全文获取类型
收费全文 | 21070篇 |
免费 | 1315篇 |
国内免费 | 1871篇 |
专业分类
林业 | 1935篇 |
农学 | 2081篇 |
基础科学 | 1045篇 |
3201篇 | |
综合类 | 6980篇 |
农作物 | 2085篇 |
水产渔业 | 1007篇 |
畜牧兽医 | 3411篇 |
园艺 | 1379篇 |
植物保护 | 1132篇 |
出版年
2024年 | 150篇 |
2023年 | 450篇 |
2022年 | 752篇 |
2021年 | 831篇 |
2020年 | 839篇 |
2019年 | 1009篇 |
2018年 | 793篇 |
2017年 | 866篇 |
2016年 | 1171篇 |
2015年 | 1412篇 |
2014年 | 1472篇 |
2013年 | 1546篇 |
2012年 | 1679篇 |
2011年 | 1438篇 |
2010年 | 1069篇 |
2009年 | 1008篇 |
2008年 | 837篇 |
2007年 | 967篇 |
2006年 | 995篇 |
2005年 | 788篇 |
2004年 | 505篇 |
2003年 | 392篇 |
2002年 | 339篇 |
2001年 | 312篇 |
2000年 | 344篇 |
1999年 | 240篇 |
1998年 | 235篇 |
1997年 | 206篇 |
1996年 | 190篇 |
1995年 | 197篇 |
1994年 | 212篇 |
1993年 | 177篇 |
1992年 | 131篇 |
1991年 | 126篇 |
1990年 | 137篇 |
1989年 | 88篇 |
1988年 | 61篇 |
1987年 | 50篇 |
1986年 | 38篇 |
1985年 | 40篇 |
1984年 | 33篇 |
1983年 | 15篇 |
1982年 | 10篇 |
1981年 | 25篇 |
1980年 | 21篇 |
1979年 | 11篇 |
1978年 | 11篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1955年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
31.
税世荣 《内蒙古农业大学学报(自然科学版)》1990,(1)
荒漠水源奇缺,常有干渴威协。骆驼长期在这种自然选择下,造就出一种十分惊人的耐干渴能力,十日不饮可照常供使役,30~40日内缺水不致有生命危险。据研究认为,骆驼高度耐渴的机理主要在于:一次能饮入60~80升甚至更多的水;能饮用含盐量相当高的水;血液和体液中保存水的能力很强;能节约散热、呼吸、排尿、排粪过程中的水份消耗;有较高排泄浓缩尿的能力;可有效利用体内的代谢水;即使高度失水(达体重的30%)也能短期耐受过去。正因其耐渴能力强,所以才使人类开发利用荒漠成为可能;使大面积缺水草埸和其它家畜所不能利用的灌木类植物得到合理利用;还能在缺水条件下持续分泌稀薄的低脂肪驼乳,为沙漠旅行者提供上等饮料。 相似文献
32.
Genetic diversity estimates in Cicer using AFLP analysis 总被引:2,自引:0,他引:2
Amplified fragment length polymorphism (AFLP) analysis was used to evaluate the genetic variation among cultivated chickpea and wild Cicer relatives. In total, 214 marker loci were assessed, of which 211 were polymorphic (98.6%) across the 95 accessions that represented 17 species of Cicer. The genetic variation within a species was highest in C. pinnatifidum followed by C. reticulatum and lowest in C. macracanthum. Three main species groups were identified by UPGMA clustering using Nei's pair‐wise distance calculations. Group I included the cultivated species C. arietinum, C. reticulatum and C. echinospermum. Within this group, C. reticulatum accessions were clustered closest to the C. arietinum cultivars ‘Lasseter’, ‘Kaniva’ and ‘Bumper’, supporting the hypothesis that C. reticulatum is the most probable progenitor of the cultivated species. Cicer bijugum, C. judaicum and C. pinnatifidum were clustered together creating group II. Group III contained all nine perennial species assessed and two annual species C. yamashitae and C. cuneatum. The genetic distance detected between group I and group III (0.13) was equivalent to the genetic distance detected between group I and group II (the primary and annual tertiary species, respectively; 0.14). This indicated that the perennial tertiary species may be as valuable for increasing variation to incorporate novel germplasm in the cultigen as the annual tertiary species. 相似文献
33.
本文运用知识工程语言 M·1构造了一个用于小麦条锈病流行程度趋势预测的专家系统雏型。专家的知识用产生式规则来表示。知识库中的知识规则可相对独立,便于知识库的扩充和完善。 相似文献
34.
华北山区位于温带——暖温带,东经107°~123°,北纬35°~43°。包括山东丘陵区,太行山区,冀北辽西山地区,阴山山地区四部分。该区属于农牧业交错区,农业、牧业(农区牧业和草地牧业)、林业十分发达,并且在迅速发展。华北山区是我国小麦、玉米和杂粮的主要产区。草地类型多样,饲草料丰富,又是养牛业、养羊业、养猪业相当发达的地区。经统计,华北山区总人口为5629万,总土地面积3545万ha,天然草地总面积为1588.91万ha,占土地总面积的44.82%,人均草地0.2823ha。各个区的草地类型不同,生产力差异显著(p<0.01)。 相似文献
35.
Improvements in human patient monitoring despite their development in animals, do not always find their way into veterinary clinical use due to financial constraints. Gastrointestinal intraluminal CO2 partial pressure (Gip1 CO2 ) monitoring, however, is not only proving very beneficial in human trauma and critical patient care but is also very likely to become relatively inexpensive. By providing information on the perfusion adequacy of a high risk, critically important tissue, the GI mucosa, GI P1 CO2 monitoring offers an easily accesible indicator of the efficacy and adequacy of resuscitative interventions. The potential for decreasing morbidity and mortality is enormous. Therefore, the practicing veterinarian should become familiar with GI P1 CO2 monitoring theory and technology so he or she can be better prepared to incorporate it into practice when in becomes available. 相似文献
36.
火鸡隐孢子虫在鹌鹑体内发育史的研究 总被引:10,自引:3,他引:7
分离自鹌鹑的火鸡隐孢子虫经口感染2日龄鹌鹑,潜在期为3d,开放期为4-18d。它在鹌鹑体内发育史过程为:卵巢经口接种后,于十二指肠,空肠,回肠肠腔中子孢子脱囊,至接种后6h全部子孢子脱囊完毕。接种后6h在小肠中出现滋养体。接种后12h在小肠中出现内含8个裂殖子的裂殖体及裂殖子,接种后48h滋养体和裂殖体开始出现于直肠。接种后54h,在小肠,直扬中出现含有16个子弹形小配子的小配子体。小配子与大配子 相似文献
37.
38.
39.
Variation was investigated in 110 doubled haploid (DH) lines of wheat derived from wheat × maize crosses. Field observation revealed visible variations in 15 DH2 lines such as extreme dwarfism, low seed fertility, alteration of spike type and stripes. Six agronomic traits, i.e., heading date, spike number/ plant, culm length, spike length, seed fertility and grain weight were statistically analyzed in the DH2 and DH3 generations. Out of the 88 DH2 lines/DH3 groups, 26 %/64 % showed significant differences from the parental variety in the means of one or more traits. Ranges of the DH3 lines were larger than those of the DH2 lines, except for spike number/plant. Furthermore, analyses of variance within and between DH lines showed the presence of heterogeneity/heterozygosity in the DH2 lines/plants. These results indicated the occurrence of gametoclonal variation in the DH lines. It is considered that most of the variations detected were due to the colchicine treatment rather than to the 2,4-D treatment or in vitro culture. 相似文献
40.