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   2047篇
  免费   2篇
  国内免费   2篇
综合类   2篇
化学工业   33篇
金属工艺   8篇
机械仪表   5篇
建筑科学   3篇
能源动力   16篇
轻工业   17篇
水利工程   2篇
石油天然气   3篇
无线电   10篇
一般工业技术   28篇
冶金工业   1888篇
原子能技术   12篇
自动化技术   24篇
  2021年   2篇
  2020年   4篇
  2019年   3篇
  2018年   2篇
  2017年   4篇
  2016年   4篇
  2015年   3篇
  2014年   4篇
  2013年   18篇
  2012年   6篇
  2011年   10篇
  2010年   7篇
  2009年   8篇
  2008年   4篇
  2007年   12篇
  2006年   13篇
  2005年   10篇
  2004年   4篇
  2003年   5篇
  2002年   3篇
  2001年   3篇
  2000年   3篇
  1999年   55篇
  1998年   635篇
  1997年   352篇
  1996年   193篇
  1995年   139篇
  1994年   98篇
  1993年   112篇
  1992年   15篇
  1991年   37篇
  1990年   28篇
  1989年   30篇
  1988年   26篇
  1987年   26篇
  1986年   20篇
  1985年   16篇
  1984年   1篇
  1983年   4篇
  1982年   7篇
  1981年   3篇
  1980年   13篇
  1978年   6篇
  1977年   24篇
  1976年   76篇
  1975年   1篇
  1973年   1篇
  1965年   1篇
排序方式: 共有2051条查询结果,搜索用时 15 毫秒
71.
BACKGROUND/AIMS: Primary carcinoma of the gallbladder is rare and associated with a late diagnosis and poor prognosis. Concurrent acute cholecystitis frequently obscures the presence of carcinoma. The information regarding gallbladder carcinoma with acute cholecystitis is limited. In order to better understand the presentation of gallbladder carcinoma with acute cholecystitis, we retrospectively reviewed the data of patients with primary carcinoma of the gallbladder. METHODOLOGY: The data of 86 patients with primary carcinoma of the gallbladder treated between 1979 and 1994 were compiled and reviewed. The patients were divided into 2 groups: Group 1 (with acute cholecystitis, 21 patients) and Group 2 (without cholecystitis, 65 patients). Clinicopathological comparisons were made and evaluated between these two groups RESULTS: The average age of Group 1 patients was older than that of Group 2 patients (75+/-2 years vs. 63+/-2 years; p<0.05). Three Group 1 patients presented with sepsis. The interval between the onset of symptoms and hospital admission in Group 2 patients was significantly (p<0.05) longer than that in Group 1 patients (243+/-95 days vs. 20+/-11 days). Leukocytosis (>11,000/mm3) was more common in Group 1 patients than in Group 2 patients (47.6% vs. 15.4%). Jaundice was more common in Group 2, and fever was common in Group 1. The majority of Group 2 gallbladder cancers were stage V (75.4%). In contrast, 52.4% of Group 1 gallbladder cancers were stage III and 38.1% were stage V. The 30-day postoperative mortality rate in Group 1 and Group 2 patients was 9.5% and 7.7%, respectively. The cumulative survival of Group 1 patients was not different from that of Group 2 patients (log-rank test, p>0.05). CONCLUSIONS: Age, the interval of symptoms prior to admission, the location of abdominal pain, fever, leukocytosis, and the absence of jaundice suggested the presence of acute cholecystitis in gallbladder carcinoma. A high index of suspicion of the disease, intraoperative examination of gallbladder specimens, and more aggressive surgical treatment may improve patient survival.  相似文献   
72.
The predominant early childhood education philosophy in the United States views formal academic instruction as inappropriate and harmful to the social development of young children. Chinese American immigrants to the United States, however, have been found to teach their young children in more formal ways, to be more directive, and to structure their children's use of time to a greater degree (C. S. Huntsinger, P. E. Jose, F.-R. Liaw, & W.-D. Ching, 1997). Forty European American (20 boys, 20 girls) and 36 2nd-generation Chinese American (18 boys, 18 girls) 1st- and 2nd-grade children and their mothers, fathers, and teachers participated in the Time 2 data collection of this longitudinal study to assess whether the formal academic environment provided by Chinese American parents is linked to poorer social adjustment in their children. Regressions showed that parents' work-oriented methods influenced academic performance but not social adjustment of their children.  相似文献   
73.
