全文获取类型
收费全文 | 5787篇 |
免费 | 1044篇 |
国内免费 | 832篇 |
专业分类
化学 | 4571篇 |
晶体学 | 101篇 |
力学 | 307篇 |
综合类 | 35篇 |
数学 | 695篇 |
物理学 | 1954篇 |
出版年
2024年 | 11篇 |
2023年 | 110篇 |
2022年 | 136篇 |
2021年 | 187篇 |
2020年 | 278篇 |
2019年 | 285篇 |
2018年 | 229篇 |
2017年 | 205篇 |
2016年 | 327篇 |
2015年 | 330篇 |
2014年 | 377篇 |
2013年 | 490篇 |
2012年 | 523篇 |
2011年 | 561篇 |
2010年 | 396篇 |
2009年 | 361篇 |
2008年 | 374篇 |
2007年 | 309篇 |
2006年 | 317篇 |
2005年 | 240篇 |
2004年 | 240篇 |
2003年 | 171篇 |
2002年 | 211篇 |
2001年 | 158篇 |
2000年 | 105篇 |
1999年 | 102篇 |
1998年 | 62篇 |
1997年 | 64篇 |
1996年 | 47篇 |
1995年 | 34篇 |
1994年 | 55篇 |
1993年 | 30篇 |
1992年 | 26篇 |
1991年 | 37篇 |
1990年 | 30篇 |
1989年 | 27篇 |
1988年 | 31篇 |
1987年 | 14篇 |
1986年 | 16篇 |
1985年 | 21篇 |
1984年 | 10篇 |
1983年 | 11篇 |
1982年 | 10篇 |
1981年 | 6篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1975年 | 8篇 |
1974年 | 6篇 |
排序方式: 共有7663条查询结果,搜索用时 66 毫秒
2.
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
3.
Annals of Operations Research - The main purpose of this study was to explore the impact of peace dividends on global changes in national productivity. First, this study assessed changes in... 相似文献
4.
5.
Qi-Jun Li Ya-Jie Ren Qin Xie Min Wu Hua-Xing Feng Li-Mei Zheng Hua-Xin Zhang Jin-Qiao Long Tian-Shun Wang 《应用有机金属化学》2020,34(10):e5813
Two nickel complexes, [Ni(tpen)](ClO4)2.0.5CH3COCH3 ( 1 ) and [Ni(tpbn)](ClO4)2 ( 2 ), of tetrapyridyl ligands N,N,N′,N′-tetrakis(2-pyridyl-methyl)-1,2-ethanediamine (tpen) and N,N,N′,N′-tetrakis(2-pyridyl-methyl)-1,4-butanediamine (tpbn) were prepared and their catalysis for water oxidation reaction (WOR) studied. In 0.1 M phosphate buffer solution (PBS) of pH 8.0, complex 1 is a homogeneous molecular catalyst with an overpotential of ~440 mV and a Faradaic efficiency of 89%. At pH ≥ 9.0, complex 1 degraded gradually during the catalytic process and formed NiOx composite (nickel oxide with general formula NixOyHz) active for WOR. In contrast, complex 2 deteriorated under measured conditions (pH 8.0–12.0) and formed NiOx composite active for WOR. The NiOx composite derived from 1 in 0.1 M PBS at pH 11.0 showed an activity with an overpotential of ~500 mV, a Tafel slope of ~90 mV/decade and a Faradaic efficiency of 97%. Mechanisms were proposed for water oxidation catalyzed by 1 and 2 . This work revealed that the catalytic activity of the nickel complexes was related to the flexibility of the tetrapyridyl ligands and the adaptability of the coordination sphere of the nickel(II) center. 相似文献
6.
