首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   313篇
  免费   4篇
  国内免费   10篇
林业   14篇
农学   146篇
基础科学   1篇
  47篇
综合类   73篇
农作物   17篇
水产渔业   1篇
畜牧兽医   17篇
园艺   2篇
植物保护   9篇
  2024年   1篇
  2023年   3篇
  2022年   13篇
  2021年   12篇
  2020年   5篇
  2019年   4篇
  2018年   3篇
  2017年   3篇
  2016年   4篇
  2015年   6篇
  2014年   16篇
  2013年   12篇
  2012年   17篇
  2011年   19篇
  2010年   13篇
  2009年   22篇
  2008年   35篇
  2007年   23篇
  2006年   25篇
  2005年   9篇
  2004年   7篇
  2003年   7篇
  2002年   17篇
  2001年   9篇
  2000年   4篇
  1999年   3篇
  1998年   4篇
  1997年   1篇
  1994年   6篇
  1993年   5篇
  1992年   3篇
  1991年   1篇
  1990年   4篇
  1989年   1篇
  1988年   4篇
  1987年   1篇
  1985年   2篇
  1982年   1篇
  1981年   1篇
  1980年   1篇
排序方式: 共有327条查询结果,搜索用时 15 毫秒
1.
Water resource allocation was defined as an input-output question in this paper, and a preliminary input-output index system was set up. Then GEM (group eigenvalue method)-MAUE (multi-attribute utility theory) model was applied to evaluate relative efficiency of water resource allocation plans. This model determined weights of indicators by GEM, and assessed the allocation schemes by MAUE. Compared with DEA (Data Envelopment Analysis) or ANN (Artificial Neural Networks), the mode was more applicable in some cases where decision-makers had preference for certain indicators  相似文献   
2.
Pentachloronitrobenzene (PCNB) is an organochlorine fungicide that is mainly used in the prevention and control of diseases in crop seedlings. Microbial removal is used as a promising method for in-situ removal of many organic pesticides and pesticide residues. A short-term field experiment (1 year) was conducted to explore the potential role of a PCNB-degrading bacterial isolate, Cupriavidus sp. YNS-85, in the remediation of a PCNB-contaminated soil on which Panax notoginseng was grown. The following three treatments were used:i) control soil amended with wheat bran but without YNS-85, ii) soil with 0.15 kg m-2 of solid bacterial inoculum (A), and iii) soil with 0.30 kg m-2 of solid bacterial inoculum (B). The removal of soil PCNB during the microbial remediation was monitored using gas chromatography. Soil catalase and fluorescein diacetate (FDA) esterase activities were determined using spectrophotometry. In addition, cultivable bacteria, fungi, and actinomycetes were counted by plating serial dilutions, and the microbial biodiversity of the soil was analyzed using BIOLOG. After 1 year of in-situ remediation, the soil PCNB concentrations decreased significantly by 50.3% and 74.2% in treatments A and B, respectively, when compared with the uninoculated control. The soil catalase activity decreased in the presence of the bacterial isolate, the FDA esterase activity decreased in treatment A, but increased in treatment B. No significant changes in plant biomass, diversity of the soil microbial community, or physicochemical properties of the soil were observed between the control and inoculated groups (P<0.05). The results indicate that Cupriavidus sp. YNS-85 is a potential candidate for the remediation of PCNB-contaminated soils under P. notoginseng.  相似文献   
3.
ANSYS has become an effective tool for finite element analysis of masonry structure, but there is few common conclusions for reference. According to the characteristics of ANSYS and the essence of the analysis, some key problems in finite element analysis of masonry structure with ANSYS, such as structural modelling, material constitution, the damage criterion, iterative algorithm, convergence criterion, simulation of prestressing force and so on, are discussed in this paper. Based on the test results of typical masonry structures, the applicability of ANSYS to masonry structural analysis is studied and some suggestions for the application of ANSYS are presented.  相似文献   
4.
A new measurement method for mass property parameters   总被引:1,自引:0,他引:1  
Mass property parameters (mass, center of mass, moment of inertia) are important technology parameters of aircraft. The traditional mass and center of mass measurement uses centroid units, and the moment of inertia measurement torsion units, which can only get results in installing direction. Because of the structural reasons, there is a need to get all high accurate physical parameters in clamping once. To solve this problem, this study merges centroid units and torsion units into one composite unit, installs a table which can tilt and rotation to measure the moment of inertia in different conditions. The moment of inertia and product of inertia relative to three axis are calculated by the method of coordinate transformation. Measurement theory of mass, center of mass and mass moment of inertia are described, the main reason of causing measurement errors is discussed, and the measurement accuracy affected by tilt error is analyzed.  相似文献   
5.
