全文获取类型
收费全文 | 3859篇 |
免费 | 305篇 |
国内免费 | 6篇 |
专业分类
林业 | 266篇 |
农学 | 123篇 |
基础科学 | 8篇 |
883篇 | |
综合类 | 298篇 |
农作物 | 143篇 |
水产渔业 | 540篇 |
畜牧兽医 | 1572篇 |
园艺 | 105篇 |
植物保护 | 232篇 |
出版年
2023年 | 30篇 |
2022年 | 34篇 |
2021年 | 41篇 |
2020年 | 75篇 |
2019年 | 72篇 |
2018年 | 142篇 |
2017年 | 140篇 |
2016年 | 173篇 |
2015年 | 98篇 |
2014年 | 143篇 |
2013年 | 325篇 |
2012年 | 241篇 |
2011年 | 262篇 |
2010年 | 149篇 |
2009年 | 105篇 |
2008年 | 192篇 |
2007年 | 221篇 |
2006年 | 175篇 |
2005年 | 177篇 |
2004年 | 173篇 |
2003年 | 174篇 |
2002年 | 154篇 |
2001年 | 122篇 |
2000年 | 81篇 |
1999年 | 68篇 |
1998年 | 33篇 |
1997年 | 33篇 |
1996年 | 30篇 |
1995年 | 40篇 |
1994年 | 30篇 |
1993年 | 37篇 |
1992年 | 28篇 |
1991年 | 23篇 |
1990年 | 26篇 |
1989年 | 23篇 |
1988年 | 30篇 |
1987年 | 13篇 |
1986年 | 17篇 |
1985年 | 19篇 |
1984年 | 16篇 |
1983年 | 17篇 |
1980年 | 15篇 |
1979年 | 16篇 |
1978年 | 11篇 |
1977年 | 12篇 |
1976年 | 11篇 |
1975年 | 13篇 |
1974年 | 10篇 |
1973年 | 10篇 |
1969年 | 13篇 |
排序方式: 共有4170条查询结果,搜索用时 31 毫秒
31.
J. P. Rodríguez M. Aro M. Coarite S.‐E. Jacobsen B. Ørting M. Sørensen C. Andreasen 《Journal of Agronomy and Crop Science》2017,203(3):254-267
Cañahua (Chenopodium pallidicaule Aellen) is a semi‐domesticated relative of quinoa (Chenopodium quinoa Willd.) with high nutritious quality. It is tolerant to frost, drought, saline soils and pests. One seed yield limitation is seed loss during the maturity stages. Two greenhouse experiments in Denmark and field experiments in Bolivia were carried out to determine seed shattering in landraces and cultivars with different growth habits. 15–21 % of the seed shattering in the fields took place whilst the plants still were flowering and 25–35 % during physiological maturity. Seed shattering varied between locations on the Bolivian Altiplano. Cañahua types with the semi‐prostrate growth (‘lasta’) had the highest seed shattering rate in the greenhouse experiments. The Umacutama landrace had lower seed shattering (1 %) than the cultivar Kullaca (7.2 %) both of the ‘lasta’ type. Under field conditions, the cultivar Illimani with the erect growth (‘saihua’) had the highest seed shattering rate (6.4–33.7 %) at both locations and at four different sowing dates. The Umacutama had the lowest rate (0.5–1.5 %). There were no significant differences between plants of the ‘lasta’ and the ‘saihua’ types. The landrace had significantly less seed loss than the cultivars. However, in the greenhouse, the landrace yield was approximately 25 % lower than the yields of the cultivars. In general, cañahua cultivars had higher yield compared to landraces, but also a higher seed shattering rate. Landraces may be used in breeding programmes to develop high‐yielding cultivars with reduced seed shattering. 相似文献
32.
Relationship between Polyamines and Other Cold‐induced Response Mechanisms in Different Cereal Species
下载免费PDF全文
![点击此处可从《Journal of Agronomy and Crop Science》网站下载免费的PDF全文](/ch/ext_images/free.gif)
O. K. Gondor G. Szalai V. Kovács T. Janda M. Pál 《Journal of Agronomy and Crop Science》2016,202(3):217-230
To find a connection between polyamines and various protective effectors involved in the development of cold tolerance, eight different cereal genotypes, including wheat, barley and oat species, were investigated during the acclimation phase to low temperature. Exposure to low temperature induced different changes in the levels of polyamines, and other signalling molecules, such as salicylic acid and abscisic acid, and of other protective compounds, namely flavonols, sugars and antioxidant enzyme activity, and in the lipid composition of certain membrane factions. The most remarkable differences were observed in the oat varieties compared to the other cereal genotypes, which was manifested in the lack of spermidine accumulation and of decrease in trans‐Δ3‐hexadecanoic acid content, in lower initial and not cold‐inducible abscisic acid content and guaiacol peroxidase activity after cold treatment. Correlation analysis revealed that spermidine shows strong positive relationship with flavonols, abscisic acid and ascorbate peroxidase, while was in negative relationship with trans‐Δ3‐hexadecanoic acid. These results suggest that spermidine may have a crucial role in the cold acclimation signalling processes in cereals. 相似文献
33.
