全文获取类型
收费全文 | 66679篇 |
免费 | 5920篇 |
国内免费 | 3167篇 |
专业分类
电工技术 | 4158篇 |
技术理论 | 9篇 |
综合类 | 4332篇 |
化学工业 | 11271篇 |
金属工艺 | 3469篇 |
机械仪表 | 4005篇 |
建筑科学 | 4730篇 |
矿业工程 | 1901篇 |
能源动力 | 2047篇 |
轻工业 | 4154篇 |
水利工程 | 1287篇 |
石油天然气 | 3654篇 |
武器工业 | 735篇 |
无线电 | 8170篇 |
一般工业技术 | 8112篇 |
冶金工业 | 3519篇 |
原子能技术 | 819篇 |
自动化技术 | 9394篇 |
出版年
2024年 | 316篇 |
2023年 | 1110篇 |
2022年 | 2133篇 |
2021年 | 2933篇 |
2020年 | 2198篇 |
2019年 | 1866篇 |
2018年 | 2037篇 |
2017年 | 2148篇 |
2016年 | 1945篇 |
2015年 | 2706篇 |
2014年 | 3240篇 |
2013年 | 4052篇 |
2012年 | 4314篇 |
2011年 | 4512篇 |
2010年 | 3981篇 |
2009年 | 3886篇 |
2008年 | 3701篇 |
2007年 | 3547篇 |
2006年 | 3620篇 |
2005年 | 2968篇 |
2004年 | 2204篇 |
2003年 | 1911篇 |
2002年 | 1964篇 |
2001年 | 1782篇 |
2000年 | 1577篇 |
1999年 | 1616篇 |
1998年 | 1394篇 |
1997年 | 1197篇 |
1996年 | 984篇 |
1995年 | 827篇 |
1994年 | 624篇 |
1993年 | 508篇 |
1992年 | 403篇 |
1991年 | 320篇 |
1990年 | 233篇 |
1989年 | 213篇 |
1988年 | 165篇 |
1987年 | 105篇 |
1986年 | 108篇 |
1985年 | 78篇 |
1984年 | 37篇 |
1983年 | 32篇 |
1982年 | 45篇 |
1981年 | 34篇 |
1980年 | 25篇 |
1979年 | 21篇 |
1977年 | 16篇 |
1976年 | 19篇 |
1974年 | 13篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
81.
In this study, crisp and fuzzy multiple-goal optimization approaches are respectively introduced to design an optimal biocompatible solvent to a two-stage extractive fermentation with cell recycling for ethanol production. When designing a biocompatible solvent for the extractive fermentation process, many issues, such as extractive efficiency, conversion, amount of solvent utilized and so on, have to be considered. An interactive multiple-goal design procedure is introduced to determine a trade-off result in order to satisfy such contradicted goals. Both approaches could be iterated to solve the interactive multiple-goal design problem in order to yield a trade-off result. However, the crisp optimization design is a tedious task that requires the designer to provide various pairs of the upper bounds for the design problem to obtain the corresponding solution. The fuzzy optimization approach is able to be trade-off several goals simultaneously and to yield the overall satisfactory grade for the product/process design problem. 相似文献
82.
You-Im Chang Yu-Sheng Chen Wei-You Cheng 《Journal of the Chinese Institute of Chemical Engineers》2008,39(1):85-100
The deposition morphology of Brownian/non-Brownian particles within a constricted tube is investigated by applying the Brownian dynamics simulation method in the present paper. Two different geometric structures, the parabolic constricted tube (PCT) and the sinusoidal constricted tube (SCT), are adopted. The effect of various types of the total interaction energy curves of the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, and of the shadow area cast by those deposited particles, on the particles’ collection efficiencies are also examined. For the PCT structure, under the same interaction energy curve, it is found that the non-Brownian particles always own a higher collection efficiency than that of the Brownian particles. Since the deposition location moves closer to the constriction part of the tube, the collection efficiencies of the Brownian/non-Brownian particles increase with the decrease of flow velocity. The SCT behaves differently, it is found that the collection efficiencies of non-Brownian particles are only slightly higher than those of Brownian particles when SCT is adopted. The steep slope of the tube wall near the constriction part of SCT dominates the whole deposition process of Brownian/non-Brownian particles. In comparison with the available experimental data, it is found that the present method can give a good simulation result. 相似文献
83.
