首页 | 官方网站   微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   634篇
  免费   12篇
  国内免费   4篇
工业技术   650篇
  2023年   5篇
  2022年   7篇
  2021年   16篇
  2020年   3篇
  2019年   8篇
  2018年   9篇
  2017年   3篇
  2016年   12篇
  2015年   8篇
  2014年   18篇
  2013年   27篇
  2012年   26篇
  2011年   32篇
  2010年   21篇
  2009年   22篇
  2008年   33篇
  2007年   22篇
  2006年   18篇
  2005年   20篇
  2004年   17篇
  2003年   16篇
  2002年   15篇
  2001年   10篇
  2000年   14篇
  1999年   15篇
  1998年   63篇
  1997年   41篇
  1996年   22篇
  1995年   15篇
  1994年   17篇
  1993年   11篇
  1992年   5篇
  1991年   3篇
  1990年   8篇
  1989年   4篇
  1988年   5篇
  1987年   2篇
  1986年   6篇
  1985年   4篇
  1984年   3篇
  1983年   5篇
  1982年   4篇
  1981年   3篇
  1980年   2篇
  1979年   8篇
  1978年   5篇
  1977年   5篇
  1976年   9篇
  1974年   1篇
  1972年   2篇
排序方式: 共有650条查询结果,搜索用时 0 毫秒
71.
Ataxia telangiectasia (AT) is an autosomal recessive gene disorder, and ATM, a housekeeping gene, has been identified as the gene responsible for AT. Recently we found that another housekeeping gene, NPAT, is located upstream of ATM on human chromosome 11. The two housekeeping genes are transcribed in opposite directions and share a 0.5-kb 5' flanking sequence. The structure and organization of NPAT were determined by direct sequencing of cosmid clones carrying the gene and by application of the long and accurate (LA)-PCR method to amplify regions encompassing the exon/intron boundaries and all of the exons. The gene spans at least 44 kb and consists of 18 exons and 17 introns. It has been suggested that AT heterozygotes have an increased risk of developing cancer, especially breast cancer in women. Frequently, loss of heterozygosity at loci on 11q22-q24 has been observed in DNA isolated from tumors of the breast, uterine cervix, and colon, perhaps suggesting the location of a tumor suppressor gene in 11q22-q24. For investigation of the role of NPAT in AT and these tumors with allelic loss of 11q22-q24, appropriate primer sequences and PCR conditions for amplification of all the NPAT exons from genomic DNA were determined. We previously reported that no recombinations are found among Atm, Npat, and Acat1 (acetoacetyl-CoA thiolase) loci as determined by fine genetic linkage mapping of the mouse AT region. The results of the LA-PCR analysis using NPAT- and ACAT-specific primers and human genomic DNA allowed us to map ACAT 12 kb centromeric to NPAT.  相似文献   
72.
The antioxidant activities of 9H-xanthene-2,7-diols and α-tocopherol were studied during the oxidation of linoleic acid in a homogeneous solution and in an aqueous micelle dispersion. The antioxidant activities of 9H-xanthene-2,7-diols for both systems were 1.0–2.4 times greater relative to α-tocopherol. In addition, the 1,3,4,5,6,8-hexamethylxanthene-2,7-diol showed less cytotoxicity toward human fibroblasts than did 2,6-di-t-butyl-4-methylphenol.  相似文献   
73.
OBJECTIVE: To investigate factors affecting the nocturnal decrease in blood pressure. DESIGN: A cross-sectional study of 823 community-based untreated subjects aged > 20 years. Screening and ambulatory blood pressures were measured and the effects of age and the ambulatory blood pressure on the nocturnal decrease were examined. RESULTS: The magnitude of the decrease and the percentage decrease in the nocturnal blood pressure increased with increasing daytime ambulatory blood pressure and decreased with increasing night-time ambulatory blood pressure. Although the magnitude of the nocturnal decrease in blood pressure increased with increasing daytime blood pressure, the nocturnal blood pressure levels in hypertensives were still higher than those in normotensive subjects. The magnitude decreased with increasing age for men but not for women, whereas the percentage decrease decreased with increasing age both for men and for women. The SD of the 24 h blood pressure correlated strongly to the magnitude of the nocturnal decrease (systolic blood pressure r = 0.62, P < 0.0001; diastolic blood pressure r = 0.52, P < 0.0001), suggesting that the SD of the 24 h blood pressure is representative of the nocturnal decrease. A minimal nocturnal decrease was observed frequently in elderly normotensive men but infrequently in hypertensive individuals from the general population. A marked nocturnal decrease was observed frequently in hypertensive women aged > 70 years. CONCLUSION: Although the magnitude of the nocturnal decrease in blood pressure increased with increasing daytime blood pressure, the nocturnal blood pressure levels increased with increasing daytime ambulatory blood pressure. Therefore, the blood pressure in hypertensive subjects should essentially be lowered throughout the 24 h period. A marked nocturnal decrease in blood pressure in some elderly hypertensive women was observed without treatment. The nocturnal blood pressure levels of such subjects should be considered during treatment.  相似文献   
74.
