全文获取类型
收费全文 | 5841篇 |
免费 | 209篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 74篇 |
综合类 | 2篇 |
化学工业 | 862篇 |
金属工艺 | 128篇 |
机械仪表 | 229篇 |
建筑科学 | 95篇 |
矿业工程 | 1篇 |
能源动力 | 143篇 |
轻工业 | 338篇 |
水利工程 | 13篇 |
石油天然气 | 2篇 |
无线电 | 691篇 |
一般工业技术 | 777篇 |
冶金工业 | 2261篇 |
原子能技术 | 43篇 |
自动化技术 | 397篇 |
出版年
2023年 | 42篇 |
2022年 | 44篇 |
2021年 | 83篇 |
2020年 | 74篇 |
2019年 | 78篇 |
2018年 | 109篇 |
2017年 | 116篇 |
2016年 | 128篇 |
2015年 | 107篇 |
2014年 | 160篇 |
2013年 | 259篇 |
2012年 | 233篇 |
2011年 | 307篇 |
2010年 | 210篇 |
2009年 | 228篇 |
2008年 | 211篇 |
2007年 | 172篇 |
2006年 | 184篇 |
2005年 | 143篇 |
2004年 | 148篇 |
2003年 | 124篇 |
2002年 | 103篇 |
2001年 | 96篇 |
2000年 | 81篇 |
1999年 | 110篇 |
1998年 | 723篇 |
1997年 | 478篇 |
1996年 | 308篇 |
1995年 | 185篇 |
1994年 | 147篇 |
1993年 | 146篇 |
1992年 | 32篇 |
1991年 | 43篇 |
1990年 | 28篇 |
1989年 | 31篇 |
1988年 | 37篇 |
1987年 | 27篇 |
1986年 | 24篇 |
1985年 | 24篇 |
1984年 | 9篇 |
1982年 | 12篇 |
1981年 | 25篇 |
1980年 | 20篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1977年 | 49篇 |
1976年 | 121篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1973年 | 5篇 |
排序方式: 共有6056条查询结果,搜索用时 453 毫秒
41.
AG Martov VIa Simonov BM Krendel'' SS Zenkov SA Moskalenko 《Canadian Metallurgical Quarterly》1993,38(3):16-19
Hyperferremia is shown to affect antioxidant system of the body, oxidation-reduction reactions in the cells seen as shifts in lymphocyte chemiluminescence. Dynamic changes in lymphocyte chemiluminescence reflect the level of hyperferremia. 相似文献
42.
JR Perry SS Deodhare JM Bilbao D Murray P Muller 《Canadian Metallurgical Quarterly》1993,32(2):157-162
Sex hormones have profound effects on immune responses and may influence the outcome of autoimmune diseases such as rheumatoid arthritis (RA). We investigated the effect of gonadal steroids on the production of interleukin-1 (IL-1) and IL-6, cytokines believed to be important in the pathogenesis of RA. Peripheral blood mononuclear cells (PBMCs) were isolated from healthy male donors and male patients with RA, and were stimulated with lipopolysaccharide (LPS) in the presence of different concentrations of 17-beta-estradiol, progesterone or testosterone. In studies of cells from normal male donors, 17-beta-estradiol at pharmacological concentrations (> or = 10(-6) M) enhanced IL-1 and IL-6 secretion as well as the production of cell-associated IL-1. Progesterone and testosterone at similar concentrations inhibited IL-1 secretion but had no significant effect on IL-6 secretion or on the production of cell-associated IL-1. In studies of male RA donors, 17-beta-estradiol failed to enhance IL-1 or IL-6 secretion and progesterone failed to inhibit IL-1 secretion. The inhibitory effects of testosterone, however, appeared to be similar to that in normal donors. It is suggested that 17-beta-estradiol may promote IL-1 and IL-6 production and release, while gestation hormone, progesterone, and testosterone may inhibit IL-1 release in vivo. These data may partly explain the gender and age differences in the incidence of RA and the development of the disease in men with low and androgen levels. 相似文献
43.
Robotic synthesis is making possible the synthesis of large, systematically designed sets of compounds. We analyze a 512-compound set that is a 2(9) full factorial experimental design using a recursive partitioning algorithm, FIRM, and a high-dimension visualization tool, TempleMVV. These techniques are used to quickly and easily identify the main trends in the data set and also identify unusual observations. We show that analytical and visualization methods can be used synergistically to analyze a large, complex, high-dimensional data set. We also show that a fractional factorial design of 128 compounds would give essentially the same information. 相似文献
44.
