全文获取类型
收费全文 | 24958篇 |
免费 | 4641篇 |
国内免费 | 2771篇 |
专业分类
化学 | 17869篇 |
晶体学 | 278篇 |
力学 | 1392篇 |
综合类 | 161篇 |
数学 | 2897篇 |
物理学 | 9773篇 |
出版年
2024年 | 31篇 |
2023年 | 522篇 |
2022年 | 586篇 |
2021年 | 848篇 |
2020年 | 1034篇 |
2019年 | 1030篇 |
2018年 | 980篇 |
2017年 | 830篇 |
2016年 | 1282篇 |
2015年 | 1206篇 |
2014年 | 1461篇 |
2013年 | 1859篇 |
2012年 | 2345篇 |
2011年 | 2474篇 |
2010年 | 1667篇 |
2009年 | 1499篇 |
2008年 | 1711篇 |
2007年 | 1488篇 |
2006年 | 1369篇 |
2005年 | 1123篇 |
2004年 | 871篇 |
2003年 | 701篇 |
2002年 | 776篇 |
2001年 | 567篇 |
2000年 | 394篇 |
1999年 | 497篇 |
1998年 | 350篇 |
1997年 | 349篇 |
1996年 | 347篇 |
1995年 | 309篇 |
1994年 | 260篇 |
1993年 | 247篇 |
1992年 | 180篇 |
1991年 | 190篇 |
1990年 | 165篇 |
1989年 | 121篇 |
1988年 | 100篇 |
1987年 | 79篇 |
1986年 | 74篇 |
1985年 | 68篇 |
1984年 | 64篇 |
1983年 | 36篇 |
1982年 | 34篇 |
1981年 | 26篇 |
1980年 | 26篇 |
1978年 | 13篇 |
1976年 | 16篇 |
1975年 | 15篇 |
1973年 | 15篇 |
1968年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
1.
The row iterative method is popular in solving the large‐scale ill‐posed problems due to its simplicity and efficiency. In this work we consider the randomized row iterative (RRI) method to tackle this issue. First, we present the semiconvergence analysis of RRI method for the overdetermined and inconsistent system, and derive upper bounds for the noise error propagation in the iteration vectors. To achieve a least squares solution, we then propose an extended version of the RRI (ERRI) method, which in fact can converge in expectation to the solution of the overdetermined or underdetermined, consistent or inconsistent systems. Finally, some numerical examples are given to demonstrate the convergence behaviors of the RRI and ERRI methods for these types of linear system. 相似文献
2.
Science China Mathematics - Linear factor models are familiar tools used in many fields. Several pioneering literatures established foundational theoretical results of the quasi-maximum likelihood... 相似文献
3.
4.
Rational Design of Two-Dimensional Magnetic Chromium Borides Based on First-Principles Calculation 下载免费PDF全文
Two-dimensional(2D) magnetic materials have been experimentally recognized recently,however,the Curie temperatures(TC) of known 2D systems are quite low.Generally,magnetic systems can be seen as constituent magnetic elements providing spins and the non-magnetic elements providing frameworks to host the magnetic elements.Short bond lengths between the magnetic and non-magnetic elements would be beneficial for strong magnetic interactions and thus high TC.Based on this,we propose to combine the magnetic element Cr and the non-magnetic element boron to design novel 2D magnetic systems.Using our self-developed software package IM2 ODE,we design a series of chromium-boride based 2D magnetic materials.Nine stable magnetic systems are identified.Among them,we find that CrB4-Ⅰ,CrB4-Ⅱ and CrBs-Ⅰ with common structural units [CrB8] are ferromagnetic metals with estimated TC of 270 K,120 K and 110 K,respectively.On the other hand,five CrB3 phases with structural units [Cr2B12] are antiferromagnetic metals.Additionally,we also find one antiferromagnetic semiconductor CrB2-Ⅰ.Our work may open new directions for identifying 2D magnetic systems with high TC. 相似文献
5.
