全文获取类型
收费全文 | 1309篇 |
免费 | 77篇 |
国内免费 | 6篇 |
专业分类
化学 | 850篇 |
晶体学 | 12篇 |
力学 | 29篇 |
数学 | 129篇 |
物理学 | 372篇 |
出版年
2023年 | 17篇 |
2022年 | 27篇 |
2021年 | 31篇 |
2020年 | 37篇 |
2019年 | 40篇 |
2018年 | 27篇 |
2017年 | 40篇 |
2016年 | 60篇 |
2015年 | 48篇 |
2014年 | 62篇 |
2013年 | 96篇 |
2012年 | 76篇 |
2011年 | 80篇 |
2010年 | 49篇 |
2009年 | 37篇 |
2008年 | 73篇 |
2007年 | 71篇 |
2006年 | 55篇 |
2005年 | 35篇 |
2004年 | 31篇 |
2003年 | 33篇 |
2002年 | 21篇 |
2001年 | 14篇 |
2000年 | 14篇 |
1999年 | 14篇 |
1998年 | 16篇 |
1997年 | 12篇 |
1996年 | 10篇 |
1995年 | 15篇 |
1994年 | 17篇 |
1993年 | 13篇 |
1992年 | 17篇 |
1991年 | 13篇 |
1990年 | 7篇 |
1989年 | 12篇 |
1988年 | 13篇 |
1987年 | 21篇 |
1986年 | 15篇 |
1985年 | 10篇 |
1984年 | 14篇 |
1981年 | 9篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1978年 | 5篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1975年 | 6篇 |
1972年 | 8篇 |
1968年 | 4篇 |
1966年 | 4篇 |
排序方式: 共有1392条查询结果,搜索用时 15 毫秒
91.
Shiwani Berry Shamsher S. Bari Pooja Yadav Ankita Garg Sadhika Khullar Sanjay K. Mandal 《合成通讯》2020,50(19):2969-2980
Abstract An efficient protocol for the stereoselective synthesis of pyrazolo[5,1-b]thiazole-3-carboxylate tethered β-lactam conjugates 8a–j from novel pyrazolo [5,1-b]thiazole-3-carboxylate substituted Schiff’s bases 6a–f is reported here. The reaction between various ketene precursors and novel Schiff’s bases 6a–f afforded exclusive formation of trans-β-lactams 8a–j. The substrate scope of this approach was investigated extensively by varying different groups (R, Z). All the novel compounds were characterized using various spectroscopic techniques, such as FT-IR, 1H NMR, 13C NMR, elemental analysis, 13C NMR (DEPT-135), and mass spectrometry in representative cases. Single crystal X-ray crystallographic study of trans-ethyl 7-(1-(4-methoxyphenyl)-4-oxo-3-phenoxyazetidin-2-yl)-6-methyl-2-(methylthio)pyrazolo[5,1-b]thiazole-3-carboxylate 8a has confirmed the molecular structure and the stereochemical outcome. To the best of our knowledge, the synthesis of such types of Schiff’s bases and β-lactam conjugates has not been reported so far. 相似文献
92.
Kaushik Dey Shebeeb Kunjattu H. Anurag M. Chahande Rahul Banerjee 《Angewandte Chemie (International ed. in English)》2020,59(3):1161-1165
Covalent organic frameworks (COFs) have attracted attention due to their ordered pores leading to important industrial applications like storage and separation. Combined with their modular synthesis and pore engineering, COFs could become ideal candidates for nanoseparations. However, the fabrication of these microcrystalline powders as continuous, crack‐free, robust films remains a challenge. Herein, we report a simple, slow annealing strategy to construct centimeter‐scale COF films ( Tp‐Azo and Tp‐TTA ) with micrometer thickness. The as‐synthesized films are porous (SABET=2033 m2 g?1 for Tp‐Azo ) and chemically stable. These COFs have distinct size cut‐offs (ca. 2.7 and ca. 1.6 nm for Tp‐Azo and Tp‐TTA , respectively), which allow the size‐selective separation of gold nanoparticles. Unlike, other conventional membranes, the durable structure of the COF films allow for excellent recyclability (up to 4 consecutive cycles) and easy recovery of the gold nanoparticles from the solution. 相似文献
93.
