全文获取类型
收费全文 | 14232篇 |
免费 | 1681篇 |
国内免费 | 1152篇 |
专业分类
化学 | 3634篇 |
晶体学 | 168篇 |
力学 | 1830篇 |
综合类 | 144篇 |
数学 | 2131篇 |
物理学 | 5895篇 |
无线电 | 3263篇 |
出版年
2024年 | 36篇 |
2023年 | 147篇 |
2022年 | 273篇 |
2021年 | 363篇 |
2020年 | 342篇 |
2019年 | 294篇 |
2018年 | 306篇 |
2017年 | 411篇 |
2016年 | 427篇 |
2015年 | 449篇 |
2014年 | 646篇 |
2013年 | 1050篇 |
2012年 | 832篇 |
2011年 | 1003篇 |
2010年 | 773篇 |
2009年 | 860篇 |
2008年 | 877篇 |
2007年 | 953篇 |
2006年 | 856篇 |
2005年 | 781篇 |
2004年 | 685篇 |
2003年 | 629篇 |
2002年 | 567篇 |
2001年 | 426篇 |
2000年 | 438篇 |
1999年 | 322篇 |
1998年 | 326篇 |
1997年 | 290篇 |
1996年 | 236篇 |
1995年 | 213篇 |
1994年 | 203篇 |
1993年 | 161篇 |
1992年 | 147篇 |
1991年 | 99篇 |
1990年 | 97篇 |
1989年 | 59篇 |
1988年 | 63篇 |
1987年 | 39篇 |
1986年 | 49篇 |
1985年 | 60篇 |
1984年 | 42篇 |
1983年 | 17篇 |
1982年 | 55篇 |
1981年 | 26篇 |
1980年 | 28篇 |
1979年 | 16篇 |
1978年 | 20篇 |
1977年 | 10篇 |
1976年 | 22篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
Franco Varsano Francesca Decker Enrico Masetti 《Monatshefte für Chemie / Chemical Monthly》2001,132(1):83-95
Summary. Ce-V mixed oxide films have been deposited by RF sputtering with the aim of increasing the Li charge capacity of counter
electrodes in smart windows. Such mixed oxides have shown high transmittance and optical passivity in the visible region.
After electrode pre-conditioning by cyclic voltammetry, a good electrochemical reversibility in LiClO4– propylene carbonate electrolyte was observed, and large Li-charge capacity under galvanostatic charging (up to 50 mCċcm−2) has been measured. The electrode charge capacity decreased after prolonged insertion-deinsertion cycles, whereas the photoptic
transmittance remained about constant. After 800 cycles the Li-charge capacity decreased to 40 mCċcm−2. The Li diffusion coefficient inside the films measured by electrochemical impedance and by galvanostatic titration ranged
from 10−11 cm2ċs−1 to 10−13cm2ċs−1. We observed that the Li charge capacity of the film electrodes is a function of the film deposition conditions, because
it increased with the vanadium oxide concentration in the target and with the oxygen content in the sputtering atmosphere.
Received June 23, 2000. Accepted (revised) August 7, 2000 相似文献
932.
H2和CO在间二甲苯中的溶解度和体积传质系数的研究 总被引:5,自引:1,他引:4
使用IL搅拌釜,在温度80~160℃,压力0.5~5.0MPa范围内,实测了H2和CO在间二甲苯中的溶解度和体积传质系数。结果表明,两者均随温度和压力的升高而增大。实验结果与工于正规溶液理论Prausnitz-Shair法计算的气体溶解度比较相符。在相同温度、压力条件下,CO的溶解度和体积传质系数比H2大。相同温度、压力下不同液相介质中H2和CO的体积传质系数排序如下:(kLa)MEF〉(kLa) 相似文献
933.
合成水凝胶是由水溶性单体聚合得到的轻度交联的高分子柔顺链网络 .高分子交联网络与水之间的相互作用决定着水凝胶的物理化学性质[1,2 ] .水凝胶常应用于生物医学材料和生物传感器等方面 .如接触眼镜的材料就常用甲基丙烯酸 -β-羟乙酯和聚乙烯醇 (PVA)为主要成分的水凝胶 ,所以对其摩擦性质的研究会丰富对生物医用材料的认识 .关于水凝胶的摩擦性质的研究 ,除 Osada等[3] 研究了聚乙烯醇及一些天然水凝胶在几牛顿到几十牛顿的负载下的摩擦行为外 ,尚少报道 .PVA水凝胶的结晶度对其性能影响甚大 ,但他们没有涉及结晶度与 PVA水凝胶的摩… 相似文献
934.