Haicun Yang Shuipi Cai Yu Jiang Zheng Cao Wenzhong Ma Fanghong Gong Guoliang Tao Chunlin Liu 《Journal of polymer science. Part A, Polymer chemistry》2022,60(10):1571-1587
The commonly used multi-center initiation methods always lead to the formation of quantities of homopolymer in the surface tailoring based on reverse atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain-transfer (RAFT) polymerization. In this study, a monocenter redox pair constructed of silica bearing tert-butyl hydroperoxide groups and ascorbic acid (SiO2-TBHP/AsAc) was applied to substitute the commonly used initiation method of R-supported RAFT grafting polymerization. All the propagating radicals were restricted on the surface of solid particles during the whole procedure theoretically, resulting in a higher grafting efficiency of 95.1% combined with the “controllable” feature at 10 h. This redox pair was also used to initiate the reverse ATRP in miniemulsion successfully with a grafting efficiency of 86.3% at 10 h. The grafting efficiency obtained under this monocenter initiation method was significantly higher than that of the frequently reported surface modification by reverse ATRP and RAFT polymerization. In addition, the high-efficient surface tailoring was traced and confirmed by nuclear magnetic resonance, Fourier transform infrared, X-ray photoelectron spectroscopy, thermogravimetric analysis, transmission electron microscopy, and other analysis tests. The advantage of this monocenter redox pair will open a new avenue for the potential “high-efficient” surface tailoring of various materials. 相似文献
6.
Xianghao Luo Anqi Tian Mengyu Pei Dr. Jiaying Yan Dr. Xiang Liu Prof. Long Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(3):e202103361
With the development of green chemistry, it is still a challenge to maintain the unstable valence state of the metal in heterogeneous catalysts and realize new catalytic synthesis methods. In this paper, it is reported that an univalent copper nanocomposite (Cu@Al/SBA-15) can efficiently catalyze the formation of novel amino-containing benzotriazoles with great fluorescence properties in a new synthetic strategy. Subsequently, its application is further verified by an acylation reaction to produce a series of novel benzotriazoles derivatives with high yield. It is worth noting that the Cu@Al/SBA-15 nanocomposites not only enable the reaction completed with high yield in a short time, but can also be recycled many times without a significant reduction in activity, and the leaching of copper and aluminum species in reaction system is negligible. Finally, the detailed and feasible reaction mechanism is also provided. 相似文献
7.
Nonlinear Dynamics - This paper proposes an optimal parameter design of control scheme for mechanical systems by adopting the Stackelberg game theory. The goal of the control is to drive the... 相似文献
8.
Guo Jiayun Ma Dongge Sun Fulin Zhuang Guilin Wang Qi Al-Enizi Abdullah M. Nafady Ayman Ma Shengqian 《中国科学:化学(英文版)》2022,65(9):1704-1709
Science China Chemistry - The heterojunction constructed of covalent organic frameworks (COFs) with adjustable structure and other photocatalysts has great potential in the field of photocatalysis.... 相似文献
9.
A capillary electrophoresis-acid barrage stacking online enrichment method has been established to detect the four isoflavones which are Daidzein, Genistein, Formononetin, and Biochanin A. The proposed method was optimized using a single factor alternative method, and the optimal conditions obtained from the optimization were: the BGE was 25 mM borax and 2 mM β-cyclodextrin, the applied separation voltage was 20 kV, and the detection wavelength was 260 nm. The time ratio of the injection of sample and the injection of acid was 150 s:20 s, and the acid used was 250 mM acetic acid. The sample solvent used was 60% v/v acetonitrile. The established method had the enrichment factor of these four isoflavones at 24.5, 32.0, 29.2, and 33.7, respectively, LOD and LOQ are as low as nanograms per milliliter. Finally, the CE-acid barrage stacking method was successfully applied to the determination of four isoflavones in rat plasma and red clover extract, verifying the applicability and feasibility of the method. 相似文献
10.
Hao Sun Cunlu Dong Aijun Huang Prof. Haijuan Zhan Dr. Gang Wang Prof. Wanyi Liu Prof. Baojun Ma Prof. Wei Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(28):e202200019
Transition metal Fe, Co, Ni and Cu doped strontium titanate-rich SrTiO3@TiO2 (STO@T) materials were prepared by hydrothermal method. The prepared doped materials exhibit better photocatalytic CO2 reduction to CH4 ability under visible light conditions. Among them, Fe-doped and undoped SrTiO3@TiO2 under visible light conditions CO2 reduction products only CO, while M-STO@T (M=Co, Ni, Cu) samples converted CO2 to CH4. The average methane yield of Ni-doped STO@T samples are as high as 73.85 μmol g−1 h−1. The production of methane is mainly due to the increase in the response of the doped samples to visible light. And the increase in the separation rate of photogenerated electrons and holes and the efficiency of electron transport caused by the generation of impurity levels. The impurity level caused by Ti3+ plays an important role in the production of methane by CO2 visible light reduction. Ni doping effectively improves the photocatalytic performance of STO@T and CO2 reduction mechanism were explained. 相似文献