全文获取类型
收费全文 | 11913篇 |
免费 | 1072篇 |
国内免费 | 527篇 |
专业分类
化学 | 7244篇 |
晶体学 | 376篇 |
力学 | 194篇 |
综合类 | 45篇 |
数学 | 2972篇 |
物理学 | 2681篇 |
出版年
2023年 | 31篇 |
2022年 | 112篇 |
2021年 | 73篇 |
2020年 | 145篇 |
2019年 | 228篇 |
2018年 | 245篇 |
2017年 | 264篇 |
2016年 | 272篇 |
2015年 | 425篇 |
2014年 | 476篇 |
2013年 | 642篇 |
2012年 | 549篇 |
2011年 | 757篇 |
2010年 | 665篇 |
2009年 | 878篇 |
2008年 | 713篇 |
2007年 | 707篇 |
2006年 | 606篇 |
2005年 | 551篇 |
2004年 | 668篇 |
2003年 | 604篇 |
2002年 | 521篇 |
2001年 | 434篇 |
2000年 | 379篇 |
1999年 | 299篇 |
1998年 | 238篇 |
1997年 | 216篇 |
1996年 | 228篇 |
1995年 | 170篇 |
1994年 | 217篇 |
1993年 | 176篇 |
1992年 | 135篇 |
1991年 | 83篇 |
1990年 | 63篇 |
1989年 | 63篇 |
1988年 | 54篇 |
1987年 | 70篇 |
1986年 | 57篇 |
1985年 | 49篇 |
1984年 | 44篇 |
1983年 | 13篇 |
1982年 | 39篇 |
1981年 | 42篇 |
1980年 | 49篇 |
1979年 | 67篇 |
1978年 | 53篇 |
1977年 | 53篇 |
1976年 | 37篇 |
1974年 | 13篇 |
1973年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Nadya Dencheva Teresa G. Nunes M. Jovita Oliveira Zlatan Denchev 《Journal of Polymer Science.Polymer Physics》2005,43(24):3720-3733
The crystalline structure of polyamide‐12 (PA12) was studied by solid‐state 13C nuclear magnetic resonance (NMR) as well as by synchrotron wide‐ and small‐angle X‐ray scattering (WAXS and SAXS). Isotropic and oriented PA12 showed different NMR spectra ascribed to γ‐ and γ′‐crystalline modifications, respectively. On the basis of the position of the first diffraction peak, the isotropic γ‐form and the oriented γ′‐form were shown to be with hexagonal crystalline lattice at room temperature. When heated, the two PA12 polymorphs demonstrated different behaviors. Above 140 °C, the isotropic γ‐PA12 partially transformed into α‐modification. No such transition was observed with the oriented γ′‐PA12 phase even after annealing at temperatures close to melting. A γ′–γ transition was observed here only after isotropization by melting point. Various structural parameters were extracted from the WAXS and SAXS patterns and analyzed as a function of temperature and orientation: the degree of crystallinity, the d‐spacings, the Bragg's long spacings, the average thicknesses of the crystalline (lc) and amorphous (la) phases, and the linear crystallinity xcl within the lamellar stacks. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3720–3733, 2005 相似文献
62.
Thi Thi Nge Naruhito Hori Akio Takemura Hirokuni Ono Tsunehisa Kimura 《Journal of Polymer Science.Polymer Physics》2003,41(7):711-714
A high magnetic field of 5 T was used to fabricate a magnetically aligned, optically anisotropic, liquid‐crystalline chitin/poly(acrylic acid) composite. The aligned mesophase was fixed by photoinitiated free‐radical polymerization. From an examination of polarized optical micrographs and an X‐ray diffraction study, a high degree of orientation of 0.70 was observed for the composite with a higher liquid‐crystalline chitin concentration (10.70 wt %); the orientation was reduced with a decreased chitin concentration at a given acrylic acid concentration. The X‐ray data for the developed composite showed a uniplanar orientation for the chitin crystallites, with its molecular long axes perpendicular to the direction of the magnetic field. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 711–714, 2003 相似文献
63.
