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   182篇
  免费   9篇
  2022年   6篇
  2021年   1篇
  2020年   1篇
  2019年   1篇
  2018年   2篇
  2017年   2篇
  2016年   1篇
  2015年   11篇
  2014年   5篇
  2013年   9篇
  2012年   18篇
  2011年   8篇
  2010年   6篇
  2009年   9篇
  2008年   7篇
  2007年   10篇
  2006年   10篇
  2005年   8篇
  2004年   6篇
  2003年   11篇
  2002年   11篇
  2001年   9篇
  2000年   4篇
  1999年   6篇
  1997年   2篇
  1996年   3篇
  1995年   2篇
  1993年   1篇
  1991年   3篇
  1988年   3篇
  1987年   2篇
  1985年   3篇
  1984年   1篇
  1982年   1篇
  1981年   2篇
  1979年   2篇
  1978年   2篇
  1976年   2篇
排序方式: 共有191条查询结果,搜索用时 15 毫秒
111.
Hepatoid adenocarcinoma is an extrahepatic tumor characterized by morphological similarities to hepatocellular carcinoma. Hepatoid adenocarcinoma of the stomach is a cancer with an extremely poor prognosis with few cases reported. Here, we describe a 75-year-old Spanish man referred to our hospital with a history of abdominal pain, general fatigue, anorexia and sickness. Initial study revealed anemia, and computed tomography scan and abdominal ultrasonography showed multiple metastases to the liver with hepatocellular carcinoma characteristics in a liver with no cirrhotic change. Further study included a serum level of alpha-fetoprotein (AFP), which resulted markedly elevated, and a conclusive esophagogastroduodenoscopy describing an elevated tumour growing through the cardia and gastroesophageal junction with foci of necrosis and haemorrhage. Gastric biopsies of the tumor revealed poorly differenciated adenocarcinoma, with hepatoid differentiation. After a diagnosis of AFP-producing hepatoid adenocarcinoma of the stomach with multiple liver metastases was made, pallitive total gastrectomy, without liver resection, was performed. Patient recovered well after surgery, and entered into a palliative systemich chemotherapy protocol. Although this illness is recognized as having poor prognosis, the patient remains alive 8 months after the operation. Accurate diagnosis of hepatoid adenocarcinoma of the stomach is important, and should be suspected under certain circumstances. We describe this rare case of hepatoid adenocarcinoma of the stomach, and review the literature concerning the clinicopathological aspects.  相似文献   
112.
A technique for testing antianginal drugs has been developed measuring hemodynamic variables, such as heart rate, left ventricular pressure and its dp/dt, aortic root and coronary sinus pressure, Veragut's index and area under the curve of LVP and metabolic variables, such as A-V difference of oxygen and lactate, oxygen content in coronary sinus, percentage extraction of oxygen, excess lactate. Physiological experimental conditions included spontaneously breathing dogs, catheters introduced under X-rays control and closed chest. A commentary about activity criteria, usefulness and inconvenients of this technique is presented.  相似文献   
113.
114.
We examined the in vitro effects of tert-butylhydroperoxide (tBu-OOH) in human bronchial muscle. tert-Butylhydroperoxide produced concentration-dependent contractions of bronchial rings (maximum effect was 56.5 +/- 9.6% of contraction by 1 mM acetylcholine; effective concentration 50% was approximately 100 microM). tert-Butylhydroperoxide (0.5 mM)-induced contraction was enhanced by epithelial removal but abolished by indomethacin (cyclooxygenase inhibitor) and zileuton (lipoxygenase inhibitor). tert-Butylhydroperoxide produced a transient rise in intracellular calcium in human cultured airway smooth muscle cells (HCASMC). The bronchial reactivity to acetylcholine and histamine was not altered by tBu-OOH. In HCASMC, tBu-OOH (0.5 mM, 30 min) increased malondialdehyde levels (MDA; from 7.80 +/- 0.83 to 26.82 +/- 1.49 nmol mg(-1) protein), accompanied by a decrease of reduced glutathione (GSH; from 16.7 +/- 2.6 to 6.9 +/- 1.9 nmol mg(-1) protein) and an increase of oxidized glutathione (from 0.09 +/- 0.03 to 0.18 +/- 0.03 nmol mg(-1) protein). N-acetylcysteine (0.3 mM) inhibited by approximately 60% the bronchial contraction resulting from tBu-OOH (0.5 mM) and protected cultured cells exposed to tBu-OOH (MDA was lowered to 19.51 +/- 1.19 nmol mg(-1) protein, and GSH content was replenished). In summary, tBu-OOH caused contraction of human bronchial muscle mediated by release of cyclo-oxygenase and lipoxygenase products without producing airways hyperreactivity. N-acetylcysteine decreases tBu-OOH-induced contraction and protects human cultured airway smooth muscle cells exposed to tBu-OOH.  相似文献   
115.
116.
