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   742篇
  免费   9篇
电工技术   4篇
化学工业   41篇
金属工艺   17篇
机械仪表   18篇
建筑科学   11篇
能源动力   1篇
轻工业   39篇
水利工程   1篇
石油天然气   2篇
无线电   87篇
一般工业技术   59篇
冶金工业   404篇
自动化技术   67篇
  2021年   4篇
  2018年   2篇
  2017年   3篇
  2016年   2篇
  2015年   4篇
  2014年   4篇
  2013年   12篇
  2012年   14篇
  2011年   21篇
  2010年   13篇
  2009年   16篇
  2008年   20篇
  2007年   12篇
  2006年   21篇
  2005年   7篇
  2004年   15篇
  2003年   13篇
  2002年   6篇
  2001年   10篇
  2000年   8篇
  1999年   15篇
  1998年   107篇
  1997年   78篇
  1996年   46篇
  1995年   31篇
  1994年   41篇
  1993年   30篇
  1992年   14篇
  1991年   12篇
  1990年   14篇
  1989年   8篇
  1988年   6篇
  1987年   5篇
  1986年   8篇
  1985年   12篇
  1984年   5篇
  1983年   3篇
  1982年   9篇
  1981年   8篇
  1980年   3篇
  1979年   4篇
  1978年   8篇
  1977年   13篇
  1976年   33篇
  1975年   6篇
  1974年   7篇
  1972年   6篇
  1961年   1篇
  1955年   2篇
  1925年   1篇
排序方式: 共有751条查询结果,搜索用时 15 毫秒
1.
This investigation retrospectively examined changes in marital satisfaction following stroke. The relationship between such changes and other pertinent factors were also examined, including severity of aphasia, knowledge of aphasia, number of months after stroke, and length of the marriage. The subjects were 40 spouses of patients with aphasia grouped according to severity of the aphasia (mild, moderate, severe). Spouses completed two different measures of marital satisfaction--the Marital Satisfaction Scale (MSS) and the Marital Comparison Level Index (MCLI). These measures were completed in both a prestroke (retrospective reporting) and a poststroke format to allow for change to be assessed. In addition, a Knowledge of Aphasia questionnaire was completed by the normal spouses to evaluate their understanding of the disorder of aphasia. There was a significant difference between prestroke and poststroke scores on both the MSS and the MCLI, indicating a lower level of satisfaction following the stroke. The amount of change between prestroke and poststroke MSS and MCLI scores was not related to either number of months poststroke or number of years married. Although there was no relationship between changes in prestroke and poststroke scores on the MCLI and Knowledge of Aphasia scores, there was a significant correlation between changes in these scores on the MSS and Knowledge of Aphasia scores. Hence, the more knowledge spouses had regarding aphasia, the less the negative impact the stroke had on marital satisfaction, as measured by the MSS. Results are discussed in terms of the interdisciplinary treatment needs of aphasic patients and the implications for future investigations.  相似文献   
2.
A prospective longitudinal study of patients with early RA was performed to examine the influence of disease duration, disease activity and physical activity on bone loss. Sixty-seven patients with non-steroid treated RA of less than 5 yr duration, including 16 patients with disease duration less than 6 months, had BMD measurements of the femoral neck and the lumbar spine over a 12-month period using dual energy X-ray absorptiometry. The BMD changes were compared with values from 72 control patients and were also correlated with serial measurements of disease activity (measured by the Stoke Index) and disability [measured by the Health Assessment Questionnaire (HAQ) score], at 3-monthly intervals over the 12-month period. No significant differences in BMD changes were found between RA patients and controls overall. Patients with disease duration of less than 6 months had significantly greater loss of BMD at the femoral neck (-3.9%, S.E.M. 1.5) than the remainder of the cohort (-0.2%, S.E.M. 0.7) (P = 0.02) and controls (-0.8%, S.E.M. 0.6). Lumbar spine BMD changes correlated with the initial Stoke Index (Rs-0.373, P = 0.01) but not mean Stoke Indices. There was no correlation of BMD changes with age or HAQ scores. These findings suggest that significant bone loss occurs within the first few months of disease in patients with RA.  相似文献   
3.
This study was designed to determine urinary sodium excretion in response to an oral glucose load in hypertensive patients. Fifteen hypertensive patients and eighteen normotensive subjects were studied after an overnight fast and for 4 h after the ingestion of 100 g glucose. A subgroup of untreated, nonobese, primary hypertensive patients (five of the 15 hypertensive patients) became hyperinsulinemic (total area under the insulin curve [TAUC]: 33,080 +/- 3348 microU ml(-1) 120 min-1) in response to an oral glucose load compared to normotensive subjects (TAUC: 3670 < 13.731 < 23,693 microU ml(-1) 120 min-1) or to be other subgroup of normoinsulinemic hypertensive individuals TAUC: 10,221 +/- 1615 microU ml-1 120 min-1) despite a similar serum glucose concentration in both groups. A significant decrease in renal sodium excretion in the entire hypertensive group (47.1 +/- 4.7%, P < 0.019) compared to the normotensive (20.0 +/- 10.5%) subjects was also observed during the oral glucose tolerance test. Decreased renal sodium excretion was followed by a transient increase in urinary acid excretion. We speculate that the increase in insulin secretion may be responsible for the sodium-dependent increase in intracellular Ca2+, cellular H+ output and blood pressure in a subgroup of salt-sensitive patients with hypertension. New studies should be designed to identify the precise mechanisms involved in the interaction between hypertension, serum insulin-glucose levels and the magnitude of the renal tubule reabsorption abnormality.  相似文献   
4.
