全文获取类型
收费全文 | 3874篇 |
免费 | 162篇 |
国内免费 | 11篇 |
专业分类
化学 | 2831篇 |
晶体学 | 23篇 |
力学 | 70篇 |
数学 | 521篇 |
物理学 | 602篇 |
出版年
2023年 | 49篇 |
2022年 | 43篇 |
2021年 | 80篇 |
2020年 | 94篇 |
2019年 | 98篇 |
2018年 | 66篇 |
2017年 | 52篇 |
2016年 | 121篇 |
2015年 | 129篇 |
2014年 | 129篇 |
2013年 | 210篇 |
2012年 | 212篇 |
2011年 | 290篇 |
2010年 | 163篇 |
2009年 | 137篇 |
2008年 | 217篇 |
2007年 | 222篇 |
2006年 | 182篇 |
2005年 | 168篇 |
2004年 | 162篇 |
2003年 | 109篇 |
2002年 | 118篇 |
2001年 | 64篇 |
2000年 | 65篇 |
1999年 | 45篇 |
1998年 | 57篇 |
1997年 | 54篇 |
1996年 | 47篇 |
1995年 | 55篇 |
1994年 | 51篇 |
1993年 | 66篇 |
1992年 | 33篇 |
1991年 | 44篇 |
1990年 | 33篇 |
1989年 | 24篇 |
1988年 | 21篇 |
1987年 | 26篇 |
1986年 | 18篇 |
1985年 | 29篇 |
1984年 | 32篇 |
1983年 | 20篇 |
1982年 | 16篇 |
1981年 | 17篇 |
1980年 | 20篇 |
1979年 | 16篇 |
1978年 | 21篇 |
1977年 | 19篇 |
1976年 | 10篇 |
1974年 | 8篇 |
1973年 | 18篇 |
排序方式: 共有4047条查询结果,搜索用时 15 毫秒
1.
Corinne Rondeau-Mouro Mireille Cambert Laurent Blondel Yves Diascorn Léo Mbaya Nor Nadiah Binti Ahmad Nazari Sarah Helary Tiphaine Lucas 《Magnetic resonance in chemistry : MRC》2022,60(7):678-691
A temperature control unit was implemented to vary the temperature of samples studied on a commercial Mobile Universal Surface Explorer nuclear magnetic resonance (MOUSE-NMR) apparatus. The device was miniaturized to fit the maximum MOUSE sampling depth (25 mm). It was constituted by a sample holder sandwiched between two heat exchangers placed below and above the sample. Air was chosen as the fluid to control the temperature at the bottom of the sample, at the interface between the NMR probe and the sample holder, in order to gain space. The upper surface of the sample was regulated by the circulation of water inside a second heat exchanger placed above the sample holder. The feasibility of using such a device was demonstrated first on pure water and then on several samples of bread dough with different water contents. For this, T1 relaxation times were measured at various temperatures and depths and were then compared with those acquired with a conventional compact closed-magnet spectrometer. Discussion of results was based on biochemical transformations in bread dough (starch gelatinization and gluten heat denaturation). It was demonstrated that, within a certain water level range, and because of the low magnetic field strength of the MOUSE, a linear relationship could be established between T1 relaxation times and the local temperature in the dough sample. 相似文献
2.
3.
4.
5.
Condeixa Lucas Dias Silva Pierry Moah Diego Farias Brenda Leiras Adriana 《Central European Journal of Operations Research》2022,30(3):921-940
Central European Journal of Operations Research - Societal awareness and legislation changes concerning sustainability have affected how organizations generate value for stakeholders, as well as... 相似文献
6.
Ralf Freund Christos Allagiannis Peter Schnholzer Karl Bernauer 《Helvetica chimica acta》1994,77(3):615-621
A crude hydrate 6 and a crystalline hemiacetal 7 of glyoxylamide 4 were prepared from crotonamide 5 (Scheme 2). Particularly hemiacetal 7 , but also 6 and the ‘dimer’ 8 (obtained from 7 ) may serve as homochiral auxiliaries. The structure of 8 was determined by X-ray analysis. By arenesulfonyl halides, tryptimines 12–14 of 4 were diastereoselectively transformed into spirotricycles 15–17 and 19 . 相似文献
7.
[3,3]-Sigmatropic rearrangements of allyl tetronates and allyl tetramates to give 3-allyltetronic or -tetramic acids, respectively, proceed within 20-60 min under microwave irradiation (300 W, 130-190 °C). Consecutive (homo)sigmatropic [1,5] H-shifts such as oxa-ene reactions are promoted less effectively, which allows the isolation of Claisen intermediates of sigmatropic domino sequences, in contrast to conventional heating. 相似文献
8.
We present an O(min(Kn,n2)) algorithm to solve the maximum integral multiflow and minimum multicut problems in rooted trees, where K is the number of commodities and n is the number of vertices. These problems are NP-hard in undirected trees but polynomial in directed trees. In the algorithm we propose, we first use a greedy procedure to build the multiflow then we use duality properties to obtain the multicut and prove the optimality. 相似文献
9.
Ralf Jäger Anatolij I. Saprykin J. Sabine Becker Hans -Joachim Dietze José A. C. Broekaert 《Mikrochimica acta》1997,125(1-4):41-44
The analytical capabilities of a high-resolution mass spectrometer in combination with a 13.56 MHz glow discharge ion source for the analysis of semiconducting materials (silicon carbide and gallium arsenide) were studied. It was shown that single positively charged ions of sample material have about 10 eV higher average energy than the ions of the discharge and residual gas. Therefore effective energy separation of the ions of analyte from the ions of the discharge and residual gas was achieved by adjusting the ion transfer optics (breadth and position of energy slit), which improves the analytical capabilities of the developed method.Some analytical applications are presented to illustrate the performance of r.f. GDMS for the bulk analysis of semiconducting materials. The results of the trace element analysis of gallium arsenide and silicon carbide samples are compared with data of independent methods (LIMS, ICP-AES, SIMS).Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthdayOn leave from the Institute of Inorganic Chemistry, 630090 Novosibirsk, Russia 相似文献
10.
The gedanken experiment of the clock paradox is solved exactly using the general relativistic equations for a static homogeneous gravitational
field. We demonstrate that the general and special relativistic clock paradox solutions are identical and in particular that
they are identical for finite acceleration. Practical expressions are obtained for proper time and coordinate time by using the destination distance as
the key observable parameter. This solution provides a formal demonstration of the identity between the special and general
relativistic clock paradox with finite acceleration and where proper time is assumed to be the same in both formalisms. By
solving the equations of motion for a freely falling clock in a static homogeneous field elapsed times are calculated for
realistic journeys to the stars.
1 Both authors contributed equally to this paper. 相似文献