全文获取类型
收费全文 | 2251篇 |
免费 | 151篇 |
国内免费 | 226篇 |
专业分类
化学 | 672篇 |
晶体学 | 31篇 |
力学 | 439篇 |
综合类 | 31篇 |
数学 | 626篇 |
物理学 | 829篇 |
出版年
2023年 | 20篇 |
2022年 | 14篇 |
2021年 | 23篇 |
2020年 | 43篇 |
2019年 | 42篇 |
2018年 | 45篇 |
2017年 | 68篇 |
2016年 | 73篇 |
2015年 | 53篇 |
2014年 | 97篇 |
2013年 | 212篇 |
2012年 | 119篇 |
2011年 | 153篇 |
2010年 | 80篇 |
2009年 | 146篇 |
2008年 | 144篇 |
2007年 | 155篇 |
2006年 | 131篇 |
2005年 | 106篇 |
2004年 | 105篇 |
2003年 | 85篇 |
2002年 | 59篇 |
2001年 | 81篇 |
2000年 | 60篇 |
1999年 | 65篇 |
1998年 | 56篇 |
1997年 | 42篇 |
1996年 | 45篇 |
1995年 | 44篇 |
1994年 | 46篇 |
1993年 | 29篇 |
1992年 | 27篇 |
1991年 | 20篇 |
1990年 | 17篇 |
1989年 | 19篇 |
1988年 | 11篇 |
1987年 | 13篇 |
1986年 | 10篇 |
1985年 | 15篇 |
1984年 | 15篇 |
1983年 | 3篇 |
1982年 | 10篇 |
1981年 | 9篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1975年 | 1篇 |
1973年 | 3篇 |
1971年 | 1篇 |
1957年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有2628条查询结果,搜索用时 93 毫秒
91.
采用低压等离子体聚合技术,通过调整工作气压和反式二丁烯(T2B)与H2流量比制备了辉光放电聚合物(GDP)涂层. 利用傅里叶变换红外吸收光谱和元素分析法讨论了工作气压和T2B与H2流量比对GDP涂层内部H原子含量及结构的影响,并且通过纳米压痕技术对GDP涂层的硬度及杨氏模量进行了表征.研究结果表明:降低工作气压和T2B与H2流量比,GDP涂层内sp3 C
关键词:
傅里叶变换红外光谱
纳米压痕
杨氏模量
硬度 相似文献
92.
In this paper, we study the directional derivative, subderivative, and subdifferential of sup-type functions without any compactness assumption on the index set. As applications, we provide an estimate of the Lipschitz modulus for sup-type functions. 相似文献
93.
鞘氨醇(sphingosine)是生物体内合成鞘脂的母体化合物, 是生物膜中的重要组分之一. 通过分析表面压力和平均分子面积(π-A)等温线数据分别研究了鞘氨醇与二棕榈酰基磷脂酰胆碱(DPPC)和二棕榈酰基磷脂酰乙醇胺(DPPE)二元组分单层膜的热力学特性, 并在恒定膜压下制备不同摩尔比例的混合脂膜用原子力显微镜进行观测. 实验结果表明: (1)鞘氨醇与DPPC组成的系统中, XD-Sph=0.2, 0.4, 0.6时, 过量分子面积与过量吉布斯自由能在所研究的表面压力下表现为负值, 而当XD-Sph=0.8时, 表现为正值; (2)鞘氨醇与DPPE组成的系统中, 当表面压力 π<25 mN8226;m-1时, 过量分子面积与过量吉布斯自由能在所研究的组分比例下表现为负值, 当π≥25 mN8226;m-1时为正值. 混合单层膜的分子面积与表面吉布斯自由能决定了分子间的相互作用, 当为负值时分子间相互作用表现为吸引力, 出现凝聚现象; 为正值时分子间相互作用表现为排斥力, 促使单层膜出现相分离现象. 过量吉布斯自由能值越小, 单层膜的热稳定性越高. 弹性系数曲线分析和AFM图片观测进一步验证了理论分析的结果. 相似文献
94.
Tijani A. Apalara 《Journal of Mathematical Analysis and Applications》2019,469(2):457-471
In this work we consider a one-dimensional porous-elastic system with memory effects. It is well-known that porous-elastic system with a single dissipation mechanism lacks exponential decay. In contrary, we prove that the unique dissipation given by the memory term is strong enough to exponentially stabilize the system, depending on the kernel of the memory term and the wave speeds of the system. In fact, we prove a general decay result, for which exponential and polynomial decay results are special cases. Our result is new and improves previous results in the literature. 相似文献
95.
