全文获取类型
收费全文 | 89819篇 |
免费 | 2328篇 |
国内免费 | 1711篇 |
专业分类
化学 | 32726篇 |
晶体学 | 916篇 |
力学 | 7420篇 |
综合类 | 60篇 |
数学 | 33259篇 |
物理学 | 19477篇 |
出版年
2024年 | 45篇 |
2023年 | 281篇 |
2022年 | 451篇 |
2021年 | 531篇 |
2020年 | 621篇 |
2019年 | 534篇 |
2018年 | 10810篇 |
2017年 | 10626篇 |
2016年 | 6637篇 |
2015年 | 1491篇 |
2014年 | 1002篇 |
2013年 | 1243篇 |
2012年 | 4874篇 |
2011年 | 11549篇 |
2010年 | 6380篇 |
2009年 | 6703篇 |
2008年 | 7330篇 |
2007年 | 9374篇 |
2006年 | 847篇 |
2005年 | 1798篇 |
2004年 | 1912篇 |
2003年 | 2254篇 |
2002年 | 1278篇 |
2001年 | 480篇 |
2000年 | 509篇 |
1999年 | 381篇 |
1998年 | 330篇 |
1997年 | 279篇 |
1996年 | 355篇 |
1995年 | 251篇 |
1994年 | 156篇 |
1993年 | 184篇 |
1992年 | 144篇 |
1991年 | 135篇 |
1990年 | 135篇 |
1989年 | 121篇 |
1988年 | 111篇 |
1987年 | 91篇 |
1986年 | 96篇 |
1985年 | 80篇 |
1984年 | 72篇 |
1983年 | 58篇 |
1982年 | 69篇 |
1981年 | 53篇 |
1980年 | 60篇 |
1979年 | 75篇 |
1978年 | 57篇 |
1973年 | 43篇 |
1914年 | 45篇 |
1909年 | 42篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Hao Xu Jie Zhu Xiong Wang Chao Shen Shengshen Meng Kai Zheng Chao Lei Longfeng Zhu 《Molecules (Basel, Switzerland)》2021,26(5)
Developing sustainable routes for the synthesis of zeolites is still a vital and challenging task in zeolite scientific community. One of the typical examples is sustainable synthesis of aluminosilicate EU-1 zeolite, which is not very efficient and environmental-unfriendly under hydrothermal condition due to the use of a large amount of water as solvent. Herein, we report a sustainable synthesis route for aluminosilicate EU-1 zeolite without the use of solvent for the first time. The physicochemical properties of the obtained EU-1 zeolite are characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry-differential thermal analysis (TG-DTA), N2 sorption, inductively coupled plasma (ICP) analysis, and solid nuclear magnetic resonance (NMR), which show the product has high crystallinity, uniform morphology, large BET surface area, and four-coordinated aluminum species. Moreover, the impact of synthesis conditions is investigated in detail. The sustainable synthesis of aluminosilicate EU-1 zeolite under solvent-free 相似文献
992.
Privileged biaryl frameworks, BINOL and NOBIN, were efficiently constructed with sole 1-DNQs as arylation reagents under one set of reaction conditions. The judicious selection of palladium-catalytic system plays a pivotal role in the excellent selectivities. This transformation accommodated fairly broad substrate generality for both 2-naphthol and N-Boc-2-naphthylamine and afforded the structurally diversified BINOLs and NOBIN derivatives in high efficiency. Notably, the bromosubstituents which cannot survive in conventional palladium-catalyzed reactions were well-compatible with this set of conditions, providing an effective handle for further enriching the library of BINOLs and NOBINs. Preliminary attempts on the asymmetric variant of this reaction were also performed with up to 80:20 er for BINOLs synthesis. 相似文献
993.
We analyze the recently found inequality for eigenvalues of the density matrix and purity parameters describing either a bipartite-system state or a single-qudit state. We rewrite the Minkowski-type trace inequality for the density matrices of the qudit states in terms of the purity parameters and discuss the properties of the inequality obtained, paying special attention to the X-states of two qubits and a single qudit. Also we study the relation of the purity inequalities obtained with the entanglement. 相似文献
994.
