全文获取类型
收费全文 | 66326篇 |
免费 | 17057篇 |
国内免费 | 7篇 |
专业分类
83390篇 |
出版年
2023年 | 272篇 |
2022年 | 324篇 |
2021年 | 935篇 |
2020年 | 2663篇 |
2019年 | 4199篇 |
2018年 | 4826篇 |
2017年 | 4887篇 |
2016年 | 5301篇 |
2015年 | 5786篇 |
2014年 | 5422篇 |
2013年 | 6514篇 |
2012年 | 4731篇 |
2011年 | 4193篇 |
2010年 | 4650篇 |
2009年 | 3026篇 |
2008年 | 2732篇 |
2007年 | 2334篇 |
2006年 | 2322篇 |
2005年 | 1995篇 |
2004年 | 1972篇 |
2003年 | 1765篇 |
2002年 | 1660篇 |
2001年 | 1283篇 |
2000年 | 1187篇 |
1999年 | 910篇 |
1998年 | 308篇 |
1997年 | 213篇 |
1996年 | 221篇 |
1995年 | 227篇 |
1994年 | 168篇 |
1993年 | 156篇 |
1992年 | 465篇 |
1991年 | 400篇 |
1990年 | 384篇 |
1989年 | 367篇 |
1988年 | 327篇 |
1987年 | 320篇 |
1986年 | 295篇 |
1985年 | 288篇 |
1984年 | 228篇 |
1983年 | 205篇 |
1982年 | 165篇 |
1979年 | 262篇 |
1974年 | 175篇 |
1973年 | 169篇 |
1972年 | 164篇 |
1971年 | 153篇 |
1970年 | 164篇 |
1969年 | 161篇 |
1968年 | 155篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
52.
53.
Hermógenes Fernández-Marín David R. Nash Sarah Higginbotham Catalina Estrada Jelle S. van Zweden Patrizia d'Ettorre William T. Wcislo Jacobus J. Boomsma 《Proceedings. Biological sciences / The Royal Society》2015,282(1807)
Fungus-farming ant colonies vary four to five orders of magnitude in size. They employ compounds from actinomycete bacteria and exocrine glands as antimicrobial agents. Atta colonies have millions of ants and are particularly relevant for understanding hygienic strategies as they have abandoned their ancestors'' prime dependence on antibiotic-based biological control in favour of using metapleural gland (MG) chemical secretions. Atta MGs are unique in synthesizing large quantities of phenylacetic acid (PAA), a known but little investigated antimicrobial agent. We show that particularly the smallest workers greatly reduce germination rates of Escovopsis and Metarhizium spores after actively applying PAA to experimental infection targets in garden fragments and transferring the spores to the ants'' infrabuccal cavities. In vitro assays further indicated that Escovopsis strains isolated from evolutionarily derived leaf-cutting ants are less sensitive to PAA than strains from phylogenetically more basal fungus-farming ants, consistent with the dynamics of an evolutionary arms race between virulence and control for Escovopsis, but not Metarhizium. Atta ants form larger colonies with more extreme caste differentiation relative to other attines, in societies characterized by an almost complete absence of reproductive conflicts. We hypothesize that these changes are associated with unique evolutionary innovations in chemical pest management that appear robust against selection pressure for resistance by specialized mycopathogens. 相似文献
54.
55.
Léniz A. Portillo M. P. Fernández-Quintela Alfredo Macarulla M. T. Sarasua-Miranda A. del Hoyo M. Díez-López I. 《Journal of physiology and biochemistry》2019,75(3):311-319
Journal of Physiology and Biochemistry - Infants born small for gestational age (SGA) are at increased risk of perinatal morbidity, persistent short stature, and metabolic alterations in later... 相似文献
56.
Late Quaternary climate change,relict populations and present‐day refugia in the northern Atacama Desert: a case study from Quebrada La Higuera (18° S) 下载免费PDF全文
57.
58.
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
59.
60.
The binding of norepinephrine (NE) to plasma proteins of fresh human blood obtained from healthy volunteers was studied by ultrafiltration at different NE concentrations and incubation times at 37 degrees C. At 1.7 nM L-[3H]-NE binding was approximately 25%. The binding was rapid and was not influenced by the incubation time. [3H]-NE could be dissociated from its binding sites by acid precipitation and, after HPLC, showed to be unchanged NE. No difference in NE binding was found between plasma collected in EGTA-GSH or heparin solution. There was no degradation of NE when incubated in plasma at 37 degrees C for 10 h, even without the addition of antioxidants. Therefore, in the present study, binding represented interaction of unchanged NE with plasma proteins. The whole plasma binding was saturable over the range of 0.66 nM to 0.59 mM of NE. Scatchard plot of specific binding revealed high-affinity sites with a Kd of 5.4 nM and a Bmax of 3.9 fmoles.mg-1 protein, and low-affinity sites with a Kd of 2.7 microM and a Bmax of 3.3 pmoles.mg-1 protein. Electrophoretic characterization of NE-binding proteins showed that about 60% of bound NE was associated to albumin, and 20% to prealbumin. NE binding to pure human plasma proteins was also studied using ultrafiltration. Scatchard analyses revealed a single class of very high-affinity binding sites for prealbumin (Kd 4.9 nM), a single class of binding sites for alpha 1-acid glycoprotein (Kd 54 microM) and two classes of binding sites for albumin with high (Kd 1.7 microM) and low (Kd 0.8 mM) affinities respectively. The main results obtained in this study - a) reversibility of NE binding, b) stability of free and bound NE in plasma, c) involvement of the prealbumin as a specific binding protein - point out to a specific transport for NE in human blood plasma. 相似文献