Rene F. Roller Ankita Malik Maria A. Carillo Monika Garg Antonella Rella Marie‐Kristin Raulf Bernd Lepenies Peter H. Seeberger Daniel Varn Silva 《Angewandte Chemie (International ed. in English)》2020,59(29):12035-12040
Glypiation is a common posttranslational modification of eukaryotic proteins involving the attachment of a glycosylphosphatidylinositol (GPI) glycolipid. GPIs contain a conserved phosphoglycan that is modified in a cell‐ and tissue‐specific manner. GPI complexity suggests roles in biological processes and effects on the attached protein, but the difficulties to get homogeneous material have hindered studies. We disclose a one‐pot intein‐mediated ligation (OPL) to obtain GPI‐anchored proteins. The strategy enables the glypiation of folded and denatured proteins with a natural linkage to the glycolipid. Using the strategy, glypiated eGFP, Thy1, and the Plasmodium berghei protein MSP119 were prepared. Glypiation did not alter the structure of eGFP and MSP119 proteins in solution, but it induced a strong pro‐inflammatory response in vitro. The strategy provides access to glypiated proteins to elucidate the activity of this modification and for use as vaccine candidates against parasitic infections. 相似文献
94.
Anju Goyal Aditya Sharma Jasanpreet Kaur Sapna Kumari Madhukar Garg Rakesh K. Sindhu Md. Habibur Rahman Muhammad Furqan Akhtar Priti Tagde Agnieszka Najda Barbara Banach-Albiska Katarzyna Masternak Ibtesam S. Alanazi Hanan R. H. Mohamed Attalla F. El-kott Muddaser Shah Mousa O. Germoush Hamdan S. Al-malky Salman H. Abukhuwayjah Ahmed E. Altyar Simona G. Bungau Mohamed M. Abdel-Daim 《Molecules (Basel, Switzerland)》2022,27(3)
95.
Har Mohindra Chawla Satya Narayan Sahu Rahul Shrivastava Satish Kumar 《Tetrahedron letters》2012,53(17):2244-2247
A series of calix[4]arene based ditopic receptors possessing bipyridyl and hydrazone units have been synthesized and evaluated for ionic recognition. It has been observed that the synthesized derivatives function as allosteric receptors for simultaneous recognition of Co2+and F? ions through non-covalent interactions. Significant bathochromic shifts in the UV–visible spectrum with a profound colour change promise their use to engineer novel applications. 相似文献
96.
Photoluminescence and atomic force microscopy studies on pre- and post-irradiated ruby with Fe3+ ion
Photoluminescence spectra measured for pristine ruby and its two irradiated samples with Fe3+ ion show R1, R2, N lines and a broad band. Decrease in intensities of these features is observed with irradiation of Fe3+ ion in ruby. Progressive structural changes and modifications on surface of irradiated rubies with Fe3+ ion have been observed by atomic force microscopy. Decrease in intensities is discussed in terms of pair formation. 相似文献
97.
98.
99.
A new integrated scheme based on resource-reservation and adaptive network flow routing to alleviate contention in optical burst switching networks is proposed. The objective of the proposed scheme is to reduce the overall burst loss in the network and at the same time to avoid the packet out-of-sequence arrival problem. Simulations are carried out to assess the feasibility of the proposed scheme. Its performance is compared with that of contention resolution schemes based on conventional routing. Through extensive simulations, it is shown that the proposed scheme not only provides significantly better burst loss performance than the basic equal proportion and hop-length based traffic routing algorithms, but also is void of any packet re-orderings. 相似文献
100.
A novel optical burst switching (OBS) high speed network architecture has been proposed. To verify its feasibility and evaluate its performance, just-enough-time (JET) signaling has been considered as a high performance protocol. In the proposed architecture, to avoid burst losses, firstly, a short-prior- confirmation-packet (SPCP) is sent over the control channel that simulates the events that the actual packet will experience. Once SPCP detects a drop at any of the intermediate nodes, the actual packet is not sent but the process repeats. In order to increase network utilization, cost effectiveness and to overcome some limitations of conventional OBS, inherent codes (e.g., orthogonal optical codes (OOC)), which are codified only in intensity, has been used. Through simulations, it shows that a decrease in burst loss probability, cost effectiveness and a gain in processing time are obtained when optical label processing is used as compared with electronic processing. 相似文献