全文获取类型
收费全文 | 399311篇 |
免费 | 4352篇 |
国内免费 | 903篇 |
专业分类
电工技术 | 6583篇 |
综合类 | 2615篇 |
化学工业 | 61318篇 |
金属工艺 | 19081篇 |
机械仪表 | 15471篇 |
建筑科学 | 10099篇 |
矿业工程 | 2745篇 |
能源动力 | 7641篇 |
轻工业 | 30848篇 |
水利工程 | 4611篇 |
石油天然气 | 6647篇 |
武器工业 | 34篇 |
无线电 | 40291篇 |
一般工业技术 | 78284篇 |
冶金工业 | 57940篇 |
原子能技术 | 7246篇 |
自动化技术 | 53112篇 |
出版年
2021年 | 2461篇 |
2019年 | 2393篇 |
2018年 | 22690篇 |
2017年 | 22192篇 |
2016年 | 16250篇 |
2015年 | 3580篇 |
2014年 | 4843篇 |
2013年 | 12381篇 |
2012年 | 11814篇 |
2011年 | 24057篇 |
2010年 | 20697篇 |
2009年 | 18440篇 |
2008年 | 19672篇 |
2007年 | 22214篇 |
2006年 | 8205篇 |
2005年 | 11110篇 |
2004年 | 9303篇 |
2003年 | 8868篇 |
2002年 | 7598篇 |
2001年 | 6311篇 |
2000年 | 6242篇 |
1999年 | 5923篇 |
1998年 | 13290篇 |
1997年 | 9438篇 |
1996年 | 7516篇 |
1995年 | 5873篇 |
1994年 | 5266篇 |
1993年 | 5167篇 |
1992年 | 4126篇 |
1991年 | 3740篇 |
1990年 | 3989篇 |
1989年 | 3852篇 |
1988年 | 3651篇 |
1987年 | 3298篇 |
1986年 | 3297篇 |
1985年 | 3856篇 |
1984年 | 3656篇 |
1983年 | 3303篇 |
1982年 | 3153篇 |
1981年 | 3218篇 |
1980年 | 3036篇 |
1979年 | 2964篇 |
1978年 | 2978篇 |
1977年 | 3237篇 |
1976年 | 4067篇 |
1975年 | 2661篇 |
1974年 | 2461篇 |
1973年 | 2625篇 |
1972年 | 2113篇 |
1971年 | 1966篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The applicability of fluidised-bed reactor (FBR) based sulphate reducing bioprocess was investigated for the treatment of iron containing (40-90 mg/L) acidic wastewater at 65 degrees C. The FBR was inoculated with sulphate-reducing bacteria (SRB) originally enriched from a hot mining environment. Ethanol or acetate was supplemented as carbon and electron source for the SRB. A rapid startup with 99.9, 46 and 29% ethanol, sulphate and acetate removals, in respective order, was observed even after 6 days. Iron was almost completely removed with a rate of 90 mg/L.d. The feed pH was decreased gradually from its initial value of 6 to around 3.7 during 100 days of operation. The wastewater pH of 4.3-4.4 was neutralised by the alkalinity produced in acetate oxidation and the average effluent pH was 7.8 +/- 0.8. Although ethanol removal was complete, acetate accumulated. Later the FBR was fed with acetate only. Although acetate was present in the reactor for 295 days, its oxidation rates did not improve, which may be due to low growth rate and poor attachment ability of acetate oxidising SRB. Hence, the oxidation of acetate is the rate limiting step in the sulphidogenic ethanol oxidation by the thermophilic SRB. 相似文献
992.
Yu. V. Balaban-Irmenin N. G. Fokina 《Power Technology and Engineering (formerly Hydrotechnical Construction)》2007,41(4):228-232
The reliability of heat-supply systems is determined primarily by internal corrosion of the pipelines. The concentration of
oxygen in the water exerts a major influence on the corrosion. In systems with a standard oxygen content, OéDF-Zn is a highly
effective corrosion inhibitor. However, there are systems in which the quality of deaeration of the make-up water of the heat-supply
system is low (or deaeration is nonexistent), and the concentration of oxygen is considerably above the standard value. Classed
among these systems, for example, are the HWS systems, which are incorporated into closed heat-supply systems. The oxygen
concentration in these systems is analyzed to assess the situation.
__________
Translated from élektricheskie Stantsii, No. 6, June 2007, pp. 35–39. 相似文献
993.
Kai Kang 《Fire Technology》2007,43(4):331-346
This paper presents an emergency evacuation analysis during a mid-platform train fire in an underground rail station. A time-based
evacuation scenario is developed taking into account the stairway inaccessibility due to smoke blockage. The calculation approach
in NFPA 130 is then applied to a parametric study of this time-based scenario and its reliability is examined using a micro-simulation
model. Both methods give consistent predictions of the exiting times. The results demonstrate that with the division of the
station into two zones, the exiting time could not meet the code requirements, whereas it does meet the required exiting time
without the division. Such division is due to smoke blockage and creates an uneven ratio of the occupant load to the available
exiting capacity. This shows that appropriate consideration of the fire and smoke effects is important for station egress
evaluation. Other issues such as the fire growth rate and the pre-evacuation time are also discussed. 相似文献
994.
