全文获取类型
收费全文 | 3724篇 |
免费 | 211篇 |
国内免费 | 273篇 |
专业分类
林业 | 323篇 |
农学 | 114篇 |
基础科学 | 170篇 |
306篇 | |
综合类 | 1924篇 |
农作物 | 282篇 |
水产渔业 | 128篇 |
畜牧兽医 | 546篇 |
园艺 | 296篇 |
植物保护 | 119篇 |
出版年
2024年 | 14篇 |
2023年 | 39篇 |
2022年 | 108篇 |
2021年 | 140篇 |
2020年 | 100篇 |
2019年 | 103篇 |
2018年 | 92篇 |
2017年 | 111篇 |
2016年 | 95篇 |
2015年 | 182篇 |
2014年 | 174篇 |
2013年 | 239篇 |
2012年 | 359篇 |
2011年 | 314篇 |
2010年 | 368篇 |
2009年 | 309篇 |
2008年 | 315篇 |
2007年 | 269篇 |
2006年 | 241篇 |
2005年 | 206篇 |
2004年 | 135篇 |
2003年 | 57篇 |
2002年 | 67篇 |
2001年 | 75篇 |
2000年 | 54篇 |
1999年 | 21篇 |
1998年 | 2篇 |
1995年 | 2篇 |
1994年 | 7篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1981年 | 1篇 |
1963年 | 1篇 |
1961年 | 1篇 |
1957年 | 1篇 |
1930年 | 1篇 |
排序方式: 共有4208条查询结果,搜索用时 203 毫秒
61.
面对目前我国农村地区土地规模化飞速蓬勃发展的局面,针对我国广大农村地区土地规模化经营的主要类型和发展趋势开展研究,分析我国土地规模化发展的进程和政策,认为1995—2008年是稳步发展阶段,2008—2014年是快速发展阶段,2014年至今是飞速发展阶段。研究了入股、流转和托管这3种主要的土地规模化发展类型的不同内涵和特点,发现土地经营的规模要适度,不宜无限扩大,认为入股类型土地规模一般不宜超过133.3 hm2(约2 000亩),流转类型土地规模一般不宜超过666.7 hm2(约1万亩),托管类型土地规模一般不宜超过6 666.7 hm2(约10万亩)。目前我国不同地区之间发展不平衡,研究发现全程托管将是未来发展的主要趋势,同时土地流转和土地托管在相当长一段时间内将共存。 相似文献
62.
黄瓜种质资源单性结实性评价 总被引:4,自引:1,他引:3
在春季日光温室条件下,对75份黄瓜种质资源的单性结实性进行了评价。结果表明:75份材料的单性结实率在0~100%呈连续分布。其中强单性结实材料40份,占53.3%,中等单性结实材料24份, 占32%,弱单性结实材料11份,占14.7%。其中的24份品种资源中,强单性结实品种20个,占83.3%,其余为中等单性结实。单性结实性强弱表现为坐果率的差异,不同种质资源无籽果实与有籽果实的单瓜重和瓜形指数基本相似。单性结实性一般随着节位升高而增强,其评价工作可侧重于20节内的低节位。 相似文献
63.
64.
水杨酸与高温锻炼对高温胁迫下葡萄叶肉细胞质膜ATPase活性的影响 总被引:1,自引:0,他引:1
采用水性两相分配法对经水杨酸(SA)和高温锻炼处理过的葡萄幼苗叶肉细胞中ATPase进行了分离和测定.结果表明:高温下,细胞质膜ATPase活性随着胁迫程度的加深均呈下降趋势,经SA和高温锻炼预处理后再经高温胁迫,发现质膜ATPase的活性低于正常条件下的水平(CK1),但明显高于未经处理直接进行高温胁迫后ATPase活性水平,即高温锻炼和SA预处理的质膜酶活仍保持了较高的活性,并且后一种处理效果更明显.说明质膜上ATPase活性的变化对高温胁迫作出了一定的响应,SA和高温锻炼对提高葡萄幼苗叶片的抗热性与二者可以维持细胞质膜上ATPase活性的稳定有关. 相似文献
65.
采用火焰原子分光光度法,测定了保定市市售的3种类型共16种蔬菜中的Ca、Cu、Zn、Fe、Mn 5种矿质元素,为指导人们日常饮食提供科学依据.结果表明:不同类型蔬菜中矿质元素含量不同,叶菜类蔬菜中的(Ca、Cu、Zn、Fe、Mn含量高于果菜类蔬菜、根茎类蔬菜;而不同品种的蔬菜其矿质元素的含量也存在很大差异,油菜中的Ca和Mn含量最高,分别为7.6 g/100g和8.98 mg/100g;Zn含量最高的为香麦16.72 mg/100g,其次为菠菜12.63 mg/100g,洋白菜的Zn含量最低仅为0.73 mg/100g;菠菜中Fe含量最高138.43 mg/100g,其次为香麦111.11 mg/100g.综合分析结果,香麦、菠菜、油菜的Ca、Cu、Zn、Fe、Mn含量要高于其它种类的蔬菜. 相似文献
66.
