全文获取类型
收费全文 | 4645篇 |
免费 | 318篇 |
国内免费 | 2篇 |
专业分类
林业 | 306篇 |
农学 | 132篇 |
基础科学 | 36篇 |
843篇 | |
综合类 | 862篇 |
农作物 | 198篇 |
水产渔业 | 234篇 |
畜牧兽医 | 1895篇 |
园艺 | 113篇 |
植物保护 | 346篇 |
出版年
2023年 | 31篇 |
2022年 | 35篇 |
2021年 | 70篇 |
2020年 | 80篇 |
2019年 | 84篇 |
2018年 | 97篇 |
2017年 | 91篇 |
2016年 | 115篇 |
2015年 | 81篇 |
2014年 | 125篇 |
2013年 | 202篇 |
2012年 | 237篇 |
2011年 | 287篇 |
2010年 | 182篇 |
2009年 | 151篇 |
2008年 | 263篇 |
2007年 | 251篇 |
2006年 | 260篇 |
2005年 | 244篇 |
2004年 | 194篇 |
2003年 | 223篇 |
2002年 | 187篇 |
2001年 | 74篇 |
2000年 | 81篇 |
1999年 | 85篇 |
1998年 | 46篇 |
1997年 | 40篇 |
1996年 | 41篇 |
1995年 | 35篇 |
1994年 | 29篇 |
1993年 | 32篇 |
1992年 | 40篇 |
1991年 | 55篇 |
1990年 | 49篇 |
1989年 | 51篇 |
1988年 | 34篇 |
1987年 | 60篇 |
1986年 | 40篇 |
1985年 | 58篇 |
1984年 | 38篇 |
1983年 | 46篇 |
1982年 | 25篇 |
1980年 | 25篇 |
1979年 | 36篇 |
1978年 | 28篇 |
1976年 | 26篇 |
1973年 | 31篇 |
1971年 | 24篇 |
1970年 | 24篇 |
1969年 | 31篇 |
排序方式: 共有4965条查询结果,搜索用时 15 毫秒
181.
Maria Richter Patricia König Ilona Reimann Martin Beer 《Veterinary microbiology》2014,168(2-4):340-347
Bungowannah virus is the most divergent atypical pestivirus that had been detected up to now, and does not fit into any of the four approved species: Bovine viral diarrhea virus type 1 (BVDV-1) and type 2 (BVDV-2), Classical swine fever virus (CSFV) and Border disease virus (BDV). However, the presence of Npro and Erns coding regions, which are unique to pestiviruses, provides clear evidence of a pestivirus. Nevertheless, the amino acid identity of Bungowannah virus Npro and BVDV-1 Npro (strain CP7) is only 51.5%. By using a BVDV-1 backbone, a novel chimeric construct was generated, in which the genomic region encoding the non-structural protein Npro was replaced by that of Bungowannah virus (CP7_Npro-Bungo). In vitro studies of CP7_Npro-Bungo revealed autonomous replication with the same efficacy as the BVDV backbone CP7 and infectious high-titer virus could be collected. In order to compare the ability of interferon (IFN) suppression, two reporter gene assays, specific for type-I IFN, were carried out. In virus-infected cells, no significant difference in blocking of IFN expression between the parental virus CP7, Bungowannah virus and the chimeric construct CP7_Npro-Bungo could be detected. In contrast, an Npro deletion mutant showed an impaired replication in bovine cells and a marked type-I IFN response.Taken together, our findings reveal the compatibility of non-structural protein Npro of atypical Bungowannah virus with a BVDV type 1 backbone and its characteristic feature as an inhibitor of type-I IFN induction with an inhibitor-activity comparable to other pestiviruses. 相似文献
182.
183.
The arthropod-borne Schmallenberg virus (SBV), family Orthobunyaviridae, emerged in Europe in 2011. SBV is associated with a mild disease in adult ruminants but fetal malformation after an infection during a critical phase of pregnancy. A number of inactivated vaccines have been developed; their efficacy after two injections was demonstrated. To make the vaccination of sheep more efficient and economic the effect of a single immunization with one of these vaccines was investigated in the present study. Five vaccinated sheep and five additional control sheep were inoculated with SBV three weeks after vaccination and the results of a competitive ELISA, a standard microneutralization test and an SBV-specific real-time RT-PCR confirmed vaccine efficacy by demonstrating complete inhibition of viral replication in immunized animals. 相似文献
184.
