全文获取类型
收费全文 | 3866篇 |
免费 | 3篇 |
专业分类
化学工业 | 15篇 |
金属工艺 | 1篇 |
机械仪表 | 1篇 |
轻工业 | 25篇 |
水利工程 | 1篇 |
无线电 | 2篇 |
一般工业技术 | 3篇 |
冶金工业 | 3809篇 |
自动化技术 | 12篇 |
出版年
2021年 | 2篇 |
2019年 | 1篇 |
2018年 | 1篇 |
2017年 | 2篇 |
2014年 | 1篇 |
2013年 | 1篇 |
2012年 | 3篇 |
2011年 | 4篇 |
2010年 | 1篇 |
2009年 | 2篇 |
2008年 | 3篇 |
2006年 | 2篇 |
2005年 | 1篇 |
2004年 | 5篇 |
2003年 | 13篇 |
2000年 | 2篇 |
1999年 | 138篇 |
1998年 | 1255篇 |
1997年 | 781篇 |
1996年 | 477篇 |
1995年 | 234篇 |
1994年 | 215篇 |
1993年 | 219篇 |
1992年 | 19篇 |
1991年 | 31篇 |
1990年 | 35篇 |
1989年 | 46篇 |
1988年 | 31篇 |
1987年 | 27篇 |
1986年 | 22篇 |
1985年 | 24篇 |
1984年 | 1篇 |
1983年 | 6篇 |
1982年 | 13篇 |
1981年 | 23篇 |
1980年 | 28篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 57篇 |
1976年 | 133篇 |
1975年 | 2篇 |
1970年 | 1篇 |
排序方式: 共有3869条查询结果,搜索用时 281 毫秒
991.
Lipoprotein lipase (LPL) is an endothelium-bound enzyme that is rate determining for the clearance of triacylglycerol-rich lipoproteins. We assessed cardiac heparin-releasable LPL activity in an acquired model of hypertension, the fructose-hypertensive rat. Fructose feeding (10% solution in drinking water ad libitum) for 2 (short-term) or 4-6 (long-term) weeks induced hypertension, hypertriglyceridemia, and hyperinsulinemia in male Wistar rats. After short- and long-term fructose treatment, LPL activity in coronary perfusates was determined by retrogradely perfusing the hearts with heparin. Short-term fructose treatment did not alter cardiac heparin-releasable LPL activity, whereas a significant decrease in LPL activity was seen in the long-term treated group. Discontinuation of fructose treatment for 2 weeks from the long-term group normalized blood pressure and cardiac heparin-releasable LPL activity. Interestingly, acute vasodilation by in vitro perfusion of coronary vasodilators like nifedipine and CGS-21680 increased cardiac heparin-releasable LPL activity in the long-term group to control levels. These studies demonstrate that long-term fructose-induced hypertension may play a significant role in regulating cardiac LPL activity. Whether or not this altered LPL activity has a role in the regulation of fatty acid supply to the hypertensive heart has yet to be determined. 相似文献
992.
PURPOSE: To determine the two-phase (hepatic arterial phase [HAP] and portal venous phase [PVP]) spiral computed tomographic (CT) findings of a nontumorous arterioportal shunt in the cirrhotic liver that can mimic a hypervascular tumor. MATERIALS AND METHODS: For 14 months, 803 patients with known or suspected hepatocellular carcinoma were referred for initial or repeated transcatheter arterial chemoembolization (TACE). Twenty-nine hyperattenuating lesions on HAP CT images obtained in 25 patients (23 men, two women; age range, 39-70 years) were regarded as nontumorous arterioportal shunts and were included in this study. The diagnosis of nontumorous arterioportal shunt was established by four radiologists who reviewed the two-phase spiral CT images and hepatic angiograms. RESULTS: The longest dimension of the lesion was 1.0-7.9 cm (mean dimension, 2.9 cm). The morphology at HAP CT was wedge-shaped in 25 (86%), geographic (ie, focal area with irregular outline) in two (7%), and nodular in two (7%) lesions. All lesions were homogeneous in attenuation. Hyperattenuating linear branching structures that represented early opacification of portal veins were demonstrated during the HAP in nine (31%) lesions. PVP CT images showed these lesions as isoattenuating (n = 20 [69%]) or slightly hyperattenuating (n = 9 [31%]). Iodized oil CT images showed faint or no accumulation of iodized oil in all lesions. CONCLUSION: In cirrhotic liver, nontumorous arterioportal shunts can be a cause of pseudolesions that mimic hypervascular tumors at two-phase spiral CT. Lesions that have the typical wedge-shaped and homogeneous appearance with or without internal linear branching structures during the HAP and that are isoattenuating or slightly hyperattenuating during the PVP can suggest this unusual condition. 相似文献
993.