基于逆向工程的车门外板曲面重构 总被引:2,自引:0,他引:2
利用三坐标测量仪测得轿车车门外板的点云数据,经数据处理后,应用CATIA软件中的相关模块进行曲面重构。以此为例探讨如何由实物或样品反求产品CAD模型的逆向设计的一般流程。 相似文献
67.
基于ADAMS的拖拉机参数化实用模型的初步研究 总被引:1,自引:1,他引:0
提出研究拖拉机虚拟样机模型的重要性。通过应用ADAMS软件,建立拖拉机整车的虚拟样机模型,介绍前后桥系统、转向系统、车身和传动系统模型的创建过程,仿真分析给出了拖拉机行驶速度、运动轨迹和转弯半径的变化曲线,为拖拉机设计和性能分析提供了研究平台。 相似文献
68.
69.
QIAN Wei LOU Guo-qiang ZHOU Zhuo-lin WANG Jia LIU Xiu-jie HAO Mao-lin WANG Wan-tie 《园艺学报》2000,36(11):2056-2061
AIM To investigate the role of curcumin (CUR) in lung ischemia/reperfusion (I/R) injury (LIRI) and its relationship with autophagy. METHODS 40 SD rats were randomly divided into sham operation (sham) group, I/R group, solvent (DMSO) group, CUR group and CUR+rapamycin (CUR-Rap) group. The rats were intraperitoneally injected with normal saline, DMSO, CUR or CUR+Rap before operation. After the rat LIRI model was established, the lung tissues were taken to measure W/D, TLW, IAR, and the contents of SOD and MDA were also measured to indicate the oxidative stress level. Light and electron microscopes were used to observed the morphology and ultrastrucure of lung tissues. The expression levels of autophagy-related proteins were determined by Western blot to evaluate autophagy levels. RESULTS Compared with sham group, wet weight/dry weight (W/D), total lung water (TLW), injured alveoli rate(IAR) and malondialdehyde (MDA) content in all other groups were increased, superoxide dismutase (SOD) activity was decreased, the levels of autophagy were increased (P <0.05), and lung tissue injury and cell ultrastructural damage were aggravated in CUR group. Compared with DMSO group, W/D, TLW and IAR and MDA content were decreased, SOD activity was decreased, autophagy levels were also decreased (P <0.05), and lung tissue and cell ultrastructural damage were attenuated. Compared with CUR group, W/D, TLW, IAR and MDA content were increased, SOD activity declined, the autophagy levels were increased (P <0.05), and damage of lung tissues and cells were more serious in CUR-Rap group. CONCLUSION Curcumin attenuates the lung I/R injury in rats, and its mechanism may be related to the reduction of oxidative stress and the inhibition of autophagy. 相似文献
70.
SUN Kai CHEN Wen-hua ZHANG Ying LI Yan AN Meng-yao PAN Ying-ying WU Yan-na KANG Yi GAO Wei-zhen LOU Jian-shi 《园艺学报》2017,33(1):116-122
AIM: To study the effects of noninvasive delayed limb ischemia preconditioning (NDLIP) on animal cardiac function, myocardial morphology and myocardial apoptosis after myocardial infarction (MI). METHODS: Healthy SD male rats[n=45, weighing (250±10) g] were randomly divided into 3 groups:MI group:the animal model of MI was established by surgical ligation of left anterior descending artery (LAD) after 2 weeks; NDLIP group:after the success of the MI animal model, NDLIP was carried out every other day until the 4th, 6th and 8th weeks; sham group:as the negative control group, the animals were taken heart LAD threading but no ligation. All rats were fed conventionally. At the end of the 4th, 6th and 8th weeks, all rats were made ventricular intubation, and then the hemodynamic parameters were recorded. The blood samples were withdrawn from the abdominal aorta and the serum was separated via centrifugation. The serum contents of Bcl-2 and Bax were measured by ELISA. Left ventricular anterior wall was homogenized. The mitochondrial respiratory chain complexes Ⅰ, Ⅱ, Ⅲ and Ⅳ in the myocardial tissues were detected by ELISA. RESULTS: At the end of the 4th, 6th and 8th weeks, compared with MI group, left ventricular systolic pressure in NDLIP group was significantly increased, while left ventricular end-diastolic pressure in NDLIP group was significantly decreased (both P<0.05). Mitochondrial respiratory chain complexesⅠ, Ⅱ, Ⅲ and Ⅳ in NDLIP group were significantly increased (P<0.05). The serum level of Bcl-2 in NDLIP group was significantly increased and Bax level was reduced remarkably (both P<0.01). CONCLUSION: NDLIP improves the hemodynamic indexes, promotes the mitochondrial respiratory function and inhibits cell apoptosis, thus improving the prognosis of MI. 相似文献