全文获取类型
收费全文 | 2904篇 |
免费 | 456篇 |
国内免费 | 334篇 |
专业分类
化学 | 2139篇 |
晶体学 | 35篇 |
力学 | 244篇 |
综合类 | 17篇 |
数学 | 367篇 |
物理学 | 892篇 |
出版年
2024年 | 15篇 |
2023年 | 77篇 |
2022年 | 107篇 |
2021年 | 119篇 |
2020年 | 172篇 |
2019年 | 135篇 |
2018年 | 135篇 |
2017年 | 109篇 |
2016年 | 150篇 |
2015年 | 178篇 |
2014年 | 185篇 |
2013年 | 230篇 |
2012年 | 247篇 |
2011年 | 268篇 |
2010年 | 186篇 |
2009年 | 159篇 |
2008年 | 168篇 |
2007年 | 143篇 |
2006年 | 127篇 |
2005年 | 92篇 |
2004年 | 77篇 |
2003年 | 65篇 |
2002年 | 79篇 |
2001年 | 72篇 |
2000年 | 57篇 |
1999年 | 48篇 |
1998年 | 46篇 |
1997年 | 37篇 |
1996年 | 36篇 |
1995年 | 22篇 |
1994年 | 22篇 |
1993年 | 20篇 |
1992年 | 19篇 |
1991年 | 20篇 |
1990年 | 14篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 6篇 |
1986年 | 8篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1964年 | 1篇 |
1957年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有3694条查询结果,搜索用时 15 毫秒
981.
芳烃与烯烃通过两分子sp2-C—H键脱氢偶联,构建多取代烯烃的反应称之为氧化Heck反应或脱氢Heck反应,也叫Fujiwara-Moritani反应.在过去的几十年里,由于此类反应直接通过C—H键官能团化形成C—C键而备受关注.然而,绝大多数的此类转化只能适用于缺电子烯烃.富电子烯烃如烯丙酯或烯丙醚类化合物参与的氧化Heck偶联很少被报道.近几年来,我们课题组以及其他研究小组发展了一些十分高效的钯催化芳烃/烯烃与烯丙酯/烯丙醚的氧化脱氢偶联新方法.本文将概述这些有趣的、原子经济的氧化偶联反应的最新研究进展. 相似文献
982.
A surface modification technique was proposed for the modification of silicon surface with glucose oxidase (GOD). The silicon surface was first graft copolymerized with acrylic acid (AAc) via surface-initiated reversible addition-fragmentation chain-transfer (RAFT)-mediated process. With the aid of a water-soluble carbodiimide, GOD was then covalently immobilized on the silicon surface through the amide linkage between the amino group of GOD and the carboxyl group of the grafted AAc polymer. The changes in the surface composition after polymer grafting and enzyme immobilization on the silicon surface were investigated using X-ray photoelectron spectroscopy (XPS). The amount of GOD immobilized could be varied by changing the thickness of the polymer layer and the immobilization time. The GOD-functionalized silicon hybrids are potential useful in the application of the silicon-based biosensors. 相似文献
983.
Liu-Lin Xiong Lu-Lu Xue Ruo-Lan Du Rui-Ze Niu Li Chen Jie Chen Qiao Hu Ya-Xin Tan Hui-Fang Shang Jia Liu Chang-Yin Yu Ting-Hua Wang 《Experimental & molecular medicine》2021,53(12):1888
In recent years, biomarkers have been integrated into the diagnostic process and have become increasingly indispensable for obtaining knowledge of the neurodegenerative processes in Alzheimer’s disease (AD). Peripheral blood mononuclear cells (PBMCs) in human blood have been reported to participate in a variety of neurodegenerative activities. Here, a single-cell RNA sequencing analysis of PBMCs from 4 AD patients (2 in the early stage, 2 in the late stage) and 2 normal controls was performed to explore the differential cell subpopulations in PBMCs of AD patients. A significant decrease in B cells was detected in the blood of AD patients. Furthermore, we further examined PBMCs from 43 AD patients and 41 normal subjects by fluorescence activated cell sorting (FACS), and combined with correlation analysis, we found that the reduction in B cells was closely correlated with the patients’ Clinical Dementia Rating (CDR) scores. To confirm the role of B cells in AD progression, functional experiments were performed in early-stage AD mice in which fibrous plaques were beginning to appear; the results demonstrated that B cell depletion in the early stage of AD markedly accelerated and aggravated cognitive dysfunction and augmented the Aβ burden in AD mice. Importantly, the experiments revealed 18 genes that were specifically upregulated and 7 genes that were specifically downregulated in B cells as the disease progressed, and several of these genes exhibited close correlation with AD. These findings identified possible B cell-based AD severity, which are anticipated to be conducive to the clinical identification of AD progression.Subject terms: Cell death in the nervous system, Neurotrophic factors 相似文献
984.
