全文获取类型
收费全文 | 8392篇 |
免费 | 689篇 |
出版年
2024年 | 9篇 |
2023年 | 41篇 |
2022年 | 35篇 |
2021年 | 232篇 |
2020年 | 137篇 |
2019年 | 182篇 |
2018年 | 215篇 |
2017年 | 184篇 |
2016年 | 322篇 |
2015年 | 460篇 |
2014年 | 488篇 |
2013年 | 594篇 |
2012年 | 670篇 |
2011年 | 627篇 |
2010年 | 425篇 |
2009年 | 386篇 |
2008年 | 484篇 |
2007年 | 496篇 |
2006年 | 389篇 |
2005年 | 378篇 |
2004年 | 371篇 |
2003年 | 319篇 |
2002年 | 321篇 |
2001年 | 147篇 |
2000年 | 110篇 |
1999年 | 119篇 |
1998年 | 104篇 |
1997年 | 82篇 |
1996年 | 51篇 |
1995年 | 54篇 |
1994年 | 50篇 |
1993年 | 37篇 |
1992年 | 65篇 |
1991年 | 51篇 |
1990年 | 53篇 |
1989年 | 49篇 |
1988年 | 50篇 |
1987年 | 31篇 |
1986年 | 36篇 |
1985年 | 30篇 |
1984年 | 27篇 |
1983年 | 26篇 |
1982年 | 27篇 |
1981年 | 22篇 |
1980年 | 13篇 |
1979年 | 14篇 |
1978年 | 12篇 |
1974年 | 9篇 |
1973年 | 11篇 |
1971年 | 8篇 |
排序方式: 共有9081条查询结果,搜索用时 343 毫秒
1.
2.
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
3.
4.
Marta Tejera-Alhambra Armanda Casrouge Clara de Andrés Ansgar Seyfferth Rocío Ramos-Medina Bárbara Alonso Janet Vega Lidia Fernández-Paredes Matthew L. Albert Silvia Sánchez-Ramón 《PloS one》2015,10(6)
Multiple sclerosis, the most common cause of neurological disability in young population after trauma, represents a significant public health burden. Current challenges associated with management of multiple sclerosis (MS) patients stem from the lack of biomarkers that might enable stratification of the different clinical forms of MS and thus prompt treatment for those patients with progressive MS, for whom there is currently no therapy available. In the present work we analyzed a set of thirty different plasma cytokines, chemokines and growth factors present in circulation of 129 MS patients with different clinical forms (relapsing remitting, secondary progressive and primary progressive MS) and 53 healthy controls, across two independent cohorts. The set of plasma analytes was quantified with Luminex xMAP technology and their predictive power regarding clinical outcome was evaluated both individually using ROC curves and in combination using logistic regression analysis. Our results from two independent cohorts of MS patients demonstrate that the divergent clinical and histology-based MS forms are associated with distinct profiles of circulating plasma protein biomarkers, with distinct signatures being composed of chemokines and growth/angiogenic factors. With this work, we propose that an evaluation of a set of 4 circulating biomarkers (HGF, Eotaxin/CCL11, EGF and MIP-1β/CCL4) in MS patients might serve as an effective tool in the diagnosis and more personalized therapeutic targeting of MS patients. 相似文献
5.
6.
7.
8.
Molecular epidemiology of plasmid mediated resistance to fosfomycin among bacteria isolated from different environments 总被引:1,自引:0,他引:1
F. Javier Terán Juan E. Suárez Carlos Hardisson M. Carmen Mendoza 《FEMS microbiology letters》1988,55(2):213-216
In this report we present data on the dispersion of a gene responsible for the plasmid-mediated resistance to fosfomycin among bacteria isolated from four hospitals and seven geographically separated domestic sewage treatment plants. Colony hybridization experiments, using a 0.85 kbp DNA fragment which carried the fosfomycin resistance determinant, have shown that the gene was present in isolates from three hospitals and six sewage plants although with different incidence and that it is carried by species of Enterobacteriaceae, Pseudomonas, Acinetobacter, Staphylococcus and Bacillus . 相似文献
9.
In the River Lobos-Ucero and its tributary the River Avión-Milanos (Duero basin, Old Castile, Central Spain), two limestone streams fed by aquifers, the population of brown trout, as compared with the populations of other European streams, shows a high growth rate, high condition coefficients, short life-span and early age at first maturity. Gonad cycle was also studied. Size distributions of unshed eggs exhibit a dynamic activity with a bi-modal distribution from June onwards, spawning occurred in the last days of November. Fecundity (F) can be predicted from trout length (L, mm) according to the equation: F= –646.47+5.6167 · L. Numbers and standing crop of trout range from 18 to 3903 ind. ha–1 and 3.6 to 452.9 Kg ha–1, reaching higher values in the sites close to the aquifers. Egg production had values of 22.4 and 18.0 eggs m–2 in the Rivers Ucero and Avión-Milanos respectively. Some factors suggested as regulators of these demographical characteristics are discussed in the light of recent literature. 相似文献
10.