全文获取类型
收费全文 | 7063篇 |
免费 | 40篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 34篇 |
综合类 | 2篇 |
化学工业 | 479篇 |
金属工艺 | 36篇 |
机械仪表 | 58篇 |
建筑科学 | 174篇 |
矿业工程 | 15篇 |
能源动力 | 68篇 |
轻工业 | 234篇 |
水利工程 | 12篇 |
石油天然气 | 21篇 |
无线电 | 238篇 |
一般工业技术 | 396篇 |
冶金工业 | 4926篇 |
原子能技术 | 28篇 |
自动化技术 | 386篇 |
出版年
2021年 | 19篇 |
2019年 | 22篇 |
2017年 | 21篇 |
2016年 | 30篇 |
2015年 | 23篇 |
2014年 | 37篇 |
2013年 | 145篇 |
2012年 | 72篇 |
2011年 | 116篇 |
2010年 | 94篇 |
2009年 | 82篇 |
2008年 | 115篇 |
2007年 | 104篇 |
2006年 | 113篇 |
2005年 | 78篇 |
2004年 | 81篇 |
2003年 | 91篇 |
2002年 | 82篇 |
2001年 | 61篇 |
2000年 | 60篇 |
1999年 | 167篇 |
1998年 | 1206篇 |
1997年 | 689篇 |
1996年 | 539篇 |
1995年 | 324篇 |
1994年 | 271篇 |
1993年 | 316篇 |
1992年 | 96篇 |
1991年 | 94篇 |
1990年 | 120篇 |
1989年 | 148篇 |
1988年 | 110篇 |
1987年 | 131篇 |
1986年 | 104篇 |
1985年 | 122篇 |
1984年 | 51篇 |
1983年 | 61篇 |
1982年 | 76篇 |
1981年 | 54篇 |
1980年 | 86篇 |
1979年 | 48篇 |
1978年 | 41篇 |
1977年 | 131篇 |
1976年 | 286篇 |
1975年 | 49篇 |
1974年 | 44篇 |
1973年 | 34篇 |
1972年 | 26篇 |
1970年 | 17篇 |
1969年 | 17篇 |
排序方式: 共有7107条查询结果,搜索用时 0 毫秒
41.
A parameter-free geometric model for nuclear absorption is derived from microscopic theory. The expression for the absorption cross section in the eikonal approximation taken in integral form is separated into a geometric contribution, described by an energy-dependent effective radius, and two surface terms which are shown to cancel in an asymptotic series expansion. For collisions of light nuclei, an expression for the effective radius is derived using harmonic-oscillator nuclear density functions. A direct extension to heavy nuclei with Woods-Saxon densities is made by identifying the equivalent half density radius for the harmonic-oscillator functions. Coulomb corrections are incorporated and a simplified geometric form of the Bradt-Peters type obtained. Results spanning the energy range of 1 MeV/nucleon to 1 GeV/nucleon are presented. Good agreement with experimental results are obtained. 相似文献
42.
The present study was undertaken to evaluate the postoperative relapse from the period of unwiring to 1 year postoperatively and its correlation to the amount of mandibular setback and change in vertical dimension after mandibular bilateral sagittal split osteotomy. Twenty-seven patients were evaluated cephalometrically by the time preoperatively, 6 weeks, 6 months and 1 year postoperatively. It was found that 1) the average amount of mandibular setback at pogonion point, 6 weeks postoperatively, is 7.6mm backward and 1.9mm downward, 2) the average amount of horizontal relapse at pogonion point, 6 months and 1 year postoperatively, are 1.9mm and 2.3mm respectively. 86% of the horizontal relapse, 1 year postoperatively, occurs in the first 6 months after removal of intermaxillary fixation, 3) the average amount of vertical relapse at pogonion point, 6 months and 1 year postoperatively, are 0.9mm and 1.1mm upward. 82% of the vertical relapse, 1 year postoperatively, occurs in the first 6 months after removal of intermaxillary fixation, 4) the amount of 1 year postoperatively horizontal relapse is significantly correlated both with the amount of horizontal mandibular set back and vertical downward change (r = 0.58, 0.67, p < 0.001), whereas the amount of vertical relapse is with the vertical downward change only, but horizontal setback isn't. 相似文献
43.
Agrees with R. W. Motta et al's (see record 1994-04005-001) conclusion that there is little evidence that human figure drawings (HFDs) have any predictive validity or definitive clinical use in personality and intellectual assessment. Use of the HFD as a personality assessment tool is reviewed in the empirical literature. It is concluded that the only defensible ways that HFDs can be used involve hypothesis generating and testing under behavioral or cognitive-behavioral perspectives. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
44.
