全文获取类型
收费全文 | 1577篇 |
免费 | 4篇 |
专业分类
电工技术 | 5篇 |
化学工业 | 60篇 |
金属工艺 | 18篇 |
机械仪表 | 5篇 |
建筑科学 | 16篇 |
能源动力 | 10篇 |
轻工业 | 23篇 |
水利工程 | 15篇 |
石油天然气 | 1篇 |
无线电 | 62篇 |
一般工业技术 | 57篇 |
冶金工业 | 1215篇 |
原子能技术 | 1篇 |
自动化技术 | 93篇 |
出版年
2021年 | 5篇 |
2019年 | 4篇 |
2018年 | 6篇 |
2017年 | 3篇 |
2016年 | 8篇 |
2015年 | 3篇 |
2013年 | 20篇 |
2012年 | 8篇 |
2011年 | 22篇 |
2010年 | 12篇 |
2009年 | 17篇 |
2008年 | 22篇 |
2007年 | 21篇 |
2006年 | 16篇 |
2005年 | 15篇 |
2004年 | 12篇 |
2003年 | 11篇 |
2002年 | 13篇 |
2001年 | 11篇 |
2000年 | 10篇 |
1999年 | 51篇 |
1998年 | 324篇 |
1997年 | 210篇 |
1996年 | 120篇 |
1995年 | 81篇 |
1994年 | 63篇 |
1993年 | 79篇 |
1992年 | 19篇 |
1991年 | 19篇 |
1990年 | 19篇 |
1989年 | 16篇 |
1988年 | 20篇 |
1987年 | 14篇 |
1986年 | 19篇 |
1985年 | 14篇 |
1984年 | 15篇 |
1983年 | 16篇 |
1982年 | 16篇 |
1981年 | 20篇 |
1980年 | 26篇 |
1979年 | 7篇 |
1978年 | 10篇 |
1977年 | 41篇 |
1976年 | 84篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1972年 | 5篇 |
1971年 | 5篇 |
1969年 | 5篇 |
排序方式: 共有1581条查询结果,搜索用时 0 毫秒
101.
Increased reporting of disease clusters is stretching health department resources while failing to uncover many significant environmental hazards. By reviewing the methodology by which health departments respond to such reports, we argue that there is a strong bias against investigating the most hazardous situations. Failure to find serious hazards is more a reflection of the methodology used than an assessment of the existence of environmental problems. The biases arise from the selection of situations that dictate full in-house consideration, the selection of the methodology used to evaluate reported or registry-based data, and the interpretation given to anomalous observations. We argue for more rigorous evaluation of statistical cluster detection methods and for use of more objective criteria in cluster investigation protocols. 相似文献
102.
EP Lopes AE Silva H Sette Junior RX Guimar?es ML Ferraz 《Canadian Metallurgical Quarterly》1995,37(5):455-460
This study was undertaken to investigate the presence of autoantibodies in patients with chronic viral hepatitis B and C, before, during and after interferon-alpha (IFN-alpha) therapy and to study their relation to dose and type of IFN-alpha and response to treatment. Fifty patients with chronic hepatitis were divided in two groups, a control-group of 21 patients (10 type B and 11 type C) who were followed for 6 months without treatment and an IFN-group consisting of 29 patients (8 type B and 21 type C) who received IFN therapy for 6 months. Serum samples were tested for a range of antibodies at the start of the study, during therapy and at the end of the 6 month period. Antibodies tested for included: antinuclear, smooth muscle, antimitochondrial, parietal cell and thyroid microsomal. Four (8%) of the total patient group had autoantibodies at the beginning of the study (two in each group). During the follow-up period no patient in the control group developed antibodies compared with 3 (11%) patients in the treatment group. Autoantibodies developed in patients treated with higher doses of IFN and were found in those patients who tended to show a poor response to IFN-therapy. Further studies are needed to establish the relationship between poor response to IFN-alpha and development of autoantibodies. 相似文献
103.
