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   1682篇
  免费   15篇
  国内免费   1篇
电工技术   1篇
综合类   1篇
化学工业   46篇
金属工艺   1篇
机械仪表   3篇
建筑科学   6篇
能源动力   7篇
轻工业   49篇
石油天然气   2篇
无线电   5篇
一般工业技术   22篇
冶金工业   1531篇
原子能技术   1篇
自动化技术   23篇
  2023年   2篇
  2022年   7篇
  2021年   8篇
  2020年   2篇
  2019年   3篇
  2018年   6篇
  2017年   8篇
  2016年   2篇
  2015年   4篇
  2014年   4篇
  2013年   21篇
  2012年   7篇
  2011年   11篇
  2010年   9篇
  2009年   8篇
  2008年   4篇
  2007年   6篇
  2006年   7篇
  2005年   3篇
  2004年   8篇
  2003年   7篇
  2002年   5篇
  2001年   2篇
  2000年   2篇
  1999年   40篇
  1998年   483篇
  1997年   267篇
  1996年   186篇
  1995年   106篇
  1994年   72篇
  1993年   119篇
  1992年   6篇
  1991年   13篇
  1990年   9篇
  1989年   19篇
  1988年   15篇
  1987年   15篇
  1986年   14篇
  1985年   8篇
  1984年   5篇
  1983年   3篇
  1982年   8篇
  1981年   10篇
  1980年   22篇
  1978年   2篇
  1977年   33篇
  1976年   90篇
  1975年   3篇
  1965年   1篇
  1955年   2篇
排序方式: 共有1698条查询结果,搜索用时 15 毫秒
91.
N-Acetyl aspartate (NAA) is the second most abundant amino acid in the human brain. NAA is synthesized by L-aspartate N-acetyl transferase or by cleavage from N-acetyl aspartyl glutamate by N-acylated alpha-linked L-amino dipeptidase (NAALADase); and it is catabolized to acetate and aspartate by N-acetyl aspartate amino hydrolase (amino acylase II). NAA is localized primarily to neurons, where it is concentrated in the cytosol. Although NAA is devoid of neurophysiological effects, it serves as an acetyl donor, an initiator of protein synthesis or a carbon transfer source across the mitochondrial membrane. The concentration of NAA in human brain increases 3-fold between midgestation and adulthood. In Canavan's Disease, an autosomal recessive disorder due to a null mutation in amino acylase II, NAA levels in brain are markedly increased and disrupt myelination. NAA levels have been found to be reduced in neurodegenerative disorders, including Alzheimer's Disease and Huntington's Disease. Since endogenous NAA can be readily detected in human brain by magnetic resonance spectroscopy, it is increasingly being exploited as a marker for functional and structural integrity of neurons in an expanding number of disorders.  相似文献   
92.
93.
Anatomic correction of transposition of the great vessels   总被引:1,自引:0,他引:1  
We present a new approach for anatomic correction of transposition of the great arteries. The two coronary arteries, with a piece of the aortic wall attached, are transposed to the posterior artery. The two aortic openings are closed with a patch. The aorta and pulmonary artery are transected, contraposed, ant then anastomosed. The interventricular septal defect is closed with a patch, through a right ventriculotomy approach, because the right ventricle is no longer part of the systemic circulation. Two patients, aged 3 months and 40 days weighing 4,200 and 3,700 grams, respectively, were operated upon with deep hypothermia and total circulatory arrest. There was good recovery from the operation, with normal cardiocirculatory conditions. Renal failure developed in the first patient, and she died on the third postoperative day. During this time the cardiocirculatory conditions were good. The second patient made an uneventful recovery. Hemodynamic studies 20 days after the operation showed complete correction of the malformation. Five and one-half months after the operation, he weighs 7,500 grams, and his development is very good. We believe that this operation will be reproducible by most cardiovascular septal defect and pulmonary hypertension.  相似文献   
94.
