全文获取类型
收费全文 | 16823篇 |
免费 | 863篇 |
国内免费 | 1741篇 |
专业分类
林业 | 1853篇 |
农学 | 2085篇 |
基础科学 | 1383篇 |
2332篇 | |
综合类 | 5611篇 |
农作物 | 1147篇 |
水产渔业 | 663篇 |
畜牧兽医 | 2575篇 |
园艺 | 724篇 |
植物保护 | 1054篇 |
出版年
2024年 | 59篇 |
2023年 | 232篇 |
2022年 | 529篇 |
2021年 | 662篇 |
2020年 | 629篇 |
2019年 | 631篇 |
2018年 | 436篇 |
2017年 | 595篇 |
2016年 | 594篇 |
2015年 | 767篇 |
2014年 | 767篇 |
2013年 | 933篇 |
2012年 | 1164篇 |
2011年 | 1120篇 |
2010年 | 1088篇 |
2009年 | 1004篇 |
2008年 | 969篇 |
2007年 | 966篇 |
2006年 | 816篇 |
2005年 | 717篇 |
2004年 | 412篇 |
2003年 | 456篇 |
2002年 | 534篇 |
2001年 | 549篇 |
2000年 | 441篇 |
1999年 | 368篇 |
1998年 | 274篇 |
1997年 | 231篇 |
1996年 | 238篇 |
1995年 | 210篇 |
1994年 | 202篇 |
1993年 | 167篇 |
1992年 | 150篇 |
1991年 | 143篇 |
1990年 | 101篇 |
1989年 | 84篇 |
1988年 | 60篇 |
1987年 | 33篇 |
1986年 | 16篇 |
1985年 | 14篇 |
1984年 | 17篇 |
1983年 | 10篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1971年 | 1篇 |
1964年 | 2篇 |
1963年 | 1篇 |
1956年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
于2018年9月,对天津大港,宝坻,华苑等地区的12个站点的大型底栖生物的群落结构及生物多样性进行了调查分析。结果表明,调查区共鉴定出大型底栖生物3门10种,其中软体动物4种,环节动物4种,水生昆虫2种,各站位丰度波动范围为20~840 ind/m^2,平均为205.33 ind/m^2,生物量范围为0.012~308.63 g/m^2,平均为59.69 g/m^2;囊螺为该地区绝对优势种。丰富度指数Margalefs.index在1.48~3.334之间波动, Goodnight修正指数在0.523~1之间波动。 相似文献
92.
为加强渔业资源保护、增殖、开发和合理利用,维护渔业生产者的合法权益,保障渔业生产安全和水产品质量安全,促进渔业发展,经修订后的《河北省渔业条例》,于2007年11月23日省十届人大常委会第三十一次会议审议通过,2008年1月1日起施行。 相似文献
93.
Ye Yuan Min Jin Jiaxiang Luo Jia Xiong Terry Lynn Ward Fei Ji Guozhong Xu Mihai Sun Qicun Zhou 《Aquaculture Nutrition》2019,25(4):828-840
An 8‐week feeding trial was conducted to evaluate the effects of dietary copper sources on growth performance and intestinal microbial communities of juvenile Pacific white shrimp (Litopenaeus vannamei). Four isonitrogenous (420 g/kg crude protein) and isolipidic (70 g/kg crude lipid) experimental diets were formulated to contain different copper sources, Diet NSC (no‐supplemented copper), Diet CS (copper sulphate), Diet Availa (copper amino acid complex from Availa®Cu100) and Diet M (1:1, copper sulphate + copper amino acid complex). A total of 360 Pacific white shrimp juveniles (initial weight: 1.86 ± 0.03 g) were randomly allocated into four groups, with three replicates per group and 30 shrimps each replicate. An Illumina‐based sequencing method was used to analyse the intestinal bacterial composition of shrimp juveniles. The results revealed that shrimps fed Diet M had significantly higher percent weight gain (PWG) than that fed Diet NSC and Diet CS, while there were no significant differences between Diet M and Diet Availa. Survival was not affected by the dietary copper sources. Proteobacteria and Bacteroidetes were dominant in the intestines of Pacific white shrimp. Shrimps fed Diet M and Diet Availa had higher bacterial richness and diversity than those fed Diet NSC and Diet CS with no significant differences among all treatments. Furthermore, Diet M and Diet Availa which contained copper amino acid complex reduced the relative abundance of Vibrionaceae in shrimp intestinal tract. This study indicated that dietary copper sources could affect the intestinal microbial communities and diets supplemented with Availa®Cu100 could have a positive impact on the growth performance and decrease the potential risk of disease in Pacific white shrimp. 相似文献
94.
