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   44866篇
  免费   907篇
  国内免费   181篇
电工技术   568篇
综合类   630篇
化学工业   4716篇
金属工艺   677篇
机械仪表   976篇
建筑科学   861篇
矿业工程   400篇
能源动力   403篇
轻工业   2080篇
水利工程   626篇
石油天然气   82篇
武器工业   4篇
无线电   1888篇
一般工业技术   3604篇
冶金工业   22587篇
原子能技术   210篇
自动化技术   5642篇
  2024年   55篇
  2023年   188篇
  2022年   136篇
  2021年   143篇
  2019年   74篇
  2018年   504篇
  2017年   725篇
  2016年   1107篇
  2015年   809篇
  2014年   467篇
  2013年   479篇
  2012年   2179篇
  2011年   2503篇
  2010年   726篇
  2009年   831篇
  2008年   678篇
  2007年   707篇
  2006年   619篇
  2005年   3363篇
  2004年   2569篇
  2003年   2045篇
  2002年   845篇
  2001年   736篇
  2000年   298篇
  1999年   660篇
  1998年   6445篇
  1997年   4017篇
  1996年   2635篇
  1995年   1546篇
  1994年   1122篇
  1993年   1160篇
  1992年   251篇
  1991年   327篇
  1990年   311篇
  1989年   282篇
  1988年   296篇
  1987年   224篇
  1986年   200篇
  1985年   177篇
  1984年   71篇
  1983年   84篇
  1982年   136篇
  1981年   189篇
  1980年   204篇
  1979年   60篇
  1978年   104篇
  1977年   650篇
  1976年   1408篇
  1975年   102篇
  1973年   50篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
Here we are presenting the case of a 70-years-old woman who has hepatic cirrhosis anti-HCV and insulin-dependent diabetes mellitus, without relevant epidemiologic ascendants or previous transfusions and HBV, HIV negatives. On admission to our hospital she showed signs of autoimmune hemolytic anaemia (AHA) which was confirmed by positive direct Coombs test and an improvement in blood test after corticoid treatment. Having discarded other possible causes such as drugs infectious diseases or essential mixed cryoglobulinemia (CME), we put forward the possible association between AHA and infection by HCV, where AHA was an extrahepatic immunological manifestation of HCV. This fact has never been brought to light in previous medical literature.  相似文献   
63.
The birthweight is the most important determinant of mortality and morbidity in the neonatal period and may have an influence on health in adult life. The high rate of low birthweight in developing countries is therefore a major health problem. Maternal malnutrition is usually assumed to be a causal factor but other environmental factors are also involved. In this study we analysed maternal nutritional and socio-economic factors as determinants of birthweight in term infants from a rural African society characterised by a high rate of chronic malnutrition. Relations of maternal weight, gestational weight gain, parity, socio-economic status and infant sex with birthweight were analysed in 1,477 women and child pairs. The selected women were followed from early pregnancy and had an uncomplicated delivery at term of a living singleton child. The gestational weight gain was 5.6 (SD 6.0) kg and the mean birthweight 2.933 kg (SD 408). Maternal weight, representing the maternal long-term nutritional situation, was the most important independent determinant of birthweight, accounting for 13.0% of the variance in birthweight. The weight gain, representing the short-term nutritional situation, explained only 5.6% of the variance. Birthweight increased by 20 g (CI 18-23) for each kg maternal weight and by 15 g (CI 12-18) for each kg gestational weight gained. The socio-economic difference in birth-weight was 153 g (CI 109-196) 88 of which (CI 48-128) remained unexplained after adjustment for differences in maternal weight, parity and gender. Improved long-term nutritional situation and living conditions seems to be the most important prerequisites to counteract low birthweight in developing countries.  相似文献   
64.
