全文获取类型
收费全文 | 1370篇 |
免费 | 152篇 |
国内免费 | 169篇 |
专业分类
1691篇 |
出版年
2024年 | 15篇 |
2023年 | 40篇 |
2022年 | 55篇 |
2021年 | 69篇 |
2020年 | 100篇 |
2019年 | 114篇 |
2018年 | 81篇 |
2017年 | 66篇 |
2016年 | 69篇 |
2015年 | 60篇 |
2014年 | 49篇 |
2013年 | 103篇 |
2012年 | 60篇 |
2011年 | 51篇 |
2010年 | 49篇 |
2009年 | 50篇 |
2008年 | 59篇 |
2007年 | 79篇 |
2006年 | 60篇 |
2005年 | 61篇 |
2004年 | 52篇 |
2003年 | 42篇 |
2002年 | 34篇 |
2001年 | 35篇 |
2000年 | 33篇 |
1999年 | 34篇 |
1998年 | 15篇 |
1997年 | 23篇 |
1996年 | 15篇 |
1995年 | 17篇 |
1994年 | 12篇 |
1993年 | 16篇 |
1992年 | 14篇 |
1991年 | 7篇 |
1990年 | 12篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1972年 | 2篇 |
排序方式: 共有1691条查询结果,搜索用时 15 毫秒
131.
Richard A. Bafford Robert W. Seagull Si-Yin Chung David F. Millie 《Journal of phycology》1993,29(1):91-95
The monoterpene derivative, 2-methylisoborneol (MIB), is produced by many blue-green algae and often is responsible for the “musty” taste/odor in aquaculturally raised finfish and potable water supplies. Although previous researchers have suggested that taste/odor metabolites are partitioned among cell constituents and that coregulation with pigment biosynthesis occurs, no structural evidence for these hypotheses exists. MIB was localized in cells of Oscillatoria limosa (Roth) Agardh at the ultrastructural level using standard gold-labeled antibody techniques. There was no apparent relationship between age of the cells and MIB synthesis; cells that were and were not undergoing active division had similar amounts of MIB label. There was no consistent partitioning of MIB label within cells. However, occasionally, specific label was observed along photosynthetic lamellae, suggesting a potential linkage of MIB synthesis and/or binding to the pigment systems. 相似文献
132.
Pittaya Dankulchai Wiwatchai Sittiwong Wanwarang Teerasamit 《Reports of Practical Oncology and Radiotherapy》2022,27(2):260
BackgroundThe most common site of recurrence of prostate cancer after definite radiation therapy is the dominant intraprostatic lesion (DIL). This study aimed to investigate the feasibility and safety of definite volumetric modulated arc therapy (VMAT) with simultaneous integrated boost (SIB) to the DIL in patients with unfavorable intermediate to high-risk prostate cancer.Materials and methodsIn this prospective uncontrolled clinical trial, patients were delivered VMAT at a dose of 87.75 Gy in 39 fractions or 70 Gy in 20 fractions to the DIL in combination with androgen deprivation therapy. Genitourinary (GU) and rectal toxicity, International Prostate Symptom Score (IPSS) and IPSS quality of life (IPSS-QOL) score were collected.ResultsForty-five patients with a median follow-up of 20 months were analyzed. The cumulative incidence of acute grade ≥ 2 GU and rectal toxicity was 33.1% and 9.5%, respectively. Regarding late toxicity, the cumulative incidence of grade ≥ 2 GU and rectal toxicity was 12.6% and 2.8%, respectively. During treatment, the mean increase of IPSS was +7.4 ± 4.2 and the mean increase of IPSS-QOL was +1.7 ± 1.3. However, both IPSS and IPSS-QOL scores returned to their baseline levels by 3-months post-treatment. No significant correlation between baseline characteristics and grade ≥ 2 GU or rectal toxicity was found.ConclusionFocal SIB to the DIL of ≥ 90 Gy EQD2 in unfavorable intermediate to high-risk prostate cancer patients resulted in tolerable toxicity profiles. The mean IPSS and IPSS-QOL scores both worsened during treatment; however, both scores returned to baseline level by 3 months after treatment. 相似文献
133.
