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   828篇
  免费   40篇
  国内免费   26篇
  894篇
  2024年   2篇
  2023年   6篇
  2022年   18篇
  2021年   19篇
  2020年   18篇
  2019年   31篇
  2018年   17篇
  2017年   14篇
  2016年   14篇
  2015年   19篇
  2014年   25篇
  2013年   48篇
  2012年   21篇
  2011年   30篇
  2010年   34篇
  2009年   31篇
  2008年   41篇
  2007年   33篇
  2006年   37篇
  2005年   43篇
  2004年   46篇
  2003年   36篇
  2002年   32篇
  2001年   19篇
  2000年   15篇
  1999年   18篇
  1998年   16篇
  1997年   14篇
  1996年   11篇
  1995年   14篇
  1994年   11篇
  1993年   22篇
  1992年   13篇
  1991年   13篇
  1990年   13篇
  1989年   13篇
  1988年   7篇
  1987年   12篇
  1986年   11篇
  1985年   11篇
  1984年   10篇
  1983年   5篇
  1982年   11篇
  1981年   7篇
  1980年   2篇
  1979年   7篇
  1978年   2篇
  1974年   1篇
  1972年   1篇
排序方式: 共有894条查询结果,搜索用时 9 毫秒
161.
As a catastrophic earthquake is unpredictable and occurs only occasionally, impacts on biotic communities are seldom known. Monthly changes in insect communities in the mangroves along the Danshui Estuary were monitored for more than 3 years from before and after two catastrophic earthquakes in Taiwan the Chi–Chi earthquake (ML = 7.3) of September 21, 1999 and the 3–31 earthquake (ML = 6.8) of March 31, 2002. Here we show that the Chi–Chi earthquake not only caused large declines in total individual number but also total species number of insects. It also resulted in greater variability among samples, and shifts in insect communities. Non-biting midges and rove beetles, whose immatures inhabited the riparian underground or aquatic sediments, were most severely affected. By 7 months after the Chi–Chi earthquake, the insect communities had recovered to a level comparable to that before the earthquake. However, the influence of the 3–31 earthquake on the insect communities was less severe. It is concluded that the more-severe impacts of the Chi–Chi earthquake than the 3–31 earthquake can be attributable to differences in ground shaking, occurrence time, biodiversity, and growing conditions of insects at those times.  相似文献   
162.
Neuropeptide Y (NPY) has been reported to be a potent anti-inflammatory peptide with ability to directly modulate activity of granulocytes and macrophages. The present study aimed to correlate the effects of NPY in vivo on lipopolysaccharide-induced air-pouch exudates cells and in vitro on peripheral blood leukocytes functions. The role of different Y receptors was examined using NPY-related peptides and antagonists with diverse subtype specificity and selectivity for Y receptors. Y1, Y2 and Y5 receptors were detected on air-pouch exudates cells (flow cytometry) and peripheral blood granulocytes (immunocitochemistry). NPY in vivo reduced inflammatory cells accumulation into the air pouch, and decreased their adherence and phagocytic capacity via Y2/Y5 and Y1/Y2 receptors, respectively. Quite the opposite, NPY in vitro potentiated adhesiveness and phagocytosis of peripheral blood granulocytes and monocytes by activating Y1 receptor. The differences between in vivo and in vitro effects of NPY on rat inflammatory cells functions are mostly due to dipeptidyl peptidase 4 activity. In addition, suppressive effect of NPY in vivo is highly dependent on the local microenvironment, peptide truncation and specific Y receptors interplay.  相似文献   
163.
164.
The interface between mitochondria and the endoplasmic reticulum is emerging as a crucial hub for calcium signalling, apoptosis, autophagy and lipid biosynthesis, with far reaching implications in cell life and death and in the regulation of mitochondrial and endoplasmic reticulum function. Here we review our current knowledge on the structural and functional aspects of this interorganellar juxtaposition. This article is part of a Special Issue entitled: Calcium Signaling In Health and Disease. Guest Editors: Geert Bultynck, Jacques Haiech, Claus W. Heizmann, Joachim Krebs, and Marc Moreau.  相似文献   
165.
Recent studies have identified paracrine and endocrine cells in the midgut of larval Drosophila melanogaster as well as midgut and hindgut receptors for multiple neuropeptides implicated in the control of fluid and ion balance. Although the effects of diuretic factors on fluid secretion by isolated Malpighian tubules of D. melanogaster have been examined extensively, relatively little is known about the effects of such factors on gut peristalsis or ion transport across the gut. We have measured the effects of diuretic hormone 31 (DH31), drosokinin and allatostatin A (AST‐A) on both K+ transport and muscle contraction frequency in the isolated gut of larval D. melanogaster. K+ absorption across the gut was measured using K+‐selective microelectrodes and the scanning ion‐selective electrode technique. Allatostatin A (AST‐A; 1 μM) increased K+ absorption across the anterior midgut but reduced K+ absorption across the copper cells and large flat cells of the middle midgut. AST‐A strongly inhibited gut contractions in the anterior midgut but had no effect on contractions of the pyloric sphincter induced by proctolin. DH31 (1 μM) increased the contraction frequency in the anterior midgut, but had no effect on K+ flux across the anterior, middle, or posterior midgut or across the ileum. Drosokinin (1 μM) did not affect either contraction frequency or K+ flux across any of the gut regions examined. Possible functions of AST‐A, DH31, and drosokinin in regulating midgut physiology are discussed.  相似文献   
166.
