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   2832篇
  免费   5篇
电工技术   6篇
综合类   16篇
化学工业   38篇
金属工艺   3篇
机械仪表   13篇
建筑科学   16篇
矿业工程   9篇
能源动力   1篇
轻工业   9篇
水利工程   5篇
石油天然气   2篇
武器工业   2篇
无线电   5篇
一般工业技术   33篇
冶金工业   2662篇
原子能技术   2篇
自动化技术   15篇
  2024年   1篇
  2022年   1篇
  2014年   5篇
  2013年   4篇
  2012年   8篇
  2011年   19篇
  2010年   10篇
  2009年   13篇
  2008年   22篇
  2007年   46篇
  2006年   12篇
  2005年   11篇
  2004年   2篇
  2003年   12篇
  2002年   6篇
  2001年   1篇
  2000年   4篇
  1999年   75篇
  1998年   774篇
  1997年   450篇
  1996年   255篇
  1995年   165篇
  1994年   150篇
  1993年   170篇
  1992年   13篇
  1991年   45篇
  1990年   35篇
  1989年   32篇
  1988年   34篇
  1987年   29篇
  1986年   39篇
  1985年   23篇
  1983年   9篇
  1982年   13篇
  1981年   28篇
  1980年   25篇
  1979年   2篇
  1978年   15篇
  1977年   98篇
  1976年   171篇
  1975年   7篇
  1959年   1篇
  1955年   2篇
排序方式: 共有2837条查询结果,搜索用时 15 毫秒
61.
Thirty-eight patients with squamous cell carcinoma of the soft palate treated between 1960 and 1975 were reviewed. Males in the seventh decade predominated. All symptomatic patients complained of sore throat and/or odynophagia. Seventy-eight percent were symptomatic less than three months. Approximately equal numbers of patients presented with T1, T2, and T3 tumors. Twenty-seven percent had cervical metastases when initially seen. The majority (89%) of patients were treated with radiation initially and the remainder (11%) received radiation therapy at the time of postsurgical recurrence with an absolute five year survival of 33%. Patients less than 60 years of age and those with small primary tumors and no neck metastases demonstrated better survival. Radiation therapy to the primary tumor and neck appears to be the preferred modality of initial treatment.  相似文献   
62.
In a retrospective study by means of a half-standardized method of interview in 154 patients with acute myocardial infarction and in a control group of the same age (n = 100) anamnestic data were established, particularly taking into consideration the preinfarction phase. 27% of the patients were surprised by an acute myocardial infarction without prodromal symptoms, in 32% the first occurrence of complaints of angina pectoris was during the last two months before the infarction. 41% had a preexisting angina pectoris which usually showed a crescendo-course with increasing approximation to the infarction. More than half of the patients reported on physical activity or/and emotional stress as causal factors of the preinfarction complaints. The correlation with the localisation of the infarction showed above all an occurrence of the prodromal symptoms in infarctions of the anterior wall and in lesions of the myocardium which in most cases could be ascertained only enzymatically. A greater accumulation of the prodromi was furthermore found in younger patients, in hypertension and preexisting restriction of the heart function. 70% of the patients with warning symptoms consulted a physician because of their heart complaints. In the control group 22% of the persons reported on heart complaints.  相似文献   
63.
水资源优化配置调度系统信息传输通道建设   总被引:2,自引:0,他引:2  
监测站分中心省中心图1信息传递流程示意图2传输通道建设本系统设分中心站2个(鞍山水文分局、辽阳水文分局),端站16个。超短波电台采用进口专用数传电台,工作频率段为国家无委专为水利系统批准的230MHz数传频点。辽宁中部地区的水系主要包括辽河干流、浑河、太子河、大辽河、绕  相似文献   
64.
