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   1973篇
  免费   85篇
  国内免费   1篇
林业   165篇
农学   83篇
  355篇
综合类   71篇
农作物   80篇
水产渔业   294篇
畜牧兽医   871篇
园艺   13篇
植物保护   127篇
  2023年   8篇
  2022年   34篇
  2021年   58篇
  2020年   38篇
  2019年   25篇
  2018年   44篇
  2017年   52篇
  2016年   70篇
  2015年   64篇
  2014年   75篇
  2013年   182篇
  2012年   99篇
  2011年   120篇
  2010年   56篇
  2009年   61篇
  2008年   119篇
  2007年   137篇
  2006年   135篇
  2005年   119篇
  2004年   87篇
  2003年   64篇
  2002年   82篇
  2001年   66篇
  2000年   44篇
  1999年   34篇
  1998年   26篇
  1997年   5篇
  1996年   11篇
  1995年   9篇
  1994年   5篇
  1993年   6篇
  1992年   14篇
  1991年   12篇
  1990年   9篇
  1989年   14篇
  1988年   9篇
  1987年   5篇
  1986年   6篇
  1985年   5篇
  1984年   3篇
  1983年   4篇
  1979年   3篇
  1978年   3篇
  1977年   4篇
  1975年   6篇
  1972年   2篇
  1971年   2篇
  1969年   4篇
  1968年   3篇
  1967年   3篇
排序方式: 共有2059条查询结果,搜索用时 15 毫秒
971.
OBJECTIVE: To identify effects of revision of the Japanese food composition tables from the fourth version to the fifth version on nutrient intake estimation. DESIGN: A database on 783 samples of 24-hour food duplicate portions was re-visited. Nutrients in the duplicate portions were estimated by use of the fourth and fifth versions of the Japanese food composition tables in parallel, together with supplemental use of other databases. The two sets of estimates were subjected to comparison. SETTING: The sample collection was conducted at 31 sites all over Japan. SUBJECTS: The sample donors were 783 women aged 20-78 years. RESULTS: Compared with the estimates by use of the fourth version of the tables, the estimates by the fifth version were substantially higher for intakes of energy, carbohydrate, dietary fibre, vitamin A and niacin, and lower for iron intake. The increase in carbohydrate intake estimates was more evident in older women than in young women, whereas the decrease in the intake estimation of iron and the increase in that of dietary fibre were more marked in young women than in older women. CONCLUSION: The recent revision of food composition tables in Japan induced substantial changes in the estimation of nutrient intakes, i.e. an increase in energy, carbohydrate, dietary fibre, vitamin A and niacin, and a decrease in iron. The extent of the changes varied depending on age.  相似文献   
972.
Abstrac

The effects of 3 oxides (Fe, Al, and Mn oxides) and 3 clay minerals (kaolin, montmorillonite, and allophane) on the adsorption and subsequent kinetic properties of acid phosphatase were compared. The amount of enzyme adsorbed by the oxides and clay minerals followed the order: montmorillonite ? kaolin > Mn oxide > Fe oxide > Al oxide ? allophane. The adsorption isotherms of the enzyme on the oxides and clay minerals, except for montmorillonite and allophane, fitted the Langmuir equation. The activity of the enzyme immobilized by the inorganic components studied was in the order of allophane > kaolin > Fe oxide > montmorillonite > Al oxide ≒ Mn oxide. Compared to the free enzyme, the V max, Km, and V max / K m values of the immobilized enzyme decreased, increased, and decreased, respectively. Among the oxides or clay minerals, the higher the ability of the inorganic components to adsorb the enzyme, the lower the value of the V max / K m ratio of the immobilized enzyme. These findings suggest that the catalytic efficiency of the enzyme complexes formed is determined by the adsorbability of the inorganic components for the enzyme.  相似文献   
973.
Soil salinization has become a serious problem all over the world. In this study, the influence of salinity of irrigation water and soil on plant nutrition and physiological disorders were investigated. The study was conducted in three agricultural fields in South Baja California, Mexico where saline stress of crops by soil salinization has become a serious problem under the arid climate.

