全文获取类型
收费全文 | 15644篇 |
免费 | 1230篇 |
国内免费 | 7篇 |
专业分类
16881篇 |
出版年
2024年 | 24篇 |
2023年 | 96篇 |
2022年 | 247篇 |
2021年 | 456篇 |
2020年 | 242篇 |
2019年 | 312篇 |
2018年 | 421篇 |
2017年 | 367篇 |
2016年 | 598篇 |
2015年 | 866篇 |
2014年 | 948篇 |
2013年 | 1116篇 |
2012年 | 1434篇 |
2011年 | 1421篇 |
2010年 | 883篇 |
2009年 | 676篇 |
2008年 | 1039篇 |
2007年 | 924篇 |
2006年 | 896篇 |
2005年 | 854篇 |
2004年 | 741篇 |
2003年 | 623篇 |
2002年 | 616篇 |
2001年 | 107篇 |
2000年 | 75篇 |
1999年 | 107篇 |
1998年 | 130篇 |
1997年 | 92篇 |
1996年 | 71篇 |
1995年 | 54篇 |
1994年 | 50篇 |
1993年 | 57篇 |
1992年 | 47篇 |
1991年 | 29篇 |
1990年 | 39篇 |
1989年 | 41篇 |
1988年 | 16篇 |
1987年 | 22篇 |
1986年 | 15篇 |
1985年 | 18篇 |
1984年 | 15篇 |
1983年 | 10篇 |
1982年 | 10篇 |
1981年 | 14篇 |
1980年 | 13篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1975年 | 10篇 |
1974年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
82.
Bastien Polizzi Andrea Fanesi Filipa Lopes Magali Ribot Olivier Bernard 《PLoS computational biology》2022,18(4)
We present a spatial model describing the growth of a photosynthetic microalgae biofilm. In this 2D-model we consider photosynthesis, cell carbon accumulation, extracellular matrix excretion, and mortality. The rate of each of these mechanisms is given by kinetic laws regulated by light, nitrate, oxygen and inorganic carbon. The model is based on mixture theory and the behaviour of each component is defined on one hand by mass conservation, which takes into account biological features of the system, and on the other hand by conservation of momentum, which expresses the physical properties of the components. The model simulates the biofilm structural dynamics following an initial colonization phase. It shows that a 75 μm thick active region drives the biofilm development. We then determine the optimal harvesting period and biofilm height which maximize productivity. Finally, different harvesting patterns are tested and their effect on biofilm structure are discussed. The optimal strategy differs whether the objective is to recover the total biofilm or just the algal biomass. 相似文献
83.
84.
Clarissa Neves Spitz Roberto Mogami Izabela Jardim Rodrigues Pitta Mariana Andrea Vilas Boas Hacker Anna Maria Sales Euzenir Nunes Sarno Marcia Rodrigues Jardim 《PLoS neglected tropical diseases》2022,16(4)
Leprosy is still a prevalent disease in Brazil, representing 93% of all occurrences in the Americas. Leprosy neuropathy is one of the most worrying manifestations of the disease. Acute neuropathy usually occurs during reaction episodes and is called neuritis. Twenty-two leprosy patients were included in this study. These patients had neural pain associated with ulnar sensory neuropathy, with or without adjunct motor involvement. The neurological picture began within thirty days of the clinical evaluation. The patients underwent a nerve conduction study and the demyelinating findings confirmed the diagnosis of neuritis. Ultrasonographic study (US) of the ulnar nerve was performed in all patients by a radiologist who was blinded to the clinical or neurophysiological results. Morphological characteristics of the ulnar nerve were analyzed, such as echogenicity, fascicular pattern, transverse cross-sectional area (CSA), aspect of the epineurium, as well as their anatomical relationships. The volume of selected muscles referring to the ulnar nerve, as well as their echogenicity, was also examined. Based on this analysis, patients with increased ulnar nerve CSA associated with loss of fascicular pattern, epineurium hyperechogenicity and presence of power Doppler flow were classified as neuritis. Therefore, patients initially classified by the clinical-electrophysiological criteria were reclassified by the imaging criteria pre-established in this study as with and without neuritis. Loss of fascicular pattern and flow detection on power Doppler showed to be significant morphological features in the detection of neuritis. In 38.5% of patients without clinical or neurophysiological findings of neuritis, US identified power Doppler flow and loss of fascicular pattern. The US is a method of high resolution and portability, and its low cost means that it could be used as an auxiliary tool in the diagnosis of neuritis and its treatment, especially in basic health units. 相似文献
85.
86.
Giovanni Pini Arne Brutschy Marco Frison Andrea Roli Marco Dorigo Mauro Birattari 《Swarm Intelligence》2011,5(3-4):283-304
Task partitioning is the decomposition of a task into two or more sub-tasks that can be tackled separately. Task partitioning can be observed in many species of social insects, as it is often an advantageous way of organizing the work of a group of individuals. Potential advantages of task partitioning are, among others: reduction of interference between workers, exploitation of individuals?? skills and specializations, energy efficiency, and higher parallelism. Even though swarms of robots can benefit from task partitioning in the same way as social insects do, only few works in swarm robotics are dedicated to this subject. In this paper, we study the case in which a swarm of robots has to tackle a task that can be partitioned into a sequence of two sub-tasks. We propose a method that allows the individual robots in the swarm to decide whether to partition the given task or not. The method is self-organized, relies on the experience of each individual, and does not require explicit communication between robots. We evaluate the method in simulation experiments, using foraging as testbed. We study cases in which task partitioning is preferable and cases in which it is not. We show that the proposed method leads to good performance of the swarm in both cases, by employing task partitioning only when it is advantageous. We also show that the swarm is able to react to changes in the environmental conditions by adapting the behavior on-line. Scalability experiments show that the proposed method performs well across all the tested group sizes. 相似文献
87.
88.
Dung Quang Nguyen Dominik Schneider Nicole Brinkmann Bin Song Dennis Janz Ingo Schöning Rolf Daniel Rodica Pena Andrea Polle 《Environmental microbiology》2020,22(8):3081-3095
Root-associated fungi (RAF) link nutrient fluxes between soil and roots and thus play important roles in ecosystem functioning. To enhance our understanding of the factors that control RAF, we fitted statistical models to explain variation in RAF community structure using data from 150 temperate forest sites covering a broad range of environmental conditions and chemical root traits. We found that variation in RAF communities was related to both root traits (e.g., cations, carbohydrates, NO3−) and soil properties (pH, cations, moisture, C/N). The identified drivers were the combined result of distinct response patterns of fungal taxa (determined at the rank of orders) to biotic and abiotic factors. Our results support that RAF community variation is related to evolutionary adaptedness of fungal lineages and consequently, drivers of RAF communities are context-dependent. 相似文献
89.
90.