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   1128篇
  免费   68篇
  国内免费   9篇
林业   70篇
农学   76篇
基础科学   27篇
  425篇
综合类   107篇
农作物   106篇
水产渔业   64篇
畜牧兽医   198篇
园艺   28篇
植物保护   104篇
  2023年   19篇
  2022年   54篇
  2021年   74篇
  2020年   75篇
  2019年   93篇
  2018年   117篇
  2017年   107篇
  2016年   82篇
  2015年   38篇
  2014年   45篇
  2013年   135篇
  2012年   58篇
  2011年   74篇
  2010年   41篇
  2009年   25篇
  2008年   38篇
  2007年   26篇
  2006年   26篇
  2005年   11篇
  2004年   9篇
  2003年   8篇
  2002年   6篇
  2000年   4篇
  1999年   1篇
  1998年   5篇
  1997年   4篇
  1996年   5篇
  1994年   3篇
  1993年   3篇
  1992年   1篇
  1991年   3篇
  1990年   2篇
  1989年   2篇
  1988年   1篇
  1986年   1篇
  1985年   1篇
  1983年   2篇
  1982年   1篇
  1981年   1篇
  1978年   1篇
  1977年   1篇
  1976年   2篇
排序方式: 共有1205条查询结果,搜索用时 15 毫秒
231.
Bio-based CaCO3 powder was synthesized via size reduction method from waste eggshells. The XRD analysis revealed that eggshell powder consists of CaCO3 in calcite form. The inclusion level of CaCO3 contents were varied of 5, 10, 15, 20 and 25 wt.% of prepared CaCO3-polyester film. Effects of different proportions of prepared chicken eggshell and commercial CaCO3 filler on the polyester resin composites films were compared by means of mechanical and physical test. It was found that the addition of CaCO3 filler to the polyester films leads to improve the mechanical properties. The findings revealed that the best and optimum CaCO3 filler content was 10 wt.% and among the prepared polyester films, eggshell CaCO3-polyester films showed the best performance. The mechanical properties of CaCO3-polyester films were measured in terms of tensile strength, elongation-at-break, tensile modulus, flexural strength and impact strength. For eggshell CaCO3- polyester films, the maximum values of the aforementioned mechanical properties were 52.70 MPa, 4.63 %, 1868.70 MPa, 101.20 MPa and 8.40 kJ/m2, respectively, whereas for commercial CaCO3-polyester films those values were 48.12 MPa, 4.50 %, 1790.30 MPa, 97.50 MPa and 8.21 kJ/m2, respectively. Further, water absorption of the composite films as a function of time had also been investigated at 10 wt.% filler content.  相似文献   
232.
Journal of Crop Science and Biotechnology - Understanding genetic architecture of a crop germplasm is necessary for designing a successful breeding program. Herein, we evaluated a large collection...  相似文献   
233.

Field experiments were conducted on wheat during 2017–2018 and 2018–2019 under rainfed conditions. The statistical significance between treatment means was determined at 5% significance level. Data were recorded on weed density, protein, fat and ash contents of wheat grains. Weed density in shallow tillage was highest (20.67?m?2) while it was lowest (14.23?m?2) in deep tillage. In weed control factor, weed density was highest in weedy check (33.10?m?2), followed by parthenium aqueous extract (21.50?m?2), and lowest (6.79?m?2) in plots treated with Affinity (isoproturon?+?carfentrazone). Results showed that the highest crude protein content (10.88%) was recorded in deep tillage, while lowest (10.45%) in shallow tillage, indicating that tillage depths have an impact on wheat grains protein content. For weed control factor, the crude protein content was highest (11.98%) in Affinity treated plots, followed by herbicides, Buctril super (bromoxynil?+?MCPA) (11.44%) and Puma super (fenoxaprop-p-ethyl) (11.12%). Hence, the control measures also affected crude protein content of wheat grains, which is also obvious from the weedy check where wheat grains crude protein content was lowest (9.73%). The two years combined data analysis also showed the highest crude fat content (1.75%) in deep tillage treatments followed by normal tillage (1.67%) and lowest fat content (1.53%) in shallow tillage. For ash content, the highest content (3.03%) was with Affinity herbicide treatments, followed by Buctril super (2.74%) and Puma super (2.48%) herbicides. In conclusion, both the tillage and herbicides indicated positive effects on the nutritive status of wheat grains.

