全文获取类型
收费全文 | 22642篇 |
免费 | 3322篇 |
国内免费 | 1854篇 |
专业分类
化学 | 14771篇 |
晶体学 | 536篇 |
力学 | 888篇 |
综合类 | 171篇 |
数学 | 699篇 |
物理学 | 10753篇 |
出版年
2024年 | 26篇 |
2023年 | 141篇 |
2022年 | 362篇 |
2021年 | 419篇 |
2020年 | 598篇 |
2019年 | 607篇 |
2018年 | 593篇 |
2017年 | 723篇 |
2016年 | 951篇 |
2015年 | 905篇 |
2014年 | 930篇 |
2013年 | 2341篇 |
2012年 | 1273篇 |
2011年 | 1353篇 |
2010年 | 1114篇 |
2009年 | 1216篇 |
2008年 | 1315篇 |
2007年 | 1314篇 |
2006年 | 1267篇 |
2005年 | 1113篇 |
2004年 | 1085篇 |
2003年 | 965篇 |
2002年 | 1121篇 |
2001年 | 764篇 |
2000年 | 807篇 |
1999年 | 665篇 |
1998年 | 579篇 |
1997年 | 427篇 |
1996年 | 378篇 |
1995年 | 401篇 |
1994年 | 302篇 |
1993年 | 259篇 |
1992年 | 245篇 |
1991年 | 172篇 |
1990年 | 158篇 |
1989年 | 121篇 |
1988年 | 124篇 |
1987年 | 111篇 |
1986年 | 102篇 |
1985年 | 88篇 |
1984年 | 85篇 |
1983年 | 41篇 |
1982年 | 66篇 |
1981年 | 34篇 |
1980年 | 38篇 |
1979年 | 41篇 |
1978年 | 16篇 |
1977年 | 10篇 |
1976年 | 8篇 |
1973年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
231.
After the laser was invented in 1960, a phase conjugation mirror has been respected to be the most fantastic one for the laser
resonator composition because it can compensate any distortions of the laser beams occurred by the many inhomogenuities of
the laser media and optical components. Among the many phase conjugation configurations, the stimulated Brillouin scattering
phase conjugation mirror is the most simple one and many researchers have tried to utilize it to develop high power/energy
laser systems. For realizing a high energy/power laser system the thermal problem is the most difficult to solve, and some
researchers suggested a beam combination technique to reduce the thermal load of the big laser media to many small sized ones.
To accomplish the beam combination using stimulated Brillouin scattering phase conjugation mirrors (SBS-PCMs), it is necessary
to lock/control the phases of the SBS-PCMs. And some researchers have developed several ways for it, but they can lock the
phases of a limited number of beams overlapped at the foci less than 5, or lock the phases by back-seeding technique but it
loses the phase conjugation characteristics. For realization of the laser fusion driver, it is necessary to combine more than
10 or 100 beams. And the authors have developed recently a new phase controlling/locking technique which is isolated and independent
totally from other beams and it can be applied to an unlimited number of beams in principle. 相似文献
232.
F. Rampf K. Binder W. Paul 《Journal of polymer science. Part A, Polymer chemistry》2006,44(18):2542-2555
We present simulation results for the phase behavior of a single chain for a flexible lattice polymer model using the Wang-Landau sampling idea. Applying this new algorithm to the problem of the homopolymer collapse allows us to investigate not only the high temperature coil–globule transition but also an ensuing crystallization at lower temperature. Performing a finite size scaling analysis on the two transitions, we show that they coincide for our model in the thermodynamic limit corresponding to a direct collapse of the random coil into the crystal without intermediate coil–globule transition. As a consequence, also the many chain phase diagram of this model can be predicted to consist only of gas and crystal phase in the limit of infinite chain length. This behavior is in agreement with findings on the phase behavior of hard-sphere systems with a relatively short-ranged attractive square well. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2542–2555, 2006 相似文献
233.
Rajesh H. Somani Igors Sics Benjamin S. Hsiao 《Journal of polymer science. Part A, Polymer chemistry》2006,44(24):3553-3570
Combined in situ rheo-SAXS (small-angle X-ray scattering) and -WAXD (wide-angle X-ray diffraction) studies using couette flow geometry were carried out to probe thermal stabilty of shear-induced oriented precursor structure in isotactic polypropylene (iPP) at around its normal melting point (162 °C). Although SAXS results corroborated the emerging consensus about the formation of “long-living” metastable mesomorphic precursor structures in sheared iPP melts, these are the first quantitative measures of the limiting temperature at which no oriented structures survive. At the applied shear, rate = 60 s−1 and duration ts = 5 s, the oriented iPP structures survived a temperature of 185 °C for 1 h after shear, while no stable structures were detected at and above 195 °C. Following Keller's concepts of chain orientation in flow, it is proposed that the chains with highly oriented high molecular weight fraction are primarily responsible for their stability at high temperatures. Furthermore, the effects of flow condition, specifically the shear temperature, on the distributions of oriented and unoriented crystals were determined from rheo-WAXD results. As expected, at a constant flow intensity (i.e., rate = 30 s−1 and duration, ts = 5 s), the oriented crystal fraction decreased with the increase in temperature above 155 °C, below which the oriented fraction decreased with the decrease in temperature. As a result, a crystallinty “phase” diagram, i.e., temperature versus crystal fraction ratio, exhibited a peculiar “hourglass” shape, similar to that found in many two-phase polymer–polymer blends. This can be explained by the competition between the oriented and unoriented crystals in the available crystallizable species. Below the shear temperature (155 °C), the unoriented crystals crystallized so rapidly that they overwhelmed the crystallization of the oriented crystals, thus depleting a major portion of the crystallizable species and increasing their contribution in the final total crystalline phase. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3553–3570, 2006 相似文献
234.
