全文获取类型
收费全文 | 1796篇 |
免费 | 118篇 |
国内免费 | 4篇 |
专业分类
林业 | 106篇 |
农学 | 66篇 |
基础科学 | 12篇 |
351篇 | |
综合类 | 268篇 |
农作物 | 53篇 |
水产渔业 | 210篇 |
畜牧兽医 | 648篇 |
园艺 | 75篇 |
植物保护 | 129篇 |
出版年
2023年 | 21篇 |
2022年 | 11篇 |
2021年 | 42篇 |
2020年 | 44篇 |
2019年 | 60篇 |
2018年 | 52篇 |
2017年 | 58篇 |
2016年 | 58篇 |
2015年 | 42篇 |
2014年 | 47篇 |
2013年 | 80篇 |
2012年 | 106篇 |
2011年 | 124篇 |
2010年 | 74篇 |
2009年 | 75篇 |
2008年 | 105篇 |
2007年 | 105篇 |
2006年 | 124篇 |
2005年 | 106篇 |
2004年 | 99篇 |
2003年 | 97篇 |
2002年 | 72篇 |
2001年 | 27篇 |
2000年 | 25篇 |
1999年 | 29篇 |
1998年 | 15篇 |
1997年 | 8篇 |
1996年 | 4篇 |
1995年 | 17篇 |
1994年 | 8篇 |
1993年 | 7篇 |
1992年 | 10篇 |
1991年 | 8篇 |
1989年 | 14篇 |
1988年 | 10篇 |
1987年 | 10篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1977年 | 5篇 |
1975年 | 5篇 |
1972年 | 10篇 |
1971年 | 7篇 |
1970年 | 6篇 |
1969年 | 5篇 |
1968年 | 4篇 |
1959年 | 5篇 |
排序方式: 共有1918条查询结果,搜索用时 359 毫秒
991.
Grant M. Campbell Calum Sharp Kevin Wall Fernán Mateos-Salvador Sabine Gubatz Alison Huttly Peter Shewry 《Journal of Cereal Science》2012
The effects of wheat properties on breakage during First Break roller milling, as described by the Double Normalised Kumaraswamy Breakage Function (DNKBF), were investigated. A set of 45 wheats from nine varieties representing the range of commercial varieties grown in the UK, and grown over three harvest years at several nitrogen fertiliser levels, were milled at five roll gaps under Sharp-to-Sharp and Dull-to-Dull dispositions. The resulting particle size distributions were fitted with a DNKBF in order to understand the physical significance of the DNKBF parameters and to relate them to shape and hardness. The DNKBF parameters related strongly to hardness as measured using either the Single Kernel Characterisation System or Particle Size Index, allowing the particle size distribution over the range 0–4000 μm to be predicted solely from wheat hardness. A residual analysis showed that the remaining variation was correlated with kernel mass, and that more elongated kernels break to give slightly larger particles than more spherical kernels of equivalent hardness. Two types of breakage are identified, one of which principally produces many small endosperm particles along with large bran particles, while the other tends to produce mid-sized particles. The former dominates under Dull-to-Dull milling and for soft wheats, while the latter becomes more prominent under Sharp-to-Sharp milling and for harder wheats. 相似文献
992.
993.
Hui-Hua Lee Kevin R. Piner Michael G. Hinton Yi-Jay Chang Ai Kimoto Minoru Kanaiwa Nan-Jay Su William Walsh Chi-Lu Sun Gerard DiNardo 《Fisheries Science》2014,80(5):869-878
The population dynamics of the blue marlin Makaira nigricans stock in the Pacific Ocean were estimated for 1971–2011 using a fully integrated length-based, age-, and sex-structured model. Fishery-specific catch, size composition, and catch-per-unit of effort were used in the modeling as likelihood components. Estimated dynamics were consistent with a stock that is fully exploited and stable over the last several years. No significant trends in recruitment were noted; however, female blue marlin were estimated to make up a majority of the catch, and historical exploitation has disproportionately changed the age structure of females relative to males. This result is due to differences in assumed life history and estimated selectivity. Changes to important life history parameters that are responsible for the productivity of the stock would potentially change the interpretation of current stock status. 相似文献
994.
