全文获取类型
收费全文 | 4712篇 |
免费 | 628篇 |
国内免费 | 677篇 |
专业分类
化学 | 2458篇 |
晶体学 | 25篇 |
力学 | 103篇 |
综合类 | 17篇 |
数学 | 1744篇 |
物理学 | 1670篇 |
出版年
2024年 | 10篇 |
2023年 | 136篇 |
2022年 | 122篇 |
2021年 | 148篇 |
2020年 | 207篇 |
2019年 | 129篇 |
2018年 | 159篇 |
2017年 | 146篇 |
2016年 | 200篇 |
2015年 | 188篇 |
2014年 | 289篇 |
2013年 | 321篇 |
2012年 | 380篇 |
2011年 | 385篇 |
2010年 | 349篇 |
2009年 | 352篇 |
2008年 | 355篇 |
2007年 | 332篇 |
2006年 | 293篇 |
2005年 | 188篇 |
2004年 | 125篇 |
2003年 | 114篇 |
2002年 | 108篇 |
2001年 | 125篇 |
2000年 | 85篇 |
1999年 | 78篇 |
1998年 | 52篇 |
1997年 | 35篇 |
1996年 | 38篇 |
1995年 | 27篇 |
1994年 | 34篇 |
1993年 | 33篇 |
1992年 | 38篇 |
1991年 | 32篇 |
1990年 | 34篇 |
1989年 | 33篇 |
1988年 | 78篇 |
1987年 | 107篇 |
1986年 | 105篇 |
1985年 | 26篇 |
1984年 | 9篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1959年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有6017条查询结果,搜索用时 390 毫秒
121.
Several reference priors and a general form of matching priors are derived for a stress–strength system, and it is concluded that none of the reference priors is a matching prior. The study shows that the matching prior performs better than Jeffreys prior and reference priors in meeting the target coverage probabilities. 相似文献
122.
Dr. Xinhao Shi Wei Gu Dr. Cuiling Zhang Longyun Zhao Prof. Li Li Weidong Peng Prof. Yuezhong Xian 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(16):5643-5648
The development of highly sensitive and selective methods for the detection of lead ion (Pb2+) is of great scientific importance. In this work, we develop a new surface‐enhanced Raman scattering (SERS)‐based sensor for the selective trace measurement of Pb2+. The SERS‐based sensor is assembled from gold nanoparticles (AuNPs) and graphene using cucurbit[7]uril (CB[7]) as a precise molecular glue and a local SERS reporter. Upon the addition of Pb2+, CB[7] forms stronger complexes with Pb2+ and desorbs from AuNPs, resulting in a sensitive “turn‐off” of SERS signals. This SERS‐based assay shows a limit of detection (LOD) of 0.3 nm and a linear detection range from 1 nm to 0.3 μm for Pb2+. The feasibility of the assay is further demonstrated by probing Pb2+ in real water samples. This SERS‐based analytical method is highly sensitive and selective, and therefore holds promising applications in environmental analysis. 相似文献
123.
124.
Compound 1 bearing urea and viologen groups has been designed and synthesized.It could be used as a colorimetric receptor for dicarboxylate anions due to the significant color changes of the solution upon the addition of dicarboxylates.More importantly,the color changes were related to the chain lengths of the dicarboxylates tested.UV-vis,’H NMR and HRMS studies demonstrated that receptor 1 utilized hydrogen bonds and electrostatic interactions to form 1:1 stoichiometry complexes with these anions.In addition,the generation of cation radical 1’ during the complexation process was also detected by EPR. 相似文献
125.
A practical and scalable synthesis of ethyl (R)-piperidine-3-acetate was achieved from commercially available 3-pyridylacetic acid in 76% overall yield. The practical synthesis was demonstrated on 100-g scale. One-pot reductive N-ethylation of the pyridinium salt with acetonitrile gave an N-ethyl piperidine derivative. 相似文献
126.
We demonstrated a 3D laser imaging system at 1550 nm with a 1.5-GHz sine-wave gated Geiger-mode InGaAs/InP avalanche photodiode (APD). An optical fiber bundle with 100 individual fiber outputs was implemented at the focal plane of the telescope, providing a 2.5-mrad imaging view. The system used single-pixel near-infrared single-photon detector to measure photons at fiber outputs instead of a photon counting array. The 1.5-GHz gated Geiger-mode InGaAs/InP APD with a timing jitter of 290 ps was operated in quasi-continuous mode with detection efficiency of ∼4.3%. We achieved higher than 6-cm surface-to-surface resolution at single-photon level, showing a potential of low-energy and eye-safe laser imaging system for long-distance measurements. 相似文献
127.
《Annals of Pure and Applied Logic》2022,173(3):103071
In standard epistemic logic, the names and the existence of agents are usually assumed to be common knowledge implicitly. This is unreasonable for various applications in computer science and philosophy. Inspired by term-modal logic and assignment operators in dynamic logic, we introduce a lightweight modal predicate logic where names can be non-rigid, and the existence of agents can be uncertain. The language can handle various de dicto/de re distinctions in a natural way. We characterize the expressive power of our language, obtain complete axiomatisations of the logics over several classes of varying-domain/constant-domain epistemic models, and show their (un)decidability. 相似文献
128.
129.
Auxiliary population information is often available in finite population inference problems, and the empirical likelihood (EL) approach has been demonstrated to be flexible and useful for such problems. The present paper concerns EL when interest centers on inference for the mean of the baseline distribution under two-sample density ratio models. Although dual EL is a convenient technical tool since it has the same maximum point and maximum likelihood as DRM-based EL, it can not combine such auxiliary information into the likelihood conveniently and may have loss of efficiency. By contrast, the classical EL approach of Qin and
Lawless\ucite{21} does not have this problem and incorporate seamlessly auxiliary information. Based on the EL using auxiliary information and the
dual EL methods, we construct both point and interval estimations and make a careful comparison. Though the point estimation efficiency gain obtained
by the former is not noticeable, we find that they may have different performances in interval estimation. In terms of coverage accuracy, the two intervals are comparable for not or moderate skewed populations, and the EL interval using auxiliary information can be much superior for severely skewed populations. 相似文献
130.
As one of the biological endogenous pigments, biliverdin (BV) and its dimethyl ester (BVE) have extremely weak fluorescence in solution with quantum yield less than 0.01%. However, the situation reverses with the addition of zinc ions. The strength for fluorescence of BVE-Zn\begin{document}$ ^{2+} $\end{document} complex is greatly enhanced and fluorescence quantum yield can increase to \begin{document}$ \sim $\end{document} 5%. Herein, we studied ultrafast excited state dynamics of BVE-Zn\begin{document}$ ^{2+} $\end{document} complex in ethanol, \begin{document}$ n $\end{document} -propanol, and DMSO solutions in order to reveal the mechanism of fluorescence quantum yield enhancement. The results show that BVE can form a stable coordination complex with zinc with 1:1 stoichiometry in solution. BVE is structurally and energetically more stable in the complex. Using picosecond time-resolve fluorescence and femtosecond transient absorption spectroscopy, we show that smaller non-radiative rate constant of BVE-Zn\begin{document}$ ^{2+} $\end{document} complex in DMSO is the key to increasing its fluorescence quantum yield and the excited state decay mechanism is also revealed. These results provide valuable information about the fluorescence property change after BVE binding to metal ions and may provide a guidance for the study of phytochromes or other fluorescence proteins in which BV/BVE acts as chromophores. 相似文献