全文获取类型
收费全文 | 932篇 |
免费 | 55篇 |
专业分类
林业 | 126篇 |
农学 | 86篇 |
基础科学 | 18篇 |
272篇 | |
综合类 | 44篇 |
农作物 | 64篇 |
水产渔业 | 49篇 |
畜牧兽医 | 230篇 |
园艺 | 15篇 |
植物保护 | 83篇 |
出版年
2023年 | 9篇 |
2022年 | 14篇 |
2021年 | 21篇 |
2020年 | 21篇 |
2019年 | 20篇 |
2018年 | 51篇 |
2017年 | 50篇 |
2016年 | 39篇 |
2015年 | 33篇 |
2014年 | 40篇 |
2013年 | 72篇 |
2012年 | 58篇 |
2011年 | 69篇 |
2010年 | 46篇 |
2009年 | 31篇 |
2008年 | 45篇 |
2007年 | 54篇 |
2006年 | 36篇 |
2005年 | 40篇 |
2004年 | 34篇 |
2003年 | 36篇 |
2002年 | 24篇 |
2001年 | 17篇 |
2000年 | 18篇 |
1999年 | 13篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 1篇 |
1995年 | 8篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 1篇 |
1986年 | 7篇 |
1985年 | 3篇 |
1984年 | 8篇 |
1983年 | 2篇 |
1982年 | 9篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 5篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1969年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有987条查询结果,搜索用时 0 毫秒
131.
Marina Hidalgo Isabel Prieto Hikmate Abriouel Ana Belén Villarejo Manuel Ramírez-Sánchez Antonio Cobo Nabil Benomar Antonio Gálvez Magdalena Martínez-Cañamero 《Plant foods for human nutrition (Dordrecht, Netherlands)》2018,73(1):1-6
Fat type in diet is responsible for specific changes in gut microbiota (GM). Extra virgin olive oil (EVOO) has been shown to be beneficial for blood pressure and to produce effects on GM. To analyze the cause-effect relationship between intestinal microbial changes and blood pressure, we studied the effect of EVOO on fecal microbiota and systolic blood pressure (SBP) levels in spontaneously hypertensive rats (SHR). SHR were fed either an enriched EVOO diet or a standard diet for a period of 12 weeks. At the end of the experimental period, the microbial profiles in the feces were studied in both groups by using PCR-denaturing gradient gel electrophoresis. Real-time PCR was used to quantify the selected bacterial groups. The results demonstrated significant differences when using Lactobacillus (p<0.05), clostridia XIV (p<0.01) and universal (p<0.05) primers. A significant (r=?0.475; p=0.04) inverse correlation between the abundance of clostridia XIV and SBP, which depends on the type of diet, was also observed. Finally, the results suggested an increase in the microbial diversity of the feces of the animals fed the EVOO diet. These results strongly connect the pattern of GM in SHR fed a diet enriched with EVOO to the lower levels of SBP observed in these animals at the end of the feeding period. 相似文献
132.
133.
Humberto González-Rodríguez Jorge Isaac Sarquís-Ramírez Israel Cantú-Silva Roque Gonzalo Ramírez-Lozano Juan Manuel López-Hernández 《Arid Land Research and Management》2016,30(4):375-388
Seasonal xylem water potentials (Ψ, MPa) and their relationship to soil water content and evaporative demand components were studied in the shrub species Acacia amentacea, Celtis ehrenbergiana, Forestiera angustifolia, and Parkinsonia texana var. macra. Predawn (Ψpd) and midday (Ψmd) water potentials were estimated at 15 days intervals, between January 15 and October 30, 2009 using a Scholander pressure bomb at 06:00 h (predawn) and 14:00 h (midday), respectively. During the humid period, Ψpd ranged from ?0.30 MPa (C. ehrenbergiana), to ?0.90 MPa (P. texana). In contrast, over the driest period, Ψpd varied between ?2.18 (P. texana) and ?3.94 MPa (F. angustifolia). At midday, P. texana and F. angustifolia showed the highest (?1.14 MPa) and lowest (?3.38 MPa) Ψ values, respectively. Average soil water content accounted for 35 to 70% of the variation in predawn Ψ. Furthermore, both Ψ reflected the environmental conditions, as indicated by typical correlations observed. The studied shrub species exhibited what seem to be different strategies to avoid damage caused by drought. Thus, P. texana behaved rather as an isohydric plant able to deal well with severe, but short periods of drought. Under exceptionally dry environmental conditions, Ψpd undercut Ψmd values. Similar observations have been made by researchers studying plants in dry ecosystems. All studied native species are recommended for reforestation of the Tamaulipan shrublands, although C. ehrenbergiana and F. angustifolia seem to have limited tolerances for extreme water stress. 相似文献
134.
