全文获取类型
收费全文 | 2619篇 |
免费 | 71篇 |
国内免费 | 258篇 |
专业分类
林业 | 223篇 |
农学 | 398篇 |
基础科学 | 78篇 |
259篇 | |
综合类 | 1043篇 |
农作物 | 423篇 |
畜牧兽医 | 135篇 |
园艺 | 343篇 |
植物保护 | 46篇 |
出版年
2024年 | 6篇 |
2023年 | 26篇 |
2022年 | 38篇 |
2021年 | 42篇 |
2020年 | 49篇 |
2019年 | 36篇 |
2018年 | 52篇 |
2017年 | 61篇 |
2016年 | 83篇 |
2015年 | 84篇 |
2014年 | 117篇 |
2013年 | 163篇 |
2012年 | 177篇 |
2011年 | 240篇 |
2010年 | 179篇 |
2009年 | 220篇 |
2008年 | 224篇 |
2007年 | 235篇 |
2006年 | 148篇 |
2005年 | 140篇 |
2004年 | 85篇 |
2003年 | 67篇 |
2002年 | 43篇 |
2001年 | 47篇 |
2000年 | 28篇 |
1999年 | 42篇 |
1998年 | 41篇 |
1997年 | 30篇 |
1996年 | 36篇 |
1995年 | 38篇 |
1994年 | 28篇 |
1993年 | 23篇 |
1992年 | 22篇 |
1991年 | 25篇 |
1990年 | 26篇 |
1989年 | 26篇 |
1988年 | 10篇 |
1987年 | 7篇 |
1986年 | 2篇 |
1984年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有2948条查询结果,搜索用时 15 毫秒
941.
[目的]运用秋季灌木叶片色彩属性变化规律,从定性、定量的视角构建哈尔滨秋季植物景观的色彩,总结地域性植物色彩设计的科学性。[方法]以能够兼容CAD和Photoshop绘图软件的NCS色卡,在温侯法界定的哈尔滨秋季时段,随秋季时序采集8种灌木的NCS色彩值,确定其色彩属性与变化规律。通过采集哈尔滨秋季气温日温的最低、最高值,分析其叶片NCS色彩值与气候温度的日温差、最低最高温度变化的规律。[结果]8种灌木NCS叶色值总体范围为NCS S 5540-G40Y~NCS S 1580-Y90R,分布于24个标准颜色中。最低气温9℃,日温差11℃,叶片开始变色3种;最低气温9℃,日温差15℃,叶片开始变色3种;最低气温7℃,日温差10℃,叶片开始变色1种;霜后,最低气温5℃,日温差13℃,叶片开始变色1种。最低气温7℃持续2d,连续日温差8~13℃,进入变色盛期7种;最低气温3℃,日温差13℃,进入变色盛期1种。[结论]利用秋季灌木叶片色彩属性变化规律构建哈尔滨秋季植物景观色彩是提升秋季季相色彩设计质量的重要途径,具有一定的科学性。 相似文献
942.
《Plant Production Science》2013,16(3):285-292
AbstractEffects of nitrogen (N) deficiency on photosynthetic gas exchange and photosystem II (PSII) photochemistry of flag leaves during grain-filling stage were investigated in six rice cultivars, Kasalath (a conventional indica), IR36 (an improved indica), Shirobeniya (a conventional japonica), Nipponbare (an improved japonica), Akenohoshi (an improved japonica-indica intermediate type) and BSI429 (an improved tropical japonica, a new plant type line) grown hydroponically in N-sufficient (NS) and N-deficient (ND) solution. From 3 to 24 days after heading (DAH), net photosynthetic rate (Pn), maximum quantum yield of photosystem II (PSII) (Fv/Fm), quantum yield of PSII electron transport ( Φpsii), and contents of chlorophyll (Chl) and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) in the flag leaves decreased, particularly under the ND condition in all six cultivars. A substantial difference was observed among the ND plants for the sustainability index (SI, the ratio of the value at 24 DAH to that at 3 DAH) of Pn, Fv/Fm, Φpsii, Chl content and Rubisco content; SIs of those parameters of Akenohoshi, BSI429, Nipponbare and Shirobeniya were higher than those of IR36 and Kasalath. The SI of Pn showed significant positive correlations with those of Fv/Fm, Φpsii, and the contents of Chl and Rubisco under the ND condition. It was concluded that the sustainability of photosynthesis in the flag leaves was mainly due to those of PSII photochemistry and electron transport, which was associated with the maintenance of Chl and Rubisco under the ND condition. 相似文献
943.
《Plant Production Science》2013,16(3):269-278
AbstractA greenhouse experiment was conducted to study the adaptive mechanism of cotton and peanut under water stress conditions. Five cultivars of cotton and six cultivars of peanut were grown in pots under two water levels; the control and water stress condition, where irrigation water equal to 100% and 50% of the daily transpiration, respectively, was daily applied. Peanut showed a greater increase than cotton in leaf temperature (Tl) and non-photochemical quenching (NPQ) and a greater decrease in water content per unit leaf area (WCLA), chlorophyll content and maximum quantum yield of photosystem II (PSII) (Fv/Fm) in the water stress condition. On the other hand, the water stress lowered the transpiration rate, actual quantum yield of PSII (ΔF/F’m) and leaf area (LA) more in cotton than in peanut. Cotton showed greater reduction in LA along with little reduction in the root dry weight (RDW) leading to high WCLA, while peanut showed increased RDW with little reduction in LA under the water stress condition. It was concluded that photodamage and down regulation in PSII were induced by water stress, coinciding with increases in leaf temperature regulated mainly by transpiration. Peanut showed more severe photodamage in PSII than cotton under the water stress condition. 相似文献
944.
