全文获取类型
收费全文 | 10932篇 |
免费 | 506篇 |
国内免费 | 322篇 |
专业分类
化学 | 4739篇 |
晶体学 | 227篇 |
力学 | 841篇 |
综合类 | 35篇 |
数学 | 1176篇 |
物理学 | 4742篇 |
出版年
2023年 | 80篇 |
2022年 | 149篇 |
2021年 | 153篇 |
2020年 | 182篇 |
2019年 | 181篇 |
2018年 | 210篇 |
2017年 | 147篇 |
2016年 | 257篇 |
2015年 | 198篇 |
2014年 | 315篇 |
2013年 | 521篇 |
2012年 | 752篇 |
2011年 | 832篇 |
2010年 | 643篇 |
2009年 | 631篇 |
2008年 | 663篇 |
2007年 | 595篇 |
2006年 | 595篇 |
2005年 | 466篇 |
2004年 | 418篇 |
2003年 | 315篇 |
2002年 | 275篇 |
2001年 | 461篇 |
2000年 | 369篇 |
1999年 | 270篇 |
1998年 | 213篇 |
1997年 | 198篇 |
1996年 | 206篇 |
1995年 | 164篇 |
1994年 | 160篇 |
1993年 | 130篇 |
1992年 | 120篇 |
1991年 | 129篇 |
1990年 | 113篇 |
1989年 | 83篇 |
1988年 | 59篇 |
1987年 | 49篇 |
1986年 | 52篇 |
1985年 | 53篇 |
1984年 | 37篇 |
1983年 | 27篇 |
1982年 | 36篇 |
1981年 | 34篇 |
1980年 | 27篇 |
1979年 | 21篇 |
1978年 | 25篇 |
1977年 | 19篇 |
1976年 | 18篇 |
1975年 | 19篇 |
1974年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
1.
Atopic dermatitis is characterized by leukocyte migration into the skin dermis and typically driven by excessive chemokine production at the site of inflammation. Conventional topical formulations such as gels, creams, and ointments are insufficient for this treatment because of low penetration of drug molecules into the targeted skin tissues. Herein, using a simple, green, sustainable strategy, we have developed novel primary zein nanoparticles embedded in curcumin (Cur) and coated with silk sericin (ZHSCs) for the topical delivery of Cur to penetrate into the dermis and exercise anti-dermatitis effects on the lesion with minimal side-effects. Transdermal delivery experiments and porcine skin fluorescence imaging indicated that ZHSCs facilitate the penetration of Cur across the epidermis layer of skin to reach deep-seated sites. Notably, ZHSCs = 1:0.25 (zein-to-silk sericin mass ratios of 1:0.25) markedly elevated the skin permeability and cumulative turnover of Cur transferred, which were provided a greater than a 3.8-fold increase relative to free Cur. The special nanoparticles of ZHS = 1:0.25 possessed the deepest localization depth and experience a transition of the particle structure and core-shell separation after penetrating into the dermis of skin. In a cell model of dermatitis induced by tumor necrosis factor α/interferon γ co-stimulation, compared with free Cur, Cur-loaded ZHS nanoparticles down-regulated the generation of inflammatory cytokines and chemokines in keratinocytes through suppression of the nuclear translocation of NF-κBp65 and hence exerted an anti-dermatitis effect. This strategy may provide new avenues and direction for the demanding issues of valid topical delivery systems. 相似文献
2.
Designs, Codes and Cryptography - The discrete logarithm problem arises from various areas, including counting the number of points of certain curves and diverse cryptographic schemes. The... 相似文献
3.
4.
5.
Designs, Codes and Cryptography - The Learning-With-Errors (LWE) problem (and its variants including Ring-LWE and Module-LWE), whose security are based on hard ideal lattice problems, has proven to... 相似文献
6.
Ding Q. Yao M. Wu Sh. Zeng M. Xue N. Wu D. Xu J. 《Journal of Applied Spectroscopy》2022,89(4):712-718
Journal of Applied Spectroscopy - Based on partial least squares (PLS) analysis, the effects of different smoothing points and different preprocessing methods on the accuracy and precision of the... 相似文献
7.
Achieving tunable band gaps in a structure by external stimuli is of great importance in acoustic applications. This paper aims to investigate the tunability of band gaps in square-lattice-like elastic periodic structures that are usually not featured with notable band gaps.Endowed with chirality, the periodic structures here are able to undergo imperfection-insensitive large deformation under extension or compression. The influences of geometric parameters on band gaps are discussed via the nonlinear finite element method. It is shown that the band gaps in such structures with curved beams can be very rich and, more importantly, can be efficiently and robustly tuned by applying appropriate mechanical loadings without inducing buckling. As expected, geometry plays a more significant role than material nonlinearity does in the evolution of band gaps. The dynamic tunability of band gaps through mechanical loading is further studied. Results show that closing, opening, and shifting of band gaps can be realized by exerting real-time global extension or compression on the structure. The proposed periodic structure with well-designed chiral symmetry can be useful in the design of particular acoustic devices. 相似文献
8.
Dr. Zhoulong Fan Katherine L. Bay Dr. Xiangyang Chen Zhe Zhuang Han Seul Park Dr. Kap-Sun Yeung Prof. Dr. K. N. Houk Prof. Dr. Jin-Quan Yu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(12):4800-4807
A simple and efficient nitrile-directed meta-C−H olefination, acetoxylation, and iodination of biaryl compounds is reported. Compared to the previous approach of installing a complex U-shaped template to achieve a molecular U-turn and assemble the large-sized cyclophane transition state for the remote C−H activation, a synthetically useful phenyl nitrile functional group could also direct remote meta-C−H activation. This reaction provides a useful method for the modification of biaryl compounds because the nitrile group can be readily converted to amines, acids, amides, or other heterocycles. Notably, the remote meta-selectivity of biphenylnitriles could not be expected from previous results with a macrocyclophane nitrile template. DFT computational studies show that a ligand-containing Pd–Ag heterodimeric transition state (TS) favors the desired remote meta-selectivity. Control experiments demonstrate the directing effect of the nitrile group and exclude the possibility of non-directed meta-C−H activation. Substituted 2-pyridone ligands were found to be key in assisting the cleavage of the meta-C−H bond in the concerted metalation–deprotonation (CMD) process. 相似文献
9.
10.
Cycloparaphenylene (CPP) shows modulated photophysical and electronic properties due to its strained structure and radially oriented π-electron system. Incorporation of CPP into metal-organic frameworks (MOFs) could transfer its extensive properties in solution to porous solids. Moreover, with the unique arrangement of the macrocycles and their interactions with the framework, emerging characteristics are anticipated. As an example of “robust dynamics”, we synthesized the first MOF structure (FDM-1001) with CPP precisely anchored to the ordered framework by employing a [8]CPP-containing linear dicarboxylate linker. Metric relationship between the dynamic macrocycles and the robust backbone creates ideal π-π interactions between them, which leads to an essentially directional arrangement of [8]CPP in the three-dimensional space. Furthermore, the MOF with [8]CPP could be successfully oxidized to generate an infinite array of radicals that show enhanced air stability compared to its molecular analogue. 相似文献