An animal model and computer software were developed to conduct across-herd genetic evaluations using data from producers participating in the Sow Productivity Index program of the American Yorkshire Club. The final data set consisted of 61,596 litter records from 1986 to early 1990. The animal model included fixed contemporary group effects and random additive direct, service sire, permanent environmental, and residual effects. Additive genetic relationships among animals were included. A separate relationship matrix for service sires and their sires was also included. A data set similar to the Yorkshire field data was simulated to use in testing the animal model. The simulated data set consisted of 40 herds, each with 120 reproducing dams and either four or five sires. Six generations of simulated data were produced, resulting in 20,605 litter records. These records were then evaluated using the animal model for number of pigs born alive. Finally, correlations between the true breeding values from the simulation and the predicted breeding values were computed. The correlation between the 918 true and predicted sire breeding values was considerably lower for the animal model without a service sire effect than when it was included (.53 vs .74, respectively). However, the difference was cut in half (.66 vs .77) when only sires with greater than five daughter records were included. The high accuracy of the animal model with a random service sire effect indicates that the proposed model adequately accounts for the variation found in records for number of pigs born alive.  相似文献   
5.
Native kainate receptors expressed by cultured hippocampal cells were studied in the whole-cell configuration of the patch-clamp technique by using a fast perfusion system. About 80% of the neurons expressed kainate receptors independently of the time in culture (0-4 days), which coincided with the number of cells immunoreactive for a monoclonal antibody against the GluR5/6/7 subunits. Three types of cells were considered: neurons in which the rapid application of kainate induced a rapidly desensitizing current, cells in which kainate induced a more slowly rising, non-desensitizing, response and those in which a mixture of both responses was apparent. Steady responses induced by 300 microM kainate were inhibited by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) in a dose-dependent manner (IC50 = 0.92 microM). CNQX was less potent in blocking transient kainate-induced responses (IC50 = 6.1 microM). Responses to kainate, whether steady or transient, were also inhibited by NS102, showing poor selectivity for the transient response (IC50 = 4.1 and 2.2 microM respectively). The new alpha-amino-3-hydroxy-5-methyl-4-isoxazole (AMPA) receptor antagonist NS394 was very potent in inhibiting steady kainate-induced currents (IC50 = 0.45 microM), but was even more effective in preventing peak responses (IC50 = 0.13 microM). In contrast, cyclothiazide did not affect transient kainate-induced responses but did potentiate current induced by activation of AMPA receptors by AMPA or kainate. These results demonstrate the lack of complete selectivity amongst some available competitive antagonists for AMPA and kainate receptors, and indicate that kainate receptors expressed by hippocampal cells lack the cyclothiazide modulatory site present at AMPA receptors. In addition, the present data support the idea that low-affinity kainate binding sites in the brain correspond to receptor channels selectively activated by kainate.  相似文献   
6.
Two once-daily electroconvulsive shocks (ECS) produced retrograde amnesia in rats trained on a Hebb-Williams maze; Verapamil (12.5 mg/kg, i.p.) or felodipine (10 mg/kg, p.o.) administered half an hour before each ECS attenuated this ECS-induced amnesia. Hence, these drugs may hold promise for the containment of amnesia induced by electroconvulsive therapy (ECT). Speculatively, one or more of several mechanisms may be involved: cerebral vasodilatation, enhancement of cholinergic tone, and inhibition of calcium-mediated impairment of neuronal function. These drugs may also act by attenuating the systolic surge in blood pressure during ECT, thereby decreasing edema due to cerebral hyperperfusion, as well as decreasing the possible transfer of potentially neurotoxic macromolecules through a putative breach in the blood-brain barrier.  相似文献   
7.
8.
A distributed Bragg reflector (DBR) laser tuned by resistive heating is presented. It has a tuning range greater than 10 nm with only a 33% reduction in output power and a 10% increase in linewidth. Its behavior is easily modeled, agreeing well with simple theory  相似文献   
9.
Obliterative or constrictive bronchiolitis is characterized by narrowing of the small airways, due to submucosal and peribronchiolar fibrosis, with chronic obstruction. The vast majority of cases of bronchiolitis obliterans are associated with other diseases and only few cases are idiopathic. We report on the main computed tomography (CT) methods used study obliterative bronchiolitis, the CT findings and the differential diagnosis with other diseases. The dynamic study of alveolar ventilation with CT uses inspiratory and expiratory CT or high-resolution CT (HRCT), spiral dynamic CT or HRCT with advanced image display, ultrafast CT. In abnormal cases HRCT shows direct and indirect signs of small airways disease. The most common (> 80%) sign of obliterative bronchiolitis is the so-called mosaic oligohemia, with low attenuating lobules, caused by air trapping and best seen on expiratory CT, associated with blood flow redistribution to more normal lobules; this finding simulates the ground-glass pattern from infiltrative lung disease. Differential diagnosis is more difficult in the presence of true ground-glass patterns associated with diffuse bronchiolar obstruction and also with mosaic oligohemia due to pulmonary vascular disease and pulmonary emphysema. HRCT can distinguish these diseases and dynamic CT is more sensitive than functional tests in detecting regional abnormalities and air trapping. The combination of HRCT, rapid volumetric scanning and advanced image display is a powerful tool study the normal and abnormal features of bronchiolar function and alveolar ventilation.  相似文献   
10.
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