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   428篇
  免费   52篇
  国内免费   23篇
  2023年   10篇
  2022年   8篇
  2021年   9篇
  2020年   19篇
  2019年   14篇
  2018年   7篇
  2017年   16篇
  2016年   13篇
  2015年   16篇
  2014年   19篇
  2013年   23篇
  2012年   25篇
  2011年   20篇
  2010年   16篇
  2009年   26篇
  2008年   19篇
  2007年   21篇
  2006年   30篇
  2005年   30篇
  2004年   18篇
  2003年   17篇
  2002年   16篇
  2001年   16篇
  2000年   12篇
  1999年   8篇
  1998年   13篇
  1997年   8篇
  1996年   14篇
  1995年   5篇
  1994年   6篇
  1993年   6篇
  1992年   8篇
  1991年   3篇
  1990年   3篇
  1989年   1篇
  1987年   4篇
  1986年   1篇
  1985年   1篇
  1982年   1篇
  1979年   1篇
排序方式: 共有503条查询结果,搜索用时 15 毫秒
1.
2.
桑白蚧恩蚜小蜂Encarsia(=Prospaltella)berlesel(Howard)是寄生桑白蚧Pseudaulacaspls pentagona(Targioni-Tozzctti)的重要寄生蜂,许多国家进行了引进移植,对控制桑白蚧的为害取得明显的成效.本记述了桑白蚧恩蚜小蜂形态特征的鉴别。以及各国引进利用的概况.并讨论了利用寄生蜂防治桑白蚧的重要性.  相似文献   
3.
The first record of Misgurnus anguillicaudatus in Germany   总被引:1,自引:0,他引:1  
Oriental weatherfish Misgurnus anguillicaudatus , from southern China, have been imported to Germany in large numbers for the garden pond trade. The first record of M. anguillicaudatus from Central Europe, a population that has been established for at least 14 years in a small nature reserve in Germany, is detailed.  相似文献   
4.
Abstract: Unlike many regions in the world where wild pigs (Sus scrofa) are threatened, in Australia they are a significant invasive species. As such, the molecular ecology of feral pigs was investigated to understand their social and population genetic structure. Samples from 269 adult animals were collected over their distribution in southwestern Australia. Using 14 highly polymorphic microsatellite markers, we identified 7 inferred feral pig populations that had moderate heterozygosity (mean = 0.580) and displayed a high level of differentiation (mean RST = 0.180). In revealing the genetic structure of feral pigs, we detected anomalies in the putative origin of some individuals. Samples from these animals were collected from 2 main areas: recently colonized regions that were previously uninfested, and established feral pig populations, where animals from geographically isolated areas had been introduced. In the latter, these corresponded to areas that were in close proximity to public road access and towns. Given the large distances immigrants were found from their population of origin (from 50 to >400 km), the generally low levels of dispersal of southwest feral pigs, and the grouping and sex of these pigs, we suggest that these individuals have been deliberately and illegally translocated to supplement recreational hunting stocks. Additionally, we could not detect any genetic contribution in these feral pigs from domestic pig herds, suggesting that the deliberate release of domestic pigs to restock feral populations is relatively uncommon. Our molecular data allowed some inferences regarding the success or lack thereof of current management practices, and offered considerable insights into the dynamics of the feral pig populations and identification of “new” approaches that may allow for better control of this highly destructive species.  相似文献   
5.
浙江省木本植物区系特征及其与引种驯化的关系   总被引:4,自引:0,他引:4  
本文对浙江省木本植物区系特征进行分析,探讨该省木本植物区系与引种驯化的关系,旨在为园林工作者更好地开展引种驯化工作、切实提高引种成功率提供参考。  相似文献   
6.
本文报道四川攀西地区引进的53科143个观赏花卉品种的引种试种情况。结果表明,所引进的品种在攀西地区均表现为适应性较强,可望成为今后该地区发展观赏花卉的主导品种。  相似文献   
7.
Re‐introduction is an important tool for recovering endangered species; however, the magnitude of genetic consequences for re‐introduced populations remains largely unknown, in particular the relative impacts of historical population bottlenecks compared to those induced by conservation management. We characterize 14 microsatellite loci developed for the Seychelles paradise flycatcher and use them to quantify temporal and spatial measures of genetic variation across a 134‐year time frame encompassing a historical bottleneck that reduced the species to ~28 individuals in the 1960s, through the initial stages of recovery and across a second contemporary conservation‐introduction‐induced bottleneck. We then evaluate the relative impacts of the two bottlenecks, and finally apply our findings to inform broader re‐introduction strategy. We find a temporal trend of significant decrease in standard measures of genetic diversity across the historical bottleneck, but only a nonsignificant downward trend in number of alleles across the contemporary bottleneck. However, accounting for the different timescales of the two bottlenecks (~40 historical generations versus <1 contemporary generation), the loss of genetic diversity per generation is greater across the contemporary bottleneck. Historically, the flycatcher population was genetically structured; however, extinction on four of five islands has resulted in a homogeneous contemporary population. We conclude that severe historical bottlenecks can leave a large footprint in terms of sheer quantity of genetic diversity lost. However, severely depleted genetic diversity does not render a species immune to further genetic erosion upon re‐introduction. In some cases, the loss of genetic diversity per generation can, initially at least, be greater across re‐introduction‐induced bottlenecks.  相似文献   
8.
苦丁茶在海南儋州的引种试种   总被引:1,自引:0,他引:1  
在海南儋州进行苦丁茶引种试验,结果表明,儋州地区适宜种植苦丁茶,且能获得料高产量。田间试验表明,适当遮阳能促进植株的生长,灌溉是种植成功并获得高产的重要条件;生产中要加强技术管理,培养合理的树冠,以便保持持续的高产、稳产。  相似文献   
9.

