全文获取类型
收费全文 | 4118篇 |
免费 | 86篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 46篇 |
综合类 | 1篇 |
化学工业 | 548篇 |
金属工艺 | 224篇 |
机械仪表 | 72篇 |
建筑科学 | 131篇 |
矿业工程 | 89篇 |
能源动力 | 87篇 |
轻工业 | 358篇 |
水利工程 | 28篇 |
石油天然气 | 5篇 |
无线电 | 330篇 |
一般工业技术 | 519篇 |
冶金工业 | 1336篇 |
原子能技术 | 40篇 |
自动化技术 | 391篇 |
出版年
2022年 | 39篇 |
2021年 | 65篇 |
2020年 | 35篇 |
2019年 | 44篇 |
2018年 | 47篇 |
2017年 | 50篇 |
2016年 | 52篇 |
2015年 | 45篇 |
2014年 | 66篇 |
2013年 | 201篇 |
2012年 | 113篇 |
2011年 | 161篇 |
2010年 | 143篇 |
2009年 | 146篇 |
2008年 | 134篇 |
2007年 | 162篇 |
2006年 | 156篇 |
2005年 | 102篇 |
2004年 | 92篇 |
2003年 | 94篇 |
2002年 | 81篇 |
2001年 | 71篇 |
2000年 | 79篇 |
1999年 | 71篇 |
1998年 | 300篇 |
1997年 | 188篇 |
1996年 | 152篇 |
1995年 | 92篇 |
1994年 | 91篇 |
1993年 | 115篇 |
1992年 | 59篇 |
1991年 | 47篇 |
1990年 | 45篇 |
1989年 | 49篇 |
1988年 | 38篇 |
1987年 | 44篇 |
1986年 | 52篇 |
1985年 | 38篇 |
1984年 | 47篇 |
1983年 | 40篇 |
1982年 | 34篇 |
1981年 | 38篇 |
1980年 | 35篇 |
1979年 | 32篇 |
1978年 | 35篇 |
1977年 | 66篇 |
1976年 | 76篇 |
1975年 | 28篇 |
1974年 | 33篇 |
1973年 | 33篇 |
排序方式: 共有4205条查询结果,搜索用时 15 毫秒
1.
John D. Rodney S. Deepapriya M. Cyril Robinson C. Justin Raj Suresh Perumal Byung Chul Kim S. Krishnan S. Jerome Das 《International Journal of Hydrogen Energy》2021,46(54):27585-27596
The production of hydrogen, a favourable alternative to an unsustainable fossil fuel remains as a significant hurdle with the pertaining challenge in the design of proficient, highly productive and sustainable electrocatalyst for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Herein, the dysprosium (Dy) doped copper oxide (Cu1-xDyxO) nanoparticles were synthesized via solution combustion technique and utilized as a non-noble metal based bi-functional electrocatalyst for overall water splitting. Due to the improved surface to volume ratio and conductivity, the optimized Cu1-xDyxO (x = 0.01, 0.02) electrocatalysts exhibited impressive HER and OER performance respectively in 1 M KOH delivering a current density of 10 mAcm?2 at a potential of ?0.18 V vs RHE for HER and 1.53 V vs RHE for OER. Moreover, the Dy doped CuO electrocatalyst used as a bi-functional catalyst for overall water splitting achieved a potential of 1.56 V at a current density 10 mAcm?2 and relatively high current density of 66 mAcm?2 at a peak potential of 2 V. A long term stability of 24 h was achieved for a cell voltage of 2.2 V at a constant current density of 30 mAcm?2 with only 10% of the initial current loss. This showcases the accumulative opportunity of dysprosium as a dopant in CuO nanoparticles for fabricating a highly effective and low-cost bi-functional electrocatalyst for overall water splitting. 相似文献
2.
Chemical engineering systems often involve a functional porous medium, such as in catalyzed reactive flows, fluid purifiers, and chromatographic separations. Ideally, the flow rates throughout the porous medium are uniform, and all portions of the medium contribute efficiently to its function. The permeability is a property of a porous medium that depends on pore geometry and relates flow rate to pressure drop. Additive manufacturing techniques raise the possibilities that permeability can be arbitrarily specified in three dimensions, and that a broader range of permeabilities can be achieved than by traditional manufacturing methods. Using numerical optimization methods, we show that designs with spatially varying permeability can achieve greater flow uniformity than designs with uniform permeability. We consider geometries involving hemispherical regions that distribute flow, as in many glass chromatography columns. By several measures, significant improvements in flow uniformity can be obtained by modifying permeability only near the inlet and outlet. 相似文献
3.
