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   3593篇
  免费   261篇
  2023年   13篇
  2022年   39篇
  2021年   67篇
  2020年   34篇
  2019年   51篇
  2018年   82篇
  2017年   56篇
  2016年   96篇
  2015年   147篇
  2014年   160篇
  2013年   223篇
  2012年   244篇
  2011年   252篇
  2010年   144篇
  2009年   133篇
  2008年   227篇
  2007年   233篇
  2006年   185篇
  2005年   171篇
  2004年   186篇
  2003年   154篇
  2002年   166篇
  2001年   51篇
  2000年   51篇
  1999年   38篇
  1998年   53篇
  1997年   33篇
  1996年   42篇
  1995年   32篇
  1994年   32篇
  1993年   32篇
  1992年   47篇
  1991年   43篇
  1990年   33篇
  1989年   36篇
  1988年   22篇
  1987年   11篇
  1986年   25篇
  1985年   28篇
  1984年   28篇
  1983年   19篇
  1982年   17篇
  1981年   11篇
  1980年   15篇
  1979年   10篇
  1978年   10篇
  1977年   18篇
  1974年   9篇
  1972年   9篇
  1971年   8篇
排序方式: 共有3854条查询结果,搜索用时 31 毫秒
81.
Evidence is presented for the selective breakdown of altered tomato β-fructofuranosidase molecules by a neutral protease from Bacillus subtilis.  相似文献   
82.
83.
Mother-infant vocal interactions play a crucial role in the development of human language. However, comparatively little is known about the maternal role during vocal development in nonhuman primates. Here, we report the first evidence of mother-daughter vocal interactions contributing to vocal development in gibbons, a singing and monogamous ape species. Gibbons are well known for their species-specific duets sung between mates, yet little is known about the role of intergenerational duets in gibbon song development. We observed singing interactions between free-ranging mothers and their sub-adult daughters prior to emigration. Daughters sang simultaneously with their mothers at different rates. First, we observed significant acoustic variation between daughters. Co-singing rates between mother and daughter were negatively correlated with the temporal precision of the song’s synchronization. In addition, songs of daughters who co-sang less with their mothers were acoustically more similar to the maternal song than any other adult female’s song. All variables have been reported to be influenced by social relationships of pairs. Therefore those correlations would be mediated by mother-daughter social relationship, which would be modifiable in daughter’s development. Here we hypothesized that daughters who co-sing less often, well-synchronize, and converge acoustically with the maternal acoustic pattern would be at a more advanced stage of social independence in sub-adult females prior to emigration. Second, we observed acoustic matching between mothers and daughters when co-singing, suggesting short-term vocal flexibility. Third, we found that mothers adjusted songs to a more stereotyped pattern when co-singing than when singing alone. This vocal adjustment was stronger for mothers with daughters who co-sang less. These results indicate the presence of socially mediated vocal flexibility in gibbon sub-adults and adults, and that mother-daughter co-singing interactions may enhance vocal development. More comparative work, notably longitudinal and experimental, is now needed to clarify maternal roles during song development.  相似文献   
84.
Chick embryos grown in ex ovo culture by the modified Cornish pasty method reported in Nagai, Lin and Sheng in this issue.  相似文献   
85.
Environmental DNA (eDNA) analysis has recently been used as a new tool for estimating intraspecific diversity. However, whether known haplotypes contained in a sample can be detected correctly using eDNA‐based methods has been examined only by an aquarium experiment. Here, we tested whether the haplotypes of Ayu fish (Plecoglossus altivelis altivelis) detected in a capture survey could also be detected from an eDNA sample derived from the field that contained various haplotypes with low concentrations and foreign substances. A water sample and Ayu specimens collected from a river on the same day were analysed by eDNA analysis and Sanger sequencing, respectively. The 10 L water sample was divided into 20 filters for each of which 15 PCR replications were performed. After high‐throughput sequencing, denoising was performed using two of the most widely used denoising packages, unoise3 and dada2 . Of the 42 haplotypes obtained from the Sanger sequencing of 96 specimens, 38 (unoise3 ) and 41 (dada2 ) haplotypes were detected by eDNA analysis. When dada2 was used, except for one haplotype, haplotypes owned by at least two specimens were detected from all the filter replications. Accordingly, although it is important to note that eDNA‐based method has some limitations and some risk of false positive and false negative, this study showed that the eDNA analysis for evaluating intraspecific genetic diversity provides comparable results for large‐scale capture‐based conventional methods. Our results suggest that eDNA‐based methods could become a more efficient survey method for investigating intraspecific genetic diversity in the field.  相似文献   
86.
Wetlands Ecology and Management - Small valley topology on terraced uplands is a unique groundwater-dependent ecosystem in East Asia. Traditionally, this characteristic valley topology has been...  相似文献   
87.
Norovirus infection cause epidemic nonbacterial gastroenteritis in patients. The immune mechanisms responsible for the clearance of virus are not completely understood. We examined whether NKT cells are effective against norovirus infection using CD1d KO mice. The body weights of 4-weeks-old CD1d KO mice that were infected with murine norovirus-S7 (MNV-S7) were significantly lower than those of non-infected CD1d KO mice. On the other hand, the body weights of infected WT mice were comparable to those of non-infected WT mice. Correspondingly, CD1d KO mice had an almost 1000-fold higher MNV-S7 burden in the intestine after infection in comparison to WT mice. The mechanism responsible for the insufficient MNV-S7 clearance in CD1d KO mice was attributed to reduced IFN-γ production early during MNV-S7 infection. In addition, the markedly impaired IL-4 production in CD1d KO mice resulted in an impaired MNV-S7-specific secretory IgA production after MNV-S7 infection which is associated with mucosal immunity. Thus, the present results provide evidence that NKT cells play an essential role in MNV-S7 clearance.  相似文献   
88.
89.
90.

To clarify physiological integration for salinity stress alleviation in Zoysia matrella, interconnected clonal stolon ramets were grown in three separate pots [basal (BR), intermediate (IR), and apical ramets (AR)]. Once ramets were well established, two experimental groups were set up: stolons connected with other ramets (Intact) and stolons cut between ramets (Severed). NaCl solution was used for IR, while tap water was used for BR and AR for 49 days. For BR and AR, there was no significant difference in NaCl content in any plant part (green leaves, brown leaves, stolons, and roots) in both groups. Therefore, we concluded that no NaCl translocation in interconnected ramets occurred for both basal and apical directions. For the IR in Intact group, water content in stolons was 1.2 times higher, and NaCl content in green and brown leaves was 16 and 29% lower, respectively than in Severed group. Dry weight of both above ground and below ground parts in Intact groups were 1.3 times higher as compared to that in Severed group. It was considered that tap water treated ramets (BR or AR) translocated water to IR and decreased the amount of NaCl in the body, thereby alleviating salt stress. For the IR in both groups, NaCl content in brown leaves was 2–3 times higher than in other parts. We conclude that Zoysia matrella does not translocate toxic component, such as NaCl between ramets, and does not distribute it to other ramets; however, ramet accumulates NaCl in brown leaves under salt stress condition.

  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