《Plant Production Science》2013,16(3):255-260
AbstractAlfalfa suppresses mugwort growth in the field. In the present study, the allelopathic effect of alfalfa on mugwort was examined using the above-ground (AGAB) and under-ground alfalfa biomasses (UGAB), and their water extracts. The sprouting of mugwort rhizomes or seed germination, growth of seedlings and leaf color changes in mugwort seedlings were evaluated in pot experiments. AGAB mixed into soil highly inhibited sprouting of mugwort rhizome fragments and growth of seedlings. The inhibitory effect was increased, and gradual leaf discoloration (yellowing) was observed in response to a higher dose of AGAB. However, UGAB affected neither sprouting of mugwort rhizome fragments nor growth of seedlings. The growth of mugwort seedlings was not significantly affected by water extracts of either AGAB or UGAB applied after emergence. The seed germination and seedling growth were significantly reduced by water extracts of AGAB and UGAB in the petri dishes experiments. These results indicated that the allelopathic effect of alfalfa along with the competitive ability and harvesting regime may play an important role in suppressing mugwort growth. 相似文献
945.
《Plant Production Science》2013,16(4):400-411
AbstractNon-destructive monitoring and diagnosis of plant nitrogen (N) concentration are of significant importance for precise N management and productivity forecasting in field crops. The present study was conducted to identify the common spectra wavebands and canopy reflectance spectral parameters for indicating leaf nitrogen concentration (LNC, mg N g-1 DW) and to determine quantitative relationships of LNC to canopy reflectance spectra in both rice (Oryza sativa L.) and wheat (Triticum aestivum L.). Ground-based canopy spectral reflectance and LNC were measured with seven field experiments consisting of seven different wheat cultivars and five different rice cultivars and varied N fertilization levels across three growing seasons for wheat and four growing seasons for rice. All possible ratio vegetation indices (RVI), difference vegetation indices (DVI), and normalized difference vegetation indices (NDVI) of key wavebands from the MSR16 radiometer were calculated. The results showed that LNC of wheat and rice increased with increasing N fertilization rates. Canopy reflectance, however, was a more complicated relationship under different N application rates. In the near infrared portion of the spectrum (760?1220 nm), canopy spectral reflectance increased with increasing N supply, whereas in the visible region (460?710 nm), canopy reflectance decreased with increasing N supply. For both rice and wheat, LNC was best estimated at 610, 660 and 680 nm. Among all possible RVI, DVI and NDVI of key bands from the MSR16 radiometer, NDVI(1220, 610) and RVI(1220, 610) were most highly correlated to LNC in both wheat and rice. In addition, the correlations of NDVI(1220, 610) and RVI(1220, 610) to LNC were found to be higher than those of individual wavebands at 610, 660 and 680 nm in both wheat and rice. Thus LNC in both wheat and rice could be indicated with common wavebands and vegetation indices, but separate regression equations are necessary for precisely describing the dynamic change patterns of LNC in wheat and rice. When independent data were fit to the derived equations, the root mean square error (RMSE) values for the predicted LNC with NDVI(1220, 610) and RVI(1220, 610) relative to the observed values were 10.50% and 10.52% in wheat, and 13.04% and 12.61% in rice, respectively, indicating a good fit. These results should improve the knowledge on non-destructive monitoring of leaf N status in cereal crops. 相似文献
946.
《Plant Production Science》2013,16(1):68-79
AbstractTo Elucidate The Genetic Mechanisms Underlying C3―C4 intermediate Photosynthesis, We investigated The Structural and Photosynthetic Characteristics of Leaves of Reciprocal Hybrids Between The C3―C4 intermediate Species Moricandia Arvensis (L.) Dc. (Mama) and The C3 Species Brassica Oleracea L. (Cabbage; Cc), Which Differ in Genome Constitution. Moricandia Arvensis Bundle Sheath (Bs) Cells included Many Centripetally Located Chloroplasts and Mitochondria, Whereas Those of Cabbage Had Few Organelles. Hybrid Leaves Were Structurally intermediate Between Those of The Parents and Showed Stronger intermediate C3―C4 Features As The Proportion of The Ma Genome increased. The P-Protein of Glycine Decarboxylase (Gdc) Was Confined Mainly To Bs Mitochondria in M. Arvensis, But Accumulated More in The Mesophyll (M) of Cabbage. in The Hybrids, The Accumulation of Gdc in Bs Cells increased With An increasing Ma:C Ratio. Hybrids Exhibited Gradients in Structural and Biochemical Features, Even in Reciprocal Crosses. The Co2 Compensation Point of Reciprocal Hybrids With High Ma:C Ratios Was Lower Than That of Cabbage But Higher Than That of M. Arvensis. Thus, The Structural and Biochemical Features in Hybrid Leaves Reduced Photorespiration. Moricandia Arvensis Had A Higher Photosynthetic Rate Than Cabbage, But The Photosynthetic Rates of Hybrids Were intermediate Between Those of The Parents Or Comparable To That of M. Arvensis. Our Results Demonstrate That The C3―C4 intermediate Characteristics Are inherited Based On The Ratio of The Parent Genomes, and That There Is No Evidence of Cytoplasmic inheritance in These Characteristics. 相似文献
947.