Further study of the viscoelastic phase separation of cyanate ester modified with poly(ether imide) 总被引:1,自引:0,他引:1
Guozhu Zhan Yingfeng Yu Xiaolin Tang Qingsheng Tao Shanjun Li 《Journal of Polymer Science.Polymer Physics》2006,44(3):517-523
In this study, the viscoelastic phase separation process was studied further by time‐resolved light scattering, differential scanning calorimetry, and scanning electron microscopy in the system of poly(ether imide)‐modified bisphenol‐A dicyanate. It was observed that the evolution time of phase structure and relaxation time of diffusion flow of the bisphenol‐A dicyanate were similar with the phase diagram of curing conversion versus content of PEI. The results suggested that the viscoelastic phase separation was affected by the curing conversion of the system at the onset point of phase separation. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 517–523, 2006 相似文献
235.
236.
利用变温X射线衍射技术,在预烧过程中分析了Nd掺杂Bi4Ti3O12后生成Bi3.15Nd0.85Ti3O12(BNT)相的形成过程以及微结构的变化.实验观察到以30℃/min的升温速率,BNT相在700℃时开始形成,其衍射峰强度随温度的继续升高而增强,衍射峰半高宽随烧结时间延长而减小.X射线衍射分析结果表明,在900℃恒温条件下,烧结约2h,可形成单一的BNT相. 相似文献
237.
Solid state laser (SSL) powers can be realistically scaled when pumped by a real, efficient and multimode pulse. In this work,
a fourth-order super-Gaussian pulse was assumed as a pump for SSL’s and a complete analytical expression for the thermal phase
shift is given. Moreover, the focal length of thermal lens in paraxial ray approximation regime was studied. The results when
applied to a Ti: sapphire crystal show an appreciable correction for abberation compared to a top-hat pulse. 相似文献
238.
Kate B. Poiesz Carol L. Grundner Nancy L. Redman-Furey 《Journal of Thermal Analysis and Calorimetry》2006,85(1):79-86
Characterization of the solid-state form (hydrate
or polymorph) of a pharmaceutical active is a key scientific and regulatory
requirement during development of and prior to seeking approval for marketing
of the drug product. A variety of analytical methods are available to perform
this task. By nature of the fundamental information it provides, TG-DTA offers
advantages over other methods in regards to monitoring and quantitation of
hydration state changes. In a single experiment with only a few milligrams
of sample, TG-DTA perceives minor changes in phase, quantitates total water
content and percent conversion, and illustrates hydrate type. All of this
is accomplished without the necessity of generating time-consuming standard
curves representing the differing ratios of hydrated to anhydrous forms. This
study describes the use of TG-DTA to monitor and quantitate humidity induced
solid–solid phase conversion of nitrofurantoin and risedronate. Percent
conversion was qualitatively observed by both TG and DTA signals and quantitated
by the TG. 相似文献
239.
In this paper the distribution of the maximum number of customers in a retrial orbit for a single server queue with Markovian
arrival process and phase type services is studied. Efficient algorithm for computing the probability distribution and some
interesting numerical examples are presented. 相似文献
240.
R. Lacaze A. Morel B. Petersson J. Schröper 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(4):509-523
We present an investigation of the 2D attractive Hubbard model, considered as an effective model relevant to superconductivity
in strongly interacting electron systems. We use both hybrid Monte-Carlo simulations and existing hopping parameter expansions
to explore the low temperature domain. The increase of the static S-wave pair correlation with decreasing temperature, which depends weakly on the band filling in the explored temperature range,
is analyzed in terms of an expected Kosterlitz-Thouless superconducting transition. Using both our data and previously published
results, we show that the evidence for this transition is weak: If it exists, its temperature is very low. The number of unpaired
electrons remains nearly constant with temperature at fixed attractive potential strength. In contrast, the static magnetic
susceptibility decreases fast with temperature, and cannot be related only to pair formation. We introduce a method by which
the Padé approximants of the existing series for the susceptibility give sensible results down to rather low temperature region,
as shown by comparison with our numerical data.
Received: 30 October 1996 / Revised: 23 October 1997 / Accepted: 29 January 1998 相似文献