全文获取类型
收费全文 | 9209篇 |
免费 | 765篇 |
国内免费 | 2篇 |
专业分类
林业 | 721篇 |
农学 | 314篇 |
基础科学 | 70篇 |
1981篇 | |
综合类 | 1012篇 |
农作物 | 487篇 |
水产渔业 | 860篇 |
畜牧兽医 | 3597篇 |
园艺 | 204篇 |
植物保护 | 730篇 |
出版年
2023年 | 79篇 |
2022年 | 99篇 |
2021年 | 218篇 |
2020年 | 245篇 |
2019年 | 278篇 |
2018年 | 336篇 |
2017年 | 358篇 |
2016年 | 358篇 |
2015年 | 264篇 |
2014年 | 352篇 |
2013年 | 501篇 |
2012年 | 582篇 |
2011年 | 678篇 |
2010年 | 393篇 |
2009年 | 329篇 |
2008年 | 548篇 |
2007年 | 492篇 |
2006年 | 476篇 |
2005年 | 427篇 |
2004年 | 341篇 |
2003年 | 367篇 |
2002年 | 320篇 |
2001年 | 181篇 |
2000年 | 171篇 |
1999年 | 133篇 |
1998年 | 62篇 |
1997年 | 64篇 |
1996年 | 49篇 |
1995年 | 55篇 |
1994年 | 45篇 |
1993年 | 47篇 |
1992年 | 51篇 |
1991年 | 67篇 |
1990年 | 66篇 |
1989年 | 62篇 |
1988年 | 38篇 |
1987年 | 68篇 |
1986年 | 44篇 |
1985年 | 69篇 |
1984年 | 48篇 |
1983年 | 51篇 |
1982年 | 28篇 |
1980年 | 28篇 |
1979年 | 35篇 |
1978年 | 28篇 |
1976年 | 27篇 |
1974年 | 24篇 |
1973年 | 30篇 |
1970年 | 27篇 |
1969年 | 32篇 |
排序方式: 共有9976条查询结果,搜索用时 31 毫秒
151.
Marcial Arellano‐Martínez Bertha Patricia Ceballos‐Vázquez César Ruíz‐Verdugo Edgar Pérez de León Rafael Cervantes‐Duarte Pedro Martin Domínguez‐Valdéz 《Aquaculture Research》2011,42(4):571-582
The lion's paw scallop, Nodipecten subnodosus (Sowerby) has considerable aquacultural potential due to its fast growth and large adductor muscle. Prior investigations throughout northwestern Mexico's littoral have reported highly variable growth rates; furthermore, no studies are available of the environment on growth and gametogenesis in this species under culture conditions. This investigation assesses the effect of food availability and temperature on the growth and gametogenesis of N. subnodosus in a suspended culture system at Guerrero Negro lagoon, Mexico. After 1 year of cultivation, N. subnodosus reached 69.13 mm in shell height (SH) (0.196 mm day?1, 14 months old). Two significant growth spurts were observed: over the two first months of culture (August and September 2001, mean growth rate 0.4 mm day?1) and in September 2002 (0.3 mm day?1), both related to high temperatures and chlorophyll a concentrations. The onset of gametogenesis occurred in April 2002, with an increase in temperature (10‐month‐old scallops, 54.5 mm SH). The first spawning occurred in October and November (86.2 and 93 mm SH), with peak temperatures. These results, together with the analysis of previous reports, indicate that N. subnodosus has a higher preference for temperate areas; therefore, the Guerrero Negro lagoon appears to be a suitable site to culture this species. 相似文献
152.
From an environmental point of view, hydrogen peroxide (HP) has beneficial attributes compared with other disinfectants in terms of its ready degradation and neutral by‐products. The rapid degradation of HP can, however, cause difficulties with regard to safe and efficient water treatment when applied in different systems. In this study, we investigated the degradation kinetics of HP in biofilters from water recirculating aquaculture systems (RAS). The potential effect of HP on the nitrification process in the biofilters was also examined. Biofilter elements from two different pilot‐scale RAS were exposed to various HP treatments in batch experiments, and the HP concentration was found to follow an exponential decay. The biofilter ammonia and nitrite oxidation processes showed quick recuperation after exposure to a single dose of HP up to 30 mg L?1. An average HP concentration of 10–13 mg L?1 maintained over 3 h had a moderate inhibitory effect on the biofilter elements from one of the RAS with relatively high organic loading, while the nitrification was severely inhibited in the pilot‐scale biofilters from the other RAS with a relatively low organic loading. A pilot‐scale RAS, equipped with two biofilter units, both a moving‐bed (Biomedia) and a fixed‐bed (BIO‐BLOK®) biofilter, was subjected to an average HP concentration of ~12 mg L?1 for 3 h. The ammonium‐ and nitrite‐degrading efficiencies of both the Biomedia and the BIO‐BLOK® filters were drastically reduced. The filters had not reverted to pre‐HP exposure efficiency after 24 h, suggesting a possible long‐term impact on the biofilters. 相似文献
153.
