全文获取类型
收费全文 | 231608篇 |
免费 | 13829篇 |
国内免费 | 655篇 |
专业分类
林业 | 23103篇 |
农学 | 13884篇 |
基础科学 | 2933篇 |
41300篇 | |
综合类 | 17401篇 |
农作物 | 17080篇 |
水产渔业 | 16200篇 |
畜牧兽医 | 84995篇 |
园艺 | 6225篇 |
植物保护 | 22971篇 |
出版年
2021年 | 2417篇 |
2020年 | 2812篇 |
2019年 | 3609篇 |
2018年 | 3816篇 |
2017年 | 4167篇 |
2016年 | 4635篇 |
2015年 | 4219篇 |
2014年 | 5558篇 |
2013年 | 16107篇 |
2012年 | 5511篇 |
2011年 | 7277篇 |
2010年 | 7046篇 |
2009年 | 7686篇 |
2008年 | 6726篇 |
2007年 | 5719篇 |
2006年 | 6424篇 |
2005年 | 5660篇 |
2004年 | 5580篇 |
2003年 | 5341篇 |
2002年 | 4654篇 |
2001年 | 5405篇 |
2000年 | 5171篇 |
1999年 | 4943篇 |
1998年 | 4070篇 |
1997年 | 4119篇 |
1996年 | 3861篇 |
1995年 | 4409篇 |
1994年 | 3782篇 |
1993年 | 3472篇 |
1992年 | 3904篇 |
1991年 | 4094篇 |
1990年 | 3765篇 |
1989年 | 3660篇 |
1988年 | 3268篇 |
1987年 | 3362篇 |
1986年 | 3181篇 |
1985年 | 3550篇 |
1984年 | 3380篇 |
1983年 | 3214篇 |
1982年 | 2701篇 |
1981年 | 2639篇 |
1980年 | 2619篇 |
1979年 | 2801篇 |
1978年 | 2589篇 |
1977年 | 2432篇 |
1976年 | 2282篇 |
1975年 | 2077篇 |
1974年 | 2159篇 |
1973年 | 2107篇 |
1972年 | 1843篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Rebecca Windsor Samuel Stewart Jessica Schmidt Mario Mosqueda Ignazio Piras Stefan M. Keller Briana Steinmetz Dori L. Borjesson Matthew Huentelman Chand Khanna 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2022,36(4):1382
BackgroundNecrotizing meningoencephalitis (NME) in the pug dogs is a fatal neuroinflammatory disease associated with rapid progression and poor response to conventional immunosuppressive therapy. Diagnosis is typically made after severe neurological abnormalities have manifested.Hypothesis/ObjectivePug dogs at genetic risk for NME might manifest neurological abnormalities before developing pathognomonic clinical signs of NME.AnimalsThirty‐six pug dogs less than 4 years of age asymptomatic for NME.MethodsProspective observational cohort study with germline genome‐wide genotyping. Neurological examinations were performed 4 weeks apart to document reproducible findings of central nervous system disease. Magnetic resonance imaging, cerebrospinal fluid analysis, and testing for infectious diseases were performed in all pugs with reproducible abnormalities detected on neurological examination.ResultsThe overall risk allele frequency in this cohort was 40%; 5 (14%) dogs were high risk, 19 (53%) dogs were medium risk, and 12 (33%) dogs were low genetic risk for NME. Reproducible abnormalities detected on neurological examination were identified in 8/24 (33%) genetically at‐risk dogs and 0/12 (0%) low risk dogs. Clinical abnormalities included multifocal spinal pain in 8/8, reduced menace response in 5/8, and lateralizing postural reaction deficits in 5/8 pugs. There was a strong association between genotype risk and the presence of this clinical phenotype (P = .03).Conclusions and Clinical ImportanceOur findings suggest the presence of a novel early clinical phenotype of NME in apparently asymptomatic genetically at‐risk pugs which might be used to plan early diagnostic and therapeutic clinical trials. 相似文献
992.
993.
Ken R. Ito Tomonori Sato Hiro Goto Katsuyoshi Sato Jun Watanabe Masaki Yokoo 《The Journal of Poultry Science》2022,59(3):247
Increasing food loss and waste (FLW) is a global problem, and efforts are being made to use waste food as potential livestock feed material. The amount of self-supplied feed is lower in Japan than in other countries, and the government recommends FLW use for animal feed. Sake (Japanese rice wine) is a traditional alcoholic beverage. During the sake manufacturing process, large amounts of squeezed solids or “lees” (sake lees) are generated. Sake lees are nutritious and functional, but are prone to spoilage. In this study, we investigated whether sake lees should be mixed with animal feed immediately or after drying. To assess the usefulness of sake lees as a poultry feed ingredient and determine the effect of sake lees on intestinal immunity, we performed a feeding trial with three treatments: a raw sake lees (RSL) diet, dried sake lees (DSL) diet, and control diet. Three-week-old broilers were fed these diets (n=8 per group) for two weeks. We then calculated feed efficiency and performed RT-qPCR to assess the effects of diet on intestinal immunity. The growth performance in the RSL diet group was equivalent to that in the control diet group. The DSL diet became difficult for broilers to eat, resulting in decreased growth performance. In the ileum of RSL-diet broilers, the mRNA expression levels of TGF-β1 and avian β-defensin (AvBD)12 were significantly increased compared to those of control diet broilers (p<0.05), and a significant correlation was observed between the two genes (p<0.05). Our results indicated that sake lees should not be dried and should be mixed immediately with feed, and this sake lees when fed to chicken activates the intestinal immunity. However, sake lees have a lower fat content than corn, and it is thus important to combine sake lees with high-energy feed. 相似文献
994.
