全文获取类型
收费全文 | 1135篇 |
免费 | 32篇 |
国内免费 | 11篇 |
专业分类
化学 | 723篇 |
晶体学 | 6篇 |
力学 | 37篇 |
数学 | 243篇 |
物理学 | 169篇 |
出版年
2023年 | 6篇 |
2021年 | 15篇 |
2020年 | 18篇 |
2019年 | 10篇 |
2018年 | 21篇 |
2017年 | 13篇 |
2016年 | 41篇 |
2015年 | 27篇 |
2014年 | 22篇 |
2013年 | 47篇 |
2012年 | 73篇 |
2011年 | 75篇 |
2010年 | 50篇 |
2009年 | 40篇 |
2008年 | 63篇 |
2007年 | 75篇 |
2006年 | 62篇 |
2005年 | 49篇 |
2004年 | 36篇 |
2003年 | 34篇 |
2002年 | 33篇 |
2001年 | 10篇 |
2000年 | 13篇 |
1999年 | 13篇 |
1998年 | 10篇 |
1997年 | 6篇 |
1996年 | 12篇 |
1995年 | 15篇 |
1994年 | 17篇 |
1993年 | 7篇 |
1992年 | 10篇 |
1991年 | 13篇 |
1990年 | 14篇 |
1989年 | 8篇 |
1988年 | 10篇 |
1987年 | 14篇 |
1986年 | 18篇 |
1985年 | 17篇 |
1984年 | 25篇 |
1983年 | 21篇 |
1982年 | 15篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 13篇 |
1978年 | 5篇 |
1976年 | 10篇 |
1975年 | 5篇 |
1974年 | 3篇 |
1972年 | 3篇 |
1933年 | 3篇 |
排序方式: 共有1178条查询结果,搜索用时 183 毫秒
1.
Pietro?CalandraEmail author Tilde?de?Caro Daniela?Caschera Domenico?Lombardo Lorena?Todaro Vincenzo?Turco Liveri 《Colloid and polymer science》2015,293(2):597-603
The spectroscopic properties and liquid structure of pure tri-n-butyl phosphate (TBP) and FeCl3/TBP solutions have been investigated by Uv–Vis and Raman spectroscopies, X-ray diffraction and conductometry. Uv–Vis and Raman spectra, supported by conductometric measurements, consistently indicate that the solubilized salt is present mostly as TBP n [FeCl3???n ] n+ and FeCl4 ? complex ions due to specific interaction with the TBP phosphate group. Thanks to this interaction, a high amount of salt (up to 13 % w/w) can be dissolved despite the relatively low dielectric constant of TBP. The X-ray diffractogram of pure TBP has been interpreted in terms of three main contributions which can be attributed to spatial pair correlations between atoms of interacting TBP molecules. In the presence of increasing FeCl3 amounts, it has been observed a progressive structuring effect, exerted by the dissolved salt, on the layers of opportunely oriented TBP molecules due to the formation of the complex ionic species. By simple treatment with NaBH4, the synthesis of Fe nanoparticles has been achieved. The absence of water, the easiness of preparation, the high amount of salt which can be suspended and the peculiar physico-chemical properties of such systems are all elements worth of note for the fields of nanoparticle synthesis and for specialized technological applications. 相似文献
2.
Synthesis and Biological Evaluation of Several Dephosphonated Analogues of CMP‐Neu5Ac as Inhibitors of GM3‐Synthase 下载免费PDF全文
Dr. Paola Rota Dr. Federica Cirillo Dr. Marco Piccoli Dr. Antonio Gregorio Prof. Guido Tettamanti Prof. Pietro Allevi Prof. Luigi Anastasia 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(41):14614-14629
Previous studies demonstrated that reducing the GM3 content in myoblasts increased the cell resistance to hypoxic stress, suggesting that a pharmacological inhibition of the GM3 synthesis could be instrumental for the development of new treatments for ischemic diseases. Herein, the synthesis of several dephosphonated CMP‐Neu5Ac congeners and their anti ‐ GM3‐synthase activity is reported. Biological activity testes revealed that some inhibitors almost completely blocked the GM3‐synthase activity in vitro and reduced the GM3 content in living embryonic kidney 293A cells, eventually activating the epidermal growth factor receptor (EGFR) signaling cascade. 相似文献
3.
Simone Madama Ermelinda Falletta Amir Mohammad Malvandi Kevin Arzoni Carlo Brogna Marco Varelli Matteo Bertelli Matteo Conti Martina Larini Federico Guidugli Pietro Traldi Simone Cristoni 《Journal of mass spectrometry : JMS》2022,57(8):e4876
In this work, the isolation step in the linear ion trap was performed using different “q values” conditions at a low collision-induced dissociation (CID) energy leading to the parent ion resolution improvements, reasonably due to better ion energy distribution. According to the results, we obtained a greater resolution and mass accuracy operating in both traditional electrospray and low voltage ionization near the q value = 0.778 and with a CID energy of 10%. This effect was evaluated with low-molecular-mass compounds (skatole and arginine). The proposed optimization yielded a superior instrument performance without adding technological complexity to mass spectrometry analyses. 相似文献
4.
