全文获取类型
收费全文 | 12189篇 |
免费 | 813篇 |
国内免费 | 6篇 |
专业分类
林业 | 1613篇 |
农学 | 427篇 |
基础科学 | 43篇 |
2674篇 | |
综合类 | 748篇 |
农作物 | 506篇 |
水产渔业 | 801篇 |
畜牧兽医 | 4777篇 |
园艺 | 300篇 |
植物保护 | 1119篇 |
出版年
2023年 | 102篇 |
2022年 | 134篇 |
2021年 | 239篇 |
2020年 | 231篇 |
2019年 | 157篇 |
2018年 | 553篇 |
2017年 | 532篇 |
2016年 | 475篇 |
2015年 | 387篇 |
2014年 | 439篇 |
2013年 | 674篇 |
2012年 | 925篇 |
2011年 | 847篇 |
2010年 | 462篇 |
2009年 | 357篇 |
2008年 | 714篇 |
2007年 | 679篇 |
2006年 | 548篇 |
2005年 | 582篇 |
2004年 | 524篇 |
2003年 | 480篇 |
2002年 | 398篇 |
2001年 | 286篇 |
2000年 | 244篇 |
1999年 | 223篇 |
1998年 | 71篇 |
1997年 | 61篇 |
1996年 | 43篇 |
1995年 | 63篇 |
1994年 | 39篇 |
1993年 | 36篇 |
1992年 | 82篇 |
1991年 | 70篇 |
1990年 | 67篇 |
1989年 | 56篇 |
1988年 | 62篇 |
1987年 | 52篇 |
1986年 | 53篇 |
1985年 | 55篇 |
1984年 | 46篇 |
1983年 | 38篇 |
1979年 | 40篇 |
1974年 | 29篇 |
1973年 | 29篇 |
1948年 | 32篇 |
1942年 | 50篇 |
1941年 | 32篇 |
1940年 | 36篇 |
1939年 | 45篇 |
1935年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
Proanthocyanidin polymers, oligomers, and the structurally related monomer (+)-catechin were labeled by incorporation of radioactive precursors in shoots of willow tree (Salix caprea L.). [1-(14)C]-Acetate and [U-(14)C]-phenylalanine precursors were fed through the cut stems or petioles of leaves. Optimization of several parameters such as the nature and origin of the plant material, leaf maturity, nature, and quantity of radioactive precursor applied and the duration of metabolism led to incorporation yields of 3.2% and to specific activities of 500 microCi/g. Detailed characterization of the products (polymerization degree, procyanidin/prodelphinidin ratio, specific activities) and purification by chromatography are reported. Some sugars bound to radiolabeled proanthocyanidin polymers were removed by enzymic treatment with a mixture of glycosidases. A radioactive purity close to 100% and specific activities suitable for bioavailability studies were obtained. 相似文献
62.
1-methylcyclopropene increases storability and shelf life in climacteric and nonclimacteric plums 总被引:2,自引:0,他引:2
Martínez-Romero D Dupille E Guillén F Valverde JM Serrano M Valero D 《Journal of agricultural and food chemistry》2003,51(16):4680-4686
The effect of 1-methylcyclopropene (1-MCP) at three different doses (0.25, 0.50, and 0.75 microL L(-1)) on the ripening processes of a climacteric, cv. Santa Rosa, and a suppressed climacteric type, cv. Golden Japan, plum was studied. For both cultivars, positive effects were observed in terms of inhibition of ethylene production and delays of the physical, chemical, and biochemical changes associated with ripening. 1-MCP-treated plums were firmer with lower weight loss, reduced degrees Brix/titratable acidity ratios, and lower color changes during cold storage and subsequent shelf life at 20 degrees C than controls. For most factors, the effectiveness of 1-MCP was dose-dependent in Santa Rosa but dose-independent for Golden Japan. 相似文献
63.
Chamkha M Cathala B Cheynier V Douillard R 《Journal of agricultural and food chemistry》2003,51(10):3179-3184
Nineteen phenolic compounds including hydroxybenzoic acids, hydroxycinnamic acids, flavonoids, phenolic alcohols, and phenolic aldehydes have been identified and quantified in two monovarietal champagnes, Chardonnay and Pinot Noir, by using a reverse-phase high-performance liquid chromatography (HPLC) system coupled with diode array detection. The identification of four hydroxycinnamic tartaric esters (caftaric, coutaric, fertaric, and 2-S-glutathionylcaftaric acids), two flavanonols (astilbin and engeletin), and some other compounds was confirmed by HPLC coupled with mass spectrometry. Caftaric acid and tyrosol were the major phenols. Hydroxybenzoic acids and flavonoids were present at low concentrations. The phenolic compositions of 2000 and 2001 Chardonnay and Pinot Noir vary quantitatively according to the year and the variety, but the chemical natures of the molecules are the same. The total phenolic content determined by colorimetric measurement ranges from 176 to 195 mg/L of gallic acid equivalent and is similar to that described in white wines. 相似文献
64.
