全文获取类型
收费全文 | 16770篇 |
免费 | 3795篇 |
国内免费 | 1976篇 |
专业分类
化学 | 11250篇 |
晶体学 | 161篇 |
力学 | 908篇 |
综合类 | 135篇 |
数学 | 2808篇 |
物理学 | 7279篇 |
出版年
2024年 | 63篇 |
2023年 | 241篇 |
2022年 | 453篇 |
2021年 | 538篇 |
2020年 | 699篇 |
2019年 | 656篇 |
2018年 | 558篇 |
2017年 | 627篇 |
2016年 | 976篇 |
2015年 | 934篇 |
2014年 | 1114篇 |
2013年 | 1746篇 |
2012年 | 1201篇 |
2011年 | 1180篇 |
2010年 | 1031篇 |
2009年 | 1090篇 |
2008年 | 1179篇 |
2007年 | 1211篇 |
2006年 | 1029篇 |
2005年 | 980篇 |
2004年 | 787篇 |
2003年 | 684篇 |
2002年 | 503篇 |
2001年 | 411篇 |
2000年 | 411篇 |
1999年 | 346篇 |
1998年 | 311篇 |
1997年 | 245篇 |
1996年 | 183篇 |
1995年 | 176篇 |
1994年 | 144篇 |
1993年 | 107篇 |
1992年 | 101篇 |
1991年 | 69篇 |
1990年 | 63篇 |
1989年 | 63篇 |
1988年 | 70篇 |
1987年 | 45篇 |
1986年 | 45篇 |
1985年 | 53篇 |
1984年 | 39篇 |
1983年 | 13篇 |
1982年 | 32篇 |
1981年 | 34篇 |
1980年 | 16篇 |
1979年 | 15篇 |
1978年 | 15篇 |
1977年 | 14篇 |
1976年 | 8篇 |
1974年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Devin Kilminster David Allingham Alistair Mees 《Annals of the Institute of Statistical Mathematics》2002,54(1):224-233
Knowing a probability density (ideally, an invariant density) for the trajectories of a dynamical system allows many significant estimates to be made, from the well-known dynamical invariants such as Lyapunov exponents and mutual information to conditional probabilities which are potentially more suitable for prediction than the single number produced by most predictors. Densities on typical attractors have properties, such as singularity with respect to Lebesgue measure, which make standard density estimators less useful than one would hope. In this paper we present a new method of estimating densities which can smooth in a way that tends to preserve fractal structure down to some level, and that also maintains invariance. We demonstrate with applications to real and artificial data. 相似文献
52.
53.
Tatsuo Nakagawa Satoshi Fukura Munenori Nakai Kazumasa Sugiyama Ryohei Kokawa Hiroyuki Kagi 《Optical Review》2006,13(4):269-275
We constructed a scanning near-field optical microscope (SNOM) on a commercially available atomic force microscopy (AFM) apparatus
(SPM-9500J2; Shimadzu Corp.) to measure the stress distribution in ceramic composite materials. Features of our SNOM system
are: (1) a compact SNOM head substituted for the original AFM head; (2) a wide scanning range (125 × 125 μm2) inherited from the original scanner; (3) use of conventional shear-force regulation; (4) an optical system for the illumination-collection
(I-C) mode; (5) excitation by a 488 nm line of an Ar-ion laser, and (6) light detection by photon counting or a polychromator
equipped with an electronically cooled charge coupled device (CCD). This SNOM system was used to measure the surface structure
and stress distribution of an Al2O3/ZrO2 eutectic composite. We simultaneously measured topographic images and fluorescence spectra of an Al2O3/ZrO2 eutectic composite. We estimated its peak intensity, peak position, and peak width from the fluorescence spectrum during
scanning, which respectively correspond to the abundance of Al2O3, stress in the grain, and the anisotropy of that stress. Mapping images showed that the stress and its anisotropy were weaker
in the center of the Al2O3 grain than its boundary between Al2O3 and ZrO2. That observation suggests that Al2O3 underwent intense anisotropic stress induced by volume expansion in the phase transition of ZrO2 from the cubic phase to the monoclinic phase during preparation. 相似文献
54.
