全文获取类型
收费全文 | 1889篇 |
免费 | 31篇 |
国内免费 | 19篇 |
专业分类
林业 | 71篇 |
农学 | 23篇 |
基础科学 | 26篇 |
156篇 | |
综合类 | 601篇 |
农作物 | 30篇 |
水产渔业 | 40篇 |
畜牧兽医 | 917篇 |
园艺 | 36篇 |
植物保护 | 39篇 |
出版年
2024年 | 11篇 |
2023年 | 23篇 |
2022年 | 47篇 |
2021年 | 43篇 |
2020年 | 30篇 |
2019年 | 32篇 |
2018年 | 31篇 |
2017年 | 11篇 |
2016年 | 7篇 |
2015年 | 14篇 |
2014年 | 19篇 |
2013年 | 12篇 |
2012年 | 142篇 |
2011年 | 162篇 |
2010年 | 43篇 |
2009年 | 32篇 |
2008年 | 116篇 |
2007年 | 138篇 |
2006年 | 106篇 |
2005年 | 129篇 |
2004年 | 121篇 |
2003年 | 105篇 |
2002年 | 80篇 |
2001年 | 62篇 |
2000年 | 65篇 |
1999年 | 33篇 |
1995年 | 6篇 |
1994年 | 12篇 |
1993年 | 12篇 |
1992年 | 8篇 |
1991年 | 11篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1987年 | 7篇 |
1980年 | 6篇 |
1979年 | 9篇 |
1973年 | 6篇 |
1970年 | 7篇 |
1966年 | 6篇 |
1963年 | 5篇 |
1959年 | 7篇 |
1957年 | 5篇 |
1956年 | 6篇 |
1955年 | 5篇 |
1954年 | 6篇 |
1953年 | 10篇 |
1947年 | 5篇 |
1941年 | 5篇 |
1934年 | 5篇 |
1905年 | 5篇 |
排序方式: 共有1939条查询结果,搜索用时 15 毫秒
101.
Priddy NH Pope ER Cohn LA Constantinescu GM 《Journal of the American Animal Hospital Association》2001,37(2):179-182
A nine-year-old, intact female Afghan hound was presented for evaluation of an intermittent, mucopurulent, unilateral nasal discharge with a three-year duration. Radiographs showed the ipsilateral canine tooth within the rostral nasal cavity. The tooth was removed through an alveolar mucosal rhinotomy. There has been no recurrence of the nasal discharge or complications associated with the surgical procedure during the 20-month follow-up period. 相似文献
102.
An adult, wild-caught, female prairie falcon (Falco mexicanus) was presented with the chief complaint of anorexia. Radiographic findings included increased densities within the air sacs, and coelomic endoscopy revealed numerous slender worms within the air sacs and on the serosal surfaces of the ovary, oviduct, liver, proventriculus, and ventriculus. The bird seemed to improve for a short period of time with antiparasitic therapy (ivermectin and fenbendazole) and supportive care. Twenty-one days after initial presentation, the bird became recumbent with increasing pelvic limb neurologic deficits and was euthanized. On histopathologic examination, mature nematodes and larvated eggs identified as Serratospiculoides amaculata were found within the subdural space of the distal thoracolumbar and synsacral spinal cord and within the coelomic cavity. This case suggests that S. amaculata can cause clinically significant lesions in its falconiform host with potentially fatal results. 相似文献
103.
大叶胡颓子茎的抗菌活性研究 总被引:1,自引:0,他引:1
[目的]研究大叶胡颓子(Elaeagnus macrophylla Thunb.)茎的抗菌活性。[方法]用乙醇对大叶胡颓子茎进行提取,并对提取物的抗菌作用进行了研究。[结果]大叶胡颓子茎提取物对铜绿假单胞菌、金黄色葡萄球菌、克氏杆菌、大肠杆菌和枯草杆菌有较强的体外抑制作用,最小抑菌浓度为3.332~6.667 mg(生药)/ml。随着pH值的变化大叶胡颓子茎提取物的抗菌效果不同。[结论]该研究可为大叶胡颓子今后更好地应用于临床提供科学依据。 相似文献
104.
Christie JL Hewson CJ Riley CB McNiven MA Dohoo IR Bate LA 《The Canadian veterinary journal. La revue veterinaire canadienne》2005,46(3):250-252
An equine abuse policy was developed as an adjunct to an equine management survey. If at least 3 of 5 categories caused concern, a report to the authorities was indicated. The policy was not used but, in the absence of other guidelines, it might assist veterinarians considering potential abuse cases. 相似文献
105.