74.
The best long-term survival for any given lung cancer patient is provided by surgical resection. However, pneumonectomy still has the highest mortality rates, often due to cardiac complications. Risk assessment can be aided by preoperative evaluation of thoracic surgery patients. The role of right heart function, intraoperative management, and postoperative conditions in myocardial ischemia and infraction are analyzed, and the benefits of different kinds of resection are weighed in light of possible cardiac complications.  相似文献   
75.
76.
77.
Early, indirect studies suggested that an important aspect of thyroid economy during pregnancy was a decline in plasma or serum inorganic iodide (PII) concentrations, but there is little information concerning circulating iodide concentrations as assessed by direct measurement. The present study was undertaken to determine the relationship between gestation and serum iodide concentrations as assessed by direct measurement of PII. PII concentrations, urinary iodide levels, and other parameters of thyroid economy were measured during the first, second, and third trimesters and after delivery in 16 women. Mean serum T4 concentrations were significantly higher in all 3 trimesters than those after delivery. Serum free T4 index concentrations were significantly higher in the first trimester than during later periods of gestation or after delivery, but serum TSH concentrations were not depressed in the first trimester. Serum thyroglobulin concentrations were similar during pregnancy and after delivery. There was wide variability in PII and urinary iodide concentrations during and after pregnancy, but there was no trend for PII concentrations to be depressed during pregnancy. Pregnancy, at least in iodine-sufficient regions, does not have an important influence on circulating concentrations of iodide.  相似文献   
78.
A method for volume selective proton spectroscopy is presented based on a multiecho sequence with short refocusing interval tcp. It is demonstrated, that by appropriate choice of tcp on the order of 4-6 ms, signals from overlapping multiplets like the glutamine and glutamate (Glu/Gln) resonances in spectra of the human brain are considerably increased compared with a conventional PRESS volume selection scheme. Thus proton spectra from J-coupled multiplet signals can be acquired with TE on the order of 20-30 ms avoiding the baseline problems arising at shorter echo times due to broad resonances. This allows to selectively acquire spectra from substances with longer T2 without the confounding effects from J-coupling occurring in conventional volume selection techniques.  相似文献   
79.
Genetic differentiation among Hereford populations from Britain, Ireland, Sweden, Canada and New Zealand together with six other beef breeds was assessed using blood type polymorphisms. Changes in the genetic structure of the British Hereford population over time were also examined. Loci surveyed were seven red cell antigen systems (A, B, C, F, L, S, Z), and two serum protein loci (transferrin and albumin). Within group variation was measured by the average expected heterozygosity, and between group relationships by genetic distance. There was significant genetic differentiation among Hereford populations from different countries. Differences between Hereford groups, however, were not as large as differences between breeds. There were also significance differences among British herds. The proportion of Canadian genes in the British 'hybrid' population was estimated to have increased from 0.42 (+/- 0.34) in the 1970s to 0.98 (+/- 0.11) in the 1990s. Canadian Hereford groups were found to be less heterozygous than other groups, and replacement of the British population with Canadian animals may lead to loss of variation. Breeding strategies that preserve original native genes in British Hereford populations should be considered by commercial breeders, in order to prevent the long-term loss of genetic variation within the breed.  相似文献   
80.
L. A. Clark and D. Watson's (1991) tripartite model groups the symptoms of depression and anxiety into 3 components: nonspecific symptoms of general distress, which do not distinguish depression and anxiety; physiologic arousal, which is relatively unique to anxiety; and anhedonia (or low positive affect), which is unique to depression. Structural equation modeling was used to test this model with self-report data from 3 different samples: outpatients seeking treatment for mood disorder, anxiety disorder, or both (n = 483) outpatients seeking treatment for substance abuse (n = 453), and college students (n = 516). The tripartite model did not fit any of the sample covariance matrices, because the nonspecific symptoms of depression and anxiety could not be adequately represented by a single General Distress factor. An alternative model, in which the Anhedonia and Nonspecific Depression factors loaded on a second-order Depression factor, while the Somatic Arousal and Nonspecific Anxiety factors loaded on a second-order Anxiety factor, produced an excellent fit in all the groups. The Nonspecific Depression and Nonspecific Anxiety factors were the most valid and specific indicators of depression and anxiety, respectively. Anhedonia and Somatic Arousal were significantly less valid measures of depression and anxiety. The implications of these findings are discussed.  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