全文获取类型
收费全文 | 7164篇 |
免费 | 376篇 |
国内免费 | 858篇 |
专业分类
林业 | 252篇 |
农学 | 616篇 |
基础科学 | 329篇 |
686篇 | |
综合类 | 3341篇 |
农作物 | 396篇 |
水产渔业 | 190篇 |
畜牧兽医 | 1965篇 |
园艺 | 237篇 |
植物保护 | 386篇 |
出版年
2024年 | 44篇 |
2023年 | 105篇 |
2022年 | 303篇 |
2021年 | 342篇 |
2020年 | 329篇 |
2019年 | 405篇 |
2018年 | 255篇 |
2017年 | 425篇 |
2016年 | 433篇 |
2015年 | 382篇 |
2014年 | 469篇 |
2013年 | 435篇 |
2012年 | 628篇 |
2011年 | 667篇 |
2010年 | 472篇 |
2009年 | 415篇 |
2008年 | 360篇 |
2007年 | 413篇 |
2006年 | 317篇 |
2005年 | 225篇 |
2004年 | 153篇 |
2003年 | 111篇 |
2002年 | 104篇 |
2001年 | 89篇 |
2000年 | 72篇 |
1999年 | 68篇 |
1998年 | 62篇 |
1997年 | 45篇 |
1996年 | 41篇 |
1995年 | 35篇 |
1994年 | 36篇 |
1993年 | 40篇 |
1992年 | 28篇 |
1991年 | 22篇 |
1990年 | 21篇 |
1989年 | 15篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1982年 | 1篇 |
1974年 | 1篇 |
1956年 | 2篇 |
排序方式: 共有8398条查询结果,搜索用时 15 毫秒
121.
122.
123.
在IPCC方法的基础上,对1980-2016年新疆畜禽温室气体排放的时空变化特征进行了研究。结果表明:新疆畜禽温室气体从1980年的1224.01×10^4 tCO2-eq波动升高至2016年的2032.80×10^4 tCO2-eq,增幅为66.08%,年均增长1.41%;畜禽肠道发酵甲烷排放是新疆畜禽温室气体的主要贡献者,占温室气体排放总量的84%,其次是畜禽粪便管理氧化亚氮和甲烷的排放;而主要畜禽温室气体排放以牛和羊为主,其次是马、驴、猪、骆驼和骡;最后通过对2015年新疆畜禽温室气体排放空间变化分析可知,伊犁州直属县(市)温室气体排放量最大,为456.78×10^4 tCO2-eq,而温室气体排放量最小的克拉玛依市仅有4.37×10^4 tCO2-eq,说明新疆畜禽温室气体排放空间差异性较大。 相似文献
124.
C. Caprari C. Bergmann Q. Migheli G. Salvi P. Albersheim A. Darvill F. Cervone G. De Lorenzo 《Physiological and Molecular Plant Pathology》1993,43(6)
Extracellular endopolygalacturonase, purified from the pathogenic fungus Fusarium moniliforme, consists of four molecular forms (38, 41·5, 45, and 48·5 kDa, respectively. Three forms (38, 41·5, and 45 kDa) were purified to homogencity by FPLC on a Mono S column followed by electroelution after SDS-PAGE. The N-terminal amino acid sequences of each of the three forms, and of a mixture containing all four forms were shown to be identical to that predicted from the nucleotide sequence of the endopolygalacturonase gene previously cloned from F. moniliforme. Enzymatic deglycosylation experiments revealed the presence of N-linked, high mannose oligosaccharide side-chains on all four forms of endo polygalacturonase. Hydrogen fluoride catalysed chemical deglycosylation of the polygalacturonase mixture yielded a single polypeptide with an apparent molecular mass of 36·2 kDa. Southern blot analysis, carried out at high stringency with an endopolygalacturonase-specific probe on genomic DNA digested with three different restriction enzymes, showed a single hybridizing restriction fragment in all three digests. A single 2·0 Mb chromosome hybridized with the endo polygalacturonase-specific probe, as shown by Southern blot analysis of F. moniliforme chromosomes separated by CHEF electrophoresis. Northern blot analysis revealed only one mRNA species 1350 nt encoding endo polygalacturonase. These data indicate that a single gene encodes the endopolygalacturonases of F. moniliforme. 相似文献
125.
