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   3948篇
  免费   1篇
  国内免费   1篇
化学工业   22篇
建筑科学   1篇
能源动力   2篇
轻工业   2篇
石油天然气   4篇
无线电   3篇
一般工业技术   10篇
冶金工业   3902篇
自动化技术   4篇
  2017年   1篇
  2016年   1篇
  2013年   2篇
  2012年   1篇
  2011年   1篇
  2010年   2篇
  2009年   3篇
  2007年   1篇
  2006年   2篇
  2005年   1篇
  2004年   3篇
  2003年   6篇
  2000年   2篇
  1999年   106篇
  1998年   1185篇
  1997年   650篇
  1996年   461篇
  1995年   219篇
  1994年   207篇
  1993年   222篇
  1992年   25篇
  1991年   68篇
  1990年   62篇
  1989年   57篇
  1988年   53篇
  1987年   56篇
  1986年   41篇
  1985年   44篇
  1983年   10篇
  1982年   19篇
  1981年   22篇
  1980年   31篇
  1979年   2篇
  1978年   11篇
  1977年   101篇
  1976年   258篇
  1975年   5篇
  1972年   1篇
  1964年   1篇
  1955年   7篇
排序方式: 共有3950条查询结果,搜索用时 796 毫秒
951.
More than 2,000 Jewish adults, aged 45-75, in urban areas of Israel were interviewed regarding consultations with practitioners of alternative medicine. 6% (122) of the respondents reported visiting such practitioners in the year prior to the interview. Homeopathy was the most frequent therapy, followed by reflexology, naturopathy, and acupuncture. The most common medical complaint was pain, particularly back pain. The most frequent reason for consulting the practitioner was disappointment with the outcome of conventional treatment. 39% of respondents who visited a practitioner were being treated by a conventional physician at the same time, for the same problem. The medical problems of a large majority had been relieved, but 22% said they were not helped by the practitioner. Women were more likely than men to consult a practitioner. Respondents with secondary or higher education were more likely to visit than those with less education. There were no age or socio-economic differences between users and nonusers. The mean payment for the whole series of treatments was NIS 770 (about $250). Respondents who visited practitioners reported worse health and more pain than nonusers, and were also more likely to have visited their conventional primary care physician in the past month. The findings suggest that nonconventional medicine should be seen as complementary to, rather than in competition with conventional medicine.  相似文献   
952.
Borrelia burgdorferi, the agent of Lyme disease, and B. turicatae, a neurotropic agent of relapsing fever, are susceptible to vancomycin in vitro, with an MIC of 0.5 microgram/ml. To determine the activity of vancomycin in vivo, particularly in the brain, we infected adult immunocompetent BALB/c and immunodeficient CB-17 scid mice with B. burgdorferi or B. turicatae. The mice were then treated with vancomycin, ceftriaxone as a positive control, or normal saline as a negative control. The effectiveness of treatment was assessed by cultures of blood and brain and other tissues. Ceftriaxone at a dose of 25 mg/kg of body weight administered every 12 h for 7 to 10 days eliminated cultivable B. burgdorferi or B. turicatae from all BALB/c or scid mice in the study. Vancomycin at 30 mg/kg administered every 12 h was effective in eliminating infection from immunodeficient mice if treatment was started within 3 days of the onset of infection. If treatment with vancomycin was delayed for 7 days or more, vancomycin failed to eradicate infection with B. burgdorferi or B. turicatae from immunodeficient mice. The failure of vancomycin in eradicating established infections in immunodeficient mice was associated with the persistence of viable spirochetes in the brain during antibiotic treatment.  相似文献   
953.
954.
A liquid chromatographic method for the analysis of ampicillin was examined in a collaborative study involving seven laboratories. The method included an isocratic part, which is used in the assay. The isocratic part is similar to the assay method for ampicillin of the US Pharmacopeia XXIII Revision. When the isocratic part is combined with gradient elution, the method is suitable for purity control. Six samples of ampicillin (anhydrous, trihydrate and sodium salt) with varying purity were analysed. The main component and related substances were determined. An analysis of variance proved the absence of consistent laboratory bias. The laboratory-sample interaction was significant. Estimates of the repeatability and reproducibility of the method, expressed as standard deviations of the result of the determination of ampicillin, were calculated to be about 0.9 and 1.1 respectively.  相似文献   
955.
Plasmodium vivax is, next to P. falciparum, the second important human malaria parasite. In view of reports on developing chloroquine resistance, research on new drugs that are active against P. vivax is necessary. Due to a requirement for continuous addition of reticulocytes, long-term in vitro culture of P. vivax is not practicable. Conventional drug assays, i.e., culturing for a time equivalent to one asexual cycle of development in the presence of drugs, and then measuring propagation, are therefore not readily performed. In this report the in vitro susceptibility of P. vivax to cyclosporin A and a new, nonimmunosuppressive derivative, SDZ NIM 811, was investigated using parasite material obtained from an infected Aotus monkey. The assay was initiated with blood containing ring-stage parasites and was ended when parasites were multinucleate, but before merozoite release. The results were compared with the in vitro susceptibility of P. falciparum to these drugs in a conventional and a short assay. As an indicator of parasite propagation [3H]hypoxanthine incorporation was measured. The susceptibility of P. vivax to cyclosporins was found to be intermediate to that of P. falciparum in the conventional and in the much less sensitive short assay, and SDZ NIM 811 proved to be as active as cyclosporin A.  相似文献   
956.
