全文获取类型
收费全文 | 1795篇 |
免费 | 119篇 |
国内免费 | 2篇 |
专业分类
林业 | 141篇 |
农学 | 26篇 |
基础科学 | 10篇 |
262篇 | |
综合类 | 255篇 |
农作物 | 50篇 |
水产渔业 | 102篇 |
畜牧兽医 | 921篇 |
园艺 | 44篇 |
植物保护 | 105篇 |
出版年
2023年 | 13篇 |
2022年 | 22篇 |
2021年 | 35篇 |
2020年 | 41篇 |
2019年 | 26篇 |
2018年 | 33篇 |
2017年 | 37篇 |
2016年 | 36篇 |
2015年 | 43篇 |
2014年 | 53篇 |
2013年 | 78篇 |
2012年 | 78篇 |
2011年 | 114篇 |
2010年 | 78篇 |
2009年 | 69篇 |
2008年 | 115篇 |
2007年 | 89篇 |
2006年 | 89篇 |
2005年 | 59篇 |
2004年 | 83篇 |
2003年 | 89篇 |
2002年 | 72篇 |
2001年 | 31篇 |
2000年 | 25篇 |
1999年 | 33篇 |
1998年 | 16篇 |
1997年 | 13篇 |
1996年 | 11篇 |
1995年 | 9篇 |
1994年 | 11篇 |
1992年 | 28篇 |
1991年 | 23篇 |
1990年 | 19篇 |
1989年 | 29篇 |
1988年 | 24篇 |
1986年 | 21篇 |
1985年 | 20篇 |
1984年 | 15篇 |
1983年 | 13篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1979年 | 12篇 |
1978年 | 8篇 |
1974年 | 12篇 |
1972年 | 7篇 |
1971年 | 8篇 |
1970年 | 13篇 |
1968年 | 12篇 |
1967年 | 7篇 |
1966年 | 7篇 |
排序方式: 共有1916条查询结果,搜索用时 15 毫秒
951.
952.
M E Kehrli B J Nonnecke R L Wood J A Roth 《Veterinary immunology and immunopathology》1989,20(2):149-163
Two separate experiments evaluated ID-1 (a commercial bovine whey product containing 5200 pg of thymosin alpha 1/ml) as an immunotherapeutic agent in lactating cows. In the first experiment, cows without mastitis were evaluated for blood leukogram, milk production, total and differential milk cell counts, lymphocyte (Lc) blastogenesis, and neutrophil (PMN) functions (random and directed migration under agarose, chemiluminescence, ingestion of bacteria, iodination, cytochrome C reduction, antibody-independent neutrophil-mediated cytotoxicity, and antibody-dependent cell-mediated cytotoxicity) before and after ID-1 therapy. ID-1 treatment resulted in a significant treatment group by time period interaction for the relative proportion of mononuclear cells (MNC) in milk (P less than 0.009) and for PMN random migration (P less than 0.01). Based on these interactions, ID-1 treatment appeared to slightly increase the proportion of small MNC in milk and to increase random migration from pretreatment levels by 73% more than increases observed in controls. No significant effect of ID-1 treatment on milk production, total milk somatic cell counts, Lc blastogenesis, or other PMN functions was observed. In cows with experimental Staphylococcus aureus intramammary infections, ID-1 treatment resulted in a significant decline in blood leukocyte count (P less than 0.001) and blood PMN count (P less than 0.02), and maintained PMN random migration (P less than 0.01) while controls declined and abrogated a depression in the ability of Lc to respond to mitogens (P less than 0.05) that developed in controls as a result of S. aureus mastitis. Injection of ID-1 into cows had no adverse effect on their overall health or level of milk production, but did cause subtle and potentially favorable changes in several in vitro immune parameters. In spite of these subtle changes which might indicate increased resistance to mastitis, cows actually developed a more severe S. aureus intramammary infection based on a 9% increase in log 10 bacterial shedding in milk. 相似文献
953.
954.
