全文获取类型
收费全文 | 648篇 |
免费 | 18篇 |
国内免费 | 6篇 |
专业分类
化学 | 351篇 |
力学 | 69篇 |
数学 | 115篇 |
物理学 | 137篇 |
出版年
2023年 | 5篇 |
2022年 | 21篇 |
2021年 | 22篇 |
2020年 | 16篇 |
2019年 | 17篇 |
2018年 | 12篇 |
2017年 | 11篇 |
2016年 | 33篇 |
2015年 | 21篇 |
2014年 | 18篇 |
2013年 | 35篇 |
2012年 | 41篇 |
2011年 | 48篇 |
2010年 | 24篇 |
2009年 | 22篇 |
2008年 | 43篇 |
2007年 | 22篇 |
2006年 | 32篇 |
2005年 | 21篇 |
2004年 | 27篇 |
2003年 | 16篇 |
2002年 | 12篇 |
2001年 | 12篇 |
2000年 | 8篇 |
1999年 | 7篇 |
1998年 | 4篇 |
1997年 | 5篇 |
1996年 | 3篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1991年 | 5篇 |
1990年 | 9篇 |
1988年 | 4篇 |
1987年 | 7篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1975年 | 6篇 |
1974年 | 5篇 |
1973年 | 6篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1967年 | 2篇 |
1966年 | 2篇 |
1958年 | 2篇 |
排序方式: 共有672条查询结果,搜索用时 15 毫秒
141.
Globally, plastics are used in various products. Concerns regarding the human body’s exposure to plastics and environmental pollution have increased with increased plastic use. Microplastics can be detected in the atmosphere, leading to potential human health risks through inhalation; however, the toxic effects of microplastic inhalation are poorly understood. In this study, we examined the pulmonary toxicity of polystyrene (PS), polypropylene (PP), and polyvinyl chloride (PVC) in C57BL/6, BALB/c, and ICR mice strains. Mice were intratracheally instilled with 5 mg/kg of PS, PP, or PVC daily for two weeks. PS stimulation increased inflammatory cells in the bronchoalveolar lavage fluid (BALF) of C57BL/6 and ICR mice. Histopathological analysis of PS-instilled C57BL/6 and PP-instilled ICR mice showed inflammatory cell infiltration. PS increased the NLR family pyrin domain containing 3 (NLRP3) inflammasome components in the lung tissue of C57BL/6 and ICR mice, while PS-instilled BALB/c mice remained unchanged. PS stimulation increased inflammatory cytokines, including IL-1β and IL-6, in BALF of C57BL/6 mice. PP-instilled ICR mice showed increased NLRP3, ASC, and Caspase-1 in the lung tissue compared to the control groups and increased IL-1β levels in BALF. These results could provide baseline data for understanding the pulmonary toxicity of microplastic inhalation. 相似文献
142.
143.
Photoacoustic amplitude and phase measurements have been carried out near the superconducting transition temperature in the
highT
csuperconductor YBa2Cu3O7. In both the samples investigated, the photoacoustic phase undergoes an anomalous step-like decrease aroundT
c≈ 96 K and increases at lower temperatures. A clear temperature hysteresis for the phase change has been noticed. No anomalous
variation has been observed in the amplitude values. Neither phase nor amplitude shows any anomaly in a non-superconducting
sample of the same composition. 相似文献
144.
145.
Isaac Gorelic 《Topology and its Applications》2006,153(15):3024-3028
Boris Shapirovskii posed the following question: “Suppose a continuous mapping from one compact space onto another is given. Suppose that the π-character of any point in the domain is greater than the weight of the target space. Will there be two disjoint closed sets in the domain mapping onto?”. There is a zero-dimensional counterexample (Corollary 12), but the one cardinal up version is true in zero-dimensional case (Corollary 14). Nevertheless, there always will be two disjoint open sets mapping densely (Theorem 7). 相似文献
146.
