全文获取类型
收费全文 | 48377篇 |
免费 | 2306篇 |
国内免费 | 5803篇 |
专业分类
林业 | 2515篇 |
农学 | 4503篇 |
基础科学 | 2281篇 |
7081篇 | |
综合类 | 21279篇 |
农作物 | 8379篇 |
水产渔业 | 1367篇 |
畜牧兽医 | 3630篇 |
园艺 | 1451篇 |
植物保护 | 4000篇 |
出版年
2024年 | 395篇 |
2023年 | 957篇 |
2022年 | 1750篇 |
2021年 | 1924篇 |
2020年 | 1781篇 |
2019年 | 2115篇 |
2018年 | 1584篇 |
2017年 | 2118篇 |
2016年 | 2888篇 |
2015年 | 2529篇 |
2014年 | 3254篇 |
2013年 | 3139篇 |
2012年 | 3786篇 |
2011年 | 3218篇 |
2010年 | 2635篇 |
2009年 | 2690篇 |
2008年 | 2219篇 |
2007年 | 2543篇 |
2006年 | 2378篇 |
2005年 | 1877篇 |
2004年 | 1435篇 |
2003年 | 1280篇 |
2002年 | 995篇 |
2001年 | 895篇 |
2000年 | 880篇 |
1999年 | 666篇 |
1998年 | 603篇 |
1997年 | 517篇 |
1996年 | 486篇 |
1995年 | 493篇 |
1994年 | 376篇 |
1993年 | 377篇 |
1992年 | 316篇 |
1991年 | 283篇 |
1990年 | 295篇 |
1989年 | 254篇 |
1988年 | 149篇 |
1987年 | 135篇 |
1986年 | 89篇 |
1985年 | 41篇 |
1984年 | 23篇 |
1983年 | 9篇 |
1982年 | 11篇 |
1981年 | 30篇 |
1980年 | 13篇 |
1979年 | 10篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1963年 | 6篇 |
1962年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 24 毫秒
81.
马铃薯渣酶法水解液制备单细胞蛋白饲料的研究 总被引:1,自引:0,他引:1
本文研究了酶法水解马铃薯渣制备膳食纤维后的滤液制备单细胞蛋白的可行性。试验结果表明,单细胞蛋白边糖化边发酵的摇瓶培养的较优工艺条件为:底物浓度为8%(添加8%的麸皮水)、初始pH值为4.5、接种量为15%、葡萄糖淀粉酶加入量为100U/g(原料中淀粉)、青霉素加入量为80U/g(原料)、培养温度为28℃、培养时间为6h、转速为250r/min。在此条件下,干酵母产量最高为19.920g/L,单细胞蛋白中的蛋白质含量达12.27%。 相似文献
82.
水稻旱作对其生长量和经济产量的影响 总被引:11,自引:0,他引:11
1998~1999年,研究了水稻旱作条件下,不同生育时期受水分胁迫后对作物生长量的影响。结果表明:不同指标对水分胁迫时期的敏感性不一,植株高度对抽穗期水分胁迫最敏感;单株绿叶面积和单株地上部干重对幼穗分化后期水分胁迫最敏感;根系干重和根冠比对幼穗分化前期水分胁迫最敏感;幼穗分化后期水分胁迫对经济产量影响程度最大,无效分蘖期水分胁迫对产量影响程度最小。 相似文献
83.
中国风水侵蚀交错区分布特征分析 总被引:6,自引:1,他引:6
风水侵蚀交错带的研究 ,对景观、土地覆盖 /土地利用、全球变化等研究具有重要意义。论文以GIS技术为支撑 ,定量计算出我国风水侵蚀带。在分布特征上 ,主要分布我国北方地区 ,其中以西部沙漠 ,北部山脉沿线为重 ,这种分布与气候、地貌分界有明显联系。 49.6 %风水侵蚀复合带的降水量小于 2 0 0mm。风水侵蚀复合带的土地利用主要以草地为主 ,占 41.8% ,其次为耕地。两种类型的分布 ,草地以与其它土地利用类型交错分布为主 ;而耕地是有重心的分散分布。风水侵蚀复合带的总体侵蚀要强于全国水平。 相似文献
84.
85.
86.
87.
AIM:The β-catenin is a key molecule in the Wnt signal pathway, which plays a critical role in normal development and tumorigenesis. However, the mechanisms of the β-catenin on the cell growth control are still not completely defined. The aim of this study was to test the hypothesis that the mutant β-catenin may regulate the hepatocyte proliferation. METHODS: The immortalized murine hepatocyte cell line, AML12, was used for this study. A plasmid that contain mutant β-catenin S33Y was transfected into the AML12 cells and a stable cell line AML12S33Y was established. The cell growth property of this cell line and the parental cell were compared by flow cytometry analysis and direct cell count. The cells were also tested for the ability to form soft agar colonies, and the ability to form tumors in the severe immune deficient mice (SCID). RESULTS:1. The mutant β-catenin containing cell line AML12S33Y has higher proliferating index compared with the parental AML12 cells (P<0.01), suggesting that mutant β-catenin promotes cell growth. 2. The mutant β-catenin cells formed small colonies in soft agar after 4 weeks of culture, but did not generate tumor in SCID mice. CONCLUSION:The mutant β-catenin promotes liver cell growth. 相似文献
88.
AIM:To investigate the effect of tea-polyphenols (TP) on the activation of NF-κB and the expression of TGF-β1 mRNA in THP-1 cells (a human acute monocytic leukemia cell line). METHODS:THP-1 cells were incubated with the different concentrations of TP, VLDL, LDL or ox-LDL. In the THP-1 cellls, the nuclear malposition rate of NF-κB was detected with immunohistochemistry technique, the positive index of the TGF-β1 mRNA expression was detected by hybridization in situ, and accumulation of total cholesterol (TC) in cells incubated with 0.4-40 μg/L TP was determined with oxidase assay. RESULTS:The nuclear malposition rate of NF-κB, the positive index of the TGF-β1 mRNA expression and TC in THP-1 cells incubated with 0.4-40 μg/L of TP were lower than those with 0 μg/L of TP in TP-V group, TP-L group and TP-O (P<0.05). The differences of these markers in THP-1 cells incubated with more than 40 μg/L TP in TP-V group, TP-L group and TP-O were not statistically significant, compared with TP-C group (P>0.05). CONCLUSION:TP inhibited the activation of NF-κB, the expression of TGF-β1 mRNA and the foam cell formation in the mono-macrophage. 相似文献
89.
Accomodation of important sources of uncertainty in ecological models is essential to realistically predicting ecological processes. The purpose of this project is to develop a robust methodology for modeling natural processes on a landscape while accounting for the variability in a process by utilizing environmental and spatial random effects. A hierarchical Bayesian framework has allowed the simultaneous integration of these effects. This framework naturally assumes variables to be random and the posterior distribution of the model provides probabilistic information about the process. Two species in the genus Desmodium were used as examples to illustrate the utility of the model in Southeast Missouri, USA. In addition, two validation techniques were applied to evaluate the qualitative and quantitative characteristics of the predictions.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献
90.