全文获取类型
收费全文 | 114776篇 |
免费 | 13675篇 |
国内免费 | 7087篇 |
专业分类
电工技术 | 21547篇 |
技术理论 | 14篇 |
综合类 | 9647篇 |
化学工业 | 14156篇 |
金属工艺 | 3859篇 |
机械仪表 | 4895篇 |
建筑科学 | 13423篇 |
矿业工程 | 3470篇 |
能源动力 | 14429篇 |
轻工业 | 3592篇 |
水利工程 | 3029篇 |
石油天然气 | 4864篇 |
武器工业 | 1069篇 |
无线电 | 8929篇 |
一般工业技术 | 11138篇 |
冶金工业 | 5401篇 |
原子能技术 | 2086篇 |
自动化技术 | 9990篇 |
出版年
2024年 | 714篇 |
2023年 | 2293篇 |
2022年 | 3914篇 |
2021年 | 4458篇 |
2020年 | 4827篇 |
2019年 | 4253篇 |
2018年 | 3759篇 |
2017年 | 4500篇 |
2016年 | 4858篇 |
2015年 | 4869篇 |
2014年 | 7774篇 |
2013年 | 7778篇 |
2012年 | 8328篇 |
2011年 | 9146篇 |
2010年 | 6865篇 |
2009年 | 7072篇 |
2008年 | 6547篇 |
2007年 | 7215篇 |
2006年 | 6068篇 |
2005年 | 4779篇 |
2004年 | 4121篇 |
2003年 | 3510篇 |
2002年 | 3018篇 |
2001年 | 2538篇 |
2000年 | 2195篇 |
1999年 | 1791篇 |
1998年 | 1442篇 |
1997年 | 1130篇 |
1996年 | 1008篇 |
1995年 | 814篇 |
1994年 | 782篇 |
1993年 | 569篇 |
1992年 | 444篇 |
1991年 | 396篇 |
1990年 | 334篇 |
1989年 | 278篇 |
1988年 | 216篇 |
1987年 | 166篇 |
1986年 | 116篇 |
1985年 | 143篇 |
1984年 | 114篇 |
1983年 | 71篇 |
1982年 | 98篇 |
1981年 | 40篇 |
1980年 | 56篇 |
1979年 | 32篇 |
1978年 | 15篇 |
1977年 | 16篇 |
1959年 | 13篇 |
1951年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
31.
This paper presents Bayes estimators for the reliability measures of the individual components in a multi-component systems in the presence of masked system life test data. The life time distributions of the system components are assumed to be geometric with different parameters. Two-sided Bayesian probability intervals of the parameters are also derived. Numerical simulation study is given in order to: (i) explain how one can apply the theoretical results obtained, (ii) study the influence of the sample size and masking level on the accuracy of point estimates. 相似文献
32.
李杏娟 《冶金标准化与质量》2003,41(5):45-48
论述了湘钢目前利用煤岩学数据指标判定进厂煤质情况,指导煤场分堆,优化配煤结构.同时在保证焦炭质量稳定的前提下,配入少量低灰的气煤,有效地提高了焦炭质量. 相似文献
33.
节能降耗提高矿山效益 总被引:1,自引:0,他引:1
节能降耗是每一个矿山提高经济效益的有效途径。我们采取提高球磨机处理能力,降低单耗;利用“分时计价”政策,采用“避峰作业”;使用新设备等措施节能降耗,提高矿山经济效益。 相似文献
34.
Argyris G. Kagiannas Thanassis Didis Dimitris Th. Askounis John Psarras 《国际能源研究杂志》2003,27(2):173-186
The needs that an energy supply system must meet are constantly changing, due to technological, social and political reasons. Effective energy planning is a dynamic process that is repeated periodically and adjusts to changing conditions. Energy decision makers and planners are no longer able to rely on inductive decision making since they have to investigate the effect of various decision parameters and possible future changes. To help in this process, models have been developed where estimates of future load growth, candidate power plants, fuels and other key factors can be introduced, from which the planners can evaluate decision parameters and the available alternatives. The paper presents the different methodologies and practices that are used by 11 energy models for energy demand forecasting, supply side management and generation expansion planning, demand side management and integrated resource planning. The paper concludes to the presentation of a strategic appraisal of the examined energy models appropriate for energy planning in Mozambique. Three models are proposed for conducting demand forecasting, generation expansion planning and demand side management. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
35.
