全文获取类型
收费全文 | 606973篇 |
免费 | 26901篇 |
国内免费 | 13760篇 |
专业分类
电工技术 | 22656篇 |
技术理论 | 56篇 |
综合类 | 20177篇 |
化学工业 | 96279篇 |
金属工艺 | 29292篇 |
机械仪表 | 29483篇 |
建筑科学 | 32024篇 |
矿业工程 | 12528篇 |
能源动力 | 16582篇 |
轻工业 | 40891篇 |
水利工程 | 8248篇 |
石油天然气 | 28626篇 |
武器工业 | 2639篇 |
无线电 | 69404篇 |
一般工业技术 | 95047篇 |
冶金工业 | 68822篇 |
原子能技术 | 10651篇 |
自动化技术 | 64229篇 |
出版年
2023年 | 5650篇 |
2022年 | 10196篇 |
2021年 | 14641篇 |
2020年 | 11389篇 |
2019年 | 10006篇 |
2018年 | 12672篇 |
2017年 | 13958篇 |
2016年 | 13076篇 |
2015年 | 14635篇 |
2014年 | 20108篇 |
2013年 | 30921篇 |
2012年 | 27061篇 |
2011年 | 31886篇 |
2010年 | 26532篇 |
2009年 | 26837篇 |
2008年 | 26827篇 |
2007年 | 26278篇 |
2006年 | 25880篇 |
2005年 | 23239篇 |
2004年 | 17376篇 |
2003年 | 15959篇 |
2002年 | 14724篇 |
2001年 | 14193篇 |
2000年 | 14355篇 |
1999年 | 16280篇 |
1998年 | 24229篇 |
1997年 | 18201篇 |
1996年 | 15162篇 |
1995年 | 12094篇 |
1994年 | 10326篇 |
1993年 | 9071篇 |
1992年 | 6825篇 |
1991年 | 6100篇 |
1990年 | 5544篇 |
1989年 | 5254篇 |
1988年 | 4755篇 |
1987年 | 4054篇 |
1986年 | 3916篇 |
1985年 | 4068篇 |
1984年 | 3693篇 |
1983年 | 3410篇 |
1982年 | 3217篇 |
1981年 | 3162篇 |
1980年 | 3154篇 |
1979年 | 2893篇 |
1978年 | 2898篇 |
1977年 | 3178篇 |
1976年 | 4148篇 |
1975年 | 2433篇 |
1973年 | 2403篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
Community studies in Guinea-Bissau have found that exposure to measles prior to 6 months of age is associated with delayed mortality later in childhood. In an attempt to understand the underlying mechanism, we examined the role of pre-exposure nutritional status and the impact of exposure to measles on growth and subsequent mortality in these outbreaks. Though exposed children were lighter than controls, there was no association between pre-exposure weight-for-age and subsequent mortality adjusting for age. Although exposure was strongly associated with excess mortality, it did not have a negative impact on growth. Adjustment for state of nutrition did not alter the mortality ratio (MR) between 6 and 59 months of age for exposed children and controls; exposed children examined anthropometrically between 6-17 months had a MR of 3.70 compared with controls. This trend was the same for anthropometric measurements obtained at 18-59 months of age. Among the controls, there was a significant association between weight-for-age and subsequent mortality to the age of 5 years. However, for exposed children there was no association; the relation between weight-for-age and subsequent mortality was significantly different for exposed children compared with controls (tests for interaction between exposure and anthropometric measurements at 6-17 months: P = 0.05). Growth faltering as a consequence of early exposure to measles does not explain the marked excess mortality among these children. Further studies of the process underlying delayed mortality after early exposure to measles are warranted. 相似文献
942.
