全文获取类型
收费全文 | 25170篇 |
免费 | 1044篇 |
国内免费 | 65篇 |
专业分类
电工技术 | 211篇 |
综合类 | 79篇 |
化学工业 | 6000篇 |
金属工艺 | 536篇 |
机械仪表 | 497篇 |
建筑科学 | 835篇 |
矿业工程 | 77篇 |
能源动力 | 915篇 |
轻工业 | 4588篇 |
水利工程 | 241篇 |
石油天然气 | 142篇 |
武器工业 | 18篇 |
无线电 | 1088篇 |
一般工业技术 | 3358篇 |
冶金工业 | 4152篇 |
原子能技术 | 184篇 |
自动化技术 | 3358篇 |
出版年
2024年 | 48篇 |
2023年 | 200篇 |
2022年 | 646篇 |
2021年 | 794篇 |
2020年 | 481篇 |
2019年 | 588篇 |
2018年 | 674篇 |
2017年 | 692篇 |
2016年 | 753篇 |
2015年 | 677篇 |
2014年 | 914篇 |
2013年 | 1614篇 |
2012年 | 1351篇 |
2011年 | 1711篇 |
2010年 | 1303篇 |
2009年 | 1298篇 |
2008年 | 1172篇 |
2007年 | 1027篇 |
2006年 | 855篇 |
2005年 | 741篇 |
2004年 | 695篇 |
2003年 | 621篇 |
2002年 | 554篇 |
2001年 | 395篇 |
2000年 | 390篇 |
1999年 | 403篇 |
1998年 | 1441篇 |
1997年 | 922篇 |
1996年 | 679篇 |
1995年 | 377篇 |
1994年 | 329篇 |
1993年 | 324篇 |
1992年 | 121篇 |
1991年 | 116篇 |
1990年 | 84篇 |
1989年 | 113篇 |
1988年 | 97篇 |
1987年 | 84篇 |
1986年 | 66篇 |
1985年 | 100篇 |
1984年 | 66篇 |
1983年 | 51篇 |
1982年 | 57篇 |
1981年 | 56篇 |
1980年 | 59篇 |
1979年 | 34篇 |
1977年 | 101篇 |
1976年 | 192篇 |
1975年 | 29篇 |
1973年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
J Alvarez-Sabín 《Canadian Metallurgical Quarterly》1997,25(142):919-923
Between 3.7% and 8.5% of all strokes occur before the age of 45 years old. In the population under 15 years of age, the annual incidence of strokes is 2.7 per 100,000 children, with ischaemic strokes making up 1.2 and haemorrhagic strokes 1.5 of this total. The main characteristic of ischaemic strokes in childhood is the wide variety of diagnoses involved. Some of these, such as congenital cardiopathy, are rare in adults, as are dissections and arterial dysplasias, arteritis, hereditary connective tissue disorders and disorders of metabolism. Similarly, the aetiology of haemorrhagic stroke is also very varied, with bursting of a vascular malformation or aneurysm being the commonest. Other aetiologies are disorders of haemostasis, arteritis, migraine, retarded post-traumatic phenomena and the use of drugs and sympathomimetic agents. The personal, family and social repercussions are considerable, since both ischaemic and haemorrhagic strokes have an appreciable mortality and morbidity. 相似文献
22.
23.
C Held P Hjemdahl N Rehnqvist NH Wallén I Bj?rkander SV Eriksson L Forslund B Wiman 《Canadian Metallurgical Quarterly》1997,95(10):2380-2386
BACKGROUND: Disturbed fibrinolytic function may influence the progression of coronary atherosclerosis and contribute to thrombotic cardiovascular (CV) events. METHODS AND RESULTS: In the Angina Prognosis Study in Stockholm (APSIS), patients with stable angina pectoris were studied prospectively during double-blind treatment with metoprolol or verapamil. Various measures of fibrinolytic function were studied in 631 (of 809) patients. During a median follow-up time of 3.2 years (2132 patient-years), 32 patients suffered a CV death, 21 had a nonfatal myocardial infarction (MI), and 77 underwent revascularization. Plasma levels of tissue plasminogen activator (TPA) activity and antigen (ag), plasminogen activator inhibitor (PAI-1) activity at test, and TPA responses to exercise were determined at baseline and after 1 month's treatment and were related to subsequent fatal and nonfatal CV events. Univariate Cox regression analysis revealed that elevated levels of TPA-ag at rest (P < .05), high PAI-1 activity (P < .05), and low TPA-ag responses to exercise (P < .05) were associated with increased risk of subsequent CV death. After adjustment for baseline risk factors, TPA-ag independently predicted CV death or MI. In addition, PAI-1 activity independently predicted CV death or MI in male patients. Verapamil treatment was associated with a 10% decrease of TPA-ag levels and metoprolol treatment with a 2% increase (P < .001 for treatment difference). CONCLUSIONS: Plasma TPA-ag levels at rest, and among male patients PAI-1 activity as well, independently predict subsequent CV death or MI in patients with stable angina pectoris. 相似文献
24.
