全文获取类型
收费全文 | 566743篇 |
免费 | 6227篇 |
国内免费 | 1004篇 |
专业分类
电工技术 | 10508篇 |
综合类 | 466篇 |
化学工业 | 90039篇 |
金属工艺 | 23335篇 |
机械仪表 | 18498篇 |
建筑科学 | 12529篇 |
矿业工程 | 4312篇 |
能源动力 | 14429篇 |
轻工业 | 45755篇 |
水利工程 | 6941篇 |
石油天然气 | 14961篇 |
武器工业 | 39篇 |
无线电 | 60277篇 |
一般工业技术 | 116222篇 |
冶金工业 | 95559篇 |
原子能技术 | 14682篇 |
自动化技术 | 45422篇 |
出版年
2021年 | 5481篇 |
2019年 | 5267篇 |
2018年 | 9201篇 |
2017年 | 9409篇 |
2016年 | 9831篇 |
2015年 | 6025篇 |
2014年 | 10243篇 |
2013年 | 26100篇 |
2012年 | 15772篇 |
2011年 | 21087篇 |
2010年 | 16968篇 |
2009年 | 18817篇 |
2008年 | 19068篇 |
2007年 | 18765篇 |
2006年 | 16286篇 |
2005年 | 14743篇 |
2004年 | 14007篇 |
2003年 | 13690篇 |
2002年 | 13246篇 |
2001年 | 12850篇 |
2000年 | 12330篇 |
1999年 | 12011篇 |
1998年 | 27648篇 |
1997年 | 20039篇 |
1996年 | 15627篇 |
1995年 | 12006篇 |
1994年 | 10859篇 |
1993年 | 10612篇 |
1992年 | 8332篇 |
1991年 | 8102篇 |
1990年 | 7990篇 |
1989年 | 7763篇 |
1988年 | 7478篇 |
1987年 | 6748篇 |
1986年 | 6534篇 |
1985年 | 7392篇 |
1984年 | 6700篇 |
1983年 | 6437篇 |
1982年 | 5776篇 |
1981年 | 5896篇 |
1980年 | 5630篇 |
1979年 | 5733篇 |
1978年 | 5663篇 |
1977年 | 6178篇 |
1976年 | 7685篇 |
1975年 | 5108篇 |
1974年 | 4903篇 |
1973年 | 4980篇 |
1972年 | 4279篇 |
1971年 | 4038篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
J. Balakrishnan W. A. Sethares C. R. Johnson 《International Journal of Adaptive Control and Signal Processing》2002,16(4):309-323
A method of approximate channel identification is proposed that is based on a simplification of the correlation estimator. Despite the numerical simplification (no multiplications or additions are required, only comparisons and an accumulator), the performance of the proposed estimator is not significantly worse than that of the standard correlation estimator. A free (user selectable) parameter moves ‘smoothly’ from a situation with small sum‐squared channel estimation error but hard‐to‐identify channel peaks, to one with a larger sum‐squared estimation error but easy‐to‐identify channel peaks. The proposed estimator is shown to be biased and its behaviour is analysed in a number of situations. Applications of the proposed estimator to sparsity detection, symbol timing recovery and to the initialization of blind equalizers are suggested. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
902.
This study tried to investigate, by the power comsumption technique, the influence of the powder's and solvent's properties on wet granulation.
It could be shown that the required amount of granulation liquid decreases when the particle size of the powder to be granulated increases. This relationship is however only true when the particle size distribution of the powder to be granulated is rather narrow.
Powders having the same solubility in different solvents require the same optimal liquid quantity for granulation, but the properties of resulting granules depend on surface tension and wetting properties of the solvent.
When the powder to be granulated contains crystallisation water, the temperature rising in the mixer can be sufficient to liberate this water, which must be taken into account in the optimal granulation liquid requirement.
The effect of a macromolecular binder (PVP, HPMC) has also been studied: the optimal liquid quantity required changes with the kind of binder used and the manufacturing process (binder used in solution or added as dry powder).
It was also shown that in the case of lactose, the optimal quantity of PVP or HPMC can be determined from the power consumption records and from the granules friability studies 相似文献
It could be shown that the required amount of granulation liquid decreases when the particle size of the powder to be granulated increases. This relationship is however only true when the particle size distribution of the powder to be granulated is rather narrow.
Powders having the same solubility in different solvents require the same optimal liquid quantity for granulation, but the properties of resulting granules depend on surface tension and wetting properties of the solvent.
