全文获取类型
收费全文 | 3426篇 |
免费 | 204篇 |
国内免费 | 214篇 |
专业分类
电工技术 | 47篇 |
综合类 | 182篇 |
化学工业 | 1081篇 |
金属工艺 | 419篇 |
机械仪表 | 96篇 |
建筑科学 | 82篇 |
矿业工程 | 36篇 |
能源动力 | 46篇 |
轻工业 | 780篇 |
水利工程 | 7篇 |
石油天然气 | 132篇 |
武器工业 | 12篇 |
无线电 | 126篇 |
一般工业技术 | 308篇 |
冶金工业 | 158篇 |
原子能技术 | 104篇 |
自动化技术 | 228篇 |
出版年
2024年 | 12篇 |
2023年 | 70篇 |
2022年 | 173篇 |
2021年 | 218篇 |
2020年 | 157篇 |
2019年 | 114篇 |
2018年 | 116篇 |
2017年 | 143篇 |
2016年 | 126篇 |
2015年 | 113篇 |
2014年 | 184篇 |
2013年 | 306篇 |
2012年 | 371篇 |
2011年 | 348篇 |
2010年 | 222篇 |
2009年 | 176篇 |
2008年 | 172篇 |
2007年 | 142篇 |
2006年 | 128篇 |
2005年 | 116篇 |
2004年 | 104篇 |
2003年 | 54篇 |
2002年 | 44篇 |
2001年 | 27篇 |
2000年 | 19篇 |
1999年 | 28篇 |
1998年 | 18篇 |
1997年 | 22篇 |
1996年 | 23篇 |
1995年 | 16篇 |
1994年 | 14篇 |
1993年 | 10篇 |
1992年 | 9篇 |
1991年 | 8篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1980年 | 2篇 |
1977年 | 1篇 |
1973年 | 2篇 |
排序方式: 共有3844条查询结果,搜索用时 31 毫秒
991.
IFN-α2a对多发性硬化患者外周血中免疫抑制因子IL-10的影响 总被引:2,自引:0,他引:2
目的观察重组人干扰素α-2a对MS的治疗效果,探讨其治疗机理。方法采用ELISA夹心法检 测22例MS患者治疗前后血清中IL-10浓度,结合临床疗效进行对比分析。结果重组人干扰素α-2a治疗组患者 血清中IL-10浓度明显增高,临床症状明显改善,与对照组比较差异有显著意义。结论重组人干扰素IFN-α2a可 提高MS患者体内IL-10水平,对MS有良好疗效。 相似文献
992.
Some individuals fear that estrogens in dairy products may stimulate growth of estrogen-sensitive cancers in humans. The presence of estrone (E1) and 17β-estradiol (E2) in raw whole cow's milk has been demonstrated. The objectives of this study were to determine if pasteurization-homogenization affects E2 concentration in milk and to quantify E1 and E2 concentrations in commercially available dairy products. The effects of pasteurization-homogenization were tested by collecting fresh raw milk, followed by pasteurization and homogenization at 1 of 2 homogenization pressures. All treated milks were tested for milk fat globule size, percentages of milk fat and solids, and E2 concentrations. Estrone and E2 were quantified from organic or conventional skim, 1%, 2%, and whole milks, as well as half-and-half, cream, and butter samples. Estrone and E2 were quantified by RIA after organic solvent extractions and chromatography. Pasteurization-homogenization reduced fat globule size, but did not significantly affect E2, milk fat, or milk solids concentrations. Estrone concentrations averaged 2.9, 4.2, 5.7, 7.9, 20.4, 54.1 pg/mL, and 118.9 pg/g in skim, 1%, 2%, and whole milks, half-and-half, cream, and butter samples, respectively. 17β-Estradiol concentrations averaged 0.4, 0.6, 0.9, 1.1, 1.9, 6.0 pg/mL, and 15.8 pg/g in skim, 1%, 2%, whole milks, half-and-half, cream, and butter samples, respectively. The amount of fat in milk significantly affected E1 and E2 concentrations in milk. Organic and conventional dairy products did not have substantially different concentrations of E1 and E2. Compared with information cited in the literature, concentrations of E1 and E2 in bovine milk are small relative to endogenous production rates of E1 and E2 in humans. 相似文献
993.
Marine S. Da Silva Jean-François Bilodeau Pierre Julien 《Critical reviews in food science and nutrition》2017,57(18):3929-3941
Evidence supports that a high dietary fat intake increases oxidative stress and the risk of diet-induced metabolic disorders such as obesity, diabetes and cardiovascular diseases. F2-isoprostanes (F2-isoP) are formed by the non-enzymatic oxidation of arachidonic acid and are widely used as reliable biomarkers of oxidative stress in clinical studies. Dietary fats may influence F2-isoP levels, as they (1) are metabolic substrates for their formation, (2) modify the lipid composition of tissues, and (3) affect the plasma lipoprotein concentrations which are involved in F2-isoP transport. This review examined the latest clinical evidence on how dietary fats can affect blood circulation and excretion of F2-isoP in individuals with healthy or deteriorated metabolic profiles. Clinical studies reported that saturated or monounsaturated fat-rich diets did not affect F2-isoP levels in adults with healthy or deteriorated metabolic profiles. Though, ω-3 polyunsaturated fatty acids decreased F2-isoP levels in numerous studies, whereas trans-fatty acids raised F2-isoP excretion. Yet, the reported heterogeneous results reveal important considerations, such as the health status of the participants, the biological fluids used to determine F2-isoP, the analytical methods employed and the specific F2-isoP isomers detected. Therefore, future clinical studies should be designed in order to consider these issues in the studies of the effects of fat intake on oxidative stress. 相似文献
994.
