全文获取类型
收费全文 | 1236篇 |
免费 | 64篇 |
国内免费 | 99篇 |
专业分类
化学 | 825篇 |
晶体学 | 13篇 |
力学 | 43篇 |
综合类 | 5篇 |
数学 | 146篇 |
物理学 | 367篇 |
出版年
2024年 | 7篇 |
2023年 | 22篇 |
2022年 | 56篇 |
2021年 | 66篇 |
2020年 | 54篇 |
2019年 | 32篇 |
2018年 | 26篇 |
2017年 | 32篇 |
2016年 | 49篇 |
2015年 | 32篇 |
2014年 | 42篇 |
2013年 | 105篇 |
2012年 | 55篇 |
2011年 | 75篇 |
2010年 | 50篇 |
2009年 | 82篇 |
2008年 | 71篇 |
2007年 | 72篇 |
2006年 | 50篇 |
2005年 | 40篇 |
2004年 | 41篇 |
2003年 | 36篇 |
2002年 | 29篇 |
2001年 | 33篇 |
2000年 | 33篇 |
1999年 | 33篇 |
1998年 | 29篇 |
1997年 | 33篇 |
1996年 | 17篇 |
1995年 | 14篇 |
1994年 | 8篇 |
1993年 | 9篇 |
1992年 | 4篇 |
1991年 | 10篇 |
1990年 | 2篇 |
1989年 | 8篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1984年 | 4篇 |
1982年 | 7篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1974年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有1399条查询结果,搜索用时 171 毫秒
991.
DNA aptamers are integrated into synthetic hydrogel networks with the aim of creating hydrogels that undergo volume changes when exposed to target molecules. Specifically, single‐stranded DNA aptamers in cDNA‐bound, extended state are incorporated into hydrogel networks as cross‐links, so that the nanoscale conformational change of DNA aptamers upon binding to target molecules will induce macroscopic volume decreases of hydrogels. Hydrogels incorporating adenosine triphosphate (ATP)–binding aptamers undergo controllable volume decreases of up to 40.3 ± 4.6% when exposed to ATP, depending on the concentration of DNA aptamers incorporated in the hydrogel network, temperature, and target molecule concentration. Importantly, this approach can be generalized to aptamer sequences with distinct binding targets, as demonstrated here that hydrogels incorporating an insulin‐binding aptamer undergo volume changes in response to soluble insulin. This work provides an example of bioinspired hydrogels that undergo macroscopic volume changes that stem from conformational shifts in resident DNA‐based cross‐links. 相似文献
992.
G. Yaari A. Nowak K. Rakocy S. Solomon 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,62(4):505-513
Anderson [Science 177, 293 (1972)] proposed the concept of complexity in order to describe the emergence and growth of macroscopic collective patterns
out of the simple interactions of many microscopic agents. In the physical sciences this paradigm was implemented systematically
and confirmed repeatedly by successful confrontation with reality. In the social sciences however, the possibilities to stage
experiments to validate it are limited. During the 90's a series of dramatic political and economic events have provided the
opportunity to do so. We exploit the resulting empirical evidence to validate a simple agent based alternative to the classical
logistic dynamics. The post-liberalization empirical data from Poland confirm the theoretical prediction that the dynamics
is dominated by singular rare events which insure the resilience and adaptability of the system. We have shown that growth
is led by few singular “growth centers" (Fig. 1), that initially developed at a tremendous rate (Fig. 3), followed by a diffusion
process to the rest of the country and leading to a positive growth rate uniform across the counties. In addition to the interdisciplinary
unifying potential of our generic formal approach, the present work reveals the strong causal ties between the “softer" social
conditions and their “hard" economic consequences. 相似文献
993.
Analysis of edge-state energies in the integer quantum
Hall effect is carried out within the semiclassical approximation.
When the system is wide so that each edge can be considered
separately, this problem is equivalent to that of a one dimensional
harmonic oscillator centered at x = xc and an infinite wall at
x = 0, and appears in numerous physical contexts. The eigenvalues
En(xc) for a given quantum number n are solutions of the
equation S(E,xc)=π[n+ γ(E,xc)] where S is the WKB
action and 0 < γ < 1 encodes all the information on the
connection procedure at the turning points.
A careful implication of the WKB connection formulae results in an
excellent approximation to the exact energy eigenvalues. The
dependence of γ[En(xc),xc] ≡γn(xc)
on xc is analyzed between its two extreme values
as xc ↦-∞ far inside the sample
and as xc ↦∞ far outside the sample.
The edge-state energiesEn(xc) obey an almost exact scaling
law of the form
and the scaling function f(y) is explicitly elucidated. 相似文献
994.
Mukhopadhyay Nitis Aoshima Makoto 《Methodology and Computing in Applied Probability》2004,6(2):161-179
Let us consider k( 2) independent random variables U1, . . . ,Uk where Ui is distributed as the Student's t random variable with a degree of freedom mi, i=1, . . . ,k. Here, m1, . . . ,mk are arbitrary positive integers. We denote m=(m1, . . . ,mk) and Uk:k=max {U1, . . . ,Uk}, the largest Student's t random variable. Having fixed 0< <1, let a a(k,) and hm hm (k,) be two positive numbers for which we can claim that (i) k(a)–k(–a)=1–, and (ii) P{–hm Uk:k hm}=1–. Then, we proceed to derive a Cornish–Fisher expansion (Theorem 3.1) of the percentage point hm. This expansion involves a as well as expressions such as i=1
k mi
–1, i=1
kmi
–2, and i=1
k mi
–3. The corresponding approximation of hm is shown to be remarkably accurate even when k or m1, . . . ,mk are not very large. 相似文献
995.
