全文获取类型
收费全文 | 1615篇 |
免费 | 54篇 |
国内免费 | 11篇 |
专业分类
化学 | 1231篇 |
晶体学 | 16篇 |
力学 | 19篇 |
数学 | 105篇 |
物理学 | 309篇 |
出版年
2023年 | 11篇 |
2022年 | 9篇 |
2021年 | 22篇 |
2020年 | 15篇 |
2019年 | 28篇 |
2018年 | 26篇 |
2017年 | 23篇 |
2016年 | 24篇 |
2015年 | 42篇 |
2014年 | 47篇 |
2013年 | 81篇 |
2012年 | 120篇 |
2011年 | 126篇 |
2010年 | 55篇 |
2009年 | 58篇 |
2008年 | 108篇 |
2007年 | 100篇 |
2006年 | 79篇 |
2005年 | 96篇 |
2004年 | 84篇 |
2003年 | 72篇 |
2002年 | 93篇 |
2001年 | 16篇 |
2000年 | 24篇 |
1999年 | 16篇 |
1998年 | 11篇 |
1997年 | 20篇 |
1996年 | 17篇 |
1995年 | 15篇 |
1994年 | 14篇 |
1993年 | 12篇 |
1992年 | 15篇 |
1991年 | 9篇 |
1990年 | 15篇 |
1989年 | 8篇 |
1988年 | 11篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1985年 | 18篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 7篇 |
1981年 | 13篇 |
1979年 | 10篇 |
1978年 | 15篇 |
1977年 | 9篇 |
1976年 | 6篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1967年 | 8篇 |
排序方式: 共有1680条查询结果,搜索用时 31 毫秒
961.
4,13-Diaza-18-crown-6 substantially increases the rate of zirconium(IV) hydrolysis of unactivated peptide amide bonds under near-physiological conditions of temperature and pH. In the presence of this azacrown ether, ZrCl(4) efficiently hydrolyses both neutral and negatively charged peptides (pH 7.0-7.3, 37-60 degrees C). 相似文献
962.
Abe H Suzuki T Ootsuki A Ozaki K Samemoto H Watano S 《Chemical & pharmaceutical bulletin》2004,52(5):510-516
The properties of the wet kneaded wax matrix were evaluated using a compression tester, whereby a newly proposed sigma index for the plastic deformation was assessed in the pressure transmission diagram. The sigma index was indicative of a characteristic of the plastic yield point in the rheological behavior, and presented an initial and abrupt deformation of wet kneaded mass when the wet kneaded mass was subjected to the pressure. The value of sigma index was confirmed to decrease along with an increase in the plasticity of wet kneaded mass. The wet mass of wax matrix was prepared under various kneading time, and then extruded. The properties of the extruded granules such as pore volume, strength and dissolution were investigated. As a result, it was found that the sigma index decreased with an increase in kneading time. The granules with small value of sigma index showed few porosities, large strength and slow dissolution. It was demonstrated that the sigma index linked the characteristics of wet kneaded mass to the dissolution and the other granule properties. Existence of this link was revealed by sigma index evaluation relevant to the plasticity. The sigma index could be a decisive criterion to permit an in-process evaluation of the kneading progress quantitatively, and also useful for anticipating the dissolution of the final granules roughly. 相似文献
963.
Tanaka M Nishikino M Kawachi T Hasegawa N Kado M Kishimoto M Nagashima K Kato Y 《Optics letters》2003,28(18):1680-1682
We demonstrate an x-ray laser at a wavelength of 13.9 nm with a beam divergence of 0.2 mrad, which is 1.8 times the diffraction limit. The x-ray laser is generated with two gain media; the seed x-ray pulse from the first medium is amplified in the second medium. The effect of refraction on x-ray propagation is reduced by spatially and temporally controlling the injection of the seed x-ray to the second medium. 相似文献
964.
MRI-negative rotator cuff tears 总被引:2,自引:0,他引:2
We report two cases of rotator cuff tear in which the T(2)-weighted MRI signal was negative at the first examination, but positive by the second examination without any changes in symptoms. Many authors have reported on correlations between the MRI and operative findings of rotator cuff tears. However, MRI findings, history of symptoms and operative findings in our patients suggest that there was a discrepancy between symptoms and MRI findings dependent on the period from the injury. Operative findings also indicate that intratendinous tears might have occurred first in these patients then progressed to partial or full thickness tears over time. We concluded that physicians should keep rotator cuff pathology in mind even in patients whose MRI findings are negative but symptoms of rotator cuff tear persist. 相似文献
965.