JW Porteous 《Canadian Metallurgical Quarterly》1996,182(3):223-232
Eight conscious chronically instrumented sheep were exposed to 1% inspired carbon monoxide (CO) for 35 min. In all sheep, carboxyhaemoglobin (COHb) levels at the end of the exposure were approximately 65%. Mean arterial blood pressure was unchanged with the exception of 2 sheep in which administration was stopped at 25 min following the sudden onset of hypotension. Oxygen delivery to the brain was sustained throughout the administration of CO due to a significant increase in cerebral blood flow (CBF). There was no evidence of either a metabolic acidosis or of lactate production by the brain suggesting the brain did not become hypoxic during the time-course of this study. Despite the apparent lack of hypoxia, oxygen consumption by the brain fell progressively and the sheep showed behavioural changes which varied from agitation to sedation and narcosis. The mechanism of these changes was therefore probably unrelated to hypoxia, but may have been due to raised intracranial pressure or a direct effect of CO on brain function. It is proposed that the time-course of progressive CO poisoning includes a phase in which CBF is elevated, blood pressure is unchanged and the brain is normoxic despite high COHb levels, but that this situation can rapidly evolve into a phase of haemodynamic collapse and severe hypoxia. 相似文献
45.
46.
47.
The role of geriatrics and geriatricians in family medicine remains unsettled. Despite a rapidly aging population, a tremendous shortage now exists of faculty with interest and expertise in geriatrics. Relatively few family practice residents choose to enter geriatric fellowship programs, and federal funding for such programs has been reduced. Despite accreditation requirements, residency programs are not always able to provide the range of geriatric experiences needed to properly prepare graduates to provide care for the broad range of older patients. Medical students' exposure to geriatrics remains limited. The Group on Geriatric Education of the Society of Teachers of Family Medicine believes that family medicine faculty must recognize and be committed to the notion that geriatrics is integral to family medicine. Both undergraduate and residency training programs should emphasize experience with geriatric patients in multiple settings. In particular, the nursing home should not be the main focus of geriatric training. The small number of certified geriatric faculty will be able to provide leadership, but a broad range of faculty must become involved in teaching geriatrics. Faculty development activities and continuing education programs to foster the necessary expertise will be essential to the accomplishment of this task. 相似文献
48.
EM de Kleijn WJ Oyen RA Claessens FH Corstens JW van der Meer 《Canadian Metallurgical Quarterly》1995,155(18):1989-1994
BACKGROUND: We assessed the utility of scintigraphy with indium 111-labeled polyclonal human IgG scintigraphy in patients with fever of unknown origin that fulfilled the criteria of temperature of 38.3 degrees C or more for at least 3 weeks and no diagnosis during 1 week of hospital admission. We compared the utility of this technique with results of scintigraphic techniques reported in the literature. METHODS: Data for all patients seen at our university hospital in whom 111In-IgG scanning was performed were analyzed and checked for the criteria for fever of unknown origin. The literature on the utility of scintigraphic techniques in patients with fever of unknown origin was reviewed. RESULTS: We studied 24 patients with fever of unknown origin. In 13 patients, focal 111In-IgG accumulation was observed. In nine (38%) of those, the positive 111In-IgG scintigram led to the final diagnosis; in the other four patients (17%), the scintigraphic findings were not helpful. In the 11 patients with negative 111In-IgG scans, extensive diagnostic workup produced no infection as the final diagnosis in nine patients (38%), one had an abscess in a renal cyst that was detected several months later, and in the other the cause of fever was an infected intravenous line. The overall sensitivity and specificity of 111In-IgG scintigraphy were 81% and 69%, respectively. The positive predictive value was 69% and the negative predictive value was 82%. CONCLUSIONS: Our results show that 111In-IgG scintigraphy significantly contributed to the diagnostic process in patients with fever of unknown origin. A positive scan increased the likelihood of finding the cause of the fever, and a negative scan ruled out an inflammatory component with a high degree of certainty. These data compare favorably with data in the literature concerning other radiopharmaceuticals; a larger prospective evaluation of this technique is indicated. 相似文献
49.
50.
PURPOSE: To assess the clinical performance of 2-year old gallium alloy restorations. Parameters evaluated include: (1) fracture at the margins, (2) tarnish, (3) surface roughness, (4) tooth fracture, (5) fracture through the body of the restoration, and (6) any medical or dental conditions arising during the study. MATERIALS AND METHODS: Nine patients received 30 Class I restorations of Galloy gallium alloy. These were placed as conservatively as possible under a rubber dam. Fifteen of the preparations were lined with a Bis-GMA resin to seal the restoration from moisture. The other 15 preparations were sealed with Amalgambond. After placement of the gallium alloy, the exposed surfaces of all restorations were sealed with the Bis-GMA resin, and the occlusion was checked. The restorations were examined at 2 weeks, 3 months, 6 months, 1 year and 2 years. RESULTS: At the 2-year recall, all restorations were intact with the exception of one tooth fracture (cause unknown). Forty-five percent of the restorations exhibited tarnish and 60% had a rough surface. The fracture at the margins of these restorations was minimal, and no significant difference could be found between those using Amalgambond and those sealed with the resin system. No medical problems were reported by the patients, and postoperative sensitivity was minimal. 相似文献