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   3460篇
  免费   6篇
  国内免费   1篇
电工技术   2篇
综合类   3篇
化学工业   23篇
金属工艺   3篇
机械仪表   2篇
建筑科学   9篇
矿业工程   1篇
能源动力   3篇
轻工业   10篇
石油天然气   1篇
武器工业   2篇
无线电   10篇
一般工业技术   8篇
冶金工业   3374篇
自动化技术   16篇
  2022年   2篇
  2021年   1篇
  2020年   1篇
  2017年   2篇
  2016年   2篇
  2014年   1篇
  2013年   6篇
  2012年   1篇
  2011年   26篇
  2010年   5篇
  2009年   2篇
  2008年   2篇
  2006年   1篇
  2005年   4篇
  2004年   5篇
  2003年   9篇
  2002年   3篇
  2000年   3篇
  1999年   118篇
  1998年   1125篇
  1997年   653篇
  1996年   389篇
  1995年   194篇
  1994年   178篇
  1993年   228篇
  1992年   13篇
  1991年   28篇
  1990年   27篇
  1989年   41篇
  1988年   33篇
  1987年   33篇
  1986年   16篇
  1985年   25篇
  1984年   1篇
  1983年   7篇
  1982年   17篇
  1981年   13篇
  1980年   26篇
  1979年   1篇
  1978年   10篇
  1977年   75篇
  1976年   136篇
  1971年   1篇
  1955年   3篇
排序方式: 共有3467条查询结果,搜索用时 11 毫秒
21.
To test the hypothesis that regional cerebral blood flow (rCBF) is normally regulated by regional metabolic activity, rCBF and the regional cerebral metabolic rate for oxygen (rCMRO2) were compared in selected human subjects. In normal subjects and patients with chronic, stable diseases of brain, rCBF correlated well with rCMRO2. In one individual with mild dementia, rCBF and rCMRO2 were measured before and during exercise of the hand and forearm contralateral to the hemisphere studied. Appropriate parallel changes occurred in both rCBF and rCMRO2 during hand exercise. In patients with acute diseases affecting the hemisphere studied, however, the correlation between rCBF and rCMRO2 was unpredictable.  相似文献   
22.
Affinity chromatography on agmatine-Sepharose was used for the separation of two active forms of urokinase (EC 3.4.99.26) from partially purified human urinary urokinase. The approximate molecular weight of the heavier form was 47 000 and of the lighter 33 400. Both forms were homogeneous by sodium dodecyl sulfate gel electrophoresis and by 3H-labeled diisopropylphosphorofluoridate and 14C-labeled p-nitrophenyl-p'-guanidinobenzoate incorporation studies. The 33 400 mol. wt. form had a single chain, and the 47 000 mol. wt. form had two chains (33 100 and 18 600 mol. wt.) linked by disulfide bonds. The specific activity of the heavier form was 104 000 CTA units/mg protein, compared with 226 000 units/mg for the lighter form but the activities per mmol of active site (molar activities) of the two forms were almost identical (9.6-10(9) and 10.2-10(9) CTA units/mmol). Isoelectric focusing on gels showed that the 47 000 material contained one major subform with a pI of 8.60 and a minor subform with a pI of 8.90, while the 33 400 material had three major subforms with pI values of 8.35, 8.60 and 8.70, respectively, and a minor subform with a pI of 8.05. 3H-labeled diisopropylphosphorofluoridate incorporation studies revealed an active-site serine residue in the heavy chain.  相似文献   
23.
The clinical, electrocardiographic, and radiologic features in a patient with a pericardial band which produced an unusual form of infundibular pulmonary stenosis are presented. The findings are unique in that the band was not calcified and, therefore, not visualized roentgenographically and developed without a previous history of pericarditis or pericardial surgery. The diagnostic value of cineangiography is stressed and illustrated.  相似文献   
24.
There is an early period of puberty in boys at the age of 10 to 13, accompanied by an increase in the level of follicle stimulating hormone and a low secretion of luteinizing hormone and testosterone, with no secondary sexual signs. The beginning of an increase in the luteinizing hormone and testosterone concentration in boys coincides with the development of secondary sexual signs. The stabilization of the level of luteinizing hormone takes place in boys already at the 2nd degree of the sexual development. The secretion of luteinizing hormone at this point corresponds already to the normal level in adult men. The level of testosterone in the blood continues to increase and does not reach its definitive level until after the age of 17, or at the 5th degree of sexual development. Like in boys, the increase of the follicle stimulating hormone in girls precedes the increase of the luteinizing hormone secretion. The beginning of the increase in the follicle stimulating hormone coincides with an increase in the level of estrogens and testosterone in the blood, and with the appearance of secondary signs of sexual maturation. The increase of the luteinizing hormone secretion takes place later in girls than in boys and is accompanied by a new and significant increase in the level of estrogens in the blood. At the 2nd degree of sexual development, the level of testosterone in the blood of girls is substantially higher than at the other stages.  相似文献   
25.
Cats injected with LSD (d-lysergic acid diethylamide) exhibit a group of behaviors that appear to be specific to hallucinogenic drugs. Two of these behaviors, limb flick and abortive grooming, have an extremely low frequency of occurrence in normal cats, but often dominate the behavior of LSD-treated cats. The frequency of occurrence of this group of behaviors is related to the dose of LSD. The behavioral changes are long-lasting following a single injection of LSD, and exhibit tolerance following the repeated administration of LSD. They are not elicited by a variety of control drugs, but are elicited by other indole nucleus hallucinogens. Because the behavioral effects are specific, reliable, easy to score, and quantifiable, they represent an animal model that can be used in studies of the effects of LSD and related hallucinogens.  相似文献   
26.
Prophylactic antibiotics were given postoperatively to a consecutive series of 74 patients who underwent vaginal hysterectomy. Antibiotics were administered in the immediate postoperative period. There was a highly significant decrease in febrile morbidity in the treated group compared to 190 control subjects having similar surgery but treated with antibiotics only on the appearance of fever and/or other signs of infection. There was a failure to relate the increased febrile morbidity in the control group to patient's age, menopausal state, type of catheterization, or to the type of operative procedure. The increased morbidity in the control group related only to the failure to use prophylactic antibiotics. The antibiotic-treated portion (58 per cent) of the control group had a longer period of hospitalization.  相似文献   
27.
In a prospective 5-year-study the development of adiposity was tested in a population group consisting of about 30,000 persons. It was shown that during the time of investigation the population decreased in its total number, the consumption of easily digestible carbohydrates and meat, however, increased. As it was established in 1968, the proportion of the adipose persons (more than 20% of the Broca-weight) and the percental average deviation from the Broca-weight (calculated in decennium classes) was more than in the comparable population groups in the GDR. Contrary to expectation the examination further showed that on an average men exhibited a trend to the increase in weight, but on the average women decreased in weight. In all age groups (with the exception of the 60- to 69-year-old persons) the proportion of obese persons was significantly lower in 1973 than in 1968. Unchangedly adipose are the diabetics who also have a by far higher average weight than the healthy population and who up to now do not reveal an inclination to the decrease in weight. With 2.9% the average frequency of diabetes is also adequately high.  相似文献   
28.
A case of primary retroperitoneal germinoma is presented in which markedly elevated serum lactic dehydrogenase levels were present before diagnosis, but declined to normal with abdominal irradiation. It is the first report of lactic dehydrogenase serving as a tumor marker in germinoma.  相似文献   
29.
30.
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