全文获取类型
收费全文 | 847篇 |
免费 | 57篇 |
国内免费 | 38篇 |
专业分类
林业 | 28篇 |
农学 | 85篇 |
基础科学 | 166篇 |
48篇 | |
综合类 | 218篇 |
农作物 | 20篇 |
水产渔业 | 62篇 |
畜牧兽医 | 236篇 |
园艺 | 69篇 |
植物保护 | 10篇 |
出版年
2024年 | 5篇 |
2023年 | 11篇 |
2022年 | 13篇 |
2021年 | 22篇 |
2020年 | 27篇 |
2019年 | 24篇 |
2018年 | 12篇 |
2017年 | 33篇 |
2016年 | 29篇 |
2015年 | 49篇 |
2014年 | 51篇 |
2013年 | 47篇 |
2012年 | 56篇 |
2011年 | 54篇 |
2010年 | 38篇 |
2009年 | 72篇 |
2008年 | 43篇 |
2007年 | 56篇 |
2006年 | 53篇 |
2005年 | 36篇 |
2004年 | 24篇 |
2003年 | 31篇 |
2002年 | 33篇 |
2001年 | 20篇 |
2000年 | 22篇 |
1999年 | 20篇 |
1998年 | 10篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 11篇 |
1994年 | 7篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有942条查询结果,搜索用时 15 毫秒
1.
以单猪屎豆碱(MO)、槲皮素(QU)和环磷酰胺(CY)为参照,观察了狗舌草600mL/L乙醇提取物(EX)对淋巴细胞性白血病L1210细胞体外试验的形态变化;利用流式细胞术,从DNA分子水平上检查了EX对L1210细胞各周期相的影响,探讨EX对L1210细胞的分化机理。结果发现,EX能够使L1210细胞向淋巴细胞方向发展;经EX作用24h后,L1210细胞G0+G1期的百分比较对照组明显升高。提示EX对L1210细胞增殖的抑制作用可能是由于G1期的阻滞所致。 相似文献
2.
AIM: To study the effect of cocaine on caspase-3 in myocardiac cells of male rats in different age. METHODS: Three-week-old(n=16), six-week-old(n=16) and twelve-week-old (n=16) male Sprague-Dawley rats were all divided into control groups and experiment groups randomly, each group had eight animals, experiment groups were given cocaine hydrochloride (15 mg·kg-1 body weight) subcutaneously daily for four weeks. The ratio of heart weight to body weight (HW/BW, mg/g) were measured. DNA fragmentation of myocardia cells was determined by gel electrophoresis, and caspase-3 activity in myocardia cells was tested by flow cytometry (FCM). RESULTS: In three experiment groups, the DNA isolated from myocardial cells displayed clear ladder pattern. The HW/BW and the caspase-3 activity were increased significantly than those of control groups (P<0.01). CONCLUSIONS: Cocaine induced apoptosis in rat myocardial cells. The increase in caspase-3 activity may be the one of important pathways related to the induction of apoptosis. 相似文献
3.
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
4.
AIM:To investigate the expression of Th1-typed cytokine IFN-γ and Th2-typed cytokine IL-4 on T lymphocytes that infiltrate in nasal polyps for searching the pathogenesis of nasal polyps. METHODS:Nasal polyps tissue samples and peripheral blood were obtained from 21 patients. Normal human inferior turbinate mucosa and peripheral blood were obtained as well. Flow cytometry was adopted to detect the expression of IFN-γ and IL-4 of T lymphocytes. RESULTS: Th cytokines were rarely detected in inferior turbinate from normal human. Nasal polyps tissue consisted of abundant T lymphocytes. The expression of IL-4 and IFN-γ increased in peripheral blood from patients compared with normal human (P<0.05). The expression of IL-4 increased but the expression of IFN-γ decreased in nasal polyps compared with that of peripheral blood from the same patient (P<0.05). CONCLUSION:There were generous of T lymphocytes infiltrating in nasal polyps. There was abnormal immune status in the local nasal mucosa from the patients, and the predomination of Th cytokine secretion changed compared with peripheral blood from the same patients, which resulted in the change of microenvironment of nasal mucosa and possibly close related to the formation of nasal polyps. 相似文献
5.
6.
AIM:To investigate expression and function of CD40 ligand by peripheral blood mononuclear cells (PBMCs) in patients with systemic lupus erythematosus (SLE).METHODS:Expression of CD40 ligand by PBMCs in patients with SLE and control were examined by flow cytometric analysis before and after stimulated by phytohemagglutinin(PHA)and depressed by Dexamethasone(Dex). The correlation between expression of CD40 ligand and SLE activity index(SLEDAI) was analysed in patients with SLE.RESULTS:The expression of CD40 ligand by PBMCs in patients with active SLE was higher than that in patients with inactive SLE and control. Though the expression of CD40 ligang by PBMCs could be stimulated by PHA in three groups, it was the highest in patients with active SLE. Dex depressed the expression of CD40 ligand by PBMCs significantly in patients with SLE, but not in control. There was high positive correlation between expression of CD40 ligand and SLEDAI in patients with active and inactive SLE.CONCLUSION:Increased expression of CD40L by PBMCs in patients with SLE may play an important role in pathogenesis of SLE. 相似文献
7.
