全文获取类型
收费全文 | 28128篇 |
免费 | 2496篇 |
国内免费 | 1986篇 |
专业分类
化学 | 10175篇 |
晶体学 | 153篇 |
力学 | 2100篇 |
综合类 | 154篇 |
数学 | 794篇 |
物理学 | 5145篇 |
综合类 | 14089篇 |
出版年
2024年 | 137篇 |
2023年 | 374篇 |
2022年 | 710篇 |
2021年 | 690篇 |
2020年 | 828篇 |
2019年 | 760篇 |
2018年 | 751篇 |
2017年 | 1030篇 |
2016年 | 1110篇 |
2015年 | 1257篇 |
2014年 | 1530篇 |
2013年 | 2114篇 |
2012年 | 1832篇 |
2011年 | 1830篇 |
2010年 | 1411篇 |
2009年 | 1477篇 |
2008年 | 1277篇 |
2007年 | 1715篇 |
2006年 | 1511篇 |
2005年 | 1344篇 |
2004年 | 1180篇 |
2003年 | 1015篇 |
2002年 | 914篇 |
2001年 | 751篇 |
2000年 | 667篇 |
1999年 | 617篇 |
1998年 | 526篇 |
1997年 | 475篇 |
1996年 | 427篇 |
1995年 | 400篇 |
1994年 | 345篇 |
1993年 | 292篇 |
1992年 | 215篇 |
1991年 | 187篇 |
1990年 | 189篇 |
1989年 | 167篇 |
1988年 | 173篇 |
1987年 | 91篇 |
1986年 | 66篇 |
1985年 | 47篇 |
1984年 | 34篇 |
1983年 | 13篇 |
1982年 | 29篇 |
1981年 | 26篇 |
1980年 | 10篇 |
1979年 | 24篇 |
1976年 | 7篇 |
1973年 | 5篇 |
1972年 | 5篇 |
1955年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
常凯 《淮北煤炭师范学院学报(自然科学版)》1996,(2)
本文采用变分法研究了量子阱中类氢杂质的束缚能的压力效应,尤其在阱较窄的情形下,其压力效应更为显著. 相似文献
22.
23.
Y. Yavin 《Journal of Optimization Theory and Applications》1993,78(1):77-91
Stochastic optimal control techniques are applied to compare the performance of identical medium-range air-to-air missiles which have different thrust-mass profiles. The measure of the performance is the probability of reaching a lock-on-point with a favorable range of guidance and flight parameters, during a fixed time interval [0,t
f
], given that, during the flight, the trajectories of the missile are subjected to a variety of constraints including dynamic pressure constraints. 相似文献
24.
简析"静止液体内部压强公式验证"实验的设计策略 总被引:1,自引:1,他引:0
“静止液体内部压强公式验证”在现行教材中有两种实验方法。通过分析实验的设计策略,说明其作用、效果及操作上的困难,指出合理的与不合理诸因素,从而提出改进实验的方法,化难为易,提高实验教学效果。 相似文献
25.
1 Introduction Inrecentyears,boththetheoreticalandexperimentalinvestigationsonlasercoolingandtrappinghavebecomeoneofthemajorfieldsinatomic,molecularandoptical physics[1~ 8] .Thedevelopmentoflasercoolingandtrappingtechnologyisimportantfortheapplicationssu… 相似文献
26.
This paper investigates mutual influence of duct and room acoustics in the whole fan-duct-plenum-room integrations. Applying the parametric design language of finite element software ANSYS (APDL), dimensional and positional influence on system acoustics has been studied. Models with different room dimensions, duct lengths, duct cross-sections, duct locations, duct discharges and duct elbow were constructed, and their characteristics were compared qualitatively. Results show that small rooms, short ducts, large duct cross-sections and bell mouth duct discharges help to increase room sound pressure levels (SPLs); SPLs in ducts and plenums are sensitive to duct dimensions and duct discharge types but insensitive to duct locations and room dimensions; duct elbows have relatively indistinct acoustic influence in each component. Based on the calculation results, a semi-experimental method was proposed for simply and approximately evaluating indoor acoustic spectra of fan-duct-plenum-room integrations, then an example was used to demonstrate the prediction process. Finally, by adopting several ideal models, sound field constitutions, duct and room wall admittances and duct end reflection were explored quantitatively. This study may give a detailed understanding of fan-duct-plenum-room acoustics for researchers, also it might provide a new, simple and approximate prediction method for professionals to evaluate and improve fan-ducted acoustics. 相似文献
27.
Bubble pressure points of ethanol–1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea refrigerant) mixtures from the third Industrial Fluid Properties Simulation Challenge are computed using publicly available molecular simulation software. Several published force fields are compared against the known answers provided in the contest guidelines and the best force fields are used to make predictions for the unknown results. 相似文献
28.
This paper presents a new generic Evolutionary Algorithm (EA) for retarding the unwanted effects of premature convergence. This is accomplished by a combination of interacting generic methods. These generalizations of a Genetic Algorithm (GA) are inspired by population genetics and take advantage of the interactions between genetic drift and migration. In this regard a new selection scheme is introduced, which is designed to directedly control genetic drift within the population by advantageous self-adaptive selection pressure steering. Additionally this new selection model enables a quite intuitive heuristics to detect premature convergence. Based upon this newly postulated basic principle the new selection mechanism is combined with the already proposed Segregative Genetic Algorithm (SEGA), an advanced Genetic Algorithm (GA) that introduces parallelism mainly to improve global solution quality. As a whole, a new generic evolutionary algorithm (SASEGASA) is introduced. The performance of the algorithm is evaluated on a set of characteristic benchmark problems. Computational results show that the new method is capable of producing highest quality solutions without any problem-specific additions. 相似文献
29.
Munish Kumar 《Journal of Physics and Chemistry of Solids》2004,65(6):1177-1180
A critical analysis of the Suzuki, Shanker, and Kumar formulations is presented by studying different classes of materials under high pressure. A similar trend for all the materials studied in the present work, demonstrates that Suzuki formulation is not capable to yield compression behaviour of solids. The Shanker formulation improves the results obtained by the Suzuki formulation in small compression range (0.9<V/V0<1). For further compressions Shanker formulation also fails. On the other hand, the Kumar formulation is found to work well for the entire range of pressure. The reasons for the failure of Suzuki and Shanker formulations are discussed. 相似文献
30.
Makoto Sakata Takafumi Itsubo Yutakata Moritomo Yasuo Ohishi 《Journal of Physics and Chemistry of Solids》2004,65(12):1973-1976
The experimental and analytical method of the high-pressure powder experiment at BL10XU, SPring-8, is described. There is no doubt that BL10XU must be one of the most appropriate beam lines for high pressure X-ray diffraction experiment taking advantage of third generation synchrotron source. As an example of the advanced charge density study under high pressure, the structural change of Cs2Au2Br6 by applying pressure is studied by Rietveld/MEM analysis. It reveals that the structural change of Cs2Au2Br6 by applying pressure occurs basically at electron level, such as valence state change and chemical bonding, which may be called the electronic phase transition. 相似文献