全文获取类型
收费全文 | 11347篇 |
免费 | 799篇 |
专业分类
林业 | 1165篇 |
农学 | 422篇 |
基础科学 | 43篇 |
2587篇 | |
综合类 | 758篇 |
农作物 | 476篇 |
水产渔业 | 768篇 |
畜牧兽医 | 4561篇 |
园艺 | 282篇 |
植物保护 | 1084篇 |
出版年
2023年 | 102篇 |
2022年 | 127篇 |
2021年 | 235篇 |
2020年 | 222篇 |
2019年 | 148篇 |
2018年 | 549篇 |
2017年 | 521篇 |
2016年 | 467篇 |
2015年 | 375篇 |
2014年 | 428篇 |
2013年 | 648篇 |
2012年 | 903篇 |
2011年 | 818篇 |
2010年 | 445篇 |
2009年 | 340篇 |
2008年 | 702篇 |
2007年 | 659篇 |
2006年 | 528篇 |
2005年 | 558篇 |
2004年 | 507篇 |
2003年 | 468篇 |
2002年 | 383篇 |
2001年 | 274篇 |
2000年 | 242篇 |
1999年 | 217篇 |
1998年 | 68篇 |
1997年 | 56篇 |
1996年 | 42篇 |
1995年 | 63篇 |
1994年 | 37篇 |
1993年 | 34篇 |
1992年 | 79篇 |
1991年 | 66篇 |
1990年 | 61篇 |
1989年 | 56篇 |
1988年 | 53篇 |
1987年 | 46篇 |
1986年 | 47篇 |
1985年 | 47篇 |
1984年 | 43篇 |
1983年 | 34篇 |
1979年 | 36篇 |
1974年 | 26篇 |
1973年 | 21篇 |
1972年 | 22篇 |
1971年 | 23篇 |
1970年 | 27篇 |
1969年 | 25篇 |
1968年 | 25篇 |
1967年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
Mattana Efisio Peguero Brígido Di Sacco Alice Agramonte Wilvin Encarnación Castillo Wilkin Rafael Jiménez Francisco Clase Teodoro Pritchard Hugh W. Gómez-Barreiro Pablo Castillo-Lorenzo Elena Terrero Encarnación Marianny Way Michael J. García Ricardo Ulian Tiziana 《New Forests》2020,51(4):705-721
New Forests - Native trees from the Caribbean were tested for seed desiccation responses, by adapting the “100-seed test” protocol. Ninety-seven seed lots of 91 species were collected... 相似文献
152.
In 1977 a silvopastoral system was started in a 8.5 há farm with the typical soil characteristics of the coastal ranges of Southern Chile, planted with Radiata pine (Pinus radiata D.Don) 2/0, with a 2.5 × 7 m spacing. The sheep management system began in June 1979.The stocking rate varied from 6 to 8 sheep per há, the ewe breeds were Romney, Suffolk × Romney, with Suffolk or Romney rams. During the 1979–1982 period ratational grazing in four paddocks with native pasture and subterranean was used. Starting from June 1982 pasture area had increased to 12 há.Forage was not conserved. Overnight, sheep were kept loose on a slatted floor sheep house.D.M./há availability, sheep and lamb weight, reproduction and growth of lambs, show that the system is feasible and practical. The 1980 production was 214 kg of live weight/há; 248kg/há in 1981; 171 for 1982, and 207 for 1983. During these years the mean wool production was between 3.5 to 4 kg per sheep.The economic results f the system are attractive as to improve farmers' income, also preventing erosion, allowing a means to promote development of an important area in Southern Chile.The research project is still in progress. 相似文献
153.
Miren del Río Hans Pretzsch Iciar Alberdi Kamil Bielak Felipe Bravo Andreas Brunner Sonia Condés Mark J. Ducey Teresa Fonseca Nikolas von Lüpke Maciej Pach Sanja Peric Thomas Perot Zahera Souidi Peter Spathelf Hubert Sterba Martina Tijardovic Margarida Tomé Patrick Vallet Andrés Bravo-Oviedo 《European Journal of Forest Research》2016,135(1):23-49
154.
Hochmalová Miroslava Purwestri Ratna Chrismiari Yongfeng Jian Jarský Vilém Riedl Marcel Yuanyong Dian Hájek Miroslav 《European Journal of Forest Research》2022,141(5):867-886
European Journal of Forest Research - Ecosystem services are investigated from many perspectives, but there are very few studies comparing the perception of forest and demand for forest ecosystem... 相似文献
155.
To determine if flower nutrient composition can be used to predict fruit quality, a field experiment was conducted over three seasons (1996-1999) in a commercial orange orchard (Citrus sinensis (L.) Osbeck cv. 'Valencia Late', budded on Troyer citrange rootstock) established on a calcareous soil in southern Portugal. Flowers were collected from 20 trees during full bloom in April and their nutrient composition determined, and fruits were harvested the following March and their quality evaluated. Patterns of covariation in flower nutrient concentrations and in fruit quality variables were evaluated by principal component analysis. Regression models relating fruit quality variables to flower nutrient composition were developed by stepwise selection procedures. The predictive power of the regression models was evaluated with an independent data set. Nutrient composition of flowers at full bloom could be used to predict the fruit quality variables fresh fruit mass and maturation index in the following year. Magnesium, Ca and Zn concentrations measured in flowers were related to fruit fresh mass estimations and N, P, Mg and Fe concentrations were related to fruit maturation index. We also established reference values for the nutrient composition of flowers based on measurements made in trees that produced large (> 76 mm in diameter) fruit. 相似文献
156.
The spectral data of a new Δ7,22 sterol, 24S-ethyl-5α-cholesta-7,22E-dien-3α-ol β-galactopyranoside, isolated from the bulbs of Autonoë madeirensis, are reported. 相似文献
157.
