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   382篇
  免费   3篇
电工技术   19篇
化学工业   84篇
金属工艺   8篇
机械仪表   6篇
建筑科学   8篇
能源动力   4篇
轻工业   39篇
水利工程   1篇
无线电   31篇
一般工业技术   58篇
冶金工业   109篇
原子能技术   3篇
自动化技术   15篇
  2023年   4篇
  2021年   5篇
  2019年   3篇
  2018年   5篇
  2017年   6篇
  2016年   4篇
  2015年   3篇
  2014年   1篇
  2013年   29篇
  2012年   10篇
  2011年   10篇
  2010年   7篇
  2009年   10篇
  2008年   11篇
  2007年   8篇
  2006年   9篇
  2005年   4篇
  2004年   9篇
  2003年   9篇
  2002年   8篇
  2001年   7篇
  2000年   9篇
  1999年   15篇
  1998年   40篇
  1997年   23篇
  1996年   18篇
  1995年   14篇
  1994年   12篇
  1993年   12篇
  1992年   3篇
  1991年   5篇
  1990年   2篇
  1989年   4篇
  1988年   7篇
  1987年   6篇
  1986年   2篇
  1984年   3篇
  1983年   1篇
  1982年   4篇
  1981年   12篇
  1980年   7篇
  1979年   10篇
  1978年   2篇
  1977年   1篇
  1976年   4篇
  1975年   1篇
  1974年   1篇
  1973年   2篇
  1971年   1篇
  1969年   1篇
排序方式: 共有385条查询结果,搜索用时 15 毫秒
361.
362.
Lyme disease     
BACKGROUND: The present article is a report of our animal experiments and also of the first clinical results of a new treatment for coronary heart disease using the human growth factor FGF-I (basic fibroblast growth factor) to induce neoangiogenesis in the ischemic myocardium. METHODS AND RESULTS: FGF-I was obtained from strains of Escherichia coli by genetic engineering, then isolated and highly purified. Several series of animal experiments demonstrated the apathogenic action and neoangiogenic potency of this factor. After successful conclusion of the animal experiments, it was used clinically for the first time. FGF-I (0.01 mg/kg body weight) was injected close to the vessels after the completion of internal mammary artery (IMA)/left anterior descending coronary artery (LAD) anastomosis in 20 patients with three-vessel coronary disease. All the patients had additional peripheral stenoses of the LAD or one of its diagonal branches. Twelve weeks later, the IMA bypasses were selectively imaged by intra-arterial digital subtraction angiography and quantitatively evaluated. In all the animal experiments, the development of new vessels in the ischemic myocardium could be demonstrated angiographically. The formation of capillaries could also be demonstrated in humans and was found in all cases around the site of injection. A capillary network sprouting from the proximal part of the coronary artery could be shown to have bypassed the stenoses and rejoined the distal parts of the vessel. CONCLUSIONS: We believe that the use of FGF-I for myocardial revascularization is in principle a new concept and that it may be particularly suitable for patients with additional peripheral stenoses that cannot be revascularized surgically.  相似文献   
363.
Small granules of horseshoe crab hemocytes contain two known major antimicrobial substances, tachyplesin and big defensin (S5), and at least five protein components (S1 to S6), with unknown functions. In the present study, we examined the biological properties and primary structure of a small granular component S2, named tachycitin. This component was purified from the acid extract of hemocyte debris by two steps of chromatography. The purified tachycitin was a single chain protein with an apparent M(r) = 8,500 on Tricine-SDS-polyacrylamide gel electrophoresis. Ultracentrifugation analysis revealed tachycitin to be present in monomer form in solution. Tachycitin inhibited the growth of both Gram-negative and -positive bacteria, and fungi, with a bacterial agglutinating property. Moreover, tachycitin and big defensin acted synergistically in antimicrobial activities. The amino acid sequence and intrachain disulfide bonds of tachycitin were determined by amino acid and sequence analyses of peptides produced by enzymatic cleavages. The mature tachycitin consisted of 73 amino acid residues containing five disulfide bonds with no N-linked sugar. A cDNA coding for tachycitin was isolated from a hemocyte cDNA library. The open reading frame coded for an NH2-terminal signal sequence followed by the mature peptide and an extension sequence of -Gly-Arg-Lys at the COOH-terminus, which is a putative amidating signal. The COOH-terminal threonine amide released after digestion of tachycitin with lysylendopeptidase was identified. The NH2-terminal 28 residues of tachycitin shows sequence homology to a part of chitin-binding regions found in antifungal chitin-binding peptides, chitin-binding lectins, and chitinases, all of which have been isolated from plants. Tachycitin showed a specific binding to chitin but did not bind with the polysaccharides cellulose, mannan, xylan, and laminarin. Tachycitin may represent a new class of chitin-binding protein family in animals.  相似文献   
364.