Effects of stocking density and water conditioners on yolk‐sac larvae of two marine finfish during simulated air transport 下载免费PDF全文
As marine finfish aquaculture expands, there is an increasing interest in the ability to ship early life stages from breeding centres to hatcheries so that each hatchery does not have to maintain its own broodstock. Here, we conducted 24 h air‐shipping simulations with yolk‐sac larvae of California yellowtail (CYT; Seriola lalandi) and white seabass (WSB; Atractoscion nobilis) to help fill in the informational gaps for shipping marine fish larvae. We examined the effects of a pH buffer on water quality, post‐shipping larval survival and subsequent survival to first feeding at larval densities of 1000, 3000, 6000 and 9000 larvae L?1. The pH buffer, 8.3 Trizma®, was tested at varying concentrations of zero (NT = 0.00 g L?1), low (LT = 0.75 g L?1), medium (MT = 1.5 g L?1) and high (HT = 3.0 g L?1). Trials were conducted using replicate 2 L aquarium bags filled with 500 mL of seawater and held in a water bath at 19–20°C. Results showed an interspecific difference in survival at the highest shipping densities under these experimental conditions. Shipping densities up to 6750 CYT larvae L?1 or 3000 WSB larvae L?1 consistently yielded >90% survival immediately after simulated shipment and >85% survival 48 h after the simulations. Furthermore, at these densities, pH was maintained at ~8.0 when buffered at 1.5 g L?1. The highest tested densities of 9580 CYT larvae L?1 and 9940 WSB larvae L?1, yielded lower survival 69–79% and 0.0–1.3% respectively after 24 h. Final pH in the high density CYT trials were unsatisfactory (below 7.0), regardless of the buffer concentration; however pH in the WSB high density trials improved with increasing buffer concentration. On the basis of the results from these air‐shipping simulations, we recommend CYT and WSB larvae be shipped in seawater with 1.5 g L?1 Trizma® at densities not greater than 6750 larvae L?1 for CYT and 3000 larvae L?1 for WSB. We believe this represents an important step in improving long distance transport protocols for these species and provides useful guidance in air transport of other economically and ecologically important marine species. Additional research is warranted to compare these simulation results with those from actual air shipments, as we did not account for factors that may vary in flight like temperature and pressure variations, and physical agitation. 相似文献
995.
Real‐time spatial management approaches to reduce bycatch and discards: experiences from Europe and the United States 下载免费PDF全文
Alyson S Little Coby L Needle Ray Hilborn Daniel S Holland C Tara Marshall 《Fish and Fisheries》2015,16(4):576-602
Spatial management measures are currently being used to manage bycatch and discards, given the spatial heterogeneity of fish distributions. However, permanent fishing closures are often poorly implemented, unresponsive to stock dynamics and do not achieve their management objectives. Recently, real‐time spatial management tools for managing bycatch and discards implemented under either a comanagement or self‐governance approach have been introduced in Europe and the US. Real‐time catch and discard information is shared among fishers to incentivise and encourage vessels to leave areas of high bycatch. Here, the similarities and differences, in governance, implementation and management of ten real‐time spatial management systems from across Europe and the US are reviewed. A framework is developed to characterize the attributes associated with voluntary, private and regulatory real‐time spatial management tools. Challenges and management practices in the different case studies are reviewed providing insights for designing these spatial management tools. The results illustrate that real‐time spatial management approaches can create incentives for fishers to develop, use and share information and technology to avoid undesired catch. Compared with Europe, the US has developed spatial management tools with more truly real‐time mechanisms and with greater involvement of the fishing industry in designing and operating the tools. 相似文献
996.