José AlvesJr Marcos V. Folegatti Larry R. Parsons Wije Bandaranayake Claudio R. da Silva Tonny J. A. da Silva Luís F. S. M. Campeche 《Irrigation Science》2007,25(4):419-428
The expansion of permanent trickle irrigation systems in Sao Paulo (Brazil) citrus has changed the focus of irrigation scheduling
from determining irrigation timing to quantifying irrigation amounts. The water requirements of citrus orchards are difficult
to estimate, since they are influenced by heterogeneous factors such as age, planting density and irrigation system. In this
study, we estimated the water requirements of young ‘Tahiti’ lime orchards, considering the independent contributions from
soil evaporation and crop transpiration by splitting the crop coefficient (Kc = ETc/ETo) into two separate coefficients; Ke,
a soil evaporation coefficient and Kcb, a crop transpiration coefficient. Hence, the water requirement in young ‘Tahiti’ lime
(ETy) is ETy = (Ke + Kcb) · ETo, where ETo is the reference crop evapotranspiration. Mature tree water requirement (ETm) is ETm = Kcb · ETo, assuming no soil water evaporation. Two lysimeters were used; one was 1.6 m in diameter and 0.7 m deep, and
the other was 2.7 m in diameter and 0.8-m deep. The first one was used to calculate evaporation and the second one was used
for transpiration. ETo was estimated by the Penman–Monteith method (FAO-56). The measurements were conducted during a period
between August 2002 and April 2005 in Piracicaba, Sao Paulo state, Brazil. The lysimeters were installed at the center of
a 1.0-ha plot planted with ‘Tahiti’ lime trees grafted on ‘Swingle’ citrumelo rootstock. The trees were 1-year old at planting,
spaced 7 × 4 m, and were irrigated by a drip irrigation system. During the study period, Kc varied between 0.6 and 1.22, and
Kcb varied between 0.4 and 1.0. The results suggested that for young lime trees, the volume of water per tree calculated by
Ke + Kcb is about 80% higher than the volume calculated using Kc. For mature trees, the volume of water per tree calculated
using just Kcb can be 10% less than using Kc. The independent influence of soil evaporation and transpiration is important to better understand the water consumption of
young lime trees during growth compared to mature lime trees. 相似文献
158.
经过10多年的科学研究,我国在微灌设备研制方面取得了一定进展,先后生产试制了微灌用聚乙烯管材与管件,研制出了一批灌水器和过滤、施肥装置,促进了微灌技术的推广运用。对微管灌水器进行的系列化研究,降低了工程造价,提高了灌水质量。 相似文献
159.
A C Durán C Rodríguez L Gil de Sola B Fernández J M Arqué V Sans‐Coma 《Journal of fish diseases》2010,33(8):675-682
This study is the first to report the occurrence of intimal thickening of coronary arteries in a holocephalan, namely the rabbitfish, Chimaera monstrosa. The sample studied consisted of five hearts from rabbitfish with body weights ranging between 12 g and 1116 g. The specimens were fixed in formalin, in methanol:acetone:water (MAW), or in paraformaldehyde and were examined by brightfield and polarization light microscopy. Coronary arteries from three larger animals displayed focal intimal thickenings, which were located in the left main coronary artery trunk, at the level of the cono‐ventricular junction, and in several intramyocardial ventricular arteries. The vascular changes were characterized by myointimal proliferation, breakage or absence of the inner elastic lamina, and, in one case, by increased collagen within the myointimal proliferation. Taking into account the severity of the coronary arterial changes, their location, and the body weight of the affected animals, we conclude that (1) these changes are age‐related in the rabbitfish and (2) local intense mechanical tension seems to be an important factor in their formation in this species. 相似文献
160.
Neetu Shahi László Ardó Gyöngyvér Fazekas Elen Gócza Shivendra Kumar Norbert Rèvèsz Zsuzsanna Jakabné Sándor Zsuzsanna Molnár Galina Jeney Zsigmond Jeney 《Aquaculture International》2018,26(3):727-741
To evaluate the effect of thermal and microbial stress on the immune response of common carp (Cyprinus carpio L.), relative mRNA expression level of pro-inflammatory cytokines [tumor necrosis factor alpha (TNF-α) and interleukin (IL)-1β] and other genes related to immune or stress response [inducible nitric oxide synthase (iNOS), heat shock protein 70 (Hsp70), superoxide dismutase one (SOD1), and glucocorticoid receptor (GR)] was measured by quantitative PCR (qPCR). In addition, total protein and total immunoglobulin level in blood plasma of experimental common carp was also assayed. All the above parameters were estimated 24 h post-challenge with Gram-negative bacterium, Aeromonas hydrophila. Common carp (54.89?±?6.90 g) were initially exposed to 20 °C (control group) and 30 °C (thermal stress group) water temperature for 30 days, followed by experimental challenge with 2.29?×?108 colony forming unit/mL (CFU/mL; LD50 dose) of A. hydrophila. Exposure of fish to thermal stress and subsequently challenge with A. hydrophila significantly (P?<?0.05) increases the IL-1β mRNA expression in head kidney and spleen of common carp by ~?39.94 and ~?4.11-fold, respectively. However, TNF-α mRNA expression in spleen decreased ~?5.63-fold in control fish challenged with A. hydrophila. Thermal stress and challenge with bacterium suppresses the iNOS and GR mRNA expression in spleen of common carp. Moreover, significant (P?<?0.05) increase in total protein content of blood plasma (~?43 mg/g) was evident in fish exposed to thermal stress and challenged with A. hydrophila. In conclusion, our study highlights the importance of elevated temperature stress and microbial infection in differential regulation of expression of several immunogenes in common carp. 相似文献