全文获取类型
收费全文 | 384908篇 |
免费 | 3309篇 |
国内免费 | 1177篇 |
专业分类
化学 | 211972篇 |
晶体学 | 6199篇 |
力学 | 15550篇 |
综合类 | 8篇 |
数学 | 40295篇 |
物理学 | 115370篇 |
出版年
2019年 | 3254篇 |
2018年 | 4328篇 |
2017年 | 4189篇 |
2016年 | 6264篇 |
2015年 | 3882篇 |
2014年 | 5950篇 |
2013年 | 16267篇 |
2012年 | 11505篇 |
2011年 | 14234篇 |
2010年 | 10020篇 |
2009年 | 9816篇 |
2008年 | 13313篇 |
2007年 | 13482篇 |
2006年 | 12684篇 |
2005年 | 11451篇 |
2004年 | 10355篇 |
2003年 | 9452篇 |
2002年 | 9163篇 |
2001年 | 10844篇 |
2000年 | 8432篇 |
1999年 | 6493篇 |
1998年 | 5367篇 |
1997年 | 5452篇 |
1996年 | 5195篇 |
1995年 | 4496篇 |
1994年 | 4503篇 |
1993年 | 4409篇 |
1992年 | 5003篇 |
1991年 | 4964篇 |
1990年 | 4801篇 |
1989年 | 4862篇 |
1988年 | 4707篇 |
1987年 | 4687篇 |
1986年 | 4430篇 |
1985年 | 5914篇 |
1984年 | 6031篇 |
1983年 | 4945篇 |
1982年 | 5353篇 |
1981年 | 5178篇 |
1980年 | 4900篇 |
1979年 | 5275篇 |
1978年 | 5583篇 |
1977年 | 5468篇 |
1976年 | 5340篇 |
1975年 | 5059篇 |
1974年 | 5024篇 |
1973年 | 5135篇 |
1972年 | 3445篇 |
1968年 | 3341篇 |
1967年 | 3781篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
Dielectric relaxation measurements of 5 mole % 4-n-hexyloxycyanobenzene (I) dissolved in 4-n-pentyloxyphenyl-trans-4-n-octylcyclohexylcarboxylate (II) were carried out from 1 kHz to 10 MHz in the nematic, smectic A and smectic B phases. The relaxation frequency of I parallel to the director is about 05 MHz in the SBphase and increases rapidly at the transition from SB to SA. 相似文献
172.
Let M be a symplectic manifold with a Hamiltonian circle action with isolated fixed points. We prove that σ (M) = b0(M) − b2(M) + b4(M) − b6(M) + … where σ (M) is the signature of M and bi(M) is the ith Betti number of M. 相似文献
173.
P. J. Wagstaffe A. Boenke E. Schnug A. S. Lindsey 《Fresenius' Journal of Analytical Chemistry》1992,344(1-2):1-7
Summary The sulphur content of three rapeseed reference materials has been certified on the basis of measurements made by inductively
coupled plasma-optical emission spectroscopy, isotope-dilution mass spectrometry and ion chromatography. Their suitability
for the calibration of x-ray fluorescence spectrometers used for measuring sulphur in rapeseed samples was established. 相似文献
174.
There is a high correlation between molecular surface area (TSA) of triorganotin and triorganolead compounds and their toxicity towards a bacterium (Escherichia coli) and an alga (Selenastrum capricornutum). Parallel attempts to correlate other Group IVA organometals incorporating silicon or germanium were unsuccessful. It was further demonstrated, however, that a high correlation was obtainable between certain series of compounds with the same organic substituent but different metal centers involving all Group IVA elements. In both instances, the inability to obtain a quantitative structure-activity relationship (QSAR) for all systems studied appears to be a function of the solubility of the compounds. While organotin TSA values have been found to correlate well with their toxicities toward various organisms, this study clearly suggests that this type of QSAR can be readily extended to include other organometal systems, provided that there is no solubility problem and the toxicity is a function of the hydrophobicity of the organometal compounds. 相似文献
175.