Pietro Dell’Acqua 《Advances in Computational Mathematics》2017,43(6):1283-1304
In recent years, several efforts were made in order to introduce boundary conditions for deblurring problems that allow to get accurate reconstructions. This resulted in the birth of Reflective, Anti-Reflective and Mean boundary conditions, which are all based on the idea of guaranteeing the continuity of the signal/image outside the boundary. Here we propose new boundary conditions that are obtained by suitably combining Taylor series and finite difference approximations. Moreover, we show that also Anti-Reflective and Mean boundary conditions can be attributed to the same framework. Numerical results show that, in case of low levels of noise and blurs able to perform a suitable smoothing effect on the original image (e.g. Gaussian blur), the proposed boundary conditions lead to a significant improvement of the restoration accuracy with respect to those available in the literature. 相似文献
5.
Margherita Modesti Colleen Szeto Renata Ristic WenWen Jiang Julie Culbert Keren Bindon Cesare Catelli Fabio Mencarelli Pietro Tonutti Kerry Wilkinson 《Molecules (Basel, Switzerland)》2021,26(6)
When bushfires occur near grape growing regions, vineyards can be exposed to smoke, and depending on the timing and duration of grapevine smoke exposure, fruit can become tainted. Smoke-derived volatile compounds, including volatile phenols, can impart unpleasant smoky, ashy characters to wines made from smoke-affected grapes, leading to substantial revenue losses where wines are perceivably tainted. This study investigated the potential for post-harvest ozone treatment of smoke-affected grapes to mitigate the intensity of smoke taint in wine. Merlot grapevines were exposed to smoke at ~7 days post-veraison and at harvest grapes were treated with 1 or 3 ppm of gaseous ozone (for 24 or 12 h, respectively), prior to winemaking. The concentrations of smoke taint marker compounds (i.e., free and glycosylated volatile phenols) were measured in grapes and wines to determine to what extent ozonation could mitigate the effects of grapevine exposure to smoke. The 24 h 1 ppm ozone treatment not only gave significantly lower volatile phenol and volatile phenol glycoside concentrations but also diminished the sensory perception of smoke taint in wine. Post-harvest smoke and ozone treatment of grapes suggests that ozone works more effectively when smoke-derived volatile phenols are in their free (aglycone) form, rather than glycosylated forms. Nevertheless, the collective results demonstrate the efficacy of post-harvest ozone treatment as a strategy for mitigation of smoke taint in wine. 相似文献
6.
We prove the existence of at least one T-periodic solution to a dynamical system of the type $$ - m_i \ddot u_i = \sum\limits_{j = 1,j \ne i}^n {\triangledown V_{ij} (u_i - u_j ,{\text{ }}t)}$$ (1) where the potentials V ij are T-periodic in t and singular at the origin, u i ε R k i=1, ..., n, and k≧3. We also provide estimates on the H 1 norm of this solution. The proofs are based on a variant of the Ljusternik-Schnirelman method. The results here generalize to the n-body problem some results obtained by Bahri & Rabinowitz on the 3-body problem in [6]. 相似文献
7.
Roberta Seraglia Giovanni Sartore Raffaella Marin Silvia Burlina Enzo Manzato Eugenio Ragazzi Pietro Traldi Annunziata Lapolla 《Journal of mass spectrometry : JMS》2013,48(1):105-110
Increased oxidation of low density lipoprotein (LDL) is characteristic of atherosclerosis. In this frame, high density lipoproteins (HDL) play an important role, being able to remove lipid peroxides (LPOs) and cholesterol from oxidized LDL, so exhibiting a protective role against atherosclerosis. A wide range of reactive compounds lead to the oxidation of methionine (Met) residues with the formation of methionine sulphoxide (MetO) in apolipoprotein A‐I (ApoA‐I). Consequently, the determination of MetO level can give both an evaluation of oxidative stress and the reduced capability of ApoA‐I in LPOs and cholesterol transport. For these reasons, the development of analytical methods able to determine the MetO level is surely of interest, and we report here the results obtained by MALDI mass spectrometry. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
8.
9.
The four stereomer 1-(4-hydroxy-3-methoxy)-phenyl-1,2,3-propanetriols were obtained in about 30% yields starting from ferulic acid by a synthesis based on osmium catalyzed asymmetric dihydroxylation. 相似文献
10.