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   434篇
  免费   3篇
  国内免费   3篇
系统科学   9篇
教育与普及   2篇
现状及发展   116篇
研究方法   107篇
综合类   198篇
自然研究   8篇
  2020年   3篇
  2019年   2篇
  2018年   12篇
  2017年   15篇
  2016年   14篇
  2015年   14篇
  2014年   7篇
  2013年   9篇
  2012年   35篇
  2011年   62篇
  2010年   11篇
  2009年   4篇
  2008年   35篇
  2007年   31篇
  2006年   27篇
  2005年   22篇
  2004年   26篇
  2003年   11篇
  2002年   12篇
  1996年   2篇
  1995年   3篇
  1994年   8篇
  1992年   3篇
  1987年   3篇
  1983年   2篇
  1982年   4篇
  1980年   6篇
  1979年   4篇
  1978年   2篇
  1977年   3篇
  1976年   2篇
  1975年   2篇
  1973年   4篇
  1972年   2篇
  1970年   2篇
  1969年   1篇
  1968年   2篇
  1967年   3篇
  1966年   3篇
  1965年   1篇
  1964年   3篇
  1963年   1篇
  1962年   1篇
  1961年   2篇
  1960年   1篇
  1959年   1篇
  1958年   2篇
  1957年   1篇
  1955年   1篇
  1946年   1篇
排序方式: 共有440条查询结果,搜索用时 15 毫秒
361.
362.
Docosahexaenoic acid (DHA) is an omega-3 fatty acid obtained from the diet or synthesized from alpha-linolenic acid through the action of fatty acid elongases (ELOVL) and desaturases. DHA plays important roles in the central nervous system as well as in peripheral organs and is the precursor of several molecules that regulate resolution of inflammation. In the present study, we questioned whether impaired synthesis of DHA affected macrophage plasticity and polarization both in vitro and in vivo models. For this we investigated the activation status and inflammatory response of bone marrow-derived M1 and M2 macrophages obtained from mice deficient of Elovl2 (Elovl2?/?), a key enzyme for DHA synthesis in mammals. Although both wild type and Elovl2?/? mice were able to generate efficient M1 and M2 macrophages, M1 cells derived from Elovl2?/? mice showed an increased expression of key markers (iNOS, CD86 and MARCO) and cytokines (IL-6, IL-12 and IL-23). However, M2 macrophages exhibited upregulated M1-like markers like CD80, CD86 and IL-6, concomitantly with a downregulation of their signature marker CD206. These effects were counteracted in cells obtained from DHA-supplemented animals. Finally, white adipose tissue of Elovl2?/? mice presented an M1-like pro-inflammatory phenotype. Hence, impairment of systemic DHA synthesis delineates an alteration of M1/M2 macrophages both in vitro and in vivo, with M1 being hyperactive and more pro-inflammatory while M2 less protective, supporting the view that DHA has a key role in controlling the balance between pro- and anti-inflammatory processes.  相似文献   
363.
364.
The crustaceans of the fresh waters of Bering Island and their link to the fauna of adjacent regions were studied. Based on original data and existing literature, the species composition of Cladocera and Copepoda was described. The compiled list includes 22 species of Cladocera and 30 species of Copepoda. In the original data, 35 species native to the Commander Islands were reported for the first time. Six species were newly reported in the Far East, and two were newly reported in Russia. The ecological peculiarities of several species and some biogeographical features of the freshwater zooplankton of the island are discussed. The main part of the fauna of the island form Holarctic widespread species (64.3%), another slightly smaller group of the fauna is comprised of Palaearctic species (20.1%), and the remainder comprise Nearctic (6.7%) and Beringian species (8.9%). Particular patterns in the distribution of freshwater zooplankton and the factors underlying the occurrence of these species on the island are considered.  相似文献   
365.
采用毛吸浸润法,研究了氧等离子及氩等离子处理对聚丙烯腈基碳纤维表面浸润特性的影响。发现了等离子处理可以使碳纤维表面对水的浸润性能大为改善,氧等离子处理效果更为明显。对在碳纤维表面预涂不饱和酸酐,经等离子处理可产生接枝的现象进行了验证,并发现接枝马来酸酐后浸润性能反而比原纤维有所下降。经等离子处理的纤维随其接触空气时间的延续,表面浸润性能不断退化,纤维对水的接触角呈曲折形式逐步增加。  相似文献   
366.
367.
Limb-girdle muscular dystrophy type 1D (LGMD1D) was linked to chromosome 7q36 over a decade ago, but its genetic cause has remained elusive. Here we studied nine LGMD-affected families from Finland, the United States and Italy and identified four dominant missense mutations leading to p.Phe93Leu or p.Phe89Ile changes in the ubiquitously expressed co-chaperone DNAJB6. Functional testing in vivo showed that the mutations have a dominant toxic effect mediated specifically by the cytoplasmic isoform of DNAJB6. In vitro studies demonstrated that the mutations increase the half-life of DNAJB6, extending this effect to the wild-type protein, and reduce its protective anti-aggregation effect. Further, we show that DNAJB6 interacts with members of the CASA complex, including the myofibrillar myopathy-causing protein BAG3. Our data identify the genetic cause of LGMD1D, suggest that its pathogenesis is mediated by defective chaperone function and highlight how mutations in a ubiquitously expressed gene can exert effects in a tissue-, isoform- and cellular compartment-specific manner.  相似文献   
368.
To identify risk variants for multiple myeloma, we conducted a genome-wide association study of 1,675 individuals with multiple myeloma and 5,903 control subjects. We identified risk loci for multiple myeloma at 3p22.1 (rs1052501 in ULK4; odds ratio (OR) = 1.32; P = 7.47 × 10(-9)) and 7p15.3 (rs4487645, OR = 1.38; P = 3.33 × 10(-15)). In addition, we observed a promising association at 2p23.3 (rs6746082, OR = 1.29; P = 1.22 × 10(-7)). Our study identifies new genomic regions associated with multiple myeloma risk that may lead to new etiological insights.  相似文献   
369.
Wilms tumor is the most common renal malignancy of childhood. To identify common variants that confer susceptibility to Wilms tumor, we conducted a genome-wide association study in 757 individuals with Wilms tumor (cases) and 1,879 controls. We evaluated ten SNPs in regions significantly associated at P < 5 × 10(-5) in two independent replication series from the UK (769 cases and 2,814 controls) and the United States (719 cases and 1,037 controls). We identified clear significant associations at 2p24 (rs3755132, P = 1.03 × 10(-14); rs807624, P = 1.32 × 10(-14)) and 11q14 (rs790356, P = 4.25 × 10(-15)). Both regions contain genes that are plausibly related to Wilms tumorigenesis. We also identified candidate association signals at 5q14, 22q12 and Xp22.  相似文献   
370.
根据Huygens-Fresnel的波束管理论,充分利用第1区的有效能量,并利用各个区所贡献的合成场强在焦点处同相的奇数分区,摒弃各合成场强在焦点处反相的偶数分区,导出了平面菲涅耳区板的一维条带的最优分区新规则.从基尔霍夫绕射公式出发进一步研究菲涅耳区板的二维圆环的分区规则.分为标量场(非极化波)绕射和矢量场(极化波)绕射2种情况,得出最优分区与传统分区在短焦距情况下存在差异、而随着焦距的增长渐趋一致的结论.  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