全文获取类型
收费全文 | 9876篇 |
免费 | 390篇 |
国内免费 | 497篇 |
专业分类
系统科学 | 380篇 |
丛书文集 | 245篇 |
教育与普及 | 194篇 |
理论与方法论 | 29篇 |
现状及发展 | 49篇 |
研究方法 | 46篇 |
综合类 | 9818篇 |
自然研究 | 2篇 |
出版年
2024年 | 48篇 |
2023年 | 134篇 |
2022年 | 176篇 |
2021年 | 192篇 |
2020年 | 141篇 |
2019年 | 73篇 |
2018年 | 91篇 |
2017年 | 123篇 |
2016年 | 131篇 |
2015年 | 246篇 |
2014年 | 313篇 |
2013年 | 284篇 |
2012年 | 322篇 |
2011年 | 383篇 |
2010年 | 374篇 |
2009年 | 405篇 |
2008年 | 447篇 |
2007年 | 537篇 |
2006年 | 391篇 |
2005年 | 484篇 |
2004年 | 298篇 |
2003年 | 230篇 |
2002年 | 272篇 |
2001年 | 299篇 |
2000年 | 302篇 |
1999年 | 489篇 |
1998年 | 458篇 |
1997年 | 498篇 |
1996年 | 437篇 |
1995年 | 348篇 |
1994年 | 318篇 |
1993年 | 275篇 |
1992年 | 283篇 |
1991年 | 224篇 |
1990年 | 225篇 |
1989年 | 185篇 |
1988年 | 142篇 |
1987年 | 112篇 |
1986年 | 59篇 |
1985年 | 9篇 |
1984年 | 1篇 |
1978年 | 2篇 |
1968年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Web-based Computing Resource Publishing is a efficient way to provide additional computing capacity for users who need more computing resources than that they themselves could afford by making use of idle computing resources in the Web.Extensibility and reliability are crucial for agent publishing. The parent-child agent framework and primary-slave agent framework were proposed respectively and discussed in detail. 相似文献
972.
The main goal of this study was to investigate whether lidamycin (LDM) could enhance the efficacy of paclitaxel (TAX) against breast cancer. In the MTT assay, LDM showed much more potent cytotoxicity than paclitaxel, and there was a synergy on the 4T1/luc breast cancer cells treated with a combination of paclitaxel and LDM. Western blot analysis showed that paclitaxel and LDM synergistically downregulated MMP9, MMP2, VEGF, and upregulated the cleaved PARP proteins. By wound closure cell migration assay, paclitaxel combined LDM obviously inhibited the migration of 4T1/luc cells. At therapeutic dosage level, LDM, paclitaxel, and the combination suppressed the pulmonary metastases by 70.2%, 53.8%, and 88.7%, respectively, and the CDI value was 0.82, indicating synergism. The results show that LDM enhances the antitumor effect of paclitaxel on 4T1/luc breast cancer, in particular, the antimetastatic effects on pulmonary metastasis. 相似文献
973.
In the present work, we report a label-free fluorescence turn-on approach for the sensitive and selective sensing of Pb2+. Pyrene with one positive charge was used as the fluorescent probe, and thrombin aptamer (TBA), which was a G-rich oligonucleotide, was employed to form G-quadruplex with lead(II). When TBA and Pb2+ were mixed with lead(II) in an aqueous solution, it was folded into a stable G-quadruplex. Subsequently, a single-stranded nucleic acid-specific nuclease S1 was added. The G-quadruplex stabilized by Pb2+ lead(II) had markedly a significant resistant ability to nuclease S1 digestion. However, in the absence of Pb2+ lead(II), no quadruplex or less stable quadruplex was formed and TBA was digested by nuclease S1 in 3 min under the optimized experimental conditions. Finally, pyrene probe was mixed with oligonucleotide in Pb2+ lead(II). Electrostatic interactions between oligonucleotide (a polyanion) and the probe induced the aggregation of the probe, which in turn produced strong emission of the strong pyrene excimer emission. The intensity of the induced excimer emission was directly proportional to the amount of Pb2+ added. Our approach shows good selectivity and sensitivity for the detection of Pb2+ with a limit of detection limit as low as 800 nmol/L. 相似文献
974.
We constructed a class of generalized statistically self-similar sets and give the necessary and sufficent conditions to ensure
a random recursive set being a generalized statistically self-similar set. The statistically self-similar sets defined by
Hutchinson, Falconer, Graf are the special cases of ours.
Foundation item: Supported by the National Natural Science Foundation of China
Biography: DENG Ai-jiao (1974-), female, Ph.D. candidate, research interes: is in stochastic process and random ractal 相似文献
975.
The electrooxidation of Mn(Ⅱ) on Pb-Sb-As alloy electrode in sulfuric acid has been investigated.In order to make the two steps of indirect electrosynthesis of benzaldehyde carried out in the same sulfuric acid concentration and also obtain high current efficiency of Mn(Ⅱ) to Mn(Ⅲ) and high yield of Mn(Ⅲ) oxidizing toluene to benzaldehyde in the mean time,the electrooxidation of Mn(Ⅱ) in 60% H2SO4 has been studied.Experimental results show that high current efficiency of Mn(Ⅲ) (about 75%) is obtained in 60%H2SO4 at 60℃.The reason affecting the current efficiency of Mn(Ⅲ) is discussed,and it is the coordination of sulfuric acid concentration and electrolytic temperature.The law is found that it is suitable for electrolysis at low temperature when sulfuric acid concentration is low and at high temperature when sulfuric acid concentration is high. 相似文献
976.
对国际GB150-89《钢制压力容器》所规定的折边锥形封头过渡段厚度、锥体厚度及与封头相接的筒体厚度进行了分析,指出了过渡段厚度偏小,提出了合理的过渡段厚度。 相似文献
977.
978.
胡庆平 《西安工程科技学院学报》1998,(4)
分析了国外的经验并结合我国的经济现状,提出了应将汽车工业作为我国的支柱产业;国家应在资金、技术和人员等方面对汽车工业给予大力扶持,并在汽车进口方面对汽车工业实行适度保护并建议国家应引导汽车产业组建8个大的汽车集团企业,必要时可以采用一定的行政手段 相似文献
979.
980.
为探索大迎角下介质阻挡放电(DBD)对高升力机翼的作用机理,采用体积力模型和Eddy Viscosity Transport Equation全湍流模型耦合进行DBD激励改善其气动特性的模拟仿真研究。在来流速度45 m/s条件下,对比实验数据与仿真模型,验证了仿真模型的正确性;并采用该模型分析了机翼弦向、展向的2组截面流线图。结果表明:DBD激励位于机翼前缘能很好地提高高升力机翼大迎角气动特性,显著改善上翼面涡结构,促进分离流附体;可将机翼最大升力系数提高11.1%,失速迎角推迟2°,且随迎角增大,流动控制效果逐渐减弱直到消失。 相似文献