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   10871篇
  免费   821篇
  国内免费   151篇
  11843篇
  2024年   14篇
  2023年   50篇
  2022年   190篇
  2021年   252篇
  2020年   222篇
  2019年   246篇
  2018年   316篇
  2017年   245篇
  2016年   461篇
  2015年   683篇
  2014年   705篇
  2013年   782篇
  2012年   1000篇
  2011年   919篇
  2010年   590篇
  2009年   522篇
  2008年   720篇
  2007年   624篇
  2006年   579篇
  2005年   467篇
  2004年   468篇
  2003年   370篇
  2002年   325篇
  2001年   128篇
  2000年   110篇
  1999年   105篇
  1998年   67篇
  1997年   58篇
  1996年   42篇
  1995年   36篇
  1994年   37篇
  1993年   26篇
  1992年   42篇
  1991年   41篇
  1990年   27篇
  1989年   42篇
  1988年   35篇
  1987年   32篇
  1986年   26篇
  1985年   19篇
  1984年   21篇
  1983年   13篇
  1982年   15篇
  1981年   13篇
  1980年   14篇
  1979年   13篇
  1976年   12篇
  1975年   18篇
  1974年   13篇
  1973年   13篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
92.
The disruption of cholesterol homeostasis leads to an increase in cholesterol levels which results in the development of cardiovascular disease. Mitogen Inducible Gene 6 (Mig-6) is an immediate early response gene that can be induced by various mitogens, stresses, and hormones. To identify the metabolic role of Mig-6 in the liver, we conditionally ablated Mig-6 in the liver using the Albumin-Cre mouse model (Alb(cre/+)Mig-6(f/f); Mig-6(d/d)). Mig-6(d/d) mice exhibit hepatomegaly and fatty liver. Serum levels of total, LDL, and HDL cholesterol and hepatic lipid were significantly increased in the Mig-6(d/d) mice. The daily excretion of fecal bile acids was significantly decreased in the Mig-6(d/d) mice. DNA microarray analysis of mRNA isolated from the livers of these mice showed alterations in genes that regulate lipid metabolism, bile acid, and cholesterol synthesis, while the expression of genes that regulate biliary excretion of bile acid and triglyceride synthesis showed no difference in the Mig-6(d/d) mice compared to Mig-6(f/f) controls. These results indicate that Mig-6 plays an important role in cholesterol homeostasis and bile acid synthesis. Mice with liver specific conditional ablation of Mig-6 develop hepatomegaly and increased intrahepatic lipid and provide a novel model system to investigate the genetic and molecular events involved in the regulation of cholesterol homeostasis and bile acid synthesis. Defining the molecular mechanisms by which Mig-6 regulates cholesterol homeostasis will provide new insights into the development of more effective ways for the treatment and prevention of cardiovascular disease.  相似文献   
93.
Root cap development in cereals and legumes is self-regulated by a repressor that accumulates in the extracellular environment, and immersing the root tip into water results in renewed cap development. By exploiting this phenomenon, root cap mitosis and differentiation can be synchronously induced among populations. In Pisum sativum L., messenger RNA (mRNA) differential display revealed changes in expression of approximately 1% of the sample mRNA population within minutes of induced cap turnover. This profile changes sequentially over a period of 30 min, then stabilizes. Microarray analysis of Medicago truncatula root caps confirmed changes in expression of approximately 1% of the target population, within minutes. A cell specific marker for cap turnover exhibited the same temporal and spatial expression profile in the gymnosperm species Norway spruce (Picea abies) as in pea. Induced cap development provides a means to profile cell-specific gene expression among phylogenetically diverse species from the early moments of mitosis and cellular differentiation.  相似文献   
94.
旨在以非肥胖糖尿病(Non-obese diabetic,NOD)小鼠为动物模型,研究高剂量昆虫细胞表达的重组热休克蛋白gp96(Recombinant gp96,rgp96)对1型糖尿病(Type 1 diabetes,T1D)的预防作用。以高剂量rgp96免疫NOD小鼠,用血糖仪监测小鼠血糖值,用流式细胞术检测小鼠脾脏CD4~+CD25~+Foxp3~+调节性T细胞(Regulatory T cells,Tregs)亚群频率,然后用一系列体外实验探究高剂量rgp96对Tregs的影响。结果显示高剂量rgp96免疫有效地预防或延缓小鼠T1D发病,免疫诱导Tregs数量明显增加。体外实验发现rgp96蛋白促进Tregs增殖,诱导Foxp3表达上调和IL-10分泌增加。研究结果为开发基于rgp96的新型T1D预防和治疗性疫苗提供了依据。  相似文献   
95.
