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   847篇
  免费   36篇
  2022年   3篇
  2021年   7篇
  2020年   6篇
  2019年   6篇
  2018年   13篇
  2017年   8篇
  2016年   19篇
  2015年   24篇
  2014年   19篇
  2013年   33篇
  2012年   51篇
  2011年   36篇
  2010年   25篇
  2009年   26篇
  2008年   45篇
  2007年   43篇
  2006年   58篇
  2005年   38篇
  2004年   63篇
  2003年   48篇
  2002年   60篇
  2001年   18篇
  2000年   23篇
  1999年   23篇
  1998年   18篇
  1997年   9篇
  1996年   9篇
  1995年   16篇
  1994年   11篇
  1993年   5篇
  1992年   13篇
  1991年   12篇
  1990年   8篇
  1989年   10篇
  1988年   6篇
  1987年   9篇
  1986年   10篇
  1985年   3篇
  1984年   6篇
  1983年   3篇
  1981年   3篇
  1978年   3篇
  1977年   3篇
  1975年   3篇
  1973年   3篇
  1971年   2篇
  1970年   2篇
  1968年   2篇
  1967年   2篇
  1966年   4篇
排序方式: 共有883条查询结果,搜索用时 625 毫秒
1.
We have previously demonstrated that blood pressure elevation by acute blood volume expansion is volume-dependent during the infusion period and resistance-dependent in the post-infusion period in normal anesthetized dogs, and that such an increase in blood pressure is associated with a potentiation of the pressor response to norepinephrine. To evaluate the possible renal contribution to these hemodynamic changes, blood volume expansion was performed for 1 h with dextran dissolved in lactated Ringer's solution (20 ml/kg) in 15 nephrectomized dogs. The mean blood pressure, cardiac output and total peripheral resistance at the end of infusion were 126%, 225% and 60%, respectively; 3 h after volume expansion they were 126%, 151%, and 92% respectively. However, in 4 dogs, there was an increase in mean blood pressure (138%) 3 h after volume expansion. This was thought to result from an increase in the total peripheral resistance (133%) associated with the recovery of cardiac output (106%). The pressor response to norepinephrine (0.5 microgram/kg) was potentiated after volume expansion. These results indicate that the handling of volume by the kidney contributed to the maintenance of an elevated level of cardiac output. However, nephrectomy did not seem to interfere with the hemodynamic switching of the causative factor for blood pressure elevation from increased cardiac output to increased total peripheral resistance. Neither was the potentiation of pressor response to norepinephrine affected.  相似文献   
2.
3.
The binding site for calcitonin gene-related peptide (CGRP) was solubilized with 3-[(3-cholamidopropyl)dimethylammonio]-1-propane sulfonate (CHAPS) in an active form from porcine spinal cord. 125I-labeled human alpha-CGRP (125I-CGRP) binding to the solubilized protein was determined by filtration using a GF/B glass filter. The maximal binding activity (approximately 60% of the crude membrane fraction) was obtained with 5 mM CHAPS. 125I-CGRP binding to the solubilized protein was of high affinity, saturability, and high specificity, having KD and Bmax values of 3.69 pM and 338 fmol/mg of protein, respectively. The binding activity was eluted in a single peak with a molecular mass of 400,000 daltons by gel filtration on TSK gel G4000SW. These results suggest that the solubilized protein may be responsible for the specific binding site.  相似文献   
4.
Summary The immunohistochemical localization of keratins in the oral epithelia of several mammals was investigated using the monoclonal antibodies to keratins, PKK1 (41–56 kilodaltons) and KL1 (55–57 kilodaltons). The staining patterns obtained in different locations of the oral mucosa and of the skin epidermis were compared. In the papillae on the dorsal surface of the tongue, some areas exhibited marked PKK1 staining, while other area were PKK1 negative. In general, rodent oral epithelia were negative for PKK1 in the basal layer, while comparatively strong PKK1 staining was observed in cells of the upper spinous layer. In the epidermis, positive PKK1 reactions were confined to the basal layer, while KL1 staining was occasionally seen in the basal layer of oral epithelia. In cats, dogs, and monkeys, different PKK1 and KL1 binding patterns were observed in oral epithelia. Also, the distribution in oral epithelia differed from that seen in the epidermis of these animals. In the epidermis, the distribution of PKK1 and KL1 was regular, with PKK1 usually being confined to the basal layer, while KL1 binding was found in the spinous and granular cell layers, and was dependent on the degree of keratinization. In the animals studies, keratin expression as detected by PKK1 and KL1-was different in the skin epidermis and oral epithelia, and the localization of these keratins differed in the various types of oral mucosa.  相似文献   
5.