Epithelial cells and lymphocytes, including gammadelta and alphabeta T cells, in the gastrointestinal tract epithelium represent a major host defense intranet that is incompletely understood. Cell-to-cell interactions between intraepithelial lymphocytes (IELs) and intestinal epithelial cells (IECs) comprise this intranet, and we have assessed the role of IECs in the regulation of gammadelta and alphabeta T cell responses. When highly purified CD3+ IEL T cells were stimulated via the TCR-CD3 complex, high proliferative responses and cytokine synthesis were induced. However, the addition of viable IECs or purified IEC membranes (mIEC) down-regulated T cell proliferative and cytokine responses. Further, the inhibitory effect of mIEC was not restored by antibodies to TGF-beta, CD1d, E-cadherin, or MHC class I or II. This inhibitory effect was noted for both gammadelta and alphabeta T cell subsets from IELs, and mRNA levels were reduced for both Th1 (IL-2 and IFN-gamma) and Th2 (IL-4 and IL-5) cytokines in gammadelta and alphabeta IELs. In contrast, a purified membrane fraction obtained from thymocytes did not inhibit IEL proliferative responses. Further, mIEC did not inhibit splenic alphabeta T cell proliferative responses. These findings show that cell-to-cell interactions between intraepithelial gammadelta and alphabeta T cells and IECs occur via cell surface molecules, suggesting an intranet to prevent potential inflammatory responses at the intestinal mucosal surface.  相似文献   
365.
The role cardiac autonomic neuropathy (CAN) plays in diabetes is not well known. The aim of this study was to identify the factors involved in CAN in diabetic patients. One hundred patients, 44 insulin-dependent (IDDM) and 56 non-insulin-dependent (NIDDM), were investigated, using five standard tests. Three of these tests were for parasympathetic control (cardiac response to the lying-to-standing, deep breathing, and Valsalva tests), and the other two measured sympathetic control (testing for orthostatic hypotension and evaluating heart and blood pressure response to the handgrip test). Results were compared to those found in a series of 40 healthy volunteers. An age-adjusted comparison with the controls, showed that 34 patients had one abnormal parasympathetic test, 23 had two, and 6 patients had three. Cardiac parasympathetic neuropathy was thus present in 63% of the patients. The handgrip test was completed by 84 diabetic patients. There was evidence of orthostatic hypotension and/or an abnormal cardiac response to the handgrip in 15 of these patients, who all had a parasympathetic abnormality as well. There was no significant association between the type of diabetes and the presence of CAN. The duration of diabetes was significantly longer in patients with CAN (9.3 +/- 0.9 years) (p < 0.01) than in those with all three parasympathetic tests normal (5.8 +/- 0.9 years) (p < 0.01). The HbA1c level was also higher in patients with CAN than in those with three normal parasympathetic tests (9.95 +/- 0.35% versus 8.17 +/- 0.42%, p < 0.005). There was a significant association between the presence of retinopathy, observed by angiofluorography, and the presence of peripheral neuropathy confirmed by the electrophysiological investigation and the presence of CAN (p < 0.001). However, more than half the patients without retinopathy or nephropathy had CAN, and 11 of the 31 patients with a normal electrophysiological investigation also had CAN. Eighteen patients (6 IDDM) without retinopathy and nephropathy, who had been diabetic for less than 2 years, also had CAN. This study shows that CAN occurs early and is frequently found in a population of unselected diabetic patients. Metabolic factors may play an important role in its occurrence. CAN is significantly associated with the presence of retinopathy, which suggests that an impairment of autonomic peripheral blood flow control might be a contributing factor in the formation of microvascular lesions.  相似文献   
366.