Intracranial tumours, often presenting with progressive hydrocephalus, are rare congenital diseases accounting for 0.5-1.5 per cent of all cases of brain tumours diagnosed during childhood. The differential diagnosis includes vascular malformations, infarctions, and haemorrhages. Sonographic signs suggestive of glioblastoma, teratoma, and astrocytoma do not establish the histological diagnosis, however. We report a case of an undifferentiated fetal glioma detected at 29 weeks' gestation. The diagnosis of an undifferentiated brain tumour was suspected by sonography because of the lack of normal brain structures in conjunction with a diffuse echogenic central lesion and an external hydrocephalus. Because of the very poor prognosis, we induced labour by intravaginal and intravenous administration of prostaglandin E2 and achieved the vaginal delivery of a stillborn child whose head circumference corresponded to 38 weeks of pregnancy. Histological and immunochemical features of this undifferentiated congenital glioma (glioblastoma) are presented.  相似文献   
65.
OBJECTIVE: To investigate the efficacy of the rectus abdominis muscle flap (RAMF) technique for the closure and augmentation of small, non-compliant bladder exstrophies. PATIENTS AND METHODS: The RAMF technique was used in two girls and two boys (mean age at operation, 31.7 months, range 3-72) with bladder exstrophy. The clinical outcome and urodynamics were assessed during a follow-up of 29 months to 6 years (mean 49.2 months) and included imaging, cystoscopy, biochemical and microbiological studies. RESULTS: There were no urinary tract infections, metabolic problems or electrolyte disturbances and kidney function remained normal in all patients. Radiography confirmed intact function and anatomy of the urinary tract and cystoscopy showed complete coverage of the inner peritoneal layer of RAMF with uroepithelium. No stone formation or mucus production were detected. Currently, three patients void using clean intermittent catheterization through the native urethra and the fourth through an appendiceal Mitrofanoff valve. However, the bladder volume was insufficient at the late follow-up and three patients required bladder augmentation. CONCLUSIONS: The RAMF technique is a good alternative for closing bladder exstrophies and achieves an increase in bladder capacity; however, although there is a mild improvement in bladder capacity and compliance. RAMF should not be used as a bladder augmentation procedure. The technique is indicated in the closure of large bladder defects, bladder exstrophies with small, inelastic, non-compliant bladder remnants and failed primary closures.  相似文献   
66.
67.
In the search for new risk factors for diabetic macroangiopathy the insertion/deletion (I/D) polymorphism in the angiotensin-converting enzyme gene was studied in 237 consecutive patients (125 men and 112 women) with non-insulin-dependent diabetes. The female population showed an excess of ischemic electrocardiographic changes or definite myocardial infarctions in the patients homozygous for the deletion [D/D; odds ratio (OR) 2.8; 95% confidence interval (CI) 1.4-5.3] and in the insertion/deletion heterozygotes (I/D; OR 1.8; CI 1.1-3.1) compared with the patients homozygous for the insertion (I/I). In the total series coronary heart disease, cerebrovascular disease, and claudication were more often observed in the patients with I/D (OR 1.5; CI 1.0-2.2) or the D/D genotype patients (OR 1.7; CI 1.1-2.6) than in those with the genotype I/I. The systolic blood pressure was lower in patients with genotype I/I (138 +/- 19 mmHg) than in those with the genotype I/D (149 +/- 22 mmHg) or D/D (150 +/- 21 mmHg; P < 0.02). The prevalence of hypertension and the median urinary albumin excretion rate also tended to be lowest in the I/I genotype patients. Multiple logistic analysis revealed that in women the angiotensin-converting enzyme D/D genotype is independently associated with coronary heart disease. Our findings suggest that variation at the angiotensin-converting enzyme gene locus is one of the factors involved in the predisposition of diabetic patients to the development of arterial disease and hypertension.  相似文献   
68.
The effect exerted by transplantation of the 5 day culture of testicles from newly born piglets on the hypogonadal state of mature X-ray irradiated (3 Gy) rats was studied. It has been found that a month after transplantation (two months after irradiation) the hypogonadal state disappeared for a while, which is confirmed by normalization of the weight of seminal vesicles, content of testosterone and biologically active lutropine, restoration of the reproductive function of rats. No significant changes in steroidogenesis activity have been found, which proves a substituent character of transplantation. The effect disappears three months later but certain restoration of the content of nucleic acids in the testicles is observed.  相似文献   
69.
70.
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