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   4350篇
  免费   23篇
电工技术   5篇
综合类   4篇
化学工业   120篇
金属工艺   15篇
机械仪表   10篇
建筑科学   8篇
矿业工程   5篇
能源动力   15篇
轻工业   39篇
水利工程   11篇
无线电   41篇
一般工业技术   83篇
冶金工业   3930篇
原子能技术   7篇
自动化技术   80篇
  2023年   7篇
  2022年   9篇
  2021年   9篇
  2020年   9篇
  2019年   11篇
  2018年   15篇
  2017年   11篇
  2016年   12篇
  2015年   9篇
  2014年   10篇
  2013年   23篇
  2012年   24篇
  2011年   28篇
  2010年   17篇
  2009年   25篇
  2008年   19篇
  2007年   20篇
  2006年   22篇
  2005年   13篇
  2004年   18篇
  2003年   11篇
  2002年   5篇
  2001年   13篇
  2000年   9篇
  1999年   150篇
  1998年   1242篇
  1997年   687篇
  1996年   433篇
  1995年   226篇
  1994年   190篇
  1993年   257篇
  1992年   30篇
  1991年   47篇
  1990年   50篇
  1989年   64篇
  1988年   66篇
  1987年   58篇
  1986年   36篇
  1985年   42篇
  1984年   3篇
  1983年   14篇
  1982年   21篇
  1981年   34篇
  1980年   23篇
  1978年   10篇
  1977年   107篇
  1976年   203篇
  1975年   10篇
  1974年   3篇
  1973年   5篇
排序方式: 共有4373条查询结果,搜索用时 15 毫秒
11.
12.
We prepared [U-14C]cellobiose by cultivating Acetobacter pasteurianus in the presence of [U-14C]glucose and hydrolyzing the [U-14C]cellulose formed with beta-glucosidase-free cellulase from Trichoderma reesei. This 14C-labeled cellobiose was used to investigate the presence of an uptake system for cellobiose in T. reesei. Evidence was obtained for the presence of a high affinity (Km for cellobiose 0.3 microM) but low activity (2.5 milliunits/mg fungal dry weight) cellobiose permease. The permease is formed constitutively, but higher levels are formed after addition of sophorose (glucosyl-beta-1,2-diglucoside), a reputed cellulase inducer. The permease appears to be specific for beta-diglucosides, as the uptake of [U-14C]cellobiose is inhibited by sophorose, gentiobiose (glucosyl-beta-1,3-glucoside), and cellobiose. Under these conditions, cellooligodextrines (n, 4-7; final concentration, 1 mM) are not inhibitors. Glucose, but no other monosaccharides, inhibits the permease. The hypersecretory mutant T. reesei RUT C-30 exhibits elevated permease activities, whereas in T. reesei QM 9979, a mutant strain defective in the induction of cellulases by cellulose or sophorose, strongly reduced permease activities were demonstrated. The results stress a hitherto not recognized point of control in the induction of cellulases by T. reesei at the level of uptake of cellulose oligosaccharides.  相似文献   
13.
OBJECTIVE: The purpose of this study was to evaluate ERCP and CT findings of ectopic drainage of the common bile duct into the duodenal bulb. CONCLUSION: Although rare, the diagnosis of ectopic drainage of the common bile duct into the duodenal bulb is important to prevent inadvertent damage during biliary tract or gastric surgery and to clarify the cause of chronic peptic ulcers.  相似文献   
14.
PURPOSE: Despite aggressive surgery and postoperative radiation therapy, only 30% of patients who have advanced, potentially resectable carcinomas of the head and neck survive for 5 years. In the hope of improving this situation we studied the effect of postoperative radiotherapy delivered concurrently with cisplatin. METHODS AND MATERIALS: Patients who had Stage IV tumors and/or involved surgical margins received 60 Gy in 30 fractions over 6 weeks plus 100 mg/m2 of cisplatin on radiotherapy days 1, 23 and 43. Fifty-two patients participated in this trial and 51 were evaluated. Forty-three (84%) patients had pathologic T3 or T4 disease, 43 (84%) had Stage IV disease, and 27 (53%) had histologically involved surgical margins. RESULTS: Severe and life-threatening toxicities occurred in 20% and 12% of patients, respectively; the most common drug-related toxicities were leukopenia, anemia, nausea, and vomiting. Seventeen patients (43%) remain alive with no evidence of disease. Four patients (8%) died with no evidence of neoplastic disease, and one patient has died of a second independent malignancy. By actuarial analysis at 3 years, 48% of patients are alive, 81% have locoregional control of disease, and 57% are free of distant metastases. CONCLUSIONS: Based on comparison with similar patients treated in a prior Radiation Therapy Oncology Group/Intergroup trial (RTOG), we conclude that postoperative radiotherapy with concurrent cisplatin may improve locoregional control rates and should be prospectively tested.  相似文献   
15.