Abstract The whole DNA of soybean was implanted into four varieties of wheat of Zhongyu5, Huaiyin 9628, Wenyou 1, Jimai 5 respectively via ion-beam mediation. There were 5 plantsobtained whose protein content was higher than 18.5%, the highest one was 21.44%. There were 3plants obtained whose protein content was lower than 11.5%, the lowest one was 10.96%. We cansee that the whole DNA of soybean transformed into wheat via ion beam implantation can inducethe increase in wheat protein content dramatically. The result also shows that the transformationefficiency of different gene types of wheat receptor varies greatly that the implanting time has acertain effect on the efficiency of transformation. 相似文献
84.
Xing Li Zuoqing Wang Cheng Kuei Jen Viens M. Cheeke J.D.N. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1996,43(2):331-336
Theoretical and experimental investigations of thin-walled tube acoustic wave devices for gravimetric sensing applications are presented. Integrated sensor configurations have been demonstrated by employing a sol-gel processed thin piezoelectric lead zirconate titanate (PZT) film. This was coated coaxially on stainless steel tubes and interdigital transducers (IDT) fabricated as the transmitter and receiver on the curved tube surfaces. We have observed tube waves along both the axial and circumferential directions between 1 and 6.6 MHz. We have also analyzed the mass sensitivities of different modes propagating along the tubes and shown that high mass sensitivity can be achieved by keeping the tube wall thin 相似文献
85.
We study tandem queues with finite intermediate buffers and develop a general blocking scheme that unifies and generalizes various blocking schemes previously studied in the literature, such as manufacturing blocking, communication blocking, kanban blocking and its variations. In the general blocking scheme, job movement and service at each stage are controlled by three parameters, which represent, respectively, the upper limits (at that stage) on work-in-process inventory, finished goods inventory, and buffer space. We derive a set of recursive equations that characterize the dynamics of the system, in terms of the job completion and departure processes, and establish comparison results for these processes in the settings of stochastic ordering, variability ordering and stochastic convexity. Free of distributional assumptions, the results provide characterization of system behavior with respect to the control parameters as well as to the arrival and service processes. We also compare system performance under two different modes of operation: make-to-order versus make-to-stock, and demonstrate the trade-off between improving service and reducing inventory. Numerical studies are also presented to illustrate the diversity of performance trade-off, including composition of inventory, offered by the general model.Supported in part by NSF under grant ECS-89-96201. 相似文献
86.
化学模式识别法在钢铁工业中的若干应用 总被引:1,自引:0,他引:1
本文涉及一种崭新的非函数数据处理法及其在工业诊断和优化中的应用。并对其进行要因分析和优化决策的原理作了介绍。结合钢铁工业生产中的实例进行了分析。还探讨了该方法在钢铁工业中应用的意义。 相似文献
87.
The author presents a personal account of the search for a design procedure for Yagi-Uda antenna arrays yielding a maximum gain, or directivity if element losses are neglected. Results on current distributions in the array are briefly reviewed. The analytical approach used to achieve gain optimization by means spacing and length perturbations is sketched. By using both spacing and length perturbations, it was possible to find the optimized array analytically in a systematic way, some examples having gain increases of nearly 80%. The effects of finite dipole radius and mutual coupling were included in the theoretical treatment 相似文献
88.
89.
RH Rau YL Chan HI Chuang CR Cheng KL Wong KH Wu TT Wei 《Canadian Metallurgical Quarterly》1997,35(2):113-118
While current psychiatric taxonomies recognise a classification of amphetamine dependence, derived from the notion of an alcohol dependence syndrome, little research has validated that such a condition exists for this drug. Current amphetamine users (N = 331), were interviewed using the World Health Organization operationalisation of DSM-III-R substance dependence criteria, and a measure of the psychological components of dependence. Structural analyses indicated that a unidimensional dependence syndrome as assessed by DSM-III-R and DSM-IV criteria exists for amphetamine, and that physiological, psychological and behavioural indicators were all important in accounting for the variance in responses. It was demonstrated that the concept of a dependence syndrome is applicable to amphetamine, and that the inclusion of the amphetamine dependence syndrome in DSM-III-R and DSM-IV is valid. 相似文献
90.