全文获取类型
收费全文 | 252251篇 |
免费 | 1956篇 |
国内免费 | 430篇 |
专业分类
电工技术 | 4237篇 |
综合类 | 326篇 |
化学工业 | 40861篇 |
金属工艺 | 15214篇 |
机械仪表 | 10235篇 |
建筑科学 | 4375篇 |
矿业工程 | 3891篇 |
能源动力 | 3939篇 |
轻工业 | 9996篇 |
水利工程 | 4155篇 |
石油天然气 | 13093篇 |
武器工业 | 65篇 |
无线电 | 20723篇 |
一般工业技术 | 63162篇 |
冶金工业 | 32288篇 |
原子能技术 | 11266篇 |
自动化技术 | 16811篇 |
出版年
2021年 | 2894篇 |
2019年 | 2816篇 |
2018年 | 5517篇 |
2017年 | 5809篇 |
2016年 | 6143篇 |
2015年 | 3173篇 |
2014年 | 5517篇 |
2013年 | 10317篇 |
2012年 | 7558篇 |
2011年 | 9213篇 |
2010年 | 7546篇 |
2009年 | 8320篇 |
2008年 | 8347篇 |
2007年 | 8027篇 |
2006年 | 6508篇 |
2005年 | 5711篇 |
2004年 | 5580篇 |
2003年 | 5394篇 |
2002年 | 5213篇 |
2001年 | 5019篇 |
2000年 | 4985篇 |
1999年 | 4312篇 |
1998年 | 7226篇 |
1997年 | 5870篇 |
1996年 | 4447篇 |
1995年 | 3678篇 |
1994年 | 3449篇 |
1993年 | 3641篇 |
1992年 | 3229篇 |
1991年 | 3373篇 |
1990年 | 3492篇 |
1989年 | 3376篇 |
1988年 | 3279篇 |
1987年 | 3268篇 |
1986年 | 3161篇 |
1985年 | 3316篇 |
1984年 | 3253篇 |
1983年 | 3149篇 |
1982年 | 2995篇 |
1981年 | 3046篇 |
1980年 | 3076篇 |
1979年 | 3260篇 |
1978年 | 3494篇 |
1977年 | 3465篇 |
1976年 | 3915篇 |
1975年 | 3209篇 |
1974年 | 3297篇 |
1973年 | 3342篇 |
1972年 | 2987篇 |
1971年 | 2756篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
981.
982.
L. L. Rokhlin T. V. Dobatkina N. R. Bochvar E. V. Lysova I. E. Tarytina 《Russian Metallurgy (Metally)》2007,(4):335-339
The effect of small chromium and yttrium additions (0.14–1.0 wt%) on the recrystallization of Al-Sc alloys having 0.1–0.4% Sc is studied with polarized light. The microstructure of cold-rolled samples annealed at 100–630°C for 1 h is examined. The chromium and yttrium additions are found to slightly affect the recrystallization temperature of the Al-Sc alloys: they increase or decrease it slightly depending on the scandium content. 相似文献
983.
We analyze the wear resistance of plasma coatings for a constant work of friction. The dependences of the wear resistance
of the coatings are obtained for a broad range of loading conditions. It is shown that the minimum sensitivity to loading
conditions is exhibited by the molybdenum coatings. It is also established that the wear resistance of the coatings decreases
as the amplitude of displacements increases and the cyclic frequency of the tests decreases due to the intensification of
fatigue processes on the surfaces. The comparative characteristics of coatings are presented.
__________
Translated from Problemy Prochnosti, No. 5, pp. 94–100, September–October, 2007. 相似文献
984.
Eighty-six cows were assigned to two equal groups with group A fed according to National Research Council recommendations for total digestible nutrients for the 8 wk before parturition and group B was fed 21% higher energy in the first 6 wk and 15% higher in the last 2 preparturient wk. Thyroxine in blood serum decreased in both groups 14 days before and on the day of delivery. It was significantly lower in group A. Findings were similar with triiodothyronine. Blood serum concentrations of reverse-triiodothyronine of group A was significantly higher in group A on day 28 and 14 than group B before delivery. Energy intake had little influence on the serum concentrations of other constituents (albumin, total protein, immunoglobulin G, total and free cholesterol, nonesterified fatty acids). Restricted energy intake that does not alter thyrotropin-thyrotropin-releasing hormone secretion results in higher rate of production of reverse-triiodothyronine and in decreased serum concentration of triiodothyronine. Slight changes of energy balance might be indicated readily by reverse-triiodothyronine concentration in blood serum. 相似文献
985.
Buffer capacity of ultrafiltered skim milk retentates at various protein concentrations and growth of direct set, frozen concentrated lactic starter cultures in such retentates were studied. Maximum buffering occurred at approximately pH 5.1 to 5.3. An average .48% lactic acid concentration was required to reduce the pH of plain skim milk to 4.6 compared with 1.01% for skim milk retentates concentrated 2.3:1 and 1.14% for skim milk retentate concentrated 2.6:1. Skim milk retentates concentrated 4.3:1 and 5.8:1 were unable to attain pH 4.6 even when titratable acid was greater than 1.8%. Lactic acid required to reduce pH to 4.6 for the two lower concentrated retentates (2.3:1 and 2.6:1) were 1.85 and 2.45%. Time to attain pH 4.6 was a function of the bacterial cell concentration of the cultures and the total protein level of retentates. Starter organism growth was unaffected by high total solids or ash of retentates. Growth rate and lactose metabolism decreased markedly below pH 5.2 at which point bacterial population was 10(9) cfu/ml. 相似文献
986.
As far as flocculation is concerned, the agglomeration of suspended particles into flocs is highly linked to the hydraulic behaviour of the agitation. The Turbomix is a special design of mixing tank; its design was developed to better control the flow during the flocculation stage. It enables a significant decrease in footprint of the process. The combination of the Turbomix and ballasted flocculation has been studied during pilot trials in terms of treatment efficiency. Its controlled hydraulic behaviour explains the efficiency of the process as proved by CFD investigation. 相似文献
987.
988.
989.
With the aim of optimizing the performance of Li/Li1+xV3O8 cells, several aspects of cathode preparation have been examined. The influence of synthesis technique, nature and amount of conductive additives, compacting pressure, cathode loading, and particle size, has been investigated. Furthermore, the role played by the solutions on cathode efficiency has been outlined. The formulations which perform best are based on small-sized particles blended with about 20% acetylene black and compacted at very high pressures to improve the contact between particles. Such cathodes can provide high capacities at high rates and good cycling efficiencies. The kinetic loss of capacity, observed during the first few cycles, may be alleviated by choosing solutions with high fluidity and conductivity. 相似文献
990.
In this paper, effectiveness of involutive criteria in the elimination of useless prolongations when computing polynomial Janet bases, which are typical representatives of involutive bases, is discussed. One of the results of this study is that the role of the criteria in an involutive algorithm is not as important as in the Buchberger algorithm. It is shown also that these criteria affect the growth of intermediate coefficients. 相似文献