全文获取类型
收费全文 | 352684篇 |
免费 | 5288篇 |
国内免费 | 897篇 |
专业分类
电工技术 | 6798篇 |
综合类 | 1188篇 |
化学工业 | 52573篇 |
金属工艺 | 10950篇 |
机械仪表 | 9854篇 |
建筑科学 | 8954篇 |
矿业工程 | 1261篇 |
能源动力 | 9253篇 |
轻工业 | 33985篇 |
水利工程 | 3138篇 |
石油天然气 | 3751篇 |
武器工业 | 14篇 |
无线电 | 41722篇 |
一般工业技术 | 62331篇 |
冶金工业 | 74359篇 |
原子能技术 | 5669篇 |
自动化技术 | 33069篇 |
出版年
2021年 | 2698篇 |
2019年 | 2391篇 |
2018年 | 4296篇 |
2017年 | 4364篇 |
2016年 | 4832篇 |
2015年 | 3466篇 |
2014年 | 5090篇 |
2013年 | 15167篇 |
2012年 | 9656篇 |
2011年 | 12834篇 |
2010年 | 8815篇 |
2009年 | 10168篇 |
2008年 | 10448篇 |
2007年 | 10374篇 |
2006年 | 9236篇 |
2005年 | 11165篇 |
2004年 | 10319篇 |
2003年 | 9562篇 |
2002年 | 8242篇 |
2001年 | 8314篇 |
2000年 | 7533篇 |
1999年 | 8101篇 |
1998年 | 22691篇 |
1997年 | 15921篇 |
1996年 | 12184篇 |
1995年 | 9105篇 |
1994年 | 8091篇 |
1993年 | 7831篇 |
1992年 | 5493篇 |
1991年 | 5310篇 |
1990年 | 5183篇 |
1989年 | 5024篇 |
1988年 | 4928篇 |
1987年 | 4068篇 |
1986年 | 4184篇 |
1985年 | 4871篇 |
1984年 | 4350篇 |
1983年 | 4100篇 |
1982年 | 3710篇 |
1981年 | 3920篇 |
1980年 | 3643篇 |
1979年 | 3470篇 |
1978年 | 3315篇 |
1977年 | 4361篇 |
1976年 | 6003篇 |
1975年 | 2874篇 |
1974年 | 2694篇 |
1973年 | 2716篇 |
1972年 | 2252篇 |
1971年 | 2009篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
The effects of the cuticle and epicuticular waxes of grapefruit, strawberry and apple on the photodegradation and penetration of chlorpyrifos-methyl were studied. Photodegradation experiments were conducted by exposing the insecticide to the light of a xenon lamp in the presence of a film of wax extracted from the fruit surface. The half-life of chlorpyrifos-methyl irradiated in absence of waxes was 9.6 min. The half-lives of pesticide irradiated in the presence of wax extracts of apple, grapefruit and strawberry were 83, 34 and 26 min, respectively. In penetration studies, fruit with and without wax layers were treated with an aqueous suspension of pesticide. The penetration of the pesticide from the cuticle to the pulp was measured after 24 h. Samples without wax contained a higher total amount of insecticide than those with wax. No pesticide was detected in samples of apple and grapefruit pulp. Residues were detected in all fractions of strawberry. The waxes and cuticle appear to have some effect on the photodegradation and penetration of chlorpyrifos-methyl in fruit samples. 相似文献
92.
93.
Kruk Menno R.; Halász József; Meelis Wout; Haller József 《Canadian Metallurgical Quarterly》2004,118(5):1062
Aggressive behavior induces an adrenocortical stress response, and sudden stressors often precipitate violent behavior. Experiments in rats revealed a fast, mutual, positive feedback between the adrenocortical stress response and a brain mechanism controlling aggression. Stimulation of the aggressive area in the hypothalamus rapidly activated the adrenocortical response, even in the absence of an opponent and fighting. Hypothalamic aggression, in turn, was rapidly facilitated by a corticosterone injection in rats in which the natural adrenocortical stress response was prevented by adrenalectomy. The rapidity of both effects points to a fast, mutual, positive feedback of the controlling mechanisms within the time frame of a single conflict. Such a mutual facilitation may contribute to the precipitation and escalation of violent behavior under stressful conditions. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
94.
95.