Andrew R. Foote Graham C. Mair Andrew T. Wood Melony J. Sellars 《Aquaculture International》2012,20(5):1003-1007
Genetic protection of improved lines of Giant Tiger shrimp, Penaeus monodon, may be achieved through the reliable production of all triploid families, as triploid shrimp are reproductively sterile. The problem with current triploid induction methods is in producing 100?% triploid progeny reliably and doing so on a commercial scale. All triploid offspring may be achievable by mating tetraploids with diploids, overcoming current limitations. However, tetraploidy in shrimp to date has been unsuccessful, with all tetraploids dying very early in development. As the induction method of heat was found to be lethal, this study investigated an alternative method using cold water to assess induction rates and lethality. Cold-water treatments between ?2 and 14?°C were applied at 18, 20, and 22?min post-spawning detection for various durations with the aim of inhibiting first mitosis. Tetraploidy was induced in treatments at or less than 1?°C; however, no nauplii hatched from these treatments. As no diploid or tetraploid nauplii hatched from any of the treatments below 3?°C, it was determined that this cold-water treatment method is not suitable for tetraploid production in P. monodon. 相似文献
955.
- 1. Even though the fragility and vulnerability of subterranean ecosystems (caves, groundwater and hyporheic habitats) is widely acknowledged, the impacts of human disturbances have been poorly quantified when compared with surface waters. In particular, limited data exist regarding the impact of organic pollution upon aquatic cave invertebrate communities.
- 2. The Peak–Speedwell Cavern system (Derbyshire, UK) was affected by two organic pollution events, during a 7‐year study (1997–2003), originating from the same source in the surface catchment but resulting in markedly different ecological responses. The first event led to the elimination of most taxa from affected sites while the second resulted in an increase in abundance of organisms within the cave associated with the increased availability of trophic resources. The second event also coincided with the invasion of the stygophilic amphipod, Gammarus pulex, at a site where it had not previously been recorded.
- 3. Recovery of the invertebrate community following both organic pollution events occurred within 12 months. Recolonization of the affected sites was facilitated by annual flooding of the cave and by the presence of refugia on unaffected subterranean tributaries.
- 4. The data highlight the problems associated with the conservation and management of subterranean ecosystems where impacts in distant surface catchments may have unseen repercussions for the subterranean environment. Aquatic subterranean habitats are not widely monitored and the impacts of pollution/disturbance may not be detected in surface waters for some time, if at all, owing to dilution effects. Caves supporting obligate subterranean organisms (stygobites) are particularly vulnerable to these pressures and require clear management strategies to protect both the subterranean and surface catchments which support them.
956.
Experiments for the production of hybrid striped bass (HSB) in in-pond circulation systems (IPCS) were carried out in 2003
and 2004. The circulation system consisted of two channels with a productive volume of 8.5 cubic meters each. The tanks were
installed tightly in a pond, which served for the biological cleaning of the expiry water. In the first year HSB fingerlings
with an average weight of 46.4 g were produced. The average yield in the basin was 51.2 kg/m3. The survival rate from stocked 0.44 g advanced fry was 97.8%. The food conversion was 1.16.
In 2004 two-year-old HSB were reared in the same IPCS. The tanks were stocked at two different stocking densities, 122 and
244 fingerlings/m3 with a mean weight of 36.5 g. In the tank with the larger stocking density, the yield was almost exactly twice as high as
in the other tank (50.0 resp. 24.8 kg), which corresponded to a stocking density of 59.1 or 29.3 kg/m3 at the end of the rearing season. The stocking density had no influence on the increase of the individual body weight. Obviously
HSB can therefore still be reared at higher stocking densities. 相似文献
957.
Todd R. Gemeinhardt Nathan J. C. Gosch Jerrod R. Hall Kasey W. Whiteman Tim L. Welker Joseph L. Bonneau 《水产资源保护:海洋与淡水生态系统》2021,31(11):3326-3333
- Large-scale movement of fishes is a challenge for conservation and management in rivers, especially when individuals can cross jurisdictional boundaries.
- Assessing large-scale movement is particularly difficult during early life stages, especially when endangered species are involved. After hatching, free embryos of the federally endangered pallid sturgeon (Scaphirhynchus albus) drift long distances during development. Following the transition to exogenous feeding, individuals may continue to move downstream, resulting in a potential two-step migration.
- Tagged age-0 pallid sturgeon were stocked into the lower Missouri River, which provided an opportunity to assess pallid sturgeon dispersal as well as the hypothesized two-step migration. From July 2018 to April 2021, 79 individuals were captured, with most dispersing 200–800 km downstream from the stocking location.