P Borel V Tyssandier N Mekki P Grolier Y Rochette MC Alexandre-Gouabau D Lairon V Aza?s-Braesco 《Canadian Metallurgical Quarterly》1998,128(8):1361-1367
The effect of the ingestion of beta-carotene with medium-chain triglycerides (MCT) or long-chain triglycerides (LCT) on the bioavailability and the provitamin A activity of beta-carotene was investigated in humans. Sixteen healthy young men ingested, on two different days, a test meal containing 120 mg beta-carotene incorporated into 40 g LCT (LCT meal) or 40 g MCT (MCT meal). This meal was followed 6 h later by a beta-carotene-free meal containing 40 g LCT. Chylomicron beta-carotene, retinyl palmitate and triglycerides were measured every hour for 12.5 h after the first meal. No significant increase in chylomicron triglycerides was detected for the 6 h after the MCT meal intake, whereas a significant increase in chylomicron triglycerides was observed after the LCT meal intake. The chylomicron beta-carotene and retinyl palmitate responses to the MCT meal (0-6 h area under the curves, AUC) were significantly (P < 0.05) lower [AUC = 68.1 +/- 26.8 and 43. 4 +/- 10.4 nmol/(L.h), for beta-carotene and retinyl palmitate, respectively] than those obtained after the LCT meal [301.4 +/- 64.0 and 166.0 +/- 29.0 nmol/(L.h), respectively]. The chylomicron beta-carotene and retinyl palmitate responses obtained after the beta-carotene-free meal (6-12.5 h AUC) were also significantly lower when the first meal provided MCT rather than LCT. The chylomicron (retinyl palmitate/beta-carotene) ratios were constant during the postprandial periods, whatever the meal ingested. We conclude that the chylomicron beta-carotene response is markedly diminished when beta-carotene is absorbed with MCT instead of LCT. This phenomenon is apparently due to the lack of secretion of chylomicrons in response to MCT; however, a lower intestinal absorption of beta-carotene or a higher transport of beta-carotene via the portal way in the presence of MCT cannot be ruled out. Finally, the data obtained show that MCT do not affect the rate of intestinal conversion of beta-carotene into vitamin A. 相似文献
994.
P Nos V Garrigues E Caballero MC Cano R Sopena J Ponce 《Canadian Metallurgical Quarterly》1998,21(8):386-390
The evaluation of gastric emptying by the double isotope technique involves some methodologic conditioning. Among them contamination correction or interference in the energy windows of the activity of the two isotopes used in the marking of the solids and fluids of the test food are important. The results of an experiment in which a phantom was used to evaluate the contamination between indio 111 (DTPA-Ca111In) and technecium 99m (colloid99mTc). Three test studies were posteriorly performed in healthy volunteers and 27 studies in a control group (13 males, mean age of 33 years, mean body mass index 39.02 kg/m). In these studies the contamination was corrected with the acquisition, following an initial swallow of juice marked with 111In, of activity in the windows of both isotopes. The contamination of 111In (isotope of greatest radiation energy) in the window of 99mTc was 24% in the phantom and 20%, 23% and 26% in the three initial study tests. The mean contamination in the control group was of 22% with limits of 19% to 29% and a standard deviation of 3%. Despite the comparable results, the usefulness of the individualized contamination calculation in the studies of gastric emptying with dual isotope to minimize the methodologic errors of this technique is discussed. 相似文献
995.
A Vallverdú JA Asturias MC Arilla N Gómez-Bayón A Martínez J Martínez R Palacios 《Canadian Metallurgical Quarterly》1998,101(3):363-370
Whether vitamin D receptor (VDR) gene polymorphisms are associated with osteoporosis is highly controversial. The relationship between VDR gene polymorphisms and bone mineral density (BMD) might, however, be modified by age-related and/or environmental factors. We studied the potential association between BMD and VDR genotypes in females from prepuberty to premenopause and prospectively investigated the interaction of VDR genotypes with dietary calcium and BMD changes during childhood. Bsm I VDR gene polymorphisms and BMD at the lumbar spine (LS) and femur (neck [FN] and midshaft [FS]) were assessed in 369 healthy Caucasian females, aged 7-56 years (143 prepubertal girls, 54 peri- and postpubertal adolescents, and 172 premenopausal adults). Femoral trochanter (FT) and distal radius BMD (metaphysis and diaphysis) were also measured in 101 of the prepubertal girls who participated in a 1-year, double-blind, randomized study of calcium supplementation (850 mg/day) versus placebo on bone mineral mass accrual. Among all females, 150 (40.7%) had bb, 167 (45.3%) Bb, and 52 (14%) BB VDR genotypes. In prepubertal and adolescent girls altogether, LS BMD (Z scores) was associated with VDR genotypes and was significantly lower in BB than in Bb or bb subjects. Trends for a similar difference were also detected at the FN level as well as on the mean BMD (Z scores) of the three sites measured (LS, FN, and FS). By contrast, no BMD differences were detectable among VDR genotypes in the adults. In 101 prospectively studied prepubertal girls, calcium supplementation significantly increased BMD at most skeletal sites, except LS. After segregation for VDR genotypes (40 bb, 47 Bb, and 14 BB), a significant calcium effect was present in Bb but not bb girls, whereas in BB girls there was a positive but nonsignificant trend for a calcium effect. Moreover, dietary calcium intake was significantly correlated with BMD changes at various independent bone sites in Bb girls but not in bb girls. In contrast, BMD gain in bb girls appeared to be higher than among the other genotypes when the dietary calcium intake was low, i.e., in the absence of calcium supplements. BMD was significantly associated with VDR gene polymorphisms only before puberty, BB girls having significantly lower BMD (Z scores) than the other genotypes. By increasing dietary calcium intake, BMD accrual was increased in Bb and possibly BB prepubertal girls, whereas bb subjects had the highest spontaneous BMD accrual and remained unaffected by calcium supplements. Taking into account complex interactions between VDR gene polymorphisms and environmental factors, including calcium intake, may thus help to understand the discordant relationships between BMD and VDR gene polymorphisms. 相似文献
996.
