全文获取类型
收费全文 | 470299篇 |
免费 | 6167篇 |
国内免费 | 1830篇 |
专业分类
电工技术 | 9304篇 |
综合类 | 582篇 |
化学工业 | 68206篇 |
金属工艺 | 19608篇 |
机械仪表 | 14387篇 |
建筑科学 | 11610篇 |
矿业工程 | 1512篇 |
能源动力 | 11849篇 |
轻工业 | 43138篇 |
水利工程 | 4099篇 |
石油天然气 | 5120篇 |
武器工业 | 71篇 |
无线电 | 60531篇 |
一般工业技术 | 87758篇 |
冶金工业 | 92086篇 |
原子能技术 | 8577篇 |
自动化技术 | 39858篇 |
出版年
2021年 | 3391篇 |
2019年 | 3254篇 |
2018年 | 5437篇 |
2017年 | 5433篇 |
2016年 | 5809篇 |
2015年 | 3989篇 |
2014年 | 6759篇 |
2013年 | 20691篇 |
2012年 | 11219篇 |
2011年 | 15501篇 |
2010年 | 12424篇 |
2009年 | 13852篇 |
2008年 | 15010篇 |
2007年 | 15054篇 |
2006年 | 13744篇 |
2005年 | 12574篇 |
2004年 | 12070篇 |
2003年 | 12014篇 |
2002年 | 11726篇 |
2001年 | 11851篇 |
2000年 | 11017篇 |
1999年 | 11771篇 |
1998年 | 29017篇 |
1997年 | 20611篇 |
1996年 | 16028篇 |
1995年 | 12207篇 |
1994年 | 10854篇 |
1993年 | 10625篇 |
1992年 | 7983篇 |
1991年 | 7596篇 |
1990年 | 7098篇 |
1989年 | 6781篇 |
1988年 | 6627篇 |
1987年 | 5663篇 |
1986年 | 5545篇 |
1985年 | 6562篇 |
1984年 | 6028篇 |
1983年 | 5426篇 |
1982年 | 5089篇 |
1981年 | 5163篇 |
1980年 | 4909篇 |
1979年 | 4589篇 |
1978年 | 4472篇 |
1977年 | 5439篇 |
1976年 | 7334篇 |
1975年 | 3945篇 |
1974年 | 3845篇 |
1973年 | 3833篇 |
1972年 | 3121篇 |
1971年 | 2914篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
Breslavs’kyi D. V. Metel’yov V. O. Morachkovs’kyi O. K. Tatarinova O. A. 《Strength of Materials》2019,51(5):753-760
Strength of Materials - Creep constitutive equations have been derived for the materials that exhibit the properties of orthotropy (transversal isotropy) and transient creep under cyclic loading. A... 相似文献
42.
43.
High Temperature - Experimental findings suggest that a strongly ionized, arc He plasma of atmospheric pressure does not exist in the state of the local thermodynamic equilibrium (LTE) expected for... 相似文献
44.
The separation of iron oxide from banded hematite jasper(BHJ) assaying 47.8% Fe, 25.6% Si O2 and 2.30%Al2O3 using selective magnetic coating was studied. Characterization studies of the low grade ore indicate that besides hematite and goethite,jasper, a microcrystalline form of quartzite, is the major impurity associated with this ore. Beneficiation by conventional magnetic separation technique could yield a magnetic concentrate containing 60.8% Fe with 51% Fe recovery. In order to enhance the recovery of the iron oxide minerals, fine magnetite, colloidal magnetite and oleate colloidal magnetite were used as the coating material. When subjected to magnetic separation, the coated ore produces an iron concentrate containing 60.2% Fe with an enhanced recovery of56%. The AFM studies indicate that the coagulation of hematite particles with the oleate colloidal magnetite facilitates the higher recovery of iron particles from the low grade BHJ iron ore under appropriate conditions. 相似文献
45.
46.
47.
Lecture capture with real‐time rearrangement of visual elements: impact on student performance 下载免费PDF全文
The primary goal of this study is to create and test a lecture‐capture system that can rearrange visual elements while recording is still taking place, in such a way that student performance can be positively influenced. The system we have devised is capable of integrating and rearranging multimedia sources, including learning content, the instructor and students' images, into lecture videos that are embedded in a website for students to review after school. The present study employed a two‐group experimental design, with 153 participants (145 females and 8 males) making up an experimental group in which lecture courses were recorded using the new lecture‐capture system, and 149 participants (140 females and 9 males) forming a control group whose lectures were recorded by traditional means. All participants were in the freshman college and studying Introduction to Computer and Information Science in one of six classes, and were randomly assigned to one of the two groups. The participants' midterm examination and final examination scores were collected as indicators of their academic performance, with their mathematics entrance scores used as a pre‐test. The findings obtained from analysis of covariance (ANCOVA) suggest that appropriate rearrangement of visual elements in lecture videos can significantly impact students' learning performance. 相似文献
48.
Hypoxia formation and breakdown were tracked during 2015 in Muskegon Lake estuary at multiple locations, and five years (2011–2015) of time-series buoy observatory data were evaluated for the effect of episodic wind-events on lake mixing. Bi-weekly water temperature and dissolved oxygen (DO) profiles at four locations revealed that hypoxia occurred at all sites and persisted for 2–3 months during summer 2015. On one date in late-summer, up to 24% of the lake’s volume was estimated to be mildly hypoxic (DO < 4 mg L?1) as defined by lake sturgeon requirements. Patterns of wind speed and water column stability in late spring indicated that high winds and low stability delayed the onset of hypoxia while in late summer low winds and high stability delayed degradation of hypoxia. Wind speeds appear to play a great role in the interannual variability of stratification and subsequent hypoxia. Water temperature and DO profiles taken before and after one mid-summer mixing event (wind speed >7.7 m s?1 for 10 h), indicated that while the wind was unable to completely mix the entire water column, it deepened the epilimnion by ~1.5 m and sheared a thin layer from the upper hypolimnion. By entraining internally loaded nutrients, such episodic wind-events may initiate and sustain algal blooms in nutrient limited surface waters. Quantifying the variable role of wind and mixing events will be key to integrating limnological processes into climate models of the future. 相似文献
49.
C. G. Prosgolitis S. G. Lambrakos A. D. Zervaki 《Journal of Materials Engineering and Performance》2018,27(10):5102-5113
This work presents simulation of microstructure evolution in the nugget zone (NZ) of a AZ31-Mg-alloy friction stir weld. The process parameters (tool geometrical characteristics, rotational speed, travel speed, applied load) have been correlated with the resulting microstructural features in the NZ of the weld (grain size and population) with the aid of the MICRESS software, which provides the ability to simulate both nucleation and grain growth during dynamic recrystallization phenomena evolving in the NZ during the weld thermal cycle. The input parameters of the developed model include the tool geometry, the welding conditions as well as the recrystallization energy, the grain boundary mobility and specific material properties. NZ microstructure obtained by simulation shows good agreement with experimental measurements for both grain population and size. 相似文献
50.
Buryakov A. M. Khusyainov D. I. Mishina E. D. Khabibullin R. A. Yachmenev A. E. Ponomarev D. S. 《Technical Physics Letters》2018,44(12):1115-1119
Technical Physics Letters - The influence of excitation photons energy on the relaxation times of photoexcited carriers is studied. The involved relaxation mechanisms are evaluated and the... 相似文献