全文获取类型
收费全文 | 38423篇 |
免费 | 2279篇 |
国内免费 | 4202篇 |
专业分类
林业 | 2760篇 |
农学 | 2836篇 |
基础科学 | 2346篇 |
4572篇 | |
综合类 | 17241篇 |
农作物 | 2535篇 |
水产渔业 | 1563篇 |
畜牧兽医 | 6419篇 |
园艺 | 2622篇 |
植物保护 | 2010篇 |
出版年
2024年 | 266篇 |
2023年 | 782篇 |
2022年 | 1894篇 |
2021年 | 1860篇 |
2020年 | 1707篇 |
2019年 | 1675篇 |
2018年 | 1192篇 |
2017年 | 1820篇 |
2016年 | 1353篇 |
2015年 | 1875篇 |
2014年 | 1997篇 |
2013年 | 2408篇 |
2012年 | 3190篇 |
2011年 | 3416篇 |
2010年 | 3043篇 |
2009年 | 2584篇 |
2008年 | 2674篇 |
2007年 | 2392篇 |
2006年 | 2017篇 |
2005年 | 1569篇 |
2004年 | 923篇 |
2003年 | 654篇 |
2002年 | 756篇 |
2001年 | 651篇 |
2000年 | 612篇 |
1999年 | 336篇 |
1998年 | 164篇 |
1997年 | 132篇 |
1996年 | 123篇 |
1995年 | 118篇 |
1994年 | 134篇 |
1993年 | 107篇 |
1992年 | 101篇 |
1991年 | 70篇 |
1990年 | 84篇 |
1989年 | 61篇 |
1988年 | 41篇 |
1987年 | 26篇 |
1986年 | 22篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1982年 | 5篇 |
1981年 | 16篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1965年 | 3篇 |
1963年 | 3篇 |
1962年 | 5篇 |
1956年 | 17篇 |
1955年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
121.
AIM: To explore interaction and biological behaviour changes of two kinds of cells-blastocysts and hepatocarcinoma cells in the same microenvironment. METHODS:The models of mouse blastocysts co-cultured with human hepatocarcinoma cell lines were established, then biological behaviours and mutual effects of the two kinds of cells in co-culture system were observed. RESULTS: Compared with control group, hepatocarcinoma cells with differently invasive and metastatic potential significantly enhanced the rates of blastocyst hatchment , attachment and outgrowth(P<0.05). There was no significant difference in those among hepatocarcinoma cells co-cultured groups (P>0.05). The blastocyst hatched and attached to hepatocarcinoma cells with differently invasive and metastatic potential. Then, differential trophoblasts invaded hepatocarcinoma cells. The clear-cut interfaces were gradually formed between both sides. Hepatocarcinoma cells on interface showed changes of growth direction and cell shapes and did not invade blastocysts. CONCLUSIONS: Hepatocarcinoma cells promoted blastocyst development. Blastocysts implanted and invaded hepatocarcinoma cells with differently invasive and metastatic potential in vitro, which indicate that blastocyst implantation in vitro does not relate with the kinds and differential level of interactional cells and the low selectivity maybe relate with high adaptability of early life. 相似文献
122.
AIM: To investigate the role of nitric oxide synthase (NOS), soluble guanylyl cyclase (sGC) and protein kinase C (PKC) signaling in tumor necrosis factor-α (TNF-α)-induced cardioprotection against hypoxia/reoxygenation (H/R) injury. METHODS: Neonatal rat ventricular myocytes were pretreated with TNF-α or sodium nitroprusside (SNP) or L-arginine (L-Arg), respectively, for 12 h and then subjected to continuous hypoxia for 12 h, followed by reoxygenation for 6 h. The manganese superoxide dismutase (Mn-SOD) activity of the cells was measured after H/R. Myocyte injury was determined by the release of lactic dehydrogenase (LDH). RESULTS: TNF-α (105 U/L) significantly increased the Mn-SOD activity and decreased release of LDH from ventricular myocytes. The cardioprotection against H/R injury was induced by the pretreatment with SNP (5 μmol/L) or L-Arg (5 mmol/L), which was blocked by ODQ (10 μmol/L), the specific sGC inhibitor, and Chel (5 μmol/L), the specific PKC inhibitor. Pretreatment with L-NAME (100 μmol/L), ODQ, Chel, antoxidant 2-MPG (400 μmol/L) or tyrosine kinase inhibitor genistein (50 μmol/L) attenuated the increased Mn-SOD activity and reduced LDH level induced by TNF-α. CONCLUSION: The results suggest that NO may play a role in TNF-α-induced cardioprotection, which is mediated by sGC and PKC. 相似文献
123.
AIM: To explore the role of Akt signal pathway in apoptosis of neural cells in adult rats treated with Zuogui Pill, a Chinese medicine. METHODS: Flowcytometry and Western blotting methods were used to investigate the changes of cellular apoptosis rate and Akt signal pathway. RESULTS: Monosodium glutamate (MSG) could increase cellular apoptosis rate and significantly restrained the phosphorylation of Akt (Ser473) and Akt (Thr308), and markedly increased the levels of phospho-FKHR (ser256), GSK-3β (Ser9) and PTEN. Zuogui Pill partly inhibited the above effects of MSG. CONCLUSION: Zuogui pill effectively inhibits the neural apoptosis induced by MSG, and Akt pathway is involved in the neuronal protection of Zuogui pill. 相似文献
124.
