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   5010篇
  免费   562篇
  国内免费   278篇
  2024年   8篇
  2023年   95篇
  2022年   89篇
  2021年   150篇
  2020年   174篇
  2019年   170篇
  2018年   154篇
  2017年   156篇
  2016年   158篇
  2015年   196篇
  2014年   371篇
  2013年   313篇
  2012年   347篇
  2011年   382篇
  2010年   275篇
  2009年   314篇
  2008年   292篇
  2007年   323篇
  2006年   320篇
  2005年   262篇
  2004年   216篇
  2003年   171篇
  2002年   119篇
  2001年   121篇
  2000年   93篇
  1999年   118篇
  1998年   79篇
  1997年   70篇
  1996年   57篇
  1995年   59篇
  1994年   42篇
  1993年   27篇
  1992年   25篇
  1991年   26篇
  1990年   21篇
  1989年   9篇
  1988年   9篇
  1987年   10篇
  1986年   10篇
  1985年   4篇
  1984年   5篇
  1983年   2篇
  1982年   5篇
  1980年   1篇
  1977年   1篇
  1976年   1篇
排序方式: 共有5850条查询结果,搜索用时 31 毫秒
1.
2.
β-Adrenergic agonists (β-agonists) are illegally used in animal husbandry, threatening the health of consumers. To realize multianalyte detection of β-agonists, a β2-adrenergic receptor (β2-AR) was cloned from Syrian hamster lung and heterogeneously expressed by Spodoptera frugiperda (Sf9) cells. The recombinant β2-AR was purified from intracellular soluble proteins of infected Sf9 cells, and was utilized to establish an enzyme-linked-receptor assay (ELRA) to detect a group of β-agonists simultaneously. This assay was based on direct competitive inhibition of binding of horseradish peroxidase-labeled ractopamine to the immobilized β2-AR proteins by β-agonists. The IC50 and limit of detection values for ractopamine were 30.38 μg L−1 and 5.20 μg L−1, respectively. Clenbuterol and salbutamol showed 87.7% and 58.5% cross-reactivities with ractopamine, respectively. This assay is simple, rapid, and environmentally friendly, showing a potential application in the screening of β-agonists in animal feeds.  相似文献   
3.
4.
5.
6.
One approach to gain an insight into the genetics of tree architecture is to make use of morphologically divergent parents and study their segregating progeny in the F2 and backcross (B1) generations. This approach was chosen in the present study in which material of a three-generation pedigree growing side by side in a replicated plantation, was analyzed. The pedigree included Populus trichocarpa (T) and P. deltoides (D) parents, their F1 and F2 hybrids and their B1 hybrids to the D parent. The trees were grown in the environment of the T parent and measured for the first 2 years of growth. Nine quantitative traits were studied at the stem, branch and leaf levels of tree architecture, in which the original parents differed. Strong F1 hybrid vigor relative to the better parent (T) was expressed in growth and its components. Most quantitative traits in the F2 and B1 hybrids were intermediate between the T and D parents but displayed a wide range of variation due to segregation. The results from the analysis of variance indicated that all morphometric traits were significantly different among F2 and B1 clones, but the B1 hybrids were more sensitive to replicates than the F2. Broad-sense heritabilities (H 2) based on clonal means ranged from moderately high to high (0.50–0.90) for the traits studied, with H 2 values varying over age. The H 2 estimates reflected greater environmental noise in the B1 than in the F2, presumably due to the greater proportion of maladaptive D alleles in those hybrids. In both families, sylleptic branch number and length, and leaf size on the terminal, showed strong genetic correlations with stem growth. The large divergence between the two original parents in the traits studied, combined with the high chromosome number in Populus (2n=38), makes this pedigree well suited for the estimation of the number of quantitative trait loci (QTLs) underlying quantitative variation by Wright's biometric method (1968). Variation in several traits was found to be under the control of surprisingly few major QTLs: 3–4 in 2nd-year height and diameter growth, a single QTL in stem diameter/height ratio.  相似文献   
7.
8.
长期进行除草剂药效试验可能会导致田间杂草种群发生适应性进化。本研究在安徽南陵县除草剂药效试验专用稻田中采集了1个稗草种群A,并以从常规稻田采集的3个稗草种群为对照,开展同质园栽培试验。结果表明: 与3个对照种群相比,A种群稗草植株的单株种子产量显著减少,种子千粒重显著增加,幼苗生长速率显著加快,结实分蘖数显著增多,生育期显著缩短;A种群稗草成株的株高、生物量及对除草剂五氟磺草胺的敏感性均显著降低。A种群稗草幼苗3~4叶期时经五氟磺草胺推荐剂量2倍量(有效成分60 g·hm-2)处理后,其株高、生物量及成熟种子产量(平均每株1066粒)显著降低,而抽穗期、结实分蘖数、单个总状花序的种子数及种子千粒重无显著差异。因此,种子较重、生活史周期短、植株矮小、结实分蘖多及对除草剂五氟磺草胺具有抗药性,使得A种群稗草对稻作系统具有特异适应性,应防止此类种群扩散至常规稻田。  相似文献   
9.
Platelet-derived growth factor (PDGF), a potent chemoattractant, induces cell migration via the MAPK and PI3K/Akt pathways. However, the downstream mediators are still elusive. In particular, the role of extracellular mediators is largely unknown. In this study, we identified the matricellular protein Cyr61, which is de novo synthesized in response to PDGF stimulation, as the key downstream mediator of the ERK and JNK pathways, independent of the p38 MAPK and AKT pathways, and, thereby, it mediates PDGF-induced smooth muscle cell migration but not proliferation. Our results revealed that, when Cyr61 was newly synthesized by PDGF, it was promptly translocated to the extracellular matrix and physically interacted with the plasma membrane integrins α6β1 and αvβ3. We further demonstrate that Cyr61 and integrins are integral components of the PDGF signaling pathway via an “outside-in” signaling route to activate intracellular focal adhesion kinase (FAK), leading to cell migration. Therefore, this study provides the first evidence that the PDGF-induced endogenous extracellular matrix component Cyr61 is a key mediator in modulating cell migration by connecting intracellular PDGF-ERK and JNK signals with integrin/FAK signaling. Therefore, extracellular Cyr61 convergence with growth factor signaling and integrin/FAK signaling is a new concept of growth factor-induced cell migration. The discovered signaling pathway may represent an important therapeutic target in growth factor-mediated cell migration/invasion-related vascular diseases and tumorigenesis.  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