首页 | 官方网站   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   3912篇
  免费   15篇
  国内免费   4篇
工业技术   3931篇
  2019年   1篇
  2018年   3篇
  2017年   2篇
  2016年   2篇
  2014年   4篇
  2013年   11篇
  2012年   10篇
  2011年   17篇
  2010年   6篇
  2009年   18篇
  2008年   15篇
  2007年   39篇
  2006年   4篇
  2005年   19篇
  2004年   5篇
  2003年   3篇
  2002年   7篇
  1999年   138篇
  1998年   1232篇
  1997年   665篇
  1996年   454篇
  1995年   253篇
  1994年   206篇
  1993年   237篇
  1992年   29篇
  1991年   41篇
  1990年   46篇
  1989年   48篇
  1988年   37篇
  1987年   29篇
  1986年   29篇
  1985年   29篇
  1983年   3篇
  1982年   22篇
  1981年   20篇
  1980年   24篇
  1979年   1篇
  1978年   4篇
  1977年   62篇
  1976年   147篇
  1975年   1篇
  1965年   1篇
  1964年   3篇
  1962年   1篇
  1955年   2篇
  1954年   1篇
排序方式: 共有3931条查询结果,搜索用时 0 毫秒
11.
基于PSOS的TM1300应用系统中的BSP研究   总被引:1,自引:0,他引:1  
通过在应用软件与板级支持包BSP之间加一层库函数的方法较好地解决了应用程序与板级支持包函数间的通信问题,减少了板级支持包函数的维护复杂度,从而为嵌入式系统板级支持包的实现提供了一个有价值的思路。  相似文献   
12.
13.
Dystrophin is a plasma membrane-associated cytoskeletal protein of the spectrin superfamily. The dystrophin cytoskeleton has been first characterized in muscle. Muscular 427 kDa dystrophin binds to subplasmalemmal actin filaments via its amino-terminal domain. The carboxy-terminus of dystrophin binds to a plasma membrane anchor, beta-dystroglycan, which is associated on the external side with the extracellular matrix receptor, alpha-dystroglycan, that binds to the basal lamina proteins laminin-1, laminin-2, and agrin. In the muscle, the dystroglycan complex is associated with the sarcoglycan complex that consists of several glycosylated, integral membrane proteins. The absence or functional deficiency of the dystrophin cytoskeleton is the cause of several types of muscular dystrophies including the lethal Duchenne muscular dystrophy (DMD), one of the most severe and most common genetic disorders of man. The dystrophin complex is believed to stabilize the plasma membrane during cycles of contraction and relaxation. Muscular dystrophin and several types of dystrophin variants are also present in extramuscular tissues, e.g. in distinct regions of the central nervous systems including the retina. Absence of dystrophin from these sites is believed to be responsible for some extramuscular symptoms of DMD, e.g. mental retardation and disturbances in retinal electrophysiology (reduced b-wave in electroretinograms). The reduced b-wave in electroretinograms indicated a disturbance of neurotransmission between photoreceptors and ON-bipolar cells. At least two different dystrophin variants are present in photoreceptor synaptic complexes. One of these dystrophins (Dp260) is virtually exclusively expressed in the retina. In the neuroretina, dystrophin is found in significant amounts in the invaginated photoreceptor synaptic complexes. At this location dystrophin colocalizes with dystroglycan. Agrin, an extracellular ligand of alpha-dystroglycan, is also present at this location whereas the proteins of the sarcoglycan complex appear to be absent in photoreceptor synaptic complexes. Dystrophin and dystroglycan are located distal from the ribbon-containing active synaptic zones where both proteins are restricted to the photoreceptor plasma membrane bordering on the lateral sides of the synaptic invagination. In addition, some neuronal profiles of the postsynaptic complex also contain dystrophin and beta-dystroglycan. These profiles appear to belong at least in part to projections of the photoreceptor terminals into the postsynaptic dendritic complex. In view of the abnormal neurotransmission between photoreceptors and ON-bipolar cells in DMD patients the dystrophin/beta-dystroglycan-containing projections of photoreceptor presynaptic terminals into the postsynaptic dendritic plexus might somehow modify the ON-bipolar pathway. Another retinal site associated with dystrophin/beta-dystropglycan is the plasma membrane of Müller cells where dystrophin/beta-dystroglycan appear to be present at particular high concentrations. At this location the dystrophin/dystroglycan complex may play a role in the attachment of the retina to the vitreous, and, under pathological conditions, in traction-induced retinal detachment.  相似文献   
14.
Seventy-three spinal cord injured patients with central cord syndrome who had undergone inpatient rehabilitation, were studied retrospectively with regard to their demographic, neurologic and functional characteristics. There were 67 males and six females with a mean age of 53.5 years. Falls was the commonest mechanism of injury (54.8%) followed by motor vehicle accidents. Eleven patients sustained cervical fractures and 41 had radiological evidence of cervical spondylosis. Seventeen patients had sensory impairment and significant spasticity was present in 14 patients. Significant improvements in the admission/discharge ASIA motor scores and Modified Barthel Index (MBI) scores (P < 0.001) were noted after rehabilitation. Ninety-two percent of patients were continent of bladder on discharge compared to 64.4% on admission. Multiple regression analysis revealed three factors associated with a better functional outcome, namely, higher admission MBI scores, absence of spasticity and younger age (P < 0.05).  相似文献   
15.
