全文获取类型
收费全文 | 48594篇 |
免费 | 1603篇 |
国内免费 | 22篇 |
专业分类
化学 | 29676篇 |
晶体学 | 263篇 |
力学 | 816篇 |
综合类 | 1篇 |
数学 | 9057篇 |
物理学 | 10406篇 |
出版年
2023年 | 343篇 |
2022年 | 365篇 |
2021年 | 534篇 |
2020年 | 718篇 |
2019年 | 663篇 |
2018年 | 996篇 |
2017年 | 904篇 |
2016年 | 1751篇 |
2015年 | 1463篇 |
2014年 | 1410篇 |
2013年 | 3177篇 |
2012年 | 3007篇 |
2011年 | 2848篇 |
2010年 | 1894篇 |
2009年 | 1610篇 |
2008年 | 2512篇 |
2007年 | 2253篇 |
2006年 | 2012篇 |
2005年 | 2069篇 |
2004年 | 1784篇 |
2003年 | 1469篇 |
2002年 | 1301篇 |
2001年 | 995篇 |
2000年 | 994篇 |
1999年 | 702篇 |
1998年 | 545篇 |
1997年 | 469篇 |
1996年 | 602篇 |
1995年 | 440篇 |
1994年 | 520篇 |
1993年 | 472篇 |
1992年 | 498篇 |
1991年 | 419篇 |
1990年 | 462篇 |
1989年 | 371篇 |
1988年 | 390篇 |
1987年 | 338篇 |
1986年 | 333篇 |
1985年 | 463篇 |
1984年 | 426篇 |
1983年 | 335篇 |
1982年 | 352篇 |
1981年 | 353篇 |
1980年 | 291篇 |
1979年 | 277篇 |
1978年 | 277篇 |
1977年 | 271篇 |
1976年 | 286篇 |
1974年 | 259篇 |
1973年 | 269篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
L. F. Capitán-Vallvey R. Avidad Castañeda M. del Olmo Iruela J. L. Vilchez Quero 《Mikrochimica acta》1993,112(1-4):55-62
Benzo(a)pyrene (BaP) and pyrene (Pyr) are two polycyclic aromatic hydrocarbons (PAHs) showing native fluorescence in solution. Both compounds have been determined in water at trace levels by solid-phase spectrofluorimetry, in which BaP and Pyr are fixed on Sephadex G-25 gel and the relative fluorescence intensity is measured after the system is packed in a 1-mm silica cell. First-derivative synchronous spectra obtained at =38 nm were used to determine BaP and Pyr in the presence of other potentially interferent PAHs. The spectral characteristics of the PAHs-gel system are described, the applicable concentration ranges being 0.4–2.5 ng/ml for BaP and 0.7–4.5 ng/ml for Pyr. The relative standard deviations were 1.1% and 1.4% for BaP and Pyr respectively. The detection limits were 0.04 ng/ml for BaP and 0.1 ng/ml for Pyr. The method was applied to the analysis of both compounds in water at trace levels and a recovery study on tap, natural and sea waters was carried out. 相似文献
992.
The influence of -irradiation on the paramagnetic properties of non-doped polyacetylene at low and high radiation doses has been studied and summarized. The dependence of the EPR spectra on the radiation dose in irradiated polyacetylene has been measured. No essential changes of the spin mobility as a consequence of irradiation were observed. Our measurements of spin concentration confirm the high resistivity of non-doped polyacetylene to radiation. 相似文献
993.
The development of a rapid and reproducible method for the separation of plutonium from soil samples is described. Tetravalent plutonium is extracted from 8M HNO3 into 30% Aliquat-336/toluene mixture. Uranium and thorium are removed with nitric and hydrochloric acid washes. Plutonium is backextracted with HCl–H2C2O4 and HCl–HF solutions. Plutonium is coprecipitated with NdF3 and filtrated onto a 0.1–0.2 m membrane filter to prepare a source for -spectrometry. The chemical yields of separation are about 50–60%. 相似文献
994.
