全文获取类型
收费全文 | 42358篇 |
免费 | 3165篇 |
国内免费 | 5985篇 |
专业分类
化学 | 29507篇 |
晶体学 | 528篇 |
力学 | 1009篇 |
综合类 | 797篇 |
数学 | 9316篇 |
物理学 | 10351篇 |
出版年
2023年 | 342篇 |
2022年 | 504篇 |
2021年 | 1396篇 |
2020年 | 1005篇 |
2019年 | 1060篇 |
2018年 | 850篇 |
2017年 | 975篇 |
2016年 | 1205篇 |
2015年 | 1186篇 |
2014年 | 1687篇 |
2013年 | 2932篇 |
2012年 | 2595篇 |
2011年 | 2141篇 |
2010年 | 1968篇 |
2009年 | 2609篇 |
2008年 | 2827篇 |
2007年 | 3040篇 |
2006年 | 2458篇 |
2005年 | 1857篇 |
2004年 | 1661篇 |
2003年 | 1578篇 |
2002年 | 1492篇 |
2001年 | 1364篇 |
2000年 | 1074篇 |
1999年 | 922篇 |
1998年 | 864篇 |
1997年 | 678篇 |
1996年 | 733篇 |
1995年 | 697篇 |
1994年 | 679篇 |
1993年 | 646篇 |
1992年 | 689篇 |
1991年 | 482篇 |
1990年 | 394篇 |
1989年 | 306篇 |
1988年 | 312篇 |
1987年 | 248篇 |
1986年 | 267篇 |
1985年 | 361篇 |
1984年 | 257篇 |
1983年 | 156篇 |
1982年 | 314篇 |
1981年 | 475篇 |
1980年 | 431篇 |
1979年 | 466篇 |
1978年 | 372篇 |
1977年 | 282篇 |
1976年 | 239篇 |
1974年 | 75篇 |
1973年 | 151篇 |
排序方式: 共有10000条查询结果,搜索用时 28 毫秒
1.
Dariusz Marek Adam Domaski Joanna Domaska Jakub Szygua Tadeusz Czachrski Jerzy Klamka 《Entropy (Basel, Switzerland)》2021,23(5)
In this article, a way to employ the diffusion approximation to model interplay between TCP and UDP flows is presented. In order to control traffic congestion, an environment of IP routers applying AQM (Active Queue Management) algorithms has been introduced. Furthermore, the impact of the fractional controller and its parameters on the transport protocols is investigated. The controller has been elaborated in accordance with the control theory. The TCP and UDP flows are transmitted simultaneously and are mutually independent. Only the TCP is controlled by the AQM algorithm. Our diffusion model allows a single TCP or UDP flow to start or end at any time, which distinguishes it from those previously described in the literature. 相似文献
2.
3.
《中国物理 B》2021,30(5):56501-056501
Thermal expansion control is always an obstructive factor and challenging in high precision engineering field. Here,the negative thermal expansion of Nb F_3 and Nb OF_2 was predicted by first-principles calculation with density functional theory and the quasi-harmonic approximation(QHA). We studied the total charge density, thermal vibration, and lattice dynamic to investigate the thermal expansion mechanism. We found that the presence of O induced the relatively strong covalent bond in Nb OF_2, thus weakening the transverse vibration of F and O in Nb OF_2, compared with the case of Nb F_3.In this study, we proposed a way to tailor negative thermal expansion of metal fluorides by introducing the oxygen atoms.The present work not only predicts two NTE compounds, but also provides an insight on thermal expansion control by designing chemical bond type. 相似文献
4.
5.
Due to their intrinsic link with nonlinear Fokker-Planck equations and many other applications, distribution dependent stochastic differential equations (DDSDEs) have been intensively investigated. In this paper, we summarize some recent progresses in the study of DDSDEs, which include the correspondence of weak solutions and nonlinear Fokker-Planck equations, the well-posedness, regularity estimates, exponential ergodicity, long time large deviations, and comparison theorems. 相似文献
6.
We propose a conjecture on the relative twist formula of l-adic sheaves, which can be viewed as a generalization of Kato—Saito's conjecture. We verify this conjecture under some transversal assumptions. We also define a relative cohomological characteristic class and prove that its formation is compatible with proper push-forward. A conjectural relation is also given between the relative twist formula and the relative cohomological characteristic class. 相似文献
7.
8.
9.
《Journal of Saudi Chemical Society》2022,26(2):101436
Continuous administration of most chemotherapeutic drugs can induce different types of side effects. There has been growing interest in exploring an alternative approach to synthesizing compounds that are most effective and have fewer side effects. We synthesized 29H,31H-Phthalocyanine, and Chloro (29H,31H- phthalocyaninato) aluminum at low temperatures using lithium in the present study with diisopropylamide as the nucleophile. The physical characteristics of 29H,31H-Phthalocyanine, and Chloro (29H,31H- phthalocyaninato) aluminum were confirmed by FT-IR method, XRD, SEM, and the impact of these compounds on human colorectal carcinoma (HCT-116) and human cervical cells (HeLa) was examined. Treatment with 29H,31H-Phthalocyanine significantly decreased cancer cell growth and proliferation, as determined by MTT and DAPI staining analysis. In contrast, Chloro (29H,31H- phthalocyaninato) aluminum treatment did not show any inhibitory action on colon or cervical cancer cells. We also calculated the inhibitory concentration (IC50) of 29H,31H-Phthalocyanine, which was 30 µg/ml (HCT-116) and 33 µg/ml (HeLa cells). The antibacterial effectiveness of 29H,31H-Phthalocyanine, and chloro (29H,31H- phthalocyaninato) aluminum was studied using Enterococcus faecalis (E. faecalis). The CFU (colony frequency unit) assay confirmed significant activity against the test bacterium after treatment with 29H,31H-Phthalocyanine. However, no activity was seen upon treatment with chloro (29H,31H- phthalocyaninato) aluminum against E. faecalis. 相似文献
10.
将有机物2,5-二溴对苯二甲酸(H2L1)和2,2′-联吡啶(L2)作为双配体,使用溶剂热法和七水合硫酸锌(ZnSO4·7H2O)、六水合硝酸钴(Co(NO3)2·6H2O)分别反应,得到配合物[Zn(L1)(L2)(H2O)]n(1)和配合物[Co(L1)(L2)(H2O)]n(2)。采用单晶X射线衍射、元素分析、红外光谱、紫外光谱、荧光光谱、热重分析等测试方法对这两种物质进行分析研究。单晶测试结果表明配合物1是单斜晶系,以Zn2+配位连接L2-1与L2形成一维链状结构,各条链在分子间氢键和π…π共轭作用下有规律地堆叠形成三维网络结构。配合物2是三斜晶系,Co1离子和Co1i离子由H2L1上的羧酸氧原子O4和O4i连接,形成双齿螯合的配位结构单元,以Co2+配位连接 L2-1和L2形成二维网格结构,各层在O—H…O分子间氢键和范德瓦耳斯力作用下有规律的堆叠形成三维网络结构。配合物1和2均含有芳香杂环、羧基杂环和氮杂环,具有良好的荧光性质和热稳定性,最大发射波长分别为345 nm和333 nm。 相似文献