The aim of this study was to investigate the influence of methodological factors on the interaction of bovine spermatozoa and homologous cervical mucus. Cervical mucus was obtained from three cows during estrus. To evaluate the penetration ability of frozen-thawed semen samples of five different bulls, fresh mucus as well as frozen-thawed mucus, stored for 1, 10 or 30 d in liquid nitrogen, were used. Penetration assays were performed at 38 degrees C for 10 min, and the most advanced spermatozoon was located and the distance determined. Semen parameters were examined by a computer-assisted videomicrographic system. Conservation of mucus in liquid nitrogen for up to 30 d did not influence the results of the penetration assay. In contrast, the mucus of individual cows showed significant differences in the migration distance of spermatozoa. Sperm concentration, mean velocity and number of forward moving spermatozoa were significantly correlated with mucus penetration. These results demonstrated that the mucus penetration assay in cattle can be performed by dividing a mucus sample from a cow into many portions and storing the sample in liquid nitrogen.  相似文献   
6.
To manipulate the quantity and quality of storage components in Brassica napus seeds, we have constructed an antisense gene for the storage protein napin. The antisense gene was driven by the 5-flanking region of the B. napus napin gene to express antisense RNA in a seed-specific manner. Seeds of transgenic plants with antisense genes often contained reduced amounts of napin. In some transgenic plants, no accumulation of napin was observed. However, the total protein content of transgenic and wild-type seeds did not differ significantly. Seeds lacking napin accumulated 1.4 to 1.5 times more cruciferin than untransformed seeds, although the oleosin content was not affected. Fatty acid content and composition in the seeds of transgenic plants were also analyzed by gas chromatography. Though the total fatty acid content of the transformants was the same as that of non-transformants, there was a reduction in 18:1 contents and a concomitant increase of 18:2 in seeds with reduced napin levels. This observed change in fatty acid composition was inherited in the next generation.  相似文献   
7.
Summary Pseudomonas oleovorans grew well and synthesized copolyesters of 3-hydroxyalkanoates and 3-hydroxy--fluoroalkanoates in the mineral medium containing 1-fluorononane and sodium gluconate. The content of fluorinated units in copolyesters could be controlled from 0 to 40 mol%. The copolyesters were shown to have a random sequence distribution of different monomeric units by analysis of the13C NMR spectra. The melting temperatures of copolyesters were 52–58°C, and the enthalpy of fusion decreased with the content of fluorinated units.  相似文献   
8.
Cells dissociated from the sponge Haliclona permollis reconstituted a new body by the following three consecutive processes: (1) Reaggregation, cells aggregate as a spheroidal mass. (2) Spreading, aggregates flatten and spread. (3) Reconstruction, aggregates coalesce into a reconstituted body. Cells in the process of reconstitution incorporated 14C-proline into proteins, converting 17% of it to hydroxyproline and synthesize collagen molecules during this process. Inhibitors of collagen biosynthesis did not affect the reaggregation, but caused incomplete morphogenesis in the processes of spreading and reconstruction: cycloheximide and 2,2'-dipyridyl inhibited spreading while 3-aminopropionitrile induced incomplete reconstruction. These findings suggested that spreading and reconstruction, but not reaggregation require both synthesis and cross-linking of collagens. Three polypeptides with molecular weights of 58 K, 160 K and 180 K were identified in sponge cells as collagens by immunoblot analysis with antibodies against sea urchin collagen and studies on susceptibilities to collagenase and pepsin. The 58 KDa polypeptide appeared in reconstituted bodies but not in dissociated cells, suggesting its importance in tissue reconstitution by dissociated cells.  相似文献   
9.
10.
Abstract: The excitatory neurotransmitter glutamate is believed to play important roles in development, synaptic plasticity, and neurodegenerative conditions. Recent studies have shown that neurotrophic factors can modulate neuronal excitability and survival and neurite outgrowth responses to glutamate, but the mechanisms are unknown. The present study tested the hypothesis that neurotrophic factors modulate responses to glutamate by affecting the expression of specific glutamate-receptor proteins. Exposure of cultured embryonic rat hippocampal cells to basic fibroblast growth factor (bFGF) resulted in a concentration-dependent increase in levels of α-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA)-receptor subunit GluR1 protein as determined by western blot, dot-blot, and immunocytochemical analyses. In contrast, bFGF did not alter levels of GluP2/3, GluR4, or the NMDA-receptor subunit NR1. Nerve growth factor did not affect GluR1 levels. Calcium-imaging studies revealed that elevation of [Ca2+]i, resulting from selective AMPA-receptor activation, was enhanced in bFGF-pretreated neurons. On the other hand, [Ca2+]i responses to NMDA-receptor activation were suppressed in bFGF-treated neurons, consistent with previous studies showing that bFGF can protect neurons against NMDA toxicity. Moreover, neurons pretreated with bFGF were relatively resistant to the toxicities of glutamate and AMPA, both of which were shown to be mediated by NMDA receptors. These data suggest that differential regulation of the expression of specific glutamate-receptor subunits may be an important mechanism whereby neurotrophic factors modulate activity-dependent neuronal plasticity and vulnerability to excitotoxicity.  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