Hybridization using kDNA and rDNA sequences as probes was performed to study phylogenetic relatedness of different species of trypanosomatids. Using this approach, we identified five organisms which had been classified as Phytomonas and Herpetomonas that were more closely correlated to each other phylogenetically than to any other species or isolates from either genera. These findings raise doubts about the validity of the current classification of Trypanosomatidae. Finally, we demonstrated the usefulness of kDNA sequences as an alternative to genomic sequences in obtaining phylogenetic information on trypanosomatids. 相似文献
104.
105.
GM Chertow JM Lazarus EP Paganini RL Allgren RA Lafayette MH Sayegh 《Canadian Metallurgical Quarterly》1998,9(4):692-698
BACKGROUND: Improvement of angina pectoris symptoms after cholesterol lowering has raised questions as to the underlying mechanisms. METHODS: Rabbit experiment: We compared arterial blood samples from New Zealand White cholesterol-supplemented rabbits (n = 6) with nonsupplemented rabbit samples (n = 4) in a closed-loop circulation diffusion system. The pH and partial pressures of oxygen (pO2) and carbon dioxide (pCO2) were measured continuously. The samples were first oxygen (O2) saturated (pO2, 160 mm Hg; pCO2, 4 mm Hg) and then desaturated in 100% nitrogen. Cholesterol levels were determined in whole blood, plasma (P Chol), red blood cells (RBCs), and RBC membranes. Human experiment: We exposed quadruple desaturated venous blood samples (n = 4) with P Chol levels of 87 to 400 mg/dL in a gas exchanger to capillary gas conditions (pO2, 23 mm Hg; pCO2, 46 mm Hg). After 15 minutes we performed blood gas analyses and compared our results to baseline values. RESULTS: In the rabbit experiment the cholesterol-supplemented group as compared to the control group showed higher plasma pO2 levels during the saturation phase and lower plasma pO2 levels during the desaturation phase. It also had a markedly increased RBC membrane cholesterol content: 121 +/- 3 (standard error of the mean [SEM]) mg/dL versus 22 +/- 1.7 mg/dL in the control group (P < .05). This barrier to RBC membrane O2 diffusion caused delayed O2 entry into the RBCs during saturation, with a higher plasma pO2, and delayed O2 release from the RBCs during desaturation, with a lower plasma pO2. In the human experiment the P Chol level was inversely correlated with the percentage change of O2 content in milliliters of O2 per deciliter of blood (P < .05). CONCLUSIONS: Increased RBC membrane cholesterol in hypercholesterolemia appears to decrease the transmembrane O2 diffusion rate. 相似文献
106.
Pyszczynski Tom; Hamilton James C.; Herring Fred H.; Greenberg Jeff 《Canadian Metallurgical Quarterly》1989,57(2):351
On the basis of self-regulatory perseveration theory, we hypothesized that the negative memory bias commonly found among depressed people is mediated by excess levels of self-focused attention and thus can be reduced by preventing depressed people from focusing on themselves. In Experiment 1, nondepressed and subclinically depressed college students were induced to either focus on themselves or externally and then to recall 10 events that had happened to themselves during the previous 2 weeks. Consistent with our hypotheses, events recalled by depressed Ss were more negative than events recalled by nondepressed Ss under conditions of self-focus but not under conditions of external focus. We conducted Experiment 2 to determine whether this effect was specific to self-referent events or generalizable to events that happened to other people. Experiment 2's findings replicated the previous findings for self-referent events but showed a different pattern for recall of events that happened to others, suggesting that self-focus reduces the negative memory bias among depressed individuals by deactivating their self-schemas. Theoretical and practical implications of these findings are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
107.
108.
