首页 | 本学科首页   官方微博 | 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   1475篇
  免费   67篇
  国内免费   2篇
电工技术   10篇
综合类   1篇
化学工业   194篇
金属工艺   12篇
机械仪表   38篇
建筑科学   27篇
矿业工程   3篇
能源动力   22篇
轻工业   122篇
水利工程   16篇
石油天然气   4篇
无线电   42篇
一般工业技术   215篇
冶金工业   763篇
原子能技术   13篇
自动化技术   62篇
  2023年   5篇
  2022年   20篇
  2021年   31篇
  2020年   24篇
  2019年   30篇
  2018年   31篇
  2017年   50篇
  2016年   33篇
  2015年   27篇
  2014年   33篇
  2013年   47篇
  2012年   60篇
  2011年   58篇
  2010年   65篇
  2009年   43篇
  2008年   35篇
  2007年   34篇
  2006年   30篇
  2005年   27篇
  2004年   29篇
  2003年   25篇
  2002年   11篇
  2001年   12篇
  2000年   9篇
  1999年   29篇
  1998年   219篇
  1997年   128篇
  1996年   83篇
  1995年   55篇
  1994年   41篇
  1993年   37篇
  1992年   9篇
  1991年   14篇
  1990年   10篇
  1989年   14篇
  1988年   8篇
  1987年   11篇
  1986年   4篇
  1985年   8篇
  1983年   3篇
  1982年   6篇
  1981年   4篇
  1980年   6篇
  1978年   3篇
  1977年   24篇
  1976年   51篇
  1975年   2篇
  1965年   1篇
  1964年   1篇
  1955年   1篇
排序方式: 共有1544条查询结果,搜索用时 31 毫秒
71.
OBJECTIVE: To reveal the relationship between fasting and 2-h postload plasma glucose and to examine the appropriate fasting glucose cutoff as the primary screening test for diabetes. RESEARCH DESIGN AND METHODS: We recruited 5,303 subjects from preventive services of the National Cheng Kung University Hospital. Exclusion criteria were age <20 years, pregnancy, known diabetes, and a history of recent surgery, trauma, or illness. All subjects received the 75-g oral glucose tolerance test. The relationship between fasting and 2-h glucose was examined. Sensitivities, specificities, efficiency, and predictive values were assessed at different cutoffs of fasting glucose for prediction of diabetes. RESULTS: The best fit model for the relationship between fasting and 2-h glucose was fasting glucose = 4.914-0.060 x (2-h glucose) + 0.0144 x (2-h glucose)2. From this model, the fasting glucose was 6.0 mmol/l when 2-h glucose was 11.1 mmol/l. A fasting glucose with 6.25 mmol/l gave the same diabetes prevalence as the World Health Organization 2-h glucose criterion. When 7.8 mmol/l was the fasting glucose cutoff, the sensitivity was 28.5%. Lowering the cutoff from 7.8 to 7.0 mmol/l increased the sensitivity by 11.2% and slightly reduced the specificity and positive predictive value. If the cutoffs were 6.25 and 6.0 mmol/l, the sensitivity increased and the specificity and the positive predictive value decreased accordingly. CONCLUSIONS: Our results suggest that fasting glucose as a screening criterion for diabetes could be revised downward to 7.0 mmol/l, because the slight reduction of positive predictive value was more than balanced by an apparent increase of sensitivity and insignificant change of specificity.  相似文献   
72.
In this study the potential of intraperitoneal (i.p.) and intravenous (i.v.) administration of chimeric iodine-131-labelled MOv18 IgG for radioimmunotherapy was determined. The dosimetry associated with both routes of administration of cMOv18 IgG was studied in patients. Eight patients suspected of having ovarian carcinoma received 150 MBq 131I-cMOv18 IgG i.p. Blood and urine were collected and serial gamma camera images were acquired. Another group of four patients received 7.5 MBq 131I-cMOv18 IgG i.v. For all patients, tissue biopsies were obtained at surgery. Activity in the blood after i.p. administration was described by a bi-exponential curve with a mean uptake and elimination half-life of 6.9+/-3.2 h and 160+/-45 h, respectively. For i.v. infusion the mean half-life for the elimination phase was 103+/-12 h. Cumulative excretion in the urine was 17%+/-3% ID and 21%+/-7% ID in 96 h for i.p. and i.v. administration, respectively. Scintigraphic images after i.p. administration showed accumulation in ovarian cancer lesions, while all other tissues showed decreasing activity with time. Tumour uptake determined in the ovarian cancer tissue specimens ranged from 3.4% to 12.3% ID/kg for i.p. administration and from 3.6% to 5.4% ID/kg for i.v. administration. Dosimetric analysis of the data indicated that 1.7-4.3 mGy/MBq and 1.7-2.2 mGy/MBq can be guided to solid or ascites cells after i.p. and i.v. administration, respectively. Assuming that an absorbed dose to the bone marrow of 2 Gy will be dose limiting, a total activity of 4.1 GBq 131I-cMOv18 IgG can be administered safely via the i.p. route and 3.5 GBq via the i.v. route. At this maximal tolerated dose, a maximum absorbed dose to 1-g tumours in the peritoneal cavity of 18 and 8 Gy can be reached after i.p. and i.v. administration, respectively. For the i. p. route of administration, dose estimates for the tumour are even higher when the electron dose of the peritoneal activity is also taken into account: total doses to the tumour of 30 Gy and 22 Gy will be absorbed at the tumour surface and at 0.2 mm depth, respectively. In conclusion, therapeutic tumour doses can be achieved with 131I-cMOv18 IgG in patients with intraperitoneal ovarian cancer lesions with no normal organ toxicity. The i.p. route of administration seems to be preferable to i.v. administration.  相似文献   
73.