高效与特异的基因组定点修饰是基因工程动物研究的前沿与难点.链霉菌噬菌体ΦC31整合酶能介导含attB位点的外源基因定点整合于多种真核生物基因组的假attP位点,可维持外源基因的正常结构及高效表达.本文探讨ΦC31整合酶介导外源基因在猪基因组内定点整合的分子基础.构建含attB位点的报告载体pEGFP-N1-attB,与ΦC31整合酶表达载体pCMV-INT共转染猪肾PK15细胞,G418筛选获得单克隆细胞系.实时荧光定量PCR筛选出单拷贝整合的转基因细胞系.TAIL-PCR鉴定出1个猪基因组假attP位点,位于猪1号染色体,watson链,坐标114220087-114220126,命名为pig-attP-1.测序结果显示,pEGFP-N1-attB在attB位点处断开插入到pig-attP-1.用荧光计测定细胞培养基上清EGFP含量发现,该转基因细胞系EGFP的表达水平是本底的50倍(13500 AU vs.280 AU),表明pig-attP-1是利于外源基因高效表达的"友好位点".该研究不仅为实现外源基因在猪基因组内的定点整合提供了新策略,也为创制基因工程猪、建立动物生物反应器等研究注入了新思路.  相似文献   
167.
目的:研究新结构化合物FLLL31抑制卵白蛋白(OVA)致敏引发的小鼠气道炎症的活性,探讨FLLL31治疗哮喘的初步疗效。方法:雄性BALB/c小鼠(18~20 g)随机分为4组,每组10只,包括正常对照组(Control组)、模型对照组(OVA组)、地塞米松组(1 mg/kg,腹腔注射)和FLLL31组(15 mg/kg,口服灌胃)。各组小鼠分别于第0 d和第14 d致敏,每只鼠腹腔注射20μg OVA和2.25 mg Al(OH)3凝胶,FLLL31自致敏第24 d开始给药,给药周期为7 d;于第28、29、30 d以气管滴入OVA进行攻击,攻击前1 h给予受试化合物FLLL31及阳性药地塞米松。结果:小鼠肺灌流液炎症细胞分类计数、肺组织病理分析等实验结果证明,FLLL31以15 mg/kg连续给药7 d后,与模型组相比,抑制了小鼠肺部气道中炎症细胞的浸润,明显改善OVA致敏引发的小鼠气道炎症症状;ELISA结果证明FLLL31降低小鼠肺灌流液中炎症因子白细胞介素6的含量;免疫组化结果显示FLLL31降低OVA致敏小鼠肺部白细胞介素6受体浓度,减少中性粒细胞标志物淋巴细胞抗原6G(Ly6G)的表达(P0.05)。结论:特异抑制STAT3的新结构化合物FLLL31在体内对OVA致敏小鼠模型气道炎症有较好的改善和免疫调节活性。  相似文献   
168.
The p38 MAPK signal transduction pathway plays an important role in inflammatory and stress responses. MAPKK6 (MKK6), a dual specificity protein kinase, is a p38 activator. Activation of the MKK6-p38 pathway is kept in check by multiple layers of regulations, including autoinhibition, dimerization, scaffold proteins, and Lys-63-linked polyubiquitination. However, the mechanisms underlying deactivation of MKK6-p38, which is crucial for maintaining the magnitude and duration of signal transduction, are not well understood. Lys-48-linked ubiquitination, which marks substrates for proteasomal degradation, is an important negative posttranslational regulatory machinery for signal pathway transduction. Here we report that the accumulation of F-box only protein 31 (FBXO31), a component of Skp1·Cul1·F-box protein E3 ligase, negatively regulated p38 activation in cancer cells upon genotoxic stresses. Our results show that FBXO31 binds to MKK6 and mediates its Lys-48-linked polyubiquitination and degradation, thereby functioning as a negative regulator of MKK6-p38 signaling and protecting cells from stress-induced cell apoptosis. Taken together, our findings uncover a new mechanism of deactivation of MKK6-p38 and substantiate a novel regulatory role of FBXO31 in stress response.  相似文献   
169.
银环蛇神经毒素的分子克隆和功能表达(英文)   总被引:5,自引:1,他引:4  
抽提银环蛇毒腺总RNA,通过反转录PCR技术扩增出其神经毒素cDNA,克隆并测定了全序列。银环蛇神经毒素的cDNA编码21个氨基酸的信号肽和74个氨基酸的成熟蛋白。该信号肽非常类似于短链神经毒素、κ-神经毒素和心脏毒素的信号肽。而成熟蛋白的氨基酸序列与从台湾产银环蛇中通过蛋白测序鉴定的α-bungarotoxin的氨基酸序列完全一样。此外,还克隆到该神经毒素缺失前体cDNA。利用麦芽糖结合蛋白融合  相似文献   
170.
丹参对心肌低氧/复氧损伤的保护作用的研究   总被引:7,自引:0,他引:7  
目的:研究中药丹参(SM)对心肌低氧/复氧损伤的保护作用。方法:运用^31P-NMR技术对离体灌流大鼠心脏的高能磷酸化合物含量及细胞内的pH值(pHi)进行动态跟踪。结果:丹参注射液能明显减轻低氧期间心肌高能磷酸合物含量的下降,促使复氧期间PCr、ATP相对含量的恢复,减少低氧及复氧阶段心肌pHi的下降。结论:丹参参改善低氧及复氧期间心肌能量代谢水平,减轻心肌低氧/复氧损伤,并能显著改善细胞内酸碱  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