B Marino MG Gagliardi MC Digilio B Polletta S Grazioli D Agostino A Giannotti B Dallapiccola 《Canadian Metallurgical Quarterly》1995,154(12):949-952
Among 41 consecutive children with classic Noonan syndrome, 27 patients (66%) presented cardiac anomalies. Eight patients (19.5%) had a congenital anomaly of the mitral valve consisting of 5 with partial atrioventricular canal defect and 3 with anomalous insertion of the mitral valve on the ventricular septum. Five patients (12%) presented with a significant left ventricular outflow tract obstruction caused by the anterior leaflet of the mitral valve: two cases with atrioventricular canal and three cases with isolated anomalous insertion of the mitral valve. Echocardiography is the best tool for the diagnosis. Cardiac defects of patients with Noonan syndrome may be explained on the basis of anomalies of the extracellular matrix involving cardiac valves including the mitral valve. CONCLUSION: In children with Noonan syndrome and left ventricular hypertrophy a careful echocardiographic assessment of the mitral valve should reveal those in whom the left ventricular outflow tract obstruction is anatomical in nature. 相似文献
997.
Tumors of the meninges in infancy and childhood are unusual; childhood meningiomatosis is thought to be more common in neurocutaneous diseases. The case presented here is one of multiple recurrent and de novo benign meningeal tumors in a child who has no other signs or symptoms of a neurocutaneous syndrome. 相似文献
998.
C Schoch D Haase T Haferlach H Gudat T Büchner M Freund H Link E Lengfelder H Wandt MC Sauerland H L?ffler C Fonatsch 《Canadian Metallurgical Quarterly》1996,10(8):1288-1295
The translocation t(8;21)(q22;q22) occurs in 6 to 12 percent of patients with AML, and usually predicts a good response to chemotherapy with a high remission rate and a relatively long median survival. The influence of additional chromosome aberrations on the clinical outcome of patients with t(8;21) is unclear. We analyzed 51 cases of acute myeloid leukemia carrying a translocation t(8;21)(q22;q22); 23 female and 28 male patients. The complete remission rate was 92 percent and median overall survival was 52.4 months. The median overall survival of female patients was significantly worse than of male patients (37.2 months vs not reached, P = 0.025). Additional chromosome aberrations were detected in 41 patients at diagnosis (80 percent), 31 (61 percent) had lost a sex chromosome, seven (14 percent) showed a partial deletion of the long arm of chromosome 9 and in three patients (6 percent) a gain of chromosome 8 was observed. Whereas the loss of a sex chromosome had no influence on prognosis, a partial deletion of the long arm of chromosome 9 was an unfavorable prognostic factor. The median overall survival of the seven patients with del(9q) was only 12.5 months and thus significantly shorter than in patients with only t(8;21) or with t(8;21) and additional sex chromosome loss (median survival not reached: P = 0.0010). 相似文献
999.
1000.
The genus Bacteroides represents about one-third of the isolates from human fecal samples. The proportions of the different species are difficult to estimate because there is no method for rapid identification of mixtures of anaerobes. Monoclonal antibodies against Bacteroides vulgatus and B. distasonis were prepared. They did not react with the other Bacteroides species of the B. fragilis group. These reagents allowed direct enumeration of B. vulgatus and B. diastasonis organisms in human fecal samples. Anaerobic bacteria resistant to 1-h contact with air were enumerated in fecal human samples, a filter was layered on the colonies, and then B. vulgatus colonies were identified by an immunoassay performed with the prepared monoclonal antibodies. Healthy human adult volunteers were tested. Most of them harbored B. vulgatus at high levels, while the B. distasonis levels were always lower. Kinetic studies suggested that time variations for each volunteer were small. The simplified quantification of Bacteroides strains at the species level described here will prove useful in complementing our knowledge of the factors which may influence the predominant human fecal flora. 相似文献