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   6983篇
  免费   549篇
  国内免费   5篇
  2023年   44篇
  2022年   47篇
  2021年   106篇
  2020年   79篇
  2019年   99篇
  2018年   213篇
  2017年   207篇
  2016年   264篇
  2015年   408篇
  2014年   325篇
  2013年   460篇
  2012年   586篇
  2011年   565篇
  2010年   321篇
  2009年   228篇
  2008年   369篇
  2007年   329篇
  2006年   333篇
  2005年   303篇
  2004年   294篇
  2003年   251篇
  2002年   216篇
  2001年   193篇
  2000年   195篇
  1999年   141篇
  1998年   60篇
  1997年   28篇
  1996年   38篇
  1995年   46篇
  1994年   24篇
  1993年   29篇
  1992年   86篇
  1991年   52篇
  1990年   57篇
  1989年   53篇
  1988年   46篇
  1987年   61篇
  1986年   45篇
  1985年   45篇
  1984年   46篇
  1983年   18篇
  1982年   21篇
  1979年   16篇
  1977年   14篇
  1975年   19篇
  1974年   29篇
  1973年   17篇
  1971年   10篇
  1970年   11篇
  1968年   15篇
排序方式: 共有7537条查询结果,搜索用时 15 毫秒
131.
Limnology - Lake Cuitzeo is Mexico’s second-largest lake (~ 425 km2). The West Basin is shallow, seasonally astatic and alkaline, and it contains saltwater; it is in this...  相似文献   
132.
Journal of Physiology and Biochemistry - Connections between the midbrain dorsolateral periaqueductal grey (dlPAG) and the pontine A5 region have been shown. The stimulation of both regions evokes...  相似文献   
133.
Leveraging existing presence records and geospatial datasets, species distribution modeling has been widely applied to informing species conservation and restoration efforts. Maxent is one of the most popular modeling algorithms, yet recent research has demonstrated Maxent models are vulnerable to prediction errors related to spatial sampling bias and model complexity. Despite elevated rates of biodiversity imperilment in stream ecosystems, the application of Maxent models to stream networks has lagged, as has the availability of tools to address potential sources of error and calculate model evaluation metrics when modeling in nonraster environments (such as stream networks). Herein, we use Maxent and customized R code to estimate the potential distribution of paddlefish (Polyodon spathula) at a stream‐segment level within the Arkansas River basin, USA, while accounting for potential spatial sampling bias and model complexity. Filtering the presence data appeared to adequately remove an eastward, large‐river sampling bias that was evident within the unfiltered presence dataset. In particular, our novel riverscape filter provided a repeatable means of obtaining a relatively even coverage of presence data among watersheds and streams of varying sizes. The greatest differences in estimated distributions were observed among models constructed with default versus AICC‐selected parameterization. Although all models had similarly high performance and evaluation metrics, the AICC‐selected models were more inclusive of westward‐situated and smaller, headwater streams. Overall, our results solidified the importance of accounting for model complexity and spatial sampling bias in SDMs constructed within stream networks and provided a roadmap for future paddlefish restoration efforts in the study area.  相似文献   
134.
Experimental and Applied Acarology - Tenuipalpid mites of the genus Brevipalpus are of significant economic and quarantine importance in agriculture. They can damage and vector phytopathogenic...  相似文献   
135.
The length–weight relationships (LWR) were estimated for five selected demersal marine fishes from the relatively undisturbed shelves and slopes of the Cabo Verde Islands. Most of them were of ecological and/or commercial interest. Occasional sampling was carried out during different fisheries research projects. LWRs were taken for the following bycatch species for which no such estimates exists in the science literature: Myroconger compressus, Synaphobranchus affinis, Physiculus cyanostrophus, Physiculus caboverdensis and Canthidermis maculata. Total length and fork length (to the nearest 0.1 cm) and total weight (to the nearest 0.1 g) were determined. The resulting length–weight equations are characterized by a high accompanying coefficient of correlation. The present data help improving the knowledge base needed for further fish biology studies and fisheries management.  相似文献   
136.
Human Ecology - We address two aspects of forest lives—violence and care—that are central to forest outcomes but often invisible in mainstream discussions on forests. We argue that...  相似文献   
137.
138.
González-Romero  M. E.  Rivera  C.  Cancino  K.  Geu-Flores  F.  Cosio  E. G.  Ghislain  M.  Halkier  B. A. 《Transgenic research》2021,30(5):649-660
Transgenic Research - In traditional, small-scale agriculture in the Andes, potatoes are frequently co-cultivated with the Andean edible tuber Tropaeolum tuberosum, commonly known as mashua, which...  相似文献   
139.

Members of the proposed phylum ‘Candidatus Poribacteria’ are among the most abundant microorganisms in the highly diverse microbiome of the sponge mesohyl. Genomic and phylogenetic characteristics of this proposed phylum are barely known. In this study, we analyzed metagenome-assembled genomes (MAGs) obtained from the coral reef excavating sponge Thoosa mismalolli from the Mexican Pacific Ocean. Two MAGs were extracted and analyzed together with 32 MAGs and single-amplified genomes (SAGs) obtained from NCBI. The phylogenetic tree based on the sequences of 139 single-copy genes (SCG) showed two clades. Clade A (23 genomes) represented 67.7% of the total of the genomes, while clade B (11 genomes) comprised 32.3% of the genomes. The Average Nucleotide Identity (ANI) showed values between 66 and 99% for the genomes of the proposed phylum, and the pangenome of genomes revealed a total of 37,234 genes that included 1722 core gene. The number of genes used in the phylogenetic analysis increased from 28 (previous studies) to 139 (this study), which allowed a better resolution of the phylogeny of the proposed phylum. The results supported the two previously described classes, ‘Candidatus Entoporibacteria’ and ‘Candidatus Pelagiporibacteria’, and the genomes SB0101 and SB0202 obtained in this study belong to two new species of the class ‘Candidatus Entoporibacteria’. This is the first comparative study that includes MAGs from a non-sponge host (Porites lutea) to elucidate the taxonomy of the poorly known Candidatus phylum in a polyphasic approach. Finally, our study also contributes to the sponge microbiome project by reporting the first MAGs of the proposed phylum ‘Candidatus Poribacteria isolated from the excavating sponge T. mismalolli.

  相似文献   
140.
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