全文获取类型
收费全文 | 5585篇 |
免费 | 1125篇 |
国内免费 | 2526篇 |
出版年
2024年 | 103篇 |
2023年 | 367篇 |
2022年 | 331篇 |
2021年 | 434篇 |
2020年 | 421篇 |
2019年 | 490篇 |
2018年 | 370篇 |
2017年 | 407篇 |
2016年 | 437篇 |
2015年 | 371篇 |
2014年 | 422篇 |
2013年 | 430篇 |
2012年 | 327篇 |
2011年 | 341篇 |
2010年 | 335篇 |
2009年 | 398篇 |
2008年 | 344篇 |
2007年 | 390篇 |
2006年 | 340篇 |
2005年 | 301篇 |
2004年 | 256篇 |
2003年 | 223篇 |
2002年 | 202篇 |
2001年 | 170篇 |
2000年 | 139篇 |
1999年 | 117篇 |
1998年 | 108篇 |
1997年 | 66篇 |
1996年 | 93篇 |
1995年 | 66篇 |
1994年 | 61篇 |
1993年 | 52篇 |
1992年 | 52篇 |
1991年 | 45篇 |
1990年 | 48篇 |
1989年 | 31篇 |
1988年 | 22篇 |
1987年 | 14篇 |
1986年 | 14篇 |
1985年 | 15篇 |
1984年 | 11篇 |
1983年 | 3篇 |
1982年 | 17篇 |
1981年 | 12篇 |
1980年 | 8篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1958年 | 8篇 |
排序方式: 共有9236条查询结果,搜索用时 155 毫秒
121.
《Saudi Journal of Biological Sciences》2018,25(2):320-325
Honey is a natural food item produced by honey bees. Ancient civilizations considered honey as a God gifted prestigious product. Therefore, a huge literature is available regarding honey importance in almost all religions. Physically, honey is a viscous and jelly material having no specific color. Chemically, honey is a complex blend of many organic and inorganic compounds such as sugars, proteins, organic acids, pigments, minerals, and many other elements. Honey use as a therapeutic agent is as old as human civilization itself. Prior to the appearance of present day drugs, honey was conventionally used for treating many diseases. At this instant, the modern research has proven the medicinal importance of honey. It has broad spectrum anti-biotic, anti-viral and anti-fungal activities. Honey prevents and kills microbes through different mechanism such as elevated pH and enzyme activities. Till now, no synthetic compound that works as anti-bacterial, anti-viral and anti-fungal drugs has been reported in honey yet it works against bacteria, viruses and fungi while no anti-protozoal activity has been reported. Potent anti-oxidant, anti-inflammatory and anti-cancerous activities of honey have been reported. Honey is not only significant as anti-inflammatory drug that relieve inflammation but also protect liver by degenerative effects of synthetic anti-inflammatory drugs. This article reviews physico-chemical properties, traditional use of honey as medicine and mechanism of action of honey in the light of modern scientific medicinal knowledge. 相似文献
122.
Pest management is expensive and there is often uncertainty about the benefits for the resources being protected. There can also be unintended consequences for other parts of the ecosystem, especially in complex food webs. In making decisions managers generally have to rely on qualitative information collected in a piecemeal fashion. A method to assist decision making is a qualitative modelling approach using fuzzy cognitive maps, a directed graphical model related to neural networks that can take account of interactions between pests and conservation assets in complex food webs. Using all available information on relationships between native and exotic resources and consumers, we generated hypotheses about potential consequences of single‐species and multi‐species pest control on the long‐term equilibrium abundances of other biotic components of an ecosystem. We applied the model to a dryland ecosystem in New Zealand because we had good information on its trophic structure, but the information on the strength of species interactions was imprecise. Our model suggested that pest control is unlikely to significantly boost native invertebrates and lizards in this ecosystem, suggesting that other forms of management may be required for these groups. Most of the pest control regimes tested resulted in greater abundances of at least one other pest species, which could potentially lead to other management problems. Some of the predictions were unexpected, such as more birds resulting from possum and mouse control. We also modelled the effects of an increase in invasive rabbits, which led to unexpected declines of stoats, weasels, mice and possums. These unexpected outcomes resulted from complex indirect pathways in the food web. Fuzzy cognitive maps allow rapid construction of prototype models of complex food webs using a wide range of data and expert opinion. Their utility lies in providing direction for future monitoring efforts and generating hypotheses that can be tested with field experiments. 相似文献
123.
124.
125.
《Bioscience, biotechnology, and biochemistry》2013,77(10):1958-1959
A sandwich chemiluminescence enzyme immunoassay for measuring the level of VEGF /VPF in serum was constructed. The detectability of the assay is very low (1.0pg/ml) and the measurable range of the assay was very wide (1–1000 pg/ml). The assay showed that the average level of VEGF /VPF in human sera from healthy blood donors was approximately 19 pg/ml. 相似文献
126.
