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   6337篇
  免费   95篇
  国内免费   14篇
电工技术   328篇
综合类   3篇
化学工业   1082篇
金属工艺   185篇
机械仪表   148篇
建筑科学   92篇
能源动力   158篇
轻工业   428篇
水利工程   31篇
石油天然气   6篇
无线电   614篇
一般工业技术   1095篇
冶金工业   1782篇
原子能技术   130篇
自动化技术   364篇
  2023年   23篇
  2022年   51篇
  2021年   92篇
  2020年   44篇
  2019年   43篇
  2018年   64篇
  2017年   63篇
  2016年   60篇
  2015年   64篇
  2014年   79篇
  2013年   197篇
  2012年   181篇
  2011年   238篇
  2010年   161篇
  2009年   189篇
  2008年   204篇
  2007年   212篇
  2006年   204篇
  2005年   189篇
  2004年   175篇
  2003年   168篇
  2002年   167篇
  2001年   155篇
  2000年   133篇
  1999年   164篇
  1998年   664篇
  1997年   416篇
  1996年   300篇
  1995年   210篇
  1994年   208篇
  1993年   168篇
  1992年   91篇
  1991年   95篇
  1990年   90篇
  1989年   79篇
  1988年   75篇
  1987年   57篇
  1986年   71篇
  1985年   83篇
  1984年   53篇
  1983年   59篇
  1982年   44篇
  1981年   52篇
  1980年   52篇
  1979年   30篇
  1978年   25篇
  1977年   55篇
  1976年   56篇
  1975年   32篇
  1973年   23篇
排序方式: 共有6446条查询结果,搜索用时 0 毫秒
821.
The neural activity pattern of the subthalmic nucleus (STN) was investigated in five patients with Parkinson's disease who were scheduled for electrode implantation for chronic stimulation of the STN. The initial target was placed 8 mm or 10 mm lateral to the midline, 3 mm to 4 mm posterior to the midcommissural point, and 5 mm to 6 mm below the intercommissural (AC-PC) line. The STN was identified by semi-microelectrode recordings with a trajectory moving laterally in 2-mm steps. The amplitudes of multi-unit activities were relatively low at depths from 8 mm to 5 mm above and from 1 mm to 4 mm below the target, while those 4 mm to 0 mm above the target were significantly higher than at the other sites (ANOVA, Fisher's test, p < 0.05), with the highest amplitude at 2 mm above the target (91.0 +/- 23.3 mu v, n = 15). In the mediolateral direction, amplitudes were relatively higher in the lateral portion, and amplitudes at 14 mm lateral to the midline were significantly higher than at the other sites (ANOVA, Fisher's test, p < 0.05). The target for chronic electrical stimulation was determined to be at the midpoint of the hyperactive STN, i.e., 12 mm lateral to the midline in three patients and 13 mm lateral in two patients. Movement-related neural activity was observed at 5 sites, i.e., 3 sites responded to passive movement of the contralateral wrist and 2 sites to passive knee and/or ankle movement. In conclusion, our data show that the lateral part of the STN is hyperactive in PD, and recordings of neural activities contributed greatly to identifying the STN and determining the target for chronic stimulation within it.  相似文献   
822.
There is strong evidence that depression can have profound negative effects on the functional status, psychologic outlook, and possibly the medical outcome of cancer patients. Its presence often is taken for granted by both patients and physicians as being either inevitable or easily explained by the grim prognosis and complex treatment regimens experienced by many cancer patients, and thereby less deserving of an aggressive approach to diagnosis and treatment. This view is inappropriate, and hinders an effective approach to the problem. Effective treatment, similar to that provided for any other depressed patient, can enhance the cancer patient's overall approach to life and the disease, irrespective of the eventual medical outcome.  相似文献   
823.
We examined the primary ischaemic changes in the pancreas in 35 patients with disseminated intravascular coagulation. In 7 (20%), multiple patchy lesions composed of degenerative acinar cells indicating coagulation necrosis were noted. None of these lesions was accompanied by fat necrosis. The patchy lesions involved the islets of Langerhans in only 1 case. The interlobular arteries of the pancreas near these lesions contained fibrin thrombi in all 7 cases. We suggest that these lesions, without fat necrosis, are the distinctive ischaemic change associated with disseminated intravascular coagulation.  相似文献   
824.
