全文获取类型
收费全文 | 1939篇 |
免费 | 137篇 |
出版年
2023年 | 11篇 |
2022年 | 22篇 |
2021年 | 37篇 |
2020年 | 20篇 |
2019年 | 41篇 |
2018年 | 55篇 |
2017年 | 41篇 |
2016年 | 76篇 |
2015年 | 75篇 |
2014年 | 87篇 |
2013年 | 127篇 |
2012年 | 138篇 |
2011年 | 118篇 |
2010年 | 91篇 |
2009年 | 86篇 |
2008年 | 111篇 |
2007年 | 84篇 |
2006年 | 89篇 |
2005年 | 110篇 |
2004年 | 93篇 |
2003年 | 79篇 |
2002年 | 81篇 |
2001年 | 31篇 |
2000年 | 19篇 |
1999年 | 26篇 |
1998年 | 14篇 |
1997年 | 23篇 |
1996年 | 18篇 |
1995年 | 16篇 |
1994年 | 26篇 |
1993年 | 21篇 |
1992年 | 22篇 |
1991年 | 16篇 |
1990年 | 13篇 |
1989年 | 14篇 |
1988年 | 10篇 |
1987年 | 11篇 |
1986年 | 12篇 |
1985年 | 14篇 |
1984年 | 9篇 |
1983年 | 12篇 |
1982年 | 7篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1978年 | 5篇 |
1976年 | 8篇 |
1975年 | 6篇 |
1974年 | 8篇 |
1970年 | 3篇 |
1966年 | 3篇 |
排序方式: 共有2076条查询结果,搜索用时 15 毫秒
41.
42.
Vincenzo Amico Rosario Currenti Giovanna Oriente Mario Piattelli Corrado Tringali 《Phytochemistry》1981,20(6):1451-1453
The major lipid component of the brown seaweed Zonaria tournefortii was identified as the acylphlorogluconol (all Z)-2′-icosa-5,8,11,14,17-pentae 相似文献
43.
44.
Beatriz Mello Qiqing Tao Jose Barba‐Montoya Sudhir Kumar 《Molecular ecology resources》2021,21(1):122-136
Simultaneous molecular dating of population and species divergences is essential in many biological investigations, including phylogeography, phylodynamics and species delimitation studies. In these investigations, multiple sequence alignments consist of both intra‐ and interspecies samples (mixed samples). As a result, the phylogenetic trees contain interspecies, interpopulation and within‐population divergences. Bayesian relaxed clock methods are often employed in these analyses, but they assume the same tree prior for both inter‐ and intraspecies branching processes and require specification of a clock model for branch rates (independent vs. autocorrelated rates models). We evaluated the impact of a single tree prior on Bayesian divergence time estimates by analysing computer‐simulated data sets. We also examined the effect of the assumption of independence of evolutionary rate variation among branches when the branch rates are autocorrelated. Bayesian approach with coalescent tree priors generally produced excellent molecular dates and highest posterior densities with high coverage probabilities. We also evaluated the performance of a non‐Bayesian method, RelTime, which does not require the specification of a tree prior or a clock model. RelTime's performance was similar to that of the Bayesian approach, suggesting that it is also suitable to analyse data sets containing both populations and species variation when its computational efficiency is needed. 相似文献
45.
Cara A. Faillace Arnaud Sentis José M. Montoya 《Biological reviews of the Cambridge Philosophical Society》2021,96(5):1933-1950
Eco-evolutionary dynamics can mediate species and community responses to habitat warming and fragmentation, two of the largest threats to biodiversity and ecosystems. The eco-evolutionary consequences of warming and fragmentation are typically studied independently, hindering our understanding of their simultaneous impacts. Here, we provide a new perspective rooted in trade-offs among traits for understanding their eco-evolutionary consequences. On the one hand, temperature influences traits related to metabolism, such as resource acquisition and activity levels. Such traits are also likely to have trade-offs with other energetically costly traits, like antipredator defences or dispersal. On the other hand, fragmentation can influence a variety of traits (e.g. dispersal) through its effects on the spatial environment experienced by individuals, as well as properties of populations, such as genetic structure. The combined effects of warming and fragmentation on communities should thus reflect their collective impact on traits of individuals and populations, as well as trade-offs at multiple trophic levels, leading to unexpected dynamics when effects are not additive and when evolutionary responses modulate them. Here, we provide a road map to navigate this complexity. First, we review single-species responses to warming and fragmentation. Second, we focus on consumer–resource interactions, considering how eco-evolutionary dynamics can arise in response to warming, fragmentation, and their interaction. Third, we illustrate our perspective with several example scenarios in which trait trade-offs could result in significant eco-evolutionary dynamics. Specifically, we consider the possible eco-evolutionary consequences of (i) evolution in thermal performance of a species involved in a consumer–resource interaction, (ii) ecological or evolutionary changes to encounter and attack rates of consumers, and (iii) changes to top consumer body size in tri-trophic food chains. In these scenarios, we present a number of novel, sometimes counter-intuitive, potential outcomes. Some of these expectations contrast with those solely based on ecological dynamics, for example, evolutionary responses in unexpected directions for resource species or unanticipated population declines in top consumers. Finally, we identify several unanswered questions about the conditions most likely to yield strong eco-evolutionary dynamics, how better to incorporate the role of trade-offs among traits, and the role of eco-evolutionary dynamics in governing responses to warming in fragmented communities. 相似文献
46.