16.
17.
Health-related quality of life (HRQOL) is an important dimension in assessing health care. Several methodologic considerations are related to the manner in which these data are obtained in children. Few multidimensional generic measures of quality of life (QOL) have been developed for children and adolescents. Most published research concerns the development of tools to be used in a disease-specific manner for clinical trials. Although several authors point out numerous advantages in assessing HRQOL in clinical practice, several barriers must be overcome for this to occur. In the current era of economic restraint, HRQOL measures must be integrated into pharmaco-economic analyses to assess fully the impact of a drug on health care resources and outcomes.  相似文献   
18.
Tone recognition is partially subserved by neural activity in the right frontal and primary auditory cortices. First we determined the brain areas associated with tone perception and recognition. This study then examined how regional cerebral blood flow (rCBF) in these and other brain regions correlates with the behavioral characteristics of a difficult tone recognition task. rCBF changes were assessed using H2(15)O positron emission tomography. Subtraction procedures were used to localize significant change regions and correlational analyses were applied to determine how response times (RT) predicted rCBF patterns. Twelve trained normal volunteers were studied in three conditions: REST, sensory motor control (SMC) and decision (DEC). The SMC-REST contrast revealed bilateral activation of primary auditory cortices, cerebellum and bilateral inferior frontal gyri. DEC-SMC produced significant clusters in the right middle and inferior frontal gyri, insula and claustrum; the anterior cingulate gyrus and supplementary motor area; the left insula/claustrum; and the left cerebellum. Correlational analyses, RT versus rCBF from DEC scans, showed a positive correlation in right inferior and middle frontal cortex; rCBF in bilateral auditory cortices and cerebellum exhibited significant negative correlations with RT These changes suggest that neural activity in the right frontal, superior temporal and cerebellar regions shifts back and forth in magnitude depending on whether tone recognition RT is relatively fast or slow, during a difficult, accurate assessment.  相似文献   
19.
A flow injection hydride atomic absorption spectrometric (FI-HAAS) method was developed for determining selenium in human milk and whole blood after microwave digestion of the sample. The sample (2 mL human milk or 0.25 mL blood) was introduced into the microwave vessel with 1.5 mL HNO3 and 0.25 mL H2O2 and 300 W (4 min) and 600 W (4 min) were applied. The digestion was completed by heating to 140 degrees C (2-3 h). Se (VI) was reduced to Se (IV) with hydrochloric acid. The instrumental conditions for FI-HAAS (concentrations of reducing agent and carrier acid, flow rate of argon carrier gas, and sample volume injected) were optimized. The detection limit of the proposed method was 0.23 ng/mL (assay) or 115 pg Se (absolute) in biological samples (1.15 ng/mL milk, 10.4 ng/mL blood). The precision values were 5.0% for milk and 4.0% for blood. The accuracy was evaluated with 2 reference materials, National Institute of Standards and Technology Non-Fat Milk Powder (found: 104.3 +/- 7.2 ng/g, certified: 110 +/- 10 ng/g) and Whole Blood Seronorm (found: 81 +/- 7.3 ng/mL, reference: 83 +/- 4 ng/mL). The results show the suitability of the method for selenium determination in human milk and whole blood. The method was applied to whole blood samples obtained from pregnant women and to human milk.  相似文献   
20.
Luteinizing hormone releasing hormone (LHRH) stimulates the development of cellular FSH immunoreactivity in the perinatal hamster adenohypophysis. Because neuropeptide Y (NPY) can act directly on rat adenohypophysial cells to stimulate FSH and LH release and potentiate the stimulatory effect of LHRH on FSH and LH release, we investigated the effects of NPY alone and in combination with a low, ineffective dose of LHRH on inducing cellular FSH immunoreactivity in the neonatal hamster adenohypophysis. Neonatal female pituitary glands were grafted beneath the right renal capsules of hypophysectomized-ovariectomized adult hamster hosts with a catheter implanted in the external jugular vein. After treatment, hosts were decapitated and graft tissue was stained for FSH and LH immunoreactivity. The mean percentage of adenohypophysial cells that stained for FSH was low (2.8%) in grafts in hosts infused continuously with heparinized saline vehicle for 7 days. In other hosts, peptides were pulsed through the catheter every 12 h for 7 days. The mean percentage of FSH cells also was low after pulsing 6 ng LHRH or 2 micrograms NPY but increased substantially when the two peptides were pulsed simultaneously. No differences in the mean percentage of LH cells existed between any of the groups. The results demonstrate that NPY and LHRH can synergize to induce cellular FSH immunoreactivity in the neonatal female hamster.  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-23

京公网安备 11010802026262号