全文获取类型
收费全文 | 26489篇 |
免费 | 3301篇 |
国内免费 | 3030篇 |
专业分类
电工技术 | 1135篇 |
技术理论 | 2篇 |
综合类 | 2134篇 |
化学工业 | 4739篇 |
金属工艺 | 402篇 |
机械仪表 | 2471篇 |
建筑科学 | 2896篇 |
矿业工程 | 886篇 |
能源动力 | 1097篇 |
轻工业 | 4286篇 |
水利工程 | 1348篇 |
石油天然气 | 746篇 |
武器工业 | 207篇 |
无线电 | 2501篇 |
一般工业技术 | 2078篇 |
冶金工业 | 917篇 |
原子能技术 | 442篇 |
自动化技术 | 4533篇 |
出版年
2024年 | 183篇 |
2023年 | 491篇 |
2022年 | 1029篇 |
2021年 | 1377篇 |
2020年 | 1255篇 |
2019年 | 1262篇 |
2018年 | 1153篇 |
2017年 | 1137篇 |
2016年 | 1249篇 |
2015年 | 1194篇 |
2014年 | 1705篇 |
2013年 | 2092篇 |
2012年 | 1846篇 |
2011年 | 1987篇 |
2010年 | 1429篇 |
2009年 | 1390篇 |
2008年 | 1345篇 |
2007年 | 1629篇 |
2006年 | 1377篇 |
2005年 | 1264篇 |
2004年 | 1014篇 |
2003年 | 952篇 |
2002年 | 701篇 |
2001年 | 562篇 |
2000年 | 433篇 |
1999年 | 401篇 |
1998年 | 384篇 |
1997年 | 343篇 |
1996年 | 254篇 |
1995年 | 231篇 |
1994年 | 194篇 |
1993年 | 174篇 |
1992年 | 125篇 |
1991年 | 90篇 |
1990年 | 77篇 |
1989年 | 68篇 |
1988年 | 52篇 |
1987年 | 41篇 |
1986年 | 44篇 |
1985年 | 37篇 |
1984年 | 44篇 |
1983年 | 29篇 |
1982年 | 21篇 |
1981年 | 56篇 |
1980年 | 27篇 |
1979年 | 13篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1973年 | 5篇 |
1951年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
21.
On irrigation schemes with rotational irrigation systems in semiarid tropics, the existing rules for water allocation are based on applying a fixed depth of water with every irrigation irrespective of the crops, their growth stages, and soils on which these crops are grown. However, when water resources are scarce, it is necessary to allocate water optimally to different crops grown in the irrigation scheme taking account of different soils in the command area. Allocating water optimally may lead to applying less water to crops than is needed to obtain the maximum yield. In this paper, a three stage approach is proposed for allocating water from a reservoir optimally based on a deficit irrigation approach, using a simulation-optimization model. The allocation results with a deficit irrigation approach are compared for a single crop (wheat) in an irrigation scheme in India, first with full irrigation (irrigation to fill the root zone to field capacity) and second with the existing rule. The full irrigation with a small irrigation interval was equivalent to adequate irrigation (no stress to the crop). It is found that practicing deficit irrigation enables the irrigated area and the total crop production in the irrigation scheme used for the case study to be increased by about 30–45% and 20–40%, respectively, over the existing rule and by 50 and 45%, respectively, over the adequate irrigation. Allocation of resources also varied with soil types. 相似文献
22.
Yilmaz Muslu 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1991,51(4):449-460
A dispersed flow model previously developed to study substrate utilization in unsaturated media was experimentally verified and its practical application was considered. For this purpose, measurements were made using tap water and a synthetic feed solution. The importance of the change in fluid regime as regards to the simultaneous transport and reaction within biological filters were demonstrated. The effect of drop formation and the breakage of liquid jets inside the filters on substrate utilization was also shown. 相似文献
23.
采用独特的分离方法和途径,综合使用多种质谱分析技术,如电子轰击谱(EI/MS)、场解吸谱(FD/MS)、快速原子轰击谱(FAB/MS)、色/质联用等,对高档齿轮油的主剂-含磷极压剂的结构组成进行了较为详尽的分析研究,提出了复酯胺盐的结构组成。 相似文献
24.
