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   3974篇
  免费   21篇
电工技术   22篇
综合类   1篇
化学工业   103篇
金属工艺   14篇
机械仪表   23篇
建筑科学   34篇
矿业工程   1篇
能源动力   16篇
轻工业   49篇
水利工程   2篇
石油天然气   7篇
无线电   216篇
一般工业技术   176篇
冶金工业   3193篇
原子能技术   9篇
自动化技术   129篇
  2021年   10篇
  2020年   6篇
  2019年   7篇
  2018年   8篇
  2017年   15篇
  2016年   12篇
  2015年   10篇
  2014年   17篇
  2013年   27篇
  2012年   28篇
  2011年   30篇
  2010年   27篇
  2009年   32篇
  2008年   46篇
  2007年   41篇
  2006年   39篇
  2005年   48篇
  2004年   18篇
  2003年   27篇
  2002年   32篇
  2001年   18篇
  2000年   17篇
  1999年   109篇
  1998年   919篇
  1997年   577篇
  1996年   349篇
  1995年   180篇
  1994年   187篇
  1993年   218篇
  1992年   36篇
  1991年   41篇
  1990年   54篇
  1989年   62篇
  1988年   55篇
  1987年   46篇
  1986年   28篇
  1985年   41篇
  1984年   16篇
  1983年   20篇
  1982年   21篇
  1981年   37篇
  1980年   49篇
  1979年   22篇
  1978年   20篇
  1977年   92篇
  1976年   220篇
  1975年   15篇
  1969年   8篇
  1963年   6篇
  1955年   5篇
排序方式: 共有3995条查询结果,搜索用时 15 毫秒
991.
Actinomycosis presents acutely as an abscess, or as a chronic lesion mimicking malignancy, tuberculosis, or aspergillosis. Most disease involves the mouth and its immediate site of lymphatic drainage, the anterior triangle of the neck. We present a case of actinomycosis at the apex of the posterior triangle, suspected of being a malignancy, and discuss the importance of being aware of this as a cause of neck lumps. The diagnosis is usually made late because of the difficulties in culturing the organism, or in identifying characteristic 'sulphur granules' in pus or biopsy specimens. For these reasons, the disease is underdiagnosed. When acute or chronic neck lesions prove difficult to diagnose, microscopy and prolonged anaerobic culture of pus and biopsy specimens should be performed in addition in Ziehl-Neelsen staining, tuberculosis and fungal cultures. The tests should be repeated if negative. Specific treatment requires prolonged courses of antibiotics, despite adequate surgical excision, to prevent relapse.  相似文献   
992.
A preterm boy was born at 34 weeks. Prenatal ultrasonography showed oligohydramnios, fetal ascites, large kidneys, and small thorax. He died 21 h after birth of respiratory insufficiency. Autopsy revealed Potter's-like facies, hypoplastic lungs, ascites, and bilateral nephromegaly (renal weight almost 10 times normal). The kidneys were finely nodular externally, solid, and cerebriform on cut section. Histologically, they showed a diffusely distorted architecture of jumbled lobules, hyperplasia of cortical-type tissue with inconspicuous proximal tubules, relative hypoplasia of medullary tissue, tubulointerstitial dysplasia, and perilobar nephrogenic rests. The renal features represent a variety of the universal or panlobar (also called pancortical or infantile) type of nephroblastomatosis. To our knowledge, this is only the third such case reported. In the brain, each lateral ventricle contained a yellow gelatinous mass. Histologically, the masses consisted of a pseudomyxoid matrix with delicate fibers and focal adipocyte clusters, all confined within choroid plexus. We consider these lesions fibrolipomatous hamartomas.  相似文献   
993.
Leptospirosis: prognostic factors associated with mortality   总被引:1,自引:0,他引:1  
To determine the prognostic factors for leptospirosis, we conducted a retrospective study of data collected in the emergency department of our hospital between 1989 and 1993. Sixty-eight patients, for whom the diagnosis of leptospirosis was based on pertinent clinical and epidemiological data and positive serology, were included in this study. Fifty-six patients (82%) were discharged from the hospital, and 12 (18%) died. Multivariate logistic regression demonstrated that five factors were independently associated with mortality: dyspnea (odds ratio [OR], 11.7; 95% confidence interval [CI], 2.8-48.5; P < .05), oliguria (OR, 9; CI, 2.1-37.9; P < .05); white blood cell count, >12,900/mm3 (OR, 2.5; CI, 1.8-3.5; P < or = .01), repolarization abnormalities on electrocardiograms (OR, 5.9; CI, 1.4-24.8; P < or = .01), and alveolar infiltrates on chest radiographs (OR, 7.3; CI, 1.7-31.7; P < or = .01). Identification of these factors on admission might provide useful selection criteria for patients who need early transfer to the intensive care unit.  相似文献   
994.
OBJECTIVE: To assess the educational value of a practice-based ambulatory program used at a school of veterinary medicine. DESIGN: Retrospective cohort study. SAMPLE POPULATION: Graduates of US veterinary medical schools between 1987 and 1994. PROCEDURE: Phase I involved use of interviews and focus groups to assist in development of the questionnaire used in phase II, a retrospective cohort study. The pretested questionnaire was sent to a study population consisting of all graduates of the University of Wisconsin-Madison, School of Veterinary Medicine, between 1987 and 1994 as well as a control group who were randomly selected from the 1994 AVMA list of veterinarians. Control-group veterinarians were matched on the basis of professional activity, region, and year of graduation. RESULTS: 728 of 1,067 veterinarians completed the questionnaire in phase II of the study (response rate, 68%). The practice-based ambulatory program at the University of Wisconsin-Madison compared favorably with university-based ambulatory programs in volume of experiences and perceived educational quality. Regardless of rotation type, female students were significantly less likely to observe or perform 12 specific clinical procedures and were significantly less likely to rate instructional quality as excellent or very good, compared with male students. CLINICAL IMPLICATIONS: Practice-based ambulatory rotations can be a good alternative to existing university-based ambulatory rotations. Implementation of these programs should emphasize performance of procedures while striving to ensure participation of female students.  相似文献   
995.
