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   1495篇
  免费   1篇
化学工业   4篇
轻工业   3篇
一般工业技术   3篇
冶金工业   1485篇
自动化技术   1篇
  2015年   1篇
  2013年   2篇
  2012年   1篇
  2010年   1篇
  2006年   1篇
  2003年   4篇
  2002年   1篇
  2000年   1篇
  1999年   36篇
  1998年   469篇
  1997年   279篇
  1996年   179篇
  1995年   91篇
  1994年   72篇
  1993年   84篇
  1992年   7篇
  1991年   23篇
  1990年   18篇
  1989年   17篇
  1988年   16篇
  1987年   26篇
  1986年   16篇
  1985年   13篇
  1982年   7篇
  1981年   14篇
  1980年   11篇
  1979年   2篇
  1978年   3篇
  1977年   24篇
  1976年   75篇
  1975年   1篇
  1955年   1篇
排序方式: 共有1496条查询结果,搜索用时 31 毫秒
991.
AMS is a preventable disease about which travellers are frequently uninformed and one which physicians may wrongfully assume is limited to the population of ultra high altitude adventurers. These studies on incidence, while not without flaws, point out the frequency of AMS, as well as its significant incidence at moderate and commonly frequented altitudes. The current literature does not fully answer questions about incidence at moderate altitudes, nor about the full effects of altitude on children. Certainly AMS is not a rare complication of travel to altitudes and may indeed be under-recognized and under-treated. Both acetazolamide and dexamethasone provide adequate prophylaxis, and the choice of medications can be to some extent based on experience and patient profile. The best prophylaxis is a slow stepwise ascent, and the best treatment descent. The availability of medications for the amelioration or prevention of symptoms, and succinct advice on prevention by travel planning will make many of our patients' holidays more enjoyable and business trips more productive.  相似文献   
992.
BACKGROUND: Nosocomial infections are a major cause of morbidity and mortality in premature infants. As a rule, their low serum gamma globulin levels at birth subsequently decline to hypogammaglobulinemic values; hence, prophylactic administration of intravenous immune globulin may reduce the rate of hospital-acquired infections. METHODS: In this prospective, multicenter, two-phase controlled trial, 2416 infants were stratified according to birth weight (501 to 1000 g and 1001 to 1500 g) and randomly assigned to an intravenous immune globulin group (n = 1204) or a control group (n = 1212). Control infants were given placebo infusions during phase 1 of the study (n = 623) but were not given any infusions during phase 2 (n = 589). Infants weighing 501 to 1000 g at birth were given 900 mg of immune globulin per kilogram of body weight, and infants weighing 1001 to 1500 g at birth were given a dose of 700 mg per kilogram. The immune globulin infusions were repeated every 14 days until the infants weighed 1800 g, were transferred to another center, died, or were sent home from the hospital. RESULTS: Nosocomial infections of the blood, meninges, or urinary tract occurred in 439 of the 2416 infants (18.2 percent): 208 (17.3 percent) in the immune globulin group and 231 (19.1 percent) in the control group (relative risk, 0.91; 95 percent confidence interval, 0.77 to 1.08). Septicemia occurred in 15.5 percent of the immune globulin recipients and 17.2 percent of the controls. During phase 1 the rate of nosocomial infections was 13.4 percent in the immune globulin group and 17.8 percent in the control group; the respective rates during phase 2 were 21.0 percent and 20.4 percent. The predominant organisms included gram-positive cocci (53.0 percent), gram-negative bacilli (22.4 percent), and candida species (16.0 percent). Adverse reactions were rarely observed during the infusions. Immune globulin therapy had no effect on respiratory distress syndrome, bronchopulmonary dysplasia, intracranial hemorrhage, the duration of hospitalization, or mortality. The incidence of necrotizing enterocolitis was 12.0 percent in the immune globulin group and 9.5 percent in the control group. CONCLUSIONS: Prophylactic use of intravenous immune globulin failed to reduce the incidence of hospital-acquired infections in very-low-birth-weight infants.  相似文献   
993.
Satellite panicum mosaic virus (SPMV) has been purified from pearl millet and obtained in a variety of different crystal forms, at least two of which appear suitable for high resolution X-ray diffraction analysis. The first is of cubic space group P4(2)32 with a = b = c = 183.1 A and two virus particles in the unit cell. The second is of a primitive orthorhombic space group with a = 166.1 A, b = 266.7 A and c = 269.1 A, with four virus particles in the unit cell. While the cubic crystal has as its asymmetric unit one twelfth of the icosahedron, or five capsid protein subunits, the asymmetric unit of the orthorhombic crystals is an entire particle. The cubic crystals diffract to at least 2.8 A resolution. We have also succeeded in crystallizing, but not yet characterizing the master virus, PMV.  相似文献   
994.
Cryptomonads are unicellular algae with plastids surrounded by four membranes. Between the two pairs of membranes lies a periplastidal compartment that harbours a DNA-containing organelle, termed the nucleomorph. The nucleomorph is the vestigial nucleus of a phototrophic, eukaryotic endosymbiont. Subcloning of parts of one nucleomorph chromosome revealed a gene coding for an Hsp70 protein. We demonstrate the expression of this nucleomorph protein-coding gene and present a model for protein transport from the host to the endosymbiont compartment.  相似文献   
995.
