全文获取类型
收费全文 | 24478篇 |
免费 | 1743篇 |
国内免费 | 950篇 |
专业分类
电工技术 | 2379篇 |
技术理论 | 6篇 |
综合类 | 2007篇 |
化学工业 | 511篇 |
金属工艺 | 576篇 |
机械仪表 | 2028篇 |
建筑科学 | 9516篇 |
矿业工程 | 381篇 |
能源动力 | 524篇 |
轻工业 | 105篇 |
水利工程 | 816篇 |
石油天然气 | 219篇 |
武器工业 | 250篇 |
无线电 | 1069篇 |
一般工业技术 | 1225篇 |
冶金工业 | 529篇 |
原子能技术 | 81篇 |
自动化技术 | 4949篇 |
出版年
2024年 | 73篇 |
2023年 | 299篇 |
2022年 | 532篇 |
2021年 | 634篇 |
2020年 | 717篇 |
2019年 | 540篇 |
2018年 | 474篇 |
2017年 | 690篇 |
2016年 | 737篇 |
2015年 | 872篇 |
2014年 | 1851篇 |
2013年 | 2063篇 |
2012年 | 1462篇 |
2011年 | 1723篇 |
2010年 | 1402篇 |
2009年 | 1541篇 |
2008年 | 1424篇 |
2007年 | 1677篇 |
2006年 | 1458篇 |
2005年 | 1235篇 |
2004年 | 981篇 |
2003年 | 816篇 |
2002年 | 724篇 |
2001年 | 616篇 |
2000年 | 505篇 |
1999年 | 397篇 |
1998年 | 299篇 |
1997年 | 265篇 |
1996年 | 194篇 |
1995年 | 191篇 |
1994年 | 176篇 |
1993年 | 115篇 |
1992年 | 89篇 |
1991年 | 89篇 |
1990年 | 62篇 |
1989年 | 40篇 |
1988年 | 32篇 |
1987年 | 32篇 |
1986年 | 11篇 |
1985年 | 37篇 |
1984年 | 26篇 |
1983年 | 27篇 |
1982年 | 16篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 10篇 |
1963年 | 1篇 |
1962年 | 1篇 |
1958年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The urban-rural planning inspector system of China is hierarchical supervision over local governments from the Central Government in respect of town and country development. The comparative analysis on planning inspection system of the UK may provide experience in seeking solutions to the problems occurring in the system of China. The planning inspector system of China can be improved in six aspects such as establishing the legal status, setting up the planning inspection agency, completing the personnel management system, enhancing the legal binding force, building the internal and external supervision channel, supplementing the relieve function, and establishing the coordination mechanism of various internal supervisions. 相似文献
992.
Valerie Spicer Andrew A. Reid Jordan Ginther Hasti Seifi Vahid Dabbaghian 《Computers, Environment and Urban Systems》2012
Criminologists have extensively researched the problems generated by licensed establishments. Violent offending and disorderly behavior resulting from pubs, taverns, dance clubs and bars are of particular interest to this field of study. The relative density of these liquor establishments has been found to be associated with the level of violence and disorder in surrounding areas. A complex systems approach can be used to further understand the dynamic interplay between licensed establishments, violent offending and disorder, and urban planning decisions. The model presented here utilizes cellular automata as the mathematical framework to view the varying impact of liquor licensing density on crime. This study uses a sample of liquor establishments and crime data from the City of Vancouver in British Columbia. The cellular automata model incorporates transition rules which govern the change of city blocks from low-risk blocks to high-risk blocks. The results represented by a 50 × 50 cellular grid show that high-risk blocks multiply when liquor licenses are grouped. Two scenarios are presented to contrast the impact of grouping high-risk blocks which contain more liquor establishments and dispersing such blocks. A third scenario demonstrates how increasing the positive influence in a grouped scenario stops high-risk blocks from taking over the entire grid. Future iterations of this model will incorporate census data, public transportation data, land use data and entertainment districts from other cities to further analyze the effect of licensed establishments on the distribution of crime. 相似文献
993.
The use of portable short-throat flume in the field is an emerging technique developed for water discharges measurement of inlet in the field. Based on the principle of critical flow and RNG k–ε three-dimensional turbulence model along with the TruVOF technique, experiments and corresponding simulations were performed for 16 working conditions on the 76 mm width flume with discharges up to 40.01 L/s to determine its hydraulic performance. Hydraulic performance of the flume obtained from simulation analyses were later compared with observed results based on time-averaged flow field, flow pattern, Froude number and velocity distribution. Comparison yielded a solid agreement between results from two methods with relative error below ±10%. Regression models developed for upstream depth versus discharge under different working conditions were satisfying with the relative error of 9.16%, which met the common requirements of flow measurement in irrigation areas. Compared to the long-throat flume, head loss of portable short-throat flume in the field was significantly less. Further, head loss under the free flow condition was less than that under the submerged flow condition of portable short-throat flume with a flat base in the field. 相似文献
994.