From regionally predictable to locally complex population structure in a freshwater top predator: river systems are not always the unit of connectivity in Northern Pike Esox lucius
下载免费PDF全文
![点击此处可从《Ecology of Freshwater Fish》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dorte Bekkevold Lene Jacobsen Jakob Hemmer‐Hansen Søren Berg Christian Skov 《Ecology of Freshwater Fish》2015,24(2):305-316
Contemporary genetic diversity is the product of both historical and contemporary forces, such as climatic and geological processes affecting range distribution and continuously moulded by evolutionary forces selection, gene flow and genetic drift. Predatory freshwater fishes, such as Northern Pike Esox lucius, commonly exhibit small population sizes, and several local populations are considered endangered. Pike inhabit diverse habitat types, including lakes, rivers and brackish marine waters, thus spanning from small isolated patches to large open marine systems. However, pike population structure from local to regional scales is relatively poorly described, in spite of its significance to developing conservation measures. We analysed microsatellite variation in a total of 1185 North European pike from 46 samples collected across both local and regional scales, as well as over time, to address two overarching questions: Is pike population structure associated with local and/or regional connectivity patterns, and which factors likely have the main influence on the contemporary distribution of genetic diversity? To answer this, we combined estimators of population diversity and structure to assess evidence of whether populations within (i) habitats, (ii) drainage systems and (iii) geographical regions are closer related than among these ranges, and whether patterns are temporally stable. Contrasting previous predictions that genetic drift obscures signals of postglacial colonisation history, we identified clear regional differences in population genetic signatures, suggesting a major effect of drainage divides on colonisation history and connectivity. However, several populations deviated from the general pattern, showing that local processes may be complex and need to be examined case‐by‐case. 相似文献
34.
L. N. Rønnow Kjærulff N. J. Dorch Lauritsen C. Thorn Ekstrøm S. Østergaard E. Olsen S. Hyldahl Laursen C. Lindegaard 《Equine Veterinary Education》2021,33(7):360-367
Caudal epidural analgesia is a well-established therapeutic modality for pain alleviation in horses. Additionally, epidural analgesia could potentially be a complementary diagnostic tool for confirmation of pain-related conditions in horses presenting with nonspecific signs of poor performance or rideability issues. To use the epidural as a diagnostic tool, the administered medications should provide efficient analgesia without accompanying adverse effects. Therefore, the objectives of the current study were to evaluate the analgesic properties and effects on locomotor function, mentation and physical examination parameters of caudal epidural co-administration of methadone and morphine in horses. Five mares received a caudal epidural injection of 0.1 mg/kg bwt methadone and 0.1 mg/kg bwt morphine diluted to a total volume of 4.4 mL/100 kg. Before and several times thereafter, horses were subjected to mechanical nociceptive threshold evaluation, physical examination, assessment of mentation and locomotor function examination. Horses were assigned ataxia scores (0–4) by a group of inexperienced raters (three senior-year veterinary students) and a group of experienced raters (two board-certified internal medicine specialists) that assessed the locomotor examinations either live or video-based. The epidural co-administration of methadone and morphine resulted in clinically relevant and statistically significant increases of horses’ tolerance to mechanical noxious stimuli at the coccygeal, perineal, sacral, lumbar and thoracic regions. Analgesia was evident after 4.4 h and lasted at least 5 h. Regional differences in the onset of analgesia reflected a cranial spread of the analgesic solution. No horses showed signs of gait disturbances; the overall median ataxia score was 0 at all times; and the average difference in scores between two randomly selected raters for a random horse at a random time point was 0.377 indicating high inter-rater agreement. There were no adverse changes of mentation and physical examination parameters. Observed side effects included signs of decreased frequency of defaecation, generalised sweating, and pruritus. 相似文献
35.
Maria Johansson Sabrina Dressel Emma Kvastegård Göran Ericsson Anke Fischer Bjørn P. Kaltenborn 《Human Dimensions of Wildlife》2016,21(2):158-168
European researchers from both the natural and social sciences show growing interest in studying interactions between society and wildlife. A wealth of theoretical frameworks, concepts, and methods are used, but an integration of perspectives is lacking. This research note summarizes results from two workshops that included 63 delegates from 25 European countries, as well as a follow-up survey of 41 respondents. Two main theoretical approaches to the study of human–wildlife interactions were identified. One approach focuses on the collective societal level relying on theories of governance, social representation, deliberative procedures, and commons theory. The other approach targets individuals or groups, and is based on theories such as the cognitive hierarchy, theory of reasoned action, and theory of planned behavior. Interdisciplinary collaboration is needed to identify the best options for wildlife conservation and management in a more politically integrated Europe. 相似文献
36.
Effects of extracerebral dopamine on salsolinol‐ or thyrotropin‐releasing hormone‐induced prolactin (PRL) secretion in goats
下载免费PDF全文
![点击此处可从《Animal Science Journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Yuki Inaba Yuki Kato Azumi Itou Aoi Chiba Ken Sawai Ferenc Fülöp György Miklos Nagy Tsutomu Hashizume 《Animal Science Journal》2016,87(12):1522-1527
The aim of the present study was to clarify the effect of extracerebral dopamine (DA) on salsolinol (SAL)‐induced prolactin (PRL) secretion in goats. An intravenous injection of SAL or thyrotropin‐releasing hormone (TRH) was given to female goats before and after treatment with an extracerebral DA receptor antagonist, domperidone (DOM), and the PRL‐releasing response to SAL was compared with that to TRH. DOM alone increased plasma PRL concentrations and the PRL‐releasing response to DOM alone was greater than that to either SAL alone or TRH alone. The PRL‐releasing response to DOM plus SAL was similar to that to DOM alone, and no additive effect of DOM and SAL on the secretion of PRL was observed. In contrast, the PRL‐releasing response to DOM plus TRH was greater than that to either TRH alone or DOM alone and DOM synergistically increased TRH‐induced PRL secretion. The present results demonstrate that the mechanism involved in PRL secretion by SAL differs from that by TRH, and suggest that the extracerebral DA might be associated in part with the modulation of SAL‐induced PRL secretion in goats. 相似文献
37.
38.
39.
40.