全文获取类型
收费全文 | 108017篇 |
免费 | 6044篇 |
国内免费 | 2812篇 |
专业分类
林业 | 5905篇 |
农学 | 6100篇 |
基础科学 | 2620篇 |
13446篇 | |
综合类 | 22130篇 |
农作物 | 4544篇 |
水产渔业 | 4949篇 |
畜牧兽医 | 48722篇 |
园艺 | 1789篇 |
植物保护 | 6668篇 |
出版年
2021年 | 1419篇 |
2020年 | 1386篇 |
2019年 | 1502篇 |
2018年 | 1624篇 |
2017年 | 2081篇 |
2016年 | 1879篇 |
2015年 | 1988篇 |
2014年 | 2271篇 |
2013年 | 4416篇 |
2012年 | 3693篇 |
2011年 | 4359篇 |
2010年 | 3335篇 |
2009年 | 3253篇 |
2008年 | 3983篇 |
2007年 | 3731篇 |
2006年 | 3787篇 |
2005年 | 3346篇 |
2004年 | 2660篇 |
2003年 | 2580篇 |
2002年 | 2430篇 |
2001年 | 3141篇 |
2000年 | 3328篇 |
1999年 | 2764篇 |
1998年 | 1422篇 |
1997年 | 1323篇 |
1996年 | 1236篇 |
1995年 | 1438篇 |
1994年 | 1304篇 |
1993年 | 1220篇 |
1992年 | 2239篇 |
1991年 | 2341篇 |
1990年 | 2150篇 |
1989年 | 2119篇 |
1988年 | 1976篇 |
1987年 | 2025篇 |
1986年 | 2032篇 |
1985年 | 1894篇 |
1984年 | 1499篇 |
1983年 | 1326篇 |
1979年 | 1370篇 |
1978年 | 1122篇 |
1977年 | 973篇 |
1976年 | 937篇 |
1975年 | 983篇 |
1974年 | 1272篇 |
1973年 | 1298篇 |
1972年 | 1234篇 |
1971年 | 1147篇 |
1970年 | 1087篇 |
1969年 | 964篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
21.
为了获得简单、易操作、准确度高的橡胶园酸性、中性土壤交换性钙、镁测定方法,本试验通过响应面优化试验,建立称样量、提取液体积、提取方式与交换性钙测定结果之间的数学模型。结果表明:在25℃条件下,以1 mol/L的乙酸铵为土壤浸提液,称样量为2 g、提取液体积175 mL、振荡36 min,为橡胶园酸性、中性土壤的最佳提取条件。将上述条件下得到的结果与标准方法条件下得到的结果相对比,两结果的相对误差在1.25~3.04之间,均属合理范围。利用标准样品对优化方法进行试验验证,结果与推荐值相符。改进后的方法分析成本低、操作简便、测定结果准确、稳定性好,可用于橡胶园酸性、中性土壤交换性钙、镁的测定。 相似文献
22.
23.
Zidi Jin Long Liu Cheng Xu Chunchi Yan Shuo Li Tuoyu Geng Daoqing Gong 《Animal Science Journal》2021,92(1):e13672
Goose fatty liver is a specific type of nonalcoholic fatty liver that is protected from harmful effects associated with severe steatosis. Our previous findings suggest that suppression of the complement C5 may be relevant, but the mechanism is unclear. Therefore, in this study, we first verified the expression pattern of complement genes (including C5) during goose fatty liver formation and then determined the liver fat content and fatty acid composition by high-performance liquid chromatography (HPLC), followed by selecting the differential metabolites to treat HepG2, goose and mouse primary hepatocytes, aiming to explore the mechanism of C5 and inflammation suppression in goose fatty liver. The data confirmed the suppression of complement genes (including C5) in goose fatty livers. Moreover, fat content was significantly higher in fatty liver versus normal ones, with oleic acid and palmitic acid dominantly accounting for the difference. In line with this, high concentration of palmitate led to down regulation of C5 expression in goose primary hepatocytes whereas upregulation in mouse primary hepatocytes and HepG2 cells. In conclusion, regulation on C5 expression by fatty liver related factors including high level of palmitic acid may contribute to the protection of goose liver from severe hepatic steatosis. 相似文献
24.
