全文获取类型
收费全文 | 16085篇 |
免费 | 1527篇 |
国内免费 | 369篇 |
专业分类
电工技术 | 688篇 |
综合类 | 502篇 |
化学工业 | 3509篇 |
金属工艺 | 659篇 |
机械仪表 | 934篇 |
建筑科学 | 643篇 |
矿业工程 | 189篇 |
能源动力 | 726篇 |
轻工业 | 1526篇 |
水利工程 | 162篇 |
石油天然气 | 368篇 |
武器工业 | 64篇 |
无线电 | 2382篇 |
一般工业技术 | 2968篇 |
冶金工业 | 694篇 |
原子能技术 | 219篇 |
自动化技术 | 1748篇 |
出版年
2024年 | 32篇 |
2023年 | 205篇 |
2022年 | 382篇 |
2021年 | 561篇 |
2020年 | 454篇 |
2019年 | 508篇 |
2018年 | 530篇 |
2017年 | 569篇 |
2016年 | 668篇 |
2015年 | 605篇 |
2014年 | 924篇 |
2013年 | 1034篇 |
2012年 | 1131篇 |
2011年 | 1329篇 |
2010年 | 1079篇 |
2009年 | 999篇 |
2008年 | 885篇 |
2007年 | 828篇 |
2006年 | 687篇 |
2005年 | 645篇 |
2004年 | 503篇 |
2003年 | 473篇 |
2002年 | 477篇 |
2001年 | 444篇 |
2000年 | 348篇 |
1999年 | 305篇 |
1998年 | 302篇 |
1997年 | 221篇 |
1996年 | 134篇 |
1995年 | 146篇 |
1994年 | 97篇 |
1993年 | 91篇 |
1992年 | 77篇 |
1991年 | 49篇 |
1990年 | 45篇 |
1989年 | 51篇 |
1988年 | 29篇 |
1987年 | 16篇 |
1986年 | 12篇 |
1985年 | 14篇 |
1984年 | 13篇 |
1983年 | 12篇 |
1982年 | 8篇 |
1981年 | 14篇 |
1980年 | 6篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1976年 | 5篇 |
1975年 | 7篇 |
1973年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Since acne vulgaris is the combined result of a bacterial infection and the inflammatory response to that infection, we examined
whether Abies koreana essential oil (AKE) possessed anti-inflammatory and antibacterial activities against skin pathogens. In this study, AKE showed
excellent antibacterial activities against drug-susceptible and -resistant Propionibacterium acnes and Staphylococcus epidermidis, which are acne-causing bacteria. In addition, AKE reduced the LPS-induced secretion of tumor necrosis factor-α (TNF-α),
interleukin-1β (IL-1β), IL-6, NO and PGE2 in RAW 264.7 cells, indicating that it has anti-inflammatory effects. Therefore, we suggest that AKE may be an attractive
candidate for promoting skin health. 相似文献
992.
利用动态力学分析(DMA)方法,研究了吡啶基官能化的SBS(极性化SBS或SBSVP)热塑弹性体与数种增粘树脂共混物的动态力学性能,以此表征SBSVP与不同增粘树脂的相容性.试验结果表明,SBSVP与不同增粘树脂共混后,共混物的玻璃化转变温度(Tg)会发生相应的变化,表明不同种类的增粘树脂与SBSVP中PS及PB相的相容性各不相同.其相客性为以下几种情况不同程度的组合:树脂与SBSVP中的PB相相容;树脂与PS相相容;树脂与PB、PS相都相容;树脂与PB、PS相都不相容.同时可能会有过渡相和中间相的产生. 相似文献
993.
994.
乙酰胆碱酯酶固定化方法的研究 总被引:3,自引:0,他引:3
以戊二醛为交联剂,牛血清白蛋白(BSA)为保护剂,将乙酰胆碱酯酶(AchE)交联固定到商品载体上,制备固定化酶片。对影响酶固定化的重要因素进行了考察,获得了最佳固定化条件。实验结果表明,以孔径为0.45μm的硝酸纤维素滤膜作栽体,乙酰胆碱酯酶用量10U,5%(体积分数)戊二醛2μL,1%(质量分数)BSA10μL,配成70μL的酶溶液,3℃固定8h,可获得较好的固定化效果。不同批次制备的酶片,其活力值标准偏差为3.27%~5.03%,酶片在0.1mol/L pH8.5磷酸盐缓冲溶液中3℃下可保存60d。‘ 相似文献
995.
化学预氧化/生物活性炭去除微污染原水中氨氮 总被引:5,自引:0,他引:5
以松花江水为研究对象,比较研究了高锰酸盐、高铁酸盐和臭氧三种氧化剂预氧化与生物活性炭(简称BAC)联用对微污染原水中NH4^+-N去除效果。试验结果表明:高锰酸盐/生物活性炭(简称P/BAC)、高铁酸盐/生物活性炭(简称F/BAC)、臭氧/生物活性炭(简称0/BAC)三种工艺按硝化能力的强弱排序为:F/BAC〉P,BAC〉0/BAC。P/BAC、F/BAC对原水的NH4^+-LN浓度变化表现出较强的适应能力,对NH4^+-N的绝对去除量的平均值可达到1.75mg/L、2.20mg/L;NH4^+-N的平均去除率为51%和64%。而O/BAC工艺对进水NH1^+-N浓度的变化较为敏感,处理效果波动较大;绝对去除量的平均值为0.73mg/L;NH4^+-N的平均去除率为21%。在原水NH4^+-N浓度变化的较大范围内,三种工艺最后出水中NO2^--N浓度都低于进水;在原水NH4^+-N浓度突然升高较大时,P/BAC、F/BAC出水中的NO2^--N出现少量的积累,而几天后又能恢复稳定运行状态时的低浓度出水。 相似文献
996.