O. A. Teplov I. G. Voropaev V. G. Dyubanov L. I. Leont’ev 《Russian Metallurgy (Metally)》2007,(4):268-275
The interaction of hydrogen with the zinc-containing electrometallurgical slime of the Severstal’ metallurgical works has been studied. The sequence of transformations in the slime heated to 1100°C in hydrogen or air has been established. The experimental and calculated weight losses coincide. Some of the carbonates are shown to decompose in the temperature range 300–700°C, and most iron and zinc oxides are reduced to a metal. In the temperature range 650–850°C, zinc is almost completely sublimated. At temperatures above 800°C, complex oxides are reduced and calcium and magnesium carbonates and sulfates are likely to decompose. Experimental digital data on the zinc sublimation rate are processed by the least squares method with approximating equations used in thermal analysis. The kinetics of nonisothermal zinc sublimation is comprehensively analyzed using a unique procedure developed for taking into account the background of a peak and the effect of accompanying processes. An equation for the calculation of the zinc sublimation rate under experimental conditions (fluidized bed) is given and tested. 相似文献
995.
I. E. Gorbatkina L. D. Konoval'chikov B. K. Nefedov B. L. Khusid 《Chemistry and Technology of Fuels and Oils》1989,25(3):127-130
Translated from Khimiya i Tekhnoloyiya Topliv i Masel, No. 3, pp. 3–5, March, 1989. 相似文献
996.
997.
V. Elliott Smith John M. Spurr John C. Filkins Jody J. Jones 《Journal of Great Lakes research》1985,11(3):231-246
Organochlorine analysis was performed on carcasses of 13 diving ducks from a 1981 wintering population that foraged on contaminated sediments in the lower Detroit River. Mean total PCB concentrations were 10 mg/kg for seven lesser scaups (Aythya affinis), 11 mg/kg for three greater scaups (A. marila), and 7.6 mg/kg for three goldeneyes (Bucephala clangula). Highest mean levels of other residues were measured for hexachlorobenzene (1.7 mg/kg) in goldeneyes, and transnonachlor (0.33 mg/kg) and 4,4’-DDE (1.3 mg/kg) in greater scaup. Quantitative analysis of 72 PCB congeners also was applied to water, seston, sediment, benthie oligochaetes, and carp from the same site. Principal congeners in most of the samples included some of the more toxic and persistent PCBs. Results of a multivariate analysis indicated that ratios of more conservative to less conservative PCBs did not vary significantly among ducks (α = .05), but differed from those in carp, oligochaetes, and sediment. For the February through March period of fat mobilization, concentrations of total PCB in lipid were inversely correlated with percent lipid (r = 0.76) in ducks. The percentage of conservative PCBs increased slightly. The distribution and partitioning of organochlorines, including toxic PCB congeners, varied considerably within this water column-sediment-fauna ecosystem. Estimates of toxic exposure based on total PCB values may be unreliable. 相似文献
998.
De Geronimo G. Bolotnikov A.E. Carini G. Fried J. O'Connor P. Soldner S.A. 《IEEE transactions on nuclear science》2006,53(2):456-461
A new version of the front-end application specific integrated circuit (ASIC) for co-planar-grid (CPG) sensors is presented. Compared to the first version, the ASIC is optimized for signal/noise performance, modified in peaking time, and it implements timing signals to measure the depth of interaction using the grids signals only. Experimental results using state-of the-art CPG sensors and different approaches for reducing the error due to electron trapping are reported. A new technique that makes use of the sum and difference of the grids signals is also presented. 相似文献
999.
The functional reanimation of paralyzed limbs has been a longstanding goal of neural prosthetic research, but clinically successful applications have been elusive. Natural voluntary limb movement requires four major elements: actuators (i.e., motor units), sensors (i.e., somatosensory afferents), commands (i.e., cerebral cortical activity), and control (i.e., integration of the previous three elements at various levels of the neuraxis). Prosthetic equivalents of each of these elements are, as yet, primitive and often cumbersome to deploy, but new technologies promise substantial improvements for all. This article focuses on one such technology, bionic neuon (BION) modular microimplants, and its relationship to alternative and complementary technologies. The challenge remains to select and integrate them into systems that can be tailored efficiently to the widely disparate needs of patients with various patterns of weakness and paralysis. 相似文献
1000.
Stormwater reuse is increasing in popularity as a technique for overcoming water shortages in urban Australia. However, technology for the reliable treatment of stormwater for reuse is still not fully developed. This paper presents the first steps in refining biofilters for stormwater reuse. Six different filter media were selected, to target specific stormwater pollutants, as well as support plant growth. They were tested in the laboratory, where the filters were dosed three times per week with semi-synthetic stormwater for five weeks. Pollutant removal performance was monitored, and revealed that all soil-based filters performed similarly (while sand filters behaved somewhat differently). All filters removed more than 80% of solids and greater than 90% of lead, copper, and zinc. Three filter types were able to remove some phosphorus (particularly in the top 30 cm of the media). Apart from sand, all filter media were net producers of nitrogen, leading to an important conclusion that non-vegetated, soil-based filters are not suitable for targeting nutrients. However, since heavy metals are the primary pollutant of concern with respect to stormwater reuse for irrigation (the most popular end-use), it was concluded that biofilters may be promising technologies for treatment of stormwater for reuse. 相似文献