There was a significant correlation (P < 0.05) between sodium (Na) concentration and electrical conductivity (EC) of the water. The soil pH was extremely high in all areas, and the Na concentration was higher than that of other elements. In spite of the salinized water and soil, vegetables did not show symptoms of nutritional disorders. Unlike the vegetables, fruit leaves showed symptoms of nutritional disorders. There was not a correlation between the concentration ratio (CR) of elements of the leaves, which showed symptoms to healthy leaves in a same tree, and the visible symptoms of the nutritional disorder.  相似文献   
974.
Because of the increasing use of maize hybrids with genetically modified (GM) stacked events, the established and commonly used bulk sample methods for PCR quantification of GM maize in non-GM maize are prone to overestimate the GM organism (GMO) content, compared to the actual weight/weight percentage of GM maize in the grain sample. As an alternative method, we designed and assessed a group testing strategy in which the GMO content is statistically evaluated based on qualitative analyses of multiple small pools, consisting of 20 maize kernels each. This approach enables the GMO content evaluation on a weight/weight basis, irrespective of the presence of stacked-event kernels. To enhance the method's user-friendliness in routine application, we devised an easy-to-use PCR-based qualitative analytical method comprising a sample preparation step in which 20 maize kernels are ground in a lysis buffer and a subsequent PCR assay in which the lysate is directly used as a DNA template. This method was validated in a multilaboratory collaborative trial.  相似文献   
975.
Cerebrospinal fluids (CSFs) from 9 Pug dogs with necrotizing meningoencephalitis (NME: Pug dog encephalitis) were examined to identify the antigens for anti-astrocyte autoantibodies. Each CSF exhibited a positive reaction to the cytoplasm of cultured canine astrocytes by an indirect fluorescent antibody test. In an immunoblotting analysis on normal canine brain proteins, eight of 9 CSFs showed a common band of 52 kDa, corresponding to glial fibrillary acidic protein (GFAP), and all of 9 CSFs reacted with purified bovine GFAP. From these results, GFAP is one of the common autoantigens in Pug dogs with NME. On the other hand, the reactivity of CSFs to chymotrypsin-digested bovine GFAP fragments were variable among dogs, indicating that the antibodies in the CSFs recognized different epitopes on GFAP.  相似文献   
976.
Traffic jams reduce hydrolytic efficiency of cellulase on cellulose surface   总被引:3,自引:0,他引:3  
A deeper mechanistic understanding of the saccharification of cellulosic biomass could enhance the efficiency of biofuels development. We report here the real-time visualization of crystalline cellulose degradation by individual cellulase enzymes through use of an advanced version of high-speed atomic force microscopy. Trichoderma reesei cellobiohydrolase I (TrCel7A) molecules were observed to slide unidirectionally along the crystalline cellulose surface but at one point exhibited collective halting analogous to a traffic jam. Changing the crystalline polymorphic form of cellulose by means of an ammonia treatment increased the apparent number of accessible lanes on the crystalline surface and consequently the number of moving cellulase molecules. Treatment of this bulky crystalline cellulose simultaneously or separately with T. reesei cellobiohydrolase II (TrCel6A) resulted in a remarkable increase in the proportion of mobile enzyme molecules on the surface. Cellulose was completely degraded by the synergistic action between the two enzymes.  相似文献   
977.