45.
46.
Cardioprotective effects of a standardized extract from leaves with flowers of Crataegus (WS-1442; content of oligomeric procyandins [OPC]: 18.75%) have recently been demonstrated in an ischemia-reperfusion model in rats. Further studies were now conducted to clarify the mechanism of action and to identify active constituents involved in these effects of WS-1442. Exhausting partitioning between ethyl acetate/water and successive ultrafiltration of the aqueous layer led to the quantitative recovery of three fractions, which were tested for their in vitro radical scavenging (RS) and human neutrophil elastase (HNE) inhibitory activity. The lipophilic ethylacetate-soluble fraction A, enriched in flavone derivatives and constituting 14.9% of WS-1442, was as active as WS-1442 in inhibiting HNE. However, its RS activity was only about half that of the primary extract. Although 67.9% of WS-1442 was recovered in a water-soluble low molecular weight fraction B, this fraction displayed only weak RS and HNE inhibiting activity. In contrast, the RS and HNE inhibiting potencies of an essentially flavone-free and OPC-rich fraction C (21.3% of WS-1442) were significantly higher (inhibition of lipid peroxidation: IC50 0.3 microgram/ml; inhibition of HNE: IC50 0.84 microgram/ml) as those of WS-1442. The RS and HNE inhibitory activities of the extract and those of its fractions correlated well with their OPC-content but not with their concentration of flavonols. These results demonstrate that OPCs of Crataegus extracts possess stronger radical scavenging activities than flavone derivatives or other constituents. In addition, the oligomeric components are potent inhibitors of HNE. Oral administration of 20 mg/kg/d of the OPC-rich fraction C to rats afforded similar protection against ischemia-reperfusion induced pathologies as treatment with WS-1442 at a dose of 100 mg/kg/d. These observations indicate that radical scavenging and elastase inhibitory activities could indeed be involved in the observed cardioprotective effects of WS-1442, and demonstrate that OPCs are major orally active constituents of WS-1442. Thus, Crataegus extracts used therapeutically for cardiovascular diseases should be analyzed and standardized for their OPC-content. 相似文献
47.
48.
49.
Myoblast-mediated gene transfer to the joint 总被引:1,自引:0,他引:1
CS Day C Kasemkijwattana J Menetrey SS Floyd D Booth MS Moreland FH Fu J Huard 《Canadian Metallurgical Quarterly》1997,15(6):894-903
Several genetic and acquired pathologic conditions of the musculoskeletal system, such as arthritis and damage to ligament, cartilage, and meniscus, may be amenable to gene therapy. Even though ex vivo gene transfer with synovial cells has been shown to deliver genes encoding for anti-arthritic proteins into the rabbit knee joint, its success has been limited by a transient transgene expression. In this study, data were investigated regarding the use of muscle cells as an alternative gene-delivery vehicle to the joint in newborn rabbit and adult severe combined immunodeficiency mice. We demonstrated that myoblasts were transduced more efficiently than synovial cells with use of the same adenoviral preparation in vitro. After intra-articular injection, the engineered muscle cells adhered to several structures in the joint, including the ligament, capsule, and synovium. In addition, myoblasts fused to form many post-mitotic myotubes and myofibers at different locations of the joint of the newborn rabbit 5 days after the injection. In the knee of the adult mouse, myoblasts fused and expressed the reporter gene for at least 35 days after the injection. The presence of post-mitotic myofibers in the knee joint raises the possibility of long-term expression of the secreted protein. Currently, numerous tissues in the joint (ligament, meniscus, and cartilage) have poor intrinsic healing capacity and frequently need surgical corrections. A stable gene-delivery vehicle to the joint producing proteins that ameliorate these different musculoskeletal conditions may change the clinical implications of these pathologies. 相似文献
50.
Kyeong Joong Kim Jong-Yeul Suh Moon Gi Kang Kyu Tae Park 《Electronics letters》1998,34(13):1302-1303
The boundary is approximated by a polygon which can be encoded with the smallest number of bits for maximum distortion. The temporal redundancy between two successive frames is efficiently removed with the proposed scheme, resulting in a lower bit rate than the conventional algorithms 相似文献