全文获取类型
收费全文 | 17027篇 |
免费 | 29篇 |
专业分类
林业 | 3672篇 |
农学 | 1316篇 |
基础科学 | 138篇 |
2809篇 | |
综合类 | 774篇 |
农作物 | 2104篇 |
水产渔业 | 1796篇 |
畜牧兽医 | 1432篇 |
园艺 | 1111篇 |
植物保护 | 1904篇 |
出版年
2023年 | 8篇 |
2022年 | 6篇 |
2021年 | 8篇 |
2019年 | 10篇 |
2018年 | 2750篇 |
2017年 | 2716篇 |
2016年 | 1187篇 |
2015年 | 74篇 |
2014年 | 23篇 |
2013年 | 39篇 |
2012年 | 817篇 |
2011年 | 2142篇 |
2010年 | 2119篇 |
2009年 | 1266篇 |
2008年 | 1322篇 |
2007年 | 1596篇 |
2006年 | 50篇 |
2005年 | 118篇 |
2004年 | 110篇 |
2003年 | 169篇 |
2002年 | 78篇 |
2001年 | 15篇 |
2000年 | 53篇 |
1999年 | 14篇 |
1996年 | 8篇 |
1993年 | 16篇 |
1992年 | 20篇 |
1991年 | 18篇 |
1990年 | 20篇 |
1989年 | 22篇 |
1988年 | 24篇 |
1987年 | 18篇 |
1986年 | 22篇 |
1985年 | 12篇 |
1984年 | 10篇 |
1983年 | 14篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1979年 | 7篇 |
1977年 | 13篇 |
1976年 | 5篇 |
1975年 | 8篇 |
1974年 | 11篇 |
1973年 | 9篇 |
1972年 | 5篇 |
1971年 | 10篇 |
1970年 | 8篇 |
1968年 | 8篇 |
1966年 | 11篇 |
1938年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
The average passage time, the rumen fluid volume and the digestibility of the organic matter were determined in addition to 3 individual feeding experiments with fertility oriented crossbreed ewes, which received pelleted straw-concentrate mixtures. The average passage time of the feed particles through the digestive tract is shorter in pregnant animals than in lactating ones. It is longest in non-pregnant sheep. High quotas of straw and coarse particles prolong the passage time, increasing feed intake and supplements of long straw shorten it. The volume of rumen fluid is lower in ewes fed ad libitum in the stage of late pregnancy and after lactation than during lactation. The rumen fluid volume is also lower in restrictively fed animals during the stage of late pregnancy than during lactation. In animals in the stage of late pregnancy it correlates negatively with the weight of the litter. On an average of all experiments at maintenance level the digestibility of the organic matter in ewes in the 4th month of pregnancy gravidity amounted to 56.6%, in the 2nd month of lactation to 59.8% and in wethers to 59.5% Due to an increase of energy intake from maintenance to 2. maintenance digestibility of the straw-concentrate mixture with 40% straw decreased by 5.5 units and of that with 60% straw by 17.8 units in the period before delivery. Pregnancy in the 4th month resulted in a digestion depression of between 3.0 and 5.8 units. 相似文献
4.
1118 Friesian cows and 101 Friesian heifers were investigated in internal pelvic measurements and their relationships to external measurements. The mean of the pelvic vertical and the medium diagonally diameter of the pelvis are 19.8 cm and 18.3 cm. 363.9 square centimetres and 76.3 centimetres were found for the pelvic surface and pelvic circumference. The difference between the biggest and smallest pelvis was 295.0 square centimetres. Medium to high coefficiences of correlation were detected between the internal pelvic measurements but relationships between internal and external pelvic measurements were low. From determined external pelvic measurements only the hip breadth provides usefull informations of the pelvic shape. 相似文献
5.
Hoffmann WE Dorner JL Morris H 《Veterinary clinical pathology / American Society for Veterinary Clinical Pathology》1983,12(2):33-38
Antiserum directed against equine intestinal Alkaline Phosphatase (ALP) was produced in rabbits and used to develop a sensitive and quantitative assay for the detection of intestinal ALP in equine serum. This assay was then used to measure the half-life of intravenously injected intestinal ALP and to determine if the intestinal ALP was present in normal horse sera, sera from horses presented for lesions not involving the gastrointestinal tract and sera from horses presented with lesions involving the gastrointestinal tract. The results suggest that intestinal ALP is not likely to appear in equine serum even when gastrointestinal disease is present and, therefore, appears to be of no diagnostic value. 相似文献
6.
