全文获取类型
收费全文 | 127357篇 |
免费 | 6890篇 |
国内免费 | 129篇 |
专业分类
林业 | 5295篇 |
农学 | 3623篇 |
基础科学 | 720篇 |
14074篇 | |
综合类 | 23490篇 |
农作物 | 4752篇 |
水产渔业 | 5711篇 |
畜牧兽医 | 67698篇 |
园艺 | 1476篇 |
植物保护 | 7537篇 |
出版年
2018年 | 1805篇 |
2017年 | 1918篇 |
2016年 | 1675篇 |
2015年 | 1526篇 |
2014年 | 1830篇 |
2013年 | 4750篇 |
2012年 | 3418篇 |
2011年 | 4180篇 |
2010年 | 2630篇 |
2009年 | 2720篇 |
2008年 | 4061篇 |
2007年 | 3882篇 |
2006年 | 3652篇 |
2005年 | 3356篇 |
2004年 | 3254篇 |
2003年 | 3367篇 |
2002年 | 3123篇 |
2001年 | 3733篇 |
2000年 | 3790篇 |
1999年 | 3010篇 |
1998年 | 1227篇 |
1997年 | 1194篇 |
1995年 | 1335篇 |
1994年 | 1173篇 |
1993年 | 1211篇 |
1992年 | 2507篇 |
1991年 | 2837篇 |
1990年 | 2649篇 |
1989年 | 2657篇 |
1988年 | 2413篇 |
1987年 | 2435篇 |
1986年 | 2536篇 |
1985年 | 2508篇 |
1984年 | 1960篇 |
1983年 | 1779篇 |
1982年 | 1190篇 |
1979年 | 1898篇 |
1978年 | 1492篇 |
1977年 | 1360篇 |
1976年 | 1266篇 |
1975年 | 1375篇 |
1974年 | 1751篇 |
1973年 | 1736篇 |
1972年 | 1736篇 |
1971年 | 1606篇 |
1970年 | 1629篇 |
1969年 | 1502篇 |
1968年 | 1355篇 |
1967年 | 1347篇 |
1966年 | 1187篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
E. Kienzle F. Möllmann S. Nater M. Wanner B. Wichert 《Journal of animal physiology and animal nutrition》2008,92(6):712-717
Hay samples from 29 horse farms in Southern Upper Bavaria and 31 horse farms in Switzerland were taken and analysed for minerals such as calcium, magnesium, phosphorus and potassium. The content of herbs and legumes in the hay was determined and the Weende analysis was performed. Comparison between Bavaria and Switzerland resulted in comparable calcium contents of approximately 4 g Ca/kg dry matter (DM) in grass hay. Hay with more than 10% of herbs and legumes found only in Switzerland showed higher Ca contents of >7 g Ca/kg DM in hay. The mineral contents of phosphorus and potassium were lower in hay from Switzerland (P: 1.8 ± 0.7 g/kg DM, K: 15.4 ± 5.1 g/kg DM) than from Bavaria (P: 3.8 ± 0.6 g/kg DM, K: 20.0 ± 6.0 DM), whereas the magnesium content of the hay showed no difference between the regions (∼1.5 g Mg/kg DM). Very late first grass hay cuts showed low magnesium and calcium (<4 g/kg DM) contents. Further minerals in the hay for horses differed from those in dairy cattle in the same region. Fertilization showed only small effects on the mineral contents of the hay produced for horses. Therefore, in calculation of ration and production of supplements for horses, these differences should be taken into account. 相似文献
993.
Rose THOROGOOD 《中国鸟类》2013,4(1):39-50
很早人们就已发现一些寄生性繁殖的杜鹃,其外形与Accipiter属的鹰类非常相似。最近的实验表明,大杜鹃(Cuculus canorus)模拟鹰类有助于其接近宿主大苇莺(Acrocephalus scirpaceus)的巢。不过,大苇莺却能够通过公众信息传递来识别大杜鹃的这一计谋。反过来,这也导致了杜鹃外形多态性的进化,以避免宿主对杜鹃的识别。通过比较研究,我们发现在寄生性的杜鹃中,模拟鹰类外形(如虹膜黄色,胸腹部具斑纹,脚黄)的杜鹃种类具有明显的外形多态性(29%的种类),远高于不模拟鹰类外形的杜鹃(仅8%的种类具有多态性)。系统发生分析进一步证实了模拟鹰类外形与杜鹃多态性进化之间的相关性。我们认为,杜鹃对鹰类的动态模拟很可能促进了杜鹃外形多态性的进化,以避免宿主对杜鹃的识别。 相似文献
994.