Andreia I. G. Raposo Susana M. F. Ferreira Rodolfo Ramos Pedro M. Santos Catarina Anjos Teresa Baptista Carla Tecelo Jos L. Costa Ana Pombo 《Aquaculture Research》2019,50(8):2023-2038
In this study, the effects of three diets were investigated to enhance Paracentrotus lividus production for commercial purposes. P. lividus were fed ad libitum for 80 days with: diet A—fresh Codium tomentosum Stackhouse, 1797; diet B—formulated using a jellified mix of macroalgae and vegetables, including C. tomentosum (20%), Coralina sp. Linnaeus, 1758 (17%), cabbage Brassica oleracea var. capitata Linnaeus, 1753 (30%), carrot Daucus carota Linnaeus, 1753 (30%) and agar (3%) as a gelling agent. Diet C consisted of maize Zea mays Linnaeus, 1753 (56%) and New Zealand spinach Tetragonia tetragonoides (Pallas, 1781) Kuntze, 1891 (44%). Their effects on the gonadal and somatic growths, gonadosomatic index (GI) and gametogenesis were evaluated, as well as on the total lipid content and fatty acid composition of sea urchin's gonads. Diet A provided high values of eicosapentaenoic acid (EPA). Gonads of sea urchins fed with diet A were found mostly in growth and maturation stages of gametogenesis and showed the lowest lipid content. Sea urchins fed with diet B presented their gonads in the reabsorption stage and had the highest values of omega‐3 polyunsaturated fatty acids (PUFAs). Sea urchins fed with diet C were in the early stages of gametogenesis and had the highest values of lipid content, plus omega‐6 PUFAs. Once as an ingredient in a balanced mix with vegetables, C. tomentosum can be a key factor to the development of new promising high‐quality and low‐cost feed for P. lividus roe enhancement. 相似文献
154.
Martin Hulak Martin Psenicka David Gela Marek Rodina & Otomar Linhart 《Aquaculture Research》2010,41(2):233-239
Exogenous steroids alter sex differentiation in fish substantially. In the present study we have evaluated the effects of 17α-methyltestosterone (MT) and oestrogen receptor antagonist Tamoxifen (TA) on gonadal development and skewness of the sex ratio in all-female tench juveniles. In the first two experiments, sexually undifferentiated juveniles were orally treated with three doses of MT and TA (50, 100 and 150 mg kg−1 ). Both the treatments resulted in a moderate dose-dependent masculinization, with neomale production ranging from 17% (50 mg kg−1 ) to 26% (150 mg kg−1 ) for the MT only treatment, and from 0% (50 mg kg−1 ) to 27% (100 mg kg−1 ) only for the TA treatment respectively. In the third experiment treatment of sexually differentiated tench females with single steroid treatments or combinations of the two resulted in populations composed of females and intersex individuals. The significantly highest occurrence of intersex individuals (45.5%) was found in the group subjected to combine treatment of MT+TA (150+200 mg kg−1 ). No masculinization effect of the single or the combined treatment occurred. It can be concluded that oral treatment with MT or TA only slightly modifies the normal process of sex differentiation in gynogenetic tench juvenile, but treatment with the above-mentioned combinations has a highly significant potential to skew the sex ratio in sexually differentiated tench females. However, from an applied point of view, the treatment procedure will need optimization before use at a commercial level. 相似文献
155.
Rocío González Jesús Domingo Celada José Manuel Carral Vanesa García María Sáez‐Royuela Álvaro González 《Aquaculture Research》2011,42(9):1385-1392
Recent advances in crayfish feeding have enabled the development of size grading studies from the start of first‐feeding. A 180‐day experiment aimed at intensive rearing of Pacifastacus leniusculus was carried out under controlled conditions, evaluating the effects of size grading at two different periods from the onset of exogenous feeding. Stage 2 juveniles were stocked in fibreglass tanks at a density of 100 m2, and fed a dry diet for salmonids combined with restricted amounts of Artemia cysts. Five groups were tested: no grading, grading at 60 days (large and small size) and grading at 100 days (large and small size). After 6 months, no significant differences were found in the survival among groups (mean: 73.06%). The highest final growth (pooled results from upper and lower classes: 17.39 mm carapace length, 1.43 g weight) was achieved by the crayfish sorted at 60 days, showing significant differences from the ungraded group. Smaller crayfish graded at 60 days grew significantly faster than smaller crayfish graded at 100 days. The food conversion ratio was lower in the graded groups (mean: 2.64), showing significant differences from the ungraded group (3.23). This study shows that size grading allows a better performance and an improved feeding efficiency. 相似文献
156.
157.
H. W. Poulsen H. G. Zuckerman C. H. Metzger W. B. Ward W. C. Edmundson E. R. Bennet R. A. Jehle A. B. Beaumont John S. Gardner E. L. Newdick Frank W. Hussey E. J. Wheeler H. C. Moore Marx Koehnke A. G. Tolaas E. E. Isaac H. O. Werner O. Butler William H. Martin K. H. Fernow E. R. Jackman E. B. Tussing E. V. Hardenburg J. B. R. Dickey K. H. Klages G. S. Ralston H. L. Bailey John Tucker 《American Journal of Potato Research》1934,11(8):207-226
158.
159.
160.