Examining common assumptions about recruitment: a meta‐analysis of recruitment dynamics for worldwide marine fisheries 下载免费PDF全文
Cody S Szuwalski Katyana A Vert‐Pre André E Punt Trevor A Branch Ray Hilborn 《Fish and Fisheries》2015,16(4):633-648
Assumptions about the future productivity of a stock are necessary to calculate sustainable catches in fisheries management. Fisheries scientists often assume the number of young fish entering a population (recruitment) is related to the biomass of spawning adults and that recruitment dynamics do not change over time. Thus, managers often use a target biomass based on spawning biomass as the basis for calculating sustainable catches. However, we show recruitment and spawning biomass are not positively related over the observed range of stock sizes for 61% of 224 stocks in the RAM Legacy Stock Assessment Database. Furthermore, 85% of stocks for which spawning biomass may not drive recruitment dynamics over the observed ranges exhibit shifts in average recruitment, which is often used in proxies for target biomasses. Our results suggest that the environment more strongly influences recruitment than spawning biomass over the observed stock sizes for many stocks. Management often endeavours to maintain stock sizes within the observed ranges, so methods for setting management targets that include changes within an ecosystem may better define the status of some stocks, particularly as climate changes. 相似文献
997.
Paul G. Wahome Kevin R. Beauchesne Anna C. Pedone John Cavanagh Christian Melander Paul Zimba Peter D. R. Moeller 《Marine drugs》2015,13(1):65-75
Aquatic microbes produce diverse secondary metabolites with interesting biological activities. Cytotoxic metabolites have the potential to become lead compounds or drugs for cancer treatment. Many cytotoxic compounds, however, show undesirable toxicity at higher concentrations. Such undesirable activity may be reduced or eliminated by using lower doses of the cytotoxic compound in combination with another compound that modulates its activity. Here, we have examined the cytotoxicity of four microbial metabolites [ethyl N-(2-phenethyl) carbamate (NP-1), Euglenophycin, Anabaenopeptin, and Glycolipid 652] using three in vitro cell lines [human breast cancer cells (MCF-7), mouse neuroblastoma cells (N2a), and rat pituitary epithelial cells (GH4C1)]. The compounds showed variable cytotoxicity, with Euglenophycin displaying specificity for N2a cells. We have also examined the modulatory power of NP-1 on the cytotoxicity of the other three compounds and found that at a permissible concentration (125 µg/mL), NP-1 sensitized N2a and MCF-7 cells to Euglenophycin and Glycolipid 652 induced cytotoxicity. 相似文献
998.
999.
Connectivity of the bay scallop (Argopecten irradians) in Buzzards Bay,Massachusetts, U.S.A. 下载免费PDF全文
Chang Liu Geoffrey W. Cowles James H. Churchill Kevin D. E. Stokesbury 《Fisheries Oceanography》2015,24(4):364-382
The harvest of bay scallops (Argopecten irradians) from Buzzards Bay, Massachusetts, U.S.A. undergoes large interannual fluctuations, varying by more than an order of magnitude in successive years. To investigate the extent to which these fluctuations may be due to yearly variations in the transport of scallop larvae from spawning areas to suitable juvenile habitat (settlement zones), a high‐resolution hydrodynamic model was used to drive an individual‐based model of scallop larval transport. Model results revealed that scallop spawning in Buzzards Bay occurs during a time when nearshore bay currents were principally directed up‐bay in response to a persistent southwesterly sea breeze. This nearshore flow results in the substantial transport of larvae from lower‐bay spawning areas to settlement zones further up‐bay. Averaged over the entire bay, the spawning‐to‐settlement zone connectivity exhibits little interannual variation. However, connectivities between individual spawning and settlement zones vary by up to an order of magnitude. The model results identified spawning areas that have the greatest probability of transporting larvae to juvenile habitat. Because managers may aim to increase scallop populations either locally or broadly, the high‐connectivity spawning areas were divided into: (i) high larval retention and relatively little larval transport to adjoining settlement areas, (ii) both significant larval retention and transport to more distant settlement areas, and (iii) little larval retention but significant transport to distant settlement areas. 相似文献