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   861篇
  免费   1篇
化学工业   7篇
轻工业   1篇
无线电   1篇
一般工业技术   1篇
冶金工业   850篇
原子能技术   1篇
自动化技术   1篇
  2020年   1篇
  2018年   2篇
  2016年   1篇
  2012年   1篇
  2008年   1篇
  2003年   1篇
  2001年   1篇
  2000年   1篇
  1999年   22篇
  1998年   242篇
  1997年   155篇
  1996年   90篇
  1995年   47篇
  1994年   51篇
  1993年   53篇
  1992年   5篇
  1991年   11篇
  1990年   9篇
  1989年   7篇
  1988年   8篇
  1987年   19篇
  1986年   7篇
  1985年   6篇
  1983年   1篇
  1982年   5篇
  1981年   5篇
  1980年   7篇
  1978年   1篇
  1977年   25篇
  1976年   74篇
  1965年   1篇
  1964年   1篇
  1955年   1篇
排序方式: 共有862条查询结果,搜索用时 15 毫秒
31.
32.
33.
Long-term ambient concentrations of inhalable particles less than 10 microm in diameter (PM10) (1973- 1992) and other air pollutants-total suspended sulfates, sulfur dioxide, ozone (O3), and nitrogen dioxide-were related to 1977-1992 mortality in a cohort of 6,338 nonsmoking California Seventh-day Adventists. In both sexes, PM10 showed a strong association with mortality for any mention of nonmalignant respiratory disease on the death certificate, adjusting for a wide range of potentially confounding factors, including occupational and indoor sources of air pollutants. The adjusted relative risk (RR) for this cause of death as associated with an interquartile range (IQR) difference of 43 d/yr when PM10 exceeded 100 microg/m3 was 1.18 (95% confidence interval [CI]: 1.02, 1.36). In males, PM10 showed a strong association with lung cancer deaths-RR for an IQR was 2.38 (95% CI: 1.42, 3.97). Ozone showed an even stronger association with lung cancer mortality for males with an RR of 4.19 (95% CI: 1.81, 9.69) for the IQR difference of 551 h/yr when O3 exceeded 100 parts per billion. Sulfur dioxide showed strong associations with lung cancer mortality for both sexes. Other pollutants showed weak or no association with mortality.  相似文献   
34.
35.
36.
BACKGROUND: An experiment was carried out to establish whether using a pre‐compacting device (expander) changes the contribution of dry matter (DM) and degradative behaviour of peas, lupins and faba beans over the different fractions (non‐washable fraction, NWF; insoluble washable fraction, ISWF; soluble washable fraction, SWF). Samples of the entire concentrate ingredients (WHO ingredients) and their different fractions (NWF, ISWF and SWF) were subjected to three processes (Retsch milling, R; expander treatment, E; expander‐pelleting, EP) and their fermentation characteristics were evaluated using an in vitro gas production technique. RESULTS: In peas and faba beans, both the E and EP processes increased the size of the NWF (P < 0.05) and decreased the size of the SWF compared with the R process. The maximum fractional rate of gas production in the first phase of fermentation was higher in the E and EP samples than in the R samples (P < 0.05). In lupins and faba beans the E and EP processes shifted the pattern of fermentation towards a more glucogenic fermentation, as represented by a lower non‐glucogenic to glucogenic ratio (NGR). Ammonia production (NH3‐N) in the E and EP samples was significantly (P < 0.05) lower than that in the R samples. CONCLUSION: It is concluded that the E and EP processes provide a certain level of protection against ruminal breakdown to dietary protein and shift the pattern of fermentation towards a more glucogenic fermentation. Copyright © 2008 Society of Chemical Industry  相似文献   
37.