Kulak MV Ilinykh FA Zaykovskaya AV Epanchinzeva AV Evstaphiev IL Tovtunec NN Sharshov KA Durimanov AG Penkovskaya NA Shestopalov AM Lerman AI Drozdov IG Swayne DE 《Avian diseases》2010,54(3):1086-1090
The ecology of avian influenza (AI) viruses in wild aquatic birds of Asia is poorly understood, especially for the H5N1 high pathogenicity AI (HPAI) viruses. From March 2006 through November 2008, 20 AI viruses were isolated in the Crimea region of Ukraine with an overall frequency of virus recovery of 3.3%. All the viruses were isolated from three species of dabbling ducks: mallard (Anas platyrhynchos), wigeon (Anas penelope), and garganey (Anas querquedula), making the frequency of virus recovery for dabbling ducks 6.3%. The viruses were predominantly isolated during the fall sampling period. All viruses were genetically and antigenically characterized. No H5N1 HPAI viruses were isolated, but other HA and NA subtypes were identified including H3N1 (2), H3N6 (3), H3N8 (4), H4N6 (6), H5N2 (3), H7N8 (1), and H10N6 (1) subtypes. All isolates were of low pathogenicity, as determined by the intravenous pathogenicity index of 0.00. For H5N2 and H7N8 isolates, the HA gene was sequenced and the phylogenetic analysis revealed possible ecologic connections of the Crimea region with AI viruses from Siberia and Europe. No influenza A isolates were recovered from other Anseriformes (diving ducks [two species of pochards] and graylag geese), Columbiformes (collared doves), Gruiformes (coot), and Galliformes (gray partridges). 相似文献
995.
996.
G. Basini S. Bussolati S. E. Santini F. Grasselli 《Journal of animal physiology and animal nutrition》2010,94(6):e374-e382
Soya and soybean products used in swine feeding contain genistein, a non‐steroidal phyto‐oestrogen which has been demonstrated to influence endocrine functions. This observation leads us to design this study to evaluate the effect of genistein on swine granulosa cell steroidogenesis and proliferation. In the attempt to unravel the genistein signal transduction mechanisms, we verified the effect of lavendustin, a Tyrosine Kinase (TK) inhibitor, and the potential involvement of NO/cGMP pathway. Finally, as angiogenesis is essential for follicle development, we tested the effect of the phyto‐oestrogen on vascular endothelial growth factor production and on granulosa cell redox status, because free‐radical species modulate neovascularization. Our data provide evidence that genistein interferes with granulosa cell steroidogenesis while it does not modulate cell growth: this effect could be at least partially produced by inhibiting TK‐dependent signalling systems. On the contrary, NO/cGMP pathway or vascular endothelial growth factor production can be excluded as signalling mechanism involved in phyto‐oestrogen effects. Remarkably, genistein stimulates hydrogen peroxide production thus potentially inhibiting follicular angiogenesis. Collectively, these results suggest that genistein consumption could potentially negatively impact swine reproductive function. 相似文献
997.
C. Elwood P. Devauchelle J. Elliott V. Freiche A. J. German M. Gualtieri E. Hall E. den Hertog R. Neiger D. Peeters X. Roura K. Savary-Bataille 《The Journal of small animal practice》2010,51(1):4-22
Emesis is a common presenting sign in small animal practice. It requires a rational approach to management that is based upon a sound understanding of pathophysiology combined with logical decision making. This review, which assesses the weight of available evidence, outlines the physiology of the vomiting reflex, causes of emesis, the consequences of emesis and the approach to clinical management of the vomiting dog. The applicability of diagnostic testing modalities and the merit of traditional approaches to management, such as dietary changes, are discussed. The role and usefulness of both traditional and novel anti-emetic drugs is examined, including in specific circumstances such as following cytotoxic drug treatment. The review also examines areas in which common clinical practice is not necessarily supported by objective evidence and, as such, highlights questions worthy of further clinical research. 相似文献
998.