E Orgnero de Gaisán C Maldonado MF Diaz Gavier A Aoki 《Canadian Metallurgical Quarterly》1997,179(5):453-460
A bioassay system for rapid detection of carcinogenic agents has been developed using male Fischer 344 rats to bridge the gap between long-term carcinogenicity tests and short-term screening assays. The system, called the medium-term liver bioassay, is fundamentally based on the 2-stage hypothesis of tumor production, employing initiation by diethylnitrosamine (200 mg/kg, i.p.) in the first stage and test chemical administration during the second, in combination with two-thirds partial hepatectomy. It requires only 8 wk for animal experimentation and a further few weeks for quantitative analysis of immunohistochemically demonstrated glutathione S-transferase placental form positive hepatic foci. A total of 291 chemicals/substances have already been analyzed in our laboratory. Among 63 chemicals that were proved to be carcinogenic in the liver of rat and/or mouse, 57 (90%) gave positive results irrespective of their mutagenicity. Negative compounds include peroxisome proliferators and tamoxifen. Even nonhepatocarcinogens were positive at a rate of 24%. Eighty-six percent (12/14) of mouse liver carcinogens were also positive. On the other hand, only 2 out of 45 noncarcinogens showed very weak positivity. Thus, the efficacy of the system for hepatocarcinogens has been well established. This bioassay is increasingly regarded as an appropriate alternative test for carcinogenicity risk assessment and is practically used for a rapid evaluation of hepatocarcinogenicity of chemicals. 相似文献
25.
A Serrano Pascual C Merino Hernáez R Ochoa Mejías A Escolano Chamois J Golbano Ablanque I Otero Tejero M Sanz Redondo F Román Ruiz 《Canadian Metallurgical Quarterly》1997,21(6):631-635
BACKGROUND AND AIMS OF THE STUDY: Surgical treatment of functional tricuspid regurgitation associated with advanced valvular disease remains controversial, mainly due to the difficulty in choosing between valve replacement or reconstructive surgery. Failure to correct tricuspid regurgitation during valvular surgery carries a poor prognosis, as reoperation may represent a significant risk to the patient. Thus correct tricuspid valve surgery is vital to achieve improved early and long-term clinical results. METHODS: A total of 142 patients underwent concomitant tricuspid annuloplasty with mitral valve replacement and their clinical outcome was assessed. RESULTS: Overall hospital mortality rate was 11.3%. Seven patients died during follow up. The overall actuarial survival rate for 10 years was 74.1 +/- 14.2%. Postoperatively, 75.8% of the patients had no residual tricuspid insufficiency, while 24.2% had first- or second-degree tricuspid insufficiency and were treated medically. All patients were in NHYA functional class I or II postoperatively. CONCLUSION: Clinically, it is important to assess the severity of functional tricuspid insufficiency before and/or during the operation. Bicuspidalization annuloplasty for functional tricuspid insufficiency has provided good results, with a low incidence of reoperation and significant clinical improvement. The technique could be used in most patients with functional tricuspid regurgitation. 相似文献
26.
The dissociation pK values of the representative loop diuretics furosemide, bumetanide and ethacrynic acid in 10, 30, 40, 50 and 70% (w/w) acetonitrile-water mixtures at 298.15 K were determined, according to the rules and procedures endorsed by IUPAC. The variation in pK values over the whole composition range studied can be explained by tacking into account the preferential solvation of ionizable substances in acetonitrile-water mixtures. With a view to determining the pK values of the loop diuretics studied in any of the binary solvent acetonitrile-water mixtures, correlations of pK values and different bulk properties of the solvent were examined, and the linear solvation energy relationships method, LSER, has been applied. The pK values were then correlated with the pi*, alpha and beta solvatochromic parameters of acetonitrile-water mixtures. The resulting equations allowed us to calculate pK values for the loop diuretics in any acetonitrile-water mixture up to 70% (w/w) acetonitrile. 相似文献
27.
28.
OBJECTIVES: To study the expression of preproendothelin-1 messenger RNA (mRNA) in tissue after Escherichia coli lipopolysaccharide challenge and to evaluate the possible effects of betamethasone both regarding endothelin-1 production as well as hemodynamic and vascular effects during E. coli lipopolysaccharide infusion in pigs in vivo. DESIGN: Prospective trial. SETTING: Laboratory at a university medical center. SUBJECTS: Ten domestic pigs, weighing 18 to 25 kg. INTERVENTIONS: Anesthetized pigs were given continuous infusions of E. coli lipopolysaccharide (15 micrograms/kg/hr for 3 hrs), with or without prior treatment with betamethasone (0.5 mg/kg im 12 hrs before the start of the surgical preparation and 0.5/kg iv at the start of the preparation). MEASUREMENTS AND MAIN RESULTS: The E. coli lipopolysaccharide infusion evoked the characteristic cardiovascular changes observed in septic shock: decreased mean arterial pressure and cardiac output; increased heart rate and increased pulmonary vascular resistance. Large increases in both arterial plasma concentrations of endothelin-1-like immunoreactivity, as well as preproendothelin-1 mRNA concentrations in tissues, were also observed during the E. coli lipopolysaccharide infusion. Treatment with betamethasone significantly attenuated the E. coli lipopolysaccharide-induced increase in endothelin-1 plasma concentrations, whereas the increased mRNA concentrations were only slightly affected. Furthermore, betamethasone treatment also affected cardiovascular parameters, with significant attenuation of the E. coli lipopolysaccharide-induced increase in heart rate and a higher cardiac output after 60 mins of the E. coli lipopolysaccharide infusion. The urine production, which was markedly decreased during the E. coli lipopolysaccharide infusion, was significantly higher in the betamethasone-treated group compared with the control group. CONCLUSIONS: The present results indicate that the increased concentrations of endothelin-1-like immunoreactivity that are observed in septic shock may have negative effects on both cardiovascular parameters as well as renal function, which is in agreement with a possible role for endothelin-1 in the pathogenesis of septic shock. 相似文献
29.
30.