4.
5.
Modeling ion implantation of HgCdTe 总被引:2,自引:0,他引:2
H. G. Robinson D. H. Mao B. L. Williams S. Holander-Gleixner J. E. Yu C. R. Helms 《Journal of Electronic Materials》1996,25(8):1336-1340
Ion implantation of boron is used to create n on p photodiodes in vacancy-doped mercury cadmium telluride (MC.T). The junction
is formed by Hg interstitials from the implant damage region diffusing into the MC.T and annihilating Hg vacancies. The resultant
doping profile is n+/n-/p, where the n+ region is near the surface and roughly coincides with the implant damage, the n- region is where Hg vacancies have been annihilated revealing a residual grown-in donor, and the p region remains doped by
Hg vacancy double acceptors. We have recently developed a new process modeling tool for simulating junction formation in MC.T
by ion implantation. The interstitial source in the damage region is represented by stored interstitials whose distribution
depends on the implant dose. These interstitials are released into the bulk at a constant, user defined rate. Once released,
they diffuse away from the damage region and annihilate any Hg vacancies they encounter. In this paper, we present results
of simulations using this tool and show how it can be used to quantitatively analyze the effects of variations in processing
conditions, including implant dose, annealing temperature, and doping background. 相似文献
6.
7.
Various models have been proposed over the years to fit crack growth data. Many papers have appeared in which one or more models are mooted and fitted, and various assessments made of the quality of the fit. At the basic level the data are plotted, together with the fitted curve, to show agreement of experimental and predicted values. In this paper we suggest that it can be useful and informative to go one step further, examining the residuals, i.e., the differences between the experimental and predicted values. We draw attention to certain statistical methods for such critical assessment and show by example that this can reveal deficiencies in fit not otherwise obvious. In this way suitable modifications to the model can be suggested. Additional plots of estimated parameters are also shown to be informative about models 相似文献
8.
The requirements on an object-oriented DBMS for management of information in a large, complex enterprise are presented. These requirements aid in the achievement of an environment characterized by data sharing, open architectures, application and data portability, and assurance of data integrity. They were defined from the point of view of a user of the DBMS; therefore they describe the expected functionality of the DBMS and do not specify the method of implementation to achieve this functionality. They encompass requirements on the data model, query and data manipulation languages, the system architecure, interfaces to the system, change management, and transaction management. 相似文献
9.
A central sleep apnea is the absence of respiratory effect, and, thus, the absence of airflow during sleep. Central hypopnea, a related disorder, is also discussed. The sensory component of central sleep apnea; defects involving the integrative and executive neurons; non-neurologic causes of central sleep apneas, including chronic obstructive pulmonary disease and congestive heart failure; diagnosis; treatment; and other topics are reviewed in detail. 相似文献
10.
J Stephen Robinson J Keith Syers Nanthi S Bolan 《Journal of the science of food and agriculture》1994,64(4):397-403
Laboratory experimental and literature data were integrated to develop a simple, conceptual model to describe and predict the dissolution of a reactive phosphate rock (Gafsa phosphate rock, GPR) in soils. The model showed that initial solution Ca concentration strongly influences the time required for a single application of GPR (at 30 kgP ha?1) to dissolve. The model predicts that all of the GPR will dissolve within a year of application in an unlimed, acid (pHw 4.5) loam. However, if the soil has previously been limed to (pHw 5.8, and contains permanent charge only, the model predicts that only about 50% of the GPR would have dissolved by the end of the second year after application. On the other hand, if a previously limed soil ((pHw 5.8) contains variable-charge components, the model predicts that virtually all of the GPR would have dissolved in this soil by the end of the second year after application. These results emphasise that, even in the presence of a high proton supply, solution Ca has an overriding influence on the dissolution of GPR. The faster rate of GPR dissolution in the limed soil with variable charge, compared to that in the limed soil with permanent charge only, demonstrates the ability of the variable-charge component of soil to act as a sink for some of the lime-derived Ca. According to the solubility product principle, this allows more GPR to dissolve. Because of the generally stronger buffering of soil for P than for Ca, a relatively large proportion of any P removed by leaching and plant uptake is buffered by the sorbed phase. Consequently, the influence of leaching and plant uptake on GPR dissolution is attributed primarily to the removal of the relatively less-strongly buffered Ca. 相似文献