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   399篇
  免费   19篇
  国内免费   2篇
林业   21篇
农学   44篇
基础科学   6篇
  111篇
综合类   32篇
农作物   30篇
水产渔业   32篇
畜牧兽医   90篇
园艺   12篇
植物保护   42篇
  2023年   4篇
  2022年   14篇
  2021年   12篇
  2020年   15篇
  2019年   20篇
  2018年   37篇
  2017年   18篇
  2016年   21篇
  2015年   11篇
  2014年   15篇
  2013年   55篇
  2012年   21篇
  2011年   19篇
  2010年   10篇
  2009年   9篇
  2008年   15篇
  2007年   6篇
  2006年   5篇
  2005年   10篇
  2004年   9篇
  2003年   6篇
  2002年   1篇
  2001年   4篇
  2000年   1篇
  1999年   1篇
  1998年   3篇
  1997年   5篇
  1996年   4篇
  1995年   3篇
  1994年   5篇
  1993年   5篇
  1992年   5篇
  1991年   6篇
  1990年   5篇
  1989年   5篇
  1988年   5篇
  1987年   4篇
  1986年   5篇
  1985年   3篇
  1984年   3篇
  1983年   1篇
  1982年   2篇
  1980年   3篇
  1978年   1篇
  1975年   2篇
  1974年   2篇
  1971年   1篇
  1970年   1篇
  1967年   2篇
排序方式: 共有420条查询结果,搜索用时 15 毫秒
101.
As maize is a chilling-sensitive crop, low temperatures during the early stages of development can be injurious to crop growth and development. Prime mechanism behind chilling-induced damage is oxidative stress. This study was undertaken to improve the chilling tolerance in hybrid maize by seed priming with KCl. For priming, seeds of the maize hybrid Hycorn 8288 were soaked in 50, 100 and 150 mg l−1 aerated solution of KCl for 24 h and then re-dried close to original weight. Primed and untreated seeds were sown at 27 °C (optimal temperature) and at 15 °C (chilling stress) under controlled conditions. Seed priming improved the performance of maize under both normal and stress conditions. It was found that the chilling tolerance in maize is well associated with the enhanced capacity of the anti-oxidative system. Priming with KCl significantly improved the chilling tolerance mainly by the activation of antioxidants including catalase, superoxide dismutase and ascorbate peroxidase enzymes. KCl treatments also improved the germination rate and time, root and shoot length, and fresh and dry weights of seedlings compared with control. Soluble sugars and α-amylase activity determined as general metabolic indicators of stress were also improved by seed priming with KCl. Other possible bases of chilling tolerance in maize included maintenance of high tissue water contents, reduced electrolyte leakage and carbohydrate metabolism. Seed treatment with 100 mg l−1 KCl was the best treatment to improve the performance of hybrid maize both under normal and chilling stress conditions.  相似文献   
102.
Drought‐induced damages in crop plants are ranked at top amid all losses instigated by diverse abiotic stresses. Terminal drought (drought at reproductive phase) has emerged as a severe threat to the productivity of wheat crop. Different seed enhancement techniques, genotypes and distribution of crop plants in different spacings have been explored individually to mitigate these losses; however, their interaction has rarely been tested in improving drought resistance in wheat. This study was conducted to evaluate the potential role of different seed enhancement techniques and row spacings in mitigating the adversities of terminal drought in two wheat cultivars during two consecutive growing seasons of 2010–2011 and 2011–2012. Seeds of wheat cultivars Lasani‐2008 (medium statured) and Triple Dwarf‐1 (dwarf height) soaked in water (hydropriming) or CaCl2 (osmopriming) were sown in 20‐, 25‐ and 30‐cm spaced rows; just before heading, the soil moisture was maintained at 100 % field capacity (well watered) or 50 % field capacity (terminal drought) till maturity. Terminal drought significantly reduced the yield and related traits compared with well‐watered crop; however, osmopriming improved the crop performance under terminal drought. Among different row spacings, wheat sown in 20‐cm spaced rows performed better during both years of study. Wheat cultivar Lasani‐2008 performed better than cultivar Triple Dwarf‐1 under both well‐watered and stress conditions. Maximum net returns and benefit–cost ratio were recorded from osmoprimed seeds of cultivar Lasani‐2008 sown in 20‐cm spaced rows under well‐watered condition. Nonetheless, osmoprimed seeds of cultivar Lasani‐2008 sown in 20‐cm spaced rows were better able to produce good yield under terminal drought.  相似文献   
103.