This paper describes the methodology for simulating a reprographic ink with a ceramic ink based on a commercially available zirconia powder for direct ceramic ink-jet printing. Of over-riding importance was matching viscosity and this was tested systematically by using a mineral oil–hexane binary system. Of secondary importance was adjustment of the pressure defect behind the nozzle to compensate for small differences in surface tension. The inks tested in the wide array print-head were based on low electrical conductivity liquids to avoid damage to the electroding system. The organic binder for the zirconia ink was paraffin wax and the dispersant was a hydroxystearic acid based polyester. 相似文献
96.
Long-range prediction of the mobile-radio fading envelope is an enabling technology for many fading compensation approaches. Because the fading envelope is well modeled as a bandlimited process, it has special predictability properties. In this paper, we find a linear predictor that is optimal in the mean-square sense when the predictor impulse response is energy constrained. This solution may be used to determine the minimum mean squared error of a prediction based on past values that are corrupted with estimation errors. 相似文献
97.
98.
A fuzzy logic based-method for prognostic decision making in breast and prostate cancers 总被引:1,自引:0,他引:1
Seker H. Odetayo M.O. Petrovic D. Naguib R.N.G. 《IEEE transactions on information technology in biomedicine》2003,7(2):114-122
Accurate and reliable decision making in oncological prognosis can help in the planning of suitable surgery and therapy, and generally, improve patient management through the different stages of the disease. In recent years, several prognostic markers have been used as indicators of disease progression in oncology. However, the rapid increase in the discovery of novel prognostic markers resulting from the development in medical technology, has dictated the need for developing reliable methods for extracting clinically significant markers where complex and nonlinear interactions between these markers naturally exist. The aim of this paper is to investigate the fuzzy k-nearest neighbor (FK-NN) classifier as a fuzzy logic method that provides a certainty degree for prognostic decision and assessment of the markers, and to compare it with: 1) logistic regression as a statistical method and 2) multilayer feedforward backpropagation neural networks an artificial neural-network tool, the latter two techniques having been widely used for oncological prognosis. In order to achieve this aim, breast and prostate cancer data sets are considered as benchmarks for this analysis. The overall results obtained indicate that the FK-NN-based method yields the highest predictive accuracy, and that it has produced a more reliable prognostic marker model than both the statistical and artificial neural-network-based methods. 相似文献
99.
Chong D. Y. R. Lim B. K. Rebibis K. J. Pan S. J. Sivalingam K. Kapoor R. Sun A. Y. S. Tan H. B. 《Advanced Packaging, IEEE Transactions on》2006,29(4):674-682
The recent advancement in high- performance semiconductor packages has been driven by the need for higher pin count and superior heat dissipation. A one-piece cavity lid flip chip ball grid array (BGA) package with high pin count and targeted reliability has emerged as a popular choice. The flip chip technology can accommodate an I/O count of more than five hundreds500, and the die junction temperature can be reduced to a minimum level by a metal heat spreader attachment. None the less, greater expectations on these high-performance packages arose such as better substrate real estate utilization for multiple chips, ease in handling for thinner core substrates, and improved board- level solder joint reliability. A new design of the flip chip BGA package has been looked into for meeting such requirements. By encapsulating the flip chip with molding compound leaving the die top exposed, a planar top surface can be formed. A, and a flat lid can then be mounted on the planar mold/die top surface. In this manner the direct interaction of the metal lid with the substrate can be removed. The new package is thus less rigid under thermal loading and solder joint reliability enhancement is expected. This paper discusses the process development of the new package and its advantages for improved solder joint fatigue life, and being a multichip package and thin core substrate options. Finite-element simulations have been employed for the study of its structural integrity, thermal, and electrical performances. Detailed package and board-level reliability test results will also be reported 相似文献
100.
On the effect of spatial variances in historical rainfall time series to CSO performance evaluation.
Historical, high-resolution rain series are the backbone of modern combined sewer overflow (CSO) structure design. These rain series are the input to the computational estimation of the performance of the measures with respect to CSO pollution abatement. However, those historical precipitation measurements are available at only a few locations. Frequently rain series have to be used from gauging stations at a significant distance. In order to judge and to compensate for this influence an estimate between rain characteristics and combined sewer outflow (CSO) performance indicators would be useful. In this paper such correlations have been sought for a collection of 37 rain series covering large areas of Europe. It was found that the mean annual rain volume can explain most of the variances for the performance indicators Number of overflows and CSO volume. For explaining the spatial differences in the efficiency of the CSO structure another rain characteristic, i.e. the maximum event with a return period of one year, is to be used. 相似文献