《Plant Production Science》2013,16(2):165-171
ArticleThe supernodulating soybean cultivar Sakukei 4 was previously characterized by its superior ability to maintain a high leaf nitrogen (N) content and high photosynthetic rate. Despite these desirable traits, the growth performance of Sakukei 4 was inferior to that of its normally nodulating parental cultivar, Enrei. The physiological basis for the unique growth characteristics of Sakukei 4 remains unclear. The objective of the present study was to characterize in further detail thevegetative growth of Sakukei 4, particularly during the period before pod expansion. In the first experiment, the growth of Sakukei 4 was compared with that of its parental cultivar Enrei under various rates of N fertilizer. The dry weight of tops, roots and nodules of the plants grown at lower rates of N application was greater in Enrei than in Sakukei 4, but it was vice versa at higher rates of N application. The number and weight of nodules were far greater in Sakukei 4 than in Enrei at any rate of N application. These genotypic differences were significant on 39 days after sowing (DAS) and became greater at the flowering stage. In the second experiment, therefore, more detailed growth analysis was made during an earlier growth stage (DAS 31-46). During this period, relative growth rate (RGR), net assimilation rate (NAR) and leaf area ratio (LAR) were lower in Sakukei 4 than in Enrei and the related non-nodulating line En1282, whereas the leaf photosynthetic rate was higher in Sakukei 4 at all leaf positions. The dry-matter partitioning to each plant part excluding nodules was similar in all three genotypes. The rate of leaf expansion in Sakukei 4 during this period was significantly slower than that in the other genotypes. These results suggest that the inferior growth of Sakukei 4 prior to flowering is probably due to excessive dry-matter partitioning to nodules and depressed capability of leaf expansion and root growth, which might limit dry-matter production of the whole plant during pre-flowering stage. 相似文献
948.
Remote Assessment of Wheat Canopies under Various Cultivation Conditions Using Polarized Reflectance
《Plant Production Science》2013,16(3):312-322
AbstractThe polarization of light reflected from crop canopies gives information on the canopy structure, such as the distribution of leaf inclinations. In order to verify those findings and to put the technique to practical use, we conducted two experiments in wheat fields. In the first experiment, the reflectance and polarized reflectance at 660 nm in the canopies of wheat plants, sown in both narrow and wide rows, and at two levels of topdressing, were measured periodically with a spectropolarimeter. We also probed the leaf orientation geometry of the plants using a 3-D digitizer and a plant canopy analyzer (LAI-2000). In the second experiment, we observed the polarization of light reflected from wheat planted in plots fertilized with basal dressing, and topdressing at the jointing and booting stages. Polarization showed a seasonal change with an upward convex clearly indicating the heading time. This pattern was not found by conventional band reflectance. Using polarization, it was possible to detect the differences in row width and fertilization conditions during the booting stage. The mean leaf inclination angle (MLI) detected with the 3-D digitizer and the mean tip angle (MTA) detected with the LAI-2000 were relatively closely correlated with the polarization than the reflectance at 660 nm and normalized difference vegetation index (NDVI) that was derived from the reflectance at 660 nm and 830 nm. Topdressing at the jointing stage was well detected by polarization obtained at the heading stage. Polarization measurements are useful in practical terms for remote detection of changes in stand geometry induced by cultivation management such as topdressing. 相似文献
949.
J.E. Danckwerts A.J. Aucamp L.P. Du Toit 《African Journal of Range and Forage Science》2013,30(3):9-14
Abstract Marked populations of Themeda triandra tillers were sequentially sampled at fortnightly intervals under normal conditions and without moisture stress respectively, covering a period from tiller initiation through to senescence after flowering. Parameters recorded were height of shoot apex, tiller mass, leaf area, leaf number, secondary tiller development and premature tiller mortality. Tillers of irrigated plants had a significantly higher mass, more elevated shoot apices, and produced a greater total number of leaves than those of non‐irrigated plants. Fewer unstressed tillers senesced prematurely than those experiencing moisture stress. 相似文献
950.
Bacteria of the genus Serratia are often associated with insects, often carry distinctive pigments and can be readily isolated onto diagnostic selective media. Bacterial marking of parasitoids has been used in studies to determine rate of oviposition and host acceptance, and it provides a rapid indication of ovipositor penetration. The technique has been applied to parasitoid-weevil and parasitoid-lepidoptera interactions. Bacterial marking has the potential to be used in parasitoid dispersal studies and its use in IPM is discussed. 相似文献