The optic disc develops at the interface between optic stalk and retina, and enables both the exit of visual fibres and the entrance of mesenchymal cells that will form the hyaloid artery. In spite of the importance of the optic disc for eye function, little is known about the mechanisms that control its development. Here, we show that in mouse embryos, retinal fissure precursors can be recognised by the expression of netrin 1 and the overlapping distribution of both optic stalk (Pax2, Vax1) and ventral neural retina markers (Vax2, Raldh3). We also show that in the absence of Bmp7, fissure formation is not initiated. This absence is associated with a reduced cell proliferation and apoptosis in the proximoventral quadrant of the optic cup, lack of the hyaloid artery, optic nerve aplasia, and intra-retinal misrouting of RGC axons. BMP7 addition to organotypic cultures of optic vesicles from Bmp7-/- embryos rescues Pax2 expression in the ventral region, while follistatin, a BMP7 antagonist, prevents it in early, but not in late, optic vesicle cultures from wild-type embryos. The presence of Pax2-positive cells in late optic cup is instead abolished by interfering with Shh signalling. Furthermore, SHH addition re-establishes Pax2 expression in late optic cups derived from ocular retardation (or) embryos, where optic disc development is impaired owing to the near absence of SHH-producing RGC. Collectively, these data indicate that BMP7 is required for retinal fissure formation and that its activity is needed, before SHH signalling, for the generation of PAX2-positive cells at the optic disc.  相似文献   
117.
Ogura cytoplasmic male sterility (CMS) occurs naturally in radishand has been introduced into rapeseed (Brassica napus) by protoplastfusion. As with all CMS systems, it involves a constitutivelyexpressed mitochondrial gene which induces male sterility tootherwise hermaphroditic plants (so they become females) anda nuclear gene named restorer of fertility that restores pollenproduction in plants carrying a sterility-inducing cytoplasm.A correlative approach using light and electron microscopy wasapplied to define what stages throughout development were affectedand the subcellular events leading to the abortion of the developingpollen grains upon the expression of the mitochondrial protein.Three central stages of development (tetrad, mid-microsporeand vacuolate microspore) were compared between fertile, restored,and sterile plants. At each stage observed, the pollen in fertileand restored plants had similar cellular structures and organization.The deleterious effect of the sterility protein expression startedas early as the tetrad stage. No typical mitochondria were identifiedin the tapetum at any developmental stage and in the vacuolatemicrospores of the sterile plants. In addition, some strikingultrastructural alterations of the cell's organization werealso observed compared with the normal pattern of development.The results showed that Ogu-INRA CMS was due to premature celldeath events of the tapetal cells, presumably by an autolysisprocess rather than a normal PCD, which impairs pollen developmentat the vacuolate microspore stage, in the absence of functionalmitochondria. Key words: Brassica napus, cell death, light and electron microscopy, mitochondria, plastids, pollen development, Ogu-INRA cytoplasmic male sterility, transgenic-restored plants, tapetum Received 30 September 2007; Revised 11 December 2007 Accepted 20 December 2007  相似文献   
118.
Modification of nucleolar components by growth temperature in meristems   总被引:3,自引:0,他引:3  
Growth temperature modifies the cycle time in Allium cepa L. root meristems, affecting neither the cell size nor the relative duration of the cycle phases. It was to be expected that a similar nucleolus would be found whose activity was merely modified by temperature as any other enzymatic reaction. However, stereology of nucleoli growing at two physiological temperatures (10 and 25 °C) showed that both the fibrillar and granular components were 1.3 and 2 times respectively more abundant at the lower temperature. These nucleoli had also twice as many active nucleolar RNA polymerases as shown after the in situ assay.  相似文献   
119.
In order to study the molecular regulation of flower development in the monoecious species oil palm (Elaeis guineensis), cDNAs of 12 MADS box genes from this plant belonging to seven distinct subfamilies were previously isolated and characterized. Here studies carried out on five of these genes, each likely to be involved in floral morphogenesis: EgSQUA1 (SQUAMOSA subfamily); EgAGL2-1 (AGL2 subfamily); EgGLO2 (GLOBOSA subfamily); EgDEF1 (DEFICIENS subfamily); and EgAG2 (AGAMOUS subfamily), are described. In order to determine where and when in the plant these genes are likely to function, their spatial and temporal patterns of expression were studied during the development of male and female inflorescences, either of normal phenotype or displaying a homeotic flowering abnormality known as mantled. In parallel, the phenotypic effects of ectopically expressing these genes in transgenic Arabidopsis thaliana plants were analysed. The data suggest a broad conservation of floral homeotic gene functions between oil palm and previously described model species, although a few minor variations in the zones of activity of certain genes cannot be excluded. The data also indicate distinct molecular identities for the morphologically similar floral organs of whorls 1 and 2. They also reveal reduced expression of putative B, C/D, and E class genes in mantled flowers, which undergo a homeotic transformation comparable to B class mutants of model species.  相似文献   
120.
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