Lie symmetry group method is applied to study the affine heat equation for surface. Its symmetry groups and corresponding optimal systems are determined, and group-invariant solutions associated to the symmetries are obtained and classified. 相似文献
935.
Michel Speetjens Arnold Reusken Wolfgang Marquardt 《Communications in Nonlinear Science & Numerical Simulation》2008,13(8):1518-1537
We consider a relatively simple model for pool-boiling processes. This model involves only the temperature distribution within the heater and describes the heat exchange with the boiling medium via a nonlinear boundary condition imposed on the fluid-heater interface. This results in a standard heat-transfer problem with a nonlinear Neumann boundary condition on part of the boundary. In a recent paper [Speetjens M, Reusken A, Marquardt W. Steady-state solutions in a nonlinear pool-boiling model. IGPM report 256, RWTH Aachen. Commun Nonlinear Sci Numer Simul, in press, doi:10.1016/j.cnsns.2006.11.002] we analysed this nonlinear heat-transfer problem for the case of two space dimensions and in particular studied the qualitative structure of steady-state solutions. The study revealed that, depending on system parameters, the model allows both multiple homogeneous and multiple heterogeneous temperature distributions on the fluid-heater interface. In the present paper we show that the analysis from Speetjens et al. (doi:10.1016/j.cnsns.2006.11.002) can be generalised to the physically more realistic case of three space dimensions. A fundamental shift-invariance property is derived that implies multiplicity of heterogeneous solutions. We present a numerical bifurcation analysis that demonstrates the multiple solution structure in this mathematical model by way of a representative case study. 相似文献
936.
We study the Riccati equation arising in a class of quadratic optimal control problems with infinite dimensional stochastic
differential state equation and infinite horizon cost functional. We allow the coefficients, both in the state equation and
in the cost, to be random.
In such a context backward stochastic Riccati equations are backward stochastic differential equations in the whole positive
real axis that involve quadratic non-linearities and take values in a non-Hilbertian space. We prove existence of a minimal
non-negative solution and, under additional assumptions, its uniqueness. We show that such a solution allows to perform the
synthesis of the optimal control and investigate its attractivity properties. Finally the case where the coefficients are
stationary is addressed and an example concerning a controlled wave equation in random media is proposed. 相似文献
937.
Wolfgang Kreitmeier 《Mathematische Nachrichten》2008,281(9):1307-1327
For a large class of dyadic homogeneous Cantor distributions in ?, which are not necessarily self‐similar, we determine the optimal quantizers, give a characterization for the existence of the quantization dimension, and show the non‐existence of the quantization coefficient. The class contains all self‐similar dyadic Cantor distributions, with contraction factor less than or equal to 1/3. For these distributions we calculate the quantization errors explicitly. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
938.
The periodic risk model with investment 总被引:1,自引:0,他引:1
We consider a periodic risk model with the possibility of investing into a risky asset, given by a geometrical Brownian motion. The aim is to maximize the adjustment coefficient of the risk process. It is shown that the optimal investment strategy only depends on the averaged data of the model and is constant over time. Thus maximizing the adjustment coefficient is a very weak optimization criterion. 相似文献
939.
Significant influence of sample preparation on thermal decomposition of polyolefin-technological oil mixtures was proved during
tests. Samples of polymer-oil mixtures were prepared with two methods: reducing size and components mixing and soaking in
temperature 170°C. Soaking causes decreasing thermal stability of the charge. This fact manifests itself in decreasing of
thermal decomposition temperature in laboratory scale, as well as in change of characteristic decomposition temperatures during
thermogravimetric analyses. Data analysis was performed with the use of classic method based on Arrhenius kinetic equation
and three-parameter model. The influence of sample composition and preparation method on values of three-parameter equation
coefficients was observed. 相似文献
940.
Magnetic susceptibility and heat capacity due to spin-state excitations in LaCoO3 were analyzed with an irregular solution model composed of Co3+ ions in the low-spin ground state and in the high-spin excited state. An energy-levels diagram proposed by Ropka and Radvanskii
[1] was used for the high-spin excited state. This analysis showed that the entropy of mixing is less than that of ideal solutions
and the enthalpy of mixing is negative, indicating that the high-spin Co ions are arranged as far apart as possible. 相似文献