OBJECT: This study is a retrospective analysis of clinical data obtained in 28 patients affected by obstructive hydrocephalus who presented with signs of midbrain dysfunction during episodes of shunt malfunction. METHODS: All patients presented with an upward gaze palsy, sometimes associated with other signs of oculomotor dysfunction. In seven cases the ocular signs remained isolated and resolved rapidly after shunt revision. In 21 cases the ocular signs were variably associated with other clinical manifestations such as pyramidal and extrapyramidal deficits, memory disturbances, mutism, or alterations in consciousness. Resolution of these symptoms after shunt revision was usually slow. In four cases a transient paradoxical aggravation was observed at the time of shunt revision. In 11 cases ventriculocistemostomy allowed resolution of the symptoms and withdrawal of the shunt. Simultaneous supratentorial and infratentorial intracranial pressure recordings performed in seven of the patients showed a pressure gradient between the supratentorial and infratentorial compartments, with a higher supratentorial pressure before shunt revision. Inversion of this pressure gradient was observed after shunt revision and resolution of the gradient was observed in one case after third ventriculostomy. In six recent cases, a focal midbrain hyperintensity was evidenced on T2-weighted magnetic resonance imaging sequences at the time of shunt malfunction. This rapidly resolved after the patient underwent third ventriculostomy. CONCLUSIONS: It is probable that in obstructive hydrocephalus, at the time of shunt malfunction, the development of a transtentorial pressure gradient could initially induce a functional impairment of the upper midbrain, inducing upward gaze palsy. The persistence of the gradient could lead to a global dysfunction of the upper midbrain. Third ventriculostomy contributes to equalization of cerebrospinal fluid pressure across the tentorium by restoring free communication between the infratentorial and supratentorial compartments, resulting in resolution of the patient's clinical symptoms.  相似文献   
65.
Transplanted olfactory ensheathing cells (OECs) have previously been demonstrated to support axonal growth and myelination in the adult rat CNS. Here, the capacity of donor OECs to control the direction of axonal regeneration has been investigated following transplantation, as elongated columns, into the thalamus of adult rats. The OECs formed a 'glial bridge' which extended from the thalamus to the hippocampus. Transplanted OECs rapidly adopted a spindle-shaped morphology which was orientated along the vertical axis of the transplant. Numerous host axons grew into the transplants and followed the highly orientated OEC cell matrix across the choroid fissure. Thus, the spontaneous elongation and orientation of donor OECs may support highly directional host axonal growth across natural barriers within the CNS.  相似文献   
66.
67.
The chicken lysozyme silencer F2 (F2) thyroid hormone response element (TRE) contains an unusual everted palindromic arrangement, has a high affinity for thyroid hormone receptor (TR) homodimers, and is especially sensitive to dominant negative inhibition by, the T3 resistance (RTH) mutant TR beta P453H. We used various TREs and TR mutations to determine the mechanisms for this sensitivity. Changing the F2 orientation from an everted palindrome to a direct repeat with a 4-bp gap (DR+4) (F2-DR) decreased the sensitivity to inhibition at high T3 concentrations, while a loss of this sensitivity occurred with a palindromic arrangement of these same half-sites. F2 contains the dinucleotide TG 5' to each consensus half-site conforming to the optimal TR-binding octamer, YRRGGTCA. A T to A change in position 1 of both F2 half-sites markedly reduced T3-induction, yet only slightly reduced TR homodimer or TR-retinoid X receptor (RXR) heterodimer binding. The TR beta ninth heptad mutation, L428R, prevents TR heterodimerization with RXR and eliminates the inhibitory effect of the P453H mutant TR on the F2-DR, but not the F2 element. Structural features of a TRE that favor strong TR binding of both TR homodimers and TR-RXR heterodimers containing the mutant TR, such as the everted palindromic conformation or the optimal TR-binding consensus octamer, enhance the sensitivity of a TRE to inhibition by the mutant TR. Thus, both half-site orientation and sequence contribute to the sensitivity of a given TRE to dominant negative inhibition by a mutant TR.  相似文献   
68.
69.
