全文获取类型
收费全文 | 4154篇 |
免费 | 60篇 |
国内免费 | 32篇 |
专业分类
电工技术 | 66篇 |
综合类 | 46篇 |
化学工业 | 530篇 |
金属工艺 | 119篇 |
机械仪表 | 111篇 |
建筑科学 | 160篇 |
矿业工程 | 13篇 |
能源动力 | 50篇 |
轻工业 | 292篇 |
水利工程 | 36篇 |
石油天然气 | 18篇 |
武器工业 | 2篇 |
无线电 | 337篇 |
一般工业技术 | 338篇 |
冶金工业 | 1814篇 |
原子能技术 | 15篇 |
自动化技术 | 299篇 |
出版年
2021年 | 28篇 |
2018年 | 31篇 |
2017年 | 34篇 |
2016年 | 28篇 |
2015年 | 40篇 |
2014年 | 97篇 |
2013年 | 143篇 |
2012年 | 76篇 |
2011年 | 161篇 |
2010年 | 91篇 |
2009年 | 122篇 |
2008年 | 105篇 |
2007年 | 120篇 |
2006年 | 119篇 |
2005年 | 98篇 |
2004年 | 80篇 |
2003年 | 75篇 |
2002年 | 76篇 |
2001年 | 74篇 |
2000年 | 65篇 |
1999年 | 96篇 |
1998年 | 467篇 |
1997年 | 287篇 |
1996年 | 198篇 |
1995年 | 143篇 |
1994年 | 118篇 |
1993年 | 117篇 |
1992年 | 57篇 |
1991年 | 39篇 |
1990年 | 79篇 |
1989年 | 77篇 |
1988年 | 61篇 |
1987年 | 57篇 |
1986年 | 46篇 |
1985年 | 49篇 |
1984年 | 47篇 |
1983年 | 41篇 |
1982年 | 41篇 |
1981年 | 38篇 |
1980年 | 36篇 |
1979年 | 27篇 |
1978年 | 29篇 |
1977年 | 65篇 |
1976年 | 113篇 |
1975年 | 25篇 |
1974年 | 25篇 |
1973年 | 22篇 |
1972年 | 20篇 |
1971年 | 23篇 |
1968年 | 19篇 |
排序方式: 共有4246条查询结果,搜索用时 0 毫秒
121.
122.
J. Wright V. Adams J. Hykin P. Gowland B. Issa P. Boulby P. Tokarczuk D. Evans R. Spiller P. Mansfield 《Magma (New York, N.Y.)》1994,2(3):467-469
Echo-planar imaging (EPI) can be used to produce snapshot images of the human stomach and antro-pyloro-duodenal segment in real time as an alternative technique to intubation and exposure to ionizing radiation. The method has been further developed to monitor simultaneous gastric motility and gastric emptying of liquid and solid meals. The model has been utilized to study the effects of pharmacological agents on gastric function.Eight normal subjects were imaged in a 0.5-T superconducting magnet for up to 6 h following ingestion of 800 ml tap water, followed by 500 ml porridge test meal + 500 ml tap water. A rapid multislice technique was adopted to image adjacent transverse slices (10 mm thick) through the gastric region. In addition, three subjects were orally dosed with 20 mg of the prokinetic agent Cisapride. Gastric volumes for each slice were calculated and summed to produce a measure of total gastric volume and gastric emptying. Contractile activity at the level of the antro-pyloric segment was detected using sequential 128 ms images at 3 s intervals. Alternate measurements of gastric volume and motility were made for the duration of the study.Gastric emptyingT
1/2's (times to empty 50% of the gastric contents) of 12.9 min for water and 116 min for porridge were in agreement with results obtained by the traditional techniques of gamma scintigraphy and impedance imaging. The frequency of gastric contractions increased from 2.4 contractions per minute (cpm) to 3.2 cpm following water and from 2.9 to 3.2 cpm following porridge. The prokinetic effect of enhanced coordination of antroduodenal contractions was also observed. These studies have demonstrated that EPI can be used to detect and image gastroduodenal function in man, totally noninvasively, and can be used to study the effects of drugs acting on the gastrointestinal tract. 相似文献
123.
124.
125.
