全文获取类型
收费全文 | 7076篇 |
免费 | 525篇 |
国内免费 | 5篇 |
出版年
2023年 | 44篇 |
2022年 | 74篇 |
2021年 | 132篇 |
2020年 | 124篇 |
2019年 | 111篇 |
2018年 | 234篇 |
2017年 | 196篇 |
2016年 | 285篇 |
2015年 | 344篇 |
2014年 | 366篇 |
2013年 | 485篇 |
2012年 | 556篇 |
2011年 | 533篇 |
2010年 | 351篇 |
2009年 | 267篇 |
2008年 | 401篇 |
2007年 | 370篇 |
2006年 | 334篇 |
2005年 | 295篇 |
2004年 | 296篇 |
2003年 | 306篇 |
2002年 | 238篇 |
2001年 | 111篇 |
2000年 | 110篇 |
1999年 | 86篇 |
1998年 | 55篇 |
1997年 | 46篇 |
1996年 | 42篇 |
1995年 | 45篇 |
1994年 | 48篇 |
1993年 | 32篇 |
1992年 | 43篇 |
1991年 | 41篇 |
1990年 | 48篇 |
1989年 | 50篇 |
1988年 | 39篇 |
1987年 | 29篇 |
1986年 | 29篇 |
1985年 | 23篇 |
1984年 | 48篇 |
1983年 | 23篇 |
1982年 | 24篇 |
1981年 | 37篇 |
1980年 | 24篇 |
1979年 | 24篇 |
1978年 | 17篇 |
1977年 | 20篇 |
1975年 | 17篇 |
1974年 | 19篇 |
1973年 | 16篇 |
排序方式: 共有7606条查询结果,搜索用时 15 毫秒
1.
Classification and ordination of plant communities along an altitudinal gradient on the Presidential Range,New Hampshire,USA 总被引:1,自引:0,他引:1
An analysis of vegetation along an altitudinal gradient on the Presidential Range, New Hampshire, USA, using the Braun–Blanquet approach followed by multivariate data analysis is presented. Twelve main plant communities have been distinguished. Floristic information is presented in twelve tables and one appendix. The relationships of the communities to complex environmental gradients are analyzed using Correspondence Analysis. Floristic composition and community structure are controlled primarily by the altitudinal gradient (temperature, precipitation), and by mesotopographic conditions (snow accumulation, exposure and cryoturbation, slope position, and soil moisture). 相似文献
2.
3.
The role of arctic zooplankton in biogeochemical cycles: respiration and excretion of ammonia and phosphate during summer 总被引:1,自引:0,他引:1
M. Alcaraz R. Almeda A. Calbet E. Saiz C. M. Duarte S. Lasternas S. Agustí R. Santiago J. Movilla A. Alonso 《Polar Biology》2010,33(12):1719-1731
The study of the structural and functional properties of key components of polar marine ecosystems has received increased
attention in order to better understand the ecological consequences of future sea temperature rise and seasonal ice retraction.
Owing to this purpose, during the ATOS-Arctic cruise, held in July 2007 in the framework of the 2007–2008 International Polar
Year, we studied the respiratory carbon demand of mesozooplankton as well as their contribution to the regeneration of inorganic
nitrogen and phosphorus (NH4-N and PO4-P) via excretion. The studied area comprised several stations along a latitudinal gradient in the East Greenland current, plus a
network of stations NW of the Svalbard islands. The specific respiratory carbon losses and phosphorus (PO4-P) excretion rates were similar or slightly higher than some reports for Arctic mesozooplankton, but the nitrogen (NH4-N) excretion rates were higher by a factor of 3 when compared with previous data sets. The mesozooplankton respiratory losses
were equivalent to 23% of primary production, and at turn zooplankton contributed by excretion to more than 50% of the N and
P required by phytoplankton. Although C:N, C:P and N:P metabolic atomic quotients almost coincided with the average Redfield’s
stoichiometric ratios, the low C:N values when compared to previous reports suggested a predominance of protein-related metabolic
substrates. The potential consequences of changes observed in the C:N, N:P and C:P metabolic ratios of mesozooplankton for
Arctic marine ecosystems are discussed. 相似文献
4.
5.
6.
7.
David Gutirrez‐Larruscain Santiago Andrs‐Snchez Enrique Rico María Montserrat Martínez‐Ortega 《植物分类学报:英文版》2019,57(1):42-54
Forty-five populations of Pentanema corresponding to seven species included in the Pentanema conyzae clade have been studied using AFLP fingerprinting. The results show that allopolyploidization could have been involved in the diversification of this group, specifically in species P. langeanum and P. maletii. Molecular data confirm the presence of P. britannicum in the Iberian Peninsula and key steps are provided to identify the species that are morphologically the most challenging. 相似文献
8.
Uranium (U) tolerant aerobic heterotrophs were isolated from the subsurface soils of one of the pre-mined U-rich deposits at Domiasiat located in the north-eastern part of India. On screening of genomic DNA from 62 isolates exhibiting superior U and heavy metal tolerance, 32 isolates were found to be positive for PIB-type ATPase genes. Phylogenetic incongruence and anomalous DNA base compositions revealed the acquisition of PIB-type ATPase genes by six isolates through horizontal gene transfer (HGT). Three of these instances of HGT appeared to have occurred at inter-phylum level and the other three instances indicated to have taken place at intra-phylum level. This study provides an insight into one of the possible survival strategies that bacteria might employ to adapt to environments rich in uranium and heavy metals. 相似文献
9.
10.
Ram Kothandan 《Bioinformation》2015,11(1):6-10
MiRNAs are small (~22nt long) non-coding RNA sequences; binds to the complementarity target sites in 3'' Untranslated Region
(UTR) of mRNA sequences but not restricted to other mRNA regions viz., 5'' UTR and Coding sequences (CDS). Complementarity
binding of miRNA to mRNA target sites either results in complete degradation of the mRNA itself or it may regulate the mRNA as
an oncogene or as a tumor suppressor gene. However, the exact mechanism involved in identifying a miRNA to be associated with
cancer is still unclear. Further, with the outburst in the number of miRNAs sequences recorded every year in miRBase, the gap is
still widening mainly due to the laborious and economically unfavorable experimental procedures associated with the functional
annotation. Motivated by the fact, we constructed a two-step support vector machine-based predictive model - miRSEQ and
miRINT. However, the major pitfall during the construction of the model is the class imbalance problem. Hence, in order to
overcome class imbalance problem, in the present study we empirically compare the effectiveness of two different methods viz.,
Synthetic Minority Oversampling Technique (SMOTE) and cost-senstive learning method. Performance measures were evaluated
in terms of Precision and Recall. Based on our result, it was observed that for miRNA dataset with high class imbalance utilized for
predicting association of cancer, cost-sensitive method outperformed the oversampling method. 相似文献