Based on the analysis of chloride ion-induced erosion mechanism of reinforced concrete and the Fick’s second law, a multi-factor model of the chloride ion erosion is established. In this model, the influences of water-cement ratio, humidity, time, temperature, and chloride ion binding capacity of concrete are taken into consideration, and the mathematic solution to the new model is provided by considering the boundary conditions. The new model is verified by analyzing the long-term exposed experiment data. Compared with the traditional model of Fick's second law, the model can indicate the development trend of the structure eroded by chloride and the chloride ion concentration in different depth, and at the same time, it can predicate the chlorine ion concentration on rebar surface in different corrosion periods and the initiation corrosion time of reinforcement.  相似文献   
6.
Indoor thermal comfort can be significantly improved by natural ventilation with reasonable architectural design. In order to compare natural ventilation effect, the distribution of velocity field, temperature field and the PMV in different architecture layout and orientation design were analyzed with house types in Best House Type Competition. It was found that indoor natural ventilation effect was obviously improved by means of altering the layout and orientation, where the maximum velocity varied from 0.24m/s to 0.82m/s. And the temperature decreased 0.9℃ and the value of PMV was more approximate to comfort.  相似文献   
7.
In order to study the rule of drivers’ pupil changing with luminance under road lighting condition,pupil area of 4 subjects under 13 lighting levels of high pressure sodium(HPS), metal halide(MH) and LED are measured, with reaction time test equipment for road lighting and iView X eye tracking system. The results indicate that the relationship between pupil area and background luminance is negative exponential function, pupil will shrink while luminance is increased, the shrink velocity of pupil will decrease while luminance’s increasing, and pupil area will tends to be constant when luminance reach some level. Under the three lighting sources used in the experiment, pupil area will fluctuate while the background luminance is between 0.7 cd/m2and 1.2 cd/m2.  相似文献   
8.
It has been verified that the ICA can isolate sources from multi channel magnetoencephalography (MEG) signals. Based on the route of constrained ICA (cICA), this paper achieves a new solution of MEG inverse problem called functional source separation (FSS) by adding a functional constraint to the cost function of a basic ICA model. Source activity is obtained by applying this method to one MEG signal dataset under a self paced finger tapping task. The result is proved effective by calculating correlation coefficients between the weight vectors of function source separation method and the spatial filter coefficients of SAM method. It is found that finger tapping related functional source was localized in motor cortex of precentral gyrus. At the same time, the temporal and frequency information provided by FSS method could be a basis of exploring cortical control timing mechanisms associated with finger movements and extracting time frequency characteristics of the functional source.  相似文献   
9.
Lighting quality indicators with space sense for urban lighting environment   总被引:1,自引:0,他引:1  
In order to find out a space sense indicator that can present the real appearance of human and natural in urban lighting environment, three common used indicators are studied, which are ratio of vertical illuminance to semi cylindrical illuminance, ratio of vertical illuminance to horizontal illuminance and ratio of average cylindrical illuminance to horizontal illuminance.An on site test is taken at Three Gorges Square Pedestrian Street of Chongqing. The variation law of ratio of vertical illuminance to horizontal illuminance is approximate to ratio of average cylindrical illuminance to horizontal illuminance, which varies with the changing of measure point location and reach maximum at the axial central section of pedestrian street between two streetlamps. The change of ratio of vertical illuminance to semi cylindrical illuminance is small correspondingly and it is more appropriate to be as a lighting quality indicator with space sense for urban illuminance environment.  相似文献   
10.
A novel resonator for accelerometer with sensing and actuating combs was designed and fabricated based on micro electromechanical system (MEMS) process. Driving force and demand voltage of the resonator were analyzed by analytical method and Finite Element Method (FEM). Sensing capacitance on resonance state and Q factor under atmosphere was calculated by these two methods. The micro fabrication process was planned and realized using MEMS (Micro electromechanical System) method. The testing results show the performance of the resonator is high; the natural frequency of the resonator is 54 523.5 Hz, which has the error of 13.6% with the theorical value.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号