全文获取类型
收费全文 | 76974篇 |
免费 | 6816篇 |
国内免费 | 35篇 |
专业分类
林业 | 3404篇 |
农学 | 2936篇 |
基础科学 | 487篇 |
9946篇 | |
综合类 | 11474篇 |
农作物 | 2693篇 |
水产渔业 | 5904篇 |
畜牧兽医 | 40232篇 |
园艺 | 916篇 |
植物保护 | 5833篇 |
出版年
2020年 | 880篇 |
2019年 | 1556篇 |
2018年 | 1814篇 |
2017年 | 1916篇 |
2016年 | 1844篇 |
2015年 | 1619篇 |
2014年 | 1820篇 |
2013年 | 3459篇 |
2012年 | 2462篇 |
2011年 | 2872篇 |
2010年 | 2194篇 |
2009年 | 1979篇 |
2008年 | 2803篇 |
2007年 | 2437篇 |
2006年 | 2433篇 |
2005年 | 2226篇 |
2004年 | 2293篇 |
2003年 | 2257篇 |
2002年 | 2143篇 |
2001年 | 2442篇 |
2000年 | 2480篇 |
1999年 | 1949篇 |
1998年 | 922篇 |
1997年 | 837篇 |
1996年 | 789篇 |
1995年 | 873篇 |
1994年 | 853篇 |
1993年 | 775篇 |
1992年 | 1533篇 |
1991年 | 1550篇 |
1990年 | 1670篇 |
1989年 | 1517篇 |
1988年 | 1456篇 |
1987年 | 1350篇 |
1986年 | 1394篇 |
1985年 | 1347篇 |
1984年 | 1132篇 |
1983年 | 1030篇 |
1979年 | 1012篇 |
1978年 | 803篇 |
1977年 | 725篇 |
1976年 | 678篇 |
1975年 | 729篇 |
1974年 | 778篇 |
1973年 | 835篇 |
1972年 | 804篇 |
1971年 | 751篇 |
1970年 | 735篇 |
1969年 | 745篇 |
1967年 | 661篇 |
排序方式: 共有10000条查询结果,搜索用时 43 毫秒
41.
C. P. Verschueren P. J. Selman J. J. M. de Vijlder J. A. Mol 《Domestic animal endocrinology》1991,8(4):509-519
Canine thyroglobulin (cTg) has been isolated and purified. It has similar electrophoretic patterns as Tg from other mammalian species. The main fraction had a MW of 660,000, whereas also fractions of a MW of approximately 1,300,000 (dimer) and 330,000 (subunit) were present. The iodine content was 0.8 to 1.0 % (w/w). cTg did not cross-react with antibodies against human Tg to a degree that would allow the use of a radioimmunoassay for human Tg for the determination of cTg in serum or plasma. Therefore a polyclonal antiserum was raised against cTg and a homologous radioimmunoassay was developed, which was sensitive (0.4 μg/l) and specific (cross-reactivity in cTg assay of human Tg, goat Tg, T4, T3, and DIT < 0.01 %).
Plasma Tg levels in normal dogs of both sexes and aged 3–15 years amounted to 192 ± 73 μg/l (mean ± SD, n=30). There was no relation between plasma Tg and T4 levels. 相似文献
42.
J.A. Díez P. Hernaiz M.J. Muñoz A. de la Torre A. Vallejo 《Soil Use and Management》2004,20(4):444-450
Abstract. The repeated application of pig slurry to agricultural soils may result in an accumulation of salts and a risk of aquifer pollution due to nitrate leaching and salinization. Under Mediterranean conditions, a field experiment on a sandy loam soil (Typic Xerofluvent) was performed with maize (Zea mays) in 1998, 1999 and 2001 to study the effects of applying optimal (P1) and excessive rates (P3) of pig slurry on soil salinization, nitrate leaching and groundwater pollution. The rate of pig slurry was established considering the optimal N rate for maize in this soil (170, 162 and 176 kg N ha?1 for 1998, 1999 and 2001, respectively). Pig slurry treatments were compared to an optimal N rate supplied as urea (U) and a control treatment without N fertilizer (P0). The composition of the slurries showed great variability between years. Mean NO3? leaching losses from 1998 to 2001 were 329, 215, 173 and 78 kg N ha?1 for P3, P1, U and P0 treatments, respectively. The amount of total dissolved salts (TDS) added to the soil in slurry application between 1998 and 2001 was 2019 kg TDS ha?1 for the P1 treatment and 6058 kg TDS ha?1 for the P3 treatment. As a consequence, the electrical conductivity (EC) of the slurry‐treated soils was greater than that of the control soil. The EC correlated significantly with the sodium concentration of the soil solution. Over the entire experimental period, 2653, 2202 and 2110 kg Na ha?1 entered the aquifer from the P3, P1 and P0 treatments, respectively. The P3 treatment did not significantly increase grain production in 1999 and 2001 compared with that achieved with the optimal N rate treatment (P1). This behaviour shows the importance of establishing application guidelines for pig slurry that will reduce the risk of soil and groundwater pollution. 相似文献
43.
