全文获取类型
收费全文 | 8197篇 |
免费 | 685篇 |
国内免费 | 581篇 |
专业分类
化学 | 1909篇 |
晶体学 | 36篇 |
力学 | 518篇 |
综合类 | 58篇 |
数学 | 1242篇 |
物理学 | 1461篇 |
综合类 | 4239篇 |
出版年
2024年 | 7篇 |
2023年 | 48篇 |
2022年 | 77篇 |
2021年 | 97篇 |
2020年 | 99篇 |
2019年 | 138篇 |
2018年 | 138篇 |
2017年 | 193篇 |
2016年 | 197篇 |
2015年 | 272篇 |
2014年 | 311篇 |
2013年 | 427篇 |
2012年 | 400篇 |
2011年 | 404篇 |
2010年 | 346篇 |
2009年 | 350篇 |
2008年 | 412篇 |
2007年 | 514篇 |
2006年 | 480篇 |
2005年 | 481篇 |
2004年 | 389篇 |
2003年 | 427篇 |
2002年 | 488篇 |
2001年 | 385篇 |
2000年 | 366篇 |
1999年 | 340篇 |
1998年 | 286篇 |
1997年 | 236篇 |
1996年 | 148篇 |
1995年 | 136篇 |
1994年 | 132篇 |
1993年 | 114篇 |
1992年 | 110篇 |
1991年 | 63篇 |
1990年 | 58篇 |
1989年 | 61篇 |
1988年 | 66篇 |
1987年 | 48篇 |
1986年 | 28篇 |
1985年 | 31篇 |
1984年 | 27篇 |
1983年 | 11篇 |
1982年 | 22篇 |
1981年 | 17篇 |
1980年 | 10篇 |
1979年 | 42篇 |
1978年 | 16篇 |
1977年 | 5篇 |
1974年 | 4篇 |
1973年 | 2篇 |
排序方式: 共有9463条查询结果,搜索用时 78 毫秒
41.
B. Velázquez-Martí C. Gracia-López 《International Journal of Infrared and Millimeter Waves》2004,25(7):1109-1122
The thermal treatment by millimeter waves for the soil disinfection can be one possible alternative to chemical treatments. This physical method is based on incrementing the soil temperature and its pathogens irradiating with high frequency electromagnetic waves. So the previous knowledge of the temperature distribution in the irradiated soil is essential for achieving an effective bad microorganism and weed seeds elimination. This report analyse the heating kinetic and spatial distribution of the maximum temperatures reached by the soil. It is presented a mathematic model about how are distributed the reached temperatures in the depth of the irradiated soil. This model concludes that when an orchard soil is irradiated superficially by microwaves, the microwaves have a big attenuation due to the soil dielectric properties and the water located in the pores of the most superficial layer. This fact causes a shield effect blocking the waves penetration in few centimetres. The heating by radiation is reduced to the superficial layer. The heating propagation in the depth is occurred by conduction following the Fourier equations. 相似文献
42.
The oxidation of aminoethanethiol (1) was investigated in acid solutions on a glass carbon anode. It was shown that at relatively low anode potentials thiyl radicals RS· are released into the solution, but this does not lead to binding of the oxygen in the solution. Raising the anode potential leads to binding of oxygen, which is probably due to the formation of the intermediate RS+. The oxidation of 1 was studied in Ce(SO4)2+H2SO4 solution. It was shown that under certain conditions the intermediate is RS+, which subsequently converts to a product that could not be identified as any previously described product of the oxidation of thiols. Proposals are made regarding its structure and conversion pathways.B. P. Konstantinov Institute of Nuclear Physics, Russian Academy of Sciences, 188350 Leningrad. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 2, pp. 278–288, February, 1992. 相似文献
43.
Jesús de la Cal Javier Cárcamo 《Journal of Mathematical Analysis and Applications》2007,334(2):1106-1115
As a consequence of Jensen's inequality, centered operators of probabilistic type (also called Bernstein-type operators) approximate convex functions from above. Starting from this fact, we consider several pairs of classical operators and determine, in each case, which one is better to approximate convex functions. In almost all the discussed examples, the conclusion follows from a simple argument concerning composition of operators. However, when comparing Szász-Mirakyan operators with Bernstein operators over the positive semi-axis, the result is derived from the convex ordering of the involved probability distributions. Analogous results for non-centered operators are also considered. 相似文献
44.
Cai-yun Jin Cao-zong Cheng Yong-tao Jin Jing Li 《应用数学学报(英文版)》2006,22(4):607-614
Two two-function minimax theorems are proved.The concavity-convexity conditions of the twofunctions involve strictly monotone transformations and mixing of the values of the two functions,and aredescribed by the inequalities as upward and weakly downward conditions. 相似文献
45.
Arthur W. Apter 《Mathematical Logic Quarterly》2006,52(5):457-463
We construct models for the level by level equivalence between strong compactness and supercompactness in which for κ the least supercompact cardinal and δ ≤ κ any cardinal which is either a strong cardinal or a measurable limit of strong cardinals, 2δ > δ + and δ is < 2δ supercompact. In these models, the structure of the class of supercompact cardinals can be arbitrary, and the size of the power set of κ can essentially be made as large as desired. This extends and generalizes [5, Theorem 2] and [4, Theorem 4]. We also sketch how our techniques can be used to establish a weak indestructibility result. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
46.
47.
Michael I. Mishchenko 《Journal of Quantitative Spectroscopy & Radiative Transfer》2006,101(3):411-415
The volume integral equation formalism is used to prove the scale invariance rule for an arbitrarily sized scatterer with an arbitrary shape, morphology, and orientation. The only assumptions are that the scatterer is made of optically isotropic linear materials and is embedded in a homogeneous, linear, isotropic, and nonabsorbing infinite medium. 相似文献
48.
随着现代外语教学的发展,传统的俄语速读方法已远远不能满足要求。笔者认为,应适应时代的要求,充分利用现代化的教学手段和教学设备来提高速读课的效率。本文将阐述计算机辅助俄语速读课教学系统及其功能、特点,并论证该系统在学生形成良好的阅读习惯和提高阅读能力中的优势。 相似文献
49.
《Electroanalysis》2006,18(24):2451-2457
This paper describes a layer‐by‐layer (LBL) self‐assembly process of chitosan (CTS) and gold nanoparticles (Au) on the pretreated negatively charged glassy carbon (GC) electrode to fabricate electrochemistry immunosensor with a nontoxic biomimetic interface, which provided an environment similar to a native system and allowed more freedom in orientation for immobilization of carcinoembryonic antibody (anti‐CEA) to monitor carcinoembryonic antigen (CEA). UV‐vis spectroscope, atomic force microscopy (AFM), and cyclic voltammetric (CV) measurements were used to follow the multilayer film formation. The performance of the biominetic interface and factors influencing the assay system were investigated in detail. The differential pulse voltammetry (DPV) current response is used for the CEA concentration assay. The dynamic range was from 0.50 to 80.00 ng mL?1 with a detection limit of 0.27 ng mL?1 at 3σ. In addition, the experiment results indicate that immobilization described in this proposed method exhibits a good sensitivity, selectivity, and stability. 相似文献
50.