Aznar I McGrath G Murphy D Corner LA Gormley E Frankena K More SJ Martin W O'Keeffe J De Jong MC 《Veterinary microbiology》2011,151(1-2):104-111
The principal wildlife reservoir of Mycobacterium bovis in Ireland is the European badger. Studies in the Republic of Ireland (RoI) have shown that badgers culled in association with cattle herd tuberculosis breakdowns (focal culling) have a higher prevalence of infection than the badger population at large. This observation is one rationale for the medium term national strategy of focal badger culling. A vaccination strategy for the control of bovine tuberculosis (bTB) in badgers is a preferred long-term option. The Bacillus Calmette-Guérin (BCG) vaccine has been shown to decrease disease severity in captive badgers under controlled conditions. As the vaccine has been tested in a controlled environment with precise information on infection pressure, it cannot be assumed a priori that the effects of vaccination are similar in the wild, where other environmental and/or ecological factors prevail. For this reason we have designed a vaccine field trial to assess the impact of vaccination on the incidence of TB infection in a wild badger population. The selected study area for the vaccine trial (approximately 755 square kilometers) is divided into three zones each of which has similar characteristics in terms of size, number of main badger setts, cattle herds, cattle and land classification type. Three vaccination levels (100%, 50% and 0%) will be allocated to the three zones in a way that a gradient of vaccination coverage North to South is achieved. The middle zone (zone B) will be vaccinated at a 50% coverage but zone A and C will be randomly allocated with 100% or 0% vaccination coverage. Vaccination within zone B will be done randomly at individual badger level. The objective of this paper is to describe the design of a field tuberculosis vaccination trial for badgers, the epidemiological methods that were used to design the trial and the subsequent data analysis. The analysis will enable us to quantify the magnitude of the observed vaccination effect on M. bovis transmission in badgers under field conditions and to improve our knowledge of the biological effects of vaccination on susceptibility and infectiousness. 相似文献
106.
107.
Dahlgren LA Nixon AJ Brower-Toland BD 《American journal of veterinary research》2001,62(10):1557-1562
OBJECTIVE: To investigate effects of beta-aminopropionitrile and a combination of insulin-like growth factor (IGF)-I and beta-aminopropionitrile on metabolism of equine tendon fibroblasts. SAMPLE POPULATION: Flexor tendon explants from 3 horses. PROCEDURE: Explants received 1 of 4 treatments (control, IGF-I, beta-aminopropionitrile, and IGF-I/beta-aminopropionitrile) for 10 days, and message expression for collagen types I and III was assessed by use of in situ hybridization. Histologic findings, new protein production, and quantitative determinations of glycosaminoglycan, DNA, and de novo collagen synthesis were made. RESULTS: Insulin-like growth factor-I stimulated an anabolic response in tendon. Collagen synthesis and glycosaminoglycan and DNA content of explants were all increased. Beta-aminopropionitrile significantly suppressed collagen synthesis, which was not ameliorated by concurrent IGF-I treatment. Beta-aminopropionitrile caused alterations in cell morphology characterized by large round cells with eccentric nuclei and decreased density of collagen fibers. Protein production and collagen type-III mRNA expression were reduced in these cells. CONCLUSIONS AND CLINICAL RELEVANCE: Treatment with beta-aminopropionitrile resulted in decreased production of protein and collagen synthesis, which could be expected to suppress tendon healing. The negative effects of beta-aminopropionitrile could not be abrogated by addition of IGF-I to the medium. Treatment resulted in alterations in cell morphology and matrix consistency, which could further delay tendon healing. Beta-aminopropionitrile may impair tendon healing at a cellular level by decreasing collagen production or increasing rate of degradation of existing matrix. Because of reduced crosslinking during beta-aminopropionitrile treatment, in combination with transiently decreased tensile strength, alterations in collagen content and structure may weaken the healing tendon. 相似文献
108.
Discovery and directed evolution of a glyphosate tolerance gene 总被引:2,自引:0,他引:2
Castle LA Siehl DL Gorton R Patten PA Chen YH Bertain S Cho HJ Duck N Wong J Liu D Lassner MW 《Science (New York, N.Y.)》2004,304(5674):1151-1154
The herbicide glyphosate is effectively detoxified by N-acetylation. We screened a collection of microbial isolates and discovered enzymes exhibiting glyphosate N-acetyltransferase (GAT) activity. Kinetic properties of the discovered enzymes were insufficient to confer glyphosate tolerance to transgenic organisms. Eleven iterations of DNA shuffling improved enzyme efficiency by nearly four orders of magnitude from 0.87 mM-1 min-1 to 8320 mM-1 min-1. From the fifth iteration and beyond, GAT enzymes conferred increasing glyphosate tolerance to Escherichia coli, Arabidopsis, tobacco, and maize. Glyphosate acetylation provides an alternative strategy for supporting glyphosate use on crops. 相似文献
109.