Two new pentacyclic triterpenes named kirmanoic acid (1) and kurramanoic acid (2) have been isolated from the chloroform-soluble portion of the whole plant of Nepeta clarkei Hook. The structures of the two new compounds were assigned on the basis of their 1H and 13C NMR spectra including two-dimensional NMR techniques such as COSY, HMQC, and HMBC experiments. Kirmanoic acid (1) was investigated for analgesic, anti-inflammatory, and CNS depressant activities. Interestingly kirmanoic acid (1) showed strong analgesic activity than standard drug in acetic induced writhing and formalin tests. Similarly kirmanoic acid (1) also showed strong anti-inflammatory activity than its standard drug. The gross behavioral study of kirmanoic acid (1) revealed that it exhibited mild CNS stimulant and muscle relaxant in the mice. Compound 1 showed a slight increase in Locomotor activity and possesses the antidepressant effect.  相似文献   
104.
Toxoplasmosis, an infection caused by Toxoplasma (T.) gondii Apicomplexa protozoan, is widespread in humans and other animal species, having already been reported in many countries and different climates. In Pakistan, no data is available on this aspect among food animals. This study was undertaken to determine the seroprevalence of T. gondii infection in sheep and goats. A total of 200 serum samples from sheep and goats, were collected from urban area of Rahim Yar Khan (Punjab), Pakistan and tested for Toxoplasmosis with a commercial latex agglutination kit (Eiken Chemical Co., Ltd. Japan). The overall seroprevalence of Toxoplasmosis was 19%. Goats had a significantly higher (p < 0.01) prevalence (25.4%) as compared to the sheep (11.2%); and higher (p < 0.01) in the female (24%) than in the males (19%) for both species. In the present study the male (both in sheep and goat) are found less seropositive T. gondii (OR = 0.23; 99% C.I. = 0.01, 1.81) as compared to female sheep and goat. The prevalence was significantly higher (p < 0.01) in adult sheep than younger animals. Among both the sheep and goats the group from 1–1.5 years are highly seropositive (OR = 1.75; 99% C.I. = 0.47, 6.51) as compared to the group less than one year of age followed by the 2–2.5 years age group (OR = 1.63; 99% C.I. = 0.50, 5.74) whereas group with more than 3 years of age least seropositive.  相似文献   
105.
Seventy-five Escherichia coli isolates with at least one targeted virulence gene were recovered from 338 lambs with (n=230) and without (n=108) diarrhoea. The isolates belonged to 36 different serogroups. Shiga toxin-producing E. coli (STEC) was isolated from 9.6% of lambs with and 24.1% of lambs without diarrhoea. Enteropathogenic E. coli (EPEC) was isolated from 6.1% of lambs with and 11.1% of lambs without diarrhoea. Of 26 EPEC isolates, seven were typical (positive for bfpA), and, of 34 stx(1) positive isolates, 25 were subtyped as stx(1c). Five of 29 stx(2) positive isolates were subtyped as stx(2d) and two as stx(2c). Seven of 45 eae positive isolates were subtyped as eae subtype zeta (eaezeta). This appears to be the first report of the isolation of typical EPEC from sheep in India.  相似文献   
106.
