全文获取类型
收费全文 | 211535篇 |
免费 | 1775篇 |
国内免费 | 625篇 |
专业分类
化学 | 115178篇 |
晶体学 | 2600篇 |
力学 | 8278篇 |
综合类 | 6篇 |
数学 | 23179篇 |
物理学 | 64694篇 |
出版年
2020年 | 1970篇 |
2019年 | 2262篇 |
2018年 | 3204篇 |
2017年 | 3113篇 |
2016年 | 4266篇 |
2015年 | 2371篇 |
2014年 | 3817篇 |
2013年 | 9260篇 |
2012年 | 6890篇 |
2011年 | 8434篇 |
2010年 | 6071篇 |
2009年 | 5921篇 |
2008年 | 8137篇 |
2007年 | 8206篇 |
2006年 | 7631篇 |
2005年 | 6936篇 |
2004年 | 6147篇 |
2003年 | 5558篇 |
2002年 | 5091篇 |
2001年 | 5741篇 |
2000年 | 4389篇 |
1999年 | 3198篇 |
1998年 | 2702篇 |
1997年 | 2824篇 |
1996年 | 2607篇 |
1995年 | 2252篇 |
1994年 | 2342篇 |
1993年 | 2372篇 |
1992年 | 2521篇 |
1991年 | 2595篇 |
1990年 | 2502篇 |
1989年 | 2462篇 |
1988年 | 2405篇 |
1987年 | 2393篇 |
1986年 | 2301篇 |
1985年 | 2988篇 |
1984年 | 3147篇 |
1983年 | 2502篇 |
1982年 | 2777篇 |
1981年 | 2659篇 |
1980年 | 2466篇 |
1979年 | 2687篇 |
1978年 | 2797篇 |
1977年 | 2831篇 |
1976年 | 2800篇 |
1975年 | 2659篇 |
1974年 | 2637篇 |
1973年 | 2786篇 |
1972年 | 1850篇 |
1967年 | 1830篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
M. S. Fedoseev V. Yu. Gusev L. F. Derzhavinskaya V. E. Antipin R. V. Tsvetkov 《Polymer Science Series D》2018,11(1):39-46
The interaction of UP-643 epoxy-novolac resin with isomethyltetrahydrophthalic anhydride in the presence of the catalysts (azo-compounds of different structure) is studied. Latency of the catalysts is found. The possibility is shown of creating epoxy binders with a long lifetime (10–40 days) at room temperatures, cured at increased temperature up to heat-resistant polymers. 相似文献
62.
63.
This paper presents the experimental characterization of the in-plane deformation field at any depth within a granular support medium (GSM) called Carbomer 940 using digital image correlation (DIC) and particle image velocimetry (PIV). A method was developed to produce a 2D plane of randomly shaped speckles within the GSM for DIC. Four different needle diameters and four different speeds were used as test specimens representative of those utilized for 3D printing of soft matter in the GSM. The results can be used to determine dimensional tolerances and assessing interactions between multiple injection needles and acceptable spacing. The displacements in the direction of needle motion (u) and transverse (v) were obtained. Subsequently, the magnitudes were determined as a function of distance from the needle path and time history. Results show that near the needle there is a region of yielded/fluidized material and away from the needle path the material acts like a viscoelastic solid. Permanent deformation decreases with increased distance from the path and recovery is enhanced by reversing back through the path. 相似文献
64.
The problem of describing the behavior of a highly filled polymeric material under compression, which was preceded by preliminary compression and unloading, is considered. The peculiarity of the compression diagrams obtained in the experiment is the downward convexity of the curves of the stress modulus versus time. To solve this problem, a variant of the non-linear endochronic theory of aging viscoelastic materials with several aging and viscosity functions and a numerical-graphical method for identifying the properties of viscoelasticmaterials proposed by the authors earlier, suggesting comparison of the deformation diagrams of intact samples and those that received preliminary damage, are used. 相似文献
65.
K. E. Prikhodko M. M. Dementyeva B. A. Gurovich D. A. Komarov L. V. Kutuzov 《Crystallography Reports》2018,63(2):241-244
The change in the free-electron density in ultrathin (5 nm) superconducting NbN films in the initial state and after irradiation by O+ ions to doses of (0.1–0.9) × 1017 cm–2 has been studied by electron energy-loss spectroscopy (EELS). The analysis has been performed on cross section samples prepared by the focused ion beam method, using plasmon oscillations with energies up to 50 eV. The radiation-induced replacement of nitrogen atoms with oxygen atoms in niobium nitride is found to change the electrical properties of the material, which leads to a decrease in the free-electron density with an increase in the irradiation dose. 相似文献
66.
An automorphism of an abelian variety induces a decomposition of the variety up to isogeny. There are two such results, namely the isotypical decomposition and Roan’s decomposition theorem. We show that they are essentially the same. Moreover, we generalize in a sense this result to abelian varieties with action of an arbitrary finite abelian group. An early version of this article was inadvertently published before all the revisions had been completed and then retracted [https://doi.org/10.1007/s00013-018-1244-3]. This article is the final peer reviewed version.
相似文献67.
Torin F. Stetina Aurora E. Clark Xiaosong Li 《International journal of quantum chemistry》2019,119(1):e25802
Despite fundamental importance, the experimental characterization of the hydrogen bond network, particularly in multicomponent protic solutions, remains a challenge. Although recent work has experimentally validated that the oxygen K-edge X-ray absorption spectra is sensitive to local hydrogen bond patterns in pure water and aqueous alcohol solutions, the generality of this observation is unknown—as is the sensitivity to the electronic structure of the alcohol cosolvent. In this work, we investigate the electronic structure of water solvated alcohol model geometries using energy specific time-dependent density functional theory to calculate oxygen K-edge X-ray excitations. We find that the geometry of dangling hydrogen bonds in pure water is the main contributor to the pre-edge feature seen in the X-ray absorption spectra, agreeing with previous experimental and theoretical work. We then extend this result to solvated alcohol systems and observe a similar phenomenon, yet importantly, the increase of electron donation from alkyl chains to the alcohol OH group directly correlates to the strength of the core excitation on the dangling hydrogen bond model geometry. This trend arises from a stronger transition dipole moment due to electron localization on the OH group. 相似文献
68.
69.
70.
Eremina T. A. Belokoneva E. L. Dimitrova O. V. Volkov A. S. 《Crystallography Reports》2019,64(1):57-62
Crystallography Reports - The structures of Rb-boroleucite Rb1.0(B0.333Si0.667)3O6 and boropollucite Cs0.87(B0.290Si0.710)3O6 were studied using single crystals, which were prepared under... 相似文献