We analyzed signal-averaged electrocardiograms (ECG) obtained in 50 patients with recent myocardial infarction (RMI: 25 anterior and 25 inferior) and 20 normal subjects to determine the relationship between the initial portion of the signal-averaged QRS complex and cardiac function and infarct size. We examined (1) the root mean square voltage (RMS10-40, microV), (2) the integration (A10-40, microV.msec) at 10-msec intervals over the first 40 msec of the signal-averaged QRS complex, and (3) the intervals (T) of the magnitude of the signal-averaged ECG achieved at 10-microV intervals over the first 40 microV (T10-40, msec). The mean RMS10-40 (p < 0.01) and A10-40 (A10, p < 0.05; A20-40, p < 0.01) were significantly lower and the T10-40 (p < 0.01) was significantly longer in RMI patients than in normal subjects. The RMS10-40 (p < 0.01) and A10-40 (p < 0.05) were significantly lower and the T10-40 (T10.20, p < 0.01; T30.40, p < 0.05) was significantly longer in patients with anterior RMI patients than in patients with inferior RMI. The A30 was correlated with the ejection fraction and total creatine kinase (CK) release in all patients (r = 0.73, and -0.78, respectively, p < 0.001). These results suggest that the A30 may be an important predictor of ventricular dysfunction and infarct size in patients with RMI.  相似文献   
38.
There are several tumors and tumorlike entities of bone that do not easily fit into the specific classifications provided elsewhere in this issue. In this article, several seemingly unrelated entities are discussed, including cystic diseases of bone (simple bone cysts and aneurysmal bone cysts), Langerhans' cell histiocytosis, benign and malignant vascular tumors of bone, and adamantinoma of long bone and its relationship to osteofibrous dysplasia.  相似文献   
39.
Signal detectability was measured in three temporal conditions as a function of the bandwidth and configuration of simultaneous maskers that either did or did not spectrally overlap the signal. The 20-ms signal was 250 Hz wide and was centered at 2500 Hz (fs). Although there were marked individual differences, performance was typically poorer when signal onset came 1 ms rather than 250 ms after the onset of a 420-ms masker, and poorest when signal onset came 1 ms after the onset of a 23-ms masker. The results support the idea that two separate across-channel processes contribute to temporal changes in signal detectability. One process contributes to the improvement observed as signal onset is delayed from masker onset, and its influence is reduced by the presence of masking components at fs only when the masker extends exclusively below fs. The other process is associated with the improvement observed as masker offset is delayed from signal offset, and its influence is reduced by the presence of masking components at fs when the masker extends exclusively above, or both below and above fs. Both of these processes are primarily activated by frequencies ranging from 0.6 to 0.8fs and 1.2 to 1.4fs. The data also demonstrate that the measured critical bandwidth narrows as signal onset is delayed from masker onset.  相似文献   
40.
METHODS: This study characterizes the performance of a newly developed whole-body PET scanner (Advance, General Electric Medical Systems, Milwaukee, WI). The scanner consists of 12,096 bismuth germinate crystals (4.0 mm transaxial by 8.1 mm axial by 30 mm radial) in 18 rings, giving 35 two-dimensional image planes through an axial field of view of 15.2 cm. The rings are separated by retractable tungsten septa. Intrinsic spatial resolution, scatter fraction, sensitivity, high count rate performance and image quality are evaluated. RESULTS: Transaxial resolution (in FWHM) is 3.8 mm at the center and increases to 5.0 mm tangential and 7.3 mm radial at R = 20 cm. Average axial resolution decreases from 4.0 mm FWHM at the center to 6.6 mm at R = 20 cm. Scatter fraction is 9.4% and 10.2% for direct and cross slices, respectively. With septa out, the average scatter fraction is 34%. Total system sensitivity for true events (in kcps/(microCi/cc)) is 223 with septa in and 1200 with septa out. Dead-time losses of 50% correspond to a radioactivity concentration of 4.9 (0.81) microCi/cc and a true event count rate of 489 (480) kcps with septa in (out). Noise-equivalent count rate (NECR) for the system as a whole shows a maximum of 261 (159) kcps at a radioactivity concentration of 4.1 (0.65) microCi/cc with septa in (out). NECR is insensitive to changes in lower gamma-energy discrimination between 250-350 keV. CONCLUSIONS: The results show the performance of the newly designed PET scanner to be well suited for clinical and research applications.  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