We construct a class of C~*-metric algebras. We prove that for a discrete group Γ with a 2-cocycle σ,the closure of the seminorm ||[M?, ·]|| on Cc(Γ, σ) is a Leibniz Lip-norm on the twisted reduced group C~*-algebra C*r(Γ, σ) for the pointwise multiplication operator M?on ?2(Γ), induced by a proper length function ? on Γ with the property of bounded θ-dilation. Moreover, the compact quantum metric space structures depend only on the cohomology class of 2-cocycles in the Lipschitz isometric sense. 相似文献
7.
A novel tiled Ti:sapphire(Ti:S)amplifier was experimentally demonstrated with>1 J amplified chirped pulse output.Two Ti:S crystals having dimensions of 14 mm×14 mm×25 mm were tiled as the gain medium in a four-pass amplifier.Maximum output energy of 1.18 J was obtained with 2.75 J pump energy.The energy conversion efficiency of the tiled Ti:S amplifier was comparable with a single Ti:S amplifier.The laser pulse having the maximum peak power of 28 TW was obtained after the compressor.Moreover,the influence of the beam gap on the far field was discussed.This novel tiled Ti:S amplifier technique can provide a potential way for 100 PW or EW lasers in the future. 相似文献
8.
Advanced Encryption Standard (AES) is one of the most widely used block ciphers nowadays, and has been established as an encryption standard in 2001. Here we design AES-128 and the sample-AES (S-AES) quantum circuits for deciphering. In the quantum circuit of AES-128, we perform an affine transformation for the SubBytes part to solve the problem that the initial state of the output qubits in SubBytes is not the |0>⊗8 state. After that, we are able to encode the new round sub-key on the qubits encoding the previous round sub-key, and this improvement reduces the number of qubits used by 224 compared with Langenberg et al.’s implementation. For S-AES, a complete quantum circuit is presented with only 48 qubits, which is already within the reach of existing noisy intermediate-scale quantum computers. 相似文献
9.
Jing Liu Xiu‐Mei Li Dong‐dong Shi Zhi‐guo Wen Pei‐Long Yang 《Biomedical chromatography : BMC》2019,33(12)
In recent years, the fingerprint of high‐performance liquid chromatography has been extensively applied in the identification and quality control of traditional Chinese medicine. It can be a potential protocol for assessing the authenticity, stability and consistency of traditional Chinese medicine and guaranteeing the expected biological activity. In this paper, a method using high‐performance liquid chromatography to identify and control the quality of the extract of Taraxacum mongolicum Hand.‐Mazz. (TME) was established. With this method, the correlation coefficients of the similarity of 10 batches were ≥0.994. The TME displayed a steady proliferative effect in Lactobacillus plantarum. In brief, this study successfully built a reliable, simple and efficient method to control and confirm the quality and the stability of biological activity of the TME. 相似文献
10.
Yihan Zhang Cui Bo Yanhao Fan Rui An Long Chen Yifan Zhang Yiqun Jia Xinhong Wang 《Biomedical chromatography : BMC》2019,33(3)
A quick and effective workflow based on ultra‐performance liquid chromatography coupled with electron spray ionization and LTQ‐Orbitrap mass spectrometry (UPLC‐LTQ‐Orbitrap MS) was established for compositional analysis and screening of the characteristic compounds of three species of Atractylodes rhizome for quality evaluation. This technique was employed to determine the seven main components in Atractylodes rhizome samples. Ultimately, 78 constituents were identified; of these, seven characteristic compounds were selected for species discrimination, comprising atractylodin (63), atractylenolide I (43), atractylenolide II (49), atractylenolide III (53), atractylon (69), methyl‐atractylenolide II (54) and (4E,6E,12E)‐tetradecadecatriene‐8,10‐diyne‐1,3‐diacetate (59). The seven main compounds, including six characteristic compounds, were simultaneously determined in 29 batches of Atractylodes rhizome samples. Thus, the method validation showed acceptable results. Quantitative analysis showed significantly different contents of the seven main components among the three species of Atractylodes rhizome, which indicates possible distinctions in the pharmacological effects. This established method can simultaneously provide qualitative and quantitative results for compositional characterization of Atractylodes rhizomes and for quality control. 相似文献