全文获取类型
收费全文 | 133598篇 |
免费 | 11207篇 |
国内免费 | 6609篇 |
专业分类
电工技术 | 8510篇 |
综合类 | 9933篇 |
化学工业 | 15231篇 |
金属工艺 | 6479篇 |
机械仪表 | 6603篇 |
建筑科学 | 6813篇 |
矿业工程 | 4123篇 |
能源动力 | 2860篇 |
轻工业 | 12272篇 |
水利工程 | 3578篇 |
石油天然气 | 3011篇 |
武器工业 | 1569篇 |
无线电 | 9702篇 |
一般工业技术 | 10078篇 |
冶金工业 | 31906篇 |
原子能技术 | 1616篇 |
自动化技术 | 17130篇 |
出版年
2024年 | 548篇 |
2023年 | 1642篇 |
2022年 | 3681篇 |
2021年 | 4602篇 |
2020年 | 3215篇 |
2019年 | 2210篇 |
2018年 | 2811篇 |
2017年 | 3210篇 |
2016年 | 3394篇 |
2015年 | 4633篇 |
2014年 | 5211篇 |
2013年 | 6113篇 |
2012年 | 9374篇 |
2011年 | 9902篇 |
2010年 | 7848篇 |
2009年 | 7315篇 |
2008年 | 7270篇 |
2007年 | 7109篇 |
2006年 | 6104篇 |
2005年 | 7625篇 |
2004年 | 5735篇 |
2003年 | 4200篇 |
2002年 | 2747篇 |
2001年 | 2488篇 |
2000年 | 1711篇 |
1999年 | 1346篇 |
1998年 | 8736篇 |
1997年 | 5281篇 |
1996年 | 3461篇 |
1995年 | 1995篇 |
1994年 | 1529篇 |
1993年 | 1619篇 |
1992年 | 360篇 |
1991年 | 419篇 |
1990年 | 421篇 |
1989年 | 386篇 |
1988年 | 382篇 |
1987年 | 299篇 |
1986年 | 267篇 |
1985年 | 219篇 |
1984年 | 78篇 |
1983年 | 96篇 |
1982年 | 167篇 |
1981年 | 215篇 |
1980年 | 263篇 |
1979年 | 76篇 |
1978年 | 109篇 |
1977年 | 761篇 |
1976年 | 1592篇 |
1975年 | 111篇 |
排序方式: 共有10000条查询结果,搜索用时 410 毫秒
761.
762.
就城市集中供热工程造价的控制问题,从对设计阶段的成本、施工过程,加强材料成本、工程结算的控制几方面对其进行了详细的阐述,最后对工料分析与检查方面进行了论述,以提高供热企业的投资效益。 相似文献
763.
A tariff system has been set up for the largest wastewater treatment plant in South-East Asia, the Samut Prakarn Wastewater Treatment Plant south of Bangkok, which is currently under completion. Fully functional the plant will have a design capacity for 500,000 m3 per day and will service a combined residential and industrial area with approximately 600,000 residents and 2,300 factories. The tariff system, which includes a tariff model, is based on water consumption and BOD load. As background for setting the tariffs a comprehensive monitoring system including an industrial permitting system has been developed. The paper presents the background and rationale for setting up the system as well as the objective, scope and content of the tariff system and the industrial permit system. Further, the feasibility of introducing cost recovery systems, which is widely accepted in developing economies on the conceptual level and to some extent implemented at the legal and regulatory level, but has yet to be implemented at large, is discussed. 相似文献
764.
In this study, nitrogen removal was investigated in pilot-scale subsurface flow (SSF) and in free water surface flow (FWS) constructed wetlands installed in the campus of TUBITAK-Marmara Research Center, Gebze, near Istanbul, Turkey. The main purposes of this study are to apply constructed wetlands for the protection of water reservoirs and to reuse wastewater. Experiments were carried out at continuous flow reactors. The effects of the type of plants on the removal were investigated by using emergent (Canna, Cyperus, Typhia spp., Phragmites spp., Juncus, Poaceae, Paspalum and Iris.), submerged (Elodea, Egeria) and floating (Pistia, Salvina and Lemna) marsh plants at different conditions. During the study period HLRs were 30, 50, 70, 80 and 120 L m(2)d(-1) respectively. The average annual NH4-N, NO(3)-N, organic N and TN treatment efficiencies in SSF and FWS wetlands are 81% and 68%, 37% and 49%, 75% and 68%, 47% and 53%, respectively. Nitrification, denitrification and ammonification rate constant (k20) values in SSF and FNS systems have been found as 0.898 d(-1) and 0.541 d(-1), 0.488 d(-1) and 0.502 d(-1), 0.986 d(-1) and 0.908 respectively. Two types of the models (first-order plug flow and multiple regression) were tried to estimate the system performances. 相似文献
765.
766.
767.
768.
The purpose of this study was to identify new trends in the changing indications for penetrating keratoplasty. We retrospectively reviewed the clinical and pathologic diagnoses of 1,104 corneal buttons that had been submitted to the Estelle Doheny Eye Pathology Laboratory, Los Angeles, during the 5-year period 1989-1993. The leading indications, in order of decreasing frequency, were pseudophakic corneal edema (24.8%), regrafts (21.3%), scarring with or without chronic inflammation (11.1%), keratoconus (7.1%), aphakic corneal edema (6.4%), and ulcerative conditions (5.8%). The incidence of pseudophakic corneal edema remained stable over the study period and was actually surpassed by regraft in the last year of the study. Although pseudophakic corneal edema remains the predominant indication for penetrating keratoplasty, our findings suggest that its occurrence rate has begun to level off. 相似文献
769.
Radio-protective effectiveness of short-term (19 and 4 h before, 4 and 24 h after irradiation), long-term (3 times/week during 30 days after irradiation) and delayed (1 or 2 days after irradiation) enrichment with crystallized beta-carotene, in single doses of 0.1, 1.0 or 5.0 mg was evaluated in experimental acute external gamma-irradiation (0.029 Gy/sec) within the range of absorbed doses 9--6 Gy. The results obtained have permitted the authors to recommend the ration enriched with carotinoid for prevention and therapy of acute radiation injuries. 相似文献
770.