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   2447篇
  免费   26篇
  国内免费   11篇
电工技术   20篇
综合类   29篇
化学工业   75篇
金属工艺   23篇
机械仪表   13篇
建筑科学   31篇
矿业工程   7篇
能源动力   8篇
轻工业   52篇
水利工程   7篇
石油天然气   14篇
武器工业   2篇
无线电   112篇
一般工业技术   64篇
冶金工业   1918篇
原子能技术   5篇
自动化技术   104篇
  2022年   5篇
  2021年   8篇
  2020年   5篇
  2019年   6篇
  2018年   6篇
  2017年   7篇
  2016年   17篇
  2015年   5篇
  2014年   14篇
  2013年   21篇
  2012年   20篇
  2011年   22篇
  2010年   16篇
  2009年   27篇
  2008年   21篇
  2007年   30篇
  2006年   27篇
  2005年   19篇
  2004年   30篇
  2003年   14篇
  2002年   36篇
  2001年   32篇
  2000年   29篇
  1999年   75篇
  1998年   646篇
  1997年   345篇
  1996年   249篇
  1995年   125篇
  1994年   110篇
  1993年   119篇
  1992年   19篇
  1991年   32篇
  1990年   33篇
  1989年   43篇
  1988年   34篇
  1987年   20篇
  1986年   27篇
  1985年   39篇
  1983年   4篇
  1982年   6篇
  1981年   7篇
  1980年   15篇
  1978年   3篇
  1977年   35篇
  1976年   67篇
  1975年   5篇
  1971年   1篇
  1970年   2篇
  1967年   1篇
  1955年   3篇
排序方式: 共有2484条查询结果,搜索用时 78 毫秒
981.
Juvenile arthritis is the fifth most common chronic illness in children. When a child is diagnosed with juvenile arthritis, the family must adjust in many ways in order to cope with the demands of this illness. This article provides an overview of the disease, presents the case history of two sisters with polyarticular arthritis, and discusses how nurses and other health team members can empower a family to manage more successfully with this disease and thereby enhance quality of life. Professional resources that aid families coping including educating the family about the disease, providing psychologic support, as well as knowledge and assistance for optimal physical functioning and maintaining energy reserves, and suggesting strategies to sustain self esteem, motivation and hope.  相似文献   
982.
Nerve growth factor signal transduction mediated through the trk receptor has been implicated in neuronal growth, differentiation, and survival. In this study, we examined the effects of gestational exposure to the developmental neurotoxicant methylmercury (CH3Hg) on the ontogeny of trk-immunoreactivity (IR). Long-Evans dams were dosed on gestational days 6-15 (p.o.) with 0, 1, or 2 mg/kg CH3Hg dissolved in saline. Pups were sacrificed and perfused with buffered paraformaldehyde on postnatal days (PND) 1, 4, 10, 21 and 85. The brains were sectioned sagitally, Nissl-stained or stained immunohistochemically for trk receptors or glial fibrillary acidic protein (GFAP), and examined throughout the medial to lateral extent of the brain. The greatest density of IR in neural cell bodies was seen in the olfactory bulb, hippocampus, cerebral, and cerebellar cortex, striatum, septum, nucleus basalis, inferior colliculus, pons, and brain stem nuclei. trk IR was not limited to nerve cell bodies, with prominent axonal and dendritic staining in the brainstem, neocortex, hippocampus, cerebellum, and olfactory tract. The regional pattern of trk IR varied in an age-dependent manner. In controls, trk-like IR appeared to peak in most regions between PND4-10 and decreased dramatically after PND21. This age-related difference in trk IR was supported by western blot analysis of PND10 and adult neocortex. This reduced and more adult-like pattern of trk IR was apparent on PND21 with some persistent trk-like IR in the olfactory bulb, hippocampus, neocortex, cerebellum and basal forebrain. In contrast to the normal regional patterns of trk IR, CH3Hg produced a dose-related decrease in trk-like IR in the absence of overt maternal toxicity or neonatal toxicity. CH3Hg-induced decreases in trk-like IR were especially apparent during the early postnatal period when trk IR was the greatest. The effects of CH3Hg exposure were restricted regionally, with the largest decrease in trk-like IR apparent in cortical regions, basal forebrain nuclei, and brain stem nuclei. Subsequent to the effects of CH3Hg on cortical trk-like IR were alterations in the development of cortical laminae on PND10 and 21 of neocortex. These alterations were characterized by quantifiable decreases in cell density, cell size and the widths of the layers of posterior neocortex. Not all of the CH3Hg-induced effects were characterized by decreased trk-like IR. Robust increases in trk IR in glial cells in the corpus callosum and brain stem were observed coincident with increased GFAP IR in cells of similar morphology. The present results localize the cellular and regional ontogeny of trk and suggest that developmental exposure to CH3Hg alters the normal ontogeny of this trophic factor receptor which may be associated with the developmental neurotoxicity of this chemical.  相似文献   
983.
Research on public opinion has seldom been incorporated into the debate about appropriate coverage of mental health and substance abuse treatment services in health insurance plans. However, several surveys have been conducted to probe for voters' awareness of and attitudes toward persons with mental illness and insurance coverage of their treatment needs. Given the current debate over mandating parity for coverage of mental health and substance abuse treatment services, these data promise to be particularly useful to politicians and health policy analysts. The author reviews reports of survey research conducted between 1989 and 1994 to assess American voters' support for expansions of mental health and substance abuse treatment coverage, including their knowledge about the origins and implications of mental illness and their willingness to pay for more generous benefits. The results suggest widespread support for such benefit expansions, but voters express concern about potential increases in their taxes or in their health insurance premiums. To facilitate the passage of meaningful reforms for mental health and substance abuse treatment benefits, policy makers must present realistic estimates of the costs of such expansions and of the benefits to be delivered to those in need.  相似文献   
984.