126.
127.
Sanae ASANO Shoshichi IKEDA Yuzo KUROKAWA Shuhei KANDA Hisao ITABASHI 《Animal Science Journal》2007,78(1):28-33
To investigate seasonal variations in the digestive functions of sika deer, five female sika deer were provided with an amount of alfalfa hay cubes equivalent to voluntary food intake during winter. We measured the rate at which the food passed through the digestive tract, digestibility and rumen fermentation during the summer (August), autumn (November), winter (February) and spring (May). Total mean retention time in the digestive tract during summer and autumn was numerically longer than that in winter and spring, but the difference did not reach significance. Organic matter and fiber were less digestible in summer and autumn than in winter and spring (P < 0.05), whereas the digestibility of the dry matter tended to vary with the seasons (P < 0.1). Ruminal pH values seasonally changed (P < 0.01), and were the lowest in autumn. The concentration of ruminal ammonia‐nitrogen differed significantly among the seasons (P < 0.05), increasing in winter and decreasing during spring and summer. The numbers of protozoa changed significantly among the seasons (P < 0.05), being higher in autumn than in winter and spring, and intermediate in summer. The concentration of total volatile fatty acids was not seasonally affected, but the molar percentages of propionic acid and butyric acid significantly changed according to season (P < 0.05 and P < 0.01, respectively), and the ratio of acetic to propionic acid tended to change with the seasons (P < 0.1). The results of this study suggested that the digestive functions in sika deer, fed a commercial diet at a restricted level, differed notably among the seasons and these variations might partially be due to environmental effects. 相似文献
128.
Effects of amino nitrogen on fermentation parameters by mixed ruminal microbes when energy or nitrogen is limited 总被引:1,自引:0,他引:1
Hiroshi KAJIKAWA Kiyoshi TAJIMA Makoto MITSUMORI Akio TAKENAKA 《Animal Science Journal》2007,78(2):121-128
Ruminal microbes harvested from a ruminally fistulated cow were incubated in simple batch and semicontinuous cultures with NH3‐N or amino‐N on nitrogen‐ or energy‐excess diets in quantity (HN and LN diets, respectively, consisting of timothy hay plus soybean meal, or corn grain), based on evaluation with the National Research Council and Cornell Net Carbohydrate and Protein System models. In a batch culture experiment, supplementation with amino‐N promoted digestion and fermentation in the course of incubation (4–24 h) on both diets, but these effects mostly disappeared when the diets were sufficiently digested (at 48 h). In a semicontinuous culture experiment using Rusitec, no effect of amino‐N was exhibited after sufficient fermentation and digestion, but significant promotion of digestion was shown in the course of incubation on the HN diet, while no such effect was detected on the LN diet. The microbial yield for 24 h did not show a significant difference between the N sources of either of the two diets. These results suggest that the stimulatory effects of amino‐N are diminished when the diets are sufficiently digested after a long retention and incubation, and also that the effectiveness of amino‐N does not require a quantitatively energy‐excess status. 相似文献
129.
130.
为研究纤维素酶和乳酸菌制剂以及尿素对小麦秸黄贮饲料品质的影响,分别设不同的处理组及对照进行小麦秸黄贮饲料的发酵试验。实验Ⅰ结果表明:尿素单独添加、尿素和纤维素酶混合添加显著提高粗蛋白的含量,尿素和乳酸菌制剂、以及尿素与乳酸菌制剂和纤维素酶混合添加都不能得到品质较好的小麦秸黄贮饲料。实验Ⅱ结果表明:各添加剂处理均显著降低黄贮饲料的pH值和中性洗涤纤维含量(P<0.05),显著提高乳酸、总酸和粗蛋白含量(P<0.05);添加剂处理能够明显改善小麦秸黄贮饲料的发酵品质,提高小麦秸的饲用价值。纤维素酶和乳酸菌制剂同时添加时,小麦秸黄贮饲料品质最好。 相似文献