74.
1. The role of the renin-angiotensin system in the regulation of myocardial contractility is still debated. In order to investigate whether renin inhibition affects myocardial contractility and whether this action depends on intracardiac rather than circulating angiotensin II, the regional myocardial effects of systemic (i.v.) and intracoronary (i.c.) infusions of the renin inhibitor remikiren, were compared and related to the effects on systemic haemodynamics and circulating angiotensin II in open-chest anaesthetized pigs (25-30 kg). The specificity of the remikiren-induced effects was tested (1) by studying its i.c. effects after administration of the AT1-receptor antagonist L-158,809 and (2) by measuring its effects on contractile force of porcine isolated cardiac trabeculae. 2. Consecutive 10 min i.v. infusions of remikiren were given at 2, 5, 10 and 20 mg min-1. Mean arterial pressure (MAP), cardiac output (CO), heart rate (HR), systemic vascular resistance (SVR), myocardial oxygen consumption (MVO2) and left ventricular (LV) dP/dtmax were not affected by remikiren at 2 and 5 mg min-1, and were lowered at higher doses. At the highest dose, MAP decreased by 48%, CO by 13%, HR by 14%, SVR by 40%, MVO2 by 28% and LV dp/dtmax by 52% (mean values; P < 0.05 for difference from baseline, n = 5). The decrease in MVO2 was accompanied by a decrease in myocardial work (MAP x CO), but the larger decline in work (55% vs. 28%; P < 0.05) implies a reduced myocardial efficiency ((MAP x CO)/MVO2). 3. Consecutive 10 min i.c. infusions of remikiren were given at 0.2, 0.5, 1, 2, 5 and 10 mg min-1. MAP, CO, MVO2 and LV dP/dtmax were not affected by remikiren at 0.2, 0.5 and 1 mg min-1, and were reduced at higher doses. At the highest dose, MAP decreased by 31%, CO by 26%, MVO2 by 46% and LV dP/dtmax by 43% (mean values; P < 0.05 for difference from baseline, n = 6). HR and SVR did not change at any dose. 4. Thirty minutes after a 10 min i.v. infusion of the AT1 receptor antagonist, L-158,809 at 1 mg min-1, consecutive 10 min i.c. infusions (n = 5) of remikiren at 2, 5 and 10 mg min-1 no longer affected CO and MVO2, and decreased LV dP/dtmax by maximally 27% (P < 0.05) and MAP by 14% (P < 0.05), which was less than without AT1-receptor blockade (P < 0.05). HR and SVR remained unaffected. 5. Plasma renin activity and angiotensin I and II were reduced to levels at or below the detection limit at doses of remikiren that were not high enough to affect systemic haemodynamics or regional myocardial function, both after i.v. and i.c. infusion. 6. Remikiren (10(-10) to 10(-4) M) did not affect contractile force of porcine isolated cardiac trabeculae precontracted with noradrenaline. In trabeculae that were not precontracted no decrease in baseline contractility was observed with remikiren in concentrations up to 10(-5) M, whereas at 10(-4) M baseline contractility decreased by 19% (P < 0.05). 7. Results show that with remikiren i.v., at the doses we used, blood pressure was lowered primarily by vasodilation and with remikiren i.c. by cardiac depression. The blood levels of remikiren required for its vasodilator action are lower than the levels affecting cardiac contractile function. A decrease in circulating angiotensin II does not appear to be the sole explanation for these haemodynamic responses. Data support the contention that myocardial contractility is increased by renin-dependent angiotensin II formation in the heart.  相似文献   
75.
