全文获取类型
收费全文 | 38479篇 |
免费 | 1403篇 |
国内免费 | 160篇 |
专业分类
化学 | 24142篇 |
晶体学 | 244篇 |
力学 | 658篇 |
综合类 | 4篇 |
数学 | 5909篇 |
物理学 | 9085篇 |
出版年
2023年 | 262篇 |
2022年 | 357篇 |
2021年 | 596篇 |
2020年 | 565篇 |
2019年 | 559篇 |
2018年 | 571篇 |
2017年 | 565篇 |
2016年 | 1151篇 |
2015年 | 1023篇 |
2014年 | 1068篇 |
2013年 | 2023篇 |
2012年 | 2081篇 |
2011年 | 2488篇 |
2010年 | 1387篇 |
2009年 | 1307篇 |
2008年 | 2183篇 |
2007年 | 2082篇 |
2006年 | 1960篇 |
2005年 | 1743篇 |
2004年 | 1380篇 |
2003年 | 1222篇 |
2002年 | 1063篇 |
2001年 | 840篇 |
2000年 | 712篇 |
1999年 | 585篇 |
1998年 | 465篇 |
1997年 | 477篇 |
1996年 | 536篇 |
1995年 | 432篇 |
1994年 | 425篇 |
1993年 | 437篇 |
1992年 | 424篇 |
1991年 | 341篇 |
1990年 | 312篇 |
1989年 | 260篇 |
1988年 | 245篇 |
1987年 | 275篇 |
1986年 | 276篇 |
1985年 | 312篇 |
1984年 | 353篇 |
1983年 | 274篇 |
1982年 | 302篇 |
1981年 | 292篇 |
1980年 | 273篇 |
1979年 | 236篇 |
1978年 | 241篇 |
1977年 | 233篇 |
1976年 | 203篇 |
1975年 | 180篇 |
1973年 | 173篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
161.
M. Olivares-Marín C. Fernández-González V. Gómez-Serrano 《Applied Surface Science》2006,252(17):5980-5983
Using cherry stones, the preparation of activated carbon has been undertaken in the present study by chemical activation with potassium hydroxide. A series of KOH-activated products was prepared by varying the carbonisation temperature in the 400-900 °C range. Such products were characterised texturally by gas adsorption (N2, −196 °C), mercury porosimetry, and helium and mercury density measurements. FT-IR spectroscopy was also applied. The carbons prepared as a rule are microporous and macroporous solids. The degree of development of surface area and porosity increases with increasing carbonisation temperature. For the carbon heated at 900 °C the specific surface area (BET) is 1624 m2 g−1, the micropore volume is 0.67 cm3 g−1, the mesopore volume is 0.28 cm3 g−1, and the macropore volume is 1.84 cm3 g−1. 相似文献
162.
Ph. Hägler B. Pire L. Szymanowski O.V. Teryaev 《The European Physical Journal C - Particles and Fields》2002,24(2):261-270
We study Pomeron-Odderon interference effects giving rise to charge and single-spin asymmetries in diffractive electroproduction
of a pair. We calculate these asymmetries, originating from both longitudinal and transverse polarizations of the virtual photon,
in the framework of QCD and in the Born approximation, in a kinematical domain accessible to HERA experiments. We predict
a sizable charge asymmetry with a characteristic dependence on the invariant mass of the pair, which makes this observable very important for establishing the magnitude of the Odderon exchange in hard processes.
The single-spin asymmetry turns out to be rather small. We briefly discuss future improvements of our calculations and their
possible effects on the results.
Received: 18 July 2002 / Published online: 25 October 2002 相似文献
163.
The direct and the exchange core polarization (ECP) contributions of the conduction electrons to the Knight shift of palladium are evaluated. To obtain the wave functions for the conduction electrons and the partial densities of states at the Fermi surface a KKR energy band calculation was performed. The contributions of the core electrons to the Knight shift were determined by using the moment perturbation method (MP). Electron-electron interactions are taken into account by individual enhancement factors for thed ands electrons. The agreement between the theoretical results and the available experimental data is quite satisfactory. 相似文献
164.
Z. Sebestyén 《Periodica Mathematica Hungarica》1989,20(1):85-87
We prove, as an application of our positive extension argument, a theorem of Parrott concerning the quotient norm with respect to spaces of Hilbert space operators. 相似文献
165.
Jaime Pfretzschner Pedro Cobo Francisco Simón María Cuesta Alejandro Fernández 《Applied Acoustics》2006,67(1):62-73
Microperforated panels (MPPs) coupled to a rigid wall have been proposed recently as an alternative to porous absorbers in situations having concerns with bacterial contamination and small particles discharge, like food, pharmaceutical and microelectronic industries. There exists also an increasing interest for MPP absorbers in the transportation industry and civil engineering. In general, an optimally designed MPP with good broadband absorption requires many submillimetric holes distributed over a panel of also submillimetric thickness. Such thin plates or foils become so fragile that they need to be protected from mechanical damage. In this paper, an alternative strategy is investigated which allows the design of MPPs with panels of millimetric thickness while maintaining their acoustic performance. These absorbers, named microperforated insertion units (MIUs), avoid the structural problems of the classical MPPs. An assessment of the sound absorption properties of these structures is presented. Comparisons between calculations and measurements are also made under two experimental conditions: plane waves at normal incidence (impedance tube) and free field (anechoic room). 相似文献
166.
Our object of study is the asymptotic behavior of the sequence of polynomials orthogonal with respect to the discrete Sobolev
inner product <formula> \langle f, g \rangle = ∈t_{E} f(ξ) \overline{g(ξ)} ρ(ξ) |d ξ|+ f(Z) A g(Z)^H, </formula> where E is a rectifiable Jordan curve or arc in the complex plane
f(Z) = (f(z_1), \ldots, f^{(l_1)}(z_1) , \ldots , f(z_m) , \ldots ,f^{(l_m)}(z_m)),
A is an M \times M Hermitian matrix, M l
1
+ ⋅s + l
m
+ m , |d ξ| denotes the arc length measure, ρ is a nonnegative function on E , and z
i
∈Ω,
i=1,2,\ldots,m , where Ω is the exterior region to E .
July 23, 1999. Dates revised: September 11, 2000 and February 16, 2001. Date accepted: February 26, 2001. 相似文献
167.
168.
It was studied the tin phase composition of the electrodeposited alloys produced at different temperatures and current densities from an acid chloride/fluoride electrolyte and an acid chloride bath. Mössbauer spectra were consistent with a Ni3Sn4 intermetallic compound, dissolved tin, and a Cu?Sn intermetallic compound formed at the interface of the copper substrate. 相似文献
169.
Oscillatory change of pH occurs during the chromate-catalyzed decomposition of hydrogen peroxide in a weakly acidic medium at elevated temperature and at high initial concentration of hydrogen peroxide. In a closed system, there are only two or three periods, but sustained oscillation occurs in a CSTR. In a CSTR bistability is also found. In closed systems the temperature exhibits a great maximum (up to 15°C increase), in a CSTR sustained oscillation occurs at a constant stationary temperature. 相似文献
170.