全文获取类型
收费全文 | 4239篇 |
免费 | 252篇 |
国内免费 | 21篇 |
专业分类
化学 | 3277篇 |
晶体学 | 16篇 |
力学 | 80篇 |
数学 | 541篇 |
物理学 | 598篇 |
出版年
2023年 | 52篇 |
2022年 | 73篇 |
2021年 | 85篇 |
2020年 | 136篇 |
2019年 | 109篇 |
2018年 | 64篇 |
2017年 | 79篇 |
2016年 | 174篇 |
2015年 | 150篇 |
2014年 | 175篇 |
2013年 | 202篇 |
2012年 | 307篇 |
2011年 | 260篇 |
2010年 | 149篇 |
2009年 | 144篇 |
2008年 | 230篇 |
2007年 | 217篇 |
2006年 | 194篇 |
2005年 | 197篇 |
2004年 | 185篇 |
2003年 | 121篇 |
2002年 | 157篇 |
2001年 | 67篇 |
2000年 | 61篇 |
1999年 | 56篇 |
1998年 | 60篇 |
1997年 | 51篇 |
1996年 | 55篇 |
1995年 | 40篇 |
1994年 | 32篇 |
1993年 | 31篇 |
1992年 | 42篇 |
1991年 | 25篇 |
1990年 | 29篇 |
1989年 | 36篇 |
1988年 | 37篇 |
1987年 | 34篇 |
1986年 | 31篇 |
1985年 | 31篇 |
1984年 | 38篇 |
1983年 | 27篇 |
1982年 | 21篇 |
1981年 | 38篇 |
1980年 | 25篇 |
1979年 | 23篇 |
1978年 | 20篇 |
1977年 | 27篇 |
1975年 | 13篇 |
1974年 | 12篇 |
1970年 | 13篇 |
排序方式: 共有4512条查询结果,搜索用时 31 毫秒
991.
A novel Stereo PIV technique, with improvements over other techniques, is presented. The key feature of the new technique
is the direct measurement of calibration data at each point in space on the measurement grid, so that no interpolation is
necessary. This is achieved through the use of a contiguous target which can be analysed using standard PIV processing software.
The technique results in three-dimensional measurements of high accuracy with a significantly simpler calibration phase. This
has the benefit of improving ease of use and reducing the time taken to obtain data. Thorough error analysis shows that while
previously-described error trends are correct, additional facets of the technique can be optimised to allow highly accurate
results. The new technique is rigorously validated here using pure translation and rotation test cases. Finally, the technique
is used to measure a complex swirling flow within a cylindrical vessel. 相似文献
992.
Christoph E. Düllmann 《Czechoslovak Journal of Physics》2006,56(1):D333-D338
The availability of physically preseparated isotopes for chemistry experiment opens up completely new possibilities, especially
for chemical investigations of transactinide elements. Many restrictions present in conventional methods that were used very
successfully in the past can be overcome by using preseparated isotopes. An overview of experiments that were performed with
preseparated isotopes is given. Studies of β-diketonates of group 4 elements are described in some more detail and used as
an example to demonstrate the power of the method. Production of preseparated long-lived transactinide isotopes is outlined
and, lastly, the new preseparator TASCA which is currently being installed at GSI, Darmstadt, is briefly described. 相似文献
993.
Ulf Peschel Christoph Bersch Georgy Onishchukov 《Central European Journal of Physics》2008,6(3):619-627
In this paper we discuss the joint propagation of a periodically modulated field and a pulse of different frequency in an
optical fiber. The pulse experiences the action of an index lattice induced via cross-phase modulation by the periodic field.
We predict effects of discreteness to show up both in the temporal and in the spatial domain. For large walk-off between the
two fields one should observe Bloch oscillations in frequency space, where discrete diffraction is expected to occur for equal
velocities of both waves.
Presented at 9-th International Workshop on Nonlinear Optics Applications, NOA 2007, May 17–20, 2007, Świnoujscie, Poland 相似文献
994.
995.
996.
Christoph Loenarz 《Angewandte Chemie (International ed. in English)》2020,59(10):3776-3780
The 2019 Nobel Prize in Physiology or Medicine honours three scientists that devoted their careers to pursuing an audacious basic science question: by what mechanisms do animals sense oxygen, and how can cells adapt to a lack of oxygen? The identification of the human hypoxia inducible factor pathway has enabled new approaches for the therapy of related diseases including cancer, cardiovascular disease, anaemia, and stroke. The intricate molecular details of oxygen sensing broadened interest in the family of iron‐ and 2‐oxoglutarate‐dependent oxygenases known from elaborate natural product chemistry, and catalysed major progress in macromolecule hydroxylation. The laureates’ work enables numerous avenues for molecular scientists, from C?H activation chemistry to PROTAC technology, medicinal chemistry, and epigenetics. 相似文献
997.
998.
999.
Lisa A. Bischoff Dr. Michael Drisch Dr. Christoph Kerpen Philipp T. Hennig Dr. Johannes Landmann Dr. Jan A. P. Sprenger Dr. Rüdiger Bertermann Dr. Matthias Grüne Qinqin Yuan Dr. Jonas Warneke Dr. Xue-Bin Wang Dr. Nikolai V. Ignat'ev Prof. Dr. Maik Finze 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(14):3560-3574
High-yield syntheses up to molar scales for salts of [BH(CN)3]− ( 2 ) and [BH2(CN)2]− ( 3 ) starting from commercially available Na[BH4] (Na 5 ), Na[BH3(CN)] (Na 4 ), BCl3, (CH3)3SiCN, and KCN were developed. Direct conversion of Na 5 into K 2 was accomplished with (CH3)3SiCN and (CH3)3SiCl as a catalyst in an autoclave. Alternatively, Na 5 is converted into Na[BH{OC(O)R}3] (R=alkyl) that is more reactive towards (CH3)3SiCN and thus provides an easy access to salts of 2 . Some reaction intermediates were identified, for example, Na[BH(CN){OC(O)Et}2] (Na 7 b ) and Na[BH(CN)2{OC(O)Et}] (Na 8 b ). A third entry to 2 and 3 uses ether adducts of BHCl2 or BH2Cl such as the commercial 1,4-dioxane adducts that react with KCN and (CH3)3SiCN. Alkali metal salts of 2 and 3 are convenient starting materials for organic salts, especially for low viscosity ionic liquids (ILs). [EMIm] 3 has the lowest viscosity and highest conductivity with 10.2 mPa s and 32.6 mS cm−1 at 20 °C known for non-protic ILs. The ILs are thermally, chemically, and electrochemically robust. These properties are crucial for applications in electrochemical devices, for example, dye-sensitized solar cells (Grätzel cells). 相似文献
1000.