全文获取类型
收费全文 | 5055篇 |
免费 | 255篇 |
国内免费 | 33篇 |
专业分类
化学 | 3595篇 |
晶体学 | 19篇 |
力学 | 125篇 |
数学 | 864篇 |
物理学 | 740篇 |
出版年
2023年 | 42篇 |
2022年 | 28篇 |
2021年 | 83篇 |
2020年 | 121篇 |
2019年 | 112篇 |
2018年 | 70篇 |
2017年 | 56篇 |
2016年 | 160篇 |
2015年 | 145篇 |
2014年 | 184篇 |
2013年 | 288篇 |
2012年 | 325篇 |
2011年 | 371篇 |
2010年 | 260篇 |
2009年 | 205篇 |
2008年 | 318篇 |
2007年 | 320篇 |
2006年 | 310篇 |
2005年 | 309篇 |
2004年 | 243篇 |
2003年 | 215篇 |
2002年 | 217篇 |
2001年 | 85篇 |
2000年 | 59篇 |
1999年 | 41篇 |
1998年 | 36篇 |
1997年 | 59篇 |
1996年 | 63篇 |
1995年 | 45篇 |
1994年 | 41篇 |
1993年 | 27篇 |
1992年 | 25篇 |
1991年 | 32篇 |
1990年 | 27篇 |
1989年 | 34篇 |
1988年 | 24篇 |
1987年 | 12篇 |
1986年 | 23篇 |
1985年 | 31篇 |
1984年 | 30篇 |
1983年 | 28篇 |
1982年 | 34篇 |
1981年 | 24篇 |
1980年 | 25篇 |
1979年 | 20篇 |
1978年 | 35篇 |
1977年 | 20篇 |
1976年 | 15篇 |
1975年 | 12篇 |
1974年 | 18篇 |
排序方式: 共有5343条查询结果,搜索用时 31 毫秒
1.
Kalina Mambourg Laurie Bodart Nikolay Tumanov Steve Lanners Johan Wouters 《Acta Crystallographica. Section C, Structural Chemistry》2020,76(3):205-211
The condensation reaction of 2‐mercapto‐3‐methoxybenzaldehyde with 3‐aminopyridine afforded an unexpected N‐alkylated [1,5]dithiocine instead of the N‐salicylideneaniline. The proposed mechanism for this condensation involves a strong intramolecular hydrogen bond between the thiol and the amine groups, leading to a second condensation. The corresponding product, i.e. 4,10‐dimethoxy‐13‐(pyridin‐3‐yl)‐6H,12H‐6,12‐epiminodibenzo[b,f][1,5]dithiocine methanol 0.463‐solvate, C21H18N2O2S2·0.463CH3OH, was characterized by single‐crystal X‐ray diffraction analysis. The supramolecular structure shows π–π stacking and S…S interactions in the crystal packing. Within the asymmetric unit, two geometries of the N atom are observed. Although a planar geometry should be expected, a pyramidal one is observed due to the crystal packing. The presence of the two geometries was further supported by density functional theory (DFT) calculations that show an electronic energy difference of less than 2 kJ mol?1 between the two conformers. 相似文献
2.
The Ramanujan Journal - In the present note, we prove new lower bounds on large values of character sums $$\varDelta (x,q):=\max _{\chi \ne \chi _0} \big \vert \sum _{n\le x} \chi (n)\big \vert $$... 相似文献
3.
We show that there is no (95, 40, 12, 20) strongly regular graph and, consequently, there is no (96, 45, 24, 18) strongly regular graph, no nontrivial regular two‐graph on 96 vertices, and no partial geometry pg(4, 9, 2). The main idea of the result is based on the star complement technique and requires a moderate amount of computation. 相似文献
4.
5.
Dmytro Strilets Dr. Shixin Fa Arthur Hardiagon Dr. Marc Baaden Prof. Tomoki Ogoshi Dr. Mihail Barboiu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(51):23413-23419
Artificial water channels mimicking natural aquaporins (AQPs) can be used for selective and fast transport of water. Here, we quantify the transport performances of peralkyl-carboxylate-pillar[5]arenes dimers in bilayer membranes. They can transport ≈107 water molecules/channel/second, within one order of magnitude of the transport rates of AQPs, rejecting Na+ and K+ cations. The dimers have a tubular structure, superposing pillar[5]arene pores of 5 Å diameter with twisted carboxy-phenyl pores of 2.8 Å diameter. This biomimetic platform, with variable pore dimensions within the same structure, offers size restriction reminiscent of natural proteins. It allows water molecules to selectively transit and prevents bigger hydrated cations from passing through the 2.8 Å pore. Molecular simulations prove that dimeric or multimeric honeycomb aggregates are stable in the membrane and form water pathways through the bilayer. Over time, a significant shift of the upper vs. lower layer occurs initiating new unexpected water permeation events through toroidal pores. 相似文献
6.
Gustavo D. Mendes Thais da Silva Pereira Júlio César Rodrigues Elaine Marcílio Santos Mariani Rafaela Souza Rodrigo Alvaro Brandão Lopes-Martins Natalícia de Jesus Antunes Ronilson Agnaldo Moreno Gilberto De Nucci 《Biomedical chromatography : BMC》2020,34(4):e4731
To assess the bioequivalence of two zolpidem hemitartrate formulations in 30 healthy volunteers. Plasma samples were obtained over a 24 h period. Plasma concentrations of zolpidem were analyzed by liquid chromatography coupled to tandem mass spectrometry with positive ion electrospray ionization using multiple reaction monitoring. Values of peak concentration (Cmax), area under curve (AUC), half-life, elimination constant, volume of distribution and clearance showed statistically significant differences when comparing women (604.34 ng h/ml, 127.36 ng/ml, 4.4 h, 0.18 1/h, 50.56 L and 8.55 L/h, respectively) and men (276.1 ng h/ml, 70.9 ng/ml, 3.3 h, 0.26 1/h, 91.42 L and 24.34 L/h, respectively), receiving the same dose (5 mg), respectively. The geometric means with corresponding 90% confidence interval for Test/Reference percentage ratios were 99.73% (CI 93.69–106.16) for Cmax, 97.44% (90% CI = 91.85–103.37%) for area under curve of plasma concentration until the last concentration observed (AUClast) and 98.30% (90% CI = 92.48–104.49) for the area under curve between the first sample (pre-dosage) and infinity (AUC0–inf). Since the 90% CI for AUClast, AUC0–inf and Cmax ratios were within the 80–125% interval proposed by the US Food and Drug Administration, it was concluded that zolpidem hemitartrate formulation (5 mg orodispersible tablet) is bioequivalent to the zolpidem hemitartrate formulation (Patz SL 5 mg sublingual tablet) with regard to both the rate and the extent of absorption. A new formulation of zolpidem 2.5 mg may be useful in women for the same clinical benefits as the 5 mg formulation in men. 相似文献
7.
8.
Dr. Pavlo Nikolaienko Marc Jentsch Dr. Ajit P. Kale Dr. Yunfei Cai Prof. Dr. Magnus Rueping 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(29):7177-7184
A hydrogen atom transfer-directed electrochemical intramolecular C−H amination has been developed in which the N-radical species are generated at the anode, and the base required for the reaction is generated at the cathode. A broad range of valuable pyrrolidines were prepared in good yields and with high chemoselectivity. The reaction was easily scaled up in both batch and continuous flow systems. 相似文献
9.
10.