985.
PURPOSE: To identify prognostic variables that predict for improved biochemical and local control outcome in patients with localized prostatic cancer treated with neoadjuvant androgen deprivation (NAAD) and three-dimensional conformal radiotherapy (3D-CRT). MATERIALS AND METHODS: Between 1989 and 1995, 213 patients with localized prostate cancer were treated with a 3-month course of NAAD that consisted of leuprolide acetate and flutamide before 3D-CRT. The purpose of NAAD in these patients was to reduce the preradiotherapy target volume so as to decrease the dose delivered to adjacent normal tissues and thereby minimize the risk of morbidity from high-dose radiotherapy. The median pretreatment prostate-specific antigen (PSA) level was 15.3 ng/mL (range, 1 to 560 ng/mL). The median 3D-CRT dose was 75.6 Gy (range, 64.8 to 81 Gy), and the median follow-up time was 3 years (range, 1 to 7 years). RESULTS: The significant predictors for improved outcome as identified in a multivariate analysis included pretreatment PSA level < or = 10.0 ng/mL(P < .00), NAAD-induced preradiotherapy PSA nadir < or = 0.5 ng/mL (P < .001), and clinical stage < or = T2c (P < .04). The 5-year PSA relapse-free survival rates were 93%, 60%, and 40% for patients with pretreatment PSA levels < or = 10 ng/mL, 10 to 20 ng/mL, and greater than 20 ng/mL, respectively (P < .001). Patients with preradiotherapy nadir levels < or = 0.5 ng/mL after 3 months of NAAD experienced a 5-year PSA relapse-free survival rate of 74%, as compared with 40% for patients with higher nadir levels (P < .001). The incidence of a positive biopsy among 34 patients pretreated with androgen ablation was 12%, as compared with 39% for 117 patients treated with 3D-CRT alone who underwent a biopsy (P < .001). CONCLUSION: For patients treated with NAAD and high-dose 3D-CRT, pretreatment PSA, preradiotherapy PSA nadir response, and clinical stage are important predictors of biochemical outcome. Patients with NAAD-induced PSA nadir levels greater than 0.5 ng/mL before radiotherapy are more likely to develop biochemical failure and may benefit from more aggressive therapies.  相似文献   
986.
The aim of this study was to evaluate the influence of androgens on TSH secretion during aging in Dutch rats. Male young (2 months) and old (16-21 months) rats were castrated (Cx) or sham-operated (C) and received testosterone propionate (TP--4 mg/Kg B.W., i.m., 7 days) or vehicle. Female adult (3 months) and old (12 and 17 months) intact rats received TP or corn oil in the same dose. The rats were decapitated, trunk blood was collected and anterior pituitaries were dissected out for in vitro incubation. In Cx young male rats, only TSH pituitary content showed lower levels than in their controls. Cx TP-treated rats showed higher serum TSH and in vitro basal and TRH-induced TSH secretion, but TP only partially reversed the decrease in pituitary TSH promoted by castration. The old male rats showed lower basal in vitro TSH secretion and pituitary TSH content. In Cx old male rats, serum and basal in vitro TSH concentrations were higher than those of old controls and TP treatment further increased basal in vitro TSH secretion, as well as, stimulated TRH-induced TSH secretion. Interestingly, TP had no effect on intact young or old male rats. However, in intact old female rats, TP stimulated in vitro TSH secretion but, as observed in the intact male, TP had no effect on adult female rats. These results suggest a stimulatory role of testosterone on TSH secretion of young and old male rats. Thereafter, it seems that the testes of old rats secrete some testicular factor that inhibits TSH secretion. However, in male rats with normal testosterone levels TP treatment did not increase further TSH secretion, but in old female rats it had a stimulatory effect.  相似文献   
987.
988.
The explanation by differential diagnosis of pathological changes of the fundus may be particularly difficult in case of diseases of sporadic occurrence. The examination findings in a 19-year-old patient with a choroidal osteoma are presented. Large arciform, atrophic areas with distinct boundaries and star-shaped vascular structures were dominant in the fundus on both sides. With peripapillar manifestation, the optic nerve head was ophthalmoscopically noncontributory. A submacular bleeding had caused sudden reduction of visual acuity and caused the patient to visit the ophthalmologist. The most important diagnostic key was supplied by echography, which established peripapillar scleral calcification. The posterior eye segment was highly reflective in ultrasonic echography (B mode), showing concave deformation and causing the sound shadow. Visually evoked potentials indicated the onset of the compression of the optic nerve by the choroidal osteoma. Diagnostic and treatment possibilities are discussed.  相似文献   
989.
Coreceptor usage by Envs from diverse primary human immunodeficiency virus type 1 isolates was analyzed by a vaccinia virus-based expression and assay system. Usage of recombinant CCR5 and CXCR4 correlated closely with fusogenicity toward macrophages and T-cell lines expressing endogenous coreceptors. Surprisingly, recombinant CCR3 was utilized by most primary and T-cell-line-adapted Envs. Endogenous CXCR4 in macrophages was functional as a coreceptor.  相似文献   
990.
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