全文获取类型
收费全文 | 2451篇 |
免费 | 168篇 |
国内免费 | 155篇 |
专业分类
化学 | 358篇 |
晶体学 | 17篇 |
力学 | 74篇 |
综合类 | 7篇 |
数学 | 840篇 |
物理学 | 1478篇 |
出版年
2023年 | 10篇 |
2022年 | 12篇 |
2021年 | 35篇 |
2020年 | 19篇 |
2019年 | 36篇 |
2018年 | 25篇 |
2017年 | 33篇 |
2016年 | 29篇 |
2015年 | 31篇 |
2014年 | 43篇 |
2013年 | 57篇 |
2012年 | 58篇 |
2011年 | 149篇 |
2010年 | 155篇 |
2009年 | 331篇 |
2008年 | 309篇 |
2007年 | 247篇 |
2006年 | 236篇 |
2005年 | 142篇 |
2004年 | 78篇 |
2003年 | 102篇 |
2002年 | 109篇 |
2001年 | 77篇 |
2000年 | 79篇 |
1999年 | 82篇 |
1998年 | 58篇 |
1997年 | 13篇 |
1996年 | 26篇 |
1995年 | 22篇 |
1994年 | 18篇 |
1993年 | 15篇 |
1992年 | 21篇 |
1991年 | 12篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1985年 | 12篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1978年 | 2篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1973年 | 9篇 |
排序方式: 共有2774条查询结果,搜索用时 125 毫秒
31.
32.
Junko Kuwahara Hideo Akisada Tamaki Kato Norikazu Nishino 《Colloid and polymer science》2005,283(7):747-752
A series of peptides containing various hydrophobic amino acids [methionine (Met), leucine (Leu), norleucine (Nle), phenylalanine (Phe), 2-aminooctanoic acid (Aoc), and 2-aminodecanoic acid (Ade)] were synthesized and their conformations were studied using circular dichroism (CD) spectroscopy in different solvents such as water, methanol, and aqueous solution of ammonium tetradecanesulfonate. Peptides containing hydrophobic amino acids with linear side chains formed -sheets in water and methanol. Electrostatic interaction between the charged side chain (lysine) and a micelle consisting of an anionic surfactant, ammonium tetradecanesulfonate, is necessary for the formation of -helices in micellar environments. The conformational transition from -helix to -sheet structure required moderate hydrophobicity and linear side chains. This conformational transition depended on the surfactant concentration. 相似文献
33.
聚对苯二甲酸乙二酯(PET)结晶速度很慢,通常加入成核剂来提高结晶速度。从专利文献来看,以离子聚合物为成核剂的例子也是很多的。离子聚合物与小分子成核剂的显著差别是:离子聚合物有一个很长的碳氢主链,其侧基为酸基,酸基被部分或全部地中和成盐。很明显,离子聚合物不象小分子成核剂那样能很好地分散在PET基体中,而是以独立的相存在。作为PET体系系列研究的继续,本文报道了离子聚合物Surlyn在PET中的相分离行为。 相似文献
34.
From the study of the CuCuBrCu2?εSC solid cell in the range of cubic digenite and “high temperature” hexagonal chalcocite we have deduced the laws of variation of the deviation from stoichiometry and the holes concentration with the equilibrium partial pressure of sulfur (δ and p are found to be proportional to ). The electronic model corresponding to the formation of associations (V×CuV′Cu) in the presence of neutral vacancies V×Cu allows one to explain these laws. In the low temperature range (range of “low temperature” hexagonal chalcocite and orthorhombic chalcocite) the study of thermal variations of Hall coefficient permits us to propose the following models: (a) the deviation from stoichiometry of the “low temperature” hexagonal chalcocite is due to the simple ionized vacancies V′Cu; (b) the deviation from stoichiometry of the orthorhombic chalcocite is due to the vacancies V′Cu and to the associations (V×CuV×Cu). 相似文献
35.
36.