The inhibitory effect of 2″-O-glycosylisovitexin (2″-O-GIV), isolated from young green barley leaves, on malonaldehyde (MA) formation from lipids was determined by gas chromatography. Two μmol of 2″-O-GIV inhibited MA formation from 0.2 mmol of squalene by almost 100% upon ultraviolet (UV) irradiation. Only 1 μmol of 2″-O-GIV inhibited 90% of MA formation from 0.2 mmol of ethyl linoleate upon UV irradiation. The effective quantities of 2″-O-GIV were much lower than those of either butylated hydroxytoluene or α-tocopherol. When ethyl linoleate, ethyl linolenate and ethyl arachidonate were oxidized by Fenton’s reagent in the presence of 2″-O-GIV or α-tocopherol, both compounds showed similar activity toward MA formation. Both compounds gave maximum inhibition at doses of 0.1–0.3 μmol for ethyl linoleate, 0.1–0.5 μmol for ethyl linolenate and 0.1–0.5 μmol for ethyl arachidonate.  相似文献   
75.
A 51-year-old man inhaled sarin during a terrorist attack on the Tokyo subway system and died 15 months later. Neuropathologic examination revealed marked nerve fiber decrease in the sural nerve, moderate nerve fiber loss in the sciatic nerve, and unremarkable dorsal root ganglia, dorsal roots, and posterior column of the spinal cord. This pathology is consistent with dying-back degeneration of the peripheral nervous system and could represent a late sequela of sarin intoxication.  相似文献   
76.
Elevated level of cellular lipid peroxidation can increase the incidence of vascular disease. The mechanism by which ketosis causes accelerated cellular damage and vascular disease in diabetes is not known. This study was undertaken to test the hypothesis that elevated levels of ketone bodies increase lipid peroxidation in endothelial cells. Human umbilical venous endothelial cells (HUVEC) were cultured for 24 h at 37 degrees C with ketone bodies (acetoacetate, beta-hydroxybutyrate). Acetoacetate, but not beta-hydroxybutyrate, caused an increase in lipid peroxidation and growth inhibition in cultured HUVEC. To determine whether ketone bodies generate oxygen radicals, studies using cell-free buffered solution were performed. They showed a significant superoxide dismutase (SOD) inhibitable reduction of cytochrome C by acetoacetate, but not by beta-hydroxybutyrate, suggesting the generation of superoxide anion radicals by acetoacetate. Additional studies show that Fe2+ potentiates oxygen radical generation by acetoacetate. Thus, elevated levels of ketone body acetoacetate can generate oxygen radicals and cause lipid peroxidation in endothelial cells, providing a possible mechanism for the increased incidence of vascular disease in diabetes.  相似文献   
77.
We have cloned a cDNA for a novel human homolog of the Drosophila discs large (dig) tumor suppressor protein, termed NE-dlg (neuronal and endocrine dig). Northern blot analysis revealed that the gene is highly expressed in neuronal and endocrine tissues. Fluorescence in situ hybridization (FISH) and radiation hybrid mapping studies localized the NE-dlg gene to chromosome Xq13. We also found that the NE-dlg gene encoded a 100 kDa protein. Immunolocalization studies using an NE-dlg antibody showed that the protein tended to be expressed in non-proliferating cells, such as neurons, cells in Langerhans islets of the pancreas, myocytes of the heart muscles, and the prickle and functional layer cells of the esophageal epithelium. Proliferative cells, including various cultured cancer cell lines and basal cells in the esophageal epithelium, showed little expression of the NE-dlg protein. In addition, yeast two-hybrid screening and in vitro binding assays revealed that the NE-dlg interacted with the carboxyl-terminal region of the APC tumor suppressor protein. These data suggest that NE-dlg negatively regulates cell proliferation through its interaction with the APC protein.  相似文献   
78.
