全文获取类型
收费全文 | 19346篇 |
免费 | 738篇 |
国内免费 | 44篇 |
专业分类
电工技术 | 237篇 |
综合类 | 24篇 |
化学工业 | 3739篇 |
金属工艺 | 467篇 |
机械仪表 | 397篇 |
建筑科学 | 948篇 |
矿业工程 | 108篇 |
能源动力 | 600篇 |
轻工业 | 1634篇 |
水利工程 | 172篇 |
石油天然气 | 68篇 |
无线电 | 1457篇 |
一般工业技术 | 3364篇 |
冶金工业 | 3855篇 |
原子能技术 | 116篇 |
自动化技术 | 2942篇 |
出版年
2023年 | 123篇 |
2022年 | 210篇 |
2021年 | 329篇 |
2020年 | 234篇 |
2019年 | 270篇 |
2018年 | 368篇 |
2017年 | 378篇 |
2016年 | 413篇 |
2015年 | 338篇 |
2014年 | 513篇 |
2013年 | 1218篇 |
2012年 | 825篇 |
2011年 | 1166篇 |
2010年 | 799篇 |
2009年 | 829篇 |
2008年 | 930篇 |
2007年 | 871篇 |
2006年 | 759篇 |
2005年 | 743篇 |
2004年 | 595篇 |
2003年 | 541篇 |
2002年 | 526篇 |
2001年 | 332篇 |
2000年 | 303篇 |
1999年 | 346篇 |
1998年 | 509篇 |
1997年 | 369篇 |
1996年 | 368篇 |
1995年 | 335篇 |
1994年 | 306篇 |
1993年 | 288篇 |
1992年 | 263篇 |
1991年 | 162篇 |
1990年 | 233篇 |
1989年 | 206篇 |
1988年 | 170篇 |
1987年 | 168篇 |
1986年 | 157篇 |
1985年 | 188篇 |
1984年 | 197篇 |
1983年 | 163篇 |
1982年 | 173篇 |
1981年 | 171篇 |
1980年 | 146篇 |
1979年 | 165篇 |
1978年 | 123篇 |
1977年 | 130篇 |
1976年 | 194篇 |
1975年 | 126篇 |
1973年 | 108篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
S Tetali E Abrams S Bakshi M Paul N Oyaizu S Pahwa 《Canadian Metallurgical Quarterly》1996,12(8):669-675
The relationship of virus load to clinical disease progression in HIV-infected children remains to be elucidated. In this study, HIV-1 proviral DNA load was determined in peripheral blood mononuclear cells (PBMCs) by the quantitative competitive DNA polymerase chain reaction assay (QC-PCR) in 47 HIV-infected children subdivided by age (group I, < or = 2 years; group II, > or = 5 years), who were further categorized to include 12 rapid progressors (RP, age < or = 2 years, Centers for Disease Control [CDC] defined clinical category C and/or immune category 3, or death before age 2 years) and slow progressors (SP, age > or = 5 years, excluding CDC categories C and/or immune category 3). Significantly higher mean proviral copies/10(3) PBMCs were detected in group I versus group II (75.4 +/- 104.3 and 13.0 +/- 17.8 respectively, p < 0.0001) and in RP (158.0 +/- 118.2) as compared to either SP (11.8 +/- 18.8, p < 0.0001) or other age-matched infected children (20.3 +/- 38.8, p < 0.0001). Thus HIV-infected children appear to have a higher cell-associated virus load early in life, especially in association with rapid disease progression. 相似文献
62.