为了解抗菌肽在饵料微藻中表达后的抗菌特性,构建海洋微拟球藻(Nannochloropsis oceanica)、湖泊微拟球藻(N.limnetica)和三角褐指藻(Phaeodactylum tricornutum)的抗菌肽(源自虹鳟,Cath-1a)表达质粒,分别转化相应的微藻,检测转化子中抗菌肽的表达量和体外抑菌效果,将藻株作为鱼饲料添加剂喂食斑马鱼,初步分析了抗菌肽及藻体自身的岩藻黄素和多不饱和脂肪酸对鱼免疫系统的影响。结果表明,外源抗菌肽在3种微藻中均可以成功表达,体外抑菌试验表明,仅三角褐指藻对水产领域常见致病菌爱德华氏菌(Edwardsiella tarda)有一定的抑菌效果,然而抗菌肽的表达并未使3种藻株的体外抑菌性增加。添加藻粉对斑马鱼的生长无明显影响,通过检测鱼体肝脏中与抗氧化和免疫相关基因的表达水平及丙二醛的含量,表明添加藻粉可增强斑马鱼的抗氧化和抗炎症能力,表达抗菌肽(PtC组)能进一步提高斑马鱼的免疫力。另外,添加Pt6(富含岩藻黄素)藻粉组比添加PtC的抗炎效果更显著,表明三角褐指藻中的岩藻黄素和二十碳五烯酸对增强鱼的抗病能力具有潜在作用。 相似文献
134.
135.
土壤-植物-大气连续体水热、CO2通量估算模型研究进展 总被引:3,自引:0,他引:3
土壤-植物-大气连续体(SPAC)水热、CO2通量的准确估算对理解陆地和大气的物质和能量交换过程有着重要意义.重点阐述了基于过程的土壤-植物-大气连续体水热、CO2通量模型,综述了统计模型、综合模型及基于遥感的模型的发展过程.其中水热通量统计模型包括基于温度和湿度以及基于温度和辐射的方法;CO2通量统计模型包括基于气候因子或蒸散因子以及基于光能利用率的方法.水热通量过程模型包括大叶、双源、多源和多层的水热传输物理模型;CO2通量过程模型包括叶片尺度及由大叶、双叶和多层方法扩展到冠层尺度的生理生态模型以及光合-蒸腾耦合模型.综合模型包括生物物理模型、生物化学模型和生物地理模型.统计模型形式简单,资料易得,对大范围的水热通量模拟具有指导意义;过程模型准确的揭示了水热和CO2通量传输的物理和生理过程,是大尺度综合模型的基础.未来生态系统水热、CO2通量估算模型将集成各种技术手段进行多尺度网络观测和大尺度机理模拟. 相似文献
136.
Matthew B. Dugas Susannah R. Halbrook Allison M. Killius Jillian F. del Sol Corinne L. Richards‐Zawacki 《Ethology : formerly Zeitschrift fur Tierpsychologie》2015,121(8):813-822
The phenomenon of aposematism, or the pairing of antipredator defence with conspicuous or distinctive signals, serves as an excellent example of how traits act in concert to shape fitness. Not only does this complex phenotype require the integration of multiple traits, it alters the fitness pay‐offs of yet others. The protection offered by aposematism may, for example, reduce the costs associated with foraging or sexual display. Thus, well‐protected aposematic lineages should be bolder, more active and less likely to respond to perceived threats of predation than more cryptic lineages. Comparisons of differently coloured morphs of the polytypic strawberry poison frog (Oophaga pumilio) have supported the predicted behavioural correlates of aposematism, with the exception of those regarding responsiveness to simulated predators. We tested the key prediction that aposematic coloration will be associated with reduced sensitivity to predators in two polymorphic O. pumilio populations. The novel approach of studying polymorphic populations allowed us to assess the effect of colour in the absence of potentially confounding habitat differences. We found that colour was associated with the probability that a frog would attempt escape and the distance at which it fled, but only in one population, and not in the predicted direction. An overall comparison of the two populations superficially supported our predictions, but this pattern actually arose because frogs occupying higher perches were less likely to respond, a pattern that may reflect the value of high perches and the costs associated with returning to them after attempted escape. These results highlight the complexity of the relationship between predators and prey, the challenges associated with understanding how and why traits are correlated, and the intimate ties between behaviour and morphological evolution. 相似文献
137.
Gjalt Huppes Arjan de Koning Sangwon Suh Reinout Heijungs Lauran van Oers Per Nielsen Jeroen B. Guine 《Journal of Industrial Ecology》2006,10(3):129-146
For developing product policy, insight into the environmental effects of products is required. But available life-cycle assessment studies (LCAs) are hardly comparable between different products and do not cover total consumption. Input-output analysis with environmental extensions (EEIOA) of full consumption is not available for the European Union. Available country studies have a low sector resolution and a limited number of environmental extensions. This study fills the gap between detailed LCA and low-resolution EEIOA, specifying the environmental effects of household consumption in the European Union, discerning nearly 500 sectors, while specifying a large number of environmental extensions. Added to the production sectors are a number of consumption activities with direct emissions, such as automobile driving, cooking and heating, and a number of postconsumer waste management sectors. The data for Europe have been constructed by using the sparse available and coarse economic and environmental data on European countries and adding technological detail mainly based on data from the United States.