邢松  周蜜  潘雷 《人类学学报》2020,39(4):521-531
东亚中更新世古人类在头骨、下颌骨、牙齿等解剖部位表现出不同程度的形态多样性,中期成员代表为直立人,而晚期成员的演化地位具有较大争议。为进一步了解东亚中更新世古人类内部的形态变异特点和为东亚中更新世晚期古人类分类提供依据,本文使用微分同胚的表面匹配(Diffeomorphic Surface Matching, DSM)和形态测量图(Morphometric map)对下颌第二臼齿(M2)釉质-齿质连接面的形状和齿冠侧面釉质厚度分布模式进行了量化分析。结果显示:1)东亚中更新世古人类与晚期人属成员(尼安德特人和现代人)存在较明显的形态差别;2)该时段晚期的东亚古人类相对中期直立人在侧面釉质厚度分布规律上具有独特性,并在釉质-齿质连接面的三维形状上与晚期人属成员更加接近。本文在以往对东亚中更新世古人类牙齿内外结构单个性状研究的基础上,使用三维形态测量方法进一步量化了M2釉质-齿质连接面三维形状和侧面釉质厚度分布模式两项重要特征的变异特点,这对未来该时段同类型牙齿的形态鉴定以及解决东亚中更新世晚期古人类的分类地位具有一定意义。  相似文献   
96.
We consider adaptive robust methods for lung cancer that are also dose-reactive, wherein the treatment is modified after each treatment session to account for the dose delivered in prior treatment sessions. Such methods are of interest because they potentially allow for errors in the delivered dose to be corrected as the treatment progresses, thereby ensuring that the tumor receives a sufficient dose at the end of the treatment. We show through a computational study with real lung cancer patient data that while dose reaction is beneficial with respect to the final dose distribution, it may lead to exaggerated daily underdose and overdose relative to non-reactive methods that grows as the treatment progresses. However, by combining dose reaction with a mechanism for updating an estimate of the uncertainty, the magnitude of this growth can be mitigated substantially. The key finding of this paper is that reacting to dose errors – an adaptation strategy that is both simple and intuitively appealing – may backfire and lead to treatments that are clinically unacceptable.  相似文献   
97.
Classical phenylketonuria, an inborn error in metabolism, is caused by a deficiency of the hepatic enzyme phenylalanine hydroxylase. The identification of putative cDNA clones coding for rat liver phenylalanine hydroxylase by hybrid-selected translation has previously been reported [Robson, K. J., Chandra, T., MacGillivray, R. T. A., & Woo, S. L. C. (1982) Proc. Natl. Acad. Sci. U.S.A. 79, 4701-4705]. The authenticity of the clones, however, could not be definitively ascertained at the time because of a lack of amino acid sequence data of the enzyme in the literature. Purified rat liver phenylalanine hydroxylase was subjected to cyanogen bromide treatment, and the resulting fragments were used for N-terminal amino acid sequence analysis. The partial amino acid sequence was then compared to that deduced from an open reading frame in the nucleotide sequence of the cDNA clones. A perfect match of 17 amino acid residues was found between the two sequences following a unique methionine codon present in the nucleotide sequence, thereby providing unambiguous evidence for the identity of the rat liver phenylalanine hydroxylase cDNA clones.  相似文献   
98.
Entomopathogenic fungi have great potential to control agricultural and horticultural insect pests, however optimizing conidial production systems to demonstrate high productivity and stability still needs additional efforts for successful field application and industrialization. Although many virulent entomopathogenic fungal isolates have been viewed as potential candidates in a laboratory environment, very few of the isolates are being used in practice for application in agricultural fields as commercial products. I. javanicus is an entomopathogenic fungus that is parasitic to various diverse coleopteran and lepidopteran insects and thought good candidate as biopesticdes. In this work, the basic characteristics of two entomopathogenic fungi, I. javanica FG340 and Pf04, were investigated in morphological examinations, genetic identification, and virulence against Thrips palmi, and then the feasibility of various grains substrates for conidial production was assessed, particularly focusing on conidial productivity and thermotolerance. Isaria javanica FG340 and Pf04 conidia were solid-cultured on 12 grains for 14?days in a Petri dish. Of the tested Italian millet, perilla seed, millet and barley-based cultures showed high conidial production. The four-grain media yielded >1?×?109 conidia/g of I. javanica FG340 and Pf04. Pf04 strain had enhanced thermotolerance up to 45?°C when cultured on Italian millet. In application, it was easy to make a conidial suspension using the cultured grains, and several surfactants were tested to release the conidia. This work suggests several possible inexpensive grain substrates by which to promote conidial production combined with enhanced stability against exposure to high temperature.  相似文献   
99.
A 25-year-old Uzbek male presented with right upper abdominal pain for 20 days. On radiologic studies, a huge cystic mass was noticed in the right liver which was suspected as parasitic. The patient received right hepatic segmentectomy (segment 7), and the surgically resected mass was confirmed as cystic echinococcosis (CE), measuring 10.5 cm in its diameter. The inner surface of the cyst was bile-stained. The patient was discharged on the 8th hospital day, and was rechecked 6 months after the surgical intervention without any evidence of recurrence. The present report describes findings of an imported case of CE which represented ultrasound images of the ''ball of wool''.  相似文献   
100.
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