全文获取类型
收费全文 | 83889篇 |
免费 | 13358篇 |
国内免费 | 12689篇 |
专业分类
化学 | 57326篇 |
晶体学 | 1347篇 |
力学 | 5777篇 |
综合类 | 1378篇 |
数学 | 11037篇 |
物理学 | 33071篇 |
出版年
2024年 | 82篇 |
2023年 | 1504篇 |
2022年 | 1951篇 |
2021年 | 2511篇 |
2020年 | 3024篇 |
2019年 | 2891篇 |
2018年 | 2633篇 |
2017年 | 2752篇 |
2016年 | 3461篇 |
2015年 | 3727篇 |
2014年 | 4504篇 |
2013年 | 5972篇 |
2012年 | 7047篇 |
2011年 | 7409篇 |
2010年 | 5508篇 |
2009年 | 5466篇 |
2008年 | 5888篇 |
2007年 | 5270篇 |
2006年 | 5111篇 |
2005年 | 4443篇 |
2004年 | 3481篇 |
2003年 | 2600篇 |
2002年 | 2293篇 |
2001年 | 2272篇 |
2000年 | 2142篇 |
1999年 | 1973篇 |
1998年 | 1558篇 |
1997年 | 1328篇 |
1996年 | 1397篇 |
1995年 | 1235篇 |
1994年 | 1185篇 |
1993年 | 1016篇 |
1992年 | 942篇 |
1991年 | 778篇 |
1990年 | 679篇 |
1989年 | 589篇 |
1988年 | 467篇 |
1987年 | 470篇 |
1986年 | 377篇 |
1985年 | 362篇 |
1984年 | 279篇 |
1983年 | 240篇 |
1982年 | 194篇 |
1981年 | 156篇 |
1980年 | 112篇 |
1979年 | 81篇 |
1978年 | 73篇 |
1977年 | 62篇 |
1975年 | 58篇 |
1973年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Annals of Global Analysis and Geometry - In this paper, we prove a family of sharp geometric inequalities for free boundary hypersurfaces in a ball in space forms. 相似文献
12.
采用态平均(CASSCF)/高度相关多参考组(MRCI)方法,对N2分子A3Σu+、B3Пg、C3Пu电子态的势能、跃迁偶极矩进行了高度相关的精确计算.计算的势能在平衡位置附近与RKR拟合的势能曲线非常一致,获得的跃迁偶极矩与已有实验值符合很好。首次对A3Σu+、B3Пg、C3Пu电子态的振转光谱常数随振动量子数v的变化进行系统定量计算,其结果与已有的实验观测数据相符.同时,获得了N2分子第一正带系的0-1、0-2、1-0、1-2、1-3、2-0、2-1、2-3、3-0、3-1和3-2光谱带分别在300,3000,6000,10000K时的谱线强度,如1-0带在3000,6000,10000K时的高温谱线带强度分别为1.58543×10-16 cm-1/(分子 cm-2)、6.07889×10-17 cm-1/(分子 cm-2)和2.3781×10-17 cm-1/(分子 cm-2).这些结果对N2分子进一步的理论研究、实际应用和高温大气的建模与研究具都有一定的参考价值. 相似文献
13.
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
14.
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
15.
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
16.
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
17.
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
18.
19.
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
20.
Journal of Fluorescence - Carbon nanodots (CDs) have exhibited excellent sensing capability for various metal ions. However, it is difficult to determine the selectivity of CDs to metal ions. In... 相似文献