A small number of products score high on environmental impact per Euro and also have a substantial share of overall consumer expenditure. Several meat and dairy products, household heating, and car driving thus have a large share of the total environmental impact. Due to their sales volume, however, products with a medium or low environmental score per Euro may also have a substantial impact. This is the case with bars and restaurants, clothing, residential construction, and even a service such as telecommunications. The limitations in real European data made heroic assumptions necessary to operationalize the model. One conclusion, therefore, is that provision of data in Europe urgently needs to be improved, at least to the level of sector detail currently available for the United States and Japan. 相似文献
A small number of products score high on environmental impact per Euro and also have a substantial share of overall consumer expenditure. Several meat and dairy products, household heating, and car driving thus have a large share of the total environmental impact. Due to their sales volume, however, products with a medium or low environmental score per Euro may also have a substantial impact. This is the case with bars and restaurants, clothing, residential construction, and even a service such as telecommunications. The limitations in real European data made heroic assumptions necessary to operationalize the model. One conclusion, therefore, is that provision of data in Europe urgently needs to be improved, at least to the level of sector detail currently available for the United States and Japan. 相似文献
138.
M. F. Moura M. C. Picanço R. N. C. Guedes E. C. Barros M. Chediak E. G. F. Morais 《Journal of Applied Entomology》2007,131(3):215-220
Abstract: A conventional sampling plan for the leafhopper Empoasca kraemeri Ross & Moore (Auchenorrhyncha: Cicadellidae) in common beans (Phaseolus vulgaris L.) is presented based on samples from 51 commercial fields. The research encompassed three phases. The first phase had the objective of determining the most suitable leaf to be used as a precise and representative sampling unit. In the second phase of the project, the available sampling methods for E. kraemeri were compared, including the approach identified in the first phase. In the third phase, the theoretical frequency distribution of the sampling data was assessed and the number of samples necessary for the sampling plan was established. The best leaves to sample adult leafhoppers were the fourth and the fifth from the apex, while the best leaf for sampling nymphs was the fifth from the apex. The best sampling technique for nymphs and adults was the beating of the apical leaves against a plastic tray. The sampling data obtained with this technique were fit to a negative binomial distribution with common aggregation parameter for adults ( K common = 1.04) and nymphs ( K common = 0.47). This sampling plan required 16.8 and 31.2 min to be carried out at an expense of US$ 0.31 and US$ 0.54 for sampling adults and nymphs in a field, respectively. 相似文献
139.
Türkân Saknç Britta Kleine Nadine Michalski Martin Kaase & Sören G. Gatermann 《FEMS microbiology letters》2009,301(1):28-34
The transferability of a large plasmid that harbors a tetracycline resistance gene tet (S), to fish and human pathogens was assessed using electrotransformation and conjugation. The plasmid, originally isolated from fish intestinal Lactococcus lactis ssp. lactis KYA-7, has potent antagonistic activity against the selected recipients ( Lactococcus garvieae and Listeria monocytogenes ), preventing conjugation. Therefore the tetracycline resistance determinant was transferred via electroporation to L . garvieae . A transformant clone was used as the donor in conjugation experiments with three different L. monocytogenes strains. To our knowledge, this is the first study showing the transfer of an antibiotic resistance plasmid from fish-associated lactic bacteria to L. monocytogenes , even if the donor L. garvieae was not the original host of the tetracycline resistance but experimentally created by electroporation. These results demonstrate that the antibiotic resistance genes in the fish intestinal bacteria have the potential to spread both to fish and human pathogens, posing a risk to aquaculture and consumer safety. 相似文献
140.
P. Poncin 《Journal of fish biology》1989,35(3):395-400
The role of photoperiod as an environmental factor controlling reproduction, particularly the duration and ending of the breeding season, in the barbel was investigated by tank experiments. The experiments used a population of barbel matured in captivity which were stripped of eggs at frequent intervals: 10–15 'spawnings'for each female were obtained at 15-day intervals.
A decreasing photoperiod (16·5 light: 7·5 dark→8L: 16D), for an annual cycle contracted to 6 months duration, inhibited the spawning of both female and male fish. This allowed two periods of reproduction (February-May and September-November) within one year. Under natural or constant (10L: 14D) photoperiod conditions, spawning came to an end spontaneously. The rate (accelerated, slow or natural) of daylength increase did not affect the onset of spawning. 相似文献
A decreasing photoperiod (16·5 light: 7·5 dark→8L: 16D), for an annual cycle contracted to 6 months duration, inhibited the spawning of both female and male fish. This allowed two periods of reproduction (February-May and September-November) within one year. Under natural or constant (10L: 14D) photoperiod conditions, spawning came to an end spontaneously. The rate (accelerated, slow or natural) of daylength increase did not affect the onset of spawning. 相似文献