135.
Ram Swaroop Verma Rajendra Chandra PadaliaVinod Arya Amit Chauhan 《Industrial Crops and Products》2012,36(1):343-348
Murraya koenigii (L.) Spreng. (Rutaceae) is characterized by a large chemical intraspecific variability among the land races. This fact makes it difficult to detect real changes occurring in their essential oil composition during annual cycle. Based on this, variations of essential oil yield and composition in two chemotypes (‘A’ and ‘B’) of M. koenigii were assessed in spring, summer, rainy, autumn and winter seasons under foot hill conditions of northern India. The essential oil yield ranged from 0.15% to 0.18% in chemotype ‘A’, while it varied from 0.12% to 0.14% in chemotype ‘B’. Essential oils of both chemotypes from different seasons were analysed by gas chromatography (GC-FID) and gas chromatography-mass spectrometry (GC-MS). A total of fifty-eight constituents representing 93.7-98.8% of chemotype ‘A’ and fifty-six constituents forming 96.1-98.7% of the total composition of chemotype ‘B’ were identified. Chemotype ‘A’ was characterized by higher percentages of α-pinene (34.6-41.9%), sabinene (26.1-36.1%), (E)-caryophyllene (2.4-5.4%) and terpinen-4-ol (1.5-5.3%), whereas chemotype ‘B’ was dominated by higher amount of α-pinene (52.7-65.3%), β-pinene (10.7-12.9%), (E)-caryophyllene (3.1-10.3%) and limonene (5.1-7.8%). Comparative results showed considerable variations in the essential oil composition of both chemotypes due to season of collection. Present study concluded that the M. koenigii leaves of desired quality may be obtained by selecting suitable chemotype and season. 相似文献
136.
Drought indices (DI) are an useful tool for assessing different sectarian droughts. Standardized Precipitation Index (SPI) has been used worldwide to assess/monitor the onset, active phase, cessation and severity of drought. Normalized Difference Vegetation Index (NDVI) provides a comprehensive vegetation dynamics, which directly linked with rainfall received in a particular region. Indo-Gangetic Region (IGR), providing employment and livelihood to tens of millions of rural families directly or indirectly and rice (Oryza sativa L.)-wheat (Triticum aestivum L.) (RW) system of the Indo-Gangetic Plains (IGP) contributes 80% of the total cereal production and is critical to food security of the region. This study tries to verify the applicability of water-vegetative indices viz., SPI, Rainfall Index (RI) and NDVI for drought assessment of rice-wheat system productivity over IGR-India. The relationship between monsoon rainfall and NDVI shows that at around 1100 mm rainfall, the NDVI reached saturation point and no further significant increase in NDVI with increase of rainfall is noticed. Even though, there was a positive correlation of seasonal monsoon rainfall and average NDVI, conflicting results are noticed between monthly distribution of rainfall and monthly anomaly of NDVI over IGR States. It is noticed that June dif NDVI (actual NDVI-mean NDVI) contributes more to rice productivity followed by July. However, the combined effect of June, July and August, explains 15% of the variation of Kharif Rice Productivity Index (KRPI). As far as wheat is concerned, statistically significant relation was found between Wheat Productivity Index (WPI) and anomaly NDVI during December-March. This explains 35% of the variability in WPI. 相似文献
137.
