首页 | 官方网站   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   6390篇
  免费   1篇
工业技术   6391篇
  2019年   1篇
  2017年   1篇
  2011年   1篇
  2010年   2篇
  2009年   1篇
  2008年   1篇
  2007年   4篇
  2006年   1篇
  2005年   4篇
  2004年   7篇
  2003年   2篇
  2000年   1篇
  1999年   179篇
  1998年   2021篇
  1997年   1130篇
  1996年   726篇
  1995年   370篇
  1994年   327篇
  1993年   385篇
  1992年   42篇
  1991年   93篇
  1990年   68篇
  1989年   77篇
  1988年   76篇
  1987年   84篇
  1986年   72篇
  1985年   69篇
  1984年   3篇
  1983年   12篇
  1982年   34篇
  1981年   44篇
  1980年   38篇
  1979年   2篇
  1978年   17篇
  1977年   158篇
  1976年   317篇
  1975年   13篇
  1965年   1篇
  1955年   7篇
排序方式: 共有6391条查询结果,搜索用时 15 毫秒
101.
102.
103.
In Study One, a sample of 230 college students were asked to estimate the abuse potential and lethality of commonly used recreational drugs, both licit and illicit. In Study Two, a sample of 103 degreed nurses were asked to estimate the lethality of the same recreational drugs. The findings indicate that the illicit drugs under consideration are perceived as presenting the greatest danger to the user and that dangers attributed to the use of licit recreational drugs are generally minimized. Perception of danger was found to be unaffected by exposure to reported drug education programs. Results are discussed in terms of public health implications.  相似文献   
104.
105.
106.
BACKGROUND: The efficacy and predictability of photorefractive keratectomy and radial keratotomy become increasingly relevant. This retrospective study compares one surgeon's experience with photorefractive keratectomy and radial keratotomy over a 3-year period from 1990 to 1993. METHODS: Photorefractive keratectomy was performed on 103 eyes of 76 patients that met the inclusion criteria for the phase IIb, phase III, and phototherapeutic keratectomy studies as delineated by the United States Food and Drug Administration. Radial keratotomy was performed on 117 eyes of 81 patients with up to 9.00 diopters (D) of myopia. RESULTS: In the photorefractive keratectomy group, 83% of the eyes achieved uncorrected visual acuity of at least 20/40; 37% saw 20/20; 88% had a refraction within 1.00 D of emmetropia, and 63% within 0.50 D of emmetropia. For the radial keratotomy group, 85% of the eyes achieved an uncorrected visual acuity of 20/40 or better; 27% saw 20/20; 88% had a refraction within 1.00 D of emmetropia; and 55% within 0.50 D of emmetropia. There were no serious complications, and only one single eye in each of the photorefractive keratectomy and radial keratotomy groups lost two lines or more of spectacle-corrected visual acuity. CONCLUSION: Photorefractive keratectomy and radial keratotomy are both effective procedures, and result in similar refractive outcomes for myopia of -1.00 to -9.00 D.  相似文献   
107.
108.
This article reports on the histologic findings from a larger study that was designed to investigate whether the attachment of scar tissue to underlying bone, which is normally found after palatal surgery, can be prevented by using biodegradable poly-(L-lactic) acid membranes. Von Langenbeck's procedure was simulated in 12-week-old beagle dogs without clefts. In one group normal wound healing was allowed. In two groups, membranes were inserted immediately after surgery or 3 weeks thereafter. Sham and control groups were also included. Histologic evaluation was carried out at regular intervals. Reports have been published on other aspects, such as clinical wound healing, contraction and maxillary arch development in beagle dogs following this treatment. After direct implantation of membranes, wound healing was retarded. Disintegration of the membranes started soon after implantation and remaining particles were surrounded by a fibroblastic sheath and a fibrous capsule. At sites where membrane particles persisted, attachment of the scar tissue to the underlying bone by Sharpey's fibers was prevented.  相似文献   
109.
110.
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-23

京公网安备 11010802026262号