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   5113篇
  免费   315篇
  国内免费   2篇
  2023年   42篇
  2022年   69篇
  2021年   146篇
  2020年   94篇
  2019年   126篇
  2018年   155篇
  2017年   144篇
  2016年   201篇
  2015年   268篇
  2014年   269篇
  2013年   355篇
  2012年   360篇
  2011年   344篇
  2010年   251篇
  2009年   201篇
  2008年   255篇
  2007年   227篇
  2006年   214篇
  2005年   171篇
  2004年   180篇
  2003年   150篇
  2002年   142篇
  2001年   98篇
  2000年   93篇
  1999年   93篇
  1998年   40篇
  1997年   39篇
  1996年   31篇
  1995年   43篇
  1994年   23篇
  1993年   28篇
  1992年   44篇
  1991年   47篇
  1990年   34篇
  1989年   40篇
  1988年   35篇
  1987年   36篇
  1986年   41篇
  1985年   27篇
  1984年   19篇
  1981年   17篇
  1979年   20篇
  1978年   17篇
  1977年   16篇
  1975年   17篇
  1974年   26篇
  1973年   18篇
  1971年   12篇
  1969年   14篇
  1968年   14篇
排序方式: 共有5430条查询结果,搜索用时 15 毫秒
101.
The decline of germination observed after storage of Pinus pinea L. seeds up to 35 years at room temperature was accompanied by an increase in their ability to leak reducing sugars, probably as a consequence of membrane alterations due to senescence. Results of studies of the cell ultrastructure of viable and non-viable seeds before and after imbibition indicate that such is the case. Noticeable changes occurred in the ultrastructure of endosperm and embryo cells with germinability loss, even in the unimbibed condition. The main alterations were spherosome coalescence, plasmalemma separation from the cell wall and chromatin aggregation.  相似文献   
102.
103.
Bioprocess and Biosystems Engineering - This study investigated the synthesis of 2-ethylhexyl oleate catalyzed by Candida antarctica lipase immobilized on magnetic poly(styrene-co-divinylbenzene)...  相似文献   
104.

Strain MG, isolated from an acidic pond sediment on the island of Milos (Greece), is proposed as a novel species of ferrous iron- and sulfur-oxidizing Acidithiobacillus. Currently, four of the eight validated species of this genus oxidize ferrous iron, and strain MG shares many key characteristics with these four, including the capacities for catalyzing the oxidative dissolution of pyrite and for anaerobic growth via ferric iron respiration. Strain MG also grows aerobically on hydrogen and anaerobically on hydrogen coupled to ferric iron reduction. While the 16S rRNA genes of the iron-oxidizing Acidi-thiobacillus species (and strain MG) are located in a distinct phylogenetic clade and are closely related (98–99% 16S rRNA gene identity), genomic relatedness indexes (ANI/dDDH) revealed strong genomic divergence between strain MG and all sequenced type strains of the taxon, and placed MG as the first cultured representative of an ancestral phylotype of iron oxidizing acidithiobacilli. Strain MG is proposed as a novel species, Acidithiobacillus ferrianus sp. nov. The type strain is MGT (= DSM 107098T = JCM 33084T). Similar strains have been found as isolates or indicated by cloned 16S rRNA genes from several mineral sulfide mine sites.

  相似文献   
105.
The noise filter hypothesis predicts that species using higher sound frequencies should be more tolerant of noise pollution, because anthropogenic noise is more intense at low frequencies. Recent work analysed continental‐scale data on anthropogenic noise across the USA and found that passerine species inhabiting more noise‐polluted areas do not have higher peak song frequency but have more complex songs. However, this metric of song complexity is of ambiguous interpretation, because it can indicate either diverse syllables or a larger frequency bandwidth. In the latter case, the finding would support the noise filter hypothesis, because larger frequency bandwidths mean that more sound energy spreads to frequencies that are less masked by anthropogenic noise. We reanalysed how passerine song predicts exposure to noise using a more thorough dataset of acoustic song measurements, and showed that it is large frequency bandwidths, rather than diverse syllables, that predict the exposure of species to noise pollution. Given that larger bandwidths often encompass higher maximum frequencies, which are less masked by anthropogenic noise, our result suggests that tolerance to noise pollution might depend mostly on having the high‐frequency parts of song little masked by noise, thus preventing acoustic communication from going entirely unnoticed at long distances.  相似文献   
106.
Prenatal and neonatal exposure to estrogenic compounds, such as ethinylestradiol (EE), promotes a variety of developmental disorders, including malformations and alterations in the morphology of glands, such as the prostate gland. Therefore, the aim of this study was to evaluate the morphological effects of neonatal exposure to EE on prostatic tissue and on the identification and quantification of gerbil gland macrophages in adult and senile Mongolian gerbils. The animals were exposed to EE (10 μg/kg/day) and to the vehicle, mineral oil (100 μL) (control group) during the first 10 days of postnatal life (lactation period). Adult gerbils were euthanized at 120 days and senile gerbils at 12 months of age. Our findings permitted verification of the presence of areas with proliferative foci in the prostate glandular portions in the adult and senile animals exposed to EE. There was also an increase in macrophages in the prostate tissue of adult and senile gerbils; these cell types alter the stromal microenvironment and possibly modify the interactions between the epithelium and stroma. Neonatal exposure to EE changes the pattern of prostatic development, leading to alterations in the arrangement of cells, including macrophages, and may be related to the onset of proliferative disorders in the prostate of adult gerbils and during aging.  相似文献   
107.
108.
The vascular cellular adhesion molecule-1 (VCAM-1) is a protein that canonically participates in the adhesion and transmigration of leukocytes to the interstitium during inflammation. VCAM-1 expression, together with soluble VCAM-1 (sVCAM-1) induced by the shedding of VCAM-1 by metalloproteinases, have been proposed as biomarkers in immunological diseases, cancer, autoimmune myocarditis, and as predictors of mortality and morbidity in patients with chronic heart failure (HF), endothelial injury in patients with coronary artery disease, and arrhythmias. This revision aims to discuss the role of sVCAM-1 as a biomarker to predict the occurrence, development, and preservation of cardiovascular disease.  相似文献   
109.
110.
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