全文获取类型
收费全文 | 993篇 |
免费 | 22篇 |
国内免费 | 11篇 |
专业分类
化学 | 601篇 |
晶体学 | 28篇 |
力学 | 54篇 |
数学 | 204篇 |
物理学 | 139篇 |
出版年
2023年 | 10篇 |
2022年 | 20篇 |
2021年 | 27篇 |
2020年 | 24篇 |
2019年 | 16篇 |
2018年 | 24篇 |
2017年 | 12篇 |
2016年 | 41篇 |
2015年 | 14篇 |
2014年 | 38篇 |
2013年 | 72篇 |
2012年 | 50篇 |
2011年 | 53篇 |
2010年 | 41篇 |
2009年 | 42篇 |
2008年 | 59篇 |
2007年 | 44篇 |
2006年 | 46篇 |
2005年 | 31篇 |
2004年 | 30篇 |
2003年 | 30篇 |
2002年 | 38篇 |
2001年 | 12篇 |
2000年 | 18篇 |
1999年 | 12篇 |
1998年 | 12篇 |
1997年 | 10篇 |
1996年 | 15篇 |
1995年 | 15篇 |
1994年 | 9篇 |
1993年 | 6篇 |
1992年 | 12篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 9篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1985年 | 12篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 10篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1975年 | 6篇 |
1968年 | 3篇 |
1916年 | 4篇 |
排序方式: 共有1026条查询结果,搜索用时 265 毫秒
41.
42.
Joseph Páez Chávez Marian Wiercigroch 《Communications in Nonlinear Science & Numerical Simulation》2013,18(9):2571-2580
We investigate complex dynamics occurring in a non-smooth model of a Jeffcott rotor with a bearing clearance. A bifurcation analysis of the rotor system is carried out by means of the software TC-HAT [25], a toolbox of AUTO 97 [6] allowing path-following and detection of bifurcations of periodic trajectories of non-smooth dynamical systems. The study reveals a rich variety of dynamics, which includes grazing-induced fold and period-doubling bifurcations, as well as hysteresis loops produced by a cusp singularity. Furthermore, an analytical expression predicting grazing incidences is derived. 相似文献
43.
Volodymyr O. Knizhnikov Zoia V. Voitenko Vladimir B. Golovko Marian V. Gorichko 《Tetrahedron: Asymmetry》2012,23(14):1080-1083
A novel regio- and diastereospecific ring cleavage of bornane-2,3-dione (camphor quinone) under Bucherer-Bergs reaction conditions has been investigated. The simplicity of this transformation provides a novel and straightforward synthetic pathway to enantiopure derivatives of cyclopentane carboxylic acid as well as functionalized hydantoins in just two steps, starting from inexpensive and easily available camphor. 相似文献
44.
Kristin Voiges Roland Adden Marian Rinken Petra Mischnick 《Cellulose (London, England)》2012,19(3):993-1004
The alditol acetate method is a common procedure for sugar analysis, also applied to determine the substituent distribution
in monomer units of polysaccharide ethers like methyl cellulose by gas liquid chromatography. Consisting of several preparation
and work-up steps this procedure is both time consuming and prone to side reactions that promote discrimination of single
constituents, especially when no peralkylation step is performed prior to hydrolysis. As a consequence results scatter in
dependence on individual treatment and conditions. In the context of this work these critical points were overcome by strict
but simplified work-up procedures and using acid instead of alkaline catalyzed acetylation. Under the acidic conditions the
tedious removal of borate is no longer necessary and a reduced time requirement was achieved as well as good reproducibility.
Comparison with independent reference methods excluded a systematic error of the method and confirmed the results obtained.
Without peralkylation, i.e. in the presence of free hydroxyl groups, another fast modification of the method using DMSO as
solvent, no removal of borate, and 1-methylimidazole as catalyst for acetylation was found to produce a systematic error. 相似文献
45.
46.
Hanna Ayoub Virginie LAIR Sophie Griveau Philippe Brunswick Fethi Bedioui Michel Cassir 《Electroanalysis》2012,24(6):1324-1333
An electrochemical sensor detects the risk of diabetes and prediabetes; low potentials are applied to nickel electrodes and electrical responses are measured. Although the contact of nickel with skin is short, the risk of allergical reactions cannot be discarded. SS 304L, with lower Ni content, was tested in carbonate buffer solutions containing chloride, lactate and urea to investigate its sensitivity to different parameters in sweat and compare it to nickel. The results show that SS 304L is a suitable material for the assessment of sudomotor dysfunction due to its high capacity to detect the deviation in Cl? concentration. Sensitivity of SS 304L to Cl? is much higher than for nickel. 相似文献
47.
A novel heterogeneous magnetic palladium nano‐biocatalyst was designed by utilizing Irish moss, a family of sulfated polysaccharides extracted from algae, as a natural biopolymer. This magnetic Irish moss decorated with palladium (Pd–Fe3O4@IM) to form a biomagnetic catalytic system was synthesized and well characterized by FT–IR analysis, X‐ray powder diffraction, field emission scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, atomic absorption spectroscopy and transmission electron microscopy. The catalyst was stable to air and moisture and displayed high catalytic activity in ligand‐free Suzuki–Miyaura cross‐coupling reactions conducted under green chemistry reaction conditions. The aromatic ketones are produced by the cross‐coupling reaction between acid chlorides and aryl boronic acid derivatives in high yields. 相似文献
48.
Jan Maier Marian Deutsch Dr. Julia Merz Prof. Dr. Qing Ye Oliver Diamond Maja-Tessa Schilling Dr. Alexandra Friedrich Prof. Dr. Bernd Engels Prof. Dr. Todd B. Marder 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(68):15989-16000
We have investigated the cannibalistic self-trapping reaction of an ortho-benzyne derivative generated from 1,11-bis(p-tolyl)undeca-1,3,8,10-tetrayne in an HDDA reaction. Without adding any specific trapping agent, the highly reactive benzyne is trapped by another bisdiyne molecule in at least three different modes. We have isolated and characterized the resulting products and performed high-level calculations concerning the reaction mechanism. During the cannibalistic self-trapping process, either a C≡C triple bond or an sp–sp3 C−C single bond is cleaved. Up to seven rings and nine C−C bonds are formed starting from two 1,11-bis(p-tolyl)undeca-1,3,8,10-tetrayne molecules. Our experiments and calculations provide considerable insight into the variety of reaction pathways which the ortho-benzyne derivative, generated from a bisdiyne, can take when reacting with another bisdiyne molecule. 相似文献
49.
Marian Apostol Victor Barsan Constantin Nantea 《Molecular Crystals and Liquid Crystals》2013,570(1):453-456
Jordan's boson representation and cut-off repolarization for the one-dimensional two-fermion model (TFT) is used to get the equivalence of the model with the two-dimensional Coulomb gas and sine-Gordon model. The scaling equations for the coupling constants are thereby obtained up to the third order. 相似文献
50.
Daniel S. Covita Dimitrios F. Anagnostopoulos Hermann Fuhrmann Hubert Gorke Detlev Gotta Alexander Gruber Albert Hirtl Tomoichi Ishiwatari Paul Indelicato Thomas S. Jensen Eric-Olivier Le Bigot Valeri E. Markushin Michael Nekipelov Vladimir N. Pomerantsev Vladimir P. Popov Joaquim M. F. dos Santos Philipp Schmid Leopold M. Simons Marian Theisen Martino Trassinelli Joao F. C. A. Veloso Johann Zmeskal 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2018,72(4):72