全文获取类型
收费全文 | 21916篇 |
免费 | 3772篇 |
国内免费 | 1804篇 |
专业分类
化学 | 5113篇 |
晶体学 | 53篇 |
力学 | 2843篇 |
综合类 | 571篇 |
数学 | 9715篇 |
物理学 | 9197篇 |
出版年
2024年 | 24篇 |
2023年 | 208篇 |
2022年 | 351篇 |
2021年 | 497篇 |
2020年 | 551篇 |
2019年 | 489篇 |
2018年 | 498篇 |
2017年 | 794篇 |
2016年 | 924篇 |
2015年 | 738篇 |
2014年 | 1232篇 |
2013年 | 1554篇 |
2012年 | 1294篇 |
2011年 | 1423篇 |
2010年 | 1267篇 |
2009年 | 1406篇 |
2008年 | 1557篇 |
2007年 | 1645篇 |
2006年 | 1341篇 |
2005年 | 1218篇 |
2004年 | 1179篇 |
2003年 | 969篇 |
2002年 | 901篇 |
2001年 | 734篇 |
2000年 | 623篇 |
1999年 | 590篇 |
1998年 | 514篇 |
1997年 | 462篇 |
1996年 | 399篇 |
1995年 | 393篇 |
1994年 | 261篇 |
1993年 | 243篇 |
1992年 | 177篇 |
1991年 | 206篇 |
1990年 | 134篇 |
1989年 | 86篇 |
1988年 | 112篇 |
1987年 | 76篇 |
1986年 | 65篇 |
1985年 | 68篇 |
1984年 | 51篇 |
1983年 | 32篇 |
1982年 | 39篇 |
1981年 | 40篇 |
1980年 | 28篇 |
1979年 | 29篇 |
1978年 | 17篇 |
1977年 | 11篇 |
1976年 | 8篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
91.
92.
能源互联网呈现物理信息深度融合的趋势,为电力系统管理研究定义了新的研究框架。作为一个先进的复杂系统,能源互联网信息物理系统(Energy Internet Cyber-Physical System,ECPS)在其发展过程中面临着一些新的挑战,其中一个就是耦合结构下的风险管理。本文结合复杂网络理论和风险传递理论,着重在拓扑层面分析了ECPS跨空间交互机理,并在此基础上定义了交互路径和交互系数;接着建立了ECPS跨空间风险传递模型,量化描述了风险的传递和演化过程,并进行了风险影响评估;最后,通过仿真实验分析了三种不同交互系数节点故障的风险传递过程和不同攻击模式下系统的崩溃过程。对仿真结果的讨论阐述了能源互联网风险跨空间传递的特点,为更深入地研究ECPS的风险管理提供了参考。 相似文献
93.
Ideal optomechanically induced transparency generation in a cavity optoelectromechanical system 下载免费PDF全文
《中国物理 B》2021,30(10):104211-104211
The ideal optomechanically induced transparency effects of an output probe field are investigated in a cavity optoelectromechanical system, which is composed of an optical cavity, a charged mechanical resonator, and a charged object.Although the charged mechanical resonator damping rate is nonzero, the ideal optomechanically induced transparency can still appear due to the non-rotating wave approximation effect in the system. The location of optomechanically induced transparency dip can be controlled via the Coulomb coupling strength. In addition, we find that both the transparency window width and the maximum dispersion curve slope are closely related to the optical cavity decay rate. 相似文献
94.
Amirali Sadeqi Shapour Moradi Kourosh Heidari Shirazi 《Mathematical and Computer Modelling of Dynamical Systems: Methods, Tools and Applications in Engineering and Related Sciences》2020,26(1):55-79
ABSTRACTThe scope of output-only/blind identification is restricted to stochastic/statistical processes, but for the first time in this study, the detectability conditions for general output-only subspace identification are investigated. This aids the range of input sources to be extended in a much realistic manner, beyond the only stochastic inputs. For this purpose, the subspace framework is assigned to make a connection between the output signal contents and the LTI system order. A few substantial hypotheses and algebraic statements are propounded affirming the sufficiency of the genuine output sequences for the identification purpose. This can be perceived as the cornerstone of state-space model reconstruction. In order to consolidate the notions according to reality, several examples are studied and examined for different input classes with stochastic disturbance. 相似文献
95.
Combining the dual least action principle with Mountain-pass lemma,we obtain the existence of brake orbits for first-order convex Hamiltonian systems with particular anisotropic growth. 相似文献
96.
分析了采用单一同轴磁场时强流相对论多注阴极的侧端发射问题,研究了在不同磁场内半径和多注漂移管长度情况下多注电子束的传输效率。研究发现:由于引导磁场尺寸有限,高压下多注阴极杆及多注阴极柱的电子束发射是影响多注电子束传输效率的主要因素,且该部分电子束对多注漂移管入口管壁的轰击直接影响了多注速调管的重频能力。设计了采用永磁铁和同轴磁场组合工作的强流相对论多注二极管,理论分析和模拟计算证明:基于组合磁场的多注二极管可明显减弱甚至抑制多注阴极发射球头以外的电子束发射,并且组合磁场的磁场位形和强度可满足强流相对论多注电子束的高效、稳定传输。 相似文献
97.
98.
99.
A photoredox catalytic ensemble consisting of CuO‐Fe2O3 nanocomposites and oligomeric derivative of phenazine has been developed. The prepared system acts as an efficient photoredox catalyst for C?N bond formation reaction via SET mechanism under ‘green’ conditions (aerial environment, mixed aqueous media, recyclable), requiring less equivalents of base and amine substrate. The present study demonstrates the significant role of supramolecular assemblies as photooxidants and reductants upon irradiation and their important contribution towards the activation of the metallic centre through energy transfer and electron transfer pathways. The potential of oligomer 4 : CuO‐Fe2O3 has also been explored for C?C bond formation reactions via the Sonogashira protocol. 相似文献
100.
Tasneem Gul Kazi Suraya Samejo Hassan Imran Afridi Asma Akhtar Jameel Ahmed Baig 《应用有机金属化学》2020,34(1):e5263
In the present study the cadmium (Cd) was determined in serum samples of psoriatic patients. The severity of psoriasis was evaluated according to criteria based on standard clinical diagnosis using Psoriasis Area Severity Index (PASI) score. In present study, an innovative tunable green solvent system based microextraction (TSS-ME) was applied for the enrichment of Cd in acid digested serum samples prior to determination with flame atomic absorption spectrometry. The hydrophobic complex of Cd-ammonium pyrrolidine thiocarbamate was extracted in a tunable solvent system which was prepared from a polybasic amine (N, N, N′, N′-tetramethyl-1, 4-diaminobutane), decanol and water system. The tunable green solvent system (TSS) which has zero ionic strength was converted to homogeneous monophasic polar hydrophilic phase via exposure to CO2 at different pressure and time duration. Then hydrophobic enriched Cd- ammonium pyrrolidine thiocarbamate was back extracted, using HNO3 (0.1 to 0.5 mol L−1) then the second round of TSS-ME was applied. The acidic aqueous phase enrich with analyte was separated from tunable solvent. The separated TSS was easily reused for up to 10 time for preconcentration purposes without loss of its enrichment character. The smoker and nonsmoker psoriatic patients at PASI >10, have two to three folds higher Cd levels in serum samples than healthy persons. 相似文献