Guillermo Portillo‐Clark Ramón Casillas‐Hernández Rosalía Servín‐Villegas Francisco J. Magallón‐Barajas 《Aquaculture Research》2012,44(1):22-30
This study was performed to determine the growth and survival patterns of the juvenile yellowleg shrimp Farfantepenaeus californiensis cohabiting with the green feather alga Caulerpa sertularioides over a range of temperatures (18, 22, 25, 28 and 32°C) found throughout the year in the Gulf of California. From an initial weight of 46 ± 10 mg, shrimp cohabiting with green feather algae increased in weight by an average of 0.57 (±0.07), 5.44 (±0.45), 6.36 (±0.37), 7.66 (±0.26) and 5.96 (±0.59) g at 18, 22, 25, 28 and 32°C, respectively, whereas shrimp grown without seaweed increased in weight by an average of 0.28 (±0.026), 2.66 (±0.24), 3.15 (±0.49), 4.00 (±0.67), and 3.54 (±0.09) g respectively. Statistically significant differences were observed for the growth rates of juvenile yellowleg shrimp in the presence of C. sertularioides and peak growth was observed at 28°C in experiments with macroalgae. No significant differences were observed for shrimp survival except at 32°C without macroalgae, where survival was lower. These results suggest a beneficial and growth‐promoting effect of cohabitation with live C. sertularioides on F. californiensis. 相似文献
138.
S. KitchluG. Ram Sushma KoulKiran Koul K.K. GuptaAshok Ahuja 《Industrial Crops and Products》2011,33(3):584-587
Podophyllum hexandrum Royle (Syn. P. emodi Wale) a perennial rhizomatous herb found in alpine region distributed in the entire range of Himalayas from Ladakh to Sikkim at an altitude of 3000-4200 m asl is an preferred commercial source of Podophyllum lignans. It contains three times more Podophyllotoxin than the American species, Podophyllum peltatum. The present study was aimed to investigate variation of Podophyllum lignans contents based on six marker compounds viz. Podophyllotoxin; Deoxypodophyllotoxin; Picropodophyllotoxin; Podophyllotoxin β-d-glucopyanoside; Isopicropodophyllone; 4′-Demethyldeoxypodophyllotoxin, β-d-lucopyanoside, in P. hexandrum population growing at three locations. Further, ontogenetic and morphogenetic variations of Podophyllum lignan contents were studied to investigate dynamics of accumulation of these compounds. Representative collections from three locations viz., Panikhar, Padam and Tangoli located in Trans Himalayan semi-desert region of Zanskar valley were harvested at three stages (dormancy, active growth and maturity). Plants were dissected into root, rhizome and rhizome-buds, dried separately and assayed for Podophyllum lignan contents by high performance liquid chromatography. 相似文献
139.
A. González-Ortiz J. J. Ramírez-García M. J. Solache-Ríos 《Water, air, and soil pollution》2018,229(10):340
Clindamycin (CLD), an antibiotic derivate of lincomycin, is widely used; the presence of this drug in the wastewater and the environment could produce resistance in bacteria. In this work, the sorption of this drug by two surfactant-modified zeolitic tuffs was studied considering contact time, initial concentration, pH, and temperature. The kinetic behavior indicates that the equilibrium times were between 15 and 12 h for all materials, and the results were best adjusted to Ho and Mc Kay model. The highest adsorption was obtained with the hexadecyltrimethylammonium-modified zeolitic tuff from Oaxaca, Mexico (1.56 mg/g). The sorption isotherms obtained showed a linear behavior, indicating a partition mechanism. The thermodynamic parameters were determined from the isotherms at different temperatures and Van Ho equation; the processes are exothermic and not spontaneous. The best pH for the adsorption is between 8 and 11. The results show that the modified zeolitic tuffs are potential materials for the adsorption of CLD from water. 相似文献
140.
The phytase is a key enzyme to hydrolyze phytic acid present in wheat grains and improves the bio-availability of micronutrients in monogastric animals. Phytase trait being contributed by specific regions of the genome requires identification of these regions, using suitable molecular markers. Hence, in the present investigation we attempted to develop a PCR-based marker that detects the phytase level in wheat. Six sets of PCR primers were designed on the basis of nucleotides sequence variation found in the sequence of both varieties. Out of six set of primers, one set amplified two different sized bands, i.e. 334 bp and 295 in two wheat cultivars C-306 (low phytase) and DBW 17 (high phytase), respectively. It exhibited a polymorphic banding pattern with length polymorphism and clearly separating low and high phytase genotypes. The primer set was also used for PCR of 46 synthetic hexaploids and 46 release varieties of wheat to validate the developed markers. Association among identified markers and phytase activity was found to be at 99.9% confidence level based on Fisher’s exact test (F-test). Therefore, this PCR primer set will be useful to select the wheat germplasm having high phytase levels and also in wheat breeding programs aimed at improving phytase levels in bread wheat cultivars. 相似文献