton relaxation measurements as a function of temperature on polystyrene latex systems it was shown that the presence of water lowers the Tg of the polymer particles (by about 10°C), the effect being slightly greater in the presence of concentrated electrolyte. The extent of electrolyte penetration into the particles was deduced by studying relaxation as a function of particle diameter in latices containing paramagnetic Mn2+ ions. Using simple theories of relaxation and spin diffusion it was concluded that for all but the smallest particles electrolyte penetration is restricted to a very thin shell of the order of 1 nm. These conclusions were supported by the results of similar measurements on PTFE particles. 相似文献
88.
Xuqi Song John R. Grace Hsiaotao Bi C. Jim Lim Edward Chan Brian Knapper Craig McKnight 《加拿大化工杂志》2006,84(2):161-169
The hydrodynamics of fluid cokers were studied in a pressurized fully cylindrical cold model of diameter 483 mm, geometrically and dynamically scaled down by a factor of ~20 from commercial units. Differential pressure fluctuations, voidage distributions, solids momentum flux distributions and steady state gas mixing behaviour in the reactor section are compared for the same operating conditions with two kinds of particles, FCC and fluid coke. The voidage distributions and core‐annular flow structures in the reactor section were similar enough that either FCC or fluid coke particles can be used for cold modelling of fluid cokers. 相似文献
89.
Edward C. Nelson 《应用聚合物科学杂志》1985,30(7):2779-2786
The homogeneous graft copolymerization of acrylamide (AM) onto cellulose initiated by t-butylperoxy-2-ethylhexanoate in a cellulose solvent, N-methylmorpholine oxide (NMMO), was investigated. The method afforded water-soluble PAM-g-cellulose copolymers in fair yields. The copolymers produced are of low molecular weight (50,000–100,000 M?w). Little apparent homopolymerization was observed. 相似文献
90.
Edward Kostansek 《Journal of Coatings Technology and Research》2004,1(1):41-44
Coagulation of latex particles is most often carried out in the diffusion limited aggregation (DLA) regime where the time
for coagulation to take place is on the millisecond timescale. This process produces aggregates of low density, irregular
shape, and a broad particle size distributions. When the coagulation is carried out in the reaction limited aggregation (RLA)
regime, a coagulation time of about 1–120 sec, the system can be controlled by mixing to yield dense, spheroidal aggregates
with a very narrow particle size distribution. The important variables in the RLA process for butyl acrylate/methyl methacrylate
(BA/MMA) latexes were found to be mixing intensity, latex copolymer composition, and coagulation temperature. Dried aggregates
formed in the RLA process were found to have excellent powder flow properties and low dustiness. 相似文献