Transesophageal echocardiography has become a commonly used screening tool for traumatic tears of the descending aorta. The role of transesophageal echocardiography for ascending aortic tears is not yet well-defined. We report an ascending aortic tear imaged by aortography but missed on transesophageal echocardiography.  相似文献   
996.
OBJECTIVES: To evaluate the Rossavik growth model for predicting birth weight in a Dutch population and to evaluate growth cessation near term. STUDY DESIGN: Birth weight was predicted at various ages between 38 and 42 weeks, menstrual age (MA), and at birth age in 50 normal infants using two sets of ultrasound measurements obtained before 28 weeks, MA. Predicted birth weights were compared to actual weights. The mean percentage difference was used as a measure of systematic error and the standard deviation as a measure of random error. Linear regression analysis was used to evaluate the relationship between percentage differences and birth age. To evaluate the individual growth potential, the Growth Potential Realization Index for weight (GPRIWT) was determined for each fetus. RESULTS: The predictions at 39 and 39.15 weeks, MA, were accurate without systematic error and with a random error of +/-9.3%. Prediction at 38 weeks showed a statistical underestimation (mean +/- SD = -5.8% +/- 8.8), and statistical overestimations were found for predictions after 39.15 weeks and at birth age. A relationship between percentage differences and birth age was not found for predictions between 39.15 and 40 weeks, MA. These findings indicate that growth cessation occurred at 39.15 weeks, MA. Using birth weights predicted at 39.15 weeks, MA, GPRIWT were calculated. The mean GPRIWT value was not significantly different from 100% (p > 0.05), and individual GPRIWT values ranged from 84% to 114%. CONCLUSIONS: The Rossavik growth model can be used to predict birth weight in a Dutch population. However, growth cessation near term appears to occur later than previously reported in other populations.  相似文献   
997.
PURPOSE: Patients frequently have ocular pain, photophobia, foreign-body sensation, and burning/stinging after radial keratotomy. This study was a prospective, randomized, double-masked, multicenter, fellow-eye comparison of diclofenac sodium (Voltaren Ophthalmic, 0.1% solution) and placebo for controlling these ocular symptoms after bilateral radial keratotomy. METHODS: Patients who were pain free in both eyes before surgery were randomly assigned to treatment with diclofenac sodium in one eye and placebo in the other. One drop of each masked trial medication was administered 30-60 min before surgery, 5 min and 6 h after surgery, at bedtime on the day of surgery, and four times daily for 2 additional days. Patients evaluated ocular symptoms in each eye 0.5, 1, 2, 4, 6, 24, and 48 h after surgery and provided a global evaluation 6, 24, and 48 h after surgery. For each assessment, the difference in scores between eyes was analyzed by using a paired t test. RESULTS: Diclofenac sodium was significantly (p < 0.001) superior to placebo in controlling each ocular symptom at each interval after surgery and for patient global assessments 6, 24, and 48 h after surgery. CONCLUSION: Diclofenac sodium 0.1% ophthalmic solution is clinically effective in controlling adverse ocular symptoms occurring after bilateral radial keratotomy.  相似文献   
998.
Haitian women in Miami, Florida, responded to recruitment for testing of HIV antibody serostatus in ways that demonstrated the value of ethnographic methods for studying reactions to this kind of test, especially pre- and posttest counseling sessions. A total of 155 women between 14 and 61 years old, recruited in Miami in 1992 and 1993, participated. Response to testing identified three primary obstacles to the women's understanding of content presented in pre- and posttest counseling sessions: (1) their confusion about the meaning of positive versus negative, (2) the investigators' difficulty in communicating the concept of antibody, and (3) vagueness of the concept of window period between exposure and presentation of antibody. Retesting of a subset of Haitian participants helped to define sexual risk among these women in terms of having partners who had other partners and perception of supernatural risk.  相似文献   
999.
We have compared our local, pedicled, and free-flap reconstructions for 90 skull base defects performed over the past 10 years. The pericranial flap was found to provide a reliable dural seal. Free-flap reconstructions exhibited a significantly higher incidence of uncomplicated primary wound healing (95 versus 62.5 percent) and a much lower incidence of flap loss (0 percent), cerebrospinal fluid leak (5 percent), meningitis, and abscess (0 percent) when compared with defects reconstructed with pedicled myocutaneous flaps. We conclude that microvascular free-tissue transfer is the safest, most economical procedure when faced with moderate to large composite defects of the cranial base.  相似文献   
1000.
Studied the implications of the model of M. Ross and M. Conway (1986) that autobiographical recall is a reconstructive process mediated by beliefs about the stability of the self and of the relevant database. At the beginning of the baseball season, 20 faculty and senior graduate students made predictions about the rank-order of finish for the teams in each Major League Division. They also provided self-ratings of baseball expertise. Six months later, the same Ss were unexpectedly asked to recall their predicted rankings. Ss who believed themselves to be stable experts produced recall protocols that were predicted by how the teams actually finished, consistent with Ross's hypothesis. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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