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   564023篇
  免费   7334篇
  国内免费   1850篇
电工技术   10695篇
综合类   454篇
化学工业   82490篇
金属工艺   20058篇
机械仪表   15838篇
建筑科学   14673篇
矿业工程   1548篇
能源动力   14552篇
轻工业   53281篇
水利工程   4562篇
石油天然气   4537篇
武器工业   20篇
无线电   74939篇
一般工业技术   104282篇
冶金工业   112952篇
原子能技术   8278篇
自动化技术   50048篇
  2021年   3622篇
  2019年   3463篇
  2018年   5492篇
  2017年   5578篇
  2016年   5860篇
  2015年   4584篇
  2014年   7621篇
  2013年   25295篇
  2012年   13392篇
  2011年   19050篇
  2010年   14886篇
  2009年   17203篇
  2008年   18260篇
  2007年   18721篇
  2006年   16873篇
  2005年   15740篇
  2004年   15346篇
  2003年   14911篇
  2002年   14450篇
  2001年   14854篇
  2000年   13855篇
  1999年   14813篇
  1998年   36614篇
  1997年   25820篇
  1996年   20146篇
  1995年   15376篇
  1994年   13666篇
  1993年   13353篇
  1992年   9602篇
  1991年   9241篇
  1990年   8826篇
  1989年   8458篇
  1988年   8021篇
  1987年   6690篇
  1986年   6679篇
  1985年   8031篇
  1984年   7392篇
  1983年   6462篇
  1982年   5999篇
  1981年   6124篇
  1980年   5616篇
  1979年   5397篇
  1978年   5126篇
  1977年   6242篇
  1976年   8421篇
  1975年   4291篇
  1974年   4121篇
  1973年   3959篇
  1972年   3250篇
  1971年   2797篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
The incidence of Campylobacter jejuni and Campylobacter coli in broiler farms was 33.9% (19/56). C. jejuni-positive flocks accounted for 20.0% (17/85) and C. coli-positive ones was 4.7% (4/85). There were 14 patterns (fla type) of restriction fragment length polymorphism (RFLP) of flagellin A gene among these 22 strains of C. jejuni and C. coli including the standard strain C. jejuni ATCC 33560. Different fla types of Campylobacter were isolated from broilers in different growing cycles on the same farms. Four strains of C. jejuni were isolated from four breeder farms and four fla types of C. jejuni were detected from their progenies reared on growing farms. Three fla types of C. jejuni detected from the progenies were different from those of each breeder. Also, the other three fla types of C. jejuni were detected from different progenies of each growing farm during the next growing cycle. These findings indicate that the RFLP analysis may contribute to epidemiological studies of C. jejuni and C. coli contamination of broilers and suggest the risk of contamination with different types of Campylobacter in every growing cycle of broilers on the farm even on the same farm. They also supported that there was little likeliness of the vertical transmission of C. jejuni and C. coli from breeders to broilers.  相似文献   
993.
994.
BACKGROUND AND STUDY AIMS: Granular cell tumors of the esophagus are rare tumors. A definite diagnosis is achieved by endoscopic biopsies in only 50% of cases. Endoscopic ultrasonography (EUS) is the best procedure in the evaluation of upper gastrointestinal tract submucosal tumors. The aim of this study was to describe the endosonographic findings of esophageal granular cell tumors. METHODS: From January 1989 to March 1994, 15 patients with 21 granular cell tumors which had negative biopsies were examined by EUS (Olympus GF UM3 or GF UM20,7,5 and 12 MHz). In five cases, the tumor was also studied with a 20 MHz Olympus miniprobe. The final histological diagnoses were obtained by subsequent endoscopic snare resection in 20 cases and surgically in one case. RESULTS: The endosonographic features (with the GF UM3 or GF UM20) of esophageal granular cell tumors were: a) a tumor size of less than 2 cm in 95% of cases; b) an hypoechoic solid pattern in 100% of cases; c) a tumor arising in the inner layers in 95% (second echo-poor layer n=15; third echo-rich layer n=5). In one case, the endosonographic finding was transmural malignant infiltration of the esophageal wall (histologically confirmed). CONCLUSION: When a granular cell tumor of the esophagus is suspected, EUS can show the inner layer location of the tumor and thus contribute to planning the endoscopic resection or follow up. When the tumor also invades the outer layers, EUS can contribute to planning the surgical resection.  相似文献   
995.
996.
997.
Penetrating injuries of the eye are an important cause of unilateral visual loss. We studied a series of 82 cases of penetrating injuries treated here from 1987 through 1993. The injuries were caused by sharp objects in 66% and blunt trauma in 6%. The prognosis after a penetrating injury is greatly influenced by the nature of the injury and the extent of the initial drainage. Among factors associated with an unfavorable visual outcome were diminished preoperative visual acuity and scleral wounds with dense vitreous hemorrhage.  相似文献   
998.
999.
1000.
The Jervell and Lange-Nielsen syndrome (JLNS) comprises profound congenital sensorineural deafness associated with syncopal episodes. These are caused by ventricular arrhythmias secondary to abnormal repolarisation, manifested by a prolonged QT interval on the electrocardiogram. Recently, in families with JLNS, Neyroud et al. reported homozygosity for a single mutation in KVLQT1 , a gene which has previously been shown to be mutated in families with dominantly inherited isolated long QT syndrome [Neyroud et al . (1997) Nature Genet ., 15, 186-189]. We have analysed a group of families with JLNS and shown that the majority are consistent with mutation at this locus: five families of differing ethnic backgrounds were homozygous by descent for markers close to the KVLQT1 gene and a further three families from the same geographical region were shown to be homozygous for a common haplotype and to have the same homozygous mutation of the KVLQT1 gene. However, analysis of a single small consanguineous family excluded linkage to the KVLQT1 gene, establishing genetic heterogeneity in JLNS. The affected children in this family were homozygous by descent for markers on chromosome 21, in a region containing the gene IsK . This codes for a transmembrane protein known to associate with KVLQT1 to form the slow component of the delayed rectifier potassium channel. Sequencing of the affected boys showed a homozygous mutation, demonstrating that mutation in the IsK gene may be a rare cause of JLNS and that an indistinguishable phenotype can arise from mutations in either of the two interacting molecules.  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