OBJECTIVE: Our purpose was to determine whether the same maternal glycemic control is necessary to achieve similar perinatal outcomes for type 1 as for type 2 diabetics. STUDY DESIGN: The subjects were all women with pregestational diabetes mellitus delivered of live-born singletons. Glycemic control was achieved with diet and insulin. Self-monitoring of blood glucose was performed before meals and at bedtime. Target glucose values were 60 to 90 mg/dl fasting and 60 to 105 mg/dl at other times. RESULTS: Of 60,628 deliveries, 46 type 1 and 113 type 2 diabetic women met inclusion criteria. Respective differences were found between type 1 and type 2 diabetics in average daily glucose levels (112 mg/dl vs 97 mg/dl, p < 0.001), percent of values within target ranges (35% vs 57%, p < 0.001), and mean amplitude of glycemic excursion (48.1 mg/dl vs 24.9 mg/dl, p < 0.001). At least one daily glucose value was < 50 mg/dl during 19% of observation days for type 1 vs 2% of observation days for type 2 pregnancies (p < 0.001). There were no statistically significant differences between type 1 and type 2 diabetic pregnancies in neonatal macrosomia (30% vs 34%), proportion of cesarean deliveries during labor for arrest disorders (67% vs 69%), shoulder dystocia (2% vs 6%), and neonatal hypoglycemia (18% vs 26%). CONCLUSIONS: Less stringent maternal glycemic control may permit comparable maternal and neonatal outcomes for type 1 compared with type 2 diabetics. Higher target values for type 1 diabetics may decrease the frequency of maternal hypoglycemic episodes.  相似文献   
16.
In this study a representative sample of German acute care hospitals is used to describe the effects of dementia within acute care hospitals. Data from hospital patients above age 60 with the diagnosis dementia (ICD 290, 293, 294 and 310), collected over an observation period of 12 years, are compared with nondemented hospital patients at the same ages. The differences in the average length of stay between demented and nondemented patients are only relatively small in German acute care hospitals. The degree of multimorbidity is higher and hospital infections are more frequent for demented patients. The main differences occur with mortality: demented inpatients of both sexes experience a hospital mortality which is about twice as high as for nondemented patients at the same ages.  相似文献   
17.
Pilot studies in human populations have demonstrated a correlation between the level of antigen receptor trans-rearrangements and risk (at the population level) of lymphoid malignancy. Irradiation of newborn severe combined immune deficiency mice results in an increased risk of subsequent development of thymic lymphoma (100% of mice so irradiated are dead of thymic lymphoma by 20 weeks of age). We, therefore, assayed the occurrence of trans-rearrangements in this well-controlled mouse mutant system and found a 50-100-fold increase in the absolute number of TCRGV-TCRBJ trans-rearrangements compared to unirradiated littermates (and a comparable fold increase over age-matched BALB/c mice) at 2 weeks following irradiation. We also found a marked disproportion in generating trans-rearrangements versus intralocus rearrangements in the severe combined immune deficiency system compared to BALB/c, independent of irradiation. The trans-rearrangements noted were polyclonal in nature. These data, again, suggest that the absolute level of antigen receptor trans-rearrangements may serve as a biomarker of lymphoma risk.  相似文献   
18.
The majority of patients with soft tissue or bone sarcomas of the upper extremity can be treated today with limb-saving procedures using combined modality therapies. For patients with a tumor in the shoulder area, sometimes an interscapulothoracic amputation is the only radical surgical treatment. However, in selected cases, in which the tumor does not involve the neurovascular bundle, a limb-sparing alternative might be the Tikhoff-Linberg resection. Normal function of the hand and forearm, with reasonable function of the elbow, can be maintained by this procedure. Four case histories are reported.  相似文献   
19.
School-based condom distribution programs have generated considerable controversy across the country. In the present study 249 sexually active African American adolescents who did (n = 119) and did not (n = 130) use a condom during their initial sexual experience were compared to assess whether condom use at the onset of sexual activity was associated with later differences in sexual behavior. The results indicated that youths who used a condom from the onset of sexual activity were more likely to have used a condom in the most recent intercourse occasion, less likely to be diagnosed with a sexually transmitted disease (STD) or to combine substance use with sexual activity, endorsed more positive attitudes toward condoms, and were older when they initiated sexual activity. The findings have implications for condom availability programs and indicate that initial condom use was not associated with earlier onset of sexual activity and was associated with higher rates of precautionary behavior among sexually active minority adolescents.  相似文献   
20.
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