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   1824篇
  免费   14篇
  国内免费   1篇
电工技术   2篇
综合类   2篇
化学工业   36篇
金属工艺   12篇
机械仪表   14篇
建筑科学   5篇
能源动力   4篇
轻工业   125篇
无线电   32篇
一般工业技术   80篇
冶金工业   1451篇
原子能技术   4篇
自动化技术   72篇
  2023年   5篇
  2021年   4篇
  2020年   8篇
  2019年   10篇
  2018年   5篇
  2017年   4篇
  2016年   7篇
  2015年   4篇
  2014年   8篇
  2013年   18篇
  2012年   11篇
  2011年   15篇
  2010年   32篇
  2009年   17篇
  2008年   17篇
  2007年   16篇
  2006年   16篇
  2005年   13篇
  2004年   14篇
  2003年   15篇
  2002年   10篇
  2001年   9篇
  2000年   8篇
  1999年   44篇
  1998年   460篇
  1997年   266篇
  1996年   151篇
  1995年   84篇
  1994年   81篇
  1993年   83篇
  1992年   19篇
  1991年   30篇
  1990年   31篇
  1989年   22篇
  1988年   25篇
  1987年   18篇
  1986年   19篇
  1985年   14篇
  1983年   5篇
  1982年   14篇
  1981年   10篇
  1980年   20篇
  1979年   7篇
  1978年   7篇
  1977年   34篇
  1976年   98篇
  1975年   5篇
  1974年   9篇
  1973年   3篇
  1972年   4篇
排序方式: 共有1839条查询结果,搜索用时 15 毫秒
21.
22.
23.
24.
25.
Divergent recommendations exist regarding the evaluation of adrenal incidentalomas. Recent data have indicated a prevalence of adrenal tumors of 71% in nonclassical congenital adrenal hyperplasia (CAH) and unmasked heterozygotes. These data expand the differential diagnosis of such incidental tumors and substantially modify the approach to their evaluation. We present two patients, female pseudohermaphrodites with the simple virilizing form of CAH and 21-hydroxylase deficiency, who functioned successfully as married phenotypic males. Both came to medical attention in the sixth decade by virtue of massive adrenal incidentalomas encountered in the evaluation of recurrent urinary tract infections. Each had a 46, XX karyotype, no palpable testes, and markedly elevated baseline levels of 17-hydroxyprogesterone (17-OH Prog) of 6086 ng/dL and 6750 ng/dL. Both responded appropriately to dexamethasone suppression with reduction of 17-OH Prog, androgens and, in the second patient, ACTH to normal or near normal levels. Histologic and autopsy examination of the first patient's tumor and computed tomographic characteristics of the second revealed a benign adenoma and myelolipoma respectively. We extend and confirm previous recommendations that CAH be included in the differential diagnosis of adrenal incidentaloma and that baseline 17-OH Prog. levels be obtained, with ACTH stimulation if necessary, to diagnose the presence of nonclassical CAH.  相似文献   
26.
27.
28.
We conducted a study to investigate ethnic group differences in levels of serum markers used in screening for Down's syndrome [serum alpha-fetoprotein (AFP), unconjugated oestriol (uE3), total human chorionic gonadotrophin (hCG), free alpha- and free beta-hCG, and dimeric inhibin-A], to estimate the extent to which maternal weight differences between ethnic groups explain these differences, and to estimate the effect of adjusting for ethnic group and maternal weight on screening performance. Serum measurements were taken from women who were screened prenatally for Down's syndrome. AFP, uE3, and hCG concentrations were available from 9462 white, 4215 black, and 4392 South Asian women with singleton pregnancies without Down's syndrome or neural tube defects between 15 and 22 weeks' gestational age. Frozen serum samples were available from a subset of 922 white, 449 black, and 135 South Asian women and were used for measurement of free alpha-hCG, free beta-hCG, and inhibin. Values were expressed as multiples of the median (MOM) for women of the same gestational age. There were statistically significant differences in the serum marker levels between ethnic groups that were not explained by differences in maternal weight. The main differences were found in black women compared with white women; black women had serum AFP levels 22 per cent higher (95 per cent confidence interval 20-24 per cent), total hCG levels 19 per cent higher (16-22 per cent), and free beta-hCG levels 12 per cent (3-21 per cent) higher. The other differences were less than 10 per cent. Adjusting for ethnic group only had a small estimated effect on screening performance: a maximum of about 0.5 per cent extra detection at a 5 per cent false-positive rate. At a fixed risk cut-off level, the false-positive rate will not be materially different between different ethnic groups. Adjusting serum markers for ethnic groups improves Down's syndrome screening performance to a very small extent. It is worthwhile because of its established value in AFP screening for open neural tube defects.  相似文献   
29.
There is agreement on the clinical diagnostic criteria for acute inflammatory demyelinating polyneuropathy (AIDP/GBS) however, there is lack of consensus for detection of demyelination. In order to critically evaluate the prevailing criteria, sixty-six patients who fulfilled NINCDS criteria and had typical features of GBS were studied for electrophysiological abnormalities of peripheral nerves by using standard methods (median, common peroneal, sural and ulnar) between 1 to 12 weeks after the onset of symptoms. The commonest abnormality on motor nerve conduction study was prolonged distal latency (75%-83%) followed by reduction in CMAP amplitude (63%-82%), decreased velocity (48%-62%), conduction block (17%-39%) and f-wave abnormalities (37.8%-59%). Sensory conduction abnormalities were detected in over 20% of median, 25% of ulnar and 33% of sural nerves. All the patients had abnormality of at least two motor conduction parameters in one nerve when values beyond 2 SD of the mean were considered abnormal and over 70% of patients had three abnormalities in two nerves or two abnormalities in three nerves. Comparison with the prevailing criteria for demyelination revealed that the number of patients fulfilling them varied widely: Albers et al. (1985): 74.2%, Albers et al. (1989): 40.9% and Cornblath: 30.3%. We believe that the current criteria for detection of demyelination in acute neuropathy are too strict, underestimate the underlying pathology in GBS and need reassessment.  相似文献   
30.
In patients with progressive systemic sclerosis (PSS) suffering from chronic dyspepsia the stomach may be affected by this disease. The objective of this study was to investigate both antral myoelectrical activity and gastric emptying in PSS patients. Electrogastrography (EGG) was performed in 17 PSS patients (16 female, one male, median age 58 years, range 32-74 years) with chronic dyspepsia. After an overnight fast during one hour in the fasting and one hour in the fed state after ingestion of a liquid-solid test meal (370 kcal; liquid phase labeled with 0.5 mCi 99mTc-colloid) antral electrical activity was measured by one pair of electrodes sonographically placed on the skin overlying the gastric antrum. Several EGG parameters including dominant frequency (DF), percentages of DF in the normal range (2-4 cycles per minute [cpm]), bradygastria (< 2 cpm) and tachygastria (4-10 cpm), dominant frequency instability coefficient (DFIC), and postprandial to preprandial power ratio (PR) were calculated. The data were correlated to results obtained in 20 age- and gender-matched healthy subjects. In addition, the data were compared to gastric retention of the radionuclide at 60 min measured by simultaneous scintigraphy. The PSS patients did not reveal electrical disturbances. They even exhibited a significant postprandial decrease in DFIC, bradygastria, and tachygastria (ns) compared to healthy subjects. Over 50% of the PSS patients showed a delayed gastric emptying. However, EGG did not correlate to radioscintigraphy significantly. Our results reflect an absent relationship between antral myoelectrical activity in EGG and gastric emptying. Therefore, electrogastrography is unsuitable to assess gastric involvement in PSS.  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