Vitamin A status (umbilical cord retinol levels) of 253 newborns in two public hospitals of Rio de Janeiro showed a high prevalence (55. 7%) of deficiency (retinol levels below 1.05 micromol/L). This rate of vitamin A deficiency (VAD) was independent of other nutritional and anthropometric parameters, such as low birth weight or small for gestational age. These data suggest that newborns can be as vulnerable to VAD as other population groups considered at high risk. They also suggest that special attention should be paid to this group, actually the most vulnerable to the harmful effects of VAD. Hypovitaminosis A should be among the first diagnostic hypotheses when an infant presents with an abnormality  相似文献   
825.
A 48-year-old woman developed hepatic metastases from malignant pheochromocytoma resected 8 years previously. Angiography revealed multiple tumor stains in the liver. Transcatheter oily chemoembolization using styrenomaleic acid neocarzinostatin and iodized oil was performed. The patient complained of severe right upper quadrant pain immediately following the transcatheter oily chemoembolization. Necrotizing cholecystitis developed on the 4th day post-transcatheter oily chemoembolization, hepatic infarction on the 12th day, and a biloma on the 19th day. Despite the administration of antibiotics and percutaneous transhepatic drainage, neither the volume of drainage nor the size of the biloma decreased. Biliary reconstruction was performed using a metallic stent, which decreased the size of the biloma.  相似文献   
826.
827.
To elucidate how the size of the expanded CAG repeat of the gene for dentatorubral pallidoluysian atrophy (DRPLA) and other factors affect the atrophy of the brainstem and cerebellum, and the appearance of high-intensity signals on T2-weighted MRI of the cerebral white matter of patients with DRPLA, we quantitatively analyzed the MRI findings of 26 patients with DRPLA, the diagnosis of which was confirmed by molecular analysis of the DRPLA gene. When we classified the patients into two groups based on the size of the expanded CAG repeat of the DRPLA gene (group 1, number of CAG repeat units > or = 66; group 2, number of CAG repeat units < or = 65), we found strong inverse correlations between the age at MRI and the areas of midsagittal structures of the cerebellum and brainstem in group 1 but not in group 2. Multiple regression analysis, however, revealed that both the patient's age at MRI and the size of the expanded CAG repeat correlated with the areas of midsagittal structures. Involvement of the cerebral white matter as detected on T2-weighted images was observed more frequently in patients belonging to group 2 than in group 1 patients. Furthermore it was demonstrated that high-intensity signals can be detected on T2-weighted images of the cerebral white matter of patients with a largely expanded CAG repeat (group 1) in their thirties. These results suggest that patient age as well as the size of the expanded CAG repeat are related to the degree of atrophy of the brainstem and cerebellum, and the white matter changes in patients with DRPLA.  相似文献   
828.
829.
We are reporting on the case of a 44-year-old woman upon which video-assisted thoracoscopic excision of a benign cystic mesothelioma of the pleura was performed. To our knowledge, this is the second report on a case of a benign cystic mesothelioma of the pleura. The cyst in our case was solitary and was easily excised. Microscopic examination revealed that the cyst was lined by a single layer of flattened and cuboidal cells. Immunohistochemical analysis revealed that the cells lining the cyst stained positively for keratin and negatively for factor VIII-related antigen. Benign cystic mesothelioma of the pleura was diagnosed based on histological findings. For seven months her condition has been monitored at our out-patient clinic with no signs of recurrence. However, continued careful observation is required because benign cystic mesothelioma often recurs locally. Local recurrence is thought to be related to incomplete resection of the tumor. Therefore, careful observations and techniques to ensure complete resection of the cyst, are important during video-assisted thoracoscopic surgery.  相似文献   
830.
L-Arginine or saline was administered intravenously by rapid infusion into 16 late-pregnant Holstein cows to study changes of prolactin, growth hormone, insulin, total protein, urea nitrogen, and subsequent lactation. Arginine was infused daily at .1 g/kg body weight starting about 7 days prior to predicted calving until calving. Blood was sampled via a jugular cannula at 0700, 0715, 0730 (infusion immediately followed 0730 h sample), 0745, 0815, 0845, 1100, 1300, 1500, 1700, and 1900 h. Arginine infusion evoked dramatic but transient increase of concentrations of blood serum prolactin, growth hormone, and insulin. Urea nitrogen also was elevated in blood serum but not total protein. The secretory response of prolactin, growth hormone, and insulin to daily arginine infusion during the entire prepartum period was not diminished. Milk production for the first 22 wk of lactation tended to be higher (by about 10%) for cows infused with arginine as compared to cows infused with saline. Therefore, repeated arginine infusion in late-pregnant cows dramatically increased prolactin, growth hormone, and insulin and tended to increase subsequent milk yield.  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