M. Teresa García-López Rosario Herranz Paloma P. Méndez-Castrillón 《Nucleosides, nucleotides & nucleic acids》2013,32(2):127-138
Abstract The synthesis of 2-(β-D-ribofuranosyl)-and 2-(tetrahydropyran-2-yl)-4-halomethylthiazoles from 2, 5-anhydro-D-allonthioamide and tetrahydropyran-2-thiocarboxamide is described. Bromination of 2-(β-D-ribofuranosyl)- and 2-tetrahydropyran-2-yl)-4-methylthiazole with NBS is studied. Cytostatic activity against HeLa cells of all the compounds is reported. 相似文献
47.
Maria Rosaria Faraone-Mennella Anna Petrella Francesco Manguso Rosario Peluso Benedetta Farina 《Biomarkers》2013,18(6):381-387
The clinical usefulness of an immunotest was evaluated by using purified poly(adenosine diphosphate (ADP)-ribose) polymerase from Sulfolobus solfataricus (PARPSso) as an antigen to detect the presence of abnormal anti-PARP antibodies in the sera of patients with systemic lupus erythematosus (SLE) at different clinical stages. Sera from 44 patients with SLE, subgrouped on the basis of disease activity (16 with inactive disease, 28 with active disease) were analysed with a new immunotest to detect anti-PARP antibodies, and with an immunofluorescent (IIF) assay for antinuclear antibodies (ANA) detection. ANA detection by IIF revealed that sera of healthy subjects were negative, whereas sera from patients with SLE were positive in all cases (13 positive at 1:80, 15 at 1:160, 15 at 1:320, 1 at 1:640, v/v). Anti-PARP activity was higher in ANA-positive patients than in controls (p?=?0.005). Within the group of SLE sera, disease and anti-PARP activity was increased more significantly in patients with active than in those with inactive disease (p?0.001 and p?=?0.001, respectively). Correlation between anti-PARP and disease activity in SLE patients was statistically significant (p?0.001). PARPSso seems to be suitable for detecting anti-PARP antibodies and could play a role as a serological marker of disease activity in patients with SLE. 相似文献
48.
Rosario Vecchio Salvatore Marchese Francesco Ferla Linda Spataro Eva Intagliata 《Parasitology international》2013,62(6):487-493
BackgroundSolitary subcutaneous hydatid cyst is not frequent and the only symptom is generally a silent growing mass. Total excision remains the mainstay of treatment. Aim of the study was to present a case surgically treated and perform a statistical analysis reviewing previous published works in order to define a correct approach to diagnosis and treatment.Methods264 documents from Medline database were considered for primary subcutaneous hydatid cyst cases. Data concerning geographic region, gender, age, job, location, evolving time, history and physical, mobility, diameter, laboratory, imaging, locularity (uni- or multilocular cyst), fine-needle aspiration, preoperative diagnosis, neoadjuvant chemotherapy, treatment, spillage, adjuvant therapy, follow-up and recurrences were ordered in a database and analysed performing t-test, Fisher's test and Pearson's test.Results23 cases, included ours, resulted suitable for our study. Lower extremities were involved in most cases (60.9%) and the thigh represented the most common site (34.8%), whereas upper extremities were the rarest location (8.7%). Patients with head and neck located cysts were younger than those with upper extremities cysts (P = 0.037). Patients who underwent multiple imaging approach received a significantly correct first diagnosis (P = 0.001) and ultrasonography, unlike other techniques, appeared to be essential (P = 0.013).Case reportA 68-year-old man who lived and worked in his farm in Sicily (Italy) presented with a 30-year-growing mass in the deltoid region measuring 10 cm. Ultrasonography and magnetic resonance imaging strongly suggested hydatid cyst. Therefore the cyst was excised and pathology confirmed the diagnosis.ConclusionSolitary subcutaneous hydatid cyst must always be considered in the differential diagnosis of silent growing mass in soft tissues. History and physical associated with ultrasound and magnetic resonance imaging are sufficient to achieve a correct preoperative diagnosis. 相似文献
49.
50.
Magelda Montoya Lionel Gresh Juan Carlos Mercado Katherine L. Williams Maria José Vargas Gamaliel Gutierrez Guillermina Kuan Aubree Gordon Angel Balmaseda Eva Harris 《PLoS neglected tropical diseases》2013,7(8)
Four dengue virus serotypes (DENV1-4) circulate globally, causing more human illness than any other arthropod-borne virus. Dengue can present as a range of clinical manifestations from undifferentiated fever to Dengue Fever to severe, life-threatening syndromes. However, most DENV infections are inapparent. Yet, little is known about determinants of inapparent versus symptomatic DENV infection outcome. Here, we analyzed over 2,000 DENV infections from 2004 to 2011 in a prospective pediatric cohort study in Managua, Nicaragua. Symptomatic cases were captured at the study health center, and paired healthy annual samples were examined on a yearly basis using serological methods to identify inapparent DENV infections. Overall, inapparent and symptomatic DENV infections were equally distributed by sex. The mean age of infection was 1.2 years higher for symptomatic DENV infections as compared to inapparent infections. Although inapparent versus symptomatic outcome did not differ by infection number (first, second or third/post-second DENV infections), substantial variation in the proportion of symptomatic DENV infections among all DENV infections was observed across study years. In participants with repeat DENV infections, the time interval between a first inapparent DENV infection and a second inapparent infection was significantly shorter than the interval between a first inapparent and a second symptomatic infection. This difference was not observed in subsequent infections. This result was confirmed using two different serological techniques that measure total anti-DENV antibodies and serotype-specific neutralizing antibodies, respectively. Taken together, these findings show that, in this study, age, study year and time interval between consecutive DENV infections influence inapparent versus symptomatic infection outcome, while sex and infection number had no significant effect. Moreover, these results suggest that the window of cross-protection induced by a first infection with DENV against a second symptomatic infection is approximately 2 years. These findings are important for modeling dengue epidemics and development of vaccines. 相似文献