全文获取类型
收费全文 | 6910篇 |
免费 | 169篇 |
国内免费 | 27篇 |
专业分类
电工技术 | 74篇 |
综合类 | 8篇 |
化学工业 | 976篇 |
金属工艺 | 157篇 |
机械仪表 | 119篇 |
建筑科学 | 51篇 |
矿业工程 | 16篇 |
能源动力 | 307篇 |
轻工业 | 243篇 |
水利工程 | 36篇 |
石油天然气 | 20篇 |
无线电 | 654篇 |
一般工业技术 | 1165篇 |
冶金工业 | 2607篇 |
原子能技术 | 35篇 |
自动化技术 | 638篇 |
出版年
2023年 | 72篇 |
2022年 | 100篇 |
2021年 | 172篇 |
2020年 | 146篇 |
2019年 | 124篇 |
2018年 | 169篇 |
2017年 | 157篇 |
2016年 | 185篇 |
2015年 | 108篇 |
2014年 | 185篇 |
2013年 | 418篇 |
2012年 | 218篇 |
2011年 | 235篇 |
2010年 | 198篇 |
2009年 | 268篇 |
2008年 | 180篇 |
2007年 | 132篇 |
2006年 | 134篇 |
2005年 | 115篇 |
2004年 | 103篇 |
2003年 | 108篇 |
2002年 | 90篇 |
2001年 | 70篇 |
2000年 | 66篇 |
1999年 | 119篇 |
1998年 | 722篇 |
1997年 | 408篇 |
1996年 | 353篇 |
1995年 | 229篇 |
1994年 | 187篇 |
1993年 | 181篇 |
1992年 | 78篇 |
1991年 | 108篇 |
1990年 | 101篇 |
1989年 | 65篇 |
1988年 | 72篇 |
1987年 | 76篇 |
1986年 | 69篇 |
1985年 | 81篇 |
1984年 | 31篇 |
1983年 | 25篇 |
1982年 | 30篇 |
1981年 | 42篇 |
1980年 | 30篇 |
1979年 | 30篇 |
1978年 | 34篇 |
1977年 | 53篇 |
1976年 | 135篇 |
1975年 | 21篇 |
1973年 | 13篇 |
排序方式: 共有7106条查询结果,搜索用时 0 毫秒
31.
AK Ma?ek O Rowiński T Ostrowski L Hilgertner M Januszewicz M Szostek 《Canadian Metallurgical Quarterly》1995,50(40-44):19-22
Subclavian steal syndrome (SSS) appears when the origin of the subclavian artery (SA) is occluded or stenosed. Introduction of transcranial Doppler sonography (TCD) provided an opportunity to evaluate parameters of the blood flow in the vertebral (VA) and basilar artery (BA). Measurements of blood flow velocities performed at rest and after the brachial hyperemia test allow one to classify hemodynamic types of SSS. The aim of the study was to categorize types of steal and to compare the differences of flow patterns before and after percutaneous transluminal SA balloon angioplasty (SA-PTA). Fourty-eight patients with angiographically confirmed SSS (aged from 27 to 68 years, mean 53; 2/1 f/m ratio) were examined with 2 MHz range-gated, pulsed transcranial Doppler device (TC 2-64B EME). Both VA and BA were evaluated by the transoccipital approach at rest and during the brachial hyperemia. In 5 cases (10.4%) permanent reversal blood flow in the BA was observed (complete basilar steal). In flow in the BA blood flow was in the normal direction at rest and altered (reversed or decreased) when induced with brachial hyperemia test (transient basilar steal). In the next 14 patients (29.2%) permanently reversed VA blood flow was observed with only a slight or no alterations of the BA flow after the hyperemia test (complete vertebral steal). In the last 19 cases (39.6%) alterations of the VA blood flow without changes in BA flow were observed (latent vertebral steal). Between 1991 and 1994 twenty seven symptomatic patients with different hemodynamic types of SSS were treated with SA-PTA. TCD evaluation of VA's and BA using the hyperemia test was performed before, 3 to 7 days and 3 months after morphologically and hemodynamically successful subclavian artery balloon PTA. Normal results of vertebrobasilar examinations were obtained in 26 cases after this procedure. In one case the latent vertebral steal was detected. The 28 months mean follow-up revealed no significant changes in TCD flow patterns recorded from VA's and BA. After collecting data of about 60 patients with SSS we examined with TCD we conclude that: in patients with a hemodynamically significant SA stenosis the presence of reversed ipsilateral VA blood flow (a radiologic steal) its not a good determinant of either the presence or type of presenting symptoms and after successful PTA or recanalisation and PTA of SA in almost all cases we examined close to normal TCD recordings in BA and VA. 相似文献
32.
