全文获取类型
收费全文 | 2994篇 |
免费 | 142篇 |
国内免费 | 1篇 |
专业分类
林业 | 100篇 |
农学 | 105篇 |
基础科学 | 10篇 |
505篇 | |
综合类 | 344篇 |
农作物 | 380篇 |
水产渔业 | 217篇 |
畜牧兽医 | 1274篇 |
园艺 | 42篇 |
植物保护 | 160篇 |
出版年
2023年 | 16篇 |
2021年 | 73篇 |
2020年 | 40篇 |
2019年 | 48篇 |
2018年 | 77篇 |
2017年 | 74篇 |
2016年 | 86篇 |
2015年 | 85篇 |
2014年 | 96篇 |
2013年 | 147篇 |
2012年 | 175篇 |
2011年 | 226篇 |
2010年 | 115篇 |
2009年 | 96篇 |
2008年 | 177篇 |
2007年 | 163篇 |
2006年 | 109篇 |
2005年 | 126篇 |
2004年 | 117篇 |
2003年 | 114篇 |
2002年 | 98篇 |
2001年 | 78篇 |
2000年 | 72篇 |
1999年 | 47篇 |
1997年 | 17篇 |
1996年 | 14篇 |
1994年 | 15篇 |
1992年 | 23篇 |
1991年 | 35篇 |
1990年 | 34篇 |
1989年 | 31篇 |
1988年 | 22篇 |
1987年 | 32篇 |
1986年 | 29篇 |
1985年 | 27篇 |
1984年 | 26篇 |
1983年 | 24篇 |
1979年 | 21篇 |
1978年 | 11篇 |
1977年 | 19篇 |
1976年 | 11篇 |
1975年 | 12篇 |
1974年 | 18篇 |
1973年 | 24篇 |
1972年 | 22篇 |
1971年 | 15篇 |
1970年 | 19篇 |
1969年 | 19篇 |
1968年 | 12篇 |
1966年 | 11篇 |
排序方式: 共有3137条查询结果,搜索用时 15 毫秒
1.
Frederick Feyrer Matthew Young Oliver Patton David Ayers 《Ecology of Freshwater Fish》2020,29(2):188-196
Clear Lake Hitch is an imperilled minnow endemic to Clear Lake, Lake County, California, United States listed as threatened under the California Endangered Species Act (ESA) and a candidate for listing under the United States ESA. It exhibits a potamodromous life cycle whereby adults, which reach up to 6 + years in age and over 350 mm in length, migrate into Clear Lake's ephemeral tributaries briefly during spring to spawn. Conservation and management of Clear Lake Hitch is inhibited, in part, by a lack of information on the lacustrine habitat of nonbreeding individuals within Clear Lake. To address this problem, we sampled Clear Lake Hitch with gill nets in a stratified random sampling design to determine the distribution and habitat associations in early summer 2017 and 2018. We identified abundance-habitat relationships for juveniles and adults using Bayesian zero-inflated negative binomial generalised linear mixed modelling. Results indicated that dissolved oxygen concentration was the most important habitat feature measured; juveniles and adults were substantially more abundant in normoxic (≥2 mg/l) than in hypoxic (<2 mg/l) habitat. Both also exhibited weak positive relationships with chlorophyll fluorescence, suggesting relatively productive habitats may support higher numbers of Clear Lake Hitch. Spatially, juveniles were most abundant in nearshore habitats while adults were ubiquitous, indicating an ontogenetic habitat expansion that may be associated with a resource availability-predation risk trade-off. Management actions undertaken to improve hypoxia problems in Clear Lake would also improve Clear Lake Hitch habitat. 相似文献
2.
We prepared solid polymer electrolytes (SPEs) composed of poly(ethylene glycol) monomethyl ether acrylate (1A9OMe) and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([EMIm][OTF]) and 1-ethyl-3-methylimidazolium bis(trifluoromethane sulfonyl) imide ([EMIm][TFSI]) as the ionic liquid. The SPEs formed by appropriately adding ionic liquids in the 1A9OMe prior to thermal cure. The ratio of 1A9OMe and ionic liquid was 1:9, 3:7, and 5:5, respectively. The characterization of solid polymer electrolytes were investigated using Fourier transform infrared spectroscopy in the attenuated total reflectance mode (FTIR-ATR), Electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and glavanostatic charge-discharge test. The highest ionic conductivity of SPEs was found to be 4.90×10?4 S/cm in a 1A9OMe/[EMIm][OTF] of 3:7. As IL contents were increased, the specific capacitance of supercapacitor was increased. The specific capacitance of supercapacitor for ionic liquid with large ion size was lower than that for ionic liquid with smaller ion size. 相似文献
3.
Byoung-Min Lee Joon-Pyo Jeun Phil-Hyun Kang Jae-Hak Choi Sung-Kwon Hong 《Fibers and Polymers》2017,18(2):272-277
Nanocrytalline cellulose (NCC) was isolated using cellulose extracted from two different precursor materials: Eucalyptus globulus and rice straw. The two ground precursor materials were autoclaved with a 10 % NaOH solution at 120 °C for 3 h. The alkali-treated precursor materials were bleached using sodium chlorite/acetic acid and sodium hypochlorite. The bleached precursor materials were acid-hydrolyzed in 65 % (w/w) sulfuric acid at 45 °C for 30-120 min. The changes in the chemical composition of the two precursor materials were studied before and after bleaching by Fourier transform infrared spectroscopy according to the NREL report and TAPPI standards. Hydrolyzates were characterized by X-ray diffractometry, thermogravimetric analysis, Zeta-potential analysis, and transmission electron microscopy. The results revealed that the physical properties of NCC were strongly dependent on the acid-hydrolysis time. 相似文献
4.