Tsushima S Hasegawa A Suekane T Hirai S Tanaka Y Nakasuji Y 《Magnetic resonance imaging》2003,21(6):673-677
Magnetic resonance imaging (MRI) with a spatial tagging sequence was used to measure the velocity distribution of clay that was forced past a sudden contraction. A spatial tagging sequence provided magnetic resonance images of clay that allowed measurement of the velocity distribution in the clay, which can provide profound insights on the deformation process of clay during the intrusion process. The experiments were conducted using a specially-designed vessel that could operate at up to 30 MPa. The vessel offers a rectangle test section with a sudden contraction step that had a ratio of contraction of 2:1. The vessel was installed into a commercial magnetic resonance imaging equipment and then the fluid motion of clay flowing into the narrow contracted channel was quantitatively investigated to examine behaviors of flowing clay as non-Newtonian fluid. MRI results are compared with those obtained by computational fluid dynamics (CFD) calculation. Velocity distributions obtained from each tag displacement did not well agree with those predicted by CFD results near the contraction step where the fluid accelerated rapidly. However, a post-processing on calculation results, in which virtual tag displacement is calculated, gave better agreement with experiment and enabled us to compare MRI results with CFD results. 相似文献
966.
Optical switching devices have been studied using thin-film optical waveguides with fluorinated silicon oxide (SiOF) films
deposited by a liquid-phase deposition (LPD) technique. This report focuses on the structure of the thermo-optical (TO) switch
and its optimization. TO devices with double-and triple-layer structures were fabricated using a material with an organic
spin-on-glass (SOG) cladding layer and a liquid-phase deposited (LPD) SiOF core layer. The maximum extinction ratio of 15.97
dB was obtained for the double-layer structure TO devices at the half-wavelength power of 2.78 W, and at the heater area of
0.02 mm2. The response time decreased with decrease in the heater area for both double-and triple-layer structures. The response time
as short as 6.3 ms was obtained at the heater area of 0.02 mm2 for the double-layer structure. For the triple-layer structure, an even shorter response time of 2ms was achieved at the
heater area of 0.08 mm2, and this was over one order of magnitude smaller than that for the double-layer structure at the same heater area (280 ms). 相似文献
967.
Kentaro Miki 《中国物理 C》2007,(12)
Azimuthal anisotropy of direct photon is measured in S_(NN)~(1/2)=200GeV Au Au collisions at RHIC- PHENIX.Direct photon is one of the most effective probes to study properties of hot dence medium at initial state(also QGP state)of heavy ion collisions because photons almost do not interact strongly with any other particles caused by its long mean free path and they keep their conditions when they axe created.Within statistical and systematic errors,the elliptic flow parameter(v_2)of direct photon is consistent with zero. Direct photon v_2 is estimated by hadron decay photon contamination are subtracted from inclusive photon v_2 in intermediate to high transverse momentum(p_T)region(0 to 10GeV/c)for 3 centrality selections(20% steps)and minimum bias. 相似文献
968.
The crossover from Bardeen–Cooper–Schrieffer (BCS) superfluid with singlet pairs to Bose–Einstein condensation (BEC) of molecules is studied in one dimension. By use of the nested Bethe ansatz method, the ground state properties of spin-1/2 fermions interacting through attractive δ-function are analyzed explicitly for strong and weak couplings. Based on those results, we confirm a crossover picture, that is, in the BEC regime (strong couplings) the system is described by molecules with weak repulsion while in the BCS regime (weak couplings) it behaves as the weakly attractive fermions. 相似文献
969.
970.
Reflectance spectra of LiH single crystals are measured at the Li+K- absorption edge for the first time. The ?2 spectrum shows a prominent peak at 57.8 eV followed by several structures at the high energy side. We attribute the peak to a transition from the Li+ 1s to the n = 1 core exciton state associated with the p-like conduction band. 相似文献