  相似文献   
234.

Salinity is a crucial problem which has affected crop productivity globally. Ascorbic acid is considered helpful against abiotic stresses due to its powerful antioxidant potential. In the pot experiment, salinity stress (0, 35, 70, and 105?mM) was applied to sweet peppers in split doses after 20 days of transplantation. To mitigate the adverse effects of salinity, ascorbic acid (0, 0.40, 0.80, and 1.20?mM) was applied as foliar spray after a 6-day interval during vegetative growth. Sweet pepper plants sprayed with distilled water (control) recorded maximum plant height (cm), leaf area (cm2), number of branches, stem diameter (mm), number of fruit plant?1, fruit diameter (cm), yield plant?1 (g), and chlorophyll content (mg 100?g?1), while the maximum polyphenol oxidase (PPO) activity (unit mg protein?1 min?1) and ascorbate peroxidase (APX) activity (unit mg protein?1 min?1) were recorded in plants treated with 70?mM NaCl application. Salinity stress beyond 70?mM significantly reduced all the studied parameters. An ascorbic acid concentration of 1.20?mM significantly mitigated the negative effects of salt stress and recorded maximum plant height (cm), number of leaves plant?1, leaf area (cm2), number of branches plant?1, stem diameter (mm), number of fruit plant?1, fruit diameter (cm), yield plant?1 (g), chlorophyll content (mg 100?g?1), PPO activity (unit mg protein?1 min?1), and APX activity (unit mg protein?1 min?1). Hence, a 1.20?mM concentration of foliar ascorbic acid could be used in saline conditions up to 70?mM of sodium chloride (NaCl) for better growth, productivity, and enzymatic activity of sweet peppers.

  相似文献   
235.

Wheat (Triticum aestivum L.) is a staple food in many countries and is regarded as a vital source of nutrition. Drought is one the most prevalent limitations to wheat growth and development. Herein a two year study was conducted using 25 diverse wheat genotypes obtained from the gene pool of various research institutes of Pakistan to characterize their drought tolerance using various physiological indices like relative water content (RWC), relative dry weight (RDW), water saturation deficit (WSD), relative water loss (RWL), flag leaf area (LA), chlorophyll content index (CC) and their association with the grain yield (GY). Analysis of variance (ANOVA) indicated the presence of significant amount of differences and genetic diversity among genotypes under study. Correlation analysis exposed positive association of CC and LA with GY. However, RWC was shown to have a highly significant and negative association with WSD and RWL. Principal component analysis (PCA) showed that out of the 7 PCs only 2 were significant having eigenvalues >?1; cumulatively accounting for 88.70% and 73.03% of the total variation under control and drought stress conditions, respectively. Strikingly the results of the PCA biplots and cluster heat map exposed G1 (Barani-17), G2 (Dharabi-11), G3 (Ehsan-16), G4 (Chakwal-50), G17 (Ujala-2016) and G23 (Kohistan-97) as potential drought tolerant genotypes. Selection of the positively associated indices would be fruitful and the tolerant genotypes having drought tolerance potential could be utilized in future wheat breeding programs to develop high yielding and drought tolerant genotypes.

