全文获取类型
收费全文 | 11512篇 |
免费 | 2517篇 |
国内免费 | 3556篇 |
专业分类
化学 | 9250篇 |
晶体学 | 364篇 |
力学 | 761篇 |
综合类 | 271篇 |
数学 | 1611篇 |
物理学 | 5328篇 |
出版年
2024年 | 14篇 |
2023年 | 253篇 |
2022年 | 466篇 |
2021年 | 468篇 |
2020年 | 548篇 |
2019年 | 534篇 |
2018年 | 463篇 |
2017年 | 529篇 |
2016年 | 518篇 |
2015年 | 634篇 |
2014年 | 739篇 |
2013年 | 933篇 |
2012年 | 1032篇 |
2011年 | 999篇 |
2010年 | 801篇 |
2009年 | 907篇 |
2008年 | 951篇 |
2007年 | 868篇 |
2006年 | 840篇 |
2005年 | 734篇 |
2004年 | 549篇 |
2003年 | 404篇 |
2002年 | 443篇 |
2001年 | 419篇 |
2000年 | 459篇 |
1999年 | 367篇 |
1998年 | 225篇 |
1997年 | 191篇 |
1996年 | 181篇 |
1995年 | 144篇 |
1994年 | 126篇 |
1993年 | 113篇 |
1992年 | 106篇 |
1991年 | 70篇 |
1990年 | 87篇 |
1989年 | 80篇 |
1988年 | 59篇 |
1987年 | 57篇 |
1986年 | 53篇 |
1985年 | 45篇 |
1984年 | 45篇 |
1983年 | 44篇 |
1982年 | 18篇 |
1981年 | 16篇 |
1980年 | 9篇 |
1979年 | 14篇 |
1978年 | 7篇 |
1973年 | 3篇 |
1957年 | 2篇 |
1936年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
Conjugated microporous polymers (CMPs) have recently received extensive attention in oil/organic solvent-water separation field as a kind of ideal porous absorbents with tunable porosity, large surface areas, and super-hydrophobicity. However, reports on the application of CMPs in adsorption of hydrophilic contaminants from water are very few. In this work, we studied the adsorption of metronidazole (MNZ), a polar antibiotic, by two kinds of CMPs. The adsorption characteristics of MNZ by the CMPs, including adsorption kinetics, mechanism, and isotherm parameters were calculated. The adsorption kinetics of MNZ was well expressed by the pseudo-second-order model, and the adsorption process was found to be mainly controlled by film diffusion. The adsorption isotherm data agreed well with the Langmuir isotherm model, and the values of free energy E indicated that the adsorption nature of MNZ on the CMPs was physisorption. Increasing dispersion degree of the CMPs in MNZ solution resulted in greater adsorption. This work may provide fundamental guidance for the removal of antibiotics by CMPs. 相似文献
82.
Dali Wang Chunlai Tu Yue Su Chuan Zhang Udo Greiser Xinyuan Zhu Deyue Yan Wenxin Wang 《Chemical science》2015,6(7):3775-3787
Despite of great advances of phospholipids and liposomes in clinical therapy, very limited success has been achieved in the preparation of smart phospholipids and controlled-release liposomes for in vivo drug delivery and clinical trials. Here we report a supramolecular approach to synthesize novel supramolecularly engineered phospholipids based on complementary hydrogen bonding of nucleosides, which greatly reduces the need of tedious chemical synthesis, including reducing the strict requirements for multistep chemical reactions, and the purification of the intermediates and the amount of waste generated relative more traditional approaches. These upgraded phospholipids self-assemble into liposome-like bilayer structures in aqueous solution, exhibiting fast stimuli-responsive ability due to the hydrogen bonding connection. In vitro and in vivo evaluations show the resulted supramolecular liposomes from nucleoside phospholipids could effectively transport drug into tumor tissue, rapidly enter tumor cells, and controllably release their payload in response to an intracellular acidic environment, thus resulting in a much higher antitumor activity than conventional liposomes. The present supramolecularly engineered phospholipids represent an important evolution in comparison to conventional covalent-bonded phospholipid systems. 相似文献
83.
Vizing conjectured that every edge chromatic critical graph contains a 2-factor. Believing that stronger properties hold for this class of graphs, Luo and Zhao (2013) showed that every edge chromatic critical graph of order with maximum degree at least is Hamiltonian. Furthermore, Luo et al. (2016) proved that every edge chromatic critical graph of order with maximum degree at least is Hamiltonian. In this paper, we prove that every edge chromatic critical graph of order with maximum degree at least is Hamiltonian. Our approach is inspired by the recent development of Kierstead path and Tashkinov tree techniques for multigraphs. 相似文献
84.
Bin Pan Dinghua Xu Yinghong Xu Yue Yu 《Mathematical Methods in the Applied Sciences》2017,40(4):957-969
This paper investigates an inverse problem for parabolic equations backward in time, which is solved by total‐variation‐like (TV‐like, in abbreviation) regularization method with cost function ∥ux∥2. The existence, uniqueness and stability estimate for the regularization problem are deduced in the linear case. For numerical illustration, the variational adjoint method, which presents a simple method to derive the gradient of the optimization functional, is introduced to reconstruct the unknown initial condition for both linear and nonlinear parabolic equations. The conjugate gradient method is used to iteratively search for the optimal approximation. Numerical results validate the feasibility and effectiveness of the proposed algorithm. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
85.
Exact boundary controllability for 1‐D quasilinear wave equations with dynamical boundary conditions 下载免费PDF全文
Yue Wang Günter Leugering Tatsien Li 《Mathematical Methods in the Applied Sciences》2017,40(10):3808-3820
By equivalently replacing the dynamical boundary condition by a kind of nonlocal boundary conditions, and noting a hidden regularity of solution on the boundary with a dynamical boundary condition, a constructive method with modular structure is used to get the local exact boundary controllability for 1‐D quasilinear wave equations with dynamical boundary conditions. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
86.
建立了火焰原子吸收光谱法(FAAS)测定锡阳极泥中银含量的方法。文章考察了不同的测定介质、酸度对测定结果的影响。实验结果表明在选定条件下,锡阳极泥中的锡、锑、铅等杂质不干扰银的测定。方法加标回收率在99.2%~103%,精密度实验结果表明,相对标准偏差(RSD,n=11)均小于4%。操作过程简单,能满足生产的需要。 相似文献
87.
The inverse problems of textile materials design on heat and moisture transfer properties are important and indispensable in applications in the body-clothing-environment system. We present an inverse problem of textile porosity determination (IPTPD) based on a nonlinear heat and moisture transfer model. Adopting the idea of the least-squares, the mathematical formulation of IPTPD is deduced to a regularized optimization problem with collocation method applied. The continuity of the regularized minimization problem is proved. By means of genetic algorithm (GA), the approximate solution of the IPTPD is numerically obtained. To reduce the computational cost, an improved algorithm based on BP neural network with GA is proposed in the numerical simulation. Compared with the direct GA searching, the computational cost is greatly reduced, which presents a similar result. 相似文献
88.
In order to verify the anti-UV aging mechanism about polypropylene-grafting-acrylonitrile (PP-g-AN) to polypropylene (PP), the structural analysis of the PP/PP-g-AN blend before and after aging was carried out via the X-ray photoelectron spectroscopy (XPS), Fourier Transform Infrared Spectrometry (FTIR) and UV-visible Absorbance Spectrum (UV–Vis). Inference on PP-g-AN anti-aging process was proposed and confirmed. 相似文献
89.
90.