33.
The change of foot length and width with age has been reported in a few anthropometric studies in the literature. However, the relationship with body height rarely is reported, and the dynamic effect of weightbearing on foot size has not been documented. In this series, 2829 children 3 to 18 years of age of equal gender distribution were included in the study. The foot length and width on weightbearing and nonweightbearing were measured with a special precision electronic caliper. The foot length and width were found to increase linearly from the age of 3 years until 12 years in girls and 15 years in boys. This was followed by a phase during which the increase plateaued. The foot length and width increased significantly on weightbearing at all ages in both genders with a mean of 2.1 to 4.4 mm or 3.1% to 4.8%, respectively. The foot length and width also were found to correlate significantly with the body height in both genders, with a correlation coefficient of 0.96 to 0.98. No significant differences were found between the sizes of the dominant and nondominant foot in either gender. 相似文献
34.
RS Strobel AK Nagy AF Knowles J Buegel MD Rosenberg 《Canadian Metallurgical Quarterly》1996,271(27):16323-16331
An ecto-ATP diphosphohydrolase (ATPDase) was purified to homogeneity from vesiculosomes shed from chicken oviduct. First, the ecto-ATPDase-enriched vesiculosomes were concentrated by filtration, differential centrifugation, and exclusion chromatography. Next, the nonionic detergent, Nonidet P-40, was used to extract the ecto-ATPDase from vesiculosomal membranes, and the solubilized enzyme was further purified by ion exchange (DEAE-Bio-Gel) and lentil-lectin-Sepharose 4B chromatography. In the final stage, immunoaffinity chromatography was utilized to obtain purified ecto-ATPDase. More than 25,000-fold purification was achieved. Specific activity of the purified enzyme was greater than 800 micronol/min/mg of protein with MgATP as the substrate, the highest ever reported for an ATPDase. The enzyme also hydrolyzed other nucleoside triphosphates in the presence of magnesium at similar rates and CaATP and MgADP at lower rates. The molecular mass of the purified glycoprotein was 80 kDa as determined by SDS-polyacrylamide gel electrophoresis and Western blot analysis. Based on its enzymatic properties, the relationship of the chicken oviduct ecto-ATPDase with other reported ATPDases and ecto-ATPases is discussed. 相似文献
35.
The University Department of Surgery at Queen Elizabeth II Medical Centre (Perth, Western Australia) has undertaken a pilot project to provide surgical services to country communities where no such service exists. Three surgeons undertake a regular schedule of appointments, and are accompanied by final-year medical students to give them experience with common conditions rarely managed in teaching hospitals. The service is supported by a central administrative office and coordinated by a general practitioner, who negotiates with the regional healthcare providers. Patients are referred by their general practitioner, who may work with the surgeon as anaesthetist or surgical assistant. 相似文献
36.
This study examined the hypolipidemic effect of 4 weeks of L-carnitine treatment (170 mg/kg b.w./day) in New Zealand White rabbits fed a high fat diet (5% corn oil/0.5% cholesterol). Specifically, [3H] glycerol and [125I] very low density lipoprotein (VLDL) turnover studies were conducted to examine the effect of treatment on VLDL kinetics. The masses of plasma VLDL-triglycerides (VLDL-TG) and VLDL-apoprotein B (VLDL-apoB) were significantly increased by the high-fat diet. Four weeks of treatment with L-carnitine significantly reduced these masses. Kinetic analysis indicated that fat feeding reduced the fractional catabolic rates (FCRs) of VLDL-TG and VLDL-apoB relative to chow-fed controls. The transport of these VLDL components was not altered by the diet. L-carnitine treatment had no effect on the FCRs of VLDL-TG and VLDL-apoB or on the transport of VLDL-apoB. Yet, treatment significantly lowered the transport of VLDL-TG. These data indicate that the lipid-lowering effect of L-carnitine in this animal model was due, in part, to a decrease in the transport and not due to an alteration in the fractional catabolic rate of VLDL-TG. 相似文献
37.
K Schesser AK Spiik JM Dukuzumuremyi MF Neurath S Pettersson H Wolf-Watz 《Canadian Metallurgical Quarterly》1998,28(6):1067-1079
38.
In vertical co-current gas-liquid flow, the transition from annular to intermittent flow occurs when gas core becomes interrupted by liquid bridges due to the instability of the interfacial capillary waves. An analytical model is formulated to explain the liquid bridging in terms of the growth of finite amplitude interfacial capillary waves. Experimental results show that the longest wave length, which is associated with the transition, is about eight times the wave length of waves moving with the velocity of the liquid film. 相似文献
39.
40.