通过使用墙体杀菌清洁与非杀菌清洁后涂料干膜的性能比较,评价了杀菌清洗对提高涂料干膜性能的有效性,揭示了怎样用杀菌清洁提高杀菌系统的特性。同时,比较了传统杀菌剂和新式杀菌剂的性能差别。 相似文献
126.
原油输送中的析蜡问题是影响管道安全运行和管理的重要因素之一。介绍了管壁结蜡影响因素,通过试验,探讨了原油输送温度和管壁温差对管壁蜡沉积速率的影响,得出了输油温度和温差与结蜡层厚度之间的关系,对于预测结蜡规律有一定的参考作用。 相似文献
127.
128.
The human choline/ethanolamine phosphotransferase 1 (CEPT1) gene codes for a dual-specificity enzyme that catalyzes the de novo synthesis of the two major phospholipids through the transfer of a phosphobase from CDP-choline or CDP-ethanolamine to DAG
to form PC and PE. We used an expression system devoid of endogenous cholinephosphotransferase and ethanolaminephosphotransferase
activities to assess the diradylglycerol specificity of CEPT1. A mixed micellar assay was used to ensure that the diradylglycerols
delivered were not affecting the membrane environment in which CEPT1 resides. The CEPT1 enzyme displayed an apparent K
m of 36 μM for CDP-choline and 4.2 mol% for di-18∶1 DAG with a V
max of 14.3 nmol min−1 mg−1. When CDP-ethanolamine was used as substrate, the apparent K
m was 98 μM for CDP-ethanolamine and 4.3 mol% for di-18∶1 DAG with a V
max of 8.2 nmol min−1 mg−1. The preferred diradylglycerol substrates used by CEPT1 with CDP-choline as the phosphobase donor were di-18∶1 DAG, di-16∶1
DAG, and 16∶0/18∶1 DAG. A major difference between previous emulsion-based assay results and the mixed micelle results was
a complete inability to use 16∶0(O)/2∶0 as a substrate for the de novo synthesis of platelet-activating factor when the mixed micelle assay was used. When CDP-ethanolamine was used as the phosphobase
donor, 16∶0/18∶1 DAG, di-18∶1 DAG, and di-16∶1 DAG were the preferred substrates. The mixed micelle assay also allowed the
lipid activation of CEPT to be measured, and both the cholinephosphotransferase and ethanolaminephosphotransferase activities
displayed the unusual property of product activation at 5 mol%, implying that specific lipid activation binding sites exist
on CEPT1. The protein kinase C inhibitor chelerythrine and the human DAG kinase inhibitor R59949 both inhibited CEPT1 activity
with IC50 values of 40 μM. 相似文献
129.
Effect of DAG on milk fat TAG crystallization 总被引:1,自引:0,他引:1
Amanda J. Wright Alejandro G. Marangoni 《Journal of the American Oil Chemists' Society》2002,79(4):395-402
The effect of milk fat and standard DAG on the crystallization behavior of milk fat TAG (MF-TAG) was investigated. When milk
fat DAG were added to MF-TAG at the 0.1 wt% level, crystallization was delayed. Racemic purity was shown to be an important
factor in the ability of DAG to influence TAG crystallization. Only sn-1,2 isomers of blends of MF-TAG with 0.1 wt% of the racemic mixtures of dipalmitin and diolein increased the activation free
energy barrier to MF-TAG nucleation (ΔG
c
) and delayed the subsequent crystallization process by increasing the crystallization induction time (τSFC) determined from solid fat content-time measurements. Although crystallization kinetics were affected, the properties of
the resulting network structures remained unchanged upon addition of milk fat minor components at the 0.1 wt% level 相似文献
130.
Sharks are the most dangerous predators of people in the sea, resulting in people being mauled and killed each year. A shark
repellent could help to diminish this danger. The aglycone of the shark repellent pavoninin-5, (25R)-cholest-5-en-3β,15α,26-triol (5a), was synthesized from diosgenin (9). Removing mercury from the Clemmensen reduction of 9 gave a higher yield of (25R)-cholest-5-en-3β,16β,26-triol, 10a, and was also more environmentally friendly. Attempted methods for the transposition of the C-16β hydroxyl to the 15α position
are described. A successful method for this transposition via the 15α-hydroxy-16-ketone, 8a, using the Barton deoxygenation reaction on the 16-alcohol 14b, is reported. 相似文献