全文获取类型
收费全文 | 25955篇 |
免费 | 854篇 |
国内免费 | 144篇 |
专业分类
化学 | 18655篇 |
晶体学 | 215篇 |
力学 | 491篇 |
数学 | 3277篇 |
物理学 | 4315篇 |
出版年
2023年 | 182篇 |
2022年 | 266篇 |
2021年 | 363篇 |
2020年 | 485篇 |
2019年 | 470篇 |
2018年 | 315篇 |
2017年 | 272篇 |
2016年 | 730篇 |
2015年 | 623篇 |
2014年 | 746篇 |
2013年 | 1224篇 |
2012年 | 1616篇 |
2011年 | 1789篇 |
2010年 | 1032篇 |
2009年 | 866篇 |
2008年 | 1487篇 |
2007年 | 1407篇 |
2006年 | 1392篇 |
2005年 | 1296篇 |
2004年 | 1133篇 |
2003年 | 855篇 |
2002年 | 895篇 |
2001年 | 434篇 |
2000年 | 368篇 |
1999年 | 369篇 |
1998年 | 361篇 |
1997年 | 339篇 |
1996年 | 349篇 |
1995年 | 291篇 |
1994年 | 319篇 |
1993年 | 299篇 |
1992年 | 262篇 |
1991年 | 191篇 |
1990年 | 218篇 |
1989年 | 185篇 |
1988年 | 195篇 |
1987年 | 172篇 |
1986年 | 161篇 |
1985年 | 272篇 |
1984年 | 257篇 |
1983年 | 183篇 |
1982年 | 200篇 |
1981年 | 185篇 |
1980年 | 182篇 |
1979年 | 164篇 |
1978年 | 195篇 |
1977年 | 180篇 |
1976年 | 137篇 |
1975年 | 132篇 |
1974年 | 157篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
161.
Ganjehi L Marchiano R Coulouvrat F Thomas JL 《The Journal of the Acoustical Society of America》2008,124(1):57-71
The influence of the planetary boundary layer on the sonic boom received at the ground level is known since the 1960s to be of major importance. Sonic boom propagation in a turbulent medium is characterized by an increase of the mean rise time and a huge variability. An experiment is conducted at a 1:100,000 scale in water to investigate ultrasonic shock wave interaction with a single heterogeneity. The experiment shows a very good scaling with sonic boom, concerning the size of the heterogeneities, the wave amplitude, and the rise time of the incident wave. The wave front folding associated with local focusing, and its link to the increase of the rise time, are evidenced by the experiment. The observed amplification of the peak pressure (by a factor up to 2), and increase of the rise time (by up to about one magnitude order), are in qualitative agreement with sonic boom observations. A nonlinear parabolic model is compared favorably to the experiment on axis, though the paraxial approximation turns out less precise off axis. Simulations are finally used to discriminate between nonlinear and linear propagations, showing nonlinearities affect mostly the higher harmonics that are in the audible range for sonic booms. 相似文献
162.
163.
Thomas I. Vogel 《Journal of Mathematical Fluid Mechanics》2013,15(2):397-413
Stability for a liquid bridge between two solid balls is studied by cutting and scaling pieces of a standardized family of Delaunay surfaces. This theoretical framework is used to analyze the problem numerically. 相似文献
164.
165.
Thomas Höche † Peter A. van Aken Michael Grodzicki Frank Heyroth Ralf Keding Reinhard Uecker 《哲学杂志》2013,93(29):3117-3132
Based on cluster molecular orbital calculations, high-energy resolution (ΔE?~ 0.4?eV) Ti–L2,3 electron energy loss near-edge structures of single-crystalline and glassy Ba2TiGe2O8 are interpreted. The finding that the Ti–L2,3 near-edge structure of the Ba2TiGe2O8 single crystal possesses less pronounced peaks than the glass under identical experimental conditions can be attributed to distinct distortions of the titanium environment caused by the very strong one-dimensional structural modulation hosted by the Ba2TiGe2O8 crystal lattice. As lattice periodicity is absent in the glass, the titanium environment is more regular in the vitreous surroundings. Moreover, the modulation in crystalline Ba2TiGe2O8 is responsible for the virtually indiscernible O–K near-edge structures of the glassy and crystalline samples. 相似文献
166.
Thomas Hellweg 《Journal of polymer science. Part A, Polymer chemistry》2013,51(14):1073-1083
Core–shell microgels are of increasing interest as smart carriers of catalysts, as sensors, or as building blocks for colloidal superstructures. In the context of colloidal assemblies, photonic applications are probably the most promising ones. This progress report presents and discusses the most recent results in this area focusing on the last 2–3 years, and also gives some background information. In addition, potential perspectives of this area will be outlined. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1073–1083 相似文献
167.
M. McCulloch S. K. Fadeff G. M. Mong R. G. Riley D. S. Sklarew B. L. Thomas 《International journal of environmental analytical chemistry》2013,93(2-4):289-293
Abstract DOE Methods for Evaluating Environmental and Waste Management Samples (DOE Methods) is a guidance/methods document to support sampling and analysis activities at DOE sites. DOE Methods is intended to supplement existing guidance documents (e.g., EPA's Test Methods for Evaluating Solid Waste, SW-846), which generally apply to low-level or nonradioactive samples. DOE Methods targets the complexities of DOE radioactive mixed waste and environmental samples. The document contains quality assurance (QA), quality control (QC), safety, sampling, organic analysis, inorganic analysis, and radioanalytical guidance as well as sampling and analytical methods. An addendum is distributed every six months (April and October) with updated guidance and additional methods. DOE Methods provides a vehicle for technology transfer within the environmental restoration (ER) and waste management (WM) (collectively known as EM) community. As DOE Methods evolves, its usefulness and applicability are anticipated to grow to meet the demands of the DOE/EM mission. At the present time, DOE Methods contains methods and guidance information supplied by DOE sites. Because the EM activities in DOE are not unique to the United States, the international environmental community could benefit from the information gathered for the DOE program. This information could provide additional resources for their EM activities. 相似文献
168.
Abstract Alkyl and aryl thioglycosides were converted in high yield into the corresponding α-glycosyl fluorides by treatment with dimethyl(methylthio)-sulfonium tetrafluoroborate. Glycosidic linkages and most protective groups are not affected by the reaction conditions. Glycosyl fluorides are proposed to be intermediates in glycosylations promoted by dimethyl(methylthio)-sulfonium tetrafluoroborate. 相似文献
169.
A new platinum acetylide complex based on 6-dialkylaminobenzimidazol-2-yl-vinyl-2-thiophene-5-ylethyne was synthesized in seven steps and 2% overall yield. 相似文献
170.