全文获取类型
收费全文 | 2783篇 |
免费 | 115篇 |
国内免费 | 135篇 |
专业分类
林业 | 183篇 |
农学 | 272篇 |
基础科学 | 116篇 |
155篇 | |
综合类 | 1808篇 |
农作物 | 152篇 |
水产渔业 | 114篇 |
畜牧兽医 | 109篇 |
园艺 | 46篇 |
植物保护 | 78篇 |
出版年
2024年 | 23篇 |
2023年 | 48篇 |
2022年 | 73篇 |
2021年 | 96篇 |
2020年 | 74篇 |
2019年 | 97篇 |
2018年 | 47篇 |
2017年 | 82篇 |
2016年 | 139篇 |
2015年 | 121篇 |
2014年 | 156篇 |
2013年 | 186篇 |
2012年 | 242篇 |
2011年 | 223篇 |
2010年 | 173篇 |
2009年 | 181篇 |
2008年 | 166篇 |
2007年 | 161篇 |
2006年 | 160篇 |
2005年 | 98篇 |
2004年 | 101篇 |
2003年 | 71篇 |
2002年 | 68篇 |
2001年 | 56篇 |
2000年 | 33篇 |
1999年 | 35篇 |
1998年 | 15篇 |
1997年 | 8篇 |
1996年 | 12篇 |
1995年 | 14篇 |
1994年 | 11篇 |
1993年 | 7篇 |
1992年 | 10篇 |
1991年 | 12篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1977年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有3033条查询结果,搜索用时 15 毫秒
81.
在今年“两会”上通过的“十一五”规划纲要中明确提出:“加快推进收入分配制度改革”和“更加注重社会公平”。表述中增加了“加快”和“更加”加以强调,于是,改革收入分配制度的紧迫性和重要性凸显出来。本论文就目前我国收入分配的基本现状以及产生收入分配不合理的成因展开论述,并就如何改善我国收入分配不合理的现状提出相应对策。 相似文献
82.
不同夜间温度对小麦旗叶光合作用和单株产量的影响 总被引:13,自引:3,他引:13
本文用不同夜间温度连续处理抽穗开花后的小麦植株,对旗叶的光合作用和单株产量进行了比较研究。结果表明夜间低温能明显延长叶片叶绿素含量缓降期和光合速率高值持续期,从而增加叶片的叶源量,提高产量。经计算缓降期延长一天,可使单株产量和千粒重分别提高2.0-2.5%和1.5-2.0%。夜间高温处理植株效果相反。试验进一步研究 相似文献
83.
为探究不同磁强磁化水灌溉对设施灵武长枣营养生长与果实品质的影响,以宁夏灵武市大泉林场基地设施栽培的灵武长枣为研究对象,对其营养生长(枣吊长、枣吊粗、叶面积等)和果实品质(可溶性糖含量、有机酸含量、Vc含量等)进行了测定分析。结果表明,采用ADS-1800磁强磁化水灌溉对枣吊生长的促进作用最大,枣吊净生长量较CK增加了15.6%;ADS-1400磁强磁化水灌溉提高了设施灵武长枣的单株产量,可达7.62 kg,增产效果最显著;ADS-800磁强磁化水灌溉可增加设施灵武长枣的可溶性固形物及可溶性糖含量,较CK分别增加了5.5%和4.38%。因此,不同磁强磁化水处理能促进灵武长枣的营养生长,影响果实品质。本研究结果为磁化水灌溉技术在设施灵武长枣生产上的应用提供了参考依据。 相似文献
84.
Estimation of the amount of nutrients in livestock manure 总被引:1,自引:0,他引:1
85.
单位面积穗数是决定小麦产量的主要因素之一。针对人工清点小麦穗数的方法容易受主观因素影响、效率低和图像处理方法鲜有进行系统部署等问题,提出一种注意力模块(Convolutional Block Attention Module,CBAM)与YOLOv5相结合的CBAM-YOLOv5网络结构,通过对特征图进行自适应特征细化,实现更准确的单位面积穗数测量。该研究以本地采集小麦图像数据和网络公开小麦图像数据为数据集,设置输入图像分辨率为1 280,得到CBAM-YOLOv5模型,可以达到0.904的F1分数和0.902的平均精度,测试集计数的平均相对误差为2.56%,平均每幅图像耗时0.045 s,综合对比,CBAM-YOLOv5模型具有显著优势。模型放置于服务器,结合手机端软件和辅助装置,形成单位面积穗数测量系统,实现育种小区麦穗图像实时采集、处理和计数,计数的平均相对误差为2.80%,抗环境干扰性强。该研究方法与装置可以实现田间小麦单位面积穗数的实时在线检测,降低主观误差,具有较高的准确率及较强的鲁棒性,为小麦单位面积穗数快速、准确估测提供一种新的技术和装备支撑。 相似文献
86.