Asymptotic Behavior of a Stochastic Predator-prey Model with Beddington-DeAngelis Functional Response and L\'{e}vy Jumps 下载免费PDF全文
A stochastic two-prey-one-predator model with Beddington-DeAngelis functional response and L\''{e}vy jumps is proposed and investigated in this paper. First of all, we prove the existence and uniqueness of the global positive solution, and stochastic ultimate boundedness of the solution. Next, under a simple assumption, by using It\^{o} formula and other important inequalities, some sufficient conditions are established to ensure the extinction and persistence in the mean of the system. The results show that neither strong white noise nor L\''{e}vy noise is conducive to the persistence of the population. Finally, the theoretical results are verified by numerical simulations. 相似文献
37.
R. S. Brusa M. Duarte Naia D. Margoni A. Zecca 《Applied Physics A: Materials Science & Processing》1995,60(5):447-453
We have determined the positron mobility (+) in polyethylene samples (67.2% crystalline, glass transition temperatureT
g=151 K) in the 64–400 K temperature range by Doppler shift measurements. A method based on the simulataneous observation of two lines from133Ba and137Cs radioactive sources together with the positron annihilation line, was employed to measure the Doppler shift of the 511 keV line as a function of the electric field applied to the samples. With this method we were able to measure at the same time the drift velocity of positrons and theS parameter. This parameter is very important in the interpretation of the mobility trend in samples where the positron states change with temperature. The positron mobility was corrected for positronium formation. + at 64 K is 31.7±0.8 cm2 V–1 s–1 then decreases up to 123 K, increases at 148 K and decreases again up to 170 K (+=26.9±0.8 cm2 V–s–). This sharp change in mobility is centred around the glass transition temperature of our samples. Then the mobility remains almost constant up to 230 K. From 250 K to 377 K, + increases and reaches the value of 38.4±1.0 cm2 V–1s–1. The corrected experimental data were well fitted by a simple model taking into account scattering and a thermally activated process (hopping mechanism). 相似文献
38.
S. Czajkowski M. Bernas P. Armbruster H. Geissel C. Kozhuharov G. Münzenberg D. Vieira Ph. Dessagne Ch. Miehe E. Hanelt G. Audi J. K. P. Lee 《Zeitschrift für Physik A Hadrons and Nuclei》1994,348(4):267-272
Neutron-rich Co and Fe isotopes produced by86Kr projectile fragmentation at 500 MeV/u were separated and identified using the fragment separator (FrS) in a bunched energy mode.66Co and65Fe ions were selectively implanted in a double PIN-diode array where the-decay signals were measured. The half-lives were deduced from time correlations between implantation and-decay signals. The remeasurement of the66Co half-life confirms the isotope identification. The value of the65Fe half-life was found to be 0.45±0.15 s. 相似文献
39.
S. Perries A. Astier L. Ducroux R. Duffait Y. Le Coz M. Meyer N. Redon F. Azaiez S. Bouneau C. Bourgeois R. Collatz I. Deloncle B. J. P. Gall F. Hannachi I. Hibbert A. Korichi A. Lopez-Martens R. Lucas V. Méot N. Poffé M. G. Porquet C. Schück H. Sergolle J. F. Sharpey-Schafer R. Wadsworth A. N. Wilson 《Zeitschrift für Physik A Hadrons and Nuclei》1996,354(1):1-2
The francium isotopes200–202Fr were produced in the reaction35Cl+170Yb using bombarding energies of 4.9–5.3 MeV/nucleon. Fusion products were separated in-flight from the primary beam using
a gas-filled recoil separator. An alpha line with the alpha particle energy and half-life of (7468±9) keV and (19
−6
+13
) ms, respectively, was assigned to200Fr. Previously reported decay properties of201,202Fr were confirmed.
Communicated by V. Metag 相似文献
40.
Ferenc Mó ricz Ká roly Tandori 《Proceedings of the American Mathematical Society》1996,124(3):877-885
We study the a.e. convergence of orthogonal series defined over a general measure space. We give sufficient conditions which contain the Menshov-Rademacher theorem as an endpoint case. These conditions turn out to be necessary in the particular case where the measure space is the unit interval and the moduli of the coefficients form a nonincreasing sequence. We also prove a new version of the Menshov-Rademacher inequality.