全文获取类型
收费全文 | 1162篇 |
免费 | 25篇 |
国内免费 | 24篇 |
专业分类
化学 | 529篇 |
晶体学 | 7篇 |
力学 | 37篇 |
数学 | 194篇 |
物理学 | 444篇 |
出版年
2021年 | 7篇 |
2019年 | 9篇 |
2017年 | 11篇 |
2016年 | 26篇 |
2015年 | 8篇 |
2014年 | 23篇 |
2013年 | 61篇 |
2012年 | 41篇 |
2011年 | 48篇 |
2010年 | 33篇 |
2009年 | 34篇 |
2008年 | 41篇 |
2007年 | 43篇 |
2006年 | 51篇 |
2005年 | 40篇 |
2004年 | 43篇 |
2003年 | 48篇 |
2002年 | 44篇 |
2001年 | 44篇 |
2000年 | 36篇 |
1999年 | 15篇 |
1998年 | 18篇 |
1997年 | 17篇 |
1996年 | 23篇 |
1995年 | 14篇 |
1994年 | 19篇 |
1993年 | 20篇 |
1992年 | 22篇 |
1991年 | 14篇 |
1990年 | 14篇 |
1989年 | 17篇 |
1988年 | 12篇 |
1987年 | 6篇 |
1986年 | 8篇 |
1985年 | 19篇 |
1984年 | 14篇 |
1983年 | 19篇 |
1982年 | 22篇 |
1981年 | 24篇 |
1980年 | 21篇 |
1979年 | 8篇 |
1978年 | 18篇 |
1977年 | 20篇 |
1976年 | 14篇 |
1975年 | 11篇 |
1974年 | 15篇 |
1973年 | 11篇 |
1972年 | 7篇 |
1971年 | 8篇 |
1967年 | 7篇 |
排序方式: 共有1211条查询结果,搜索用时 0 毫秒
71.
72.
Manfred Bortz Robert Bau Jörg J. Schneider Sax A. Mason 《Journal of Cluster Science》2001,12(1):285-291
The structure of H3Co2[C5H2(t-Bu)3]2 has been analyzed by low-temperature single-crystal neutron diffraction techniques, and shown to consist of two CoCp moieties with three hydride ligands bridging the central Co–Co bond. Despite a fairly extensive twinning problem, the structure could be solved and successfully refined to a final R factor of 9.2% for 2024 reflections. Average molecular parameters in the H3Co2 core of the molecule are as follows: Co–Co=2.275(21) Å, Co–H=1.637(16) Å, HH=2.050(20) Å, Co–H–Co=88.0(9)°, H–Co–H=77.0(7)°. Also included in this paper is a discussion on the molecular dimensions of symmetric hydride-bridged dinuclear systems (M(-H)nM, n=1, 2, 3, 4) that have been studied to date by neutron diffraction. 相似文献
73.
74.
M. A. Śmiałek N. C. Jones R. Balog N. J. Mason D. Field 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,62(2):197-203
Experiments were carried out to determine the dependence of the physical form of supercoiled DNA films on the initial temperature
of the substrate. Such films are often used in irradiation experiments involving low energy particles, like electrons or photons.
In order to obtain absolute values for cross sections for such experiments, the spatial distribution of the sample in the
film has to be well estimated. These investigations aim to correlate the size and form of a DNA film with the initial temperature
of the substrate, on which the liquid sample is deposited prior to evacuation. From our previous studies we concluded that
the presence of agents preventing DNA structural water evaporation is required in order to preserve the supercoiled plasmid
DNA form under vacuum conditions. Therefore, we examined the temperature dependence on films prepared from plasmid suspended
in solutions containing magnesium hydroxide, Tris-Cl buffer and various concentrations of sodium hydroxide.
To visualise the films we used a conventional light microscope with a CCD camera and a scanning electron microscope. The results
revealed a significant influence of the temperature of the substrate on both the area of the substrate covered by the film
as well as on the spatial distribution of DNA molecules. An increase in the amount of sodium hydroxide that stabilises supercoiled
DNA under vacuum increases DNA aggregation. After these investigations we conclude that the best temperature of the substrate
to produce uniform and thin films should be between –5 °C and -10 °C for substrates which are not atomically flat and above
0 °C for atomically flat substrates. 相似文献
75.
Blagovest Bahnev Mark D. Bowden Agnieszka Stypczyńska Sylwia Ptasińska Nigel J. Mason Nicholas St.J. Braithwaite 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2014,68(6):1-5
The coupled-channel optical method (CCOM) is implemented in this work to study the scattering of electron on rubidium atom at 20 eV. In order to provide a realistic calculation, the continuum effect of the scattering system is accounted by incorporate an ab initio optical potential into the CCOM calculation. The differential cross sections (DCS), as well as the reduced Stokes parameters of 5p excitation are reported and compared to the available experimental and theoretical data. 相似文献
76.
Ellis AL Christian Mason J Lee HW Strekowski L Patonay G Choi H Yang JJ 《Talanta》2002,56(6):1099-1107
Intracellular calcium concentration in biological cells varies from 0.1 to 10 μM depending upon cell signaling and disease states. A direct estimate of calcium concentration in cell tissues within this range is possible with a novel calcium-selective reagent 15C5-774. The molecule of 15C5-774 consists of a near-infrared (NIR) chromophore (λmax=774 nm) and a metal complexing moiety of benzo-15-crown-5. The reagent shows a strong calcium binding affinity in a 1:1 ratio and metal selectivity in the order Ca2+>Mg2+>Sr2+≈K+≈Na+>Zn2+>Li+. The high sensitivity is achieved by conducting absorption measurements in the NIR region where background interference from the biological matrix is low. 相似文献
77.
78.
Nonspherical particles can uniquely probe soft system dynamics. We show that laser tweezers stably trap thin coinlike microdisks in 3D with an edge-on orientation. Scattered light forms a streak that we track using a fast camera to measure the disk's angular displacement. Linearly polarized tweezers rotationally trap a birefringent disk, and we measure its harmonically bound Brownian rotation over 5 decades in time. Near a surface, the disk exhibits a translational-orientational switchback oscillation. Circularly polarized tweezers rotate the disk and streak, yielding a colloidal lighthouse. 相似文献
79.
Bryant WS Jones JW Mason PE Guzei I Rheingold AL Fronczek FR Nagvekar DS Gibson HW 《Organic letters》1999,1(7):1001-1004
[formula: see text] Inspired by folded, nonpseudorotaxane complexes of bis(m-phenylene)-32-crown-10 systems, we synthesized a new bicyclic crown ether containing two 1,3,5-phenylene units linked by three tetra(ethyleneoxy) units. The new cryptand forms a "pseudorotaxane-like" inclusion complex with N,N'-dimethyl-4,4'-bipyridinium bis(hexafluorophosphate) with association constant Ka = 6.1 x 10(4) M-1, 100-fold greater than that of an analogous simple crown ether. 相似文献
80.
W.C. Sperry G.A. Beer M.S. Dixit S.K. Kim J.A. MacDonald G.R. Mason A. Olin R.M. Pearce C. Sabev C. Wiegand 《Physics letters. [Part B]》1979,86(1):29-30
The intensity per stopped π?of|Δn|=2 pionic X-rays are observed to have larger variations with atomic number Z than do the |Δn|=1. The 6–4 intensity has a well-defined maximum at Z=34 with a FWHM of ΔZ ~10. 相似文献