Daniel Thiel Juergen Kreyling Sabrina Backhaus Carl Beierkuhnlein Constanze Buhk Kolja Egen Gerhard Huber Monika Konnert Laura Nagy Anke Jentsch 《European Journal of Forest Research》2014,133(2):247-260
Climate extremes are expected to increase in frequency and magnitude as a consequence of global warming, threatening the functioning, services and goods of forest ecosystems. Across Europe, the ecologically and economically important tree species Fagus sylvatica is expected to suffer particularly under such conditions. The regional introduction of provenances from drier and warmer climates is one option to adapt beech forest ecosystems to these adverse effects of climate change. Marginal populations from the drought-prone southern and north-eastern edges of the species’ distribution come into focus in search of suitable candidates for Central European deciduous forests. Here, we test three marginal provenances (Spain, Bulgaria and Poland) and three provenances from the centre of the distribution range (Germany) for their response to drought in two different soil types (sand, loam) in a full factorial common garden experiment in Landau, Germany. Drought impacted all growth parameters negatively (leaf damage +22 % (percentage points), height ?40 % and diameter increment ?41 %), and the sandy substrate exacerbated this effect. However, provenances differed in their response to drought and soil type. Evidence for a local adaptation to summer drought was detected, especially in terms of mortality rates. The Bulgarian and Spanish provenance showed a stable performance under drought conditions (BG ?27 % in diameter increment; ES ?32 %), compared to the Polish (?48 %) or the most sensitive German provenances (?57 %), yet for Bulgaria on a low level of total increment. This may indicate a trade-off between drought tolerance and growth. Therefore, a sole focus on drought-resistant marginal provenances seems to not be conducive, as they might be less adapted to other climatic factors, e.g. frost, as well. However, intermixed with local Central European provenances, these may act as functional insurance in future drought-prone forest stands. 相似文献
185.
N. B. Martin D. F. Houlihan C. Talbot R. M. Palmer 《Fish physiology and biochemistry》1993,12(2):131-141
Body composition and fractional rates of protein synthesis (percentage of the protein mass synthesized per day) were determined
in female Atlantic salmon returning to the River Tay, Scotland in July and in October after a 95 day period without food,
during which time the animals became sexually mature. During the 95 day period of starvation/sexual maturation the ventricle
and red muscle remained as a constant proportion of fresh weight whereas the liver, gill and ovary increased and the stomach
and white muscle decreased. Fractional rates of protein synthesis increased markedly in the liver, stomach and ovary during
the period of starvation/sexual maturation. In the gill, ventricle and white muscle fractional protein synthesis rates increased
slightly or remained constant. From the estimated rates of protein loss or gain in the various tissues it is concluded that
there is considerable protein turnover and repartitioning of amino acids during the period of starvation and sexual maturation.
The absolute rate of protein synthesis rates in the ovary indicates that this tissue made the largest contribution to the
energy and amino acid demands of the fish, whilst most of the amino acids required for maturation of the ovary were derived
from white muscle, principally as the result of increased muscle protein degradation. 相似文献
186.
Martin Holmstrup Johannes Overgaard Thomas F. Sørensen Guillaume Drillet Benni W. Hansen Hans Ramløv & Kirsten Engell-Sørensen 《Aquaculture Research》2006,37(6):625-631
Copepods have proven to be an ideal source of live food for the production of marine fish larvae in aquaculture. Therefore, there is a need to develop new methods for production and storage of copepod eggs that can be hatched and used at fish farms. In the present study quiescent eggs of Acartia tonsa were stored for periods up to 35 weeks at different temperatures, salinities and oxygen conditions in a full factorial experiment. None of these storage conditions seemed to induce diapause in eggs even though this has been reported by other authors. The most promising storage conditions were those involving low temperature (<5°C), medium salinity (10–20 ppt) and anoxia. The practical aspects of these results for aquaculture are discussed. 相似文献
187.
