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   1376359篇
  免费   128761篇
  国内免费   1487篇
  1506607篇
  2021年   17926篇
  2019年   16232篇
  2018年   17878篇
  2017年   16565篇
  2016年   28209篇
  2015年   42565篇
  2014年   50622篇
  2013年   76927篇
  2012年   37723篇
  2011年   26572篇
  2010年   43866篇
  2009年   45237篇
  2008年   24965篇
  2007年   23022篇
  2006年   28124篇
  2005年   29173篇
  2004年   28115篇
  2003年   25969篇
  2002年   23987篇
  2001年   36064篇
  2000年   33466篇
  1999年   32909篇
  1998年   25823篇
  1997年   25782篇
  1996年   25223篇
  1995年   23409篇
  1994年   23167篇
  1993年   22423篇
  1992年   28822篇
  1991年   27384篇
  1990年   25675篇
  1989年   26409篇
  1988年   24196篇
  1987年   23089篇
  1986年   21944篇
  1985年   23814篇
  1984年   23370篇
  1983年   20727篇
  1982年   21115篇
  1981年   20159篇
  1980年   18938篇
  1979年   19530篇
  1978年   18370篇
  1977年   17559篇
  1976年   16715篇
  1975年   16149篇
  1974年   16552篇
  1973年   16835篇
  1972年   14263篇
  1971年   13104篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
These siblings of a Czech family aged 21, 19 and 6 years, respectively, with congenital dyserythropoietic anemia, type II, (HEMPAS) are reported. In two elder siblings ferrokinetic studies revealed a rapid plasma 59Fe clearance, markedly decreased erythrocyte incorporation and shortened 51Cr red-cell survival. Direct anti-globulin test was found positive in one of them. Further investigations revealed low values of blood plasma cholesterol, total lipids, beta-lipoproteins, beta-carotine and vitamin E and A as well as low values of the prothrombin complex. Liver biopsy demonstrated siderosis and disseminated intravascular coagulation in the liver in both patients. The possible reasons for these humoral aberrations are discussed.  相似文献   
992.
993.
994.
Summary It has been suggested that the immune system might figure prominently in the regulation of forelimb regeneration. However, neither the nature of this influence nor the aspect(s) of regeneration influenced are clearly known. The determination of which components of the immune system are indispensable for regeneration would be a logical first step in attempting to address such questions. This investigation, therefore, examined the effects of removing the spleen, a major lymphoid organ in the newt, upon the progress of regeneration. Splenectomies performed concomitantly with or after forelimb amputation failed to alter the time course of regeneration. Splenectomies, but not sham-splenectomies, performed prior to amputation reduced the time required to achieve successive stages of regeneration under some, but not all conditions, i.e., when performed 10–20 days before amputation, during the late fall and winter. Up until 35 days after amputation, no gross morphological distortions were observed as a result of splenectomy. It was concluded that the spleen is not required for regeneration to occur.Portions of this work constitute part of the thesis submitted by M.E. Fini in partial fulfillment of the requirements for the M.S. degree in Biology at Boston College  相似文献   
995.
The use of hormone replacement to support limb regeneration in hypophysectomized newts has been the subject of many investigations. Growth hormone, as well as prolactin (PL) in combination with exogenously supplied thyroxine, have all been shown to he effective. However, the bovine growth hormone used to support limb regeneration was contaminated by prolactin and thyroidstimulating hormone (TSH). The present investigation evaluates the significance of (1) prolactin contamination and (2) endogenous thyroxine synthesis resulting from TSH contamination on limb regeneration in hypophysectomized newts. The effect of supplying exogenous thyroxine was also evaluated. Our studies showed that when hypophysectomized newts were injected with contamination levels of PL and TSH, regeneration occurred, suggesting that the newt's thyroid synthesized sufficient thyroxine to support a prolactin-thyroxine synergism. The endogenous thyroxine was synthesized by thyroid glands that were indistinguishable from those of saline-injected, hypophysectomized controls.  相似文献   
996.
997.
Abstract In a 2-year field survey, the phylloplane mycoflora on the haulm base of wheat was studied by the dilution plate technique. No significant colonisation was registered before the end of May. Cladosporium spp., 'white' and 'red' yeasts were found to be the most abundant fungi.  相似文献   
998.
Cellular fatty acid composition of Leuconostoc oenos   总被引:3,自引:0,他引:3  
The cellular fatty acid composition of 70 lactic acid bacteria was examined by capillary gas chromatography. Fifty-four Leuconostoc oenos strains, including three reference, type strains from the other Leuconostoc spp., nine Pediococcus spp. and two Lactobacillus spp. were studied. Eighteen fatty acids were determined, of which 10 were identified by gas chromatography-mass spectrometry. The relative percentages of the 18 fatty acids of the Leuconostoc strains were analyzed numerically and grouped using the unweighted pair-group method. Results show that four clusters could be defined at r = 0.920, with five strains unassigned. The major fatty acids of the Leuc. oenos strains were found to be palmitic acid (C16:0), palmitoleic acid (C16:1–9), oleic acid (C18: 1–9), vaccenic acid (C18: 1–11), dihyrosterculic acid (C19-cyclopropane-9) and lactobacillic acid (C19-cyclopropane-11). It was mainly on the basis of the amounts of oleic acid and the C19-cyclopropane fatty acids that the strains of Leuc. oenos could be distinguished from each other. This is the first report of the occurrence of dihydrosterculic acid in lactic acid bacteria. For the majority of Leuc. oenos strains, the result obtained with the cellular fatty acid analysis confirmed the phenotypic relationships.  相似文献   
999.
Analogs of the molluscan neuropeptide FMRFamide were tested on four different molluscan muscle preparations which show qualitatively different responses to the peptide; the structure-activity relations are basically similar, but not identical. The C-terminal amide and the Arg3 residue are critical for FMRFamide-like activity on all four preparations. In contrast, analogs extended at the N-terminal or with conservative substitutions for the Phe1 or Met2 residue are approximately equipotent to FMRFamide. These structural requirements parallel those for the C-terminal tetrapeptide amide of gastrin.  相似文献   
1000.
Gari starter cultures (Gastat) were developed by mixing pure single strains of the organisms that ferment cassava. They were propagated and maintained as granules on dried cocoyam slurry. The cultures were tested for fermentative and acid-producing activity. The acidity produced at 30°C varied from 0.07% to 0.85% lactic acid with maximum levels occurring after 48 h. High levels of reducing sugar were produced during the first 24 h. The amounts produced were about 50% more than those from the self-inoculated cassava. The quality of the gari produced by the starter cultures was good and well accepted. The texture was similar to that produced by natural fermentation. These results highlight the possibility of using starter cultures in the large-scale production of gari.  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