全文获取类型
收费全文 | 60462篇 |
免费 | 2066篇 |
国内免费 | 408篇 |
专业分类
化学 | 40963篇 |
晶体学 | 489篇 |
力学 | 1738篇 |
综合类 | 1篇 |
数学 | 7936篇 |
物理学 | 11809篇 |
出版年
2023年 | 302篇 |
2022年 | 520篇 |
2021年 | 904篇 |
2020年 | 938篇 |
2019年 | 923篇 |
2018年 | 708篇 |
2017年 | 686篇 |
2016年 | 1549篇 |
2015年 | 1369篇 |
2014年 | 1591篇 |
2013年 | 3253篇 |
2012年 | 3842篇 |
2011年 | 4488篇 |
2010年 | 2444篇 |
2009年 | 2166篇 |
2008年 | 3766篇 |
2007年 | 3674篇 |
2006年 | 3545篇 |
2005年 | 3297篇 |
2004年 | 2861篇 |
2003年 | 2366篇 |
2002年 | 2248篇 |
2001年 | 1106篇 |
2000年 | 994篇 |
1999年 | 710篇 |
1998年 | 612篇 |
1997年 | 661篇 |
1996年 | 845篇 |
1995年 | 624篇 |
1994年 | 608篇 |
1993年 | 592篇 |
1992年 | 566篇 |
1991年 | 471篇 |
1990年 | 379篇 |
1989年 | 373篇 |
1988年 | 397篇 |
1987年 | 336篇 |
1985年 | 543篇 |
1984年 | 471篇 |
1983年 | 364篇 |
1982年 | 453篇 |
1981年 | 436篇 |
1980年 | 399篇 |
1979年 | 370篇 |
1978年 | 362篇 |
1977年 | 335篇 |
1976年 | 326篇 |
1975年 | 334篇 |
1974年 | 319篇 |
1973年 | 342篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
A high-performance liquid chromatographic procedure was developed for the quantitation of homoharringtonine in plasma. Harringtonine was used as an internal standard, and 1 ml of sample was required. The single-step extraction with dichloromethane resulted in almost 100% recovery for homoharringtonine and harringtonine. Analysis was performed on a reversed-phase CN column with amperometric detection. Chromatography was completed in 12 min. At an oxidation potential of +1.0 V, the detection limit was 1 ng/ml at a signal-to-noise ratio of 2. The mean analytical recovery for homoharringtonine was 99.5%. The within-run precision and between-run precision were both less than 11%. The method is equally applicable for plasma or serum, and it has been demonstrated to be applicable for study of the pharmacokinetics of homoharringtonine in patients suffering from acute non-lymphocytic leukaemia. 相似文献
132.
133.
We study the multiplicity of critical points for functionals which are only differentiable along some directions. We extend to this class of functionals the three critical point theorem of Pucci and Serrin and we apply it to a one-parameter family of functionals Jλ, λ∈I⊂R. Under suitable assumptions, we locate an open subinterval of values λ in I for which Jλ possesses at least three critical points. Applications to quasilinear boundary value problems are also given. 相似文献
134.
Masanobu Haraguchi David F. P. Pile Toshihiro Okamoto Masuo Fukui Dmitri K. Gramotnev 《Optical Review》2006,13(4):228-230
We have numerically shown the existence of coupled wedge plasmons (CWPs) which propagates along a nano gap of a twin metal
wedge. The CWPs are formed by wedge plasmons which can interact with each other. The dispersion relations of the wavenumber,
propagation distance, and beam area of CWPs, are described and show that the characteristics of CWPs are similar to those
of wedge plasmons and of gap plasmons. We also propose a new plasmon waveguide composed of twin metal wedges with a nano gap. 相似文献
135.
This study investigates a holographic recording effect of biphotonic polarization gratings (BPGs) written on dye-doped liquid crystal (DDLC) films. One linearly polarized green light (λG = 514.5 nm) and a polarization-modulated interference pattern formed by two mutually coherent orthogonal (±45° with respect to the polarization of the green light) polarized red lights simultaneously excite the DDLC films to generate a BPG. The formation of BPGs depends primarily on the dichroism of the dye molecules and a sequence of mechanisms: photoisomerization, anisotropic adsorption and inhibition of dye adsorption. The cis-isomer absorbance-modulated distribution associated with the red polarization-modulation pattern induces the dye adsorption-modulated pattern, in turn, yielding the permanent BPG which generates a modulated twisted nematic (TN) structure pattern in the sample. It is found that each BPG is verified to be electrically switchable and thermally erasable. The switching time is in the order of milliseconds. Additionally, the recording time to form a BPG decreases with increasing intensity of the green pump beam. 相似文献
136.