We conducted a field trial to evaluate the effectiveness of Aquaflor (50% florfenicol) for controlling mortality associated with Streptococcus iniae in freshwater-reared subadult sunshine bass (female white bass Morone chrysops X male striped bass M. saxatilis). Bacterial samples collected from moribund fish representing a reference population were presumptively identified microbiologically and were later confirmed to be S. iniae by biochemical characterization and polymerase chain reaction. The trial comprised a 1-d acclimation period, 10-d treatment period, and 14-d posttreatment period. During the treatment period, Aquaflor-medicated feed was administered to treated tanks (N = 3) at a target dose of 10 mg of florfenicol x kg of fish(-1) x d(-1), and nonmedicated feed was administered to control tanks (N = 3). At the end of the posttreatment period, mean (+/- SD) cumulative mortality in treated tanks (9 +/- 11%) was significantly (P = 0.040) less than that in control tanks (52 +/- 13%). Analysis of medicated feed samples revealed that treated tanks had received an actual dose of 8.3 mg florfenicol x kg fish(-1) x d(-1) (83% of target). No florfenicol was detected in control feed samples. Although the actual florfenicol dose administered to treated tanks was less than the target dose, the trial was accepted by the U.S. Food and Drug Administration Center for Veterinary Medicine as demonstrating the efficacy of Aquaflor to control mortality associated with S. iniae in cultured sunshine bass populations. 相似文献
999.
C.C. Chiang C.J. Chang H.C. Peh S.E. Chen B. Yu M.T. Chen H. Nagahata 《Veterinary immunology and immunopathology》2010,133(2-4):125-132
Polymorphonuclear neutrophils (PMN), which comprise over 70% of the somatic cells in goat milk, are a major cellular component of innate immunity in the goat mammary gland. However, the function of milk PMNs is modified after diapedesis compared to PMNs in blood. As many aspects of PMN activity depend directly on intracellular Ca2+ concentration ((Ca2+)i), the present study aimed to determine the changes in Ca2+ homeostasis of milk PMNs from lactating goats compared to autologous blood PMNs, and to examine the significance of these variations to the immuno-competency of milk PMNs. The intracellular Ca2+ store of freshly prepared milk cells was estimated from the elevation of (Ca2+)i after ionomycin treatment, which was found to be significantly less than blood PMNs. Replenishment of the intracellular Ca2+ store in milk cells after intracellular Ca2+ depletion by Bapta-AM followed by spiking with 2.5 mM Ca2+ for 20 min was also compared to that of blood PMNs, showing that after depletion/spiking the intracellular Ca2+ store in milk cells was much less than blood PMNs. The production of superoxide anion (O2?) in vitro in response to (Ca2+)i-dependent or (Ca2+)i-independent modulators was used to evaluate the relevance of altered Ca2+ homeostasis on the immuno-competency of milk cells compared to blood PMNs. The results indicated that milk cells produced similarly low levels of O2? as blood PMNs when treated with ionomycin. However, the amount of O2? produced by milk cells in response to phorbol 12-myristate 13-acetate (PMA) stimulation, although greater than ionomycin treatment, was significantly less than that of blood PMNs. The capacity for O2? production by both cell types in response to PMA reverted to the resting state with use of the protein kinase C (PKC) inhibitor, staurosporine. In conclusion, the current study demonstrated an irreversible shortage of intracellular Ca2+ in the milk PMNs of lactating goats compared to blood PMNs. It also showed that preliminary O2–production, primed by ionomycin treatment, remained unchanged in milk PMNs, despite the shortage in intracellular Ca2+, but decreased O2? production capacity, mediated via the PKC pathway, in milk PMN. It is suggested that the defects in Ca2+ homeostasis in milk PMNs of lactating goats is partially attributable for the post-diapedesis functionality modifications. 相似文献
1000.