Bernstein-Kantorovich quasi-interpolants K^(2r-1)n(f, x) are considered and direct, inverse and equivalence theorems with Ditzian-Totik modulus of smoothness ω^2rφ(f, t)p (1 ≤ p ≤+∞) are obtained. 相似文献
96.
Bernstein-Kantorovich quasi-interpolants K(2r-1) n (f, x) are considered and direct,inverse and equivalence theorems with Ditzian-Totik modulus of smoothness ω2rψ(f, t)p (1 ≤ p≤+∞) are obtained. 相似文献
97.
George E. Andrews 《数学学报(英文版)》2009,25(9):1437-1442
A variety of interesting connections with modular forms, mock theta functions and Rogers- Ramanujan type identities arise in consideration of partitions in which the smaller integers are repeated as summands more often than the larger summands. In particular, this concept leads to new interpretations of the Rogers Selberg identities and Bailey's modulus 9 identities. 相似文献
98.
We give a geometric analysis of relaxation oscillations and canard cycles in a singularly perturbed predator–prey system of Holling and Leslie types. We discuss how the canard cycles are found near the Hopf bifurcation points. The transition from small Hopf-type cycles to large relaxation cycles is also discussed. Moreover, we outline one possibility for the global dynamics. Numerical simulations are also carried out to verify the theoretical results. 相似文献
99.
Potential hydrogen storage ternaries Zr3FeH7 and Zr2FeH5, are studied from ab initio with the purpose of identifying changes in electronic structures and bonding properties. Cohesive energy trends: Ecoh. (ZrH2) > Ecoh. (Zr2FeH5) > Ecoh. (Zr3FeH7) > Ecoh. (hypothetic-FeH) indicate a progressive destabilization of the binary hydride ZrH2 through adjoined Fe so that Zr3FeH7 is found less cohesive than Zr2FeH5. From the energy volume equations of states EOS the volume increase upon hydriding the intermetallics leads to higher bulk moduli B0 explained by the Zr/Fe–H bonding. Fe–H bond in Zr2FeH5 leads to annihilate magnetic polarization on Fe whereas Fe magnetic moment develops in Zr3FeH7 identified as ferromagnetic in the ground state. These differences in magnetic behaviors are due to the weakly ferromagnetic Fe largely affected by lattice environment, as opposed to strongly ferromagnetic Co. Hydrogenation of the binary intermetallics weakens the inter-metal bonding and favors the metal–hydrogen bonds leading to more cohesive hydrides as with respect to the pristine binaries. Charge analyses point to covalent like Fe versus ionic Zr and hydrogen charges ranging from covalent H−0.27 to more ionic H−0.5. 相似文献
100.
Jessica M. Torres Christopher M. Stafford David Uhrig Bryan D. Vogt 《Journal of Polymer Science.Polymer Physics》2012,50(5):370-377
The modulus and glass transition temperature (Tg) of ultrathin films of polystyrene (PS) with different branching architectures are examined via surface wrinkling and the discontinuity in the thermal expansion as determined from spectroscopic ellipsometry, respectively. Branching of the PS is systematically varied using multifunctional monomers to create comb, centipede, and star architectures with similar molecular masses. The bulk‐like (thick film) Tg for these polymers is 103 ± 2 °C and independent of branching and all films thinner than 40 nm exhibit reductions in Tg. There are subtle differences between the architectures with reductions in Tg for linear (25 °C), centipede (40 °C), comb (9 °C), and 4 armed star (9 °C) PS for ≈ 5 nm films. Interestingly, the room temperature modulus of the thick films is dependent upon the chain architecture with the star and comb polymers being the most compliant (≈2 GPa) whereas the centipede PS is most rigid (≈4 GPa). The comb PS exhibits no thickness dependence in moduli, whereas all other PS architectures examined show a decrease in modulus as the film thickness is decreased below ~40 nm. We hypothesize that the chain conformation leads to the apparent susceptibility of the polymer to reductions in moduli in thin films. These results provide insight into potential origins for thickness dependent properties of polymer thin films. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012 相似文献