全文获取类型
收费全文 | 6772篇 |
免费 | 666篇 |
国内免费 | 83篇 |
专业分类
系统科学 | 1143篇 |
丛书文集 | 55篇 |
教育与普及 | 36篇 |
理论与方法论 | 279篇 |
现状及发展 | 874篇 |
研究方法 | 3篇 |
综合类 | 5131篇 |
出版年
2024年 | 16篇 |
2023年 | 19篇 |
2022年 | 39篇 |
2021年 | 53篇 |
2020年 | 30篇 |
2019年 | 21篇 |
2018年 | 746篇 |
2017年 | 752篇 |
2016年 | 458篇 |
2015年 | 80篇 |
2014年 | 76篇 |
2013年 | 81篇 |
2012年 | 334篇 |
2011年 | 1027篇 |
2010年 | 890篇 |
2009年 | 531篇 |
2008年 | 597篇 |
2007年 | 824篇 |
2006年 | 58篇 |
2005年 | 101篇 |
2004年 | 166篇 |
2003年 | 193篇 |
2002年 | 92篇 |
2001年 | 28篇 |
2000年 | 24篇 |
1999年 | 32篇 |
1998年 | 26篇 |
1997年 | 28篇 |
1996年 | 25篇 |
1995年 | 29篇 |
1994年 | 38篇 |
1993年 | 24篇 |
1992年 | 29篇 |
1991年 | 18篇 |
1990年 | 13篇 |
1989年 | 9篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1967年 | 1篇 |
排序方式: 共有7521条查询结果,搜索用时 125 毫秒
741.
以创新性能力培养为目标对食品微生物学的理论和实践教学进行了一系列改革。在理论教学方面通过优化课程知识体系、创新课程教学手段、改革课程考核模式,构建了"知识点"与"能力点"并重的教学体系;在实践教学方面通过优化实验项目、革新教学手段、完善考核方式,形成了技能和意识并重的教学理念。通过这些改革措施的实践,学生在自主学习能力、课堂参与激情、创新兴趣等方面得到了明显提高。 相似文献
742.
给出了多元线性EV模型下协变量具有随机缺失(MAR)时参数的稳健估计方法,并证明了估计的渐近正态性.模拟研究表明估计量在有限样本下具有很好的效果. 相似文献
743.
744.
745.
以葡萄糖为原料水热法合成粒径均一单分散碳球,研究反应时间、反应温度、葡萄糖浓度、pH值、甲醛用量对碳球形貌及粒径的影响,采用SEM、FTIR、XRD对碳球的形貌和结构进行表征。结果表明,单分散碳球的最佳制备工艺为:反应温度160℃、反应时间6h、葡萄糖浓度0.25mol/L、体系pH值为8、甲醛用量2g;所制碳微球粒径约为350nm,分散系数为0.011,产率约为20%;制备出的碳球表面含有—OH、—CO、COOH官能团,碳球中含有无定形炭。 相似文献
746.
Jessica L. Slack Corey P. Causey Paul R. Thompson 《Cellular and molecular life sciences : CMLS》2011,68(4):709-720
The recent approvals of anticancer therapeutic agents targeting the histone deacetylases and DNA methyltransferases have highlighted
the important role that epigenetics plays in human diseases, and suggested that the factors controlling gene expression are
novel drug targets. Protein arginine deiminase 4 (PAD4) is one such target because its effects on gene expression parallel
those observed for the histone deacetylases. We demonstrated that F- and Cl-amidine, two potent PAD4 inhibitors, display micromolar
cytotoxic effects towards several cancerous cell lines (HL-60, MCF7 and HT-29); no effect was observed in noncancerous lines
(NIH 3T3 and HL-60 granulocytes). These compounds also induced the differentiation of HL-60 and HT29 cells. Finally, these
compounds synergistically potentiated the cell killing effects of doxorubicin. Taken together, these findings suggest PAD4
inhibition as a novel epigenetic approach for the treatment of cancer, and suggest that F- and Cl-amidine are candidate therapeutic
agents for this disease. 相似文献
747.
A Note on the Property of ψ-Function 总被引:1,自引:0,他引:1
About the accurate value of ψ ( x ) = Γ′ ( x ) / Γ ( x), we know only ψ (1)and ψ (1/ 2).In this paper, by calculating the accurate values of some series expansion of a function and applying some skills of complex analysis, we prove that the expression of the ψ-function admits a finite expression in elementary function for rational number z. As an application, some examples are given. 相似文献
748.
Eoin E. Kelly Conor P. Horgan Mary W. McCaffrey Paul Young 《Cellular and molecular life sciences : CMLS》2011,68(2):185-194
Long-term potentiation (LTP) defines persistent increases in neurotransmission strength at synapses that are triggered by
specific patterns of neuronal activity. LTP, the most widely accepted molecular model for learning, is best characterised
at glutamatergic synapses on dendritic spines. In this context, LTP involves increases in dendritic spine size and the insertion
of glutamate receptors into the post-synaptic spine membrane, which together boost post-synaptic responsiveness to neurotransmitters.
In dendrites, the material required for LTP is sourced from an organelle termed the endosomal-recycling compartment (ERC),
which is localised to the base of dendritic spines. When LTP is induced, material derived from the recycling compartment,
which contains α-amino-3-hydroxy-5-methyl-4-isoxazole propionate-type glutamate receptors (AMPARs), is mobilised into dendritic
spines feeding the increased need for receptors and membrane at the spine neck and head. In this review, we discuss the importance
of endosomal-recycling and the role of key proteins which control these processes in the context of LTP. 相似文献
749.
Pure CoAPO-36 crystal grains were synthesized by hydrothermal reaction. Porous α-Al2O3, stainless steel and K2Ti6O13 supported CoAPO-36 films were fabricated using in situ crystallization for the first time. SEM images and XRD measurements demonstrate that a continuous CoAPO-36 film was obtained
on the K2Ti6O13 substrate. Diffuse reflectance UV-Vis spectra indicate that Co2+ has been incorporated into the ATS framework. Both CoAPO-36 crystal grains and the K2Ti6O13 supported CoAPO-36 film exhibit satisfactory catalytic activities for the oxidation of cyclohexane. 相似文献
750.
The distributed detection of botnets may induce heavy computation and communication costs to network devices. Each device in related scheme only has a regional view of Internet, so it is hard to detect botnet comprehensively. In this paper, we propose a lightweight real-time botnet detection framework called Bot-Guard, which uses the global landscape and flexible configurability of software defined network (SDN) to identify botnets promptly. SDN, as a new network framework, can make centralized control in botnet detection, but there are still some challenges in such detections. We give a convex lens imaging graph (CLI-graph) to depict the topology characteristics of botnet, which allows SDN controller to locate attacks separately and mitigate the burden of network devices. The theoretical and experimental results prove that our scheme is capable of timely botnet detecting in SDNs with the accuracy higher than 90% and the delay less than 56 ms. 相似文献