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   519篇
  免费   0篇
综合类   1篇
化学工业   3篇
机械仪表   1篇
轻工业   1篇
石油天然气   1篇
无线电   1篇
一般工业技术   1篇
冶金工业   510篇
  2019年   1篇
  2016年   1篇
  2013年   1篇
  2009年   2篇
  2008年   3篇
  2006年   2篇
  2004年   4篇
  2003年   2篇
  2002年   2篇
  1999年   15篇
  1998年   150篇
  1997年   87篇
  1996年   76篇
  1995年   30篇
  1994年   28篇
  1993年   32篇
  1992年   4篇
  1991年   6篇
  1990年   6篇
  1989年   6篇
  1988年   8篇
  1987年   5篇
  1986年   3篇
  1985年   6篇
  1983年   1篇
  1982年   3篇
  1981年   2篇
  1980年   5篇
  1977年   12篇
  1976年   16篇
排序方式: 共有519条查询结果,搜索用时 0 毫秒
511.
512.
513.
Recent studies demonstrate the relationship of microvessel density to malignant progression in breast cancer (N. Weidner, J. P. Semple, W. R. Welch, and J. Folkman, N. Engl. J. Med., 324: 1-8, 1991), underscoring the importance of angiogenesis in this tumor. Crucial in tumor angiogenesis are the paracrine actions of tumor-secreted factors (e.g., vascular endothelial growth factor), which have been thought to derive from the tumor epithelial cells themselves. We demonstrate that in response to hypoxic conditions, human mammary fibroblasts dramatically up-regulate vascular endothelial growth factor mRNA and increase vascular endothelial growth factor protein levels in accordance with the degree of oxygen deprivation. Thus, mammary stromal cells, only recently considered in the regulation of breast carcinomas, may play a hitherto unrealized role in breast cancer angiogenesis.  相似文献   
514.
McKeen’s expansive soil classification methodology relies on a parameter referred to as the “total suction-water content index” for describing the slope of the soil–water characteristic curve on a semilog plot. The swelling potential of expansive soils is qualitatively classified (e.g., “low” or “high”) based on the magnitude of the total suction-water content index. This study examines the validity of using a “benchmark intercept simplification” for indirectly estimating the total suction-water content index when complete soil–water characteristic measurements are not available or economical. Suction indices estimated using the benchmark intercept simplification are compared with indices measured directly using the noncontact filter paper technique for 80 undisturbed expansive shale specimens from the Colorado Front Range Corridor. The results show that the suction-water content index is consistently overestimated using the benchmark simplification by amounts ranging from negligible to 50%, and averaging 23%. For 49 of the 80 specimens (61%), the estimated indices fall in different swelling potential categories than the measured indices. In 44 of the 49 cases (90%), the estimated indices fall in higher swelling potential categories than the measured indices. These discrepancies reflect potential errors that may arise from the use of the benchmark intercept simplification in classifying expansive soils.  相似文献   
515.
Seventy patients with squamous carcinoma or adenocarcinoma of the lung were HLA typed at the time of their diagnosis and initial therapy. No abnormal HLA antigen frequencies were found. However, the possession of HLA-Aw19 or HLA-B5 was significantly correlated with two year disease-free survival. Twelve of 21 patients (57%) with either Aw 19 or B5 were disease-free at two years. In contrast, only six of 48 patients (13%) not having either antigen were disease-free (p less than .001). One patient was lost to follow-up. It is possible that Aw 19 and/or B5 confer resistance to progression of bronchogenic carcinoma on their possessors.  相似文献   
516.
The MMPI was administered to 40 undergraduate students with 20 subjects asked to imagine that they were applying for a job and 20 subjects asked to imagine that they were applying for psychotherapy. Subjects in the job group dissimulated (faked good) and those in the therapy group malingered (faked bad) as evidenced by differences between the subtle and obvious scores. The combined subtle and obvious score was higher for the psychotherapy group. It was concluded that the subtle, obvious, and combined subtle and obvious scores on the MMPI were a function of the demand characteristics of the testing situation.  相似文献   
517.
Sports injuries result from frequently repeated similar movements performed with submaximal force. In practice the term is also used, incorrectly, for many other injuries sustained during, or even outside, the practising of sports. Running may lead to injuries of muscles (rupture, chronic compartment syndrome), of tendons (peritendinitis, tendinosis, partial rupture, insertion tendinitis), of bone (stress fracture) and of cartilage (athrosis). Jumping mostly puts the ankle at risk, especially of development of an anterior or posterior impingement syndrome. Throwing puts much strain on the shoulder muscles; possible problems are microruptures in the rotator cuff, avulsion of the glenoid rim, chronic tendinitis of the biceps tendon and entrapment of the suprascapular nerve. The main element of the treatment is rest. If symptoms persist, surgery may be considered. Previous diagnostic imaging may then be of value.  相似文献   
518.
Surgical correction of unilateral coronal synostosis offers a unique opportunity to examine the molecular differences between an abnormal and a normal cranial suture. We isolated and identified a cDNA fragment whose expression was up-regulated in the premature fusing and fused coronal sutures, as compared with normal coronal sutures. The nucleotide sequence of the full-length cDNA of this gene, human NELL-1, has approximately 61% homology with the chicken Nel gene. Both chicken Nel and human NELL-1 are comprised of six epidermal growth factor-like repeats. The human NELL-1 messages were localized primarily in the mesenchymal cells and osteoblasts at the osteogenic front, along the parasutural bone margins, and within the condensing mesenchymal cells of newly formed bone in sites of premature sutural fusion. Human multiorgan tissue mRNA blot showed that NELL-1 was specifically expressed in fetal brain but not in fetal kidney, liver, or lung. We also showed that Nell-1 was expressed in rat calvarial osteoprogenitor cells and was largely absent in rat tibiae and fibroblast cell cultures. In conclusion, our data suggest that the NELL-1 gene is preferentially expressed in cranial intramembranous bone and neural tissue (both of neural crest cell origin) and is up-regulated during unilateral premature closure of the coronal suture. The precise role of this gene is unknown.  相似文献   
519.
Isokinetic leg strength and fatigue were measured in 24 male U.S. Marine Corps volunteers in a simulated sleep loss and unusually heavy work scenario. Knee extension and flexion peak torque (PT) were measured at three isokinetic speeds (1.57, 2.62 and 3.66 rad.s-1) followed by 45 consecutive maximal reciprocal contractions at 3.14 rad.s-1 to measure fatigue index (FI). All subjects were retested 2 days later following 30-h sleep deprivation (SD). The exercise group (n = 12) spent 25 1-h sessions performing computer tasks, filling out questionnaires and walked 1.61 km with a 50% gross body mass pack load, during each of the 25 sessions. The control group (n = 12) did likewise but did not exercise. Repeated measures ANOVA indicated that flexion PT at 1.57 rad.s-1 decreases (P < 0.013) after SD. Exercise did not affect FI but did decrease PT. It was concluded that carrying a 50% load produces decrements in PT for both extension and flexion but more so for flexion. SD affected PT but had no effect on FI.  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