When the powder to be granulated contains crystallisation water, the temperature rising in the mixer can be sufficient to liberate this water, which must be taken into account in the optimal granulation liquid requirement.
The effect of a macromolecular binder (PVP, HPMC) has also been studied: the optimal liquid quantity required changes with the kind of binder used and the manufacturing process (binder used in solution or added as dry powder).
It was also shown that in the case of lactose, the optimal quantity of PVP or HPMC can be determined from the power consumption records and from the granules friability studies 相似文献
903.
904.
905.
Mechanical properties of polypropylene-g-poly(methacrylic acid) fibers, prepared by graft copolymerization of methacrylic acid onto polypropylene fiber using simultaneous gamma ray irradiation technique, were evaluated. In general, an improvement in the mechanical behavior of the polypropylene fiber by grafting was observed. Denier and initial modulus of the fiber showed a linear increase with the percent graft, and elongation showed an opposite trend. The results have been explained in terms of reinforcing effect of poly(methacrylic acid) grafts and reduction in the segmental mobility of the polymeric chains. Tenacity also increases up to certain graft level, beyond which a sharp decrease occurs, probably due to the influence on the compactness of the macromolecular chains with the further grafting. 相似文献
906.
C. L. J. A. Verbraak J. Van Dam A. K. Van Der Vegt 《Polymer Engineering and Science》1985,25(7):431-433
Orientation-induced crystallization of crystallizable polymer melts can occur, under certain conditions, during flow through converging channels. Attempts have been made to achieve this phenomenon in a two-phase system, i.e., during simultaneous extrusion of a continuous concentric core of polypropylene within a polystyrene matrix through a conical duct. On one occasion, using Carlona P SY6100 (MFI = 11.0) with Hostyren N2000-V-01 (MFI = 25.0), a highly oriented polypropylene thread with a modulus of 14.6 GPa and a melting point of 178°C was extruded at a die temperature of approximately 170°C and a pressure lower than 40 MPa. It is, in principle, possible to form highly oriented, fiber-like structures as reinforcing elements in a polymer matrix. 相似文献
907.
Juan Carlos Benítez Carlos A. Giúdice Vicente J. D. Rascio 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1985,35(8):387-394
This paper discusses the bioactivity of antifouling paints based on organotin toxicants, such as tributyltin fluoride (TBTF) and triphenyltin fluoride (TPTF). These compounds were used alone or mixed as the main toxicant in formulations. The use of TPTF or mixtures of TPTF and TBTF, with vinyl binders, led to paints with satisfactory bioactivity during a 24 months immersion period. With the same binders, TBTF alone provided only 12 months of antifouling protection. The correlation coefficients calculated from the fouling attachment values and the rosin content in the binder showed that the bioactivity of the tested formulations depended on the solubility of the toxicant in sea water and on the composition and solubility of the binders. 相似文献
908.
The nature of damage produced by low energy Ar+ ion and Ar atom milling in the II–VI semiconductors CdTe, ZnS and ZnSe is studied in detail by conventional and high resolution transmission electron microscopy. It is demonstrated that the damage consists of dense arrays of small dislocation loops near to each milled surface. When ion or atom milling of this type is used for thin specimen preparation prior to microscopy the loop arrays can seriously obscure images and so complicate their interpretation. This problem concerning the presence of artifactual defects can be greatly reduced by the use of reactive I+ ion milling for specimen thinning and, in the case of CdTe, spurious dislocation loop formation can be completely suppressed. 相似文献
909.
A. I. Ivaneshkin 《Cybernetics and Systems Analysis》1991,27(6):833-840
The paper considers integrated optimization of a single-server semi-Markov queue with input conflicts, controllable message size, and a finite buffer with different types of storage organization. The optimization is based on an additive performance criterion.Translated from Kibernetika i Sistemnyi Analiz, No. 6, pp. 45–53, November–December, 1991. 相似文献
910.
It is shown that the existence of duplicate values in some attribute columns has a significant impact on the computational complexity of the sorting and joining operations. This is especially true when the number of distinct tuple values is a small fraction of the total number of tuples. The authors characterize a multirelation M (n , L ) by its cardinality n and the number of distinct elements L it contains. Under this characterization, the worst time complexity of sorting such a multirelation with binary comparisons as basic operations is investigated. Upper and lower bounds on the number of three-branch comparisons needed to sort such a multirelation are established. Thereafter, the methodology used to study the complexity of sorting is applied to the natural join operation. It is shown that the existence of duplicate values in the join attribute columns can be exploited to reduce the computational complexity of the natural join operation 相似文献