全文获取类型
收费全文 | 6171篇 |
免费 | 357篇 |
国内免费 | 3篇 |
专业分类
林业 | 1088篇 |
农学 | 173篇 |
基础科学 | 17篇 |
1304篇 | |
综合类 | 559篇 |
农作物 | 176篇 |
水产渔业 | 226篇 |
畜牧兽医 | 2425篇 |
园艺 | 140篇 |
植物保护 | 423篇 |
出版年
2023年 | 37篇 |
2022年 | 42篇 |
2021年 | 88篇 |
2020年 | 85篇 |
2019年 | 60篇 |
2018年 | 195篇 |
2017年 | 189篇 |
2016年 | 168篇 |
2015年 | 147篇 |
2014年 | 175篇 |
2013年 | 392篇 |
2012年 | 337篇 |
2011年 | 371篇 |
2010年 | 184篇 |
2009年 | 183篇 |
2008年 | 304篇 |
2007年 | 341篇 |
2006年 | 320篇 |
2005年 | 296篇 |
2004年 | 271篇 |
2003年 | 289篇 |
2002年 | 233篇 |
2001年 | 195篇 |
2000年 | 181篇 |
1999年 | 111篇 |
1998年 | 52篇 |
1997年 | 41篇 |
1996年 | 50篇 |
1995年 | 84篇 |
1994年 | 57篇 |
1993年 | 32篇 |
1992年 | 36篇 |
1991年 | 25篇 |
1990年 | 31篇 |
1989年 | 33篇 |
1988年 | 35篇 |
1986年 | 36篇 |
1985年 | 34篇 |
1984年 | 25篇 |
1983年 | 23篇 |
1982年 | 16篇 |
1980年 | 30篇 |
1979年 | 16篇 |
1977年 | 25篇 |
1976年 | 17篇 |
1975年 | 15篇 |
1973年 | 15篇 |
1972年 | 16篇 |
1967年 | 20篇 |
1966年 | 19篇 |
排序方式: 共有6531条查询结果,搜索用时 46 毫秒
111.
Johansson L Rytkonen A Bergman P Albiger B Källström H Hökfelt T Agerberth B Cattaneo R Jonsson AB 《Science (New York, N.Y.)》2003,301(5631):373-375
The human-specific bacterial pathogen Neisseria meningitidis is a major cause of sepsis and/or meningitis. The pili of N. meningitidis interact with CD46, a human cell-surface protein involved in regulation of complement activation. Transgenic mice expressing human CD46 were susceptible to meningococcal disease, because bacteria crossed the blood-brain barrier in these mice. Development of disease was more efficient with piliated bacteria after intranasal, but not intraperitoneal, challenge of CD46 transgenic mice, suggesting that human CD46 facilitates pilus-dependent interactions at the epithelial mucosa. Hence, the human CD46 transgenic mice model is a potentially useful tool for studying pathogenesis and for vaccine development against meningococcal disease. 相似文献
112.
Sabine Augustin Jan Evers Hans-Peter Dietrich Johannes Eichhorn Thomas Haussmann Regina Icke Ansgar Isenberg Wolfgang Lux Monica Musio Hans Pretzsch Winfried Riek Thomas Rötzer Bernd Schultze Andreas Schulze Jörg Schröder Walter Seidling Nicole Wellbrock Klaus von Wilpert Barbara Wolff 《European Journal of Forest Research》2005,124(4):251-260
In the 1970s unexpected forest damages, called “new type of forest damage” or “forest decline”, were observed in Germany and
other European countries. The Federal Republic of Germany and the German Federal States implemented a forest monitoring system
in the early 1980s, in order to monitor and assess the forest condition. Due to the growing public awareness of possible adverse
effects of air pollution on forests, in 1985 the ICP Forests was launched under the convention on long-range transboundary
air pollution (CLRTAP) of the United Nations Economic Commission for Europe (UN-ECE). The German experience in forest monitoring
was a base for the implementation of the European monitoring system. In 2001 the interdisciplinary case study “concept and
feasibility study for the integrated evaluation of environmental monitoring data in forests”, funded by the German Federal
Ministry of Education and Research, concentrated on in-depths evaluations of the German data of forest monitoring. The objectives
of the study were: (a) a reliable assessment of the vitality and functioning of forest ecosystems, (b) the identification
and quantification of factors influencing forest vitality, and (c) the clarification of cause-effect-relationships leading
to leaf/needle loss. For these purposes additional data from external sources were acquired: climate and deposition, for selected
level I plots tree growth data, as well as data on groundwater quality. The results show that in particular time series analysis
(crown condition, tree growth, and tree ring analysis), in combination with climate and deposition are valuable and informative,
as well as integrated evaluation of soil, tree nutrition and crown condition data. Methods to combine information from the
extensive and the intensive monitoring, and to transfer process information to the large scale should be elaborated in future.
