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   3969篇
  免费   16篇
  国内免费   4篇
电工技术   4篇
综合类   9篇
化学工业   27篇
金属工艺   9篇
机械仪表   16篇
建筑科学   13篇
矿业工程   6篇
能源动力   1篇
轻工业   33篇
水利工程   6篇
石油天然气   5篇
武器工业   1篇
无线电   17篇
一般工业技术   33篇
冶金工业   3777篇
原子能技术   4篇
自动化技术   28篇
  2019年   3篇
  2018年   3篇
  2017年   2篇
  2016年   5篇
  2015年   3篇
  2014年   4篇
  2013年   13篇
  2012年   9篇
  2011年   21篇
  2010年   8篇
  2009年   21篇
  2008年   18篇
  2007年   40篇
  2006年   5篇
  2005年   20篇
  2004年   7篇
  2003年   4篇
  2002年   9篇
  2000年   1篇
  1999年   140篇
  1998年   1237篇
  1997年   668篇
  1996年   456篇
  1995年   253篇
  1994年   207篇
  1993年   238篇
  1992年   29篇
  1991年   41篇
  1990年   47篇
  1989年   48篇
  1988年   37篇
  1987年   30篇
  1986年   29篇
  1985年   30篇
  1984年   2篇
  1983年   3篇
  1982年   22篇
  1981年   20篇
  1980年   25篇
  1979年   3篇
  1978年   5篇
  1977年   62篇
  1976年   148篇
  1975年   2篇
  1974年   1篇
  1965年   1篇
  1964年   3篇
  1962年   1篇
  1955年   2篇
  1954年   1篇
排序方式: 共有3989条查询结果,搜索用时 0 毫秒
21.
Ensuring the competency of staff members at all levels of practice is an ongoing challenge for perioperative clinical educators. The authors developed a competency-based orientation program using AORN's perioperative nursing competency statements as a conceptual framework. The model also incorporates requirements from external regulatory agencies (e.g., the Joints Commission on Accreditation of Healthcare Organizations) that influence the direction of health care institutions seeking accreditation. The model provides the components necessary to validate the orientation of perioperative staff members and the delivery of comprehensive nursing care in perioperative settings.  相似文献   
22.
Reactive oxygen species increase during exhaustive contraction of skeletal muscle, but characterization of the specific species involved and their rates of production during nonexhaustive muscle contraction have not been investigated. We hypothesized that the production rate of hydroxyl radical (.OH) increases in contracting muscle and that this rate is attenuated by pretreatment with deferoxamine (Def) or dimethylthiourea (DMTU). We measured the rate of production of .OH before, during, and after 5 min of intermittent static contraction of the triceps surae muscles in cats (n = 6) using the formation of p-, m-, and o-tyrosines by hydroxylation of phenylalanine. L-Phenylalanine (30 mg/kg i.v.) was administered to each animal 3 min before contraction. Blood samples were collected from the popliteal vein 1 min before contraction; 1, 3, and 4.5 min during contraction; and 1 min after contraction. During and after contraction, the cumulative production rates of p-, m-, and o-tyrosines were elevated by 42.84 +/- 5.41, 0.25 +/- 0.04, and 0.21 +/- 0.03 nmol.min-1.g-1, respectively, compared with noncontracting triceps surae muscles. Pretreatment with Def (10 mg/kg i.v.; n = 5) or DMTU (10 mg/kg i.v.; n = 4) decreased the cumulative rates of production of p-, m-, and o-tyrosines during and after contraction. Additionally, the rate of tyrosine production increased in proportion to the percentage of maximal tension developed by the triceps surae muscles. These results directly demonstrate that .OH is produced in vivo in the skeletal muscle of cats during intermittent static contraction and that production can occur before the onset of fatigue.  相似文献   
23.
A double-blind clinical study was performed to evaluate prednisolone as treatment for idiopathic feline lower urinary tract disease. No differences in response were observed in prednisolone- and placebo-treated cats.  相似文献   
24.
25.
Apoptosis in the failing human heart   总被引:1,自引:0,他引:1  
BACKGROUND: Loss of myocytes is an important mechanism in the development of cardiac failure of either ischemic or nonischemic origin. However, whether programmed cell death (apoptosis) is implicated in the terminal stages of heart failure is not known. We therefore studied the magnitude of myocyte apoptosis in patients with intractable congestive heart failure. METHODS: Myocardial samples were obtained from the hearts of 36 patients who underwent cardiac transplantation and from the hearts of 3 patients who died soon after myocardial infarction. Samples from 11 normal hearts were used as controls. Apoptosis was evaluated histochemically, biochemically, and by a combination of histochemical analysis and confocal microscopy. The expression of two proto-oncogenes that influence apoptosis, BCL2 and BAX, was also determined. RESULTS: Heart failure was characterized morphologically by a 232-fold increase in myocyte apoptosis and biochemically by DNA laddering (an indicator of apoptosis). The histochemical demonstration of DNA-strand breaks in myocyte nuclei was coupled with the documentation of chromatin condensation and fragmentation by confocal microscopy. All these findings reflect apoptosis of myocytes. The percentage of myocytes labeled with BCL2 (which protects cells against apoptosis) was 1.8 times as high in the hearts of patients with cardiac failure as in the normal hearts, whereas labeling with BAX (which promotes apoptosis) remained constant. The near doubling of the expression of BCL2 in the cardiac tissue of patients with heart failure was confirmed by Western blotting. CONCLUSIONS: Programmed death of myocytes occurs in the decompensated human heart in spite of the enhanced expression of BCL2; this phenomenon may contribute to the progression of cardiac dysfunction.  相似文献   
26.
27.
28.
According to a 1991 study of sexual behavior based on a random sample of heterosexual undergraduates at a Midwestern university, 80% of the males and 73% of the females had experienced vaginal or anal intercourse. The average age at first vaginal intercourse was 17.2 years for both sexes. Seventeen percent of the sexually experienced males and 18% of the sexually experienced females had engaged in heterosexual anal intercourse; among these respondents, the average age at first anal intercourse was 20.3 for males and 19.1 for females. Although less than four years, on average, had elapsed since the respondents had first had vaginal intercourse, males reported an average of 8.0 lifetime vaginal-sex partners and females reported an average of 6.1. Overall, the findings from this random sample of students are similar to those from a 1988 convenience sample of the same college population.  相似文献   
29.
Older patients with diabetes mellitus or pulmonary diseases and those receiving immunosuppressive drugs are at an increased risk of infection with environmentally-acquired, opportunistic fungal diseases. Aspergillus most often produces invasive pulmonary or sinus infection in severely immuno-compromised patients. Chronic necrotizing pulmonary and sino-orbital aspergillosis present subacutely and are often misdiagnosed. Mucormycosis classically presents with rhinocerebral disease in diabetic patients with ketoacidosis, whereas pulmonary infection mimics invasive pulmonary aspergillosis and occurs mostly in patients who are neutropenic. Cryptococcal meningitis in the older patient may manifest simply as confusion. Amphotericin B is the preferred initial treatment for all three fungal infections.  相似文献   
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