全文获取类型
收费全文 | 2234篇 |
免费 | 68篇 |
国内免费 | 15篇 |
专业分类
化学 | 1193篇 |
晶体学 | 17篇 |
力学 | 90篇 |
数学 | 559篇 |
物理学 | 458篇 |
出版年
2023年 | 19篇 |
2022年 | 70篇 |
2021年 | 86篇 |
2020年 | 82篇 |
2019年 | 82篇 |
2018年 | 60篇 |
2017年 | 70篇 |
2016年 | 103篇 |
2015年 | 74篇 |
2014年 | 92篇 |
2013年 | 127篇 |
2012年 | 154篇 |
2011年 | 150篇 |
2010年 | 80篇 |
2009年 | 77篇 |
2008年 | 87篇 |
2007年 | 80篇 |
2006年 | 61篇 |
2005年 | 78篇 |
2004年 | 61篇 |
2003年 | 43篇 |
2002年 | 62篇 |
2001年 | 33篇 |
2000年 | 35篇 |
1999年 | 18篇 |
1998年 | 23篇 |
1997年 | 12篇 |
1996年 | 31篇 |
1995年 | 17篇 |
1994年 | 21篇 |
1993年 | 17篇 |
1992年 | 22篇 |
1991年 | 12篇 |
1990年 | 16篇 |
1989年 | 14篇 |
1988年 | 19篇 |
1987年 | 15篇 |
1986年 | 10篇 |
1985年 | 16篇 |
1984年 | 23篇 |
1983年 | 8篇 |
1982年 | 25篇 |
1981年 | 19篇 |
1980年 | 16篇 |
1979年 | 18篇 |
1977年 | 14篇 |
1976年 | 19篇 |
1975年 | 8篇 |
1974年 | 8篇 |
1973年 | 6篇 |
排序方式: 共有2317条查询结果,搜索用时 0 毫秒
81.
Van T. Tran Zi‐Qi Li Omar Apolinar Joseph Derosa Matthew V. Joannou Steven R. Wisniewski Martin D. Eastgate Keary M. Engle 《Angewandte Chemie (International ed. in English)》2020,59(19):7409-7413
We report that Ni(COD)(DQ) (COD=1,5‐cyclooctadiene, DQ=duroquinone), an air‐stable 18‐electron complex originally described by Schrauzer in 1962, is a competent precatalyst for a variety of nickel‐catalyzed synthetic methods from the literature. Due to its apparent stability, use of Ni(COD)(DQ) as a precatalyst allows reactions to be conveniently performed without use of an inert‐atmosphere glovebox, as demonstrated across several case studies. 相似文献
82.
Quach Thi Thanh Van Le Thi Vien Tran Thi Hong Hanh Phan Thi Thanh Huong Nguyen The Cuong Nguyen Phuong Thao 《Natural product research》2020,34(9):1276-1281
AbstractUsing various chromatographic separations, three new acylated flavonoid glycosides, namely barringosides G–I (1–3), were isolated from the water-soluble extract of Barringtonia racemosa branches and leaves. The structure elucidation was performed by extensive analysis of the 1D and 2D NMR and HR-QTOF-MS data. Of the isolated compounds, barringoside I (3) showed moderate inhibitory effects on LPS-induced NO production in RAW264.7 cells with an IC50 of 52.48?±?1.04?µM. 相似文献
83.
Le Hoang Vien Le Thi Hanh Tran Thi Hong Thanh Nguyen Van Nam Nguyen Hoai 《Natural product research》2020,34(8):1061-1067
AbstractFrom the MeOH extract of the Vietnamese sea cucumber Holothuria edulis, eight triterpene glycosides (1–8), including one new compound namely holothurin A5 (1), were isolated by using various chromatographic separations. Their structures were established by spectroscopic experiments including 1D, 2D NMR and HR-ESI-MS. Holothurin A5 (1) has a hydroperoxy group at C-25. To the best of our knowledge, this is the first report of this group in triterpene saponins obtained from sea cucumbers to date. In addition, the in vitro cytotoxicity against five human cancer cell lines (HepG2, KB, LNCaP, MCF7 and SK-Mel2) of all isolated compounds was also evaluated using SRB assays. 相似文献
84.
Hue Thi Buu Bui Phuong Hong Nguyen Quan Minh Pham Hoa Phuong Tran De Quang Tran Hosun Jung Quang Vinh Hong Quoc Cuong Nguyen Quy Phu Nguyen Hieu Trong Le Su-Geun Yang 《Molecules (Basel, Switzerland)》2022,27(7)
Epigenetic alterations found in all human cancers are promising targets for anticancer therapy. In this sense, histone deacetylase inhibitors (HDACIs) are interesting anticancer agents that play an important role in the epigenetic regulation of cancer cells. Here, we report 15 novel hydroxamic acid-based histone deacetylase inhibitors with quinazolinone core structures. Five compounds exhibited antiproliferative activity with IC50 values of 3.4–37.8 µM. Compound 8 with a 2-mercaptoquinazolinone cap moiety displayed the highest antiproliferative efficacy against MCF-7 cells. For the HDAC6 target selectivity study, compound 8 displayed an IC50 value of 2.3 µM, which is 29.3 times higher than those of HDAC3, HDAC4, HDAC8, and HDAC11. Western blot assay proved that compound 8 strongly inhibited tubulin acetylation, a substrate of HDAC6. Compound 8 also displayed stronger inhibition activity against HDAC11 than the control drug Belinostat. The inhibitory mechanism of action of compound 8 on HDAC enzymes was then explored using molecular docking study. The data revealed a high binding affinity (−7.92 kcal/mol) of compound 8 toward HDAC6. In addition, dock pose analysis also proved that compound 8 might serve as a potent inhibitor of HDAC11. 相似文献
85.