Boulanger Yan Arseneault Dominique Boucher Yan Gauthier Sylvie Cyr Dominic Taylor Anthony R. Price David T. Dupuis Sébastien 《Landscape Ecology》2019,34(1):159-174
Landscape Ecology - Forest landscapes at the boreal–temperate ecotone have been extensively altered. Reducing the gap between current and presettlement forest conditions through... 相似文献
65.
Baudron Frédéric Schultner Jannik Duriaux Jean-Yves Gergel Sarah E. Sunderland Terry 《Landscape Ecology》2019,34(2):341-356
Landscape Ecology - It remains unclear how agricultural landscapes can best serve multiple purposes such as simultaneously maintaining agricultural productivity and conserving biodiversity. Our... 相似文献
66.
Ana E. González-Santiago Belinda Vargas-Guerrero Pedro M. García-López Alma L. Martínez-Ayala José A. Domínguez-Rosales Carmen M. Gurrola-Díaz 《Plant foods for human nutrition (Dordrecht, Netherlands)》2017,72(2):134-140
Lupinus albus seeds contain conglutin gamma (Cγ) protein, which exerts a hypoglycemic effect and positively modifies proteins involved in glucose homeostasis. Cγ could potentially be used to manage patients with impaired glucose metabolism, but there remains a need to evaluate its effects on hepatic glucose production. The present study aimed to analyze G6pc, Fbp1, and Pck1 gene expressions in two experimental animal models of impaired glucose metabolism. We also evaluated hepatic and renal tissue integrity following Cγ treatment. To generate an insulin resistance model, male Wistar rats were provided 30% sucrose solution ad libitum for 20 weeks. To generate a type 2 diabetes model (STZ), five-day-old rats were intraperitoneally injected with streptozotocin (150 mg/kg). Each animal model was randomized into three subgroups that received the following oral treatments daily for one week: 0.9% w/v NaCl (vehicle; IR-Ctrl and STZ-Ctrl); metformin 300 mg/kg (IR-Met and STZ-Met); and Cγ 150 mg/kg (IR-Cγ and STZ-Cγ). Biochemical parameters were assessed pre- and post-treatment using colorimetric or enzymatic methods. We also performed histological analysis of hepatic and renal tissue. G6pc, Fbp1, and Pck1 gene expressions were quantified using real-time PCR. No histological changes were observed in any group. Post-treatment G6pc gene expression was decreased in the IR-Cγ and STZ-Cγ groups. Post-treatment Fbp1 and Pck1 gene expressions were reduced in the IR-Cγ group but increased in STZ-Cγ animals. Overall, these findings suggest that Cγ is involved in reducing hepatic glucose production, mainly through G6pc inhibition in impaired glucose metabolism disorders. 相似文献
67.
Rocío Toraya-Avilés Maira Segura-Campos Luis Chel-Guerrero David Betancur-Ancona 《Plant foods for human nutrition (Dordrecht, Netherlands)》2017,72(2):149-155
Cassava (Manihot esculenta Crantz) native starch was treated with pyroconversion and enzymatic hydrolysis to produce a pyrodextrin and an enzyme-resistant maltodextrin. Some nutritional characteristics were quantified for both compounds. Pyroconversion was done using a 160:1 (p/v) starch:HCl ratio, 90 °C temperature and 3 h reaction time. The resulting pyrodextrin contained 46.21% indigestible starch and 78.86% dietary fiber. Thermostable α-amylase (0.01%) was used to hydrolyze the pyrodextrin at 95 °C for 5 min. The resulting resistant maltodextrin contained 24.45% dextrose equivalents, 56.06% indigestible starch and 86.62% dietary fiber. Compared to the cassava native starch, the pyrodextrin exhibited 56% solubility at room temperature and the resistant maltodextrin 100%. The glycemic index value for the resistant maltodextrin was 59% in healthy persons. Its high indigestible starch and dietary fiber contents, as well as its complete solubility, make the resistant maltodextrin a promising ingredient for raising dietary fiber content in a wide range of foods, especially in drinks, dairy products, creams and soups. 相似文献
68.
