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   2387篇
  免费   0篇
  国内免费   1篇
化学工业   4篇
金属工艺   1篇
机械仪表   17篇
轻工业   1篇
无线电   2篇
一般工业技术   3篇
冶金工业   2355篇
自动化技术   5篇
  2014年   1篇
  2011年   1篇
  2009年   2篇
  2006年   4篇
  2005年   2篇
  2004年   2篇
  2003年   3篇
  2002年   1篇
  2001年   2篇
  2000年   2篇
  1999年   76篇
  1998年   706篇
  1997年   441篇
  1996年   274篇
  1995年   147篇
  1994年   130篇
  1993年   147篇
  1992年   13篇
  1991年   23篇
  1990年   24篇
  1989年   24篇
  1988年   22篇
  1987年   16篇
  1986年   13篇
  1985年   17篇
  1983年   6篇
  1982年   14篇
  1981年   8篇
  1980年   27篇
  1979年   3篇
  1978年   10篇
  1977年   64篇
  1976年   157篇
  1975年   4篇
  1964年   1篇
  1955年   1篇
排序方式: 共有2388条查询结果,搜索用时 140 毫秒
91.
In a retrospective case-control study of 58 cases of human brucellosis, adjusted mean serum calcium levels were found to be significantly higher in patients with brucellosis compared with controls: mean (95% confidence interval) = 2.39 (2.35-2.42) mmol/L versus 2.30 (2.26-2.34) mmol/L (P = 0.0012). The possible mechanisms underlying the cause of hypercalcemia in human brucellosis are discussed.  相似文献   
92.
OBJECTIVE: To demonstrate that cause-of-death statements can be generated by a computer algorithm from an autopsy database composed of diagnostic terms. DATA SOURCES: Over 49 000 autopsy facesheets contributed by over a dozen institutions were collected from a publicly accessible Internet autopsy database. This database is available at the following web site: http:@www.med.jhu.edu/pathology/iad.html STUDY SELECTION: To test the feasibility of creating and using a publicly available autopsy database, and to identify the technical and medicolegal problems that may arise with such a novel resource, a prototype study was designed by selecting autopsy facesheets from fetal and neonatal deaths. An algorithm was developed to determine the cause of death from the listing of anatomic diagnoses. DATA EXTRACTION: One thousand six hundred twenty-five fetal and neonatal autopsy facesheets were selected encompassing fetal and neonatal deaths occurring up to 28 days after birth. DATA SYNTHESIS: The algorithm determined causes of death from autopsy facesheet data in all cases. On review by an experienced pediatric pathologist, these automatically generated cause-of-death statements required no modification or only slight modification in over 90% of cases. CONCLUSIONS: A large multi-institutional autopsy database composed of demographic and diagnostic information has been deposited on the Internet. This information can be freely downloaded and used by any researcher without violating patient confidentiality. As a demonstration of one possible application of the database, fetal and neonatal autopsies generated cause-of-death statements using a computer algorithm. One can anticipate that the wealth of information contained in autopsy facesheets can be assembled into a database that will serve the public interest.  相似文献   
93.
OBJECTIVES: This study evaluated the contributions of lower socioeconomic status (SES) and neighborhood socioeconomic characteristics to neural tube defect etiology. The influence of additional factors, including periconceptional multivitamin use and race/ethnicity, was also explored. METHODS: Data derived from a case-control study of California pregnancies from 1989 to 1991. Mothers of 538 (87.8% of eligible) case infants/fetuses with neural tube defects and mothers of 539 (88.2%) nonmalformed infants were interviewed about their SES. Reported addresses were linked to 1990 US census information to characterize neighborhoods. RESULTS: Twofold elevated risks were observed for several SES indicators. Risks were somewhat confounded by vitamin use, race/ethnicity, age, body mass index, and fever but remained elevated after adjustment. A risk gradient was seen with increasing number of lower SES indicators. Women with 1 to 3 and 4 to 6 lower SES indicators had adjusted odds ratios of 1.6 (1.1-2.2) and 3.2 (1.9-5.4), respectively, compared with women with no lower SES indicators. CONCLUSIONS: Both lower SES and residence in a SES-lower neighborhood increased the risk of an neural tube defect-affected pregnancy, with risks increasing across a gradient of SES indicators.  相似文献   
94.
The protein fusion technique was applied in the synthesis of an artificial dimer of ribonuclease H (305 residues). 1H NMR spectroscopy was used to analyze the structure of this dimer. Spectral profiles and pKa values of the histidine residues obtained using 1H NMR indicate that the dimer retains the secondary and tertiary structures of the intact monomer. Selective spin-lattice relaxation measurements suggest that the two monomeric units in the dimer are in tight contact. Furthermore, the 2D 1H NMR and paramagnetic relaxation filter results show that the two monomers bind together through interactions between the N- and C-terminal sites of the linked regions.  相似文献   
95.
1. Many human fetuses have to adapt to a limited supply of nutrients. In doing so they permanently change their structure and metabolism. 2. These 'programmed' changes may be the origins of a number of diseases in later life, including coronary heart disease and the related disorders stroke, diabetes and hypertension. 3. This review examines the evidence linking these diseases to fetal undernutrition and provides an overview of previous studies in this area.  相似文献   
96.
We present a case of a patient who is HIV positive and developed both thrombotic thrombocytopenia purpura and visceral Kaposi's sarcoma (KS) with hemorrhage. This case presents a difficult management problem in that the patient's bleeding originated from KS lesions and did not quickly abate with plasmapheresis therapy despite both clinical and laboratory improvement after 2-4 days. Chemotherapy was initiated on day 13 and the patient's condition improved markedly afterward. We believe the addition of chemotherapy to plasmapheresis hastened the improvement of our patient's thrombotic thrombocytopenic purpura (TTP) and KS-related bleeding. Therefore, under similar conditions, we recommend combining plasmapheresis and chemotherapy at the onset of therapy.  相似文献   
97.