  相似文献   
236.
Precision Agriculture - Recently, agriculture has gained much attention regarding automation by artificial intelligence techniques and robotic systems. Particularly, with the advancements in...  相似文献   
237.
Precision Agriculture - This study evaluated the agronomic and economic prospects of Site-Specific Seeding (SSS) for consumption and seed potato production based on Management Zone (MZ) maps...  相似文献   
238.
Precision Agriculture - A correction to this paper has been published: https://doi.org/10.1007/s11119-021-09824-9  相似文献   
239.
Understanding the mechanism of soil organic carbon(SOC) sequestration is of paramount importance in sustaining crop productivity and mitigating climate change. Long-term trials were employed to investigate the responses of total SOC and its pools, i.e., mineral-associated OC(MOC), particulate OC(POC, containing Light-POC and Heavy-POC), to fertilization regimes at Yangling(25-year), Tianshui(35-year) and Pingliang(37-year) under a rain-fed cropping system in the Loess Plateau. The fertilization regimes in each trial included three treatments, i.e., control(no nutrient input, CK), chemical fertilizers(CF), and organic manure plus chemical fertilizers(MCF). Relative to the CK, long-term fertilization appreciably increased SOC storage by 134, 89 and 129 kg ha~(–1) yr~(–1) under CF, and 418, 153 and 384 kg ha~(–1) yr~(–1) under MCF in plough layer soils(0–20 cm), respectively, at the Yangling, Tianshui and Pingliang sites. The MOC pools accounted for 72, 67 and 64% of the total SOC at the above three sites with sequestration rates of 76, 57 and 83 kg ha~(–1) yr~(–1) under CF and 238, 118 and 156 kg ha~(–1) yr~(–1) under MCF, respectively. Moreover, the MOC pool displayed a saturation behavior under MCF conditions. The POC accordingly constituted 27, 33 and 36% of SOC, of which Light-POC accounted for 11, 17 and 22% and Heavy-POC for 17, 16 and 15% of SOC, respectively. The sequestration rates of POC were 58, 32 and 46 kg ha~(–1) yr~(–1) under CF, and 181, 90 and 228 kg ha~(–1) yr~(–1) under MCF at the three respective sites, in which Light-POC explained 59, 81 and 72% of POC under CF, and 60, 40 and 69% of POC under MCF, with Heavy-POC accounting for the balance. Compared with CK, the application of CF alone did not affect the proportions of MOC or total POC to SOC, whereas MCF application markedly reduced the proportion of MOC and increased the POC ratio, mainly in the Light-POC pool. The distribution of SOC among different pools was closely related to the distribution and stability of aggregates. The present study confirmed that organic manure amendment not only sequestered more SOC but also significantly altered the composition of SOC, thus improving SOC quality, which is possibly related to the SOC saturation level.  相似文献   
240.
We investigated the role of gibberellins-producing endophyte Penicillium janthinellum LK5 associated with Solanum lycopersicum (host), abscisic acid (ABA)-deficient tomato mutant Sitiens and its wild-type Rheinlands Ruhm (Rhe) plants under cadmium (Cd) stress. A 100-μM Cd application to host, Sitiens and Rhe reduced the shoot growth, chlorophyll content and stomatal conductance. However, these parameters were significantly (P?<?0.0011) higher (1.0- to 2.6-folds) in host, Sitiens and Rhe under endophytic association than in non-endophyte infected plants (control) under Cd stress. Furthermore, endophytic association minimized the Cd-induced membrane injury and oxidative stress to host, Sitiens and Rhe plants by reducing electrolytes and lipid peroxidation while increasing the content of reduced glutathione and catalase activities as compared to non-endophyte-infected plants. Stress-responsive ABA content significantly increased (~2-folds) in Sitiens and Rhe under endophyte association, while in host plants it was decreased under Cd stress. Salicylic acid content was ~?1.7-fold higher in host, Sitiens and Rhe plants under Cd stress and endophyte association than in the control. Besides gibberellins production, the endophyte has the potential to solubilize phosphates (12.73?±?0.24 mg/l) since higher P was observed in the roots of Sitiens, Rhe and host plants. Similarly, nutrients like sulfur and calcium were more efficiently assimilated in roots of endophyte-associated plants than control under Cd stress. Conversely, Cd accumulation was significantly decreased (P?<?0.001) in the roots of endophyte-inoculated host, Sitiens and Rhe than control. In conclusion, endophyte symbiosis can counteract heavy metal stress which can exert negative effects on plant growth.  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