全文获取类型
收费全文 | 39799篇 |
免费 | 2353篇 |
国内免费 | 3838篇 |
专业分类
林业 | 3947篇 |
农学 | 4354篇 |
基础科学 | 2843篇 |
5841篇 | |
综合类 | 14801篇 |
农作物 | 2502篇 |
水产渔业 | 1755篇 |
畜牧兽医 | 5889篇 |
园艺 | 1859篇 |
植物保护 | 2199篇 |
出版年
2024年 | 161篇 |
2023年 | 668篇 |
2022年 | 1515篇 |
2021年 | 1884篇 |
2020年 | 1709篇 |
2019年 | 1631篇 |
2018年 | 1200篇 |
2017年 | 1862篇 |
2016年 | 1474篇 |
2015年 | 1881篇 |
2014年 | 1960篇 |
2013年 | 2408篇 |
2012年 | 2945篇 |
2011年 | 3061篇 |
2010年 | 2877篇 |
2009年 | 2705篇 |
2008年 | 2362篇 |
2007年 | 2295篇 |
2006年 | 1824篇 |
2005年 | 1538篇 |
2004年 | 820篇 |
2003年 | 719篇 |
2002年 | 872篇 |
2001年 | 852篇 |
2000年 | 737篇 |
1999年 | 636篇 |
1998年 | 459篇 |
1997年 | 450篇 |
1996年 | 375篇 |
1995年 | 359篇 |
1994年 | 344篇 |
1993年 | 242篇 |
1992年 | 234篇 |
1991年 | 228篇 |
1990年 | 152篇 |
1989年 | 153篇 |
1988年 | 123篇 |
1987年 | 61篇 |
1986年 | 36篇 |
1985年 | 17篇 |
1984年 | 29篇 |
1983年 | 16篇 |
1982年 | 16篇 |
1981年 | 19篇 |
1980年 | 10篇 |
1979年 | 13篇 |
1978年 | 5篇 |
1965年 | 5篇 |
1964年 | 6篇 |
1956年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
早熟籽用型工业大麻新品种云麻2号的选育 总被引:1,自引:0,他引:1
利用三个品种复合杂交法选育而成的云麻2号,为早熟籽用型工业大麻品种.雌雄异株、雌雄比例为2.2:1,全生育期约120天,株高2.4-3.0m、茎粗1.3-1.7cm,千粒重20g,籽粒含油量33.11%,四氢大麻酚(THC)含量平均0.059%.种子成熟期落粒性不强,便于收获.2003-2004两年异地多点试验结果,麻籽平均产量1545kg/hm2,较对照增产18.84%.在高温高湿环境条件下轻感叶褐斑病,抗倒伏力强.适宜于云南省北纬23°以北、海拔1500-3000m的适宜地区种植. 相似文献
992.
993.
AIM: To investigate the effect of transketolase-like protein 1 (TKTL1) on proliferation of human nasopharyngeal carcinoma cells in vitro. METHODS: The siRNA against TKTL1 mRNA was constructed and transfected into human nasopharyngeal carcinoma cells (CNE cell line). The activity of transketolase was detected before and after RNA interference.Real-time PCR was used to determine the mRNA expression of transketolase (TKT) gene family in the CNE cells.Flow cytometry and MTT test were used to detect the effect of anti-TKTL1 siRNA on cell proliferation and cell cycle in the CNE cells. RESULTS: The total transketolase activity was significantly decreased in the CNE cells transfected with siRNA TKTL1 construct compared with the cells transfected with control vector or untransfected CNE cells. No significant difference in the expression level of TKT and TKTL2 gene between the CNE cells transfected with siRNA TKTL1 construct and the cells transfected with control vector or untransfected CNE cells was observed (P>0.05). However, the expression level of TKTL1 gene was significantly downregulated in the CNE cells transfected with siRNA TKTL1 construct compared with the cells transfected with control vector.Cancer cells were arrested in G0/G1 phase, and cancer cell proliferation was significantly inhibited in the CNE cells transfected with siRNA TKTL1 construct. CONCLUSION: TKTL1 plays an important role in the total transketolase activity and cell proliferation of human nasopharyngeal carcinoma. TKTL1 may be considered as a potential target for novel anti-cancer therapy. 相似文献
994.
995.
996.
Effects of fruit bagging on coloring and related physiology,and qualities of red Chinese sand pears during fruit maturation 总被引:1,自引:0,他引:1
Chunhui Huang Bo Yu Yuanwen Teng Jun Su Qun Shu Zaiquan Cheng Liqiong Zeng 《Scientia Horticulturae》2009
Red Chinese sand pears (Pyrus pyrifolia Nakai) are particular to China. In order to determine the effects of fruit bagging treatments (including bag types, bag removal patterns and dates) on fruit qualities and to understand the mechanism of coloring of red Chinese sand pears, two experiments were carried out. In the first experiment, fruit of ‘Meirensu’ were firstly covered by light-impermeable paper bags with different levels of light permeable liners during their early development stage, then, the whole bag were/not removed or only the outer layer of bags were removed 3, 2 or 1 weeks before harvest. Thus, the fruit were/not totally re-exposed or were under different levels of sunlight transmission (80.31% or 34.71%). Non-bagged fruit were used as the control. Bagging treatments significantly affected the concentration of anthocyanin and the visual qualities of pear fruit. Compared to control, fruit re-exposed totally for 2 or 3 weeks accumulated the largest amount of anthocyanin and fruit receiving 80.31% and 34.71% of sunlight for 1–3 weeks could synthesize a little anthocyanin, indicating that high light intensity is imperative for coloring in red Chinese sand pears. Bagging treatments did not affect contents of total soluble sugars, but decreased organic acids contents in fruit. In the second experiment, fruit of ‘Meirensu’ and ‘Yunhongli No. 1’ were covered with only one type of light-impermeable bag during the early development stage and totally re-exposed after the bag removal 15 days before harvest. Fruit were then collected at different intervals to trace the time-course of coloring, and related physiology and inner qualities. With increasing time after the bag removal, the concentration of chlorophyll, carotenoid, flavonoid and total phenols changed little, but the concentration of anthocyanin accumulated extremely fast within 10 days after the bag removal in both cultivars and thereafter kept constant. ‘Yunhongli No. 1’ had higher anthocyanin contents and lower hue angle than ‘Meirensu’, indicating a higher potential of anthocyanin synthesis. After the bag removal, the sucrose contents and PAL activities increased gradually and correlation analysis revealed that they were highly correlated with anthocyanin accumulation in two cultivars. This study suggests that anthocyanin biosynthesis in red Chinese sand pears is a highly light dependent process and modified by genotypes. Based on the current results, in order to obtain red Chinese sand pear fruit with attractive appearance and good inner qualities, fruit must be covered with light-impermeable bags at the early stage of fruit development and the bag should be removed totally at least 10 days before harvest. 相似文献
997.
998.
999.
1000.
The effects of salinity on hemolymph osmotic pressure, gill Na+/K+‐ATPase activity and dopamine (DA), norepinephrine (NE), serotonin (5‐HT) in the gills, and hemolymph of the adult Charybdis japonica were studied. DA levels increased significantly (P < 0.05), while the NE and 5‐HT revealed contrary change in hemolymph and gills. The iso‐osmotic point of C. japonica (911.4 mOsm/kg) was at salinity of 27.87 ppt. The Na+/K+‐ATPase activity of gill showed negative correlation with salinity in the hypotonic environment (<27.87 ppt). The results of this experiment indicated that C. japonica had great capability to acclimate to low salinity. 相似文献