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   2764篇
  免费   0篇
化学工业   14篇
建筑科学   5篇
轻工业   26篇
石油天然气   2篇
无线电   12篇
一般工业技术   13篇
冶金工业   2687篇
自动化技术   5篇
  2014年   1篇
  2013年   15篇
  2012年   2篇
  2010年   1篇
  2005年   1篇
  2004年   2篇
  2003年   5篇
  2001年   2篇
  2000年   2篇
  1999年   80篇
  1998年   818篇
  1997年   474篇
  1996年   306篇
  1995年   172篇
  1994年   136篇
  1993年   175篇
  1992年   34篇
  1991年   40篇
  1990年   27篇
  1989年   34篇
  1988年   49篇
  1987年   36篇
  1986年   30篇
  1985年   27篇
  1984年   2篇
  1983年   3篇
  1982年   13篇
  1981年   18篇
  1980年   23篇
  1979年   4篇
  1978年   6篇
  1977年   50篇
  1976年   155篇
  1975年   10篇
  1974年   1篇
  1971年   1篇
  1968年   1篇
  1967年   2篇
  1966年   1篇
  1957年   2篇
  1955年   3篇
排序方式: 共有2764条查询结果,搜索用时 31 毫秒
991.
992.
A 31% incidence of focal posterior knee pain was noted in our initial experience with all-inside meniscal repair using the absorbable Meniscal Arrow system (Bioscience, Tampere, Finland). The pain was transient, resolved by 6 months in all cases, and was unrelated to the length of implant. A typical case is presented to assist surgeons in counseling patients who experience transient posterior knee pain after meniscal repair with this system.  相似文献   
993.
OBJECTIVE: To determine changes in the incidence of candidemia in a neonatal intensive care unit (NICU) during a 15-year period (1981 to 1995) and to compare the prevalence and case fatality rates of Candida albicans and Candida parapsilosis infections. METHODS: A retrospective study was conducted of candidemia occurring in infants in a NICU between January 1, 1981, and December 31, 1995. Cases were identified through computerized searching of a microbiology blood culture database. Candidemia was considered contributory to mortality if death occurred within 3 days of positive blood cultures or if there was autopsy evidence of disseminated candidiasis. RESULTS: One hundred eleven cases of candidemia occurred in 107 infants, representing 1% of all NICU patients during the study period. The rate of candidemia in the NICU increased from 2.5 cases per 1000 admissions in 1981 to 1985, to 4.6 per 1000 admissions in 1986 to 1990 and to 28.5 per 1000 in 1991 to 1995 (P = 0.001). C. albicans was the predominant cause of candidemia between 1981 and 1990. C. parapsilosis was the most prevalent species between 1991 and 1995, causing 53 of 89 cases (60%). The mortality from C. albicans, 13 of 50 cases (26%), was significantly higher than the mortality from C. parapsilosis, 2 of 54 (4%) (P = 0.002; relative risk, 7; 95% confidence interval, 1.7 to 30). CONCLUSIONS: The rate of candidemia in our neonatal intensive care unit increased >11-fold in the 15 years from 1981 to 1995; the prevalent Candida species shifted from C. albicans to C. parapsilosis; and candidemia associated with C. albicans has significantly higher mortality than with C. parapsilosis.  相似文献   
994.
DR McEwen 《Canadian Metallurgical Quarterly》1994,59(1):225-32; quiz 235-7, 239-40
Long-term hemodialysis remains the most important support for patients with ESRD, and reliable vascular access is an essential component of this management plan. Recent refinements in AV fistula surgical techniques have produced this dependable, well-tolerated, long-term access route for hemodialysis.  相似文献   
995.
PURPOSE: The Octopus program Octosmart is able to classify visual fields into six classes. In the program a horizontal bar indicates these classes, and an indicator points to the most probable position, related to the measured pathology. The width of this dashed indicator shows the range of possible fluctuations in the measurement and, therefore, its precision. This study sets out to analyse the suitability of this display mode using other visual-field index data. METHODS: The visual fields of 83 glaucomatous eyes of 61 patients of various etiological groups and glaucoma suspects were studied for periods varying from 1 to 5 years in a retrospective study. All examinations were performed with the G1 Octopus program and analyzed with the Octosmart program. The statistical significance of linear trends of the visual-field indices, mean defect (MD) and corrected loss variance (CLV), and the class shown by the indicator (POI = position of indicator) were determined, and their regression coefficients were analyzed by means of a linear trend test as a function of time. RESULTS: Of the sample of 83 tested eyes, a total of 18 significant trends were recorded after five examinations. All visual-field indices showed a trend towards amelioration. CONCLUSIONS: The 18 significant trends observed must be attributed to perturbing long-term fluctuations and, despite their statistical significance, are of little clinical value. It is questionable whether an increased number of examinations per eye would have attenuated the threshold fluctuations sufficiently to make the change in field class more reliable.  相似文献   
996.
