全文获取类型
收费全文 | 154446篇 |
免费 | 24822篇 |
国内免费 | 15063篇 |
专业分类
化学 | 102726篇 |
晶体学 | 1625篇 |
力学 | 10677篇 |
综合类 | 1005篇 |
数学 | 19636篇 |
物理学 | 58662篇 |
出版年
2024年 | 144篇 |
2023年 | 2912篇 |
2022年 | 3090篇 |
2021年 | 4596篇 |
2020年 | 5861篇 |
2019年 | 5692篇 |
2018年 | 5010篇 |
2017年 | 4525篇 |
2016年 | 7114篇 |
2015年 | 6854篇 |
2014年 | 8373篇 |
2013年 | 11192篇 |
2012年 | 13607篇 |
2011年 | 14299篇 |
2010年 | 9602篇 |
2009年 | 9313篇 |
2008年 | 9877篇 |
2007年 | 9028篇 |
2006年 | 8380篇 |
2005年 | 7106篇 |
2004年 | 5439篇 |
2003年 | 4199篇 |
2002年 | 3556篇 |
2001年 | 3154篇 |
2000年 | 2794篇 |
1999年 | 3215篇 |
1998年 | 2877篇 |
1997年 | 2608篇 |
1996年 | 2790篇 |
1995年 | 2410篇 |
1994年 | 2330篇 |
1993年 | 1894篇 |
1992年 | 1719篇 |
1991年 | 1543篇 |
1990年 | 1251篇 |
1989年 | 994篇 |
1988年 | 789篇 |
1987年 | 681篇 |
1986年 | 628篇 |
1985年 | 578篇 |
1984年 | 411篇 |
1983年 | 308篇 |
1982年 | 269篇 |
1981年 | 213篇 |
1980年 | 153篇 |
1979年 | 88篇 |
1978年 | 88篇 |
1975年 | 89篇 |
1974年 | 91篇 |
1973年 | 87篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Based on the primal mixed variational formulation, a stabilized nonconforming mixed finite element method is proposed for the linear elasticity on rectangular and cubic meshes. Two kinds of penalty terms are introduced in the stabilized mixed formulation, which are the jump penalty term for the displacement and the divergence penalty term for the stress. We use the classical nonconforming rectangular and cubic elements for the displacement and the discontinuous piecewise polynomial space for the stress, where the discrete space for stress are carefully chosen to guarantee the well-posedness of discrete formulation. The stabilized mixed method is locking-free. The optimal convergence order is derived in the $L^2$-norm for stress and in the broken $H^1$-norm and $L^2$-norm for displacement. A numerical test is carried out to verify the optimal convergence of the stabilized method. 相似文献
22.
Mathematical Programming - Convergence analysis of accelerated first-order methods for convex optimization problems are developed from the point of view of ordinary differential equation solvers. A... 相似文献
23.
Ultrasound has been recognized as an exciting tool to enhance the therapeutic efficacy in tumor chemotherapy owing to the triggered drug release, facilitated intracellular drug delivery, and improved spatial precision. Aiming for a precise localized drug delivery, novel dendritic polyurethane-based prodrug (DOX-DPU-PEG) was fabricated with a drug content of 18.9% here by conjugating DOX onto the end groups of the functionalized dendritic polyurethane via acid-labile imine bonds. It could easily form unimolecular micelles around 38 nm. Compared with the non-covalently drug-loaded unimolecular micelles (DOX@Ph-DPU-PEG), they showed excellent pH/ultrasound dual-triggered drug release performance, with drug leakage of only 4% at pH 7.4, but cumulative release of 14% and 88% at pH 5.0 without and with ultrasound, respectively. The ultrasound responsiveness was attributed to the unique strawberry-shaped topological structure of the DOX-DPU-PEG, in which DOX was embedded in the skin layer of the hydrophobic DPU cores. With ultrasound, the DOX-DPU-PEG unimolecular micelles possessed enhanced tumor growth inhibition than free DOX but showed no obvious cytotoxicity on the tumor cells without ultrasound. Such feature makes them promising potential for precise localized drug delivery. 相似文献
24.
Hao Lu Xiaodong Wang Hang Wang Andong Zhang Xinming Zheng Na Yu Zheng Tang Xinjun Xu Yahui Liu Ya-Nan Chen Zhishan Bo 《中国科学:化学(英文版)》2022,65(3):594-601
Three nonfused ring electron acceptors (NFREAs) TTC6,TT-C8T and TT-TC8 were purposefully designed and synthesized.The molecular geometry can be adjusted by the steric hindrance of lateral substituents.According to the DFT calculations,from TTC6 to TT-C8T and TT-TC8,planarity of the molecular backbone is gradually improved,accompanying with the enhancing of intramolecular charge transfer effect.As for TT-TC8,the two phenyl substituents are almost perpendicular to the molecular backbone,which endues the acceptor with good solubility and suppresses it to form over-aggregation.Multidirectional regular molecular orientation and closer molecular stacking are formed in TT-TC8 film.As a result,TT-TC8 based devices afford the highest PCE of 13.13%,which is much higher than that of TTC6 (4.41%) and TT-C8T (10.42%) and among the highest PCE values based on NFREAs. 相似文献
25.
Xu Yifan Zhang Hehe Ding Tangjing Tian Ruiqi Sun Dongmei Wang Ming-Sheng Zhou Xiaosi 《中国科学:化学(英文版)》2022,65(9):1807-1816
Science China Chemistry - Due to their enormous potential for large-scale energy storage, rechargeable potassium-ion batteries have been widely researched and developed. However, the drastic volume... 相似文献
26.
Theoretical and Mathematical Physics - We theoretically calculate general higher-order soliton solutions of the space-shifted parity–time-symmetric nonlocal multicomponent nonlinear... 相似文献
27.
In this paper, we study the well-posedness and the asymptotic stability of a one-dimensional thermoelastic microbeam system, where the heat conduction is given by Gurtin-Pipkin thermal law. We first establish the well-posedness of the system by using the semigroup arguments and Lumer-Phillips theorem. We then obtain an explicit and general formula for the energy decay rates through perturbed energy method and some properties of the convex functions. 相似文献
28.
Science China Mathematics - In this paper, we obtain a necessary and sufficient condition for a U(n)-invariant complex Finsler metric F on domains in ?n to be strongly convex, which also... 相似文献
29.
30.
In this paper,we investigate the non-autonomous Hamilton-Jacobi equation ■ where H is 1-periodic with respect to t and M is a compact Riemannian manifold without boundary.We obtain the viscosity solution denoted by T_(t_0)~tφ(x) and show T_(t_0)~tφ(x) converges uniformly to a time-periodic viscosity solution u~*(x,t) of ?_tu+H(t,x,?_xu,u)=0. 相似文献