5.
Derakhshan-Nejad Zahra Lee Woojin Han Seunghee Choi Jaeyoung Yun Seong-Taek Lee Giehyeon 《Journal of Soils and Sediments》2020,20(4):2107-2120
Journal of Soils and Sediments - Carbon capture and storage (CCS) has been frequently discussed as a strategy for meeting CO2 emission reduction and its targets. However, some critical issues have... 相似文献
6.
Lee Kiuk Kim Yu Jeong Hong Yang Ki Song Mi Young Lee Wan Ok Hwang Keum Taek 《Fisheries Science》2020,86(3):573-580
Fisheries Science - The objective of this study is to determine the lipid content and fatty acid composition of Anguilla japonica caught in South Korea. Seventy-nine eels caught at four different... 相似文献
7.
Xu Gao Jung Rok Lee Seo Kyoung Park Chul Won Kim Ju Hee Kim Han Gil Choi 《Aquaculture Research》2019,50(7):1985-1992
The red alga Chondria crassicaulis has a wide‐ranging bioactive chemical composition and is used as a local foodstuff, representing a potentially new cultivar in Korea. The cultivation techniques were developed by examining the monthly changes in frond weight in a field population of C. crassicaulis from November 2016 to October 2017. For seedling production, temperature and irradiance effects on the attachment and growth of vegetative propagules of C. crassicaulis were evaluated. In addition, effects of day length and salinity on the propagule growth were examined. C. crassicaulis is a year‐round species with a maximum frond wet weight of 817 mg observed in July 2017, as seawater temperature increases to 20°C. The attachment of vegetative propagules was significantly affected by temperature and irradiance, with maximal values detected at 20–25°C and 60 µmol photons m?2 s?1. The relative growth rates of vegetative propagules of C. crassicaulis were the highest at 20–25°C, 60 µmol photons m?2 s?1, and a salinity of 25 psu. In conclusion, due to its tremendous tolerance under variable environmental conditions, the vegetative propagules of C. crassicaulis can be used as seedlings for mass cultivation. 相似文献
8.
正Many proteins are regulated by post-translational modifications,such as the reversible covalent attachment of ubiquitin and ubiquitin-like proteins in eukaryotes(Kerscher et al, 2006). Post-translational modification of proteins by the SUMO protein family is involved in diverse cellular processes, including development, hormonal responses, and biotic and abiotic stress signaling(Park et al, 2011). SUMO modification can modulate protein-protein interactions, intracellular localization or the activities of the protein(Gareau and Lima, 2010). 相似文献
9.
Xu Gao Han Gil Choi Seo Kyoung Park Ju Hyoung Kim Ok Hwan Yu Ki Wan Nam 《Aquaculture Research》2019,50(3):856-861
Juvenile sporophytes and gametophytes of Ecklonia stolonifera were incubated in combinations of three pCO2 levels (360, 720 and 980 ppmv) and two temperatures (10 and 15°C for sporophytes; 15 and 20°C for gametophytes) to examine potential effects of climate change on photosynthesis and growth. Sporophytes had significantly higher maximum quantum yields (Fv/Fm) and maximum relative electron transport rates (rETRmax) at 720 ppmv than 360 and 980 ppmv. Also, these parameters were significantly lower at higher temperature of 15°C than at 10°C. Growth of female gametophytes was maximal at 360 ppmv rather than enriched pCO2 levels. Female gametophytes had significantly lower growth at higher temperature of 20°C than at 15°C. These results indicate effects of elevated pCO2 varied between generations: stimulating sporophytic photosynthesis and inhibiting gametophytic growth. Ocean acidification and warming would constitute a grave threat to seedling cultivation of E. stolonifera caused by growth inhibition of gametophytes at high pCO2 levels and temperatures. 相似文献
10.
Chang‐Hoon Shin Hien Thi Dieu Bui Samad Rahimnejad Ji‐Hoon Cha Byung‐Woo Yoo Bo‐Kyeun Lee Hyung‐Jin Ahn Soo‐Il Choi Yun‐Jeong Choi Yong‐Ho Park Jeong‐Dae Kim Kyeong‐Jun Lee 《Journal of the World Aquaculture Society》2014,45(3):258-268
This study was conducted to evaluate the effects of dietary supplementation of Barodon, an anionic alkali mineral complex, on growth, feed utilization, humoral innate immunity and disease resistance of olive flounder. A basal experimental diet was used as a control and supplemented with 0.1, 0.2, 0.3, 0.4, or 0.5% Barodon. Triplicate groups of fish (26.4 ± 0.2 g) were fed one of the diets to apparent satiation twice daily for 10 wk. The growth performance was enhanced (P < 0.05) linearly and quadratically in fish fed diets containing Barodon compared with that in fish fed the control. Feed utilization was significantly improved by Barodon supplementation. Serum lysozyme and antiprotease activities were increased quadratically in Barodon fed groups. Also, significantly higher superoxide dismutase activity was found in Barodon‐fed fish. Dietary supplementation of 0.1–0.3% Barodon resulted in significant enhancement of fish disease resistance against Streptococcus iniae. The findings in this study indicate that dietary supplementation of Barodon can enhance growth, feed utilization, innate immunity, and disease resistance of olive flounder and that the optimum level seems to be 0.1% in diets. 相似文献