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   673篇
  免费   39篇
  2023年   1篇
  2022年   2篇
  2021年   15篇
  2020年   7篇
  2019年   8篇
  2018年   20篇
  2017年   13篇
  2016年   23篇
  2015年   30篇
  2014年   43篇
  2013年   31篇
  2012年   58篇
  2011年   65篇
  2010年   36篇
  2009年   41篇
  2008年   43篇
  2007年   48篇
  2006年   37篇
  2005年   32篇
  2004年   41篇
  2003年   33篇
  2002年   28篇
  2001年   9篇
  2000年   3篇
  1999年   4篇
  1998年   2篇
  1997年   1篇
  1996年   4篇
  1995年   3篇
  1994年   1篇
  1993年   2篇
  1990年   3篇
  1989年   1篇
  1988年   3篇
  1987年   3篇
  1986年   1篇
  1985年   1篇
  1984年   3篇
  1982年   1篇
  1980年   1篇
  1979年   2篇
  1978年   2篇
  1975年   1篇
  1974年   1篇
  1973年   1篇
  1972年   2篇
  1971年   1篇
  1908年   1篇
排序方式: 共有712条查询结果,搜索用时 15 毫秒
1.
2.
During embryogenesis and maturation of an embryo the tissuescovering it produce phenolic compounds the localization of whichchanges during maturation of the embryo. In the ovary containinga globular embryo, phenolics are located in the epidermis ofthe integumentum externum and the innermost layer of the integumentuminternum. In the ovule at the stage at which heart- and torpedo-shapedembryos are present, phenolic compounds are visible in the stellarcells, the innermost cells of the integumentum internum andthe endosperm. In hard, green seeds, after the integumentuminternum and layers over the stellar cells gradually disappear,the remaining tissue contains cell walls impregnated with phenolics.Mature, black seeds contain only one distinct layer of cells—stellarcells, which, like the other compressed cell walls, are impregnatedwith phenolics. In this way they constitute a barrier betweenthe embryo and its environment.Copyright 1994, 1999 AcademicPress Brassica napus, seed coat, integumentum, phenolic compounds  相似文献   
3.
The identification of quantitative trait loci (QTL) such as height and their underlying causative variants is still challenging and often requires large sample sizes. In humans hundreds of loci with small effects control the heritable portion of height variability. In domestic animals, typically only a few loci with comparatively large effects explain a major fraction of the heritability. We investigated height at withers in Shetland ponies and mapped a QTL to ECA 6 by genome-wide association (GWAS) using a small cohort of only 48 animals and the Illumina equine SNP70 BeadChip. Fine-mapping revealed a shared haplotype block of 793 kb in small Shetland ponies. The HMGA2 gene, known to be associated with height in horses and many other species, was located in the associated haplotype. After closing a gap in the equine reference genome we identified a non-synonymous variant in the first exon of HMGA2 in small Shetland ponies. The variant was predicted to affect the functionally important first AT-hook DNA binding domain of the HMGA2 protein (c.83G>A; p.G28E). We assessed the functional impact and found impaired DNA binding of a peptide with the mutant sequence in an electrophoretic mobility shift assay. This suggests that the HMGA2 variant also affects DNA binding in vivo and thus leads to reduced growth and a smaller stature in Shetland ponies. The identified HMGA2 variant also segregates in several other pony breeds but was not found in regular-sized horse breeds. We therefore conclude that we identified a quantitative trait nucleotide for height in horses.  相似文献   
4.
5.
The geometric and energetic characteristics of root surfaces of two wheat (Triticum L.) varieties, Al tolerant (Inia 66/16) and Al sensitive (Henika), were estimated from experimental water vapor adsorption–desorption data. Roots stressed for around 1 week at pH 4 without and with a toxic aluminium level (0.741 mol m–3) were studied at the tillering and shooting stages. Roots grown continuously at pH 7 were taken as control. The surface properties of the pH 4 stressed roots were apparently the same as those of the control roots whatever the root age. For the roots of both varieties, the surface area and total micropore volume increased markedly after aluminium treatment. The average micropore radius increased significantly for the sensitive wheat, whereas it increased only slightly for the resistant one. Under Al treatment the number of large pores increased while small pores were fewer for both plants, indicating a possible alteration of the build-up of root tissue. The root surface pores were fractal. The fractal dimension of the sensitive wheat roots decreased under Al treatment, whereas for the resistant wheat this remained apparently unchanged. The adsorption energy distribution functions had different shapes for the sensitive and the resistant wheat varieties: the sensitive variety had greater number of high energy adsorption centers, which implies that the root tolerance on Al stress may be connected with lower polarity of the surface.  相似文献   
6.