Ecological assessment requires the integration of many physical, chemical, and/or biological quality elements. The choice of the aggregation method of such partial assessments into an overall assessment can considerably affect the assessment outcome – an issue that has been controversially discussed within the scientific community for the last decade. Current practice often considers only two different aggregation methods, the weighted arithmetic mean (additive aggregation) and the one-out, all-out method (minimum aggregation). However, both have important drawbacks. Additive aggregation compensates a bad status of one quality element by a number of elements featuring good status. Minimum aggregation can lead to overly pessimistic assessment results, since only the quality element in the worst status is considered. Here, we introduce a toolbox containing current and new aggregation methods, demonstrate and discuss their properties with simple, didactical examples, and suggest in which situations best to use them. Then, we illustrate the consequences of selected aggregation schemes for ecological river assessment with the case study of the Swiss Modular Concept of stream assessment (SMC), which we apply to ten river reaches in the Mönchaltdorfer Aa catchment in Switzerland. To be able to do so, we used multi-criteria decision analysis, i.e., multi-attribute value theory, to arrange the SMC quality elements into an objectives hierarchy, and to translate their individual assessments into value functions. Our case study revealed that choosing the most appropriate aggregation method particularly matters, if objectives with significantly different qualities are aggregated. We argue that redundant objectives (i.e., quality elements), often found at the lower levels of the objectives hierarchy, should best be aggregated additively allowing for compensation to increase the statistical significance of the results. Further, we suggest that complementary sub-objectives that often occur at higher levels may be optimally aggregated with a mixture of additive and minimum aggregation. Such a mixed method will allow some compensation, but nevertheless penalize for very bad states. Since here we compare commonly used aggregation methods with some which we believe have never been discussed in an assessment context before, our study concurrently informs ecological assessment in theory and in practice. 相似文献
127.
J. P. Grime 《Journal of Ecology》1998,86(6):902-910
128.
科学认识社会生态系统演进机制是对其进行有效管理的重要基础。以文化与政治生态学为理论基础,提出适合杭州—西湖社会生态系统的综合研究框架,识别了杭州—西湖社会生态系统的5个演进阶段,并分析出系统演进中的3种潜在状态。自然、政治、经济以及社会驱动力是影响杭州—西湖社会生态系统的主导因素,人类行为影响整个生态系统中扰动的频率、大小和形式并改变西湖生态系统的结构与功能,进而影响西湖为城市提供生态系统服务的潜能。在不同历史时期,基于自然、社会、经济、文化等多层面的需求,西湖在不同系统状态下为城市供给不同类别和质量的生态系统服务,总体而言供给与调节服务比例逐渐下降,文化服务逐渐上升,并且后者逐步成为最主要的生态系统服务类别。杭州与西湖在长期的互馈共生中建立了社会生态系统的自适应性调节机制,其背后的生态智慧可为现代风景园林规划提供重要启示。 相似文献
129.
野生田头菇菌株的驯化及其子实体营养成分分析 总被引:1,自引:0,他引:1
采自湖南洞庭湖大通湖区芦苇湿地的野生菌株,经鉴定为田头菇Agrocybe praecox。通过驯化实现人工栽培,栽培原料以芦苇屑为主,使用液体菌种和覆土栽培方式,初潮菇平均生物转化率为45.6%。营养成分分析表明:以芦苇屑为栽培培养基,子实体中矿物元素含量分别为K(2 190mg/kg)、Fe(16.2mg/kg)、Mg(59.7mg/kg)、Ca(33.4mg/kg),必需氨基酸含量占比高达44.85%,谷氨酸、蛋氨酸、天冬氨酸含量高,是一种高蛋白、低脂肪、高钾低钠的食用菌。 相似文献
130.
Qiang Zeng Yanqing Lai Liangxing Jiang Fangyang Liu Xiaojing Hao Lianzhou Wang Martin A. Green 《Liver Transplantation》2020,10(14)
Solar energy is one of the most abundant renewable energy sources. For efficient utilization of solar energy, photovoltaic technology is regarded as the most important source. However, due to the intermittent and unstable characteristics of solar radiation, photoelectric conversion (PC) devices fail to meet the requirements of continuous power output. With the development of rechargeable electric energy storage systems (ESSs) (e.g., supercapacitors and batteries), the integration of a PC device and a rechargeable ESS has become a promising approach to solving this problem. The so‐called integrated photorechargeable ESSs which can directly store sunlight generated electricity in daylight and reversibly release it at night time, has a huge potential for future applications. This review summarizes the development of several types of mainstream integrated photorechargeable ESSs and introduces different working mechanisms for each photorechargeable ESS in detail. Several general perspectives on challenges and future development in the field are also provided. 相似文献