In this study growth and yield response of wheat crop to phosphobacterium inoculum was observed under sandy loam conditions. The investigations were carried out at field experiment. The experiment was laid out in Randomized Complete Block Design. The treatments were; 120-0-0 NPK kg/ha−1 (T 1), 120-50-0 kg/ha−1 (T 2), 120-100-0 NPK kg/ha−1 (T 3), T 1 + Phosphobacterium inoculum (T 4), T 2 + Phosphobacterium inoculum (T 5) and T 3 + Phosphobacterium inoculum (T 6).The results showed that bacterial strain (Pseudomonas spp.) was able to effect on yield and its attributes in wheat crop. The crop showed significant positive results. The inoculation significantly stimulates the germination count (m−2), number of tillers and spikes (m−2), 1000 grains weight (g) and grain yield (kg/ha−1). We suggest that application of 120-100-0 kg/ha−1 NPK along with coating of seed with phosphobacterium (Pseudomonas spp.) all the way through inoculation is a better practice to reduce the exploit of phosphatic fertilizers which are much costly.  相似文献   
107.
A range of formulations of deltamethrin were prepared, some containing an ultraviolet (UV) absorber compound or a combination of the UV absorber and an oil, and applied to blue cotton tsetse fly target samples which were then exposed to the effect of simulated sunlight and water in the laboratory. The residue of insecticide remaining on the targets and the activity of the latter against tsetse flies was determined. Formulations containing the UV absorber and coconut oil or silicone oil remained the most effective against tsetse flies. A coconut oil formulation of the insecticide was selected for field evaluation in comparison with a commercial deltamethrin formulation, Glossinex 200′ S.C., which contains 10% UV absorber. Target samples treated with these formulations were exposed to natural tsetse fly habitat in Ghana for a period of five months and evaluated for deltamethrin residues and activity against four species of tsetse fly. After five months, 4–13 times more deltamethrin remained on the targets treated with the coconut oil formulation than on those treated with ‘Glossinex’, and consequently the former were more active against tsetse flies than the latter. Target samples sequentially dipped in the coconut oil formulation resulted in uniform insecticide concentration on the targets, whereas those dipped in ‘Glossinex’ contained gradually decreasing deltamethrin concentrations.  相似文献   
108.
109.
The levels of N-acetyl-beta-D-glucosaminidase (NAGase) were measured in the endometrial epithelial tissue of the bovine uterus during the oestrous cycle and during pregnancy. NAGase levels were significantly (P<0.001) higher in the epithelial tissue of the cow's uterus during the luteal phase of the cycle and during pregnancy than during the non-luteal phase. There were significantly (P<0.001) higher mean NAGase values in the epithelial than the subepithelial layers of the uterus in the two cycle phases and in pregnancy. Leucocyte numbers were significantly (P<0.05 and P<0.001) higher in the cows' uteri during the non-luteal phase than during the luteal phase and pregnancy, respectively. It is concluded that the endometrial epithelial layer is significantly active in terms of NAGase release and that this may be related to increased progesterone concentrations. In addition, the epithelial tissue (not leucocytes) appears to be the main contributor to the total NAGase activity in uterine tissue.  相似文献   
110.
The impact of increased shading stress on agronomic traits, photosynthetic performance and antioxidants activities in leaves of two soybeans cultivars(D16 and E93) was studied. Soybean seedlings were grown in pots and exposed to no shade(S0), slight shade(S1), moderate shade(S2), and heavy shade(S3). Our findings showed that under the S3 in both cultivars, leaf fresh weight(LFW), specific leaf area(SLA) and leaf thickness decreased significantly, accompanied by a reduction in photochemical parameters including the maximum quantum yield(F_v/F_m) and electron transport rate(ETR). Furthermore, compared to S0, S1 significantly increased the ETR, sucrose content and the activity of catalase(CAT) in both D16 and E93 cultivars while S2 and S3 decreased the activity. However, under all treatments of shading stress, the antioxidant activities of superoxide dismutase(SOD) and peroxidase(POD) were lowered in both cultivars. Such morphological and physiological plasticity to adapt S1 compensates for the decrease in biomass and leads to seed weight compared to that obtained with an amount of normal light. Through configuring the space in the intercropping systems, S1 could be helpful for optimum growth and yield. Redesigning photosynthesis through S1 for the intercropping systems could be a smart approach.  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