全文获取类型
收费全文 | 231832篇 |
免费 | 14081篇 |
国内免费 | 655篇 |
专业分类
林业 | 23135篇 |
农学 | 13903篇 |
基础科学 | 2934篇 |
41402篇 | |
综合类 | 17424篇 |
农作物 | 17103篇 |
水产渔业 | 16247篇 |
畜牧兽医 | 85169篇 |
园艺 | 6233篇 |
植物保护 | 23018篇 |
出版年
2021年 | 2442篇 |
2020年 | 2844篇 |
2019年 | 3631篇 |
2018年 | 3851篇 |
2017年 | 4199篇 |
2016年 | 4661篇 |
2015年 | 4233篇 |
2014年 | 5580篇 |
2013年 | 16138篇 |
2012年 | 5548篇 |
2011年 | 7321篇 |
2010年 | 7055篇 |
2009年 | 7697篇 |
2008年 | 6743篇 |
2007年 | 5738篇 |
2006年 | 6439篇 |
2005年 | 5671篇 |
2004年 | 5588篇 |
2003年 | 5353篇 |
2002年 | 4669篇 |
2001年 | 5409篇 |
2000年 | 5173篇 |
1999年 | 4944篇 |
1998年 | 4072篇 |
1997年 | 4119篇 |
1996年 | 3861篇 |
1995年 | 4410篇 |
1994年 | 3783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 15 毫秒
231.
The rice( Oryza L. ) variety, Lijiangxintuanheigu(LTH), is a universally susceptible variety. A set of near-isogenic lines (NILs) of rice which has single resistance gene for each line was developed by use of LTH as recurrent parent and Kusabue,Tsuyuake, K1, PiNo. 4, K60 and BL1, which are from Kiyosawa‘s differential varieties(KDV), as donor parents. Differentiating ability of these NILs to Philippine isolates was compared with that of their donor parents, KDV and IRRI‘ s NILs. The results of comparative studies were as follows: (1) Differentiating ability of Chinese NILs to Philippine isolates was much stronger than that of their donor parents and that of KDV. (2) Chinese NILs had similar ability to differentiate races to IRRI‘s NILs or higher differentiating ability than them. But IRRI‘s NILs almost had no differentiating ability to isolates from japonica rice-growing regions. They can not be used to differentiate races of isolates from japonica ricegrowing regions. Whereas, Chinese NILs can be used to differentiate races of isolates from both japonica ricegrowing regions and indica rice-growing regions. It was concluded that the set of Chinese NILs can be used as international differentials. 相似文献
232.
L. G. Paisley L. Vraa-Andersen L. Dybkjr K. Mller G. Christensen J. Mousing J. F. Agger 《Acta veterinaria Scandinavica》1993,34(4):319
A total of 578 slaughter pigs from 2 Danish conventional farrow-to-finish operations (Herds A and B) were followed from an age of 14 days to slaughter. Pigs were weighed at 3 weeks intervals and at slaughter and an extended post mortem examination of the plucks was done. Comparison of growth rates in pigs with and without specific types of lesions by the t-test and those with multiple lesions with regression models demonstrated that Mycoplasma-like pneumonia, complicated pneumonia, anterio-ventral pleuritis, fissures and atrophic rhinitis significantly reduced mean daily gain and increased the time required to reach slaughter weight. The total impact of the lesions in Herd A was an estimated reduction in mean daily gain of 27 grams and a 2 day increase in the interval from 14 days of age until slaughter (MDG14). Decreases in MDG14 in Herd B were more substantial, 98 grams and 16.7 days. Reductions in mean daily gains during the interval from the fourth weighing until slaughter were 31 grams in Herd A and 137 grams in Herd B. Chronic dorso-caudal and parietal pleuritis, without other lesions present, had no significant adverse effects on growth rates in either herd. Interactions between lesions did not significantly alter the estimates. The R2 values obtained for the regression models showed that the presence, absence or extent of lesions at slaughter explained only 13-27% of the variations in growth rates in the 2 herds. 相似文献
233.
A combined ultracentrifugationl/precipitation method for the measurement of lipoprotein cholesterol concentrations was developed and validated for use with canine plasma. Very low density lipoproteins (VLDL) were isolated by flotation ultracentrifugation and low density lipoproteins (LDL) separated from high density lipoproteins (HDL) by precipitation with heparin-manganese chloride. Effective separation of these classes was confirmed by agarose gel electrophoresis of native lipoproteins and by sodium dodecyl sulphate polyacrylamide gel electrophoresis of their apolipoprotein distributions. There was trace contamination of the LDL precipitate with HDL, but this represented less than 4 and 9 per cent of the total plasma HDL in normo- and hypercholesterolaemic dogs, respectively. The intra-assay and interassay coefficients of variation for LDL- and HDL-cholesterol concentrations were between 3·3 and 6·9 per cent, and 7·2 and 9·0 per cent, respectively, for plasma cholesterol concentrations between 2·67 and 8·14 mmoll/litre. The intra-assay coefficient of variation for VLDL-cholesterol was 53·8 and 18·4 per cent at plasma cholesterol concentrations of 2·67 and 8·14 mmol/litre, respectively. The interassay coefficient of variation for VLDL was 22·5 per cent. Storage of plasma at -20°C for between two and eight weeks did not affect VLDL-cholesterol concentrations, but led to an increase in LDL-cholesterol and a decrease in HDL-cholesterol concentrations of approximately 10 per cent. The method described is appropriate for the measurement of lipoprotein concentrations in plasma from normo- and hypercholesterolaemic dogs, but samples should not be subjected to prolonged storage before analysis. 相似文献
234.