D.J. Brusveen 《Journal of dairy science》2009,92(4):1412-1422
This study was designed to evaluate whether decreasing circulating progesterone (P4) or increasing circulating estradiol-17β (E2) near the time of artificial insemination (AI) in an Ovsynch protocol would increase pregnancies per AI (P/AI) in lactating dairy cows. Six hundred nineteen lactating Holstein cows (n = 772 inseminations) received Ovsynch (GnRH-7 d-PGF2α-56 h-GnRH-16 h-timed AI). Cows were randomized in a 2 × 2 factorial experiment of 4 treatments to receive or not receive 25 mg of PGF2α 24 h after the standard PGF2α of Ovsynch, or 0.5 mg of E2 at the time of the final GnRH of Ovsynch, or both. Blood samples were collected 24 h after normal PGF2α and at final GnRH to evaluate circulating P4. Ovarian ultrasound was done at final GnRH to determine preovulatory follicle size. Ovulation was confirmed by ultrasound 5 d after AI. Treatment with additional PGF2α increased the percentage of cows that had complete luteal regression (95.6%) compared with control cows (84.6%). In contrast, additional PGF2α had no detectable effect on P/AI (control = 41.5% vs. + PGF2α = 44.7%). Supplementation with E2 increased expression of estrus (84.4 vs. 37.2%), but had no effect on overall fertility and even tended to have a negative effect on fertility in cows that ovulated to the second GnRH (control = 51.5% vs. +E2 = 44.0%). Thus, additional treatments with PGF2α or E2 during Ovsynch can be used to increase synchronization and expression of estrus during Ovsynch, although the lack of improvement in fertility makes these treatments unwarranted. 相似文献
995.
996.
997.
Wet and dry tribological behaviors of circular islandic protrusion patterns on M2 steel discs under spinning condition 总被引:1,自引:0,他引:1
Under spinning conditions, lubricant on islandic spot patterned M2 steel disc experiences centrifugal and tangential force components. Depending upon the relative position of the spots and the flow of lubricant, accumulation of lubricant in front of patterned islandic spots creates thrusting to mating part and subsequently reduces contact between the mating couple. Whilst wear debris is likely to be spun off the plateau of the spots to their neighbouring valleys so as to reduce wear. Hence, it gives favorable tribological characteristics. Aiming at verifying such mechanisms, studies were performed on M2 steel disc specimens slid with ASSAB 17 tool steel pin. The M2 steel disc specimens were respectively (i) machined with non-patterned (NP), (ii) etched to produce in-lined (INE) islandic patterns, and (iii) etched to produce staggered (STE) islandic spot patterns. Results indicated that the INE patterned discs gave most favorable wear characteristics, the NP of the worse characteristics whilst the STE ranged in the middle. However, the actual contact mechanism leads to the descending sequence of favorable friction behaviors nominally as: NP, INE and STE. 相似文献
998.
介绍了一种以市售1-溴代烷和α,ω-二醇为原料,经α,ω-二醇单溴代、与对甲苯磺酰氯成酯,再与1-溴代烷的格氏试剂偶联来合成更高级1-溴代烷的简便方法。 相似文献
999.
制备了金属间化物(DyxSm1-x)2Fe17Ny(x=0.2,0.4,0.6,0.8;2<y<3)的取向样品,并通过变温穆斯堡尔谱等手段研究金属间化物(DyxSm1-x)2Fe17Ny(x=0.4;2<y<3)的自旋重取向现象,进而对其中的各向异性产生机制等方面进行了分析。由试验得出以下结论:1)取向样品(DyxSm1-x)2Fe17Ny(x=0.4;2<y<3)在100~150K温度之间存在自旋重取向现象,即由易C轴各向异性变为易锥面各向异性;2)金属间化物(DyxSm1-x)2Fe17Ny(x=0.4;2<y<3)中Dy次格子的单轴各向异性较强,导致在较低温度下出现自旋磁结构的相变。 相似文献
1000.
目的 解决已涂胶的水松纸黏上烟末、复合型滤棒添加物颗粒或其他杂物而产生的烟支水松纸夹末、皱纹、漏气等一系列产品质量问题。方法 在ZJ17型卷烟机MAX部分汇合鼓轮与靠拢鼓轮之间加装两道清洁烟末装置,实现电气一体化控制。该装置与设备原本的接装纸切刀辊防护罩左下方吹气装置形成三道吹风清洁装置。结果 三道吹气装置在汇合鼓轮与靠拢鼓轮之间形成一层隔离气帘。隔离气帘能够隔离烟末、复合型滤棒添加物颗粒等杂物,产品质量缺陷率由2.68%降至0.36%。结论 所研制的清洁装置效果显著,降低了烟支夹末质量缺陷率,保证了产品质量,在ZJ118、ZJ116等机型上具有较广泛的推广应用价值。 相似文献