36.
This study addresses the rolling and lifting probabilities for sediment entrainment by incorporating the probabilistic features of the turbulent fluctuation and bed grain geometry. The lognormally distributed instantaneous velocity and uniformly distributed initial grain position, along with a relation between lift coefficient and particle Reynolds number, are used to extend the theoretical formulation of the entrainment probabilities in smooth-bed flows. The two threshold conditions identified herein enable us to precisely define the probabilities of entrainment in the rolling and lifting modes. The results obtained in this study coincide well with the published data. The lifting probability increases monotonously with the dimensionless shear stress θ, which is consistent with the earlier results yet displays improved agreement with the experimental data. The maximum value of rolling probability, with a magnitude of 0.25, occurs at θ ≈ 0.15. For θ<0.05 (or θ>0.6), the rolling (or lifting) probability makes up more than 90% of the total entrainment probability and thus can be used as an approximation to the total probability of entrainment. The proposed rolling and lifting probabilities are further linked to the two separate criteria for incipient motion to explore the critical entrainment probabilities. The results reveal that a consistent probability corresponding to the critical state of sediment entrainment cannot be found. 相似文献
37.
本文通过对中州分公司正在考虑建设的信息网建设实际情况,结合山东分公司、广西分公司取得的经验,对计量管理信息网的应用进行了探讨。 相似文献
39.
P. S. Lawson 《Biomass & bioenergy》1992,2(1-6):319-330
In recent years it has been recognised by an increasing number of nations that there is considerable energy potential within MSW. As a result many countries have established R,D& D programmes to examine methods of exploiting this potential. The IEA's MSW Conversion Activity was set up in 1986 to provide an infrastructure for sharing information and co-ordinating work in this area internationally. This Activity was extended in 1989 and currently a total of 9 nations participate in it.
To cope with the wide scope of the area (encompassing both biological and thermal processing of MSW) the Activity was divided into three subgroups or Expert Working Groups (EWGs). Each of these dealt with a distinct area of expertise:
- 1. •Downstream effects of source separation and screening of MSW
- 2. •Sampling and analytical protocols
- 3. •Landfill gas
In addition to these groups a central secretariat based at Harwell (UK) has provided guidance, established and administered databases of contacts and produced a series of national reports.
This paper describes the achievements of the Activity and discusses work proposed for the future. 相似文献
40.
Uniformity of bulk density distribution during the die filling process is required to minimize quality problems, such as distortion and cracking, for powder compacts. Understanding the die filling process is necessary in ensuring a uniform powder deposition. The second-generation pressure deposition tester (PDT-II) was used to investigate the deposition process and final pressure distribution of powder filling in toroidal, cylindrical, and E-shaped dies. All tests were conducted using a spray-dried free-flowing granular powder. The results indicated that for toroidal dies: (1) the area around 0° orientation (the leeward end) had the highest pressure values (1186.7 to 2498.0 Pa), with the average pressure values of the remaining area 353.7-648.0 Pa; (2) the pressure distribution was symmetrical about the centerline parallel to the feed shoe movement direction; (3) the highest feed shoe speed (500 mm/s) led to the most nonuniform pressure distribution among the three speeds; (4) higher feed shoe speed did not always result in higher final pressure values; and (5) the right die tended to have higher final pressure values (215.0 to 2498.0 Pa) than the center die (95.4 to 2052.5 Pa). For E-shaped dies: (1) the final pressure values of the middle leg (308.9 to 760.7 Pa) were higher than those of the left and the right legs (148.9 to 530.3 Pa); (2) the area along the backside had the highest final pressure value (1054.6 to 1303.8 Pa); (3) the pressure distribution was symmetrical about the centerline parallel to the feed shoe movement direction; and (4) neither the center die nor the right die always had higher pressure values than the other one at all locations. Comparison between cylindrical and toroidal dies indicated that: (1) neither of the two die shapes (cylinder and toroid) led to consistently higher or lower final pressure values at all locations and (2) for all three feed shoe speeds, the toroidal die had higher average final pressure values in the 0° orientation. 相似文献