全文获取类型
收费全文 | 17201篇 |
免费 | 1150篇 |
国内免费 | 1132篇 |
专业分类
林业 | 1780篇 |
农学 | 1326篇 |
基础科学 | 620篇 |
1829篇 | |
综合类 | 8399篇 |
农作物 | 853篇 |
水产渔业 | 815篇 |
畜牧兽医 | 2460篇 |
园艺 | 553篇 |
植物保护 | 848篇 |
出版年
2024年 | 31篇 |
2023年 | 256篇 |
2022年 | 361篇 |
2021年 | 423篇 |
2020年 | 468篇 |
2019年 | 493篇 |
2018年 | 351篇 |
2017年 | 543篇 |
2016年 | 643篇 |
2015年 | 601篇 |
2014年 | 846篇 |
2013年 | 874篇 |
2012年 | 1251篇 |
2011年 | 1308篇 |
2010年 | 1057篇 |
2009年 | 1154篇 |
2008年 | 1090篇 |
2007年 | 1191篇 |
2006年 | 996篇 |
2005年 | 891篇 |
2004年 | 656篇 |
2003年 | 480篇 |
2002年 | 465篇 |
2001年 | 436篇 |
2000年 | 369篇 |
1999年 | 302篇 |
1998年 | 235篇 |
1997年 | 245篇 |
1996年 | 213篇 |
1995年 | 203篇 |
1994年 | 203篇 |
1993年 | 149篇 |
1992年 | 158篇 |
1991年 | 112篇 |
1990年 | 115篇 |
1989年 | 97篇 |
1988年 | 54篇 |
1987年 | 52篇 |
1986年 | 28篇 |
1985年 | 13篇 |
1984年 | 16篇 |
1983年 | 12篇 |
1982年 | 3篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 6篇 |
1956年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
Differences in early developmental rate and yolk conversion efficiency in offspring of trout with alternative life histories 下载免费PDF全文
Travis E. Van Leeuwen Shaun S. Killen Neil B. Metcalfe Colin E. Adams 《Ecology of Freshwater Fish》2017,26(3):371-382
Partial migration, in which some individuals of a population migrate while other individuals remain resident, is generally associated with ontogenetic shifts to better feeding areas or as a response to environmental instability, but its underlying mechanisms remain relatively unknown. Brown trout (Salmo trutta) exhibit partial migration, with some individuals remaining in freshwater (freshwater resident) while others undertake an anadromous migration, where they spend time at sea before returning to breed in freshwater (migrant). We reared full‐sibling groups of offspring from freshwater‐resident and anadromous brown trout from the same catchment in the laboratory under common garden conditions to examine potential differences in their early development. Freshwater‐resident parents produced eggs that were slower to hatch than those of anadromous parents, but freshwater‐resident offspring were quicker to absorb their yolk and reach the stage of exogenous feeding. Their offspring also had a higher conversion efficiency from the egg stage to the start of exogenous feeding (so were larger by the start of the fry stage) than did offspring from anadromous parents despite no difference in standard metabolic rate, maximal metabolic rate or aerobic scope. Given these differences in early development, we discuss how the migration history of the parents might influence the migration probability of the offspring. 相似文献
83.
Quantifying subjective human dimensions of recreational fishing: does good health come to those who bait? 下载免费PDF全文
Shane P Griffiths Joanne Bryant Henry F Raymond Peter A Newcombe 《Fish and Fisheries》2017,18(1):171-184
Recreational fishing is a popular sport and leisure activity in many countries worldwide. There has been growing interest by recreational fishing groups and researchers in the perceived physical and psychological health and social (or ‘biopsychosocial’) benefits of recreational fishing. However, quantifying the key subjective ‘human dimensions’ of fishing that satisfy both the needs of recreational fishing groups and fishery managers is a major obstacle. We propose the use of psychometrically valid health‐related quality of life (HRQOL) measures widely used in the medical and health sciences – namely the Short‐Form Health Survey (SF‐36) – as rapid, reliable and cost‐effective instruments for quantifying HRQOL of recreational fishers. The widespread use of SF‐36 and availability of population normative data allows comparisons of the HRQOL of recreational fishers across multiple temporal and spatial scales, with participants of other activities, and the general population. The use of such measures in periodic surveys allows the biopsychosocial status of a recreational fishery's participants to be assessed using a modified Kobe plot, a graphical format that is easily interpretable and consistent with existing reporting formats used in fisheries stock assessment. Future biopsychosocial research in recreational fisheries can further benefit from interdisciplinary collaboration to develop a suite of standardized psychometrically valid and reliable instruments for assessing specific issues that commonly affect recreational fisheries from regional to international scales, such as drivers of fisher motivation, behaviour and satisfaction. 相似文献
84.