A simple and reliable method for the determination of progesterone in milk fat by radioimmunoassay has been developed. Application of the assay under field conditions has shown that all samples diagnosed " questionable" in the former milk progesterone test (MPT) could be characterized as positive or negative. Thus the total figure of animals daignosed correctly rose from 72.3% to 85.8%. The borderlines (ng progesterone / 10 mcl milk fat) set up for this assay were (1) pregnant and (1) nonpregnant (Day 20) and (.3) in estrus and (.3) not in estrus ( Day 0). Within the application for diagnosis of pregnancy, 81.4% were diagnosed correctly as pregnant while 96.3% were diagnosed correctly as not pregnant. The latter figure is somewhat lower than in the MPT (100%), but under the practical conditions the error lies within the range of false diagnosis due to problems with sample identification. 相似文献
7.
A. Schots J. De Boer A. Schouten J. Roosien J. F. Zil Verentant H. Pomp L. Bouwman-Smits H. Overmars F. J. Gommers B. Visser W. J. Stiekema J. Bakker 《European journal of plant pathology / European Foundation for Plant Pathology》1992,98(2):183-191
Engineering resistance against various diseases and pests is hampered by the lack of suitable genes. To overcome this problem we started a research program aimed at obtaining resistance by transfecting plants with genes encoding monoclonal antibodies against pathogen specific proteins. The idea is that monoclonal antibodies will inhibit the biological activity of molecules that are essential for the pathogenesis. Potato cyst nematodes are chosen as a model and it is thought that monoclonal antibodies are able to block the function of the saliva proteins of this parasite. These proteins are, among others, responsible for the induction of multinucleate transfer cells upon which the nematode feeds. It is well documented that the ability of antibodies to bind molecules is sufficient to inactivate the function of an antigen and in view of the potential of animals to synthesize antibodies to almost any molecular structure, this strategy should be feasible for a wide range of diseases and pests.Antibodies have several desirable features with regard to protein engineering. The antibody (IgG) is a Y-shaped molecule, in which the domains forming the tips of the arms bind to antigen and those forming the stem are responsible for triggering effector functions (Fc fragments) that eliminate the antigen from the animal. Domains carrying the antigen-binding loops (Fv and Fab fragments) can be used separately from the Fc fragments without loss of affinity. The antigen-binding domains can also be endowed with new properties by fusing them to toxins or enzymes. Antibody engineering is also facilitated by the Polymerase Chain Reaction (PCR). A systematic comparison of the nucleotide sequence of more than 100 antibodies revealed that not only the 3′-ends, but also the 5′-ends of the antibody genes are relatively conserved. We were able to design a small set of primers with restriction sites for forced cloning, which allowed the amplification of genes encoding antibodies specific for the saliva proteins ofGlobodera rostochiensis. Complete heavy and light chain genes as well as single chain Fv fragments (scFv), in which the variable parts of the light (VL) and heavy chain (VH) are linked by a peptide, will be transferred to potato plants. A major challenge will be to establish a correct expression of the antibody genes with regard to three dimensional folding, assembly and intracellular location. 相似文献
8.
H Hoffmann 《DTW. Deutsche tier?rztliche Wochenschrift》1990,97(1):24-26
A Pig Health Service in Bavaria was established in 1958, there was one veterinary-officer working. The department Pig-Health Service of the "Tiergesundheitsdienst Bayern" has twenty-one veterinary-officers now. They mostly are working in the pig health scheme, doing stress susceptibility test, giving advice and expert evidence. 相似文献
9.
Neural lesions of Marek's disease, Marek's disease tumours in the ovary, liver, and kidney, as well as spleen and bursa of Fabricii of chickens bearing Marek's disease tumorous infiltrations, were examined by a new immunohistochemical technique basing upon Sternbergers unlabelled antibody enzyme method which allows the exact localization of lymphoid cells based on their surface antigens. Type C neural lesions contained T-lymphocytes almost exclusively. Type B neural lesions had relatively high proportions of T- and B-lymphocytes, and severe type A neural lesions possessed one part of heavily labelled T-lymphocytes and a number of cells stained weakly by rabbit-anti-chicken-T-cell-globulin. Tumorous infiltrations had similar characteristics as type A neural lesions. Spleen and interfollicular spaces of bursa of Fabricius were infiltrated by T-lymphocytes. 相似文献
10.
Olga Seco Diaz MRCVS Anne Desrochers DMV Vickie Hoffmann VMD Virginia B. Reef DVM 《Veterinary radiology & ultrasound》2005,46(1):83-85
An 8-day-old Arabian-Morgan cross colt underwent cardiac evaluation. The foal was tachycardic, tachypneic, exercise intolerant and had a loud right-sided heart murmur and cyanotic mucous membranes. Total anomalous pulmonary venous connection was diagnosed with echocardiography and confirmed at postmortem examination. Total anomalous pulmonary venous connection is a very rare congenital cardiac abnormality that has not been reported before in the horse. 相似文献