全文获取类型
收费全文 | 3791篇 |
免费 | 228篇 |
国内免费 | 400篇 |
专业分类
林业 | 389篇 |
农学 | 337篇 |
基础科学 | 315篇 |
788篇 | |
综合类 | 1687篇 |
农作物 | 139篇 |
水产渔业 | 159篇 |
畜牧兽医 | 360篇 |
园艺 | 73篇 |
植物保护 | 172篇 |
出版年
2024年 | 30篇 |
2023年 | 93篇 |
2022年 | 152篇 |
2021年 | 161篇 |
2020年 | 177篇 |
2019年 | 170篇 |
2018年 | 137篇 |
2017年 | 198篇 |
2016年 | 253篇 |
2015年 | 201篇 |
2014年 | 222篇 |
2013年 | 225篇 |
2012年 | 285篇 |
2011年 | 259篇 |
2010年 | 225篇 |
2009年 | 215篇 |
2008年 | 165篇 |
2007年 | 179篇 |
2006年 | 127篇 |
2005年 | 104篇 |
2004年 | 104篇 |
2003年 | 77篇 |
2002年 | 80篇 |
2001年 | 55篇 |
2000年 | 40篇 |
1999年 | 57篇 |
1998年 | 36篇 |
1997年 | 32篇 |
1996年 | 38篇 |
1995年 | 49篇 |
1994年 | 25篇 |
1993年 | 36篇 |
1992年 | 54篇 |
1991年 | 42篇 |
1990年 | 33篇 |
1989年 | 32篇 |
1988年 | 24篇 |
1987年 | 11篇 |
1986年 | 7篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有4419条查询结果,搜索用时 31 毫秒
21.
中国耕地非农化现象日益明显。基于社会燃烧理论分析了耕地非农化的驱动原理,建立了耕地非农化影响机制模型,并运用SPSS 19.0软件对分类驱动因素进行了主成分及回归分析。结果表明,人均GDP和固定资产投资所占GDP比重等经济发展变量对耕地非农化水平的正向影响最大;粮食单产、总产等农业技术变量对耕地非农化水平具有最大的逆向影响。最后在模型拟合的基础上提出了相应的对策与建议,旨在为合理有效保护耕地提供参考。 相似文献
22.
《Communications in Soil Science and Plant Analysis》2012,43(19):2330-2339
This study evaluates the effect of soil particle size (SPS) on the measurement of exchangeable sodium (Na) (EXC-Na) by near-infrared reflectance (NIR) spectroscopy. Three hundred thirty-two (n = 332) top soil samples (0–10 cm) were taken from different locations across Uruguay, analyzed by EXC-Na using emission spectrometry, and scanned in reflectance using a NIR spectrophotometer (1100–2500 nm). Partial least squares (PLS) and principal component regression (PCR) models between reference chemical data and NIR data were developed using cross validation (leaving one out). The coefficient of determination in calibration (R2) and the root mean square of the standard error of cross validation (RMSECV) for EXC-Na concentration were 0.44 (RMSECV: 0.12 mg kg–1) for soil with small particle size (SPS-0.053) and 0.77 (RMSECV: 0.09 mg kg–1) for soils with particle sizes greater than 0.212 mm (SPS-0.212), using the NIR region after second derivative as mathematical transformation. The R2 and RMSECV for EXC-Na concentration using PCR were 0.54 (RMSECV: 0.07 mg kg–1) and 0.80 (RMSECV: 0.03 mg kg–1) for SPS-0.053 and SPS-0.212 samples, respectively. 相似文献
23.
24.
25.
In component-based system regression testing, the dependence model of component-based system should be built in order to confirm the part which will be affected by modify. Since high reusability and high complexity, the existing dependence models may not be applicable to component-based systems, a hierarchical dependence model is proposed to describe component-based. Through the forward slicing of modified points in the model, the modified and affected parts can be gotten, then traverse these parts and get affected testing path, thereby regression testing examples can be chosen effectively, the efficiency of regression testing can be improred. 相似文献
26.
Data Mining can distill the connotative, unknown and potential value information or pattern from many data. It is a problem that must be settled during the developing of Decision Support System how to discover knowledge from Data Warehouse. In order to realize the continuous mathematical forecast that will be used in the Marketing Decision Support System for Industrial Enterprise, the authors use the method of regression to discuss how to design the algorithm for Data Mining, how to design the model for Data Mining, and so on. When the algorithm applied to the sales forecast, the result processing to simulation data indicates it can realize the expected effect. 相似文献
27.
Yi Shuping Gai Xuchang Xu Xiangsui 《保鲜与加工》1992,(2):65-70
Based on Group Technology, part families of the norm of working hour are formed according to the similarity among components. With the progressive regerssion, the models of the norm of working hour are built for every part family. A computer aided norm model building program and a computer aided norm of working hour planning system are developed. The system is successfully integrated with CAD/CAPP system. Some examples of the model building and calculation results are illustrated as well. 相似文献
28.
Basing eliminating on the idea that the generator who has the most influence on the power flow of line is mostly in favor of transmission congestion, the model of congestion management with the object of minimizing adjustments of bufions varied with generation outputs is proposed. It can eliminate the congestion effectively by judging the generators who should be adjusted and the amounts of adjustment. The test on IEEE-RTS24 buses system and other practical systems show that the proposed method is effective. 相似文献
29.
WANG Hong -chun 《保鲜与加工》2002,(7):49-52
The kernel function of kernel estimator for regression function is often defined with compact support, the moment of Y is bigger than one. The convergence rate of the improved kernel estimator is discussed under the improved kernel function. The result is also discussed under random censorship. The class of applicable kernels include those having unbounded support and even not integral .The condition of moment of Y is discarded under the improved kernel estimator. The results are wholly the same as usual and generalize the relative results of the paper . 相似文献
30.
In extensive cattle production systems, the composition of grazing areas may significantly influence productivity. In dual-purpose cattle production systems in the lowland tropics, pasture lands with trees, so-called silvopastoral areas, are considered as being important, particularly to facilitate the management of crossbred European native cattle. The aim of the study was to quantify the effects of silvopastoral areas on production at dual-purpose cattle farms in the semi-humid lowlands of central Nicaragua. The relationships between seasonal milk production and herd data, and the proportions of land use types were examined for 74 farms by stepwise regression analysis. 相似文献