相似文献
Sabine AugustinEmail: |
113.
Samuli Junttila Mikko Vastaranta Jarno Hämäläinen Petri Latva-käyrä Markus Holopainen Rocío Hernández Clemente 《Scandinavian Journal of Forest Research》2017,32(2):154-165
The effect of forest structure and health on the relative surface temperature captured by airborne thermal imagery was investigated in Norway Spruce-dominated stands in Southern Finland. Airborne thermal imagery, airborne scanning light detection and ranging (LiDAR) data and 92 field-measured sample plots were acquired at the area of interest. The surface temperature correlated most negatively with the logarithm of stem volume, Lorey’s height and the logarithm of basal area at a resolution of 254?m2 (9?m radius). LiDAR-derived metrics: the standard deviations of the canopy heights, canopy height (upper percentiles and maximum height) and canopy cover percentage were most strongly negatively correlated with the surface temperature. Although forest structure has an effect on the detected surface temperature, higher temperatures were detected in severely defoliated canopies and the difference was statistically significant. We also found that the surface temperature differences between the segmented canopy and the entire plot were greater in the defoliated plots, indicating that thermal images may also provide some additional information for classifying forests health status. Based on our results, the effects of forest structure on the surface temperature captured by airborne thermal imagery should be taken into account when developing forest health mapping applications using thermal imagery. 相似文献
114.
Hellal F Hurtado A Ruschel J Flynn KC Laskowski CJ Umlauf M Kapitein LC Strikis D Lemmon V Bixby J Hoogenraad CC Bradke F 《Science (New York, N.Y.)》2011,331(6019):928-931
Hypertrophic scarring and poor intrinsic axon growth capacity constitute major obstacles for spinal cord repair. These processes are tightly regulated by microtubule dynamics. Here, moderate microtubule stabilization decreased scar formation after spinal cord injury in rodents through various cellular mechanisms, including dampening of transforming growth factor-β signaling. It prevented accumulation of chondroitin sulfate proteoglycans and rendered the lesion site permissive for axon regeneration of growth-competent sensory neurons. Microtubule stabilization also promoted growth of central nervous system axons of the Raphe-spinal tract and led to functional improvement. Thus, microtubule stabilization reduces fibrotic scarring and enhances the capacity of axons to grow. 相似文献
115.