Pablo M. Vergara Luis O. Meneses Audrey A. Grez Madelaine S. Quiroz Gerardo E. Soto Christian G. Pérez-Hernández Paola A. Diaz Ingo J. Hahn Andrés Fierro 《Landscape Ecology》2017,32(2):279-293
Context
Interactions between landscape-scale processes and fine-grained habitat heterogeneity are usually invoked to explain species occupancy in fragmented landscapes. In variegated landscapes, however, organisms face continuous variation in micro-habitat features, which makes necessary to consider ecologically meaningful estimates of habitat quality at different spatial scales.Objectives
We evaluated the spatial scales at which forest cover and tree quality make the greatest contribution to the occupancy of the long-horned beetle Microplophorus magellanicus (Coleoptera: Cerambycidae) in a variegated forest landscape.Methods
We used averaged data of tree quality (as derived from remote sensing estimates of the decay stage of single trees) and spatially independent pheromone-baited traps to model the occurrence probability as a function of multiple cross-scale combinations between forest cover and tree quality (with scales ranging between 50 and 400 m).Results
Model support and performance increased monotonically with the increasing scale at which tree quality was measured. Forest cover was not significant, and did not exhibit scale-specific effects on the occurrence probability of M. magellanicus. The interactive effect between tree quality and forest cover was stronger than the independent (additive) effects of tree quality and particularly forest cover. Significant interactions included tree quality measured at spatial scales ≥200 m, but cross-scale interactions occurred only in four of the seven best-supported models.Conclusions
M. magellanicus respond to the high-quality trees available in the landscape rather than to the amount of forest per se. Conservation of viable metapopulations of M. magellanicus should consider the quality of trees at spatial scales >200 m.69.
Context
Sustained timber harvesting conflicts with the long-term viability of boreal caribou (Rangifer tarandus caribou) populations. The spatial arrangement of harvest blocks in the landscape could mitigate the impact of logging on caribou populations. For the forest industry, however, these measures represent constraints that reduce the annual allowable cut (AAC).Objective
Estimate the long-term impacts of spatial constraints to harvesting, applied alone or in combination, on AAC and boreal caribou populations.Methods
We divided a 30,000 km2 region into 20 harvest block sizes varying from 50 to 1000 km2, and modeled the implementation of spatially explicit harvest schedule plans in combination with wildfire and caribou population dynamics. We then evaluated the probability of persistence of boreal caribou populations.Results
The probability of maintaining an AAC target declined with increasing target AAC, increasing size of operating area, and increasing adjacency constraints. In contrast, the probability of maintaining caribou populations declined with increasing AAC, decreasing size of operating areas, and decreasing adjacency constraints. An increase in operating area size from 50 to 300 km2 produced a considerable gain in AAC for all adjacency constraints.Conclusions
Because adjacency constraints led only to a small increase in the probability of maintaining caribou populations, we recommend adopting less constraining landscape management actions, such as a 70-year period between two consecutive harvests in the same ~300-km2 operating area.70.
Yujiao Liu Yaxi Liu Yong Zhou Charlene Wight Zhien Pu Pengfei Qi Qiantao Jiang Mei Deng Zaoxia Wang Yuming Wei Wenguang Cao Dengcai Liu Youliang Zheng Chunji Liu Judith Frégeau-Reid Jirui Wang 《Euphytica》2017,213(1):19
Pre-harvest sprouting (PHS) causes significant yield loss and degrade the end-use quality of wheat, especially in regions with prolonged wet weather during the harvesting season. Unfortunately, the gene pool of Triticum durum (tetraploid durum wheat) has narrow genetic base for PHS resistance. Therefore, finding out new genetic resources from other wheat species to develop PHS resistance in durum wheat is of importance. A major PHS resistance QTL, Qphs.sicau-3B.1, was mapped on chromosome 3BL in a recombinant inbred line population derived from ‘CSCR6’ (Triticum spelta), a PHS resistant hexaploid wheat and ‘Lang’, a PHS susceptible Australian hexaploid wheat cultivar. This QTL, Qphs.sicau-3B.1, is positioned between DArT marker wPt-3107 and wPt-6785. Two SCAR markers (Ph3B.1 and Ph3B.2) were developed to track this major QTL and were used to assay a BC2F8 tetraploid population derived from a cross between the durum wheat ‘Bellaroi’ (PHS susceptible) and ‘CSCR6’ (PHS resistant). Phenotypic assay and marker-assisted selection revealed five stable tetraploid lines were highly PHS resistant. This study has successfully established that PHS-resistance QTL from hexaploid wheat could be efficiently introgressed into tetraploid durum wheat. This tetraploid wheat germplasm could be useful in developing PHS resistant durum cultivars with higher yield and good end-use quality. 相似文献