In this paper, we propose a multi-period mixed-integer linear programming model for optimal enterprise-level planning of industrial gas operations. The objective is to minimize the total cost of production and distribution of liquid products by coordinating production decisions at multiple plants and distribution decisions at multiple depots. Production decisions include production modes and rates that determine power consumption. Distribution decisions involve source, destination, quantity, route, and time of each truck delivery. The selection of routes is a critical factor of the distribution cost. The main goal of this contribution is to assess the benefits of optimal coordination of production and distribution. The proposed methodology has been tested on small, medium, and large size examples. The results show that significant benefits can be obtained with higher coordination among plants/depots in order to fulfill a common set of shared customer demands. The application to real industrial size test cases is also discussed. 相似文献
995.
This paper studies a real-world problem arising in the area of motorail transportation. The considered problem deals with the loading of cars and motorcycles onto motorail wagons under realistic technical and legal constraints. The load planning problem, introduced as motorail transportation problem (MTP), occurs during the booking process and afterwards during the loading process at motorail terminals. Optimization based decision support is highly valuable due to the combinatorial nature of these problems. In practical applications, the fast generation of good solutions is essential. Previous model formulations in literature reveal considerable optimality gaps in real-world instances. Hence, we propose and evaluate two novel integer linear programming formulations of the MTP. The first formulation is a simplified reformulation of the original problem, uses less variables and provides a tighter LP relaxation. The second model is a column-generation formulation of the reformulated model which is solved using branch-and-price. Both novel model formulations are compared and evaluated on the basis of real-world data sets and considerably outperform previous approaches in terms of solution quality and speed. 相似文献
996.
Production planning is concerned with finding a release plan of jobs into a manufacturing system so that its actual outputs over time match the customer demand with the least cost. For a given release plan, the system outputs, work in process inventory (WIP) levels and job completions, are non-stationary bivariate time series that interact with time series representing customer demand, resulting in the fulfillment/non-fulfillment of demand and the holding cost of both WIP and finished-goods inventory. The relationship between a release plan and its resulting performance metrics (typically, mean/variance of the total cost and the fill rate) has proven difficult to quantify. This work develops a metamodel-based Monte Carlo simulation (MCS) method to accurately capture the dynamic, stochastic behavior of a manufacturing system, and to allow real-time evaluation of a release plan's performance metrics. This evaluation capability is then embedded in a multi-objective optimization framework to search for near-optimal release plans. The proposed method has been applied to a scaled-down semiconductor fabrication system to demonstrate the quality of the metamodel-based MCS evaluation and the results of plan optimization. 相似文献
997.
车站建筑群作为轨道类交通体系中的一部分,具有城市代表性,它是城市基础性建筑。要把车站建筑工程与其他基础性工程视为同等重要的工作来考虑。在逐步完善和优化资源配置的过程中,最终建设与这个城市发展配套的现代化交通轨道衔接体系。 相似文献
998.
Production planning of final assembly systems is a challenging task, as the often fluctuating order volumes require flexible solutions. Besides, the calculated plans need to be robust against the process-level disturbances and stochastic nature of some parameters like manual processing times or machine availability. In the paper, a simulation-based optimisation method is proposed that utilises lower level shop floor data to calculate robust production plans for final assembly lines of a flexible, multi-stage production system. In order to minimise the idle times when executing the plans, the capacity control that specifies the proper operator–task assignments is also determined. The analysed multi-stage system is operated with a pull strategy, which means that the production at the final assembly lines generates demands for the preceding stages providing the assembled components. In order to guarantee the feasibility of the plans calculated for the final assembly lines, a decomposition approach is proposed to optimise the production plan of preceding stages. By this way, the robust production can be ensured resulting in reduced losses and overall production costs even though the system is exposed to changes and disturbances. 相似文献
999.
如何改善商务区的可持续发展是一个重要的课题。本文着重研究了商务园区的设计方法以及一个可持续的商务园区的特征。通过介绍悉尼和英国的两个商务花园案例,分析了商务花园的可持续设计。 相似文献
1000.
文章分析了濉溪县中小河流治理存在问题及规划的必要性和紧迫性,提出了治理对策。 相似文献