Huiqing Zhu Suyue Xu Guoshuo Shang Xiaofei Pan Jingya Zhao Bingqian Zhao Zeyu Sun Xue Yang Sisi He Jintao Xue 《先进技术聚合物》2024,35(3):e6332
The purpose of this paper is to study the stability, radical scavenging activities, and bio-safety of cysteine-conjugated hyaluronic acid nanoparticles (Cys-conj-HA NPs). Additionally, the feasibility of utilizing these NPs as drug delivery systems is discussed. The structures of synthesized Cys-conj-HA polymers were analyzed using 1H nuclear magnetic spectrum (1H NMR) and Fourier transform infrared spectroscopy (FTIR) spectra. The stability, radical scavenging activity, and bio-safety of fabricated Cys-conj-HA NPs were investigated. Transmission electron microscopy (TEM) photograph illustrated that Cys-conj-HA NPs possessed spherical shapes with an average diameter of approximately 230 nm. Furthermore, these NPs exhibited high stability at temperatures of 4, 25, and 37°C. Notably, Cys-conj-HA NPs demonstrated significant free radical scavenging capabilities. The high cell viability observed indicated the absence of cytotoxicity from Cys-conj-HA NPs. Additionally, bio-safety studies revealed that these NPs did not induce acute toxicity in the blood and viscera of cargo-free NPs treated mice. Elisa assays indicated that there was no significant difference in the concentrations of interferon-γ (INF-γ) and tumor necrosis factor-α (TNF-α) between Cys-conj-HA NPs and normal saline (NS) treated mice (ns, p > 0.05), suggesting the absence of an inflammatory reaction caused by these NPs. Consequently, it can be concluded that Cys-conj-HA NPs are sufficiently safe to be employed as a vehicle for delivering oxidizing drugs. 相似文献
985.
Jingchao Wang Jianwu Yu Liang Huang Hong Luo Xiaopan Liu Zhentao Shang 《固体物理学:研究快报》2024,18(3):2300385
The modulation mechanism of iron (Fe) and manganese (Mn) in transition-metal elements on the interface bonding and mechanical properties of bronze (Cu3Sn)-based/diamond composites is investigated through first-principles calculations. Transition-elements-doping scenarios are investigated employing six-layer slab models. It is revealed that the doping of Fe or Mn can make the Cu3Sn/diamond interface more stable, which effectively improves the wettability of the Cu3Sn/diamond interface based on the calculation results and analysis of interface energy, differential charge density model, and density of states. However, co-doping with both Fe and Mn weakens the wettability of the Cu3Sn/diamond interface. Finally, wettability tests and microstructure characterizations demonstrate that the doping of Fe and Mn represents an effective approach to controlling the interface bonding performance of bronze/diamond composites. 相似文献
986.
987.
L. H. Shang X. Li X. F. Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(3):369-373
We investigate the evolution of cooperative behaviors of small-world networking agents in a snowdrift game mode, where two
agents (nodes) are connected with probability depending on their spatial Euclidean lattice distance in the power-law form
controlled by an exponent α.
Extensive numerical simulations indicate that the game dynamics crucially depends on the spatial topological structure of
underlying networks with different values of the exponent α. Especially, in the distance-independent case of α=0, the small-world
connectivity
pattern contributes to an enhancement of cooperation compared with that in
regular lattices, even for the case of having a high cost-to-benefit ratio r. However, with the increment of α>0, when r≥0.4,
the spatial distance-dependent small-world (SDSW) structure tends to inhibit the evolution of cooperation in the snowdrift
game. 相似文献
988.
Jiang Chun ZHON Shang Zhong LIU Qing Hua BIAN Ming Ming YIN Min WANG 《中国化学快报》2006,17(5):584-586
The research on optical alicyclic β-amino acids has recently attracted increasingly attention due to their significant pharmacological properties endowed by rigid frameworks, stable conformation1. Numerous biologically active peptides, β-lactams and some other natural products2 contain optical alicyclic β-amino acids. Cyclopropyl-modified alanines have been proved to be useful intermediates in medicine synthesis because of their rigid framework and reactive functional groups (amino and carb… 相似文献
989.
Shaofeng Liu Weiwei Zuo Shu Zhang Peng Hao Deligeer Wang Wen‐Hua Sun 《Journal of polymer science. Part A, Polymer chemistry》2008,46(10):3411-3423
A series of 6‐(benzimidazol‐2‐yl)‐N‐organylpyridine‐2‐carboxamide were synthesized and transformed into 6‐benzimidazolylpyridine‐2‐carboxylimidate as dianionic tridentate ligands. Bis(2‐(6‐methylpyridin‐2‐yl)‐benzimidazolyl)titanium dichloride ( C1 ) and titanium bis(6‐benzimidazolylpyridine‐2‐carboxylimidate) ( C2 – C8 ) were synthesized in acceptable yields. These complexes were systematically characterized by elemental and NMR analyses. Crystallographic analysis revealed the distorted octahedral geometry around titanium in both complexes C1 and C4 . Using MAO as cocatalyst, all complexes exhibited from good to high catalytic activities for ethylene polymerization. The neutral bis(6‐benzimidazolylpyridine‐2‐carboxylimidate)titanium ( C2 – C8 ) showed high catalytic activities and good stability for prolonged reaction time and elevated reaction temperature; however, C1 showed a short lifetime in catalysis as being observed at very low activity after 5 min. The elevated reaction temperature enhanced the productivity of polyethylenes with low molecular weights, whereas the reaction with higher ethylene pressure resulted in better catalytic activity and resultant polyethylenes with higher molecular weights. At higher ratio of MAO to titanium precursor, the catalytic system generated better activity with producing polyethylenes with lower molecular weights. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3411–3423, 2008 相似文献
990.
The multiple exact solutions for the nonlinear evolution equations describing the interaction of laser–plasma are developed. The extended hyperbolic function method are employed to reveal these new solutions. The solutions include that of the solitary wave solutions of bell-type for n and E, the solitary wave solutions of kink-type for E and bell-type for n, the solitary wave solutions of a compound of the bell-type and the kink-type for n and E, the singular traveling wave solutions, periodic traveling wave solutions of triangle function types, and solitary wave solutions of rational function types. In addition to re-deriving all known solutions in a systematic way, several new and more general solutions can be obtained by using our method. 相似文献