The central zinc(II) atom in the title complex is tetrahedrally coordinated by four nitrogen atoms derived from 4‐methyl‐5‐imidazolecarboxyaldehyde ligands with Zn? N in the range 2.007(3) to 2.026(4) Å. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
64.
《The European Physical Journal A - Hadrons and Nuclei》2003,17(2):241-244
The helicity dependence of the γ
p↦pη reaction has been measured for the first time at a center-of-mass angle θ*
η = 70° in the photon energy range from 780 MeV to 790 MeV. The experiment, performed at the Mainz microtron MAMI, used a 4π-detector
system, a circularly polarized, tagged photon beam, and a longitudinally polarized frozen-spin target. The helicity 3/2 cross-section
is found to be small and the results for helicity 1/2 agree with predictions from the MAID analysis.
Received: 19 December 2002 / Accepted: 10 March 2003 / Published online: 20 May 2003 相似文献
65.
Runqing Ou Rosario A. Gerhardt Robert J. Samuels 《Journal of Polymer Science.Polymer Physics》2003,41(8):823-841
The relationships of the structure and electrical properties of anisotropic HCl‐doped polyaniline (PANI) films cast from N,N′‐dimethylpropylene urea (DMPU) solutions and stretched to different draw ratios were studied. The anisotropic structure of the stretched PANI films was examined by X‐ray diffraction, near‐infrared wave‐guide coupling, and polarized infrared measurements. The PANI emeraldine base (EB) films cast from DMPU solutions had a single‐phase noncrystalline structure, and stretching of the films did not cause crystallization to occur. The transition moment angles of two weakly absorbing infrared bands were determined, and the Hermans' orientation functions for the PANI EB films were calculated. The PANI films were then doped with HCl, and the electrical properties were determined by impedance spectroscopy. With a specially designed test fixture, the in‐plane and through‐plane impedance was obtained. The conductivity along the stretch direction increased with orientation. The in‐plane conductivity was significantly higher than the through‐plane conductivity. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 823–841, 2003 相似文献
66.
67.
金淦 《Annals of Differential Equations》1998,(4)
1IntroductionStabilityintermsoftwomeasures,thisconceptenableustounifyava-rietyofstabilityconceptsandtoofferageneralandunifiedframeworkforinvestigationofstabilitytheory.AndtheoriginalLiapunovtheoremshavebeenextended,generalizedandweakenedinvariousaspects[3… 相似文献
68.
In this paper we face the problem of stowing a containership, referred to as the Master Bay Plan Problem (MBPP); this problem
is difficult to solve due to its combinatorial nature and the constraints related to both the ship and the containers. We
present a decomposition approach that allows us to assign a priori the bays of a containership to the set of containers to
be loaded according to their final destination, such that different portions of the ship are independently considered for
the stowage. Then, we find the optimal solution of each subset of bays by using a 0/1 Linear Programming model. Finally, we
check the global ship stability of the overall stowage plan and look for its feasibility by using an exchange algorithm which
is based on local search techniques. The validation of the proposed approach is performed with some real life test cases.
This work has been developed within the research area: “The harbour as a logistic node” of the Italian Centre of Excellence
on Integrated Logistics (CIELI) of the University of Genoa, Italy 相似文献
69.
Carlo Carlini Valentina De Luise Anna Maria Raspolli Galletti Glauco Sbrana 《Journal of polymer science. Part A, Polymer chemistry》2006,44(1):200-206
Novel catalytic systems, prepared in situ by the oxidative addition of 8‐hydroxyquinoline ligands to bis(1,5‐cyclooctadiene)nickel(0) and activated by methylaluminoxane, were studied in ethylene polymerization. When 8‐hydroxyquinoline was employed, only oligomeric products were obtained. On the contrary, 5,7‐dinitro‐8‐hydroxyquinoline gave linear polyethylene (PE), but with a modest activity. For the catalyst based on 5‐nitro‐8‐hydroxyquinoline, the productivity was largely dependent on the content of free trimethylaluminum (TMA) present in the commercial aluminoxane. The progressive optimization of the TMA/oligomeric methylaluminoxane ratio increased the productivity, which reached 700 kg of PE/(mol of Ni × h), by an order of magnitude. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 200–206, 2006 相似文献
70.