CONTEXT: Although blacks receive lower doses of hemodialysis than whites, their survival when receiving dialysis treatment is better than that for whites. Previous studies of the relationship between the dose of dialysis and patient survival have not controlled for differences in patient characteristics. OBJECTIVE: To examine the association of mortality with the dose of hemodialysis for clusters of patients categorized by race and sex. DESIGN: Retrospective analysis of laboratory data and mortality outcomes from 1994, using a national database of hemodialysis patients. PATIENTS: A total of 18144 black and white patients receiving hemodialysis 3 times weekly who either lived the entire year receiving hemodialysis or died. MAIN OUTCOME MEASURES: The fractional reduction of urea in a single dialysis session as the measured hemodialysis dose (urea reduction ratio [URR]) after controlling for race, sex, age, and diabetes mellitus. Mortality was determined by strata of URRs and albumin and creatinine levels. RESULTS: Across all age categories, blacks had lower URRs than whites, and men had lower URRs than women. In an age-adjusted model for evaluating interactions among URRs, race, sex, and diabetes, the association of URR with mortality risk was weak among blacks, particularly black men. After adjustment for age and diabetes, death probability curves were most steep for white women with URR values less than 60%. The death probability curves were least steep for black men. There was no meaningful difference between death probability and albumin or creatinine concentration among the race by sex clusters. CONCLUSION: Using URR, the usual measure of hemodialysis dose, the assumption that the association between dialysis dose and survival is uniform across demographic groups appears incorrect. Comparisons of the quality of dialysis patient care should not rely on URR alone to predict patient survival.  相似文献   
98.
Uric acid, the naturally occurring product of purine metabolism, is a strong peroxynitrite scavenger, as demonstrated by the capacity to bind peroxynitrite but not nitric oxide (NO) produced by lipopolysaccharide-stimulated cells of a mouse monocyte line. In this study, we used uric acid to treat experimental allergic encephalomyelitis (EAE) in the PLSJL strain of mice, which develop a chronic form of the disease with remissions and exacerbations. Uric acid administration was found to have strong therapeutic effects in a dose-dependent fashion. A regimen of four daily doses of 500 mg/kg uric acid was required to promote long-term survival regardless of whether treatment was initiated before or after the clinical symptoms of EAE had appeared. The requirement for multiple doses is likely to be caused by the rapid clearance of uric acid in mice which, unlike humans, metabolize uric acid a step further to allantoin. Uric acid treatment also was found to diminish clinical signs of a disease resembling EAE in interferon-gamma receptor knockout mice. A possible association between multiple sclerosis (MS), the disease on which EAE is modeled, and uric acid is supported by the finding that patients with MS have significantly lower levels of serum uric acid than controls. In addition, statistical evaluation of more than 20 million patient records for the incidence of MS and gout (hyperuricemic) revealed that the two diseases are almost mutually exclusive, raising the possibility that hyperuricemia may protect against MS.  相似文献   
99.
PURPOSE: To evaluate the usefulness of Doppler ultrasonography (US) in the diagnosis of hyperfiltration in patients with insulin-dependent diabetes mellitus (IDDM). MATERIALS AND METHODS: Eighty-one consecutive patients with IDDM were studied. All patients were normotensive and had normal creatinine and blood urea nitrogen levels. The glomerular filtration rate (GFR) was evaluated by means of plasma clearance of chromium-51 ethylenediaminetetraacetic acid, urinary albumin excretion, US evaluation of renal volume, and Doppler evaluation of resistance index (RI) in the renal interlobar arteries. The patients were divided according to GFR into the following groups: those with hyperfiltering kidneys (group 1, n = 40) and those with normofiltering kidneys (group 2, n = 41). RESULTS: The median renal volume was 351 mL (95% CI = 337 mL, 379 mL) in group 1 and 318 mL (95% CI = 300 mL, 335 mL) in group 2 (P = .005). The number of patients with microalbuminuria was significantly lower in group 1 than in group 2 (P = .02). The median RI was significantly lower in group 1 (0.55; 95% CI = 0.53, 0.57) than in group 2 (0.57; 95% CI = 0.56, 0.59) (P = .04). An RI of less than 0.5, a renal volume greater than 410 mL/m2, and the absence of microalbuminuria were independent predictors of hyperfiltration. An RI of less than 0.5 and a renal volume greater than 410 mL/m2 showed high specificity (98% and 95%, respectively) and poor sensitivity (25% and 23%, respectively) in the diagnosis of hyperfiltration in IDDM patients. CONCLUSION: Both RI and renal volume showed correlation with GFR, but neither parameter is sufficiently sensitive in screening for hyperfiltration in IDDM patients.  相似文献   
100.
We have developed a flexible physiological monitoring and analysis system for physiological studies in which data are obtained over extended periods. Our system uses low-cost personal computer hardware to concentrate data from existing multiple monitoring devices. All monitored parameters are displayed on a single screen and recorded in a single file. The system automates the process of physiological record keeping by providing continuous displays of vital signs. In addition, audible and visual alarms are produced when vital signs are outside of acceptable ranges, prompting the experimenter to take corrective actions. The central element of the system is a program running in a dedicated manner on an IBM PC-compatible computer. The program is written in the C language and makes use of a graphics library to display traces and analysis results in real time on any standard display for the PC. This program assigns the analog channels of an A/D board to particular physiological parameters by initially reading a configuration file, which also describes the alarm conditions and analysis routine for each parameter. All hardware specific code is isolated into well-defined modules. The program is both highly flexible with regard to different sets of parameters and highly portable for different experimental and computer environments.  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