Intradermal testing is a common diagnostic procedure used in the evaluation of dogs with suspected atopic dermatitis (AD). To do this, most investigators assess the appearance of wheals that develop at the sites of intradermal allergen injections. However, wheals are rarely seen in dogs with naturally occurring AD. Furthermore, infiltration of inflammatory cells into the injection sites can occur 6-24h later, a phenomenon known as the late-phase reaction. The histological appearance of these late-phase reactions closely approximates that seen in the natural disease, suggesting that they might be more relevant than the immediate reactions. In this paper, we review the literature on immediate and late-phase reactions and re-assess the evidence for using current intradermal testing procedures as a diagnostic test in dogs. 相似文献
235.
Application of Airway Pressure Therapy in Veterinary Critical Care: Part II: Airway Pressure Therapy
Deborah R. Van Pelt DVM MS Wayne E. Wingfield MS DVM Timothy B. Hackett DVM Linda G. Martin DVM 《Journal of Veterinary Emergency and Critical Care》1993,3(2):71-81
As the specialties of emergency medicine and critical care have grown and evolved in both human and veterinary medicine, so has the need for more advanced care of patients with primary lung disease. Treatment of acute respiratory failure has been the focus of several articles in the human medical literature of the past few years.1,8 This paper deals with airway pressure therapy and its application in cases of acute respiratory failure in veterinary medicine. The reader is referred to part I of this paper for a reveiw of respiratory mechanics and hypoxemia as they apply to respiratory therapy. 相似文献
236.
237.
238.
Abstract— An objective method for measuring corneocyte numbers before and after antiseborrheic shampoo therapy was assessed in dogs. Corneocytes were collected from six skin regions on the dorsal trunk of nine colony-raised beagles with clinically normal skin. Forty-eight collection sites were randomly assigned a treatment with one of seven medicated shampoos or water alone; six additional sites served as non-treated controls. Corneocytes were collected immediately before the first treatment, and 14 and 28 days after initiation of therapy with a 0.1% Tween 80 surfactant and a quantitative cup-scrub technique. Pretreatment corneocyte counts were not significantly different among the nine dogs nor among the randomly assigned treatment and control sites (3.55 · 104 cells.cm-2 , SEM 0.17). Corneocyte counts increased in all treatment and control sites from days 0 to 14. Corneocyte counts were similar in the non-treated and water-treated sites from days 14 to 28. Corneocyte counts were not significantly different when the same treatments were compared on days 0, 14 and 28, or when different treatments were compared on the same day. The corneocyte collection technique used in this study proved to be a reliable method for assessing the rate of cell desquamation and cell surface cohesion in dogs. 相似文献
239.
Abstract. Changes in chemical and physical properties and erodibility of a vertisol were studied in relation to land use. The vertisol, which occurs extensively in the semi-arid south-east of Zimbabwe, is derived from basalt and has a self mulching surface layer. Irrigated crops show static yields despite introduction of improved varieties. Four uncultivated sites were selected as controls and compared with five irrigated and four dryland sites. Surface soils were analysed for a range of chemical and physical properties, and laboratory rainfall simulation was used to measure soil erodibility under high intensity rain. The irrigated soils had greater exchangeable sodium and available phosphorus than the uncultivated soils. In contrast, dryland soils showed no such changes apart from a decrease in the amount of small water-stable aggregates. The soils are very erodible under high intensity rain but no significant differences were found between sites. We conclude that, although soil chemical changes have taken place in the irrigated soils, significant soil degradation has not occurred at the sites examined. The static yields probably result from management problems. However, immediate measures should be taken to improve drainage and irrigation management in the irrigated soils to avoid further sodium increases. 相似文献
240.
Sandy‐textured Mediterranean soils are invariably depleted in organic matter and supply only small amounts of N to crops. To compensate for these deficiencies, we tested the N supply from six organic wastes applied to a Cambic Arenosol in pots growing ryegrass. The results showed that the behaviour of the wastes in supplying N to a ryegrass crop grown in this soil can be predicted by observing their performance in laboratory aerobic incubations. The N made available during these incubations fitted well to a one‐pool kinetic model. 相似文献