《中国科学B辑(英文版)》2007,(6)
Five polymer bonded explosives (PBXs) with the base explosive ε-CL-20 (hexanitrohexaazaisowurtzi- tane), the most important high energy density compound (HEDC), and five polymer binders (Estane 5703, GAP, HTPB, PEG, and F2314) were constructed. Molecular dynamics (MD) method was employed to investigate their binding energies (Ebind), compatibility, safety, mechanical properties, and energetic properties. The information and rules were reported for choosing better binders and guiding formula- tion design of high energy density material (HEDM). According to the calculated binding energies, the ordering of compatibility and stability of the five PBXs was predicted as ε-CL-20/PEG > ε-CL-20/ Estane5703 ≈ε-CL-20/GAP > ε-CL-20/HTPB > ε-CL-20/F2314. By pair correlation function g(r) analyses, hydrogen bonds and vdw are found to be the main interactions between the two components. The elasticity and isotropy of PBXs based ε-CL-20 can be obviously improved more than pure ε-CL-20 crystal. It is not by changing the molecular structures of ε-CL-20 for each binder to affect the sensitivity. The safety and energetic properties of these PBXs are mainly influenced by the thermal capability (C°p) and density (ρ) of binders, respectively. 相似文献
55.
R. Jayakumar Y.‐S. Lee S. Nanjundan 《Journal of polymer science. Part A, Polymer chemistry》2003,41(18):2865-2878
The calcium salt of mono(hydroxyethoxyethyl)phthalate [Ca(HEEP)2] was synthesized by the reaction of diethylene glycol, phthalic anhydride, and calcium acetate. Calcium‐containing poly(urethane ether)s (PUEs) were synthesized by the reaction of hexamethylene diisocyanate (HMDI) or tolylene 2,4‐diisocyanate (TDI) with a mixture of Ca(HEEP)2 and poly(ethylene glycol) (PEG300 or PEG400) with di‐n‐butyltin dilaurate as a catalyst. A series of calcium‐containing PUEs of different compositions were synthesized with Ca(HEEP)2/PEG300 (or PEG400)/diisocyanate (HMDI or TDI) molar ratios of 2:2:4, 3:1:4, and 1:3:4 so that the coating properties of the PUEs could be studied. Blank PUEs without calcium‐containing ionic diols were also prepared by the reaction of PEG300 or PEG400 with HMDI or TDI. The PUEs were well characterized by Fourier transform infrared, 1H and 13C NMR, solid‐state cross‐polarity/magic‐angle‐spinning 13C NMR, viscosity, solubility, and X‐ray diffraction studies. The thermal properties of the polymers were also studied with thermogravimetric analysis and differential scanning calorimetry. The PUEs were applied as top coats on acrylic‐coated leather, and their physicomechanical properties were also studied. The coating properties of PUEs, such as the tensile strength, elongation at break, tear strength, water vapor permeability, flexing endurance, cold crack resistance, abrasion resistance, color fastness, and adhesive strength, were better than the standard values. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2865–2878, 2003 相似文献
56.
Pearson-χ~2距离的若干性质 总被引:18,自引:0,他引:18
李开灿 《数学的实践与认识》2003,33(1):49-53
本文对数理统计中常用的 Pearson- χ2距离的分析特性进行了讨论 ,得到了这一距离的一些解析性质 ,最后我们还给出了几个常用距离的关系 . 相似文献
57.
Letters in Mathematical Physics - 相似文献
58.
选用新方法合成了2-碘—N-甲基苯磺酰胺,通过^1H NMR,^13C NMR,^13C DEPT NMR(Distortionless Enhancement by Polarization Transfer NMR)和MS确证的其结构。 相似文献
59.
M. I. Gil' 《Proceedings of the American Mathematical Society》2003,131(12):3737-3746
A linear operator in a separable Hilbert space is called a quasinormal one if it is a sum of a normal operator and a compact one. In the paper, bounds for the spectrum of quasinormal operators are established. In addition, the lower estimate for the spectral radius is derived. Under some restrictions, that estimate improves the well-known results. Applications to integral operators and matrices are discussed. Our results are new even in the finite-dimensional case.
60.