全文获取类型
收费全文 | 16279篇 |
免费 | 2726篇 |
国内免费 | 3024篇 |
专业分类
化学 | 12559篇 |
晶体学 | 263篇 |
力学 | 936篇 |
综合类 | 236篇 |
数学 | 2046篇 |
物理学 | 5989篇 |
出版年
2024年 | 34篇 |
2023年 | 401篇 |
2022年 | 564篇 |
2021年 | 710篇 |
2020年 | 837篇 |
2019年 | 801篇 |
2018年 | 631篇 |
2017年 | 697篇 |
2016年 | 909篇 |
2015年 | 930篇 |
2014年 | 1060篇 |
2013年 | 1384篇 |
2012年 | 1363篇 |
2011年 | 1449篇 |
2010年 | 1086篇 |
2009年 | 1021篇 |
2008年 | 1134篇 |
2007年 | 955篇 |
2006年 | 880篇 |
2005年 | 738篇 |
2004年 | 622篇 |
2003年 | 474篇 |
2002年 | 582篇 |
2001年 | 466篇 |
2000年 | 397篇 |
1999年 | 319篇 |
1998年 | 243篇 |
1997年 | 163篇 |
1996年 | 182篇 |
1995年 | 132篇 |
1994年 | 162篇 |
1993年 | 114篇 |
1992年 | 83篇 |
1991年 | 114篇 |
1990年 | 100篇 |
1989年 | 47篇 |
1988年 | 44篇 |
1987年 | 34篇 |
1986年 | 36篇 |
1985年 | 43篇 |
1984年 | 18篇 |
1983年 | 21篇 |
1982年 | 10篇 |
1981年 | 9篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1977年 | 3篇 |
1974年 | 4篇 |
1957年 | 3篇 |
1936年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
121.
A double hydrophilic block copolymer composed of poly(acrylic acid) (PAA) and poly(4‐vinyl pyridine) (P4VP) was obtained through hydrolysis of diblock copolymer of poly(tert‐butyl acrylate) (PtBA) and P4VP synthesized using atom transfer radical polymerization. Water‐soluble micelles with PAA core and P4VP corona were observed at low (acidic) pH, while micelles with P4VP core and PAA corona were formed at high (basic) pH. Two metalloporphyrins, zinc tetraphenylporphyrin (ZnTPP) and cobalt tetraphenylporphyrin (CoTPP), were used as model compounds to investigate the encapsulation of hydrophobic molecules by both types of micelles. UV–vis spectroscopic measurements indicate that micelles with P4VP core are able to entrap more ZnTPP and CoTPP as a result of the axial coordination between the transition metals and the pyridine groups. The study found that metalloporphyrins encapsulated by the micelles with PAA core could be released on pH increase, while those entrapped by the micelles with P4VP core could be released on pH decrease. This behavior originates from the two‐way pH change‐induced disruption of PAA‐b‐P4VP micelles. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1734–1744, 2006 相似文献
122.
Positive Steady States of a Prey-predator Model with Diffusion and Non-monotone Conversion Rate 总被引:1,自引:0,他引:1
Rui PENG Ming Xin WANG Wen Van CHEN 《数学学报(英文版)》2007,23(4):749-760
In this paper, we study the positive steady states of a prey-predator model with diffusion throughout and a non-monotone conversion rate under the homogeneous Dirichlet boundary condition. We obtain some results of the existence and non-existence of positive steady states. The stability and uniqueness of positive steady states are also discussed. 相似文献
123.
The difficulty suffered in optimization-based algorithms for the solution of nonlinear equations lies in that the traditional
methods for solving the optimization problem have been mainly concerned with finding a stationary point or a local minimizer
of the underlying optimization problem, which is not necessarily a solution of the equations. One method to overcome this
difficulty is the Lagrangian globalization (LG for simplicity) method. This paper extends the LG method to nonsmooth equations
with bound constraints. The absolute system of equations is introduced. A so-called Projected Generalized-Gradient Direction (PGGD) is constructed and proved to be a descent direction of the reformulated nonsmooth optimization problem. This projected
approach keeps the feasibility of the iterates. The convergence of the new algorithm is established by specializing the PGGD.
Numerical tests are given.
This author's work was done when she was visiting The Hong Kong Polytechnic University.
His work is also supported by the Research Grant Council of Hong Kong. 相似文献
124.
In the discrete-time Sparre Andersen risk model with investments and dividend payments, the company controls the dividend payments and the proportions of venture investments in order to maximize the cumulative expected discounted dividends prior to ruin. The paper gets the algorithm of the optimal dividend strategy by analyzing a Hamilton-Jacobi-Bellman equation and transforming the value function. Furthermore, the existence of the optimal solution of the transformation function is proved by using compression mapping and fixed point principle. In order to make the calculation easier, this paper also proposes an
innovative random simulation method for the optimal strategy, and proves that the simulation result is the consistent estimate of the real value. Finally, the random simulation method in the Matlab is used for numerical analysis in an example, which shows the innovative simulation method is a very good and helpful method for making dividend payment and investment decisions. 相似文献
125.
Phase-Locked Fibre Array for Coherent Combination and Atmosphere Aberration Compensation 总被引:1,自引:0,他引:1 下载免费PDF全文
We report a fibre amplifier array that not only achieves coherent beam combination by compensation of phase noises of fibre amplifier, but also accomplishes correction of atmosphere aberration. It is of master-oscillatormultiple-amplifier (MOPA) configuration, which can be phase-locked by the multidither principle or heterodyne detection principle. First laboratory experiments of atmosphere aberration compensation of a three-element fibre amplifier array are reported. The atmosphere aberration is created by a phase screen in the experiment. The phase changes of the beam, which are introduced by the fibre amplifier and the phase screen, are both detected by the heterodyne detection method. Phase modulators are controlled to compensate for the phase in the three paths. No matter whether there is a phase screen producing atmosphere aberration or not, the dim dynamic interference fringes in the far field turn to a clear and stable pattern, and the peak intensity is maximized. It is indicated that the fibre amplifier array is phase-locked, and coherent combination of the three beams is achieved. It can be used not only to obtain high power fibre laser array but also in laser space communication. 相似文献
126.
127.
128.
从实验上探讨了掺Nd^3+的氟化物玻璃光纤正向双程超荧光基本特性,包括输入-输出特性、输出-带宽特性以及输出-波长(激发)特性。并给出了理论上的拟合公式,实验表明利用氟化物玻璃光纤有望获得性能优异的有应用前景的低相干度集成化光源。 相似文献
129.
130.
电流控阈技术及二值I~2L施密特电路设计黄瑞祥,杭国强(杭州大学电子工程系杭州310028)在数字电路中,以往对施密特电路的分析与研究大多局限于用电压信号来表示逻辑值的电路,例如TTL、CMOS、ECL等电路[1-3].然而,对于以电流为信号的电流型?.. 相似文献