85.
大兴安岭北部林区森林防火基础设施建设项目是建国后国家一次性用于国有林区森林防火投资最大的基础设施建设工程。介绍了该项目建设的基本情况,总结了主要建设成效,分析了存在问题,提出了相关对策建议。 相似文献
86.
高端人才的缺乏以及人才素质问题已经成为制约辽宁科技特派行动的主要因素。分析科技特派行动高端人才支撑体系在运行机制、体系构建及内外部协调等方面存在的问题,提出具体的完善措施。 相似文献
87.
88.
Banana anthracnose incited by Colletotrichum musae is a serious disease in post harvest marketing stage. It occurs in almost all the banana growing countries. In the current study, 5 isolates of C. musae infecting banana cv nendran were collected from various district of Tamil Nadu. C5 isolate collected from Tiruchirappalli showed maximum virulent with (66.60%) PDI. In vitro efficacy of six Pseudomonas fluorescens superior strains were tested for their inhibition on mycelial growth of C. musae. P. fluorescens (FP7) showed significantly higher inhibition of 41.12 per cent over control and with a mean mycelial growth of 52.10 mm. Water in oil emulsion was used in the present research for formulation of P. fluorescens (FP7). The emulsion contained the following ingredients (w/w), sterile deionized water (45.25%), glycerine (4.00%), water-soluble wax ((0.75%), Tween 20 (2.50%), and a mixture of 19.00% soybean oil + 28.50% castor oil. The application of water in oil emulsion formulation significantly increased the yield (68.12 t/ha) compared to control (66.49 t/ha), and also increase in the activity of defense related enzymes viz., phenyl alanine ammonia lyase, peroxidase, polyphenol oxidase, catalase and β-1, 3 glucanase was observed which was followed by talc based formulation of Pf1 and FP7. 相似文献
89.
据笔者在石塘镇水产畜牧兽医站工作十余年,本文对石塘镇牛品改工作存在的问题及整改措施进行了分析,只有剖析与解决了制约牛品改工作发展的不利因素,才能促进石塘镇牛品改工作的顺利发展,提高广大养殖户的经济收入。 相似文献
90.
SmartStax® insect-protected corn (Zea mays L.) contains genes for six Bacillus thuringiensis (Bt) proteins controlling both lepidopteran pests and the corn rootworm complex (Diabrotica spp.). The properties of SmartStax, particularly the multiple effective modes of action (i.e., each Bt protein provides a high level of control of the target pests with a low probability of cross-resistance among the proteins), have provided the opportunity to add to previously approved structured refuge options by combining the non-Bt refuge seed with SmartStax seed in a seed mix. Seed mixes ensure that a refuge is present in every Bt field, remove concerns about grower compliance with refuge requirements, and provide grower convenience. However, seed mixes could increase the likelihood that larval insects move between Bt and non-Bt plants and vice versa. Assessing the insect resistance management (IRM) value of a seed mix refuge requires an assessment of the amount of larval movement, and the consequences of that movement, for the key target pests. The studies here present such data for control of corn rootworm by SmartStax corn, which contains the rootworm-active protein Cry3Bb1 and the binary protein Cry34Ab1/Cry35Ab1. In a growth chamber experiment, SmartStax was most effective against first instars and significantly effective against second instars, but did not control third instars. In a field study of movement from a heavily infested non-Bt plant onto surrounding plants, a larger percentage of insects successfully dispersed from the infested plant when the surrounding plants were non-Bt plants than when they were SmartStax plants. A paired-plant study showed that few larvae migrated from infested SmartStax plants and survived on nearby non-Bt plants; larvae that migrated from infested non-Bt plants had low survival if the adjacent plants were SmartStax. Replicated field studies of plant-to-plant movement indicated that the non-Bt plants in a 5% or 10% seed mix consistently supported large populations of susceptible insects and represented a productive refuge, whereas the SmartStax plants had few or no survivors. The timing of emergence from seed mix plots containing 5% or 10% non-Bt plants was more similar to that of the non-Bt plots than that of the SmartStax plots. Thus, the available growth chamber and field data indicate that a seed mix of 5% or more will provide an effective refuge for corn rootworm in SmartStax corn. 相似文献