内蒙古沙尘暴的成因、趋势及其预报 总被引:2,自引:0,他引:2
本文利用内蒙古1961~2001年的天气气候资料,对内蒙古中西部地区沙尘暴作了统计分析,阐述了沙尘暴的危害并给出了沙尘暴的基本定义。分析了引起沙尘暴的天气和气候因子的变化趋势,研究了他们对沙尘暴的影响,结果表明近40年内蒙古的沙尘暴总体呈减少趋势,但从1998年开始有所增加;沙尘暴的空间分布以阿拉善盟偏北地区为最高发区;降水、气温、大风、寒潮、北半球极涡、西太平洋副热带高压、亚洲西风环流、东亚大槽和南方涛动等天气和气候因素均对该地区沙尘暴的发生有不同程度的影响。 相似文献
125.
侧沟茧蜂触角感觉器的扫描电镜观察 总被引:11,自引:0,他引:11
扫描电镜观察表明:侧沟茧蜂Microplitis sp.的触角上存在5种感觉器,分别为毛状感觉器A型、B型、C型,槽状感觉器,锥形乳头状感觉器,刺形感觉器和钟形感觉器。对触角感觉器的形态和分布进行了描述,并对两性间的差别进行了讨论,为研究该蜂寻找生境和寄生行为提供依据。 相似文献
126.
甘蓝多酚氧化酶的生物化学性质及其杀虫剂的诱导作用 总被引:2,自引:0,他引:2
采用时间动力学法,在研究了甘蓝多酚氧化酶的最适反应条件的基础上,对有机溶剂和杀虫剂对多酚氧化酶活性的影响进行了研究。结果表明:甘蓝多酚氧化酶反应的最适pH值为6.4,最适反应温度为55℃;丙酮和乙醇对多酚氧化酶活性有明显的激活作用;高效氯氰菊酯、灭多威和辛硫磷以及小菜蛾和桃蚜取食的胁迫会对多酚氧化酶的活性产生影响。 相似文献
127.
AIM: To assess the effect of indomethacin on tumor invasion in a human laryngeal cancer Hep-2 cell line in vitro. METHODS: Hep-2 cells were exposed to indomethacin at different concentrations for 48 h. Then cell growth rate, the colony formation in soft agar medium and cell mobility were examined, and monolayer invasion assay was performed to assess cell invasion index. RESULTS: Preteatment with indomethacin inhibited the colony formation of Hep-2 cells and the cell mobility, and decreased the invasion index. CONCLUSION: Indomethacin can inhibit the invasion of Hep-2 cells. 相似文献
128.
NAD(P)H oxidase was initially found in phagocytes and it participates in the generation of reactive oxygen species(ROS). Recent researches have showed that NAD(P)H oxidase also expresses in other tissues including blood vessels and it plays a critical role in vascular remodeling through ROS which are important signaling molecules in vascular cells.This article reviews the biochemical characterization, activation paradigms, structure, and function of this enzyme. 相似文献
129.
AIM: To investigate the effects of β-mercaptoethanol (β-ME) and all-trans rentinal acid (RA) on glial fibrillary acidic protein (GFAP) expression in mesenchymal cells derived from mouse fetal liver in vitro. METHODS: Cells suspension from 14.5-days-old mouse fetal liver were cultured in DMEM/HEPES/F12 supplemented with 20% FCS and mesenchymal cells were acquired after discarding nonadherent cells. The 5th passage cells were induced by β-ME and RA. The characteristics of treated cells were assayed by immunocytochemistry staining at 5 hours and 5 days after induction. β-actin as an internal control, GFAP gene expression of mesenchyal cells was detected with semi-quantitative RT-PCR. RESULTS: After being inducted by β-ME and RA, 80% approximately of the cells exhibited typical neural morphology and about 85% expressed GFAP phenotype. Semi-quantitative RT-PCR showed that mRNA expression of GFAP increased in treated cells versus untreated cells (P<0.01). CONCLUSION: GFAP expression in mesenchymal cells derived from mouse fetal liver in vitro increases after being treated with β-ME and RA. 相似文献
130.
脂蛋白LPPQ是丝状霉形体丝状亚种SC型(MmmSC)非洲株、欧洲株和疫苗株所特有的。LPPQ N末端域具有良好的免疫原性,在牛体内可诱导产生强大、特异、早期、持续的免疫反应。本研究根据已发表的LPPQ基因序列设计引物,用Pyrobest^TM高保真DNA聚合酶从MmmSC HVRI X株中扩增出了LPPQ N末端基因序列,并进行了克隆与序列测定。核苷酸序列比较结果显示,HVRI X株的LPPQ N末端基因序列与国外发表的序列同源性为99.7%,由其推导的氨基酸序列同源性为99,1%,为脂蛋白LPPQ N末端基因体外表达奠定了基础。 相似文献