Improving green development efficiency is urgently required, yet challenging, since it comprehensively reflects the bidirectional evolutionary relationship between regional development and resource and environmental consumption. The issue of regional green development efficiency has become a key topic; however, where the increase in efficiency originates and its spatial spillover effect remains unclear to date. Therefore, the spatial spillover effect of the green development efficiency of Shandong Province was quantified through the slack variable (SBM)-Undesirable and Spatial Durbin model. The green development efficiency showed clear spatial differentiation in Shandong Province. This was more obvious than the polarized development trend of the provincial capital circle that has Jinan at its core and the eastern coastal region with Qingdao at its core. Green development efficiency has a significant spatial spillover effect. The regression coefficient of the direct effect of the economic development level is positive. The regression coefficient of the indirect effect of the marketization level and government financial support level is negative. Science and technology played a positive role in the promotion of the green development efficiency of local and neighboring cities. This study contributes empirical evidence to the green development efficiency associated with regional development and resource and environment consumption of Shandong Province. 相似文献
25.
王旭 《农业图书情报学刊》2018,30(9):46-50
在一带一路基本国策的指导下,中国将重点建设海洋学科,为把中国建设成为海洋强国而努力。在这种背景下,文中梳理了全球知名的海洋学研究机构,并对各国海洋学机构进行分析和研究。为中国海洋学机构向全球知名海洋学机构学习,并与全球知名海洋学机构进行交流合作提供依据。 相似文献
26.
27.
Epidermal growth factor (EGF)-like activity was measured in mares' colostrum and milk by radioreceptor assay. Milk samples were collected from 22 mares 1 or more times during early lactation. Samples of colostrum were taken after parturition and before the foal first suckled (presuckle), within 6 hours after the foal first suckled (postsuckle), and on days 1, 2, 4, and 8 of lactation. In the 5 mares from which milk samples were obtained at each sampling time, presuckle colostral mean EGF-like activity (17.8 ng/ml) was greatest (P less than 0.05). The mean values for EGF-like activity at all other sampling times were not significantly different from each other (postsuckle colostrum, 9.7 ng/ml; day 1, 9.6 ng/ml; day 2, 8.5 ng/ml; day 4, 8.0 ng/ml; day 8, 7.8 ng/ml). 相似文献
28.
K A Hahn D W Knapp R C Richardson C L Matlock 《Journal of the American Veterinary Medical Association》1992,200(3):355-357
In 11 dogs with nasal adenocarcinoma, IV treatment with 2 to 8 cycles of cisplatin at a dosage of 60 mg/m2 of body surface, given at 3-week intervals, resulted in a survival time of 8 to 128 weeks (mean, 32.7 weeks; median, 20 weeks). Radiography revealed complete remission in 2 dogs and partial remission in 1 dog, for an overall response rate of 27%. Clinical problems such as nasal discharge (n = 11), sneezing (n = 6), and epistaxis (n = 4) resolved in 1 to 2 weeks in all dogs after beginning chemotherapy. 相似文献
29.
Historical and physical signs associated with prostatic disease diagnosed in dogs over a 5.5-year period were defined. One hundred seventy-seven male dogs were determined to have prostatic abnormality. Of the 177 dogs, 87 were determined to have specific prostatic disease. The most common prostatic disease identified in this study was bacterial prostatitis, followed by prostatic cyst, prostatic adenocarcinoma, and benign hyperplasia. The most common prostatic disease identified in neutered dogs was prostatic adenocarcinoma. Mean age at onset of prostatic disease was 8.9 years; statistically significant difference was not observed between age at onset of the various types of prostatic disease identified. Doberman Pinscher was the most common breed with prostate disease. Twenty-nine percent of dogs with a specifically identifiable prostatic disease had signs of systemic illness, 41% had signs of lower urinary tract disease, 28% had signs of gastrointestinal tract abnormalities, and 13% had signs of locomotor difficulty. 相似文献
30.
The influence of extruded oilseeds on total tract digestibility and ruminal digestion in dairy cows was studied in three cows fed a hay-concentrate (60.5/39.5; 3.7% fatty acids in diet on DM basis) control diet (C) or the same diet supplemented with raw (R) or extruded (ER) rapeseeds (8.0% fatty acids in diet DM). The experimental design was a 3 x 3 Latin square design. Compared with diet C, diets containing rapeseed decreased ruminal OM digestibility (9.5%, P less than .10) and increased (P less than .05) the proportion of propionate in ruminal fluid VFA. Extrusion had no effect on DM and OM total tract digestibilities and increased (P less than .10) N digestion. Microbial N flow at the duodenum was calculated taking into account solid-adherent bacteria (SAB) and liquid-associated bacteria (LAB). Duodenal flows of total, SAB, and LAB of OM and N did not change with diet. Extrusion of the rapeseeds did not modify (P less than .10) the proportion of bacterial N at the duodenum and had no effect on crude fiber digestibility. This trial demonstrates that rapeseeds in hay-based diets can be fed at levels of up to 14% of the diet without adversely affecting crude fiber digestibility. 相似文献