Interaction of sub-epithelial connective tissue components with Staphylococcus aureus and coagulase-negative staphylococci from bovine mastitis 总被引:4,自引:0,他引:4
Staphylococcus aureus and coagulase-negative staphylococci (CNS) isolated from bovine mastitis were examined for their ability to interact with 125I-labelled fibronectin, fibrinogen and type II collagen. Their relative surface hydrophobicity and production of extracellular capsule were also investigated. Almost all S. aureus strains bound fibronectin (mean value 23%), fibrinogen (mean value 12%) and type II collagen (mean value 16%). CNS bound fibronectin (mean value 6%) and type II collagen (mean value 7%), but not fibrinogen (mean value 2%). The specificity of binding of these proteins to S. aureus strain F1440 and to coagulase-negative Staphylococcus chromogenes strain BO52 was studied by adding an excess of unlabelled proteins. Fibronectin and collagen binding were observed to be specific, varying between 50 and 75%, whereas the specificity of fibrinogen binding to S. aureus strain F1440 was lower (26%). Most of the S. aureus strains (63%) showed very high surface hydrophobicity (autoaggregation) or lower hydrophobicity (29% of the strains) and the rest were hydrophilic. None of the CNS strains autoaggregated, 44% were classified as hydrophilic strains. Hydrophilic strains (except the reference strains) did not show extracellular capsule production. However, the encapsulated (reference) strains showed low binding to these proteins as compared to their unencapsulated variants. Pre-treatment of S. aureus strain F1440 and S. chromogenes strain BO52 with trypsin decreased their fibronectin binding capacity and surface hydrophobicity, whereas pre-treatment with bovine milk (except on collagen binding to strain F1440) did not significantly affect binding to these proteins. These data indicate that S. aureus and CNS isolated from bovine udder infection have the ability to bind to tissue matrix and plasma proteins which may be exposed in the traumatized or toxin-damaged udder epithelial lesions. 相似文献
116.
Balázs Kucska László Pál Tamás Müller Márk Bódis Ádám Bartos László Wágner Ferenc Husvéth & Mikós Bercsényi 《Aquaculture Research》2006,37(1):96-101
Fat content and fatty acid profile of two pike yearling groups grown on two different diets were compared. The groups originated from culture on artificial feed. One group (cultured pike fed first pellet then prey‐fish (PF)) was fed with natural food, live prey‐fish, while the other one (cultured pike fed exclusively pellet (PP)) by trout feed through a 3‐month experimental period. Growth of pike was lower with PP than with PF. The trout feed resulted in an increase of the fat content of fillet and the formation of abdominal fat depots. Feeding of natural food decreased the fat content. The proportion of the saturated fatty acids in fillet was higher in the (PF) group. The n‐6 fatty acids (arachidonic C20:4n‐6 and docosatetraenic C22:4n‐6 acids) were lowest in PP‐fed pike. Regarding total n‐3 fatty acids ratio there was no significant difference between the groups, but the level of α‐linolenic (C:18:3n‐3) acid showed significant difference among groups. 相似文献
117.
Massimiliano Cardinale Valerio Bartolino Marcos Llope Luigi Maiorano Mattias Sköld Jacob Hagberg 《Fish and Fisheries》2011,12(3):289-298
Increased knowledge on the spatial distribution of marine resources is crucial for the implementation of a true ecosystem approach to management and the conservation of marine organisms. For exploited fish species characterized by aggregation behaviour during spawning time, the identification and tracking of spawning areas is essential for a correct assessment of their productivity and population abundance. To elucidate this concept, we reconstructed the spatio‐temporal distribution of adult plaice (Pleuronectes platessa, Pleuronectidae) during spawning time along the 20th century. Historical data reveal that not only the abundance but also the former population richness was much higher than previously estimated and has declined because of protracted over‐exploitation during the last 30 years. We conclude that forecast of stock recovery to former levels of abundance neglecting spatial reorganizations might be over‐optimistic and shaded by a lost memory of the past population richness. These results reinforce the importance of managing exploited marine resources at a greater spatial resolution than has been carried out in the history of fishery management. 相似文献
118.
C. Börner 《Journal of pest science》1932,8(4):38-40
Ohne Zusammenfassung
„Mitteilungen über Blattl?use” 1–8, s. diese Zeitschrift 1931, S. 8–11; 9–11 S. 28–30; 12–13 S. 42–43; 14 S 117; 15–16 S.
128–130; 17–20, 1932, S. 32–33. 相似文献
119.
Carl Börner 《Journal of pest science》1932,8(5):52-54
Ohne Zusammenfassung 相似文献
120.