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   6005篇
  免费   13篇
  国内免费   3篇
综合类   4篇
化学工业   54篇
金属工艺   15篇
机械仪表   6篇
建筑科学   3篇
矿业工程   2篇
能源动力   13篇
轻工业   32篇
水利工程   1篇
石油天然气   2篇
无线电   4篇
一般工业技术   36篇
冶金工业   5825篇
自动化技术   24篇
  2023年   3篇
  2022年   2篇
  2021年   6篇
  2020年   9篇
  2019年   9篇
  2018年   8篇
  2017年   12篇
  2016年   14篇
  2015年   6篇
  2014年   17篇
  2013年   22篇
  2012年   24篇
  2011年   19篇
  2010年   6篇
  2009年   9篇
  2008年   2篇
  2007年   5篇
  2006年   3篇
  2005年   4篇
  2004年   7篇
  2003年   12篇
  2000年   2篇
  1999年   184篇
  1998年   1917篇
  1997年   1096篇
  1996年   701篇
  1995年   377篇
  1994年   275篇
  1993年   357篇
  1992年   42篇
  1991年   42篇
  1990年   53篇
  1989年   44篇
  1988年   36篇
  1987年   38篇
  1986年   35篇
  1985年   44篇
  1983年   9篇
  1982年   19篇
  1981年   37篇
  1980年   52篇
  1979年   2篇
  1978年   14篇
  1977年   129篇
  1976年   291篇
  1975年   13篇
  1973年   2篇
  1965年   1篇
  1963年   1篇
  1955年   4篇
排序方式: 共有6021条查询结果,搜索用时 0 毫秒
981.
Prognostic significance of cathepsin-D in patients with breast cancer   总被引:1,自引:0,他引:1  
The expression of the protease cathepsin-D has been evaluated using an immunohistochemical technique with a polyclonal antibody in paraffin-embedded tissue from 359 patients treated between the years 1975-1981 for Stage I and II breast cancer. One hundred and twenty seven patients (35%) have strongly positive, granular staining, 138 (38%) are intermediately stained in the cytoplasm, and in 94 (26%) no staining is observed. There is a strong positive association between expression of cathepsin-D and the presence of tumour in axillary lymph nodes (P < 0.006). Expression of the protease is associated with significantly poorer survival of patients in univariate analysis (P = 0.025); however, this is not independent of other tumour variables.  相似文献   
982.
The majority of equations used to predict values for basal metabolic rates (BMRs) are the result of indirect calorimetry measurements performed in the 1930s and 1950s. To assess the reliability of these equations in predicting the resting energy expenditure (REE) of the children in our community, indirect calorimetry was performed on 92 male and 107 female healthy children 2-3 h postprandial. Each individual was measured for a duration of 15-20 min. The data for analysis were obtained from 5-15 min steady-state periods. Subjects ranged in age from 5 to 16 years. The results were compared with BMRs calculated from the Harris-Benedict equation (Harris J, Benedict F. A biometric study of basal metabolism in man. Washington, DC: Carnegie Institute of Washington, publication no. 279, 1919.), the Food and Agriculture Organization/World Health Organization/United Nations University (FAO/WHO/UNU) equations, and the equations proposed by Schofield for use by the 1985 FAO/WHO/UNU Nutrition Committee. The values predicted by the FAO/WHO/UNU and Schofield equations were consistent with the measured resting values for all the children in the study population. Ninety-two children weighed between 90-110% of their ideal body weight. When the measured REE and estimated BMR were compared by gender and age in these children, the Schofield equations provided the best estimates. Ninety-four of the study subjects weighed > 110% of their ideal body weight. The predicted estimates by all equations were consistent with the measured values in this subgroup of the population. We conclude that the FAO/WHO/UNU and Schofield equations are reliable estimates of metabolic rate in healthy children when measurement of REE is not possible.  相似文献   
983.
Recurrent hyperparathyroidism (HPT) occurs in a small percentage of patients undergoing parathyroidectomy for primary HPT and is usually due to inadequate excision of hyperfunctioning parathyroid tissue in the neck, a missed ectopic and hyperplastic parathyroid, or, less commonly, parathyroid carcinoma and parathyroid autografts. In order to determine the incidence, clinical characteristics, and outcome of patients with recurrent HPT due to parathyroid autografts, we reviewed our experience with 604 consecutive patients operated on for primary HPT between 1965 and 1989. One hundred of these patients received parathyroid autografts consisting of portions of one or more parathyroid glands. Three patients with autografts, placed in the sternocleidomastoid muscle, developed recurrent HPT due to their autografts for an incidence of 3 per cent. Recurrent disease was diagnosed between 62 and 113 months with an average of 89 months. The autotransplants in all three of these patients were from hyperplastic or adenomatous parathyroid tissue. Two patients had a history of neck irradiation. Preoperative thallium scans accurately localized the hyperfunctioning parathyroid tissue in all three patients. At operation, the hyperfunctioning autografts had grown into a discrete mass with a single vascular pedicle and were resected. Histologic examination disclosed either hyperplastic or adenomatous tissue, and corresponded to the histology and location of the original tissue transplanted in each case. Follow-up ranges from 12 to 67 months, with an average of 48 months. All patients remain cured and none require oral calcium supplementation. We conclude that graft-dependent recurrent HPT is due to the autotransplantation of hyperplastic or adenomatous parathyroid tissue and that thallium scanning is instrumental for diagnosis and localization.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
984.