A Avraméas D McIlroy A Hosmalin B Autran P Debré M Monsigny AC Roche P Midoux 《Canadian Metallurgical Quarterly》1996,26(2):394-400
Dendritic cells (CD) are the most efficient antigen presenting cells for T lymphocytes. CD1a+ CD14- CD with high antigen-presenting capacities can now be obtained easily from adherent peripheral blood monocytes by culture in the presence of granulocyte/macrophage colony-stimulating factor and interleukin-4 (Sallusto et al., J. Exp. Med. 1994. 179: 1109). Human macrophages express a membrane lectin, or sugar-specific receptor, which specifically mediates the binding and endocytosis of mannose- and fucose-terminated glycoproteins and is involved in the phagocytosis of pathogens. A similar lectin activity was sought on cultured human DC using flow cytometry and confocal microscopy to detect binding and internalization of fluoresceinated neoglycoproteins [bovine serum albumin (BSA) substituted with sugar residues]. Several neoglycoproteins, especially alpha-L-fucosyl-, alpha-D-mannosyl-, N,N'-di-acetyl-beta-chitobiosyl- and beta-D-glucosyl-BSA, were endocytosed by cultured human CD1a+ DC as well as by CD1a- CD14- cells which were also obtained in the culture. Fuc-BSA and Man-BSA had the same number of binding sites (1.7 x 10(6)/cell) on CD1a+ DC, and bound with an affinity constant close to 10(7) 1/mol. Inhibition experiments indicated that these two neoglycoproteins bound to the same membrane lectin. CD1a+ and CD1a- cells were both labeled by an antiserum specific for the human macrophage mannose receptor. The membrane lectin specific for mannose and fucose that is evidenced in these experiments on cultured DC may be similar to the macrophage membrane lectin or may share functional and structural properties with it. 相似文献
943.
We investigate the error probability bit error rate (BER) of minimum shift keying (MSK) modulation with differential detection in a two-path fading channel without noise (error floor). We develop a new method for the computation of the BER: we show that errors occur if the phasors of the instantaneous impulse response fall into certain regions of the complex plane; then we average over the statistics of the phasors to arrive at the mean BER. With this method, we derive analytical expressions for the BER for arbitrary amplitude statistics of the paths. For the special case of two Rayleigh-fading paths with small delay, we find that the BER is proportional to the square of the mean delay spread (normalized to the bit length) if we sample between the two pulses. This proves the qualitative behavior of previous estimates, but our results allow also a more exact quantitative formulation. The quadratic dependence of the BER on the delay spread breaks down if we have one Rayleigh-fading and one Rician-fading path. We find that the bit combinations 1-11 and -11-1 do not lead to errors in the two-path model. However, additional Monte Carlo simulations show that these bit combinations do lead to errors in a three-path model 相似文献
944.
随着GIS的工作电压不断提高和发展,一系列新的现象和问题也同时出现。从国外一些科研,设计,制造部门所研究发表的内容看,大致有隔离开关操作和高速瞬变过程,粒子影响和对干扰定位的技术,元件的监督,现场试验等课题,本文对以上问题加以综合介绍。 相似文献
945.
基于STEP的零件加工工艺计划模型 总被引:1,自引:0,他引:1
为了满足CIMS环境下工艺系统与其它系统集成的需要,建立了标准工艺计划模型具十分重要的意义。本文描述了一个基于STEP的零件加工工艺计划模型,介绍了建立这一模型的关键技术,给出了参照STEP建立工艺计划模型的方法。 相似文献
946.
We propose a new principle for a low temperature semiconductor detector of charged particles with possibly submicron lateral resolution based on point contacts formed in the 2-dimensional electron gas (2DEG) of a GaAs-AlxGa1-xAs heterostructure using split-gates. The detector operates up to liquid nitrogen temperatures. Impinging particles excite locally extra donors in the doping layer of the heterostructure. By measuring simultaneous increase in the conductances of 3 point contacts due to the impacts of charged particles the position of penetration is calculated using the Thomas-Fermi approximation for screening in 2DEG. 相似文献
947.
本文利用选区电子衍射,并结合X射线衍射对六种不同成份的急冷合金及其退火后的相组成进行了鉴定,得到了它们的相组成。 相似文献
948.
Scientific-Technical Center “Atomtekhénergo.” Leningrad Nuclear Power Plant. N. V. Sultanov Institute of Nuclear Reactors,
Russian Scientific Center “Kurchatovskii institut.” Translated from Atomnaya énergiya, Vol. 76, No. 6, pp. 470–473, June,
1994. 相似文献
949.
950.
G. P. Ledneva 《Journal of Engineering Physics and Thermophysics》1994,67(3-4):960-964
Heating of spherical alumina particles by high-intensity laser radiation under vacuum conditions to the melting temperature is investigated with account for the nonuniform distribution of energy sources with respect to the particle volume.B. I. Stepanov Institute of Physics, Academy of Sciences of Belarus, Minsk. Translated fron Inzhenerno-Fizicheskii Zhurnal, Vol. 67, Nos. 3–4, pp. 307–312, September–October, 1994. 相似文献