957.
Radioligands that specifically target dopamine uptake sites can provide a means of determining dopamine fiber loss at intrastriatal mesencephalic grafts in Parkinsonian patients, using Positron Emission Tomography (PET). The BTCP derivative, 1-[1-(2-benzo(b)thiophenyl)cyclohexyl]-4-(2-hydroxyethyl)-piperazine, shows in vitro high affinity and selectivity for the dopamine transporter. To evaluate the potential of such a compound as a potential dopaminergic PET tracer the positron-emitting analogues, 1-[1-(2-benzo(b)thiophenyl)cyclohexyl]-4-(2-[18F]fluoroethyl)-piperazine and 1-[1-(2-benzo(b)thiophenyl)cyclohexyl]-4-[11C]methylpiperazine, were synthesized. Radiofluorination was carried out by the reaction of 1-[1-(2-benzo(b)thiophenyl)cyclohexyl]-4-(2-chloroethyl)-piperazine with cyclotron-produced n.c.a. 18F-(half life 109.9 min) obtained by the (p,n) reaction on 18O-enriched water. Labelling with carbon-11 (half life 20.4 min) was achieved by 11C methylation of 1-[1-(2-benzo(b)thiophenyl)cyclohexyl]-piperazine with [11C]methyl iodide. After intravenous administration to rats these two compounds enter the brain, but despite their high in vitro affinity they display a high non specific binding in vivo which greatly limits their use as PET radioligands.  相似文献   
958.
The purpose of this study was to investigate the extent of the effects of hormonal replacement therapy (HRT) on the mammographic breast pattern in postmenopausal women. In a hospital-based study mammographic examinations of 81 postmenopausal women were evaluated retrospectively, before and after 1-2 years of treatment with oestrogens or a combination of oestrogens and progestagens. Each individual mammographic film was examined separately, and the glandular tissue was classified according to a modified Wolfe classification. In a screening-centre-based study two consecutive mammograms, with a 2-year interval, of 645 women, of whom 70 were using some kind of hormone therapy, were evaluated retrospectively. In the hospital-based study 31 % of patients treated with combination HRT showed an increase in fibroglandular tissue compared with only 8.7 % in the group treated with oestrogens alone. The difference was statistically significant (p = 0.046). In the screening-based study 14.3 % of the women using hormonal therapy showed an increase, whereas in the non-users no increase was found (p = 1.24 x 10(-10)). After beginning HRT many women (between 14 and 25 % in our experience) can be expected to undergo a mammographically detectable increase in fibroglandular tissue. Radiologists should be aware of the aetiology of such changes, and can obtain information on HRT most conveniently by having the technologist routinely question each patient.  相似文献   
959.
OBJECTIVE: Alterations in cortical benzodiazepine receptor density have been described in postmortem and in vivo studies of alcoholic subjects. The authors attempted to replicate these findings using single photon emission computed tomography and the benzodiazepine receptor radiotracer [123I]iomazenil. METHOD: They measured the distribution volume of benzodiazepine receptors in 11 recently detoxified patients with type II alcoholism and 11 healthy comparison subjects. The tracer was given as a bolus followed by a continuous infusion to achieve sustained binding equilibrium at the benzodiazepine receptors. Data were analyzed by using a region of interest method (regions of interest were identified on coregistered magnetic resonance imaging scans) and by a pixel-by-pixel method (distribution volume maps were analyzed with statistical parametric mapping for between-group differences). RESULTS: The region of interest analysis revealed that alcoholic patients had significantly lower benzodiazepine distribution volume than comparison subjects in the frontal, anterior cingulate, and cerebellar cortices. Statistical parametric mapping revealed two large excursions in which the distribution volume in alcoholic patients was significantly lower than in comparison subjects: the anterior cingulate, extending into the right middle frontal gyrus, and the left occipital cortex. CONCLUSIONS: Benzodiazepine receptor distribution volume is significantly lower in several cortical regions and the cerebellum in alcoholic subjects than in healthy comparison subjects. These results are consistent with previous reports and might indicate either a toxic effect of alcoholism on benzodiazepine receptors or a vulnerability factor for developing alcoholism.  相似文献   
960.
A 40-year experience consisting of 91 cases of acute slipped capital femoral epiphysis (SCFE) was reviewed to assess the safety of manipulative reduction and to determine whether urgent reduction has an effect on the development of avascular necrosis (AVN) of the capital femoral epiphysis. All patients had a history of sudden onset of severe hip pain and were documented to have an unstable (acute) slipped epiphysis. Treatment modalities included manipulative reduction under general anesthesia followed by internal fixation (41 hips), epiphysiodesis and internal fixation (15 hips), epiphysiodesis and cast immobilization (31 hips), and cast immobilization alone (three hips). One case was treated with cast immobilization after reduction by skeletal traction. Patient follow-up averaged 44 months, and ranged from 12 to 216 months. Radiographic review identified 13 (14%) cases of AVN in the series of 91 hips. Of 42 hips reduced in <24 h from presentation, AVN developed in three (7%). Of 49 hips reduced in >24 h from presentation, AVN developed in 10 (20%). Manipulative reduction of the acute SCFE may be accomplished without increased risk of AVN. Time to reduction may be an important risk factor for development of AVN after acute SCFE.  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