BACKGROUND: The surgical treatment of acute complicated type B aortic dissection continues to be a challenge and is still associated with high morbidity and mortality rates. METHODS: Seventy consecutive patients with an acute type B aortic dissection underwent an elephant trunk procedure through a median sternotomy during deep hypothermic circulatory arrest. An endoprosthesis that was 22 to 24 mm in diameter was inserted through an incision in the arch and held in place with only proximal sutures. RESULTS: The mean arrest time was 31.4 +/- 8.7 minutes, and it was possible to adequately position the endoluminal graft in every patient. The procedure was done in association with other procedures in 13 patients. There were six in-hospital deaths not related to the endoprosthesis, and four late deaths. Late reoperation was necessary in 6 patients to manage leakage at the proximal suture line. CONCLUSIONS: The insertion of an endoprosthesis through the arch for the management of a complicated acute type B dissection has several advantages over the conventional thoracotomy approach. The hospital mortality rate in this series of 70 patients was 20%, and the actuarial 5-year survival rate was 62.5%. We consider the elephant trunk procedure the treatment of choice in patients with type B acute dissections, regardless of whether the dissection is complicated or not.  相似文献   
997.
998.
Treatment of a skeletodental Class II vertical growth problem, combined with a severe arch length deficiency in both arches, presents a challenging orthodontic problem. This is the case report of a small-statured, 11-year, 10-month-old boy with a history of juvenile chronic arthritis and marked mandibular retrognathia who was treated with first premolar extractions in both arches. Unexpected favorable growth, with significant decrease of the mandibular plane angle over a long treatment period, provided a very satisfactory result. [This case report was presented to the American Board of Orthodontics in partial fulfillment of the requirements for the certification process.]  相似文献   
999.
To elucidate the mechanisms that facilitate tolerance at the maternal-fetal interface, we are investigating the role of genes that are involved in peripheral self-tolerance in couples with idiopathic recurrent miscarriage. CTLA-4 is a negative regulator of T-cell proliferation and has been associated with human autoimmune disease. An AT(n) polymorphism in the 3'-untranslated region (UTR) of the human gene results in AT stretches that vary in length from 16 to 46 bp. We hypothesized that long stretches of AT repeats would result in mRNA instability, and reduced fetal survival in humans. We examined the transmission of AT(n) alleles in 60 couples with a history of > or = 3 unexplained spontaneous abortions to their 51liveborn children and 10 abortuses. The shorter allele was transmitted from heterozygous mothers to 26 of 35 liveborn children (chi2 = 8.3, P = 0.0040) and to three of nine aborted fetuses (chi2 = 1.0, P = 0.317). The shorter allele was transmitted from heterozygous fathers to 15 of 32 liveborn children (chi2 =0.12, P=0.726) and to five of eight aborted fetuses (chi2 = 0.5, P = 0.480). Furthermore, liveborn fetuses who inherited smaller alleles were more likely to represent the first successful pregnancy than liveborn fetuses who inherited larger maternal alleles (Pexact = 0.044) and fetuses of first pregnancies that inherited the smaller allele were significantly more likely to survive to term (Pexact = 0.0086). The preferential transmission of maternally-inherited shorter alleles to liveborn children, but random transmission of paternally-inherited alleles, suggests that CTLA-4 may be imprinted in humans and that this gene may play a role in inducing or maintaining tolerance at the maternal-fetal interface.  相似文献   
1000.
We have recently shown that expression of the multidrug resistance-associated protein (MRP) gene is a powerful prognostic indicator in childhood neuroblastoma and have suggested that the MYCN oncogene may regulate MRP gene expression. To address this hypothesis, we have examined the relationship between MYCN and MRP gene expression in neuroblastoma tumours and cell lines. MYCN and MRP gene expression were highly correlated in 60 primary untreated tumours both with (P = 0.01) and without MYCN gene amplification (P < 0.0001). Like MRP, high MYCN gene expression was significantly associated with reduced survival, both in the overall study population and in older children without MYCN gene amplification (relative hazards = 13.33 and 19.61, respectively). Inhibition of MYCN, through the introduction of MYCN antisense RNA constructs into human neuroblastoma cells in vitro, resulted in decreased MRP gene expression, determined both by RNA-PCR and Western analysis. The data are consistent with MYCN influencing neuroblastoma outcome by regulating MRP gene expression.  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