全文获取类型
收费全文 | 225089篇 |
免费 | 19357篇 |
国内免费 | 14558篇 |
专业分类
电工技术 | 32323篇 |
技术理论 | 7篇 |
综合类 | 20544篇 |
化学工业 | 16652篇 |
金属工艺 | 9370篇 |
机械仪表 | 20328篇 |
建筑科学 | 20390篇 |
矿业工程 | 11404篇 |
能源动力 | 7513篇 |
轻工业 | 8034篇 |
水利工程 | 7420篇 |
石油天然气 | 12527篇 |
武器工业 | 3265篇 |
无线电 | 15376篇 |
一般工业技术 | 12830篇 |
冶金工业 | 9894篇 |
原子能技术 | 2152篇 |
自动化技术 | 48975篇 |
出版年
2024年 | 895篇 |
2023年 | 2538篇 |
2022年 | 4385篇 |
2021年 | 5460篇 |
2020年 | 6437篇 |
2019年 | 5068篇 |
2018年 | 4613篇 |
2017年 | 6493篇 |
2016年 | 7224篇 |
2015年 | 7826篇 |
2014年 | 14657篇 |
2013年 | 13266篇 |
2012年 | 16524篇 |
2011年 | 17796篇 |
2010年 | 13137篇 |
2009年 | 13330篇 |
2008年 | 12957篇 |
2007年 | 16132篇 |
2006年 | 14719篇 |
2005年 | 12736篇 |
2004年 | 10752篇 |
2003年 | 9389篇 |
2002年 | 7625篇 |
2001年 | 6397篇 |
2000年 | 5518篇 |
1999年 | 4425篇 |
1998年 | 3439篇 |
1997年 | 3035篇 |
1996年 | 2469篇 |
1995年 | 2046篇 |
1994年 | 1763篇 |
1993年 | 1198篇 |
1992年 | 979篇 |
1991年 | 761篇 |
1990年 | 574篇 |
1989年 | 519篇 |
1988年 | 360篇 |
1987年 | 242篇 |
1986年 | 171篇 |
1985年 | 175篇 |
1984年 | 179篇 |
1983年 | 138篇 |
1982年 | 140篇 |
1981年 | 100篇 |
1980年 | 76篇 |
1979年 | 86篇 |
1978年 | 55篇 |
1977年 | 51篇 |
1964年 | 17篇 |
1959年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
介绍了引黄工程五座泵站的火灾自动报警系统的组成及功能,对泵站的火灾探测系统、报警系统、联动控制系统、灭火系统、控制台等原理进行了详细说明,供同行参考借鉴。 相似文献
22.
暖通空调工程设计常见问题 总被引:1,自引:0,他引:1
通过对施工图审查工作进行总结,指出了暖通空调和防火防排烟设计中存在的问题及防火规范本身的一些不足。 相似文献
23.
Thermal history and solute precipitation behavior of suspended solution droplets of sodium chloride (NaCl), magnesium sulphate (MgSO4), and zirconium hydroxychloride (ZrO(OH)Cl) evaporating at atmospheric and reduced pressures are studied. Experimental measurements on the variation of droplet diameter, solution concentration, and temperature during the evaporation period are presented and discussed. The results of solute precipitation behavior in solution droplets observed under an optical microscope are displayed and discussed. Results indicate that reducing the pressure (∼ 33 kPa) results in a change in the solution droplet evaporation rate, but the thermal histories of a particular solution droplet are similar at the atmospheric and reduced pressures. At atmospheric and reduced pressures used in this study, the d2 law for solution droplets is valid at early stages of the evaporation and before the solute precipitation initiates. Drying of MgSO4 and ZrO(OH)Cl solution droplets results in the formation of spherical particles, whereas drying of spherical NaCl solution droplets results in the formation of cubic particles. 相似文献
24.
针对企业集团分权化管理的缺点,设计出一套利用互联网络技术实现企业集团财务集中控制的模式,给出了模式的图示及说明。 相似文献
25.
L. Serra-Majem L. Bassas R. Garcí a-Glosas L. Ribas C. Ingl s I. Casals P. Saavedra A. G. Renwick 《Food Additives & Contaminants》2003,20(12):1097-1104
Cyclamate and its metabolite cyclohexylamine affect male fertility in high dose animal studies, but this affect has not been investigated in epidemiological studies. This paper reports the first epidemiological study designed to investigate the possibility of a relationship between cyclamate and cyclohexylamine and male fertility in humans, in which 405 cases of clinically defined infertility in men and 379 controls were surveyed. Semen evaluation, urine analysis for cyclamate and cyclohexylamine and dietary questionnaires were compared between cases and controls. No evidence was found of a significant association between cyclamate intake and male infertility; neither high cyclamate nor high cyclohexylamine excretion were associated with elevated risk. The lack of association remained after adjusting by age, area of residence, education, total energy intake and other variables. No significant correlations were observed between cyclamate intake, metabolism or excretion, and sperm count and motility. The results demonstrate no effect of cyclamate or cyclohexylamine on male fertility at the present levels of cyclamate consumption. 相似文献
26.
27.
建(构)筑物机械拆除方法综述 总被引:1,自引:0,他引:1
介绍了几种常用的建(构)筑物机械拆除方法,对其工作原理、特点、应用条件及局限性加以分析和说明。 相似文献
28.
Sipra Mahapatra Turaga P. Prasad 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1992,53(2):201-203
Hydrolysis of Fe(OH)SO4 was carried out in the presence of metallic iron in order to prevent the formation of iron(III) oxides with strongly bonded sulphate. Under the conditions of the experiment, the products were found to be mixtures of ?-Fe2O3 and α-FeOOH. The occluded sulphate, if any, could be easily washed out with water. The hydrolysis reaction passes through an equilibrium state before coming to completion. The entropy with enthalpy of the hydrolysis corresponding to the equilibrium state were found to be 4 e.u. and 0·5 kJ/mol, respectively. The activation energy of the hydrolysis reaction was found to be 21 kJ/mol. 相似文献
29.
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
30.
关于项目管理中施工进度控制的研究 总被引:5,自引:1,他引:4
阐述了项目管理中施工进度控制的地位与作用,分析了影响工程进度的因素,提出项目进度控制需做好的工作,以提高进度控制水平,确保合同工期的实现。 相似文献