Hu Pan Renpeng Yan Xudong Li Xin Fa Yufei Ma Rongwei Fan Xin Yu Deying Chen 《Journal of Russian Laser Research》2016,37(3):259-264
We present a compact high-peak-power, high-repetition-rate burst-mode laser from a master-oscillator power amplifier (MOPA) at 1064 nm for laser-based measurement applications. The oscillator is an 808 nm pulsed laser diode side-pumped acousto-optical (A-O) Q-switched Nd:YAG laser at repetition rates ranging from 10–100 kHz, producing a pulse train with a pulse number of 2–25. The maximum output energy of the oscillator is 15.6 mJ at 10 kHz, whereas it is 1.7 mJ at 100 kHz. After twostage amplifiers, a single-pulse energy of 85.2 mJ with a pulse-width of 14.5 ns is achieved at 10 kHz, which produces a peak power of 6.1 MW. At 100 kHz, the total burst energy reaches 220 mJ with a single-pulse energy of 8.8 mJ in the pulse burst laser system. 相似文献
995.
Zhouqiang Zhang Shuhai Jia Fei Wang Yonglin Wang 《Journal of Russian Laser Research》2016,37(3):285-290
We study quartz tuning fork (QTF) characteristics using a 532 nm semiconductor laser with a power of 39 mW and calculate QTF vibrations caused by thermal noise and disturbance of the air using the equipartition theorem; the vibration value is about 1.152 Pm. The signal-to-noise ratio and QTF resonance amplitude acquired experimentally are 104.56 and 214.75 Pm, respectively. In addition, we develop a new photo-acoustic spectroscopic system for detection of trace acetylene using a CW diode laser source with distributed feedback operating near 1,532 nm, measure the absorption spectrum of acetylene employing this system, and show that the method elaborated is more sensitive than photoelectric detectors that provides new directions for research in photo-acoustic spectroscopy. 相似文献
996.
We review the notion of weighted quantum entropy and consider the weighted quantum entropy for bipartite and noncomposite quantum systems. We extend the subadditivity condition, the inequality known for the weighted entropy information, to the case of indivisible qudit system, such as a qutrit. We discuss the new inequality for the qutrit density matrix for different weights and states, as well as the role of weighted entropy with respect to nonlinear quantum channels. 相似文献
997.
We present a sophisticated optical design method for reducing the number of photodetectors for a specific sensing task. The chosen design parameter is the point spread function, and the selected task is object recognition. The point spread function is optimized iteratively with a genetic algorithm for object recognition based on a neural network. In the experimental demonstration, binary classification of face and non-face datasets was performed with a single measurement using two photodetectors. A spatial light modulator operating in the amplitude modulation mode was provided in the imaging optics and was used to modulate the point spread function. In each generation of the genetic algorithm, the classification accuracy with a pattern displayed on the spatial light modulator was fed-back to the next generation to find better patterns. The proposed method increased the accuracy by about 30 % compared with a conventional imaging system in which the point spread function was the delta function. This approach is practically useful for compressing the cost, size, and observation time of optical sensors in specific applications, and robust for imperfections in optical elements. 相似文献
998.
The interrogation of fiber-Bragg-grating (FBG) sensors using a vertical-cavity surface-emitting laser (VCSEL) is discussed. A long-wavelength (1.54 μm) VCSEL was used as a wavelength-tunable source by variation in the current. Temperature stabilization was performed with a thermoelectric device. Characteristics of temperature and strain sensing were investigated. FBGs with different reflectivities were compared. For temperature sensing, the root-mean-square error in the measurement was reduced to 1/3 that without temperature stabilization. The dependence of the measurement error on the reflectivities of the FBGs was investigated. The measurement error was larger for FBGs with lower reflectivities in both temperature and strain sensing. Improvement on the sensing with low-reflectivity FBGs is discussed. 相似文献
999.
1000.