The gauge symmetry group of any slave boson representation allows to gauge away the phase of bosonic fields. One benefit of this radial field formulation is the elimination of spurious Bose condensations when saddle-point approximation is performed. Within the Kotliar–Ruckenstein representation, three of the four bosonic fields can be radial while the last one has to remain complex. In this work, the procedure to carry out the functional integration involving constrained fermionic fields, complex bosonic fields, and radial bosonic fields is presented. The correctness of the representation is verified by exactly evaluating the partition function and the Green's function of the Hubbard model in the atomic limit. 相似文献
86.
Martin Krtký Katarína Svr
kov Quynh Anh Vu rka tpnkov Jarmila Vinov 《Molecules (Basel, Switzerland)》2021,26(4)
Based on the broad spectrum of biological activity of hydrazide–hydrazones, trifluoromethyl compounds, and clinical usage of cholinesterase inhibitors, we investigated hydrazones obtained from 4-(trifluoromethyl)benzohydrazide and various benzaldehydes or aliphatic ketones as potential inhibitors of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). They were evaluated using Ellman’s spectrophotometric method. The hydrazide–hydrazones produced a dual inhibition of both cholinesterase enzymes with IC50 values of 46.8–137.7 µM and 19.1–881.1 µM for AChE and BuChE, respectively. The majority of the compounds were stronger inhibitors of AChE; four of them (2-bromobenzaldehyde, 3-(trifluoromethyl)benzaldehyde, cyclohexanone, and camphor-based 2o, 2p, 3c, and 3d, respectively) produced a balanced inhibition of the enzymes and only 2-chloro/trifluoromethyl benzylidene derivatives 2d and 2q were found to be more potent inhibitors of BuChE. 4-(Trifluoromethyl)-N’-[4-(trifluoromethyl)benzylidene]benzohydrazide 2l produced the strongest inhibition of AChE via mixed-type inhibition determined experimentally. Structure–activity relationships were identified. The compounds fit physicochemical space for targeting central nervous systems with no apparent cytotoxicity for eukaryotic cell line together. The study provides new insights into this CF3-hydrazide–hydrazone scaffold. 相似文献
87.
Dr. Tran Quang Hung Dr. Ferial Terki Dr. Souleymane Kamara Mourad Dehbaoui Prof. Salam Charar Brajalal Sinha Prof. CheolGi Kim Dr. Philippe Gandit Il'ya A. Gural'skiy Dr. Gabor Molnar Dr. Lionel Salmon Dr. Helena J. Shepherd Dr. Azzedine Bousseksou 《Angewandte Chemie (International ed. in English)》2013,52(4):1185-1188
88.
Tran Thu Ha Nguyen Hong Phong François-Xavier Le Dimet Hong Son Hoang 《Comptes Rendus Mecanique》2019,347(5):423-444
This article presents a correction method for a better resolution of the problem of estimating and predicting pollution, governed by Burgers' equations. The originality of the method consists in the introduction of an error function into the system's equations of state to model uncertainty in the model. The initial conditions and diffusion coefficients, present in the equations for pollution and concentration, and also those in the model error equations, are estimated by solving a data assimilation problem. The efficiency of the correction method is compared with that produced by the traditional method without introduction of an error function.Three test cases are presented in this study in order to compare the performances of the proposed methods. In the first two tests, the reference is the analytical solution and the last test is formulated as part of the “twin experiment”.The numerical results obtained confirm the important role of the model error equation for improving the prediction capability of the system, in terms of both accuracy and speed of convergence. 相似文献
89.
We present the first realisation of ferromagnetic Fe nanotips. Studies of the field emitted beams of electrons and metallic ions above and under the Curie temperature Tc were made. We have observed a reversible splitting of the electron beams when the temperature crossed through Tc and multiple spot patterns for the emitted metallic ion beams. These phenomena were not observed with Fe microtips or non-magnetic nanotips and thus were correlated to a strong magnetic interaction at the atomic scale apex of the nanotips. The Fe nanotips constitute an atomic scale beam-splitter. 相似文献
90.
Synthesis of cation-exchanged laponite suspensions by laser ablation of microsized-metal particles in liquid 总被引:1,自引:0,他引:1
Laser ablation in the liquid technique has been used to synthesize cation-exchanged laponite suspensions. In summary, laser ablation of the microsize-metal powder (Co, Al, and Cu) dispersed in an aqueous solution containing deionized water laponite crystals was carried out using laser beam generated by a single-mode, Q-switched Nd-Yag laser operating at 532 nm with a pulse duration of 5.5 ns and 10 Hz repetition rate. Laser fluence was 0.265 J/cm2 for all tests. For all samples, the mass fraction of laponite was 1%. General observations of the prepared samples indicated that an aqueous suspension of 1 wt% laponite retained its free flowing liquid phase characteristics even after aging for several weeks. When bivalent cationic metals (Cu, Co, Al) were ablated in it for about 1 h, even with a small amount of the metal (0.025% and 0.050%) were generated, the suspension became highly viscous and behaved as a shear-thinning and thixotropic material. That is, the suspension gelled strongly when it was allowed to rest. The gels, however, could easily be reverted to a low viscosity liquid with simple shaking. Information from TEM and XRD analysis indicated that such a sol-gel transformation might be due to the charge exchange between the cationic species produced during the laser ablation and the sodium ions in the interlayers of the clay sheets. 相似文献