全文获取类型
收费全文 | 9449篇 |
免费 | 673篇 |
国内免费 | 3篇 |
专业分类
林业 | 846篇 |
农学 | 371篇 |
基础科学 | 63篇 |
2569篇 | |
综合类 | 242篇 |
农作物 | 468篇 |
水产渔业 | 996篇 |
畜牧兽医 | 3604篇 |
园艺 | 140篇 |
植物保护 | 826篇 |
出版年
2024年 | 17篇 |
2023年 | 76篇 |
2022年 | 118篇 |
2021年 | 239篇 |
2020年 | 221篇 |
2019年 | 166篇 |
2018年 | 461篇 |
2017年 | 465篇 |
2016年 | 469篇 |
2015年 | 365篇 |
2014年 | 403篇 |
2013年 | 620篇 |
2012年 | 730篇 |
2011年 | 651篇 |
2010年 | 389篇 |
2009年 | 322篇 |
2008年 | 543篇 |
2007年 | 545篇 |
2006年 | 443篇 |
2005年 | 432篇 |
2004年 | 370篇 |
2003年 | 326篇 |
2002年 | 272篇 |
2001年 | 204篇 |
2000年 | 205篇 |
1999年 | 175篇 |
1998年 | 35篇 |
1997年 | 40篇 |
1996年 | 28篇 |
1995年 | 18篇 |
1993年 | 18篇 |
1992年 | 57篇 |
1991年 | 41篇 |
1990年 | 40篇 |
1989年 | 48篇 |
1988年 | 36篇 |
1987年 | 40篇 |
1986年 | 45篇 |
1985年 | 47篇 |
1984年 | 35篇 |
1983年 | 34篇 |
1982年 | 21篇 |
1981年 | 14篇 |
1979年 | 32篇 |
1978年 | 30篇 |
1977年 | 27篇 |
1974年 | 26篇 |
1973年 | 45篇 |
1972年 | 30篇 |
1971年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
B. Carrasco R. García-Gonzáles C. Díaz P. Ávila P. Cáceres G. A. Lobos H. Silva P. D. S. Caligari 《Genetic Resources and Crop Evolution》2014,61(7):1423-1432
The Austral papaya (Vasconcellea chilensis) is an endangered species that has valuable characteristics for introgression into other papaya species. These characteristics include disease resistance, cold tolerance and latex with low proteolytic activity. It is a species that grows under extreme environmental conditions of drought, salinity and temperature; it is found growing naturally in Chile but today only as three remnant populations. The results presented here, using inter simple sequence repeat molecular markers, along with morphological trait analyses, suggest that these relict populations are the result of a relatively recent fragmentation. This implies that the fragmentation has not yet had its full effect on the genetic variation and so emphasises the need for clear and urgent conservation measures to preserve the remaining genetic variation, particularly for the most northern of the three populations which is presently unprotected. 相似文献
32.
A. San Bautista S. López-Galarza A. Martínez B. Pascual J. V. Maroto 《Journal of plant nutrition》2013,36(9):1527-1539
To determine their influence on leaf tipburn incidence and yields six nutrient solutions with different proportions of potassium (K), calcium (Ca), and magnesium (Mg) were tested in ‘Camarosa’ strawberry plants. Response models were made to predict tipburn incidence, yields and fruit weight. A high Ca proportion in the nutrient solution was determinant for high yields in the first season, while a high Mg content was fundamental for high marketable yields during the two last seasons. In 2001 and 2002, the average fruit weight was higher with high Mg levels, and in 2000 the lowest fruit weights coincided with low levels of Ca in the nutrient solution. The models for tipburn incidence in 2000 and 2002 indicated that solutions with intermediate to high levels of Mg and intermediate to low levels of Ca resulted in a more frequent incidence of tipburn. Conversely, in 2001, the highest tipburn incidence appeared with high K contents. 相似文献
33.
A. Madueño-Molina D. García-Paredes J. Martínez-Hernández R. Bugarín-Montoya J. I. Bojórquez-Serrano 《Journal of plant nutrition》2013,36(11):1701-1710
The objective of this study was to evaluate the effects of induced drought conditions and phosphorous (P) application on osmotic adjustment as reflected in the accumulation of organic solutes in the leaves of frijolillo. The experiment took place under greenhouse conditions without climate control. Plastic containers were used measuring 20 cm high × 15 cm in diameter. In each container, five plants were evaluated from emergence to vegetative growth phase. Three soil moisture regimes were evaluated (25%, 50%, and 100% of field capacity) combined with four concentrations of phosphorous (0, 50,100 and 150 mg kg?1 of soil). A completely randomized block design with a factorial arrangement of 3×4 with four replications was used. The cellular osmotic adjustment as a response to drought stress in frijolillo was associated with the accumulation of sugars, amino acids and proline in that higher concentrations than the control were measured with moisture at 25%. Concentrations of chlorophyll and carotene increased as soil moisture levels decreased. 相似文献
34.