Scopelophila ligulata (Spruce) Spruce, S. cataractae (Mitt.) Broth., and Mielichhoferia japonica Besch. (Mielichhoferia mielichhoferi (Hook.) Wijk et Marg. var. japonica (Besch.) Wijk et Marg.) are well known “copper mossess” which show peculiar ecological characteristics consisting of a preference for metal-rich soils, lithosols, rocks, etc. as their substrates. The total and water-soluble element contents in the substrates and heavy metal contents in the moss body were analyzed in this study. The results of these chemical analyses were as follows: The iron contents in the moss body and substrate of S. ligulata were higher than those of S. cataractae and M. japonica. On the contrary the copper contents of the former were lower than those of the latter. The pH values of substrate of S. ligulata were lower than those of S. cataractae and M. japonica. The concentrations of water-soluble iron and sulfate in the substrate of S. ligulata were higher than those of S. cataractae and M. japonica. On the contrary, the water-soluble copper concentrations in the substrate of S. ligulata were lower than those of the others. Although in the substrate of S. cataractae the iron content was several times higher than the copper content, in the moss body the copper content was higher than iron content.  相似文献   
978.
Andosols are characterized by an abundance of black humic acids (HAs) belonging to Type A with a high content of aromatic carbon (C) in particular condensed aromatic C. Black HAs are also observed in other soils, such as Chernozems and the subsoil of paddy field, and extracted after washing with an acid or using chelating agent such as sodium pyrophosphate (Na4P2O7). However, contribution of condensed aromatic structures to those soil HAs are unknown. To obtain the information about C skeletal structures of black HAs in soils other than Andosols, HAs were obtained from 2 Chinese Chernozem samples, 2 subsoil samples from Japanese paddy fields (Fulvisols), and a Rendzina-like soil (Cambisols) as well as an Andosol sample (reference) by successive extraction with 0.1 M NaOH (HAs1) and 0.1 M Na4P2O7 (HAs2), and 13C nuclear magnetic resonance and X-ray diffraction 11-band profile analyses were applied. In the black HAs2 from the non-Andosol samples, the proportion of C present as aromatic C, size of C layer planes, and relative C layer plane content ranged from 52 to 59%, 0.48 to 1.92 nm (mean size, 0.76–0.91 nm), and 58 to 100 AU (arbitrary unit) mg?1, respectively, with a positive correlation between total C layer plane content and the degree of humification. Those ranges were similar to the distribution ranges of Andosols HAs1 reported by our previous study.  相似文献   
979.
The bacteria capable of degrading pentachlorophenol (PCP) were isolated from soil. In the soil perfused with 40 ppm PCP solution, PCP was decomposed and five chlorine atoms of PCP were liberated as chloride ion after about 3 weeks. Re-addition of PCP after its degradation, accelerated the rate of PCP degradation and de-chlorination. After the addition of PCP to the soil three times, bacteria which grew on PCP agar were counted to be about 2 × 107 per gram dry soil. In the liquid medium inoculated with the perfused soil, PCP degradation and complete de-chlorination were found. In this case, multiplication of bacteria capable of growing on PCP agar was found. The bacteria capable of growing on and degrading PCP in the medium with inorganic salts and 40 ppm PCP as a sole source of carbon were isolated from the agar plates for enumeration of the bacteria. From the morphological and physiological properties of the isolated bacteria, the genus of the bacteria was considered to be Pseudomonas or a closely related one. In the culture medium with PCP and inorganic salts, the bacteria degraded PCP and completely de-chlorinated it. The de-chlorination process corresponded approximately to PCP disappearance. Pathways of PCP metabolism are not yet elucidated.  相似文献   
980.
We performed a field experiment in thebiodegradation of heavy oil spilled from the Russian tankerNakhodka on a beach in the Sea of Japan. We collectedoil-contaminated cobbles and treated half with nitrogen andphosphorus slow-release fertilizers to stimulate microbialdegradation of the oil; the other half acted as unfertilizedcontrols. The cobbles were placed in porous acrylic vessels andsubmerged. We monitored changes in the oils, macronutrients,microbial community structure and amount of chlorophyll a. There were no significant differences in these criteriabetween the fertilized and unfertilized vessels, apart from anincrease in chlorophyll a in the fertilized vessels.However, there was a major intrinsic degradation of semi-volatile oil compounds in the unfertilized vessels; this occurred at a rate similar to that in the fertilized vessels, despite the low concentration of macronutrients in the seawater at the site.  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