全文获取类型
收费全文 | 35483篇 |
免费 | 2053篇 |
国内免费 | 4110篇 |
专业分类
林业 | 3580篇 |
农学 | 5020篇 |
基础科学 | 3315篇 |
5860篇 | |
综合类 | 12009篇 |
农作物 | 2138篇 |
水产渔业 | 1098篇 |
畜牧兽医 | 5194篇 |
园艺 | 1363篇 |
植物保护 | 2069篇 |
出版年
2024年 | 147篇 |
2023年 | 540篇 |
2022年 | 1343篇 |
2021年 | 1693篇 |
2020年 | 1531篇 |
2019年 | 1516篇 |
2018年 | 1019篇 |
2017年 | 1502篇 |
2016年 | 1300篇 |
2015年 | 1796篇 |
2014年 | 1717篇 |
2013年 | 2099篇 |
2012年 | 2430篇 |
2011年 | 2651篇 |
2010年 | 2485篇 |
2009年 | 2132篇 |
2008年 | 2079篇 |
2007年 | 1927篇 |
2006年 | 1777篇 |
2005年 | 1511篇 |
2004年 | 809篇 |
2003年 | 715篇 |
2002年 | 721篇 |
2001年 | 792篇 |
2000年 | 706篇 |
1999年 | 693篇 |
1998年 | 632篇 |
1997年 | 503篇 |
1996年 | 472篇 |
1995年 | 428篇 |
1994年 | 352篇 |
1993年 | 310篇 |
1992年 | 299篇 |
1991年 | 290篇 |
1990年 | 203篇 |
1989年 | 154篇 |
1988年 | 131篇 |
1987年 | 86篇 |
1986年 | 39篇 |
1985年 | 22篇 |
1984年 | 21篇 |
1983年 | 15篇 |
1982年 | 18篇 |
1981年 | 18篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1963年 | 4篇 |
1962年 | 2篇 |
1956年 | 3篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
入世后我国甜樱桃面临的机遇与挑战及发展对策 总被引:5,自引:0,他引:5
甜樱桃作为一种早熟、优质、保健果品,而且种植效益较高,在国内国际都正处于发展时期。根据世界甜樱桃生产和贸易情况,指出了我国在甜樱桃科学技术与生产上与世界先进甜樱桃生产国的差距,分析了我国加入WTO之后,我国甜樱桃面临的机遇和挑战,并且机遇大于挑战。如果有适当的科技投入,我国甜樱桃产业将可克服现在科技滞后的状态,发挥我国劳动力低廉和国土辽阔的优势,迅速扩大其生产总量,提高品质,扩大出口,增加农民的收入,2015年可望形成32.4~43.2亿元的社会总产值。 相似文献
142.
AIM:To establish rat chronic obstructive pulmonary disease(COPD) models by passive cigarette smoking plus intratracheal instillation of lipopolysacchride(LPS) or passive cigarette smoking only, which would be similar to the pathogenesis of human COPD. METHODS:48 Wistar rats were randomly divided into 4 groups.(1) Healthy control I group(n=12), rats were bred 4 weeks;healthy control II group(n=12), rats were bred for 3months. (2) Model group I (n=12), 200μg lipopolysaccharide(LPS) was instilled intratracheally once for every two weeks and the rats were exposured to 5% of cigarette smoke, 0.5 h/d for 4 weeks.(3) Model group II(n=12),rats were exposed to 5% of cigarette smoke, 0.5 h/d for 3 months. The pathologic changes of airways and lung tissues, pulmonary function and blood gas analysis were determined. The airway wall lymphocytes and alveolar macrophages were counted. The cross areas of epithelial layer, smooth muscle layer and lamina propria of bronchi were measured. The hydroxyproline of lung tissue homogenates was determined by biochemistry method.RESULTS:The pathologic changes of airways and lung tissue of two models were similar to but milder than those of COPD patients(biopsy data). The collagen deposition and the cross areas of epithelial layer and smooth muscle layer in airway walls of two model groups were significantly increased than those of control groups(P<0.01,P<0.05).FEV0.3/FVC% of two model groups, PaO2 and SaO2 of model I group were significantly decreased, while Ri and Re in model I group were significantly increased than that of control I group(P<0.05). The PaCO2 and the counts of lymphocytes and alveolar macrophages of both model groups were significantly increased than those of the control groups (P<0.01). Lots of alveolar macrophages had phagocyted smoke granules. The amounts of hydroxyproline of two model groups were significantly increased than those of control group((P<0.05) and were negatively related to the FEV0.3/FVC%, respectively (P<0.01,P<0.01) and positively related to airway resistance of model I group(P<0.01). CONCLUSIONS:COPD rat models were successfully established by passive cigarette smoking plus intratracheal instillation of LPS and cigarette smoking only. The pathologic changes were similar but milder than those of COPD patients. The airway obstruction of model I group was more severe than that of model II group, but they have no significant difference. 相似文献
143.
AIM: To investigate the relationship between somatostatin and the pathologic type, estrogen receptor,DNA ploidy of nuclei in tumor cells of breast cancer.METHODS: 67 cases of primary breast cancer and 25 cases of benign breast tumor were examined by immunohistochemical stretomyces avidin peroxidase method. 26 cases of breast cancer selected at random were analyzed by flow cytometry.RESULTS: Somatostatin expressed significantly higher in low malignant breast cancer than that in high malignant breast cancer (P<0.05). Most of cancers with positive staining of somatostatin were diploidy,most of cancers with negative staining were aneuploidy,there had significant difference between two groups (P<0.05).CONCLUSION: Somatostatin may delay the progress of breast cancer,and somatostatin levels in cancer tissues may become a useful indicator for assessing prognosis of patients with breast cancer. 相似文献
144.
145.
146.
147.
148.
灰葡萄孢菌nit突变体的诱导及其在营养体亲和性测定中的应用初探 总被引:5,自引:1,他引:5
从山西运城、临汾、长治、晋中、大同等地保护地黄瓜灰霉病病株上采集、分离的分属于3个不同菌丝融合群的8个灰葡萄孢菌单孢菌株,经氯酸盐诱导处理,共获得了抗氯酸盐的硝酸盐利用缺陷突变体(nit突变体)59株,其中nit1型38株,nit3型10株,nitM型11株。所有nit突变株分别在PDA斜面转管培养3次(21 d)后,除6株恢复成野生菌株外,其余多数nit突变菌株表现稳定。来源于同一野生菌株的不同类型nit突变体间或同一菌丝融合群不同野生菌株的nit突变体间可产生互补反应而形成异核体,其中以nitM型突变株互补性最好,在利用nit突变体测定灰葡萄孢菌营养体亲和性时应作为标准菌株。来源于不同菌丝融合群的nit突变体间不能产生互补反应。 相似文献
149.
150.