The fertility of male coypu sperm following seminal vesicle extirpation was investigated using the penetration test into the egg of Syrian golden hamster (Mesocricetus auratus). Ejaculates were obtained from five males by means of electro-ejaculation under halothane narcosis. The results of the zona-free hamster eggs (ZFHE) penetration test showed that the ejaculates of all the surgically treated coypu males were fertile and that ZFHE value fluctuated from 54 to 76.6%. The results obtained in experiments with natural mating revealed that the extirpation of male coypu seminal vesicles did not affect their fertility. In total 47 foetuses were found post mortem in ten coypu females covered by surgically treated males, which on average represented 4.7 foetuses per female. 相似文献
44.
45.
46.
W Petchpoo P Tan-ariya V Boonsaeng C R Brockelman P Wilairat S Panyim 《Veterinary parasitology》1992,42(3-4):189-198
A genomic library of Babesia bovis DNA from the Mexican strain M was constructed in plasmid pUN121 and cloned in Escherichia coli. Several recombinants which hybridized strongly to radioactively labeled B. bovis genomic DNA in an in situ screening were selected and further analyzed for those which specifically hybridized to B. bovis DNA. It was found that pMU-B1 had the highest sensitivity, detecting 25 pg of purified B. bovis DNA, and 300 parasites in 10 microliters of whole infected blood, or 0.00025% parasitemia. pMU-B1 contained a 6.0 kb B. bovis DNA insert which did not cross-hybridize to Babesia bigemina, Trypanosoma evansi, Plasmodium falciparum, Anaplasma marginale, Boophilus microplus and cow DNA. In the Southern blot analysis of genomic DNA, pMU-B1 could differentiate between two B. bovis geographic isolates, Mexican strain M and Thai isolate TS4. Thus, the pMU-B1 probe will be useful in the diagnosis of Babesia infection in cattle and ticks, and in the differentiation of B. bovis strains. 相似文献
47.
48.
Ariana M.P. Nap Yvonne W.E.A. Pollak Walter E. van den Brom Ad Rijnberk DVM PhD 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1994,8(4):302-303
Thyroidal 99m TcO4 (pertechnetate) uptake percentages were determined in unanesthetized euthyroid (n = 13) and hyperthyroid (n = 18) cats. Maximal uptakes were observed 60 minutes after IV injection of the radionuclide and ranged from 0.3 to 3.9% of the dose in euthyroid cats (median 2.23%) and from 5.2% to 23.9% of the dose in hyperthyroid cats (median 14.8%) ( P < .05). There were no overlaps in pertechnetate uptake percentages during any of the intervals evaluated. It is concluded that the optimal time for visualization of the thyroid by 99m TcO4 -scanning is 60 minutes after IV injection of the radionuclide. Calculation of the percentage uptake is of additional diagnostic value. 相似文献
49.
Changes in bone structure and conformation can occur very rapidly in growing animals. Injury to the bones or articular surfaces warrant special consideration because of the potential devastating consequences of secondary growth deformities in the animal. Disturbance of normal growth plate activity, imperfect fixation of an articular fracture, and conformational defects in long bones may create lifelong problems for the animal. 相似文献
50.
P Dom F Haesebrouck 《Zentralblatt für Veterin?rmedizin. Reihe B. Journal of veterinary medicine. Series B》1992,39(4):303-306
The virulence of a NAD-independent Actinobacillus pleuropneumoniae serotype 2 strain and NAD-dependent serotype 2, 3 and 9 strains was compared under experimental conditions. Hysterectomy-derived piglets were inoculated endobronchially with 50-500 cfu of these strains. All 23 piglets inoculated with the NAD-dependent strains developed acute disease within 12 hours post inoculation. Twenty-two of these piglets died within 24 hours after the first clinical signs. Three of nine piglets inoculated with the NAD-independent strain did not develop clinical disease. In the other six piglets, disease signs were similar as in the piglets inoculated with the NAD-dependent strains. No differences in clinical disease were observed between colostrum deprived piglets and piglets that obtained colostrum from a SPF sow. 相似文献