95.
AIM: To study the effect of inhibiting nuclear factor-kappa B (NF-κB) activity on the expression of angiotensinogen (AGT) and the production of angiotensinⅡ (AngⅡ) induced by tumor necrosis factor-α (TNF-α) in glomerular mesangial cells (MCs) of SD rats. METHODS: The MCs of SD rats were isolated and divided into three groups as follows: control; MCs treated with TNF-α, and the MCs treated with TNF-α + pyrrolidinedithiocarbamate (PDTC). The activity of nuclear factor-kappa B was measured by electrophoretic mobility shift assay. The expression of AGT was determined by RT-PCR for mRNA and Western blotting for protein. The concentration of angiotensinⅡ in supernatant was measured by RIA. RESULTS: The NF-κB activity in the MCs treated with TNF-α (20.67±9.14)×102 μg/cell was significantly higher than that in control cells [(8.25±4.35)×102 μg/cell, P<0.01] and the MCs treated with TNF-α+PDTC [(7.20±4.57)×102 μg/cell, P<0.01], and no significant difference was found between control and the MCs treated with TNF-α+PDTC (P>0.05). The AGT mRNA level in the MCs treated with TNF-α (0.27±0.05) was higher than that in the control cells (0.20±0.05, P<0.05), and no significant difference was observed when compared with that in the MCs treated with TNF-α+PDTC (0.22±0.06, P>0.05). The expression of AGT protein in the MCs treated with TNF-α (0.60±0.19) μg/cell was higher than that in the control [(0.37±0.15)μg/cell, P<0.05] and the MCs treated with TNF-α+PDTC [(0.37±0.17)μg/cell, P<0.05], and no significance was found between the MCs treated TNF-α+PDTC and the control (P>0.05). The AngⅡ level in supernatant of cultured MCs treated with TNF-α [(9.73±2.38)×10-5 ng·L-1/cell] was significantly higher than that in the control [(7.50±1.51)×10-5 ng·L-1/cell, P<0.05] and in the MCs treated with TNF-α+PDTC [(6.94±1.46)×10-5 ng·L-1/cell, P<0.05], however, the difference between the MCs treated with TNF-α+PDTC and the control was of no significance (P>0.05). CONCLUSION: TNF-α activates the NF-κB in glomerular MCs, induces the AGT expression and the production of AngⅡ. Inhibition of NF-κB decreases the AGT expression and the production of AngⅡ. Therefore, the effects of TNF-α on AGT and AngⅡ may be mediated by NF-κB. 相似文献
96.
97.
黄糊精/秸秆纤维复合材料弯曲性能分 总被引:1,自引:1,他引:0
利用模压方法制备了黄糊精/秸秆纤维复合材料,并利用试验方法研究黄糊精/秸秆纤维复合材料的弯曲性能.研究结果表明:在试验条件下,通过对黄糊精/秸秆纤维复合材料弯曲强度和弯曲弹性模量的极差分析发现最优组合相同,即热压温度A=170℃、热压压力B=9.8 MPa、热压时间C=20 min、黄糊精质量D=30 g,并对最优组合进行了试验验证,得出其弯曲强度为15.34 MPa,弯曲弹性模量为2 522.78 MPa.通过对复合材料的弯曲强度和弯曲弹性模量的方差分析发现,热压时间是不显著因素,而热压压力是显著因素. 相似文献
98.
99.
100.