Zoltán Füredi 《Journal of Geometry》1993,46(1-2):55-65
Let s1 (n) denote the largest possible minimal distance amongn distinct points on the unit sphere
. In general, let sk(n) denote the supremum of thek-th minimal distance. In this paper we prove and disprove the following conjecture of A. Bezdek and K. Bezdek: s2(n) = s1([n/3]). This equality holds forn > n0 however s2(12) > s1(4).We set up a conjecture for sk(n), that one can always reduce the problem of thek-th minimum distance to the function s1. We prove this conjecture in the casek=3 as well, obtaining that s3(n) = s1([n/5]) for sufficiently largen.The optimal construction for the largest second distance is obtained from a point set of size [n/3] with the largest possible minimal distance by replacing each point by three vertices of an equilateral triangle of the same size . If 0, then s2 tends to s1([n/3]). In the case of the third minimal distance, we start with a point set of size [n/5] and replace each point by a regular pentagon. 相似文献
995.
996.
Using a new graph counting technique suitable for self-similar fractals, exact 18th-order series expansions for SAWs on some Sierpinski carpets are generated. From them, the critical fugacityx
c and critical exponents SAW and SAW are obtained. The results show a linear dependence of the critical fugacity with the average number of bonds per site of the lattices studied. We find for some carpets with low lacunarity that SAW<0.75, thus violating the relation SAW(fractal) > SAW (d) for SAWs on the fractals which are embedded in ad-dimensional Euclidean space. 相似文献
997.
H. Glesková V. V. Il'chenko V. A. Skryshevsky V. I. Strikha 《Czechoslovak Journal of Physics》1993,43(2):169-178
The paper concerns the possibility of using CW (continuous wave) CO2-laser annealing (=10.6 m,P 100 W/cm2) for formation of a barrier in the Al/a-Si:H/SS (SS-stainless steel) structures with good rectifyingI–V characteristics. The infrared absorption spectra, photoelectric properties, temperature effect on the conductivity and saturation current were analyzed and various contact models are discussed.We thank P. imanec for useful and stimulating discussion, J. Stuchlík for kindly manufacturing the a-Si:H films for us and D. N. Goncharov for the aid with the measurement of the conductivity temperature dependences. 相似文献
998.
The problem of calculation of Sturmian functions (positive energy Weinberg states) for nonlocal (exchange) interactions is considered. It is shown that the method of continued fractions proposed by Horáek and Sasakawa makes the calculation of Sturmian eigenfunctions and eigenvalues feasible even for complicated nonlocal interactions. As an example Sturmian functions and Sturmian eigenvalues for the low energy electron-hydrogen scattering in the static exchange approximation are calculated. In addition a very general proof of convergence of the method of continued fractions is presented.Dedicated to the memory of Professor Jozef Kvasnica. 相似文献
999.
P. PŘikryl F. Vodák O. Kapičková J. Drchalová R. černý 《Czechoslovak Journal of Physics》1993,43(1):63-71
The influence of the microgravity environment on solidification processes is discussed. A simple model of the solidification of a binary-alloy is presented with the chemical diffusion influenced by the gravitational field. Using the results of Mullins and Sekerka, we employ the linear theory of hydrodynamic stability to investigate the interfacial instability driving the pattern-forming processes in solidification. As a result, we estimate the characteristic size of the elements of the emerging pattern. We show that, in spite of good agreement of our result with the size of cellulae observed in experiments, the model cannot explain the changes in the patterns occurring in space environment. In conclusion we shortly discuss the possibility of adding realism to our simple model by including the effect of convection. 相似文献
1000.
We simulate the classical diffusion of a particle of massM in an infinite one-dimensional system of hard point particles of massm in equilibrium. Each computer run corresponds to about 108 collisions of the diffusive particle. We find that (t) 1/t
fort large enough, and a crossover from an M m regime where=2 to=3 forM=m. The diffusion constant has a sharp maximum atM=m. We study moments x(t)2 and x(t)4, and examine the behavior ofq
2
(t)=x(t)4/3x(t)22. We find thatq(t)1 (consistent with a normal distribution) in theM limit (for all timest) and in the t limit for allM.
On sabbatical leave from IVIC-Instituto Venezolano de Investigaciones Cientificas. 相似文献