995.
Landscape Ecology and Species Conservation 总被引:6,自引:0,他引:6
996.
An aggregation index (AI) to quantify spatial patterns of landscapes 总被引:43,自引:0,他引:43
There is often need to measure aggregation levels of spatial patterns within a single map class in landscape ecological studies. The contagion index (CI), shape index (SI), and probability of adjacency of the same class (Qi), all have certain limits when measuring aggregation of spatial patterns. We have developed an aggregation index (AI) that is class specific and independent of landscape composition. AI assumes that a class with the highest level of aggregation (AI =1) is comprised of pixels sharing the most possible edges. A class whose pixels share no edges (completely disaggregated) has the lowest level of aggregation (AI =0). AI is similar to SI and Qi, but it calculates aggregation more precisely than the latter two. We have evaluated the performance of AI under varied levels of (1) aggregation, (2) number of patches, (3) spatial resolutions, and (4) real species distribution maps at various spatial scales. AI was able to produce reasonable results under all these circumstances. Since it is class specific, it is more precise than CI, which measures overall landscape aggregation. Thus, AI provides a quantitative basis to correlate the spatial pattern of a class with a specific process. Since AI is a ratio variable, map units do not affect the calculation. It can be compared between classes from the same or different landscapes, or even the same classes from the same landscape under different resolutions. 相似文献
997.
David L. Kaplan Roy Hartenstein Edward F. Neuhauser Michael R. Malecki 《Soil biology & biochemistry》1980,12(4):347-352
Survival and/or growth were used to assess optimum and potentially deleterious physico-chemical conditions in the environment of the earthworm Eisenia foetida. Maximum weight was gained between 20 and 29°C with horse manure or activated sludge as food. Maximum weight gain as a function of moisture in activated sludge occurred between 70 and 85%. All worms died within a week at pH values <5 or >9; optimum pH for gain in weight centered around 7.0 Soluble salts in excess of 0.5% were lethal, though ammonium acetate caused 100% mortality at a concentration of 0.1%; concentrations in manures contaminated by urine or cattle slurry may be lethal, while those present in noncontaminated manure, with an electrolytic conductivity of 1.5–3mmhos, support weight gain. Inorganic chemicals that are commonly used to coagulate sludges, often as a preliminary to land application, were innocuous at concentrations higher than those normally used at wastewater treatment plants. Anaerobically digested sludges are toxic to earthworms, and are characterized by low oxidation-reduction potentials; when placed upon a soil substrate the redox potential increases slowly, and though the sludge tested in this study was nontoxic at Eh values in excess of 250 mV, it provided insufficient nutriment to E. foetida to allow weight gain. With activated sludge as food, growth of E. foetida occurred more rapidly when soil was present, independently of whether it was placed as a substrate beneath the sludge or mixed into the sludge. Growth occurred more rapidly when activated sludge was placed on substrates which allowed drainage, though loam or ashed loam appeared superior to others, such as glass beads or sand; the growth promoting factor is related to the inorganic fraction of the soil. 相似文献
998.
J.E. Satchell 《Soil biology & biochemistry》1980,12(4):303-310
A long-term experiment set up by G. W. Dimbleby to test the effect of birch as a soil improver on a heather moor podzol is described. After 30 yr, an acid woodland type of vegetation developed under the birch trees with Deschampsia flexuosa and Vaccinium myrtillus locally dominant. The mean annual dry matter production of stems and branches was approximately 2.9 t ha?1. The raw humus layer removed as an experimental treatment had re-formed. Its pH, about 3.4, had remained unchanged for 15 yr. The mean extractable Ca content of the upper 3 cm horizon of the birch plots and of the control plots under heather had increased and on some of the birch plots the concentrations of exchangeable Ca were somewhat higher than those under heather. The N content of the Ol + Of, Oh and Ea horizons was higher under the birch than under heather but there was no evidence of movement of Fe out of the ironpan under the influence of birch. The profile under birch remained a fully differentiated podzol. 相似文献
999.
1000.
A 20 s exposure to 2450 MHz microwave radiation had a marked differential effect on the viable count of soil micro-organisms, had little influence on numbers of heterotrophic bacteria, but reduced fungal colonies on dilution plates to zero. The growth of fungi from soil particles was also reduced following treatment. Prolonging the exposure to microwave radiation progressively inhibited nitrification and S-oxidation, but stimulated ammonification. Brief exposures (20s) also stimulated S-oxidation and increased the numbers of thiobacilli in soil. Most of these effects are explained by reference to the marked increase in soil temperature resulting from microwave treatment. 相似文献