利用农业资源公里网点监测技术,调查235户农户农业收支情况,分析农户收入及生产成本构成特点。对生产成本进行评价,提出农业生产成本控制的途径选择及促进农民节本增收的建议。 相似文献
87.
基于1978-2009年以来的省级面板数据,本文首先利用泰尔指数估计了中国居民收入差距演进趋势,然后按地区结构和城乡结构进行了分解。结果显示,城乡收入差距占据了整体收入差距的70%以上,三大地区间的收入差距虽较为明显,但并没有地区内的收入差距显著。究其原因,中国收入差距的演进除了内在的经济规律使然外,经济政策也有较为明显的影响。因此,加快经济发展、强化农村偏向型的经济政策是缩小收入差距的必然途径。 相似文献
88.
M. Hühn 《Journal of Agronomy and Crop Science》1998,181(4):249-255
A general approach to determine the effect of accuracy of sowing technique on yield per area
Caused by nonperfect seed placement accuracy of sowing machines as well as by many other abiotic and biotic factors the resulting plant stands exhibit nonregular plant distributions. Based on several simplifying assumptions a stochastic approach provides a quantitative determination of the effects of accuracy of sowing technique on yield per area. In this approach, two random variables are assigned to each individual plant: single plant yield E and single plant area A, which is calculated in this paper by the construction and quadrature of the so-called Thiessen-polygons. The yield per area F is calculated as the expectation of the ratio E/A. By assuming a deterministic mathematical relationship between E and A, the calculation of F reduces to the calculation of the expectation of a function of only one random variable A. A simple approximation with sufficient accuracy for many applications only depends on the mean and on the variance of the areas of the individual plants. For demonstration purposes, the theoretical approaches and results have been finally applied to three data sets for drilled seeds of winter oilseed rape (plant density: 60 plants/m2 and distance between rows: 10 cm). These data sets exhibit different accuracies of the longitudinal distributions within rows which have been quantitatively measured by the coefficient of variation for the distances between plants within rows: Yield depression increases with an increasing variability of plant distances within rows. 相似文献
Caused by nonperfect seed placement accuracy of sowing machines as well as by many other abiotic and biotic factors the resulting plant stands exhibit nonregular plant distributions. Based on several simplifying assumptions a stochastic approach provides a quantitative determination of the effects of accuracy of sowing technique on yield per area. In this approach, two random variables are assigned to each individual plant: single plant yield E and single plant area A, which is calculated in this paper by the construction and quadrature of the so-called Thiessen-polygons. The yield per area F is calculated as the expectation of the ratio E/A. By assuming a deterministic mathematical relationship between E and A, the calculation of F reduces to the calculation of the expectation of a function of only one random variable A. A simple approximation with sufficient accuracy for many applications only depends on the mean and on the variance of the areas of the individual plants. For demonstration purposes, the theoretical approaches and results have been finally applied to three data sets for drilled seeds of winter oilseed rape (plant density: 60 plants/m
89.
Improves investment decision method NPV method by introducing risk. This paper CAPM and certainty equivalent wealthare applied because of NCF'S volatility of venture capital projects, on the basis of which, debt capital is introduced. the dissertation derives a levered risky project's NPV formula, which broadens applying range and lessens constrain conditions. For risky projects investment decision, the research provides a new theoretical basis. 相似文献
90.
The relationship of investors and venture capitalists is an important part in venture capital. Based on asymmetric information, this paper analyzes the principal agent relationship between investors and venture capitalists with game theory. And this paper mainly discusses the choosing, controlling and incentive problem. It suggests that only the capable and self confident venture capitalists could accept the terms of the limited partnership. It also indicates that recompense mechanism which holds the interest of investors and that of venture capitalists tightly is the center of the limited partnership. Rate of yield is the key of recompense mechanism, it not only reflects the incentive on venture capitalists, also reflects the share of risk between investors and venture capitalists. At last, the market credit play an important role in venture capital. 相似文献