以收集的16份茉莉花资源及50份实生种质为材料,以玉米B73为内参,采用流式细胞术估测茉莉花基因组大小,并以二倍体品种为对照,计算茉莉花染色体倍性。结果表明:内参与待测样品峰值能完全分开,无重叠峰,峰型清晰集中,可对茉莉花基因组大小进行有效估测;供试材料中有56份二倍体,基因组大小为0.54~0.63 Gb,有7份三倍体,基因组大小为0.79~0.96 Gb,有3份四倍体,基因组大小为1.04~1.12 Gb;从收集的资源中鉴定出二倍体和三倍体,未见四倍体,而从实生种质中鉴定出3个四倍体、2个三倍体,表明实生选种是茉莉花种质创新的一条有效途径;在已明确花冠类型的材料中,三倍体及四倍体均为单瓣型茉莉。该研究结果为茉莉花倍性育种及实生选种提供科学依据。 相似文献
8.
通过对工厂化循环水养殖进水流速的智能调控,可降低饵料残留,避免水质恶化。为此,本研究采用数值模拟方法探究了进水流速对工厂化循环水养殖池流场特性的影响,并基于该研究设计出一套确定进水流速调控的实验方法。首先,通过对比Standard k-ε、RNG k-ε和Realizable k-ε 3种湍流模型及多种壁面函数的仿真效果,确定RNG k-ε模型和标准壁面函数作为仿真配置。同时,针对多相流模型,对欧拉多相流模型和DPM离散相模型进行对比,为提高计算准确性选用DPM离散相模型,并基于上述模型进行网格无关性验证、制定网格划分方案。其次,以大菱鲆(Scophthalmus maximus)养殖为例,模拟不同进水流速下养殖池流场、排污和水温调节的效果。最后,针对仿真结果提出进水流速调控方案。结果显示,日常采用1.0 m/s的进水流速,可有效提高适宜流速区面积并控制水处理成本;投饵前,采用0.2 m/s的进水流速可以解决循环水养殖中存在的饵料浪费问题;进食结束后,采用1.2 m/s的进水流速可快速排出残饵避免水质恶化;水温异常时,采用15 ℃的水、以1.2 m/s的进水流速注水230 s,可使20 ℃的水下降到正常水平,精准化控制水温。采用本研究提出的方法,可针对不同养殖生物和养殖环境设计进水流速智能调控策略,可用于解决循环水养殖过程中饵料浪费、水质变差和水温异常等问题。 相似文献
9.
基于流式细胞术(FCM)研究体系,构建能快速、准确鉴定桦木属植物倍性和测定DNA含量的研究体系,是测定不同桦木属植物倍性与基因组大小的有效方法。使用流式细胞术检测7种桦树属类物种,以物种不同生长状态(嫩叶、幼叶、成熟叶)为实验材料,不同存储方式(常温、冷藏和聚乙烯吡咯烷酮保存PVP)进行实验处理,对9种常用的裂解液进行筛选与优化。结果表明:桦木属植物DNA含量测定中,新鲜幼叶以1% PVP浸泡常温保存,并使用MgSO4裂解液制备细胞核悬浮液上机效果最佳;桦木属植物中,基因组倍性依次为黑桦((2.09 ± 0.04) Gb,8倍体) > 坚桦((1.53 ± 0.08) Gb,6倍体) > 光皮桦((0.87 ± 0.05) Gb,4倍体)=岳桦((0.80 ± 0.07) Gb,4倍体) > 垂枝桦((0.46 ± 0.03) Gb,2倍体)=河桦((0.51 ± 0.01) Gb,2倍体)。因此,桦木属植物DNA倍性和DNA含量可以通过FCM研究体系进行测定,且3倍体((0.66 ± 0.02) Gb)子代的鉴定结果表明光皮桦与河桦之间不存在生殖隔离。 相似文献
10.
DEAE-Sepharose Fast Flow分离纯化刺芹侧耳木质素降解酶 总被引:1,自引:0,他引:1
[目的]为Pleurotus eryngii—Co60-7木质素降解酶的分离纯化和综合利用提供试验依据。[方法]采用DEAE—Sepharose^TM Fast Flow离子交换介质,分别考察缓冲液pH值、流速和洗脱方式等对刺芹侧耳木质素降解酶分离纯化的影响,确定了最佳分离纯化层析条件。[结果]DEAE-Sephalose^TM Fast Flow分离纯化Pleurotus eryngii-Co60-7木质素降解酶的最佳层析条件为:选择20mmol/L,pH值为5.0醋酸钠一醋酸缓冲体系,3ml/min的流速,进行分步洗脱(100、200~300和1000mmoL/L NaCl的三步洗脱),可较好地实现刺芹侧耳发酵液木质素降解酶初分,该纯化操作目标蛋白回收率达85%,纯化分离因素为2.71。[结论]该技术在分离纯化刺芹侧耳木质素降解酶上可行,具有潜在的工业应用价值。 相似文献