全文获取类型
收费全文 | 350955篇 |
免费 | 2733篇 |
国内免费 | 406篇 |
专业分类
电工技术 | 5635篇 |
综合类 | 196篇 |
化学工业 | 55847篇 |
金属工艺 | 19796篇 |
机械仪表 | 12920篇 |
建筑科学 | 6390篇 |
矿业工程 | 4492篇 |
能源动力 | 6196篇 |
轻工业 | 17237篇 |
水利工程 | 5708篇 |
石油天然气 | 16553篇 |
武器工业 | 31篇 |
无线电 | 30273篇 |
一般工业技术 | 83602篇 |
冶金工业 | 51393篇 |
原子能技术 | 13626篇 |
自动化技术 | 24199篇 |
出版年
2021年 | 3598篇 |
2019年 | 3466篇 |
2018年 | 6757篇 |
2017年 | 6984篇 |
2016年 | 7452篇 |
2015年 | 3896篇 |
2014年 | 6832篇 |
2013年 | 14277篇 |
2012年 | 9745篇 |
2011年 | 12186篇 |
2010年 | 9950篇 |
2009年 | 11032篇 |
2008年 | 11167篇 |
2007年 | 10841篇 |
2006年 | 9047篇 |
2005年 | 8049篇 |
2004年 | 7824篇 |
2003年 | 7601篇 |
2002年 | 7397篇 |
2001年 | 7275篇 |
2000年 | 7092篇 |
1999年 | 6552篇 |
1998年 | 13027篇 |
1997年 | 9984篇 |
1996年 | 7465篇 |
1995年 | 5910篇 |
1994年 | 5393篇 |
1993年 | 5592篇 |
1992年 | 4641篇 |
1991年 | 4735篇 |
1990年 | 4860篇 |
1989年 | 4671篇 |
1988年 | 4558篇 |
1987年 | 4434篇 |
1986年 | 4362篇 |
1985年 | 4563篇 |
1984年 | 4404篇 |
1983年 | 4292篇 |
1982年 | 4019篇 |
1981年 | 4210篇 |
1980年 | 4142篇 |
1979年 | 4424篇 |
1978年 | 4735篇 |
1977年 | 4798篇 |
1976年 | 5755篇 |
1975年 | 4338篇 |
1974年 | 4388篇 |
1973年 | 4464篇 |
1972年 | 4055篇 |
1971年 | 3688篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Levels of aluminium in 82 different infant formulae from nine different manufacturers in Spain were determined by acid-microwave digestion and graphite furnace atomic absorption spectrophotometry. The influence of aluminium content in tap water in reconstituted powder formulae was examined and an estimate was made of the theoretical toxic aluminium intake in comparison with the provisional tolerable weekly intake (PTWI). Possible interactions between aluminium and certain essential trace elements added to infant formulations have been studied according to the type or main protein-based infant formula. In general, the infant formulae contained a higher aluminium content than that found in human milk, especially in the case of soya, preterm or hydrolysed casein-based formulae. Standard formulae gave lower aluminium intakes amounting to about 4% PTWI. Specialized and preterm formulae resulted in a moderate intake (11-12 and 8-10% PTWI, respectively) and soya formulae contributed the highest intake (15% PTWI). Aluminium exposure from drinking water used for powder formula reconstitution was not considered a potential risk. In accordance with the present state of knowledge about aluminium toxicity, it seems prudent to call for continued efforts to standardize routine quality control and reduce aluminium levels in infant formula as well as to keep the aluminium concentration under 300 μg l-1 for all infant formulae, most specifically those formulae for premature and low birth neonates. 相似文献
972.
Processes of corrosion cracking of the metal of turbine blades in the region of initial steam condensation are considered. Possible ways of preventing corrosion-fatigue damage to the blades are proposed. 相似文献
973.
Different designs of proportioners and screw feeders for colorant and decolorizing agents for glass melt are discussed.__________Translated from Steklo i Keramika, No. 4, pp. 8 – 9, April, 2005. 相似文献
974.