Lubica Pospíšilová Markéta Komínková Ondřej Zítka René Kizek Gabriela Barančíková Tadeáš Litavec 《Acta Agriculturae Scandinavica, Section B - Plant Soil Science》2013,63(6):517-528
Composition of humic acids (HA) is a function of plant-derived inputs, degradation processes regulated by microorganisms, organo-mineral interactions and age. Characterization of different origin humic substances is important for evaluation of their contribution to stabile and labile carbon pool in the environment. The relative abundance of chemical components in HA isolated from soils, compost, commercial lignohumates, alginite, acadiane and lignite was studied with aim to quantify content of important biomarkers such as amino acid, lipids and polyphenols. HA were considered as a heterogeneous complex and high concentration of peptides, polyphenols and lipids was determined in acadian-HA to compare with soil-HA. Compost-HA contained much more amino acids to compare with soil-HA samples. Alginite-HA and lignite-HA were similar in biomarkers content to soil-HA. Fourier transform infrared spectroscopy confirmed that chemical composition and functional groups content differs with the origin, humification degree and the age of studied samples. Soil-HA are typically composed of a variety of ?OH, COOH?, C–O, C–H2, (aliphatic and aromatic) groups, quinines, lignin fragments, polysaccharide, monosaccharide and proteins fragments, which are linked together by ?O?, ?NH?, ?H=, >C=O, metal ions and –S? groups. 13C NMR spectroscopy showed that aromatic carbon content was the highest in lignite-HA and soil-HA. 相似文献
35.
Vasquez-Caicedo AL Heller A Neidhart S Carle R 《Journal of agricultural and food chemistry》2006,54(16):5769-5776
Accumulation of beta-carotene and trans-cis isomerization of ripening mango mesocarp were investigated as to concomitant ultrastructural changes. Proceeding postharvest ripening was shown by relevant starch degradation, tissue softening, and a rising sugar/acid ratio, resulting in a linear decrease (R (2) = 0.89) of a ripening index (RPI(KS)) with increasing ripening time. A modest accumulation of all-trans-beta-carotene and its cis isomers resulted in a slight pigmentation of the mango chromoplasts, because ambient temperatures of 18.2-19.5 degrees C provided suboptimal ripening conditions, affecting color development and beta-carotene biosynthesis. The ultrastructures of chromoplasts from mango mesocarp and carrot roots were comparatively studied by means of light and transmission electron microscopy. Irrespective of the ripening stage, mango chromoplasts showed numerous plastoglobuli varying in size and electron density. They comprised the main part of carotenoids, thus supporting the partial solubilization of the pigments in lipid droplets. However, because different pigment-carrying tubular membrane structures were also observed, mango chromoplasts were assigned to the globular and reticulotubular types, whereas the crystalline type was confirmed for carrot chromoplasts. The large portions of naturally occurring cis-beta-carotene in mango fruits contrasted with the predominance of the all-trans isomer characteristic of carrots, indicating that the nature of the structure where carotenoids are deposited and the physical state of the pigments are crucial for the stability of the all-trans configuration. 相似文献
36.
37.
Ana Claudia Ochogavía Mercedes Gil Liliana Picardi Graciela Nestares 《Breeding Science》2014,64(4):416-421
Chlorosis level is a useful parameter to assess imidazolinone resistance in sunflower (Helianthus annuus L.). The aim of this study was to quantify chlorosis through two different methods in sunflower plantlets treated with imazapyr. The genotypes used in this study were two inbred lines reported to be different in their resistance to imidazolinones. Chlorosis was evaluated by spectrophotometrical quantification of photosynthetic leaf pigments and by a bioinformatics-based color analysis. A protocol for pigment extraction was presented which improved pigment stability. Chlorophyll amount decreased significantly when both genotypes were treated with 10 μM of imazapyr. Leaf color was characterized using Tomato Analyzer® color test software. A significant positive correlation between color reduction and chlorophyll concentration was found. It suggests that leaf color measurement could be an accurate method to estimate chlorosis and infer chlorophyll levels in sunflower plants. These results highlight a strong relationship between imidazolinone-induced chlorosis and variations in leaf color and in chlorophyll concentration. Both methods are quantitative, rapid, simple, and reproducible. Thus, they could be useful tools for phenotyping and screening large number of plants when breeding for imidazolinone resistance in this species. 相似文献
38.
39.
Savlík M Fimanová K Szotáková B Lamka J Skálová L 《Research in veterinary science》2006,80(3):267-274
Fenbendazole (FEN) and flubendazole (FLU) are benzimidazole anthelmintics often used in pig management for the control of nematodoses. The in vivo study presented here was designed to test the influence of FLU and FEN on cytochrome P4501A and other cytochrome P450 (CYP) isoforms, UDP-glucuronosyl transferase and several carbonyl reducing enzymes. The results indicated that FEN (in a single therapeutic dose as well as in repeated therapeutic doses) caused significant induction of pig CYP1A, while FLU did not show an inductive effect towards this isoform. Some of the other hepatic and intestinal biotransformation enzymes that were assayed were moderately influenced by FEN or FLU. Strong CYP1A induction following FEN therapy in pigs may negatively affect the efficacy and pharmacokinetics of FEN itself or other simultaneously or consecutively administered drugs. From the perspective of biotransformation enzyme modulation, FLU would appear to be a more convenient anthelmintic therapy of pigs than FEN. 相似文献
40.
The study developed management instructions for even-aged Pinus sylvestris stands in Galicia (north-western Spain). Although these stands are highly productive, no silvicultural management schedules have been proposed so far for them on the basis of systematic analyses. This study used data from 2160 optimisation runs to develop the management instructions. Land expectation value was used as the objective function. Different prices of timber assortments were considered and the discounting rate was varied from 0.5 to 5%. The method employed to find the optimal management schedules of stands was the combination of a stand simulator and an optimisation algorithm. The simulator uses an earlier growth and yield model for Pinus sylvestris in Galicia to predict the future development of the stand with a given management schedule while the optimisation algorithm seeks the best management schedule among all the possible alternatives. The results show that optimal rotation lengths vary widely between 42 and 170 years, high discounting rates and good site quality resulting in the shortest rotations. Four thinnings were found to be suitable for all sites and discounting rates. With discounting rates higher than 1% the commercial thinnings should gradually decrease the stand basal area towards the end of the rotation. 相似文献