Masursky H Batson RM McCauley JF Soderblom LA Wildey RL Carr MH Milton DJ Wilhelms DE Smith BA Kirby TB Robinson JC Leovy CB Briggs GA Duxbury TC Acton CH Murray BC Cutts JA Sharp RP Smith S Leighton RB Sagan C Veverka J Noland M Lederberg J Levinthal E Pollack JB Moore JT Hartmann WK Shipley EN De Vaucouleurs G Davies ME 《Science (New York, N.Y.)》1972,175(4019):294-305
At orbit insertion on 14 November 1971 the Martian surface was largely obscured by a dust haze with an extinction optical depth that ranged from near unity in the south polar region to probably greater than 2 over most of the planet. The only features clearly visible were the south polar cap, one dark, spot in Nix Olympica, and three dark spots in the Tharsis region. During the third week the atmosphere began to clear and surface visibility improved, but contrasts remained a fraction of their normal value. Each of the dark spots that apparently protrude through most of the dust-filled atmosphere has a crater or crater complex in its center. The craters are rimless and have featureless floors that, in the crater complexes, are at different levels. The largest crater within the southernmost spot is approximately 100 kilometers wide. The craters apparently were formed by subsidence and resemble terrestrial calderas. The south polar cap has a regular margin, suggsting very flat topography. Two craters outside the cap have frost on their floors; an apparent crater rim within the cap is frost free, indicating preferentia loss of frost from elevated ground. If this is so then the curvilinear streaks, which were frost covered in 1969 and are now clear of frost, may be low-relief ridges. Closeup pictures of Phobos and Deimos show that Phobos is about 25 +/-5 by 21 +/-1 kilometers and Deimos is about 13.5 +/- 2 by 12.0 +/-0.5 kilometers. Both have irregular shapes and are highly cratered, with some craters showing raised rims. The satellites are dark objects with geometric albedos of 0.05. 相似文献
110.
Bandini LA Neto AF Pena HF Cavalcante GT Schares G Nishi SM Gennari SM 《Veterinary parasitology》2011,176(2-3):151-156
Neospora caninum is widely distributed in the world and this parasite is one of the major causes of abortion in cattle. Dogs and coyotes are definitive hosts of N. caninum and several species of domestic and wild animals are intermediate hosts. Dogs can become infected by the ingestion of tissues containing cysts and then excrete oocysts. It is not yet known whether sporulated oocysts are able to induce a patent infection in dogs, i.e. a shedding of N. caninum oocysts in feces. The objective of this study was to experimentally examine the infection of dogs by sporulated oocysts. The oocysts used in the experiment were obtained by feeding dogs with brain of buffaloes (Bubalus bubalis) positive for anti-N. caninum antibodies by indirect fluorescent antibody test (IFAT ≥200). Oocysts shed by these dogs were confirmed to be N. caninum by molecular methods and by bioassay in gerbils, and sporulated N. caninum oocysts were used for the oral infection of four dogs. The dogs were 8 weeks old and negative for antibodies to N. caninum and Toxoplasma gondii. Dogs 1 and 4 received an inoculum of 10,000 sporulated oocysts each; dog 2 an inoculum of 5000 sporulated oocysts and dog 3 received 1000 sporulated oocysts of N. caninum. The total feces excreted by these dogs were collected and examined daily for a period of 30 days. No oocysts were found in their feces. The dogs were monitored monthly for a 6-month period to observe a possible seroconversion and when this occurred the animals were eliminated from the experiment. Dogs 1 and 4 seroconverted 1 month after the infection with titer, in the IFAT, of 1600 and 800, respectively; the other two dogs presented no seroconvertion during the 6-month period. Dogs 1 and 2 were euthanized 180 days after infection and were examined for the detection of N. caninum in tissues (brain, muscle, lymph node, liver, lung, heart and bone marrow) by immunohistochemistry and PCR with negative results in both techniques. Bioassay in gerbils with brain of these dogs was also performed and again the results were negative. In conclusion, dogs infected with sporulated oocysts of N. caninum were not able to shed oocysts in feces. However, a higher dose of infection stimulated the production of antibodies against N. caninum in the dogs. 相似文献