Background

During standard gene cloning, the recombinant protein appearing in bacteria as the result of expression leakage very often inhibits cell proliferation leading to blocking of the cloning procedure. Although different approaches can reduce transgene basal expression, the recombinant proteins, which even in trace amounts inhibit bacterial growth, can completely prevent the cloning process.

Methods

Working to solve the problem of DNase II-like cDNA cloning, we developed a novel cloning approach. The method is based on separate cloning of the 5′ and 3′ fragments of target cDNA into a vector in such a way that the short Multiple Cloning Site insertion remaining between both fragments changes the reading frame and prevents translation of mRNA arising as a result of promoter leakage. Subsequently, to get the vector with full, uninterrupted Open Reading Frame, the Multiple Cloning Site insertion is removed by in vitro restriction/ligation reactions, utilizing the unique restriction site present in native cDNA.

Results

Using this designed method, we cloned a coding sequence of AcDNase II that is extremely toxic for bacteria cells. Then, we demonstrated the usefulness of the construct prepared in this way for overexpression of AcDNase II in eukaryotic cells.

Conclusions

The designed method allows cloning of toxic protein coding sequences that cannot be cloned by standard methods.

General significance

Cloning of cDNAs encoding toxic proteins is still a troublesome problem that hinders the progress of numerous studies. The method described here is a convenient solution to cloning problems that are common in research on toxic proteins.  相似文献   
10.
Detailed knowledge about the geographical pathways followed by propagules from their source to the invading populations—referred to here as routes of invasion—provides information about the history of the invasion process and the origin and genetic composition of the invading populations. The reconstruction of invasion routes is required for defining and testing different hypotheses concerning the environmental and evolutionary factors responsible for biological invasions. In practical terms, it facilitates the design of strategies for controlling or preventing invasions. Most of our knowledge about the introduction routes of invasive species is derived from historical and observational data, which are often sparse, incomplete and, sometimes, misleading. In this context, population genetics has proved a useful approach for reconstructing routes of introduction, highlighting the complexity and the often counterintuitive nature of the true story. This approach has proved particularly useful since the recent development of new model‐based methods, such as approximate Bayesian computation, making it possible to make quantitative inferences in the complex evolutionary scenarios typically encountered in invasive species. In this review, we summarize some of the fundamental aspects of routes of invasion, explain why the reconstruction of these routes is useful for addressing both practical and theoretical questions, and comment on the various reconstruction methods available. Finally, we consider the main insights obtained to date from studies of invasion routes.  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