Investigation of the Effects of Salinity and Dietary Protein Level on Growth and Survival of Pacific White Shrimp, Litopenaeus vannamei 总被引:3,自引:0,他引:3
Martin Perez-Velazquez Mayra L. González-Félix Fernando Jaimes-Bustamente Luis R. Martínez-Córdova Denisse A. Trujillo-Villalba D. Allen Davis 《Journal of the World Aquaculture Society》2007,38(4):475-485
It is presumed that in hypo‐ and hypersaline environments, shrimp’s requirements for some specific nutrients, such as protein, may differ from those known in the marine habitat; however, few investigations have been conducted in this area of study. In the present investigation, the effects of salinity and dietary protein level on the biological performance, tissue protein, and water content of Pacific white shrimp, Litopenaeus vannamei, were evaluated. In a 3 × 4 factorial experiment, juvenile shrimp with an average initial weight of 0.36 ± 0.02 g were exposed for 32 d to salinities of 2, 35, and 50 ppt and fed experimental diets with crude protein contents of 25, 30, 35, and 40%. A significant effect of salinity on growth of shrimp was detected, with the growth responses (final weight, weight gain) ranked in the order 2 ppt (3.87, 3.50 g) > 35 ppt (3.40, 3.04 g) > 50 ppt (2.84, 2.47 g). No effects of dietary protein level or an interaction between salinity and protein on growth of shrimp were observed under the experimental conditions of this study. Percent survival of shrimp fed the highest protein content (40%, survival of 74%) was, however, significantly lower than those of shrimp fed the other feeds (25, 30 and 35% protein, survival of 99, 91, and 94%, respectively), a result likely associated with the concentration of total ammonia nitrogen, which increased significantly at increasing protein levels. Final water content of whole shrimp was significantly lower in animals exposed to 50 ppt (70.8%) than in shrimp held at 2 (73.7%) and 35 ppt (72.3%). No effect of salinity, protein, or their interaction was observed on the protein content of whole shrimp. The results of the present study are in agreement with reports of superior and inferior growth of L. vannamei reared in hypo‐ and hypersaline environments, respectively, as compared to what is generally observed in seawater. 相似文献
188.
Stephen Joslyn Suzanna Richards Susanne Boroffka Mark Mitchell Gawain Hammond Martin Sullivan 《Veterinary radiology & ultrasound》2014,55(1):63-67
Enhancement of extra‐ocular muscles has been reported in cases of orbital pathology in both veterinary and medical magnetic resonance imaging. We have also observed this finding in the absence of orbital disease. The purpose of this retrospective study was to describe extra‐ocular muscle contrast enhancement characteristics in a group of dogs with no known orbital disease. Magnetic resonance images (MRI) from dogs with no clinical evidence of orbital disease and a reportedly normal MRI study were retrieved and reviewed. Contrast enhancement percentages of the medial, lateral, ventral, and dorsal rectus muscles were calculated based on signal‐to‐noise ratios that were in turn determined from hand‐traced regions of interest in precontrast, immediate postcontrast and 10‐min postcontrast scans. Comparison measurements were made in the pterygoid muscle. Contrast enhancement of the extra‐ocular muscles was observed in all patients (median contrast enhancement percentage 45.0%) and was greater than that of pterygoid muscle (median contrast enhancement percentage 22.7%). Enhancement of the extra‐ocular muscles persisted 10 min after contrast administration (median contrast enhancement percentage 43.4%). Findings indicated that MRI contrast enhancement of extra‐ocular muscles is likely normal in dogs. 相似文献
189.
Manuel Martin‐Flores Daniel M Sakai Luis Campoy RD Gleed 《Veterinary anaesthesia and analgesia》2014,41(3):269-277
ObjectiveTo evaluate if return of spontaneous ventilation to pre-relaxation values indicates complete recovery from neuromuscular blockade.Study designProspective, with each individual acting as its own control.AnimalsTen healthy adult female Beagle dogs weighing 6.2–9.4 kg.MethodsDogs were anesthetized with propofol, dexemedetomidine and isoflurane. Spontaneous ventilation was assessed by measuring end-tidal CO2, expired tidal volume, peak inspiratory flow, respiratory rate and minute ventilation. Vecuronium 25 μg kg?1 IV was administered and neuromuscular block was evaluated by measuring the train-of-four (TOF) ratio with acceleromyography in the hind limb. During spontaneous recovery from neuromuscular block, the TOF ratio when each ventilatory variable returned to baseline was recorded.ResultsThis dose of vecuronium produced moderate neuromuscular block in all dogs, with TOF ratio values of 0–18% at maximal block. Expired tidal volume, peak inspiratory flow and minute ventilation returned to pre-relaxation values when the median TOF ratio was ≤ 20%. The median TOF ratio was 42% when the end-tidal CO2 returned to pre-relaxation values.Conclusions and clinical relevanceSignificant residual neuromuscular block could be measured at the hind limb with acceleromyography when ventilation had spontaneously returned to pre-vecuronium values. Monitoring spontaneous ventilation, including end-tidal CO2, expired tidal volume, peak inspiratory flow or minute ventilation cannot be used as a surrogate for objective neuromuscular monitoring, and this practice may increase the risk of postoperative residual paralysis. 相似文献