BACKGROUND: The purpose of this study was to evaluate the diagnostic value of transvaginal ultrasound measurement of endometrial thickness, cytology obtained by Gynoscann, and histology of the endometrium sampled by Uterine Explora Curette compared with histology of the uterine specimen as the gold standard. METHODS: Consecutive patients admitted for hysterectomy had transvaginal ultrasound, sampling by Gynoscann, and Uterine Explora Curette done just before surgery, after informed consent. RESULTS: A total of 181 women entered the study. Sixteen had endometrial cancer, seven had atypical hyperplasia and nine had complex hyperplasia. A total of 168 patients had a transvaginal ultrasound done. At a cutoff limit of 4mm (endometrial thickness of 4mm or less indicating normal endometrium), the sensitivity was 90.3%, the specificity 24.8%, the positive predictive value 21.4% and the negative predictive value 91.9%. One endometrial cancer, one atypical and one complex hyperplasia were missed. The Gynoscann method showed a sensitivity of 62.5%, a specificity of 94.0%, a positive predictive value of 69.0% and a negative predictive value of 92.1%. Two cancers, three atypical and six complex hyperplasia were missed. The Uterine Explora Curette showed a sensitivity of 90.6%, a specificity of 100.0%, a positive predictive value of 100.0% and a negative predictive value of 98.0%. One endometrial cancer and two complex hyperplasia were missed. CONCLUSION: Transvaginal ultrasound is a reliable method in excluding endometrial pathology. The Uterine Explora Curette was superior to Gynoscann in diagnosing neoplasia of the endometrium. It was found to have the same diagnostic accuracy as conventional dilatation and curettage.  相似文献   
367.
368.
In order to prepare porous, macroscopically homogeneous filters without a separate packing process, ethylene was polymerized by radiation in glass tubes. The bulk density of the polyethylene is approximately proportional to ρ (? M)2I0.9t2, where ρ M is average ethylene density, ? M is average ethylene fugacity, I is radiation dose rate, and t is reaction time. The effect of the bulk density on “treatment capacity” was investigated by experiments where air samples containing 0.1 wt-% iodine vapor were filtered. Treatment capacity is difined as that amount of air per gram of polyethylene which passes through a filter until the polyethylene reaches the break point. The treatment capacity is approximately constant at 9 × 102 cm3/g over the bulk density range from 0.03 to 0.07 g/cm3, and it is lower at the outside of this range. The pressure drop due to the polyethylene filters varies with the 2.7th power of the bulk density when the bulk density is more than 0.03 g/cm3; below 0.03 g/cm3 this exponent increases with decreasing bulk density. Because of both the necessity of high Treatment capacity and that of low pressure drop, the optimum bulk density of polyethylene in the filter is about 0.03 g/cm3.  相似文献   
369.
The present study showed that (1) the critical area of spatial integration was larger for equiluminous chromatic stimuli than for luminance stimuli, and that (2) the critical area became smaller as the chromatic saturation of the adaptation field was increased. The latter suggests that the chromatic coding systems, which are assumed to posses poorer spatial resolution or larger spatial integration than the luminance system, could change their spatial integrating organization independently of the luminance system which could also change its own spatial organization. © 1993 John Wiley & Sons, Inc.  相似文献   
370.
Among the nonthermal effects of ultrasound, acoustic cavitation may have the highest potential for therapeutic applications if it can be somehow controlled. Recent in vitro and in vivo experiments have demonstrated that sonochemically active cavitation can be enhanced an order of magnitude by superimposing the second harmonic onto the fundamental in insonation. Moreover, they have shown that sonochemically active cavitation can be controlled with relative ease, thereby even in a progressive wave field. The effect of second-harmonic superimposition on the rectified diffusion through the gas-liquid interface of cavitated microbubbles is estimated theoretically. The theoretical rectified diffusion rate explained an asymmetric behavior of the threshold for producing sonodynamic tissue damage as a function of the fundamental and the second-harmonic amplitudes. The tissue damage was produced with a focused progressive wave in a liver lobe of a mouse administered with a sonodynamically active agent. The result suggests that the acceleration of the rectified diffusion is a primary mechanism of the enhancement of sonodynamically effective cavitation by second-harmonic superimposition  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