OBJECTIVES: The Probucol Angioplasty Restenosis Trial was a prospective, randomized, controlled study that investigated the effectiveness of probucol therapy in reducing the rate of restenosis after percutaneous transluminal coronary angioplasty (PTCA). BACKGROUND: Antioxidants have an inhibitory effect on smooth muscle cell growth in experiments in vitro and in vivo, which suggests a possible pharmacologic effect on restenosis after PTCA. METHODS: One hundred one patients were randomly assigned to receive 1,000 mg/day of probucol or control (no lipid-lowering) therapy 4 weeks before PTCA. After 4 weeks of premedication, both groups underwent PTCA. Probucol was continued until follow-up angiography 24 weeks after PTCA. Angiographic results were analyzed at a core laboratory by quantitative coronary angiography. RESULTS: Dilation was successful in 46 of 50 patients in the probucol group and 45 of 51 in the control group. At follow-up angiography 24 weeks after angioplasty, angiographic restenosis occurred in 9 (23%) of 40 patients in the probucol group and 22 (58%) of 38 in the control group (p = 0.001). Minimal lumen diameter was 1.49 +/- 0.75 mm (mean +/- SD) in the probucol group and 1.13 +/- 0.65 mm in the control group (p = 0.02). Percent diameter stenosis at follow-up angiography in the probucol group was significantly lower than that in the control group (43.9% vs. 56.4%, p = 0.009). The late loss was 0.37 +/- 0.69 mm in the probucol group and 0.60 +/- 0.62 mm in the control group (p = 0.13). The loss/gain ratio was 0.32 +/- 0.74 in the probucol group and 0.56 +/- 0.81 in the control group (p = 0.059). Net gain was greater in the probucol group than in the control group (0.77 +/- 0.70 vs. 0.48 +/- 0.59 mm, p = 0.053). CONCLUSIONS: Probucol administered beginning 4 weeks before PTCA appears to reduce restenosis rates.  相似文献   
79.
This paper proposes a new robust feedforward tracking servo system for optical disk recording systems in the case of a sudden disturbance for the optical disk recording system. In optical recording systems, the tracking servo system must suppress tracking error below its tolerance. This paper designs the robust feedback control system by using the coprime factorization and disturbance observer. The proposed robust feedback control system suppresses the sudden disturbance caused by walking and running. The detecting signal of optical disk recording systems is only a tracking error. Hence, the feedforward controller of the proposed tracking control system is constructed based on both Zero Phase Error Tracking (ZPET) control theory and prediction of tracking error. The experimental results point out that the proposed tracking servo system has a quick and precise tracking response and keeps the residual tracking error below its tolerance. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 156(4): 60– 68, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20257  相似文献   
80.
OBJECTIVE: The American Diabetes Association has recommended that pregnant women with low-risk factors need not be tested for gestational diabetes mellitus (GDM). The aim of this study was to determine the prevalence of GDM in women with low-risk factors and to see if the pregnancy outcomes of women with GDM from a low-risk group were different from the outcomes of other women with GDM. RESEARCH DESION AND METHODS: Over an 18-month period, all pregnant women were offered a test for GDM using a 75-g glucose tolerance test at the beginning of the 3rd trimester. GDM was diagnosed if the 2-h glucose level was > or =8.0 mmol/l. The prevalence of GDM was determined in women with defined low-risk factors (Caucasian ethnic origin, age <25 years, and BMI <25 kg/m2). The pregnancy outcomes of women with GDM from a low-risk group were compared with those of other women with GDM. RESULTS: From a tested population of 2,907 women, 573 were identified as coming from a low-risk group. The prevalence of GDM in this low-risk group was 2.8%. The pregnancy outcomes of women with GDM from a low-risk group were no different from the pregnancy outcomes of other women with GDM, with respect to frequency of insulin use, units of insulin per day, morbidity, emergency caesarian section, and the percentage of both large- and small-for-gestational-age babies. In our population, if low-risk women were excluded, 80% of women would still require testing and nearly 10% of all cases of GDM would be missed. CONCLUSIONS: Women from a low-risk group have a 2.8% prevalence rate of GDM. The pregnancy outcomes of women with GDM from a low-risk group are similar to the outcomes of other women with GDM. Concerning the use of the 75-g glucose tolerance test in pregnancy, the recommendation not to test women from a low-risk group requires further evaluation in different populations before it can be endorsed.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司    京ICP备09084417号-23

京公网安备 11010802026262号