全文获取类型
收费全文 | 8491篇 |
免费 | 1429篇 |
国内免费 | 1215篇 |
专业分类
化学 | 6818篇 |
晶体学 | 98篇 |
力学 | 400篇 |
综合类 | 119篇 |
数学 | 916篇 |
物理学 | 2784篇 |
出版年
2024年 | 10篇 |
2023年 | 153篇 |
2022年 | 195篇 |
2021年 | 284篇 |
2020年 | 342篇 |
2019年 | 378篇 |
2018年 | 317篇 |
2017年 | 284篇 |
2016年 | 408篇 |
2015年 | 415篇 |
2014年 | 461篇 |
2013年 | 568篇 |
2012年 | 737篇 |
2011年 | 794篇 |
2010年 | 552篇 |
2009年 | 500篇 |
2008年 | 632篇 |
2007年 | 503篇 |
2006年 | 461篇 |
2005年 | 439篇 |
2004年 | 368篇 |
2003年 | 296篇 |
2002年 | 360篇 |
2001年 | 292篇 |
2000年 | 216篇 |
1999年 | 175篇 |
1998年 | 125篇 |
1997年 | 93篇 |
1996年 | 142篇 |
1995年 | 124篇 |
1994年 | 87篇 |
1993年 | 54篇 |
1992年 | 53篇 |
1991年 | 69篇 |
1990年 | 53篇 |
1989年 | 36篇 |
1988年 | 25篇 |
1987年 | 31篇 |
1986年 | 16篇 |
1985年 | 25篇 |
1984年 | 4篇 |
1983年 | 16篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1957年 | 2篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
41.
42.
Shan He Wu 《Journal of Mathematical Analysis and Applications》2007,332(1):741-750
In this paper, we generalize Hu Ke's sharpness of Hölder's inequality. As application, the obtained result is used to improve the well-known Opial-Olech inequality. 相似文献
43.
N. Chai W.D. Kulatilaka S.V. Naik N.M. Laurendeau R.P. Lucht J.P. Kuehner S. Roy V.R. Katta J.R. Gord 《Applied physics. B, Lasers and optics》2007,88(1):141-150
We report the application of electronic-resonance-enhanced coherent anti-Stokes Raman scattering (ERE-CARS) for measurements
of nitric oxide concentration ([NO]) in three different atmospheric pressure flames. Visible pump (532 nm) and Stokes (591 nm)
beams are used to probe the Q-branch of the Raman transition. A significant resonance enhancement is obtained by tuning an
ultraviolet probe beam (236 nm) into resonance with specific rotational transitions in the (v’=0, v”=1) vibrational band of
the A2Σ+–X2Π electronic system of NO. ERE-CARS spectra are recorded at various heights within a hydrogen-air flame producing relatively
low concentrations of NO over a Hencken burner. Good agreement is obtained between NO ERE-CARS measurements and the results
of flame computations using UNICORN, a two-dimensional flame code. Excellent agreement between measured and calculated NO
spectra is also obtained when using a modified version of the Sandia CARSFT code for heavily sooting acetylene-air flames
(φ=0.8 to φ=1.6) on the same Hencken burner. Finally, NO concentration profiles are measured using ERE-CARS in a laminar,
counter-flow, non-premixed hydrogen-air flame. Spectral scans are recorded by probing the Q1 (9.5), Q1 (13.5) and Q1 (17.5) Raman transitions. The measured shape of the [NO] profile is in good agreement with that predicted using the OPPDIF
code, even without correcting for collisional effects. These comparisons between [NO] measurements and predictions establish
the utility of ERE-CARS for detection of NO in flames with large temperature and concentration gradients as well as in sooting
environments.
PACS 07.88.+y; 42.62.Fi; 42.65.Dr 相似文献
44.
45.
强混合样本下回归加权估计的一致渐近正态性 总被引:5,自引:0,他引:5
在强混合样本下,讨论固定设计回归模型的加权函数估计的一致渐近正态性,给出一致渐近正态性的收敛速度,这个速度接近n-1/6. 相似文献
46.
47.
Kai Wang Huan-yu Li Jian-ping Li Zhi-gang Zhang Ning Zhang Lu Chai Qing-yue Wang 《Optics Communications》2006,265(2):369-372
Recently, the semiconductor saturable absorber mirror (SESAM) has become a key component of passive mode-locked solid-state lasers. Here we present a simple method based on the reflection Z-scan technique to measure the key optical parameters of SESAM such as saturation fluence and modulation depth. The experimental results demonstrate that our method is able to perform with a high accuracy of 10−4 and a dynamic range of over four orders of magnitude. 相似文献
48.
The feature selection consists of obtaining a subset of these features to optimally realize the task without the irrelevant
ones. Since it can provide faster and cost-effective learning machines and also improve the prediction performance of the
predictors, it is a crucial step in machine learning. The feature selection methods using support machines have obtained satisfactory
results, but the noises and outliers often reduce the performance. In this paper, we propose a feature selection approach
using fuzzy support vector machines and compare it with the previous work, the results of experiments on the UCI data sets
show that feature selection using fuzzy SVM obtains better results than using SVM. 相似文献
49.
Tian Le LIN Bao Zhen YAN Gao Fei HU Mei WANG 《中国化学快报》2006,17(7):937-940
Complex formation between aluminium and quercetin(Q) in methanol was investigated by means of 27^Al solid-state, 13^C and 1^H NMR and MS(ESI), UV and IR spectra. Formation of the 1:2 complex was favored in methanol relative to all other solvent and the predominant species observed of Al(Ⅲ) has a 1:2 stoichiometry. The fine structure of 1:2 aluminum complex of quercetin was that the aluminum central atom chelated with two quereetin molecules and two methoxyl groups between two five membered rings, its coordination is six, the chelated site was 3-hydroxy-4-carbonyl. 相似文献
50.
Jun Hua YU Xue Song WANG Bao Wen ZHANG* Yi CAO Technical Institute of Physics Chemistry Chinese Academy of Sciences Beijing 《中国化学快报》2002,13(10)
Porphyrin derivatives attract much more interest in photodynamic therapy (PDT). Their importance as therapeutic drugs and targeting agents has been widely recognized1, and many of the efforts have been put towards crafting new porphyrin-based molecular entities to achieve enhanced tumor localization, better tissue penetration and increased singlet oxygen quantum yield2. The states of porphyrins in tissue models such as micelles, lipid bilayers are extensively investigated focusing more or l… 相似文献