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131.
根据适地适树和经济效益的原则,设计了一个国有林场森林资源结构秩序的理想换型,并对该国有林场森林资源结构秩序进行静态和动态的调整,使各树种的时空秩序趋于合理,达到森林资源永续利用的目的。 相似文献
132.
ZHANG Jun-hui HAN Shi-jie SONG Guo-zheng 《林业研究》2005,16(4):303-305
The turbulence statistics parameters (variables) of natural airflow within a large Open Top Chamber (OTC), 4 m in high height and 3 m in diameter, were measured with a three-dimensional ultrasonic anemometer/thermometer at Research Station of Changbai Mountain Forest Ecosystems Jilin Province, China in May 2004, for improving the field application of OTP. Results showed that because of the physical limitation, turbulence within OTC exhibited unique map compared with that of natural environments. There were clear daily pat- terns for most parameters. Turbulence here seemed to be isotropic and closely linked at all directions. Shape of eddies looked like a 'cylinder' which was very similar to the shape of OTC. Continuous airflow was always interpreted by large scale eddies from top of OTC and showed high interactive intermittence at all directions. 相似文献
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134.
Apple bruising, as a mechanical damage, occurs due to impact, compression, vibration or abrasion during handling. However, the symptoms of this damage, browning and softening of the tissue, appear not immediately but after a certain period of time after bruising. For sorting and grading systems, the information about how long the bruise exists in affected fruit can be valuable. VNIR (visible and near-infrared) and SWIR (short wavelength infrared) spectral characteristics of sound and bruised apple tissues were analyzed during a two week period after bruising. Supervised classification methods, including support vector machines, linear logistic regression, neural networks and decision trees, were used and compared to check their effectiveness for distinguishing time after bruising with respect to five varieties of apples. The detection system included hyperspectral cameras equipped with sensors working in the visible and near-infrared (400–1000 nm) and short wavelength infrared (1000–2500 nm) ranges. The results of supervised classification revealed good applicability of hyperspectral imaging in VNIR and SWIR spectral ranges for detecting the number of days after bruising. The linear logistic regression neural networks models were found to be the best classifiers in the majority of models developed. Prediction accuracies higher than 90% were obtained for classification models on spectral data pretreated with the second derivative. 相似文献
135.
采用时序图和自相关图相结合的方法,对大型灌区的日退水量时间序列进行了分析,建立了灌区日退水量时间序列ARIMA模型,并以宁夏青铜峡灌区为例进行了实证研究,取得了较为精确的结果,为灌区退水量的准确预测提供了理论依据。 相似文献
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137.
Effect of historic landscape change on the genetic structure of the bush-cricket Metrioptera roeseli
Stephanie I. J. Holzhauer Klemens Ekschmitt Anna-Christine Sander Jens Dauber Volkmar Wolters 《Landscape Ecology》2006,21(6):891-899
This study investigates the impact of past and present landscape structure on the current genetic structure of the bush-cricket
Metrioptera roeseli (Orthoptera, Tettigoniidae) in a rural landscape in Germany. Assuming that land-use types, such as grassland, arable land
and forest, as well as linear structures, mainly roads, differentially affect the connectivity of the bush-cricket's habitat
and therefore migration and gene flow, we correlated landscape parameters between sampling locations as derived from GIS-maps
with genetic similarities between individual bush-crickets as estimated by RAPD-PCR. Fifty bush-crickets were sampled with
distances between sampling locations varying between 15 m and 2 km. Corresponding landscape configurations were recorded in
8 years between 1945 and 1998. Landscape configuration 50 years ago appeared to have influenced the present genetic structure
of the bush-cricket (R
2 = 0.18). Crossing roads and land use other than grassland along the transect between sampling locations tended to decrease
genetic similarity, whereas grassland and parallel roads tended to increase genetic similarity between bush-crickets. Following
shifts in land use during 1953–1973 the correlation between landscape and present genetic structure decreased gradually. Our
study suggests that it needs time for the landscape to build a visible effect on the genetic structure of the bush-cricket
population, and that this effect cannot be detected if the landscape changes faster than the genetic structure responds to
it. 相似文献
138.
大平顶枣采后生理特性研究 总被引:11,自引:2,他引:11
研究了不同成熟度大平顶枣采后在20、4.5、1.5、0、-1.5℃条件下呼吸强度、品质、脆枣率等变化情况。枣果分别于9月14日和24日两批采摘。结果表明:大平顶枣属非跃变型果实,全红果呼吸强度显著高于半红和初红果。在4.5~-1.5℃的范围内,以1.5℃为界,温度越低,贮藏后期果实维生素C含量和脆果率越低,果皮叶绿素含量下降越快,贮藏30、39d,1.5℃贮藏效果最好,4.5℃适宜10d左右短期贮藏,大平顶枣不适宜在0℃以下贮藏。反映枣果贮藏效果的主要指标是枣果维生素C含量和脆枣率,贮藏过程中鲜枣维生素C含量与脆果率之间呈极显著正相关,脆果率与货架期呼吸强度间呈极显著正相关。 相似文献
139.
140.