1-(3-Alkyl-2,3-dideoxy-alpha,beta-D-erythro-pentofuranosyl)uracils and 1-(3-alkyl-2,3-dideoxy-alpha,beta-D-threo-pentofuranosyl)uracils have been prepared from (E)-4,5-di-O-acetyl-2,3-dideoxy-aldehydo-D-glycero-pent-2-enose by a Michael addition reaction of the appropriate organocopper reagent followed in subsequent order by glycosidation of the resulting 3-alkyl-4,5-diacetoxypentanal with methanolic hydrogen chloride, protection with p-methoxybenzoyl chloride, and trimethylsilyl triflate catalyzed coupling with 2,4-di-O-(trimethylsilyl)uracil. The nucleosides were deprotected by treatment with 33% methylamine in absolute ethanol and separated by reversed-phase HPLC. 相似文献
176.
The temperature dependence of the principal values of the refractive index in Sr1−x
CaxTiO3 (x=0.014) has been measured in the 17–275 K range under various conditions of sample illumination with 1.96 eV photons. The
spontaneous photorefractive contribution δn
ph to the temperature-induced variation of the refractive index of Sr1−x
CaxTiO3, which appears after illumination of the sample in the ferrophase (transition temperature T
c=32 K) and persists in the paraphase under heating up to 150 K, has been separated. The photoinduced polarization has been
estimated.
Fiz. Tverd. Tela (St. Petersburg) 39, 711–713 (April 1997) 相似文献
177.
Zi‐Cai Li Tzon‐Tzer Lu Hung‐Tsai Huang Alexander H.‐D. Cheng 《Numerical Methods for Partial Differential Equations》2007,23(1):93-144
In this article we survey the Trefftz method (TM), the collocation method (CM), and the collocation Trefftz method (CTM). We also review the coupling techniques for the interzonal conditions, which include the indirect Trefftz method, the original Trefftz method, the penalty plus hybrid Trefftz method, and the direct Trefftz method. Other boundary methods are also briefly described. Key issues in these algorithms, including the error analysis, are addressed. New numerical results are reported. Comparisons among TMs and other numerical methods are made. It is concluded that the CTM is the simplest algorithm and provides the most accurate solution with the best numerical stability. © 2006 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2007 相似文献
178.
C. Ziegler F. Baudenbacher H. Karl H. Kinder W. Göpel 《Fresenius' Journal of Analytical Chemistry》1991,341(3-4):308-313
Summary The influence of different preparation conditions and substrate surface orientations on the superconducting properties of thin YBa2Cu3O7–x (YBCO) films on silicon was studied. Comparative electrical and surface spectroscopic measurements were performed. SAM and SIMS depth profile analysis show an enrichment of barium at the interface between the superconductor and silicon for samples with Tc<76 K. Comparison with XPS data obtained for thin silicon films on YBCO indicates the formation of barium and yttrium silicates at the interface under these conditions. 相似文献
179.
M A Aguilar-Mendez E San Martin-Martinez J E Morales A Cruz-Orea M R Jaime-Fonseca 《Analytical sciences》2007,23(4):457-461
Water vapor diffusion coefficient (WVDC) and thermal diffusivity (alpha) were determined in gelatin-starch films through photothermal techniques. The effect of different variables in the elaboration of these films, such as starch and glycerol concentrations and pH, were evaluated through the response surface methodology. The results indicated that an increase in the glycerol concentration and pH favored the WVDC of the films. On the other hand, alpha was influenced principally by the starch content and pH of the film-forming solution. The minimum alpha value was 4.5 x 10(-4) cm2/s, which is compared with alpha values reported for commercial synthetic polymers. 相似文献
180.
H. Caines 《The European Physical Journal C - Particles and Fields》2007,49(1):297-301
The soft physics, pT<2 GeV/c, observables at both RHIC and the SPS have now been mapped out in quite specific detail. From these results there
is mounting evidence that this regime is primarily driven by the multiplicity per unit rapidity, dNch/dη. This suggests that the entropy of the system alone is the underlying driving force for many of the global observables
measured in heavy-ion collisions. That this is the case and there is an apparent independence on collision energy is surprising.
I present the evidence for this multiplicity scaling and use it to make some extremely naive predictions for the soft sector
results at the LHC. 相似文献