C. C. Price
M. Salama
《Computers & Mathematics with Applications》1993,26(12):17-24Criteria are established to determine the optimal policy for allocating a set of uniform tasks onto a multiprocessor hypercube ensemble. It is shown that the optimal policy depends on the ratio of computation to intertask communication required by the distributed program, and that based on this ratio, tasks should be placed either all on one processor or uniformly distributed over the largest possible hypercube. 相似文献
25.
26.
Thomas J. R. Hughes Arif Masud Isaac Harari 《International journal for numerical methods in engineering》1995,38(19):3193-3210
Finite element methods for dynamic analysis employing elements with drilling degrees of freedom are presented. The formulation is based on a variational principle in which displacements and rotations are interpolated independently. The issue of zero masses corresponding to rotational degrees of freedom is addressed and techniques for defining consistent and lumped rotational mass matrices are presented. 相似文献
27.
Rates of ammonia (NH3) loss from a ryegrass sward measured using a system of small wind tunnels were compared with concurrent measurements made using a micrometeorological mass balance method. Measurements were made during two experiments within a circular plot (radius 10m) treated with urea at a rate of 200kgNha?1. In the first experiment, air speed through the tunnels was adjusted as necessary to maintain a value of approximately 1ms?1. This value differed on most occasions from the mean ambient wind speed which was measured at a height of 250mm and which ranged from 0.61 to 2.95ms?1. Rates of loss measured using the wind tunnels differed by a factor of between two and five from those measured using the mass balance method; there was no consistent pattern in the differences between the rates of loss. The total losses of NH3 measured during 15 days were equivalent to 49.1 and 30.2kg Nha?1 for the mass balance and wind tunnel methods, respectively. In the second experiment, air speed through the tunnels was adjusted as necessary to maintain a value as close as possible to the mean ambient wind speed measured at a height of 250mm. Rates of NH3 loss measured using the two methods did not differ significantly; total losses of NH3 during 17 days were equivalent to 96.9 and 101kg Nha?1 for the mass balance and wind tunnel methods, respectively. The difference between the findings of the two experiments could be attributed to the direct effect of air speed through the tunnels rather than to differences between ambient temperatures and those inside the tunnels. During and following periods of rain the rates of loss measured using the tunnels were up to six times greater than those observed with the mass balance method. Rates of loss measured by the two methods became similar again when the tunnels were moved following rain. The study demonstrates that enclosures can be designed and operated to provide reliable measurements of the rate of NH3 loss from grassland. Potential applications of the two methods are discussed. 相似文献
28.
29.
A methodology for evaluating the reactivity of titanium with mould materials during casting has been developed. Microhardness
profiles and analysis of oxygen contamination have provided an index for evaluation of the reactivity of titanium. Microhardness
profile delineates two distinct regions, one of which is characterised by a low value of hardness which is invariant with
distance. The reaction products are uniformly distributed in the metal in this region. The second is characterised by a sharp
decrease in microhardness with distance from the metal-mould interface. It represents a diffusion zone for solutes that dissolve
into titanium from the mould. The qualitative profiles for contaminants determined by scanning electron probe microanalyser
and secondary ion mass spectroscopy in the as-cast titanium were found to be similar to that of microhardness, implying that
microhardness can be considered as an index of the contamination resulting from metal-mould reaction. 相似文献
30.
Martijn Hendriks Barend van den Nieuwelaar Frits Vaandrager 《International Journal on Software Tools for Technology Transfer (STTT)》2006,8(6):633-647
For a case-study of a wafer scanner from the semiconductor industry it is shown how model checking techniques can be used
to compute (1) a simple yet optimal deadlock avoidance policy, and (2) an infinite schedule that optimizes throughput. in
the absence of errors. Deadlock avoidance is studied based on a simple finite state model using Smv, and for throughput analysis a more detailed timed automaton model has been constructed and analyzed using the Uppaal tool. The Smv and Uppaal models are formally related through the notion of a stuttering bisimulation. The results were obtained within 2 weeks, which
confirms once more that model checking techniques may help to improve the design process of realistic, industrial systems.
Methodologically, the case study is interesting since two models were used to obtain results that could not have been obtained
using only a single model.
Supported by the European Community Project IST-2001-35304 (Ametist), http://ametist.cs.utwente.nl/. 相似文献