Morpholinoalkyl esters (HCl salts) of naproxen 1 and indomethacin 3 were synthesized and evaluated in vitro and in vivo for their potential use as prodrugs for oral delivery. Prodrugs were freely soluble in simulated gastric fluid (SGF) and pH 7.4 phosphate buffer and showed a minimum of a 2000-fold increase in solubility over the parent drugs. All prodrugs were more lipophilic than parent drugs as indicated by n-octanol/pH 7.4 buffer partition coefficients but less lipophilic in terms of n-octanol/SGF partition coefficients. Potentiometrically determined pKa's for prodrugs were in the range of 6.89 to 8.62 at 25 degrees C. All prodrugs were quantitatively hydrolyzed to their respective parent drugs by enzymatic and/or by chemical means. An increase in carbon chain length rendered the prodrugs more stable at pH 7.4 but less stable in SGF. The esters were generally found to be hydrolyzed rapidly in rat plasma at 37 degrees C, the half-lives being in the range of 1.2-31.0 min. Based on in vitro results, prodrugs 2c and 4c were chosen to evaluate solid-state stability, in vivo bioavailability, and ulcerogenicity. At elevated temperatures, the solid-state decomposition of 2c and 4c followed biphasic kinetics, with rapid decomposition occurring initially. The prodrugs were 30-36% more bioavailable orally than the parent drugs following a single equimolar solution dose in rats. Prodrugs 2c and 4c were significantly less irritating to gastric mucosa than parent drugs following single-dose and chronic oral administration in rats.  相似文献   
985.
986.
Leukocyte depletion improves early postischemic ventricular performance in neonatal models of global myocardial ischemia. However, the rate of leukocyte reaccumulation after cardiopulmonary bypass and its subsequent impact on myocardial function is not known. This laboratory study examined the effect of leukocyte depletion on myocardial performance during the initial 6-hour period after bypass in an in situ, in vivo porcine model of neonatal cardiac surgery. Fifteen 3- to 5-day-old piglets (eight control and seven leukocyte depleted animals) were instrumented by placement of left ventricular short-axis sonomicrometry crystals and an intraventricular micromanometer catheter. Mechanical leukocyte depletion was achieved with Pall RC100 filters (Pall Biomedical, Inc., Fajardo, Puerto Rico) in the cardiopulmonary bypass circuit. Neonatal hearts were subjected to 90 minutes of hypothermic ischemia after a single dose of cold crystalloid cardioplegia. Two control animals died after the operation and were excluded from data analysis. Leukocyte filtration reduced the granulocyte count during initial myocardial reperfusion to 0.8% of control values. However, circulating granulocyte counts increased in leukocyte depleted animals throughout the postoperative period, reaching 68% of control values by 6 hours. Despite this rapid return of circulating granulocytes, animals subjected to leukocyte depletion had significantly better preservation of left ventricular performance (measured by preload recruitable stroke work, p < or = 0.02), left ventricular systolic function (measured by end-systolic pressure-volume relationship, p < or = 0.05), and ventricular compliance (p < or = 0.04) during the experiment. These changes in ventricular function were associated with a significant increase in left ventricular water content (p < or = 0.02) and tissue myeloperoxidase activity (p < or = 0.005) in control animals compared with leukocyte depleted animals. This study demonstrates that leukocyte depletion during initial reperfusion results in sustained improvement in postischemic left ventricular function despite the rapid return of granulocytes to the circulation.  相似文献   
987.
988.
Antihypertensive drugs may affect serum lipoprotein levels in mixed populations but data in hyperlipidemic patients are scanty. Atenolol versus celiprolol effects on serum lipoproteins were compared in 159 hyperlipoproteinemic hypertensive patients. This was a randomized, double-blind, parallel-group, positive-controlled multicenter trial with centralized lipoprotein laboratory and diet constancy monitoring. Blood pressure reduction and serum lipoprotein and apoprotein levels were monitored for 3 months. Both drugs reduced systolic and diastolic blood pressures. Atenolol had greater effects than celiprolol on diastolic pressure, but effects on systolic blood pressure were not different. Patients receiving atenolol had lower serum high-density lipoprotein cholesterol levels and higher low-density lipoprotein/high-density lipoprotein cholesterol ratios, whereas patients treated with celiprolol showed no contrasting changes. These differences in lipoprotein levels between drug treatment groups were statistically significant at weeks 9 and 12. The difference between drug treatments was also significant if the values of the 9- and 12-week visits were averaged. Patients taking atenolol had statistically significantly higher serum levels of total cholesterol, triglycerides and apoprotein B at 9 weeks. These divergent directional changes were consistent throughout and statistically significantly different between drugs.  相似文献   
989.
The present status of some general questions about DNA recombination is assessed. Topics include the mechanisms of synapsis and strand exchange, and the functions of recombination in nature.  相似文献   
990.
The contrasting agent Gd-DTPA (Magnevist, Schering AG, Germany) was tested when used in magnetic resonance tomography using extra-low (0.04 T) magnetic field intensity in 68 patients with various brain and spine tumors. The agent was injected intravenously in a dose of 0.1 mmol/kg. No complications were found. The tests showed its high efficiency in the diagnosis of brain neoplasms (particularly in malignant intracerebral disorders, meningiomas and neurinomas). Benign astrocytomas induced no noticeable signal intensification on post-contrasting T1-weighed tomograms. In all cases of spinal tumors, the application of Gd-DTPA could specify the extent of tumor invasions, the presence of cysts and identify accessory tumor nodes in one case.  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