975.
Various aspects of biofilm adaptation to sulfate reduction in horizontal-flow anaerobic immobilized biomass (HAIB) reactors subjected to increasing sulfate concentrations and different COD/sulfate ratios are presented and discussed. Four bench-scale HAIB reactors filled with vegetal carbon (R1 and R2) and polyurethane foam matrices (R3 and R4) were utilized. Influent sulfate concentrations ranging from 500 to 3000 mg/L were applied at COD/sulfate ratios ranging from 5.0 to 1.7. Reactors R1 and R4 were operated with higher sulfate loads than those applied to R2 and R3. For the same COD/sulfate ratio, the highest sulfate reduction efficiency (approximately 80%) was displayed by the vegetal carbon reactor (R2) subjected to low sulfate loads. According to the results of our molecular biology analyses, the different support materials provided different biomass colonization conditions. The lowest diversity of sulfate-reducing bacteria was found in the HAIB filled with polyurethane foam matrices operating with high sulfate loads. 相似文献
976.
Alignment of single wall carbon nanotubes (SWNT) in liquid crystalline (LC) polymer matrix imparting orientation to the nanotubes along the nematic director was studied by atomic force microscopy, measurements of electrical conductivity and Raman spectroscopy of the composite in the directions parallel and perpendicular to the nematic director. The composites were prepared through dispersion of SWNT with LC monomer in a common solvent, their alignment in nematic monomer and consequent UV polymerization of the monomer. The anisotropy of electrical and optical properties of the system depends strongly on the concentration of the nanotubes in the range of 1-10% SWNT being especially strong for smaller concentrations and negligible at higher loads. A simple semi-quantitative model is suggested to account for the orientational behavior of nanotubes in nematic matrices. It successfully describes the observed anisotropy of physical properties at microscale (up to 200 μm) in terms of anchoring of the polymer chains to the nanotubes surface and adjustment of the nanotubes orientation to the nematic direction due to such coupling. The increasing disorientation of the nematic domains at higher nanotubes loads is explained as a development of larger number of LC defects induced by the nanotubes in the nematic matrix due to their intrinsic nature of aggregation. The anisotropy of physical properties at macro scale (several millimeters) is much smaller and less dependable on SWNT concentration because differently oriented LC domains effectively wash out the anisotropy. 相似文献
977.
Measures taken to develop and put into operation three new exterior channels for emergency process water with two additional
60VTs pumping units, which remain operational even during an earthquake and were installed in the second block pumping station,
are described. In addition, the three existing 12NDS horizontal pumping units were used as a basis to develop a third channel
for the emergency process water. Above-ground water ducts with thermal insulation and heating systems to prevent freezing
during the anticipation state, which is the constant state of the emergency system, were laid.
As a result of upgrading with the development of three channels, the emergency process water feeding reached an adequately
safe level of reliability.
__________
Translated from Atomnaya énergiya, Vol. 100, No. 3, pp. 173–177, March, 2006. 相似文献
978.
N. V. Kolesov M. V. Tolmacheva 《Journal of Computer and Systems Sciences International》2007,46(2):262-268
A suboptimal algorithm of scheduling in hierarchic systems is considered. The algorithm does not practically require the enumeration of possibilities. The results on the efficiency of this algorithm are given based on the random generation of examples. 相似文献
979.
Bednars'ka L. M. Horelenko Yu. K. Kovbuz M. O. Hertsyk O. M. Kotur B. Ya. Nosenko V. K. 《Materials Science》2003,39(2):291-294
Alloying of amorphous Fe-Me-Si-B metallic compositions with nickel and molybdenum results in a decrease in the values of saturation magnetization in fields with a magnetic intensity of 0.72 MA/m. The same alloying additions decrease the temperature of formation of new magnetic Fe3B-type phases, which are stable up to 873 ± 5 K. 相似文献
980.