Tze Chi Jao Munmaya K. Mishra Isaac D. Rubin Jean Duhamel Mitchell A. Winnik 《Journal of Polymer Science.Polymer Physics》1995,33(8):1173-1181
Pyrene-labeled functionalized ethylene-propylene (EP) copolymer was prepared by grafting 1-pyrenebutyrylhydrazine onto EP copolymer through maleic anhydride pendants. The EP copolymer contained 60 mol % ethylene; its weight-average molecular weight (Mw) was 148,000. The pyrene-labeled amide functionalized EP copolymer, PA-EP(60/40), was made to simulate the amine functionalized EP copolymers that are commonly used as dispersant additives in motor oils. UV absorption spectra, fluorescence emission and excitation spectra, and fluorescence decay profiles of the pyrene were studied to determine the copolymer conformation and dynamics in methylcyclohexane and tetrahydrofuran (THF). The pyrene fluorescence characteristics of PA-EP(60/40) were highly dependent on the solvent. The dependence of fluorescence emission intensity on the excitation wavelength was large in methylcyclohexane and moderate in THF. A frequency shift of about 2 nm was observed between the excitation spectrum obtained with the emission line at 377 nm and that at 550 nm in the methylcyclohexane solutions, but no shift was found in the corresponding tetrahydrofuran solutions. The ratios of the preexponential factors (a21/a22) of the excimer decays obtained in both methylcyclohexane and THF solutions were different from ?1.0. However, the deviation of the excimer formation process from the Birks scheme is small in THF but large in methylcyclohexane. In addition, the Huggins constants obtained from intrinsic viscosity measurements of the PA-EP(60/40) copolymer solutions suggest that copolymer aggregation occurs in methylcyclohexane but not in THF. H-bonding between two pyrene-containing pendants is apparently the main driving force for the formation of the ground state pyrene complex. THF is found to be effective in inhibiting the H-bonding formation. © 1995 John Wiley & Sons, Inc. 相似文献
147.
Isaac Efrat 《Communications in Mathematical Physics》1988,119(3):443-451
Determinants of the Laplace and other elliptic operators on compact manifolds have been an object of study for many years (see [MP, RS, Vor]). Up until now, however, the theory of determinants has not been extended to non-compact situations, since these typically involve a mixture of discrete and continuous spectra. Recent advances in this theory, which are partially motivated by developments in mathematical physics, have led to a connection, in the compact Riemann surface case, between determinants of Laplacians on spinors and the Selberg zeta function of the underlying surface (see [DP, Kie, Sar, Vor]).Our purpose in this paper is to introduce a notion of determinants on non-compact (finite volume) Riemann surfaces. These will be associated to the Laplacian shifted by a parameters(1–s), and will be defined in terms of a Dirichlet series (w, s) which is a sum that represents the discrete as well as the continuous spectrum. It will be seen to be regular atw=0, and our main theorem (see Sect. 1) will express exp
as the Selberg zeta function of the surface times the appropriate -factor.A Sloan Fellow and partially supported by NSF grant DMS-8701865 相似文献
148.
Applications of Mathematics - In this paper, we consider the direct and inverse problem for time-fractional diffusion in a domain with an impenetrable subregion. Here we assume that on the boundary... 相似文献
149.
Isaac Chaujun Lee 《Results in Mathematics》1995,27(1-2):63-76
From group-theoretical point of view, we discuss affine rotation surfaces in R3 and projective rotation surfaces in RP3. These pave a way toward generalized affine rotation surfaces in R3. We will follow closely the modern approach introduced by Nomizu in the study affine differential geometry [N]. In this paper, we have the following results on generalized affine rotation surfaces:
- Many nice properties showing duality between x2 + y2 = g2(z) and x2 ? y2 = g2(z).
- In this set, any surface with zero Pick invariant is a quadratic surface.
- Excluding the Caley surface z = xy ? x3/3 and the surface z = xy + log x, any affine unimodular homogeneous surface belongs to this set.
- In this set, the following surfaces are characterized by some affine invariants: $${\matrix{x^{2}+\epsilon\ y^{2}=z \cr \qquad \qquad \qquad \qquad \qquad \qquad \qquad y^{2}=z(x+\epsilon\ (z+a)^{2/3}(z+6a)),\cr \qquad \qquad \qquad \ \ \ y^{2}=z(x+\epsilon\ z^{3}),\cr \qquad \qquad \ \ \ \ \ \ y^{2}=x+\epsilon\ z^{2/3},\cr \qquad \qquad \ \ \ \ \ \ \ y^{2}=x+\epsilon\ z^{-2/3},\cr \qquad \qquad \ \ \ y^{2}=x+\epsilon\ {\rm log}z,\cr}} $$ where ? represents 1 or ?1 in this paper.
150.
M. C. P. Isaac V. R. Vanin O. A. M. Helene 《Zeitschrift für Physik A Hadrons and Nuclei》1990,335(3):243-246
The Internal Bremsstrahlung Electron Capture spectrum from55Fe was measured with a HPGe detector. The total spectrum was unfolded taking into account the secondary detection effects and agrees with Glauber and Martin calculations. The measured intensity relative to K capture in the range 35 to 231 keV is 3.24(6)·10?5 while the calculated one is 3.20·10?5. TheQ value for the electron capture was deduced as 230.7(19) keV. 相似文献