Little is known about the effects of coffee that are not related to the presence of caffeine. The aim of the study was to analyse changes in kidney function and nucleotide metabolism related to high intake of decaffeinated coffee. Mice consumed decaffeinated coffee extract for two weeks. Activities of AMP deaminase, ecto5′-nucleotidase, adenosine deaminase, purine nucleoside phosphorylase were measured in kidney cortex and medulla by analysis of conversion of substrates into products using HPLC. Concentration of nucleotides in kidney cortex, kidney medulla and serum were estimated by HPLC. Activity of ecto5′-nucleotidase increased from 0.032 ± 0.006 to 0.049 ± 0.014 nmol/mg tissue/min in kidney cortex of mice administered high-dose decaffeinated coffee (HDC) together with increase in cortex adenosine concentration and decrease in plasma creatinine concentration. HDC leads to increased activity of ecto5′-nucleotidase in kidney cortex that translates to increase in concentration of adenosine. Surprisingly this caused improved kidney excretion function.  相似文献   
7.
8.
Epidemiological studies indicate a high risk of stroke, heart failure and myocardial infarction in patients with multiple sclerosis, especially in its secondary progressive (SPMS) phase. Some ischaemic events are directly associated with abnormal platelet functions and their prothrombotic activity. Recent reports, including this study, confirm the increased activation of circulating platelets in SPMS, and also show increased platelet reactivity, among other responses, as well as strong aggregation. In this current study, we conducted a comparative analysis of the platelet proteome in SPMS patients and in healthy controls, to demonstrate the quantitative and qualitative differences likely to affect functional changes observed in SPMS. During densitometry evaluation of 2‐D fluorescence difference gel electrophoresis, we observed differences between the electrophoretic patterns of SPMS platelets and the control samples. To determine a detailed characterisation of the proteome changes in the SPMS patients’ blood platelets, in the next stage, we performed mass spectrometry of selected spots and indicated the increased presence of four proteins (fibrinogen, α‐2 macroglobulin, septin‐14 and tubulin β‐1 chain). The most important of these is the increased amount of prothrombotic protein, fibrinogen, which seems to confirm the accuracy of the imaging and potentially explains the increased risk of platelet‐origin thrombotic events. This study provides new knowledge of the potential existence of the molecular mechanisms responsible for the acceleration of the platelet pro‐coagulant function in SPMS. This can help to identify new targets for therapy, which can then be used not only in the second stage of the disease.  相似文献   
9.
ObjectivesTo review the available data about stereotactic body-radiotherapy (SBRT) for oligometastatic lymph node cancer recurrence.MethodsThe inclusion criteria for this study were as follows: Medline search for the (1) English language (2) full paper (abstracts were excluded) on (3) adult oligometastatic solid cancer recurrence limited to lymph node that underwent SBRT (4) outcome data available and (5) published up to the 30th April 2014.Results38 papers fulfilling the inclusion criteria have been found: 7 review articles and 31 patient series (20 and 11 retrospective and prospective studies, respectively) including between 1 and 69 patients (636 lymph nodes). Twelve articles reported only lymph node SBRT while in 19 – all types of SBRT including lymph node SBRT were presented. Two-year local control, 4-year progression free survival and overall survival was of up to 100%, 30% and 50%, respectively. The progression was mainly out-field (10–30% of patients had a recurrence in another lymph node/nodes). The toxicity was low with mainly mild acute events and single grade 3–4 late events. When compared to SBRT for any oligometastatic cancer, SBRT for lymph node recurrence carried better prognosis and showed lower toxicity.ConclusionsSBRT is a feasible approach for oligometastatic lymph node recurrence, offering excellent in-field tumor control with low toxicity profile. The potential abscopal effect has been hypothesized as a basis of these findings. Future studies are warranted to identify the patients that benefit most from this treatment. The optimal combination with systemic treatment should also be defined.  相似文献   
10.
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