With increasing frequency, ambulatory patients maintained on multiple medications are seeking dental care. Because new medications are approved for use each year and new interactions and side effects are regularly exposed for existing medications, it is important to keep current in this area. With the availability of regularly updated computer programs to help analyze accurate patient medication lists, the treatment of the polymedication patient has become much easier. The close, careful attention to patient medications should help prevent medical problems as well as reveal much about the patient's ability to withstand dental procedures.  相似文献   
996.
BACKGROUND: The purpose of this study was to analyse long-term results of an active approach to surgical treatment of Crohn's disease. METHODS: One hundred and thirty-six patients were studied after first resection for primary Crohn's disease during 1968-77. RESULTS: Mean follow-up was 16.6 years; 18 patients had died (3 of Crohn's disease). Cumulative risk for a second resection was 0.40 (95% confidence interval, 0.29-0.51) at 10 years and 0.45 (0.32-0.58) at 15 years, similar in classical disease and colitis. Cumulative risk of a third and fourth resection was 0.5 at 10 years. Median resected bowel length at the first operation was 8%. After two and three resections the cumulative resection was 23% and 33%, respectively. Of the patients 73% claimed full working capacity and 7% had disability pension. CONCLUSIONS: An active surgical approach in Crohn's disease is associated with low operative mortality and morbidity and good functional results and offers good symptomatic relief.  相似文献   
997.
There are many advantages to the computerization of colour vision tests. However, previous computerized colour vision tests have involved equipment and methods not commonly used in clinical practice. We created computer emulations of the City University Colour Vision Test (CUT), Ishihara plates and American Optical Hardy-Rand-Rittler (AO-HRR) plates using a commonly available 24-bit colour Macintosh computer. Our colour monitor was calibrated to standard display white (D65), and colour plates were imaged with a colour scanner. The computerized colour images were compared with the standard test plates in a sample of 21 subjects with normal colour vision, 10 patients with congenital red-green defect and 1 patient with an acquired mixed colour defect. The computer images of the three tests correlated well with their conventional counterparts on kappa statistic analysis (p < 0.001), for both the colour normal and colour defective groups. We conclude that our computer emulations of the CUT, Ishihara and AO-HRR tests screen subjects with normal colour vision with high specificity and delineate congenital colour defects with a sensitivity comparable to that of their conventional counterparts.  相似文献   
998.
The aim of this study was to describe the sexual behaviour of a sample of genitourinary medicine (GUM) clinic attenders, 5 years after the launch of the UK government HIV media campaigns. A gender-specific and anonymous cross-sectional self-completion questionnaire was modified from the National Survey of Sexual Attitudes and Lifestyle and completed by 250 men and 250 women. The majority of the respondents were in their twenties, lived in London and were employed or students. Sixty-eight per cent of the men reported that one or more of their last 3 partners was not a regular partner. For those men whose last sexual encounter was with a new partner, 27% of heterosexuals and 33% of homosexuals reported using a condom. Fifty-one per cent of women reported one or more non-regular partners among their last 3 partners. For those women whose last sexual encounter was with a new partner, 43% of heterosexuals and 75% of bisexuals used a condom. Seventy-eight per cent of men and 75% of women had had a previous sexually transmitted disease (STD). These findings highlight the persistence of practices associated with the risk of contracting or transmitting HIV infection and which needs to be addressed in future educational campaigns. The GUM clinic population is an important population to monitor over time, either by longitudinal or serial cross-sectional studies. The results of this study provide a baseline against which to gauge the effects of future educational interventions.  相似文献   
999.
A guinea pig passage-adapted strain of the arena-virus Pichinde (adPIC) is highly virulent in inbred guinea pigs, whereas the related strain PIC3739 is attenuated. Both viruses were macrophage tropic and infected peritoneal, splenic, liver, and alveolar macrophages during experimental Pichinde virus infection. Infection with the virulent strain was associated with unlimited viral replication in the face of exaggerated delayed-type hypersensitivity response, manifested by the macrophage disappearance reaction. Histopathological lesions unique to adPIC-infected guinea pigs included intestinal villus blunting with mucosal infiltration by pyknotic debris-laden macrophages and apoptosis of crypt epithelial cells. Splenic red pulp necrosis was also significantly associated with adPIC infection but not PIC3739 infection. These findings may provide clues to the pathogenesis of a group of poorly understood human viral hemorrhagic fevers.  相似文献   
1000.
Serum samples from cigarette smokers, nonsmokers, and persons reporting "smoke sensitivity" were tested for IgE antibodies to tobacco leaf and smoke extracts by the radioallergosorbent test. Results indicated that none of the serum samples tested contained detectable IgE antibodies to smoke extracts. Occasionally, serum specimens from smokers or nonsmokers demonstrated reactivity to leaf antigen. The most significant reaction to leaf antigens was detected in serum from one of the 7 smoke-sensitive subjects tested. These results demonstrate that smoking, nonsmoking, and clinical "smoke sensitivity" are not correlated with the presence of IgE antibodies to tobacco leaf or smoke antigen.  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