OBJECTIVE: To estimate the prevalence of hearing loss among community-dwelling older persons according to clinical criteria and to develop a brief self-report screening instrument to detect hearing loss. DESIGN: Survey. SETTING: National probability sample of noninstitutionalized older persons. PARTICIPANTS: A total of 2506 persons aged 55 to 74 who participated in the National Health and Nutrition Examination Survey. MAIN OUTCOME MEASURES: Hearing loss as defined by Ventry and Weinstein (VW) criteria and by the High Frequency Pure-Tone Average (HFPTA) scale. RESULTS: Hearing loss by VW criteria was present in 14.2% and by HFPTA criteria in 35.1% of those surveyed. The prevalence increased with advancing age and was higher among men and those with less education. A logistic regression model identified six independent factors for hearing loss by VW criteria: age > or = 70 years (adjusted odds-ratio (AOR) 2.7, 95% confidence interval (95% CI) 1.6, 4.4), male gender (AOR 3.0, 95% CI 1.9, 4.8), < or = 12th grade education (AOR 3.8, 95% CI 1.8, 7.7), having seen a doctor for deafness or hearing loss (AOR 8.9, 95% CI 5.3, 14.9), unable to hear a whisper across a room (AOR 3.2, 95% CI 2.0, 5.1), and unable to hear a normal voice across a room (AOR 6.2, 95% CI 2.6, 14.9). A clinical scale based on the logistic model had 80% sensitivity and 80% specificity in predicting hearing loss using VW criteria and 59% sensitivity and 88% specificity in predicting hearing loss using HFPTA criteria. CONCLUSIONS: Hearing loss, as defined by two clinical criteria, is common and can be screened for accurately using simple questions that assess sociodemographic and hearing-related characteristics.  相似文献   
70.
OBJECTIVES: Beta2-integrin (CD11b/CD18) expression, an indicator of neutrophil activation, has been associated with the development of acute respiratory distress syndrome. Leumedins act directly on leukocytes to inhibit the up-regulated expression of beta2-integrins involved in leukocyte adhesion. We examined the effect of such a new anti-inflammatory agent, NPC 15669 (N-[9H-(2,7-dimethylfluorenyl-9-methoxy)-carbonyl]-L-leucine), on neutrophil-mediated acute lung injury in an animal model. DESIGN: Prospective, randomized, blinded, controlled animal study. SETTING: An animal laboratory in a university setting. SUBJECTS: Adult New Zealand rabbits. INTERVENTIONS: After repeated lung lavages with normal saline to induce acute lung injury, anesthetized rabbits were randomly assigned to one of two groups (n = 6 per group): a) treatment group (pretreated with NPC 15669 [10 mg/kg i.v. bolus] 30 mins before lavage, followed by a continuous infusion [5 mg/kg/hr] for the duration [4 hrs] of the experiment); or b) control group (pretreatment and continuous infusion with placebo). All animals were mechanically ventilated with identical pressure settings over 4 hrs and were killed at the end of the experiment. MEASUREMENTS AND MAIN RESULTS: PaO2, PaCO2, and tidal volumes were repeatedly measured and airway pressure settings were noted every 30 mins. At the end of the experiment, lungs were taken out for measurements of the myeloperoxidase content, for conventional histology (hematoxylin and eosin staining), and for intracellular adhesion molecule-1 immunohistostaining. Pretreatment with NPC 15669 profoundly improved oxygenation from a PaO2 of 52 +/- 5 torr (6.9 +/- 0.7 kPa) to 250 +/- 161 torr (33.3 +/- 21.5 kPa) within 60 mins after lung lavage (p < .05). Oxygenation continued to improve throughout the study, reaching a maximal PaO2 value of 395 +/- 98 torr (52.7 +/- 13.1 kPa) at 4 hrs. In the control group, oxygenation remained poor throughout the observation period. PaO2 values differed significantly (51 +/- 20 torr [6.8 +/- 2.7 kPa] vs. 306 +/- 126 torr [40.8 +/- 16.8 kPa], p < .005) at 90 mins and at all subsequent measurements from those values in the NPC 15669 group. Dynamic lung compliance improved significantly 60 to 90 mins after repeated lung lavage. Histology demonstrated markedly less lung damage (hyaline membrane formation and leukocyte infiltration) in treated animals (p < .05) than in controls. CONCLUSIONS: NPC 15669 seems to block inflammatory reactions by inhibiting the sequestration of neutrophils in acute, ventilator-associated lung injury. As a result, gas exchange and total lung compliance improve. Application of this and similar compounds affecting neutrophil adhesion warrants further investigation as a treatment modality for acute lung injury.  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