The voltammetric behaviour of Imatinib (STI 571) and its main metabolite (N-demethylated piperazine derivative) were studied by square-wave techniques, resulting in to two methods for their determination in aqueous and urine samples at pH 2. The application of the square-wave (SW) without the adsorptive accumulation and voltammetric stripping (AdSV) exhibit a peak at a reduction potential of −0.70 V for an accumulation potential of −0.45 V. The sensitivity was higher for the stripping technique because a signal four times higher than that provided by the square-wave method without the previous accumulation was obtained. Due to the fact that Imatinib and its metabolite show the same voltammetric reduction process, some experiments were performed in order to compare the voltammetric response of Imatinib and its main metabolite in a similar ratio than that of the therapeutic concentration. The calibration curve for Imatinib in urine was linear in the range from 1.9 × 10−8 to 1.9 × 10−6 M in stripping mode with an accumulation time (tacc) of 10 s. The relative standard deviations obtained for concentration levels of Imatinib as low as 2.0 × 10−7 M for square-wave was 2.17% (n = 9) and for stripping square-wave was 2.65% (n = 9) in the same day. The limits of detection for square-wave and stripping square-wave were 5.55 × 10−9 and 5.19 × 10−9 M, respectively. Thus, the presented method are straightforward, rapid and sensitive and has been applied to the determination of Imatinib and its main metabolite altogether in urine samples from real patients. 相似文献
996.
Two new inorganic ion exchangers, stannic selenoiodate and stannic selenosilicate have been synthesized. The ion-exchange capacity of stannic selenoiodate and stannic selenosilicate for K+ was found to be 1.84 and 1.23 meq g–1, respectively. pH titration studies reveal monofunctional and bifunctional behavior for stannic selenosilicate and stannic selenoiodate, respectively. Distribution coefficients of metal ions in dimethylformamide–HCl and formamide–HCl systems have been determined. Some important and analytically difficult quantitative binary and ternary separations, and selective separations of Ag+, Sn4+, Zr4+, Co2+, and Ni2+ have been achieved on stannic selenoiodate columns. The practical utility of the material has been demonstrated by analyzing the metal ion content of electroplating waste. 相似文献
997.
Yousef?Haikyhaik@uaeu.ac.ae" title="haik@eng.fsu.edu yhaik@uaeu.ac.ae" itemprop="email" data-track="click" data-track-action="Email author" data-track-label="">Email author Jhunu?Chatterjee Ching?Jen Chen 《Journal of nanoparticle research》2005,7(6):675-679
Stable composition of Iron Neodymium Boron nanoparticles are formed by a chemical method. Conventional borohydride reduction
method was used. The particles are in the size range of 30–100 nm. Silica coating was applied to stabilize and prepare the
particles for in vitro applications such as cell separation and diagnostics. Morphology of particles has been studied along with the structure and
magnetic properties. 相似文献
998.
F. Li W. X. Shu J. G. Jiang H. L. Luo Z. Ren 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(2):355-361
Spatiotemporal dynamics of Bose-Einstein condensates in
moving optical lattices have been studied. For a weak lattice
potential, the perturbed correction to the heteroclinic orbit in a
repulsive system is constructed. We find the boundedness
conditions of the perturbed correction contain the Melnikov
chaotic criterion predicting the onset of Smale-horseshoe chaos.
The effect of the chemical potential on the spatiotemporal
dynamics is numerically investigated. It is revealed that the
variance of the chemical potential can lead the systems into
chaos. Regulating the intensity of the lattice potential can
efficiently suppress the chaos resulting from the variance of the
chemical potential. And then the effect of the phenomenological
dissipation is considered. Numerical calculation reveals that the
chaos in the dissipative system can be suppressed by adjusting the
chemical potential and the intensity of the lattice potential. 相似文献
999.
Alexander G. Yushchenko Sergey F. Shibalkin 《International Journal of Infrared and Millimeter Waves》2007,28(2):129-137
An original transmission line based on a planar waveguide splitter with central dielectric filling is proposed. A rigorous
electrodynamics model is presented for calculating propagation and attenuation parameters of even eigenmodes. The presence
of the lowest quasi–H wave having low dissipation loses was detected in the spectrum of hybrid modes. Numerical experiments
prove that new line is very promising for different millimeter wave applications, such as antennae and three-dimensional integrated
circuits (TDIC). 相似文献
1000.
The optical properties of novel polymer poly(phthalazinone ether sulfone ketone, PPESK) film waveguide are studied by prism coupler. The optical properties of PPESK-8020, including refractive index, birefringence, thermo-optical coefficient and optical loss, are demonstrated. This kind of material has the advantages of low optical loss (less than 0.24 dB/cm at 1310 nm and 0.52 dB/cm at 1550 nm) and high thermal stability (1% weight loss temperature: 488 ℃). Due to these excellent properties, it may have great potential in optical waveguide applications. 相似文献