Danny E. Akin W. Herbert Morrison III Luanne L. Rigsby Franklin E. Barton II David S. Himmelsbach Kevin B. Hicks 《Applied biochemistry and biotechnology》2006,129(1-3):104-116
Information is presented on structure, composition, and response to enzymes of corn stover related to barriers for bioconversion
to ethanol. Aromatic compounds occurred in most tissue cell walls. Ferulic acid esterase treatment before cellulase treatment
significantly improved dry weight loss and release of phenolic acids and sugars in most fractions over cellulase alone. Leaf
fractions were considerably higher in dry weight loss and released sugars with esterase treatment, but stem pith cells gave
up the most phenolic acids. Results help identify plant fractions more appropriate for coproducts and bioconversion and those
more suitable as residues for soil erosion control. 相似文献
137.
K.E. Lee T.L. Phan N.D. Ha M.H. Phan S.C. Yu C.O. Kim 《Journal of magnetism and magnetic materials》2006
Influences of oxygen-partial pressure and annealing on the electrical and magnetic properties of CoFeAlO thin films were systematically investigated by means of resistivity, permeability, magnetization and ferromagnetic resonance (FMR) measurements. It was found that, with increasing oxygen-partial pressure or under annealing, the electrical resistivity of the film increased and the magnetic softness decreased, which is attributed to the microstructural change of the film. Interestingly, an as-deposited Co45.30Fe20.65Al19.34O14.71 film was found to exhibit an inverted hysteresis loop with negative coercivity, and this peculiar phenomenon disappeared upon effects of oxygen-partial pressure and annealing. It was also found that the as-deposited films owned a narrow FMR line width that increased with increasing oxygen-partial pressure or under annealing. 相似文献
138.
Area,coarea, and approximation in <Emphasis Type="Italic">W</Emphasis><Superscript>1,1</Superscript>
David Swanson 《Arkiv f?r Matematik》2007,45(2):381-399
Let Ω⊂ℝ
n
be an arbitrary open set. We characterize the space W
1,1
loc(Ω) using variants of the classical area and coarea formulas. We use these characterizations to obtain a norm approximation
and trace theorems for functions in the space W
1,1(ℝ
n
). 相似文献
139.
D. Fong J. H. Hamilton A. V. Ramayya J. K. Hwang C. Goodin K. Li J. Kormicki J. O. Rasmussen Y. X. Luo S. C. Wu I. Y. Lee A. V. Daniel G. M. Ter-Akopian G. S. Popeko A. S. Fomichev A. M. Rodin Yu. Ts. Oganessian M. Jandel J. Kliman L. Krupa J. D. Cole M. A. Stoyer R. Donangelo W. C. Ma 《Physics of Atomic Nuclei》2006,69(7):1161-1167
The hot bimodal fission of 252Cf is reexamined with new high-statistics data. We constructed a γ-γ-γ coincidence cube for binary fission and LCP-gated γ-γ matrix for ternary fission. By identifying the secondary fission fragments from their γ-ray transitions, we measured the yields for various fission splits. The normal neutron yield distribution is found to be
Gaussian for Xe-Ru. However, the binary fission split of Ba-Mo is found to exhibit a bimodal neutron distribution with the
“hot mode” corresponding to ≈3.1% of the total yield. In α ternary fission, the first measurements of yields for specific fission splits are presented. The Te-α-Ru and Xe-α-Mo neutron yields fit well with a single mode, but the Ba-α-Zr split shows evidence for an enhanced hot mode with an intensity of ≈13.8% of the normal mode.
The text was submitted by the authors in English. 相似文献
140.
High-frequency characteristics of CoFeVAlONb thin films were studied. A thin film of Co43.47Fe35.30V1.54Al5.55O9.93Nb4.21 is observed to exhibit excellent magnetic properties; magnetic coercivity of 1.24 Oe, uniaxial in-plane anisotropy field of 66.99 Oe, and saturation magnetization of 19.8 kG. The effective permeability of the film is as high as 1089 and is stable up to 1.8 GHz, and with ferromagnetic resonance over 3 GHz. This film also has very high electrical resistivity of about 628 μΩ cm. These superior properties make it ideal for high-frequency magnetic applications. 相似文献