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   341543篇
  免费   38252篇
  国内免费   192篇
  2018年   2947篇
  2017年   2790篇
  2016年   4030篇
  2015年   5593篇
  2014年   6500篇
  2013年   9135篇
  2012年   10382篇
  2011年   10420篇
  2010年   7091篇
  2009年   6388篇
  2008年   9215篇
  2007年   9695篇
  2006年   8911篇
  2005年   8614篇
  2004年   8333篇
  2003年   8071篇
  2002年   8058篇
  2001年   18368篇
  2000年   18588篇
  1999年   14320篇
  1998年   4356篇
  1997年   4581篇
  1996年   4408篇
  1995年   4102篇
  1994年   4039篇
  1993年   3864篇
  1992年   11623篇
  1991年   11279篇
  1990年   10845篇
  1989年   10394篇
  1988年   9630篇
  1987年   8976篇
  1986年   8186篇
  1985年   8086篇
  1984年   6508篇
  1983年   5671篇
  1982年   4201篇
  1981年   3702篇
  1980年   3431篇
  1979年   6215篇
  1978年   4640篇
  1977年   4204篇
  1976年   3843篇
  1975年   4431篇
  1974年   4584篇
  1973年   4483篇
  1972年   4165篇
  1971年   3576篇
  1970年   3239篇
  1969年   3030篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
801.
In these studies we describe the production of three mAb raised to an idiotype on an IgG anticasein antibody isolated from the serum of one IgA-deficient blood donor. These are IgM kappa and block the binding of casein Ag to anticasein antibody. Sera of unrelated IgA-deficient donors were tested for the presence of the idiotype; 15 of 56 IgA-deficient sera (25%) contain the anticasein idiotype, whereas 1 of 45 normal sera was positive. Anticasein antibodies as a whole were predominantly of the IgG1 and IgG3 subclass; idiotype-positive anticaseins are predominantly of the IgG1 subclass. For IgA-deficient donors, the relative amount of idiotype-positive anticasein antibody was correlated with the level of anticasein present in the serum. Studies were done to investigate the potential inheritance of the idiotype in families; in three of four families the idiotype was inherited in an apparent autosomal dominant pattern. Our data show that a common cross-reactive idiotype can be detected in the sera of IgA-deficient individuals and their family members. This suggests that V region markers may be conserved in this humoral immunodeficiency disease.  相似文献   
802.
This study was designed to assess the changes in fiber-type distribution of the extensor digitorum longus (EDL) muscle of the mouse during the first 21 days of age following neonatal sciatic neurectomy. Denervated and normal muscles were compared at 7, 14, and 21 days of age and the normal EDL was also studied at 1 day of age. Frozen sections of the EDL were treated histochemically to detect NADH-tetrazolium reductase and myosin ATPase reactions. Quantitative assessment included measurements of cross-sectional areas and fiber counting. Denervation resulted in muscle atrophy which was due primarily to a decrease in individual fiber area as opposed to fiber loss. Histochemical maturation of the EDL was severely affected by neonatal denervation during the first three postnatal weeks. By 21 days, two extrafusal fiber types which were both oxidative could be distinguished. One type was highly atrophied and resembled an immature fiber exhibiting myosin ATPase staining at both acid and alkaline preincubation conditions, whereas another type was less atrophied and showed myosin ATPase staining resembling fast-twitch (type IIA) fibers. These findings emphasize the importance of an intact nerve supply in determining the phenotypic expression of skeletal muscle, and point to the early postnatal period as a critical stage in fiber type differentiation.  相似文献   
803.
804.
The anatomical basis for the application of neurovascular pedicled muscle transfers of the digastric and stylohyoid muscles in the treatment of velopharynx incompetence is described. The fact that the neurovascular pedicle is located in the cranial third of the muscle bellies provides the safety of the operative procedure. The muscles have to be dissected with respect to that. The direction in which the transferred muscles pull is described. The muscle transposition is combined with the classic Wardill-Kilner operation to lengthen the soft palate. The transferred muscles have to avoid scar contraction and shortening of the soft palate and to gain a muscular function of the soft palate. The clinical use is justified in rare cases as demonstrated in one case.  相似文献   
805.
806.
807.
This article describes the calibration of a spectroscopic scanning instrument for the measurement of selected contaminants in a complex biological process stream. Its use is for the monitoring of a process in which contaminants are to be removed selectively by flocculation from yeast cell homogenate. The main contaminants are cell debris, protein, and RNA. A low-cost instrument has been developed for sensitivity in the region of the NIR spectrum (from 1900 to 2500 nm) where preliminary work found NIR signatures from cell debris, protein, and RNA. Calibration models have been derived using a multivariate method for concentrations of these contaminants, such as would be found after the flocculation process. Two strategies were compared for calibrating the NIR instrument. In one case, samples were prepared by adding materials representative of the contaminants to clarified yeast homogenate so the contaminant levels were well known but outside the range of interest. In the other case, where samples were like those from the process stream after flocculation and floc removal, there was uncertainty of analysis of contaminant level, but the calibration was in the range of interest. Calibration using process stream samples gave results close to those derived from traditional assays. When the calibration models were used to predict the contaminant concentrations in previously unseen samples, the correlation coefficients between measurements and predictions were above 90% in all cases but one. The prediction errors were similar to the errors in the traditional assays.  相似文献   
808.
809.
810.
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