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   48925篇
  免费   2169篇
  国内免费   62篇
电工技术   343篇
综合类   40篇
化学工业   10638篇
金属工艺   930篇
机械仪表   964篇
建筑科学   1469篇
矿业工程   99篇
能源动力   1299篇
轻工业   8328篇
水利工程   441篇
石油天然气   216篇
武器工业   7篇
无线电   1876篇
一般工业技术   7500篇
冶金工业   10247篇
原子能技术   273篇
自动化技术   6486篇
  2024年   92篇
  2023年   388篇
  2022年   833篇
  2021年   1307篇
  2020年   925篇
  2019年   1110篇
  2018年   1629篇
  2017年   1624篇
  2016年   1726篇
  2015年   1361篇
  2014年   1733篇
  2013年   3442篇
  2012年   2699篇
  2011年   2907篇
  2010年   2276篇
  2009年   2176篇
  2008年   2004篇
  2007年   1780篇
  2006年   1375篇
  2005年   1210篇
  2004年   1114篇
  2003年   995篇
  2002年   929篇
  2001年   666篇
  2000年   661篇
  1999年   711篇
  1998年   3187篇
  1997年   2162篇
  1996年   1433篇
  1995年   840篇
  1994年   686篇
  1993年   764篇
  1992年   280篇
  1991年   284篇
  1990年   204篇
  1989年   227篇
  1988年   220篇
  1987年   200篇
  1986年   165篇
  1985年   215篇
  1984年   168篇
  1983年   131篇
  1982年   163篇
  1981年   178篇
  1980年   190篇
  1979年   97篇
  1978年   97篇
  1977年   350篇
  1976年   744篇
  1973年   84篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
132.
A rearranged tpr-met oncogene was identified in a MNNG-transformed human Xeroderma pigmentosum (XP) cell line (ASKMN). A 2016 bp cDNA was cloned and sequenced, disclosing an ORF with a coding capacity for a 523 aa protein. The sequence of this tpr-met cDNA was very similar to that previously reported in another human MNNG-transformed cell line (MNNG-HOS).  相似文献   
133.
134.
135.
136.
Two studies designed to investigate the effect of recombinant human erythropoietin (rHuEPO) treatment of anemia in chronic dialysis patients on hemocompatibility were conducted. Study 1, whose main aim was to establish whether treatment with rHuEPO enhances coagulation activation during dialysis, included 15 patients before rHuEPO therapy at a mean hematocrit (HCT) of 22.3% and then during therapy at a HCT of 29.3%. The plasma concentrations of the thrombin-antithrombin III complex were not higher during rHuEPO therapy than before it when performing hemodialysis with a Cuprophan membrane. No significant difference was demonstrated either in the values of activated clotting times (Hemochron), thrombocyte or white blood cell counts (Coulter S+II), or in plasma C5a concentrations (ELISA) established during dialysis sessions before and during rHuEPO therapy. In Study 2, which focused primarily on the question of whether or not rHuEPO therapy increases thrombocyte activation during hemodialysis, 8 patients on chronic dialysis were examined both before therapy at a mean HCT value of 22.1% and during rHuEPO therapy at a HCT of 31.5%, invariably during dialysis with either a Cuprophan or polyacrylonitrile (AN69HF) membrane. The plasma concentrations of beta-thromboglobulin (ELISA) did not differ between the examinations made during rHuEPO and before rHuEPO therapy; however, statistically significant differences were found between dialysis sessions involving Cuprophan and AN69HF membranes. No significant difference between examination before and during rHuEPO was demonstrated in activated clotting time nor thrombocyte and white blood cell counts in this study either. The authors conclude that rHuEPO therapy does not enhance coagulation activation during hemodialysis, does not have an effect on thrombocyte activation, and does not influence complement activation and changes in white blood cell counts.  相似文献   
137.
The activation of oncogenes and the mutation/deletion of suppressor genes may be involved in tumor heterogeneity. In an attempt to study tumor heterogeneity, we transformed cell lines from epithelial (PAM 212), mesenchymal (NIH-3T3), or melanocytic origin (L-BIOBR) with the wild type E1a oncogene. To make the cell lines tumorigenic, cells were infected with Harvey sarcoma virus carrying the v-H-ras oncogene. The transformed cells were injected into nude mice and the tumors studied by optical and electron microscopy. The tumors formed by v-H-ras-transformed cells consisted of epitheliod melanomas, spindle cells sarcomas and poorly-differentiated carcinomas, depending on the cell of origin. In contrast, the tumors obtained from cells also carrying the E1a oncogene showed a predominant small and undifferentiated cell pattern regardless of the cell of origin. We conclude that the E1a oncogene products induce a negative control of differentiation, independent of the cell type, and that tumors formed by cells carrying the E1a oncogene display an undifferentiated cell pattern.  相似文献   
138.
139.
Psychosomatic symptoms among children are believed to be commonplace. In this investigation by questionnaire, 47% of 1333 schoolchildren reported one or several symptoms, such as recurrent abdominal pain, headache, chest pains, loss of appetite and disturbances in bowel function. Coexistence of such symptoms was considerable and if a child had one of these, the probability that it would have one or more other symptoms was significantly increased. This correlation may strengthen both the suspicion that these symptoms are often psychosomatic and the idea that they have common CNS origin. There were appreciable differences in the frequency of the symptoms, between children at the more socially stable schools and schools with social problems. In the latter, the frequencies of symptoms differed between Swedish and immigrant children, which was not the case in the more socially stable schools.  相似文献   
140.
OBJECTIVE: Retrospective study of urological complications in our series of reno-pancreatic transplants. MATERIAL AND METHODS: Between February 1983 and May 1994 our group has conducted 93 RPT, 80 of which, mean age 36 +/- 6 years (24-54 years), are studied in this paper: 57 male and 23 female with an average time in dialysis of 20 +/- 15 months (0-84 months) and diabetes evolution of 21 +/- 5 years (11-37 years). RESULTS: Actuarial annual survival of patient, renal graft and pancreatic graft has been 85%, 79% and 74% respectively. Haematuria: 25% incidence, with graft pancreatitis etiology in 16 cases, rejection in 8 and urinary fistula in 6. Urinary infection: 85% incidence, symptomatic in 23 patients (29%) and asymptomatic in the remaining cases. Dysuria, urethritis and urethral stenosis: 14 patients, all male, most with both conditions associated. Reconversion of pancreatic exocrine secretion by intestinal route was performed in 7 patients. Urinary fistula: secondary to surgery in 9 cases and rejection in 4. Etiology of one case remained unknown. In 4 cases it was resolved with conservative treatment, and with surgical correction in 8. One patient required pancreatic transplantectomy and one patient died of AMI. CONCLUSIONS: Urological complication in RPT account for a significant morbidity, urinary fistula being the one with greater repercussion on the patient and pancreatic graft survival.  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