A total of 88 Fallopian tubes from 44 patients was examined with hysterosalpingo contrast sonography (HyCoSy), hysterosalpingogram (HSG), and laparoscopic chromopertubation (LC) in order to assess their relative accuracy for measuring tubal patency. HyCoSy was done by transvaginal ultrasound and the contrast was SH U 454 (Echovist). The flow of multiple fractions of the contrast medium through each Fallopian tube was observed in real time in appropriate imaging planes by means of a transvaginal probe. Compared with laparoscopic results, we found a sensitivity of 85.2%, a specificity of 85.2%, a positive predictive value (PPV) of 71.9%, a negative predictive value (NPV) of 92.9% and concordance (HyCoSy/LC) of 85.2%, while the corresponding values for HSG were sensitivity = 85.2%, specificity = 83.6%, PPV = 69.7%, NPV = 92.7% and concordance (HSG/LC) of 84.1%. Compared with HSG results, HyCoSy obtained a co-positivity of 66.7%, a co-negativity of 81.8% and a concordance of 76.1%. In conclusion, HyCoSy with SH U 454 proved to be a reliable and safe modality for evaluating tubal patency; it is suitable as an outpatient diagnostic procedure to be used before more invasive procedures.  相似文献   
76.
77.
78.
In two children with histoplasmosis pulmonary perfusion and ventilation studies revealed mismatched abnormalities characterized by almost unilaterally absent perfusion but normal ventilation in the right lung. Chest roentgenograms demonstrated right hilar enlargement and pulmonary contrast angiograms revealed narrowing of the right pulmonary arteries by extrinsic fibrotic granulomata but no pulmonary emboli were present. Fibrosing mediastinitis due to histoplasmosis was found by mediastinoscopic examination in one of the patients. Non-embolic causes of V/Q mismatch lung imaging are discussed briefly, and the correlation with clinical findings is stressed for the diagnosis of pulmonary emboli.  相似文献   
79.
Starch-chitosan hydrogels were produced by oxidation of soluble starch to produce polyaldehyde and subsequently cross-linked with chitosan via reductive alkylation. The swelling ratio of starch-chitosan membranes was increased gradually with increasing starch ratio, but it was always lower than the native chitosan. In dry state, starch-chitosan membranes with low starch ratio (0.16, 0.38) showed similar tensile strength values to those of native chitosan while these values decreased with increasing starch ratios (0.73-1.36). Membranes in physiological buffer solution (PBS) gave a tensile modulus between 2.8 and 1.0 MPa, decreasing with increasing starch ratio (0.16-1.36 (Wstarch/Wchitosan)). When the membranes were incubated in PBS only, a moderate weight loss was observed for the first two weeks. Original weights of low starch weight ratio membranes (0-0.38) were at near 85%, while high ratio samples (0.73-1.55) were kept around 70% after three months. However, for the membranes incubated in alpha-amylase solution, very fast weight loss was observed. For low starch ratio membranes (0.16, 0.38, 0.73), the residual original weights were measured to be 11%, 6%, 20%, while for high ratio membranes (1.04 and 1.36) these were 45% and 30%, respectively, after two months of enzyme incubation. Scanning electron microscopy analysis of alpha-amylase degraded membranes exhibited rough surface morphology.  相似文献   
80.
The aim of this study was to assess microleakage in class V cavities prepared by air abrasion or high-speed dental bur and restored with different glass ionomer cements. Sixty bovine incisors were equally divided into 6 groups: I, II and III (preparation by high-speed) and IV, V and VI (preparation by air abrasion). Groups I and IV were restored with Fuji IX; groups II and V with Ketac Molar; and groups III and VI with Vitremer. After 24 h (37 °C), specimens were thermocycled, isolated with nail varnish, immersed in a 0.2% Rhodamine B solution for 24 hours, sectioned longitudinally and analyzed for microleakage using an optical microscope connected to a digital camera and a computer. The images were digitized and a software allowed the quantitative evaluation of microleakage in millimeters. Data were analyzed by Wilcoxon and Kruskal-Wallis tests. It was observed that there were significant differences (p ≤ 0.05) between incisal (enamel) and cervical (dentine/cementum) margins, mainly for Ketac Molar; there was no difference (p ≥ 0.05) between preparation methods, except for group II (high-speed/Ketac Molar) that showed higher infiltration; regarding the materials, Ketac Molar demonstrated the highest microleakage values (p ≤ 0.05), and only Vitremer sealed completely both margins of restorations. It was concluded that air abrasion preparation did not influence microleakage in class V restorations with the employed glass ionomer cements.  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