- The observed dispersal of pallid sturgeon supports the two-step downstream migration hypothesis. This migration may lead to dispersal into the Mississippi River, which highlights the need for expanded monitoring into the Mississippi River for an effective evaluation of pallid sturgeon recovery actions. This study also reinforces the importance of inter-jurisdictional management and collaboration to better account for the large-scale movement of river fishes.
958.
- The waters of the Patagonian Shelf in the south-west Atlantic are nutrient rich, support large concentrations of wildlife, and are exploited by several fisheries, including the large Asian squid-jigging fishery. Although the squid-jigging fishery has previously been observed to have few problems with the accidental mortality of seabirds, the deliberate catch for consumption of seabirds by the crew has been identified as a possible issue.
- Four cruises were made between Uruguay and the Falkland Islands during 2005–2006 to quantify the impact of jiggers on seabirds from indirect observation platforms. Monitoring included closely approaching 116 jigging vessels and boarding seven for inspection.
- The use of non-jigging fishing gear, either for catching fish or seabirds, was observed at the stern of 33 vessels. Twelve seabird carcasses were observed floating close to vessels during 13 days of monitoring. Although the results recorded here are not sufficient to put a confident estimate on the magnitude of this mortality, the density of carcasses floating in the water among the jigging fleet indicated the potential significance of this problem.
- The results were considered sufficiently concerning for the Falkland Islands Government to take preventative actions, including educational efforts, improving humanitarian conditions onboard vessels, introducing relevant legislation and licence conditions, and prosecuting intentional seabird take inside the Falkland Islands jurisdiction. This has resulted in the apparent elimination of these mortalities within Falkland waters since the late 2000s.
- Nevertheless, it is likely that the same initial conditions exist for the crews of squid jiggers on vessels operating on the high seas, and so the possibility of the targeting of seabirds for consumption continues. Squid fisheries with substantial numbers of jiggers overlap with important foraging areas for a range of albatross and other species in high-seas areas such as the Patagonian Shelf, the Humboldt and Kuroshio currents, and the south-west Pacific Ocean. These areas of overlap may be important to investigate, especially in the foraging grounds of declining seabirds.
959.
Ian Mayer Ewen McLean Tim J. Kieffer Larry M. Souza Edward M. Donaldson 《Fish physiology and biochemistry》1994,13(4):295-300
Since somatostatin (SRIF) inhibits the release of growth hormone (GH), its immunoneutralization may provide an alternative
to GH therapy as a means of enhancing somatic growth in fish. The present study examined the feasibility of accelerating growth
in juvenile chinook salmon by means of antiSRIF administration. Yearling salmon of Nicola River stock (BC, Canada) were injected
intraperitoneally every 5 days, for a total of 40 days, with either SRIF (1 μg g-1 body wt.), antiSRIF (SOMA-10, 1 μg g−1), recombinant bovine GH (rbGH, 2.5 μg g−1), recombinant porcine GH (rpGH, 2.5 μg g−1) or saline (controls). No significant differences were observed in length, weight or final condition factor (k) between the SRIF-treated and control fish over the experimental period. However, the fish treated with the antiSRIF were
significantly (p ≤ 0.05) longer and heavier than the control salmon after 25 and 30 days respectively. Furthermore, antiSRIF
treatment caused a lowering in k when compared to the control salmon. Fish injected with rbGH or rpGH were significantly longer and heavier than all other
groups (p ≤ 0.05), after only 5 days. GH treated groups also returned higher k when compared against all other treatments
(p ≤ 0.05). No differences were observed in growth between the two rGH treatments over the experimental period. 相似文献
960.
E. A. Omer D. L. Smith K. V. Wood B. S. El-Menshawi 《Plant foods for human nutrition (Dordrecht, Netherlands)》1994,45(3):247-249
The volatile constituents ofTirmania nivea (white desert truffle) have been analysed, using gas chromatography/mass spectrometric technique. 11 compounds have been identified in the ascocarp volatiles. The major components were found to be unsaturated fatty acids; whereas haxadecanoic acid represented 49% of the volatiles isolate. 相似文献