997.
A study was carried out to increase the CLA contents in ewes’ milk fat under field conditions by dietary means and to investigate
the extent of the changes and consequences for milk processing and cheese quality. During a 3-mon period, ewes’ bulk milk
samples were collected every week from two different herds. For the first 4 wk the ewes were fed a conventional diet. Then
the following 6 wk a supplement enriched in α-linolenate (whole linseed) was incorporated into the ovine diet. Finally, in
the last 3 wk the feeding was the same as in the first 4 wk. The FA profile in milk fat was monitored by GC, and the distribution
of CLA isomers was thoroughly tested by combining GC-MS of 4,4-dimethyloxazoline derivatives (DMOX) with silver ion-HPLC (Ag+-HPLC) of FAME. Reconstructed mass spectral profiles of CLA characteristic ions from DMOX were used to identify positional
isomers, and Ag+-HPLC was used to quantify them. An increase in total CLA in milk fat was observed, and total CLA remained elevated during
the weeks of enriched α-linolenate feeding. In our experimental conditions there was a linear relationship between trans-vaccenic acid (trans-11-octadecenoic acid; trans-11 18∶1) and 9-cis, 11-trans CLA in ewes’ milk fat. Concerning the CLA isomer profile, increases in the 11,13- and 12,14–18∶2 positional isomers were
considerable when linseed was included in the diet. Organoleptic characteristics of cheeses made with CLA-enriched milk did
not substantially differ from those made with nonsupplemented ewes’ milk. CLA total content and isomer profile did not change
during ripening. 相似文献
998.
Jung Joon Lee Heeyeon Kim Jae Hyun Koh Ara Jo Sang Heup Moon 《Applied catalysis. B, Environmental》2005,61(3-4):274-280
The performance of a new type of CoMoS/Al2O3 catalyst, with added fluorine and prepared by sonochemical and chemical vapor deposition (CVD) methods, was investigated in the hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). The catalyst, which was designed to contain optimum amounts of fluorine and cobalt, exhibited a higher activity, ca. 4.6 times higher activity particularly in the HDS of 4,6-DMDBT, than a fluorine-free catalyst prepared by a conventional impregnation method. The enhanced activity of the new catalyst can be attributed to the cumulative effects of individual factors involved in the catalyst preparation. That is, the use of a sonochemical synthesis led to a high dispersion of small MoS2 crystallites on the alumina, and the addition of the Co species to the catalyst by CVD caused a close interaction between the Co species and the MoS2 crystallites to produce numerous CoMoS species, which are the catalytically active species for HDS. The addition of fluorine increased the amounts of acidic sites in the catalyst, which promoted hydrogenation (HYD) route to a greater extent than the direct desulfurization (DDS) route in DBT HDS and both HYD and DDS routes to similar extents in the case of 4,6-DMDBT HDS. Accordingly, the addition of fluorine led to a greater increase in catalytic activity for 4,6-DMDBT HDS than for DBT HDS. 相似文献
999.
Highly Efficient Overall Water Splitting Through Optimization of Preparation and Operation Conditions of Layered Perovskite Photocatalysts 总被引:1,自引:0,他引:1
Jindo Kim Dong Won Hwang Hyun Gyu Kim Sang Won Bae Jae Sung Lee Wei Li Se Hyuk Oh 《Topics in Catalysis》2005,35(3-4):295-303
The layered perovskite materials were found to give the high photocatalytic activity in water splitting reaction under UV
irradiation, where the electronic structure of perovskite slab constructing the layered structure (the total cation valency)
was the most crucial factor to the high photocatalytic activity. Both the excessive cation valency and the layered structure
were required for active photocatalysts, while the slab thickness of layered perovskites had an insignificant effect on water-splitting
activity. In order to identify key variables that affected photocatalytic activity and to optimize the performance of (110)
layered perovskite, La2Ti2O7 was modified by various methods. The optimum amount of loaded nickel had a great effect and the amount depended on the surface
area of the perovskite phase. When an alkaline-earth element such as Ba, Sr, and Ca was doped on La2Ti2O7, the photocatalytic activity was enhanced markedly. Introduction of an alkaline hydroxide into the reaction system as an
external additive enhanced the activity further showing extremely high quantum yields close to 50%. 相似文献
1000.
The effective parameters on the diameter of carbon nanotubes (CNTs) by plasma enhanced chemical vapor deposition (PECVD) were presented.Among lots of influential parameters,the effects of the catalytic film thickness and the pretreatment plasma power on the growth of CNTs were investigated.The results show that the size of catalytic islands increases by increasing the thickness of catalytic layer,but the density of CNTs decreases.The pretreatment duration time of 30 s is the optimal condition for growing CNTs with about 50 nm in diameter.By increasing the pretreatment plasma power,the diameter of CNTs decreases gradually.However,the diameter of CNTs does not change drastically from 80 to 120 W.The uniformly grown CNTs with the diameter of 50 nm are obtained at the pretreatment plasma power of 100 W. 相似文献