Oxidation of catechol estrogens (CE) leads to the reactive electrophilic CE quinones. Reaction of CE-3,4-quinones with DNA has been implicated in tumor initiation. One pathway to prevent this reaction is conjugation of CE quinones with glutathione (GSH). Four CE, 4-hydroxy estrone (4-OHE1), 4-hydroxyestradiol (4-OHE2), 2-OHE1, and 2-OHE2, were conjugated with GSH after oxidation catalyzed by horseradish peroxidase (HRP), lactoperoxidase (LP), or rat liver microsomal cytochrome P450. This reaction is a free-radical chain autoxidation that produces very high yields of products. Six mono-GSH conjugates, 4-OHE1(E2)-2-SG, 2-OHE1(E2)-1-SG, and 2-OHE1(E2)-4-SG, and four di-GSH conjugates, 4-OHE1(E2)-1,2-bisSG and 2-OHE1(E2)-1,4-bisSG, were identified and quantified. These di-GSH conjugates were also obtained quantitatively from oxidation of mono-GSH conjugates by the same enzymes. HRP and LP gave very similar product profiles. Phenobarbital- and 3-methylcholanthrene-induced microsomes with either NADPH or cumene hydroperoxide as cofactor oxidized 4-OHE2 to form similar amounts of GSH conjugates. Enzymatic oxidation of 2-OHE1(E2) in the presence of GSH produced more 2-OHE1(E2)-4-SG than the 1-isomer. This contrasts with the direct reaction of E1(E2)-2,3-Q and GSH, in which the 1-isomer is formed more abundantly than the 4-isomer (Cao, K., Devanesan, P. D., Ramanathan, R., Gross, M. L., Rogan, E. G., and Cavalieri, E. L. (1998) Chem. Res. Toxicol. 11, 909-916). Competitive enzymatic oxidation of equimolar 4-OHE2 and 2-OHE2 in the presence of an equimolar amount of GSH yielded more 2-OHE2 conjugates than 4-OHE2 conjugates, despite E2-3,4-Q being more reactive with GSH than E2-2,3-Q. These results suggest that 2-OHE2 is a better substrate than 4-OHE2 in the catalytic oxidation to quinones, despite the greater reactivity of E2-3,4-Q, compared to E2-2,3-Q, with GSH. 相似文献
109.
Single amino acid replacement analogs of Manduca adipokinetic hormone (M-AKH) pGlu-Leu-Thr-Phe-Thr-Ser-Ser-Trp-GlyNH2 were tested for activity in bioassays as well as receptor binding assays. Amino acids were replaced by Ala and by D-analogs. In addition an extended M-AKH and analogs containing photo affinity labels were tested. All analogs had reduced activity. All the peptides which had enough activity to allow a full dose response curve reached the same maximal activity as native M-AKH. The use of analogs, in which L-Phe4 was replaced by Ala or by D-Phe and of L-Thr3 replaced by D-Thr, as competitors led to improved binding of M-AKH in our competitive receptor binding assay. In the bioassay an inactive concentration of Ala4 M-AKH increased the activity of a half optimal concentration of native M-AKH. 相似文献
110.
CD Vizza JP Lynch LL Ochoa G Richardson EP Trulock 《Canadian Metallurgical Quarterly》1998,113(3):576-583
AIM OF STUDY: To measure the effect of specific preoperative information on postoperative anxiety, satisfaction with information, and demand for analgesia, of Chinese males having transurethral resection of the prostate (TURP). DESIGN: A controlled experimental design. The researchers allocated all patients (n = 30) undergoing TURP in a general hospital in Hong Kong, during a 3-month period, to one of two groups. The experimental group (n = 15) received a specific information pamphlet and a general preoperative counselling video. The control group (n = 15) received a video alone. PROCEDURE AND MEASURES: Following ethical approval, a researcher took baseline measures of state and trait anxiety using the Chinese State-Trait Anxiety Inventory (C -STAI). Five days after surgery the researcher administered the C-STAI (A-State), a patients' satisfaction questionnaire, and, recorded requests for analgesia during the first 5 postoperative days. RESULTS: Experimental subjects reported significantly lower anxiety levels post-operatively and a significantly higher level of satisfaction with the preoperative information, than controls. Postoperative demand for analgesia did not significantly differ between groups. CONCLUSIONS: The findings support the importance of providing patients with specific, written preoperative information about their surgery and its effects to minimize their postoperative anxiety levels, and improve their satisfaction with the care provided. 相似文献