J. K. Richard Weber† Collin D. Anderson Dennis R. Merkley Paul C. Nordine† 《Journal of the American Ceramic Society》1995,78(3):577-582
Solidification of aluminum oxide from undercooled melts was investigated in containerless experiments. Specimens were levitated in a gas jet, stabilized with an acoustic positioning device, and melted with cw CO2 laser beams. Cooling curves were obtained by optical pyrometry when the laser intensity was reduced. The materials examined were high-purity Verneuil sapphire, 99.5% polycrystalline alumina, and oxide materials recovered from the effluent of an aluminum-fueled rocket motor. The degree of undercooling, the apparent temperature behavior during the thermal arrest on solidification, and the structure of the materials formed were different in argon and oxygen atmospheres. Undercooling of the sapphire and alumina materials was 360 ± 10 K in an oxygen atmosphere and approximately 450 K in argon. Melting and solidification of high-purity sapphire resulted in a dendritic and porous polycrystalline material in oxygen. Dense, larger crystals were obtained in argon. Products formed from 99.5% alumina were discolored and the cores were white, indicating impurity segregation effects. More reproducible behavior was observed for the sapphire and 99.5% alumina than for the tungstencontaminated rocket motor effluent materials. 相似文献
63.
Empirical studies suggest a very high prevalence of atopic disorder in people with depression. Research indicates that individuals with allergy have cholinergic hyperresponsiveness and beta-adrenergic hyporesponsiveness in the autonomic nervous system. Evidence is reviewed that similar imbalances in CNS cholinergic–adrenergic activity play a causal role in depression behaviors. It is hypothesized that the allergic state or allergic reactions can accentuate cholinergic–adrenergic activity imbalances in the CNS of a small subgroup of people at risk for endogenous depression thereby producing depression symptomatology. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
64.
Packaging engineers need to be able to accurately determine the forces present in the shipping environment in order to protect packaged goods. The purpose of this study was to determine the vertical vibration levels measured in three separate truck-trailer suspension systems; conventional leaf-spring, conventional air-ride and damaged air-ride. The main conclusion reached in this study is that the air-ride suspension when maintained gives lower power density (PD) levels on all road surfaces studied. A damaged air-ride suspension and leaf-spring suspension are very similar in response frequencies, although the damaged air-ride produces higher vibration levels at lower frequencies. 相似文献
65.
Ellen Y. Sun Kathleen B. Alexander Paul F. Becher Shyh-Lung Hwang 《Journal of the American Ceramic Society》1996,79(10):2626-2632
Interfacial microstructures in βP-Si3 N4 ( w )-Si-Al-Y-O-N-glass systems were investigated by systematically varying the nitrogen content and the Al:Y ratio of the glass matrix. High-resolution and analytical transmission electron microscopy (HREM and AEM) studies revealed that the interfacial microstructure is a function of the glass composition. No interfacial phases were formed in glasses with low Al:Y ratios and in glasses with high Al:Y ratios and low nitrogen content, whereas epitaxial growth of an interfacial layer (100–200 μm thick) on the βP-Si3 N4 ( w ) occurred in a glass matrix with high Al:Y ratio and high nitrogen content. The interfacial layer was identified to be a β'-SiAION phase. Interfaces containing the SiAION layer exhibited high debonding energy compared to Si3 N4 ( w )–glass interfaces. HREM studies indicated that the lattice-mismatch strain in the SiAION layer was relieved by dislocation formation at the SiAION–Si3 N4 ( w ) interface. The difference in interfacial debonding energy was, hence, attributed to the local atomic structure and bonding between the glass-β-Si3 N4 and the glass–β'-SiAION phases. This observation was clear evidence of the strong influence of glass chemistry on the interfacial debonding behavior by altering the interfacial microstructure. 相似文献
66.
67.
68.
Shannon’s entropy plays an important role in the context of information theory. Since this entropy is not applicable to a system which has survived for some units of time, the concept of residual entropy has been developed in the literature. Here we generalize the residual entropy by choosing a convex function ? with ?(1) = 0. In this paper, some orderings and aging properties have been defined in terms of the generalized residual entropy function and their properties have been studied. Quite a few results available in the literature have been generalized and some distributions (viz. uniform, exponential, Pareto, power series, finite range) have been characterized through the generalized residual entropy. 相似文献
69.
70.