A case of right atrial myxoma is described. The patient had vague and variable symptoms and it was not until five years after first presentation that she had developed clinical and electrocardiographic evidence of right atrial hypertrophy, and angiocardiographic evidence of a fist-sized myxoma which was subsequently removed surgically.  相似文献   
95.
The sera of 30 healthy male beagles were analyzed by reversed-phase high-performance liquid chromatography. The profiles were compared with those obtained from the sera of 30 healthy human donors. The chromatograms of each group were very reproducible; however, there were characteristic differences between the two groups. The compounds observed in both the human and canine profiles were identified as creatinine, uric acid, tyrosine, hypoxanthine, xanthine, kynurenine, inosine and tryptophan. Compounds present only in the canine profiles were identified as cytindine, riboflavin and 5-methyl-cytidine. Compounds present only in the human profiles include uridine, guanosine, hippuric acid and the dietary dependent compounds theobromine and caffeine. The compounds present in both human and canine sera were quantitated and compared statistically. The amounts of these compounds were very similar, except for uric acid.  相似文献   
96.
Departments of public health and agriculture in all 50 states of the United States and the District of Columbia were queried in 1977 to determine which of some selected zoonoses are reportable, the method of reporting and the diagnostic stage at which reporting is required. Fifty-three of the 62 diseases on the public health questionnaire were listed as reportable, with hepatitis A required by 49 of the 51 jurisdictions. Telephone reporting was required in nearly 19% of the disease-jurisdiction combinations and, in nearly 55%, reporting was required when the disease first was suspected. Thirty-three of the 41 diseases on the agriculture questionnaire were reportable, with anthrax most frequent. Telephone reporting was required in 30% of the reportable situations and suspected diagnoses were reportable in 54%. The disease lists varied markedly between the public health and agriculture agencies.  相似文献   
97.
In this work a previously proposed solid-shell finite element, entirely based on the Enhanced Assumed Strain (EAS) formulation, is extended in order to account for large deformation elastoplastic thin-shell problems. An optimal number of 12 enhanced (internal) variables is employed, leading to a computationally efficient performance when compared to other 3D or solid-shell enhanced elements. This low number of enhanced variables is sufficient to (directly) eliminate either volumetric and transverse shear lockings, the first one arising, for instance, in the fully plastic range, whilst the last appears for small thickness values. The enhanced formulation comprises an additive split of the Green-Lagrange material strain tensor, turning the inclusion of nonlinear kinematics a straightforward task. Finally, some shell-type numerical benchmarks are carried out with the present formulation, and good results are obtained, compared to well-established formulations in the literature.Funding by Ministério da Ciência e do Ensino Superior (FCT and FSE) (Portugal) under grant PRAXIS XXI/ BD/21662/99; as well as the funding by FEDER, under grant POCTI/EME/47289/2002, are gratefully acknowledged.  相似文献   
98.
The application of output value analysis, a type of benefit/cost analysis, to a psychiatric patient population is reported. A method for discounting the value of the program if a patient was readmitted within a year after discharge was introduced. The application of this discount factor reduces the value produced by the program and thereby reduces both productivity and effectiveness indices. When applied to groups known to differ in readmission rates, such as first admissions and readmissions or voluntary and involuntary admissions, the discount factor can accentuate group differences markedly. When selected diagnostic groups were compared, the discount factor could even reverse the relative standing of the groups.  相似文献   
99.
100.
The quantitative growth, the colony size, and the rate of growth of 47 clinical anaerobic isolates were compared on five different media, namely Brucella agar, brain heart infusion agar, Columbia agar, Schaedler agar, and tryptic soy agar. There was no significant difference in the quantitative growth of the anaerobes inoculated onto the five media. Although no single medium was superior for the growth of all isolates, 12 of 22 isolates, inoculated onto media stored for 4 weeks or less, grew best on Schaedler agar. The effects of supplementation of the media with reducing agents and reduction of the media before use were also analyzed and were found to be affected by the composition and length of storage of the media, as well as the bacteria tested.  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