全文获取类型
收费全文 | 1541篇 |
免费 | 288篇 |
国内免费 | 119篇 |
专业分类
化学 | 1186篇 |
晶体学 | 14篇 |
力学 | 85篇 |
综合类 | 3篇 |
数学 | 109篇 |
物理学 | 551篇 |
出版年
2024年 | 9篇 |
2023年 | 31篇 |
2022年 | 41篇 |
2021年 | 70篇 |
2020年 | 58篇 |
2019年 | 62篇 |
2018年 | 58篇 |
2017年 | 41篇 |
2016年 | 74篇 |
2015年 | 81篇 |
2014年 | 82篇 |
2013年 | 97篇 |
2012年 | 150篇 |
2011年 | 151篇 |
2010年 | 94篇 |
2009年 | 80篇 |
2008年 | 112篇 |
2007年 | 97篇 |
2006年 | 90篇 |
2005年 | 94篇 |
2004年 | 57篇 |
2003年 | 36篇 |
2002年 | 41篇 |
2001年 | 25篇 |
2000年 | 26篇 |
1999年 | 25篇 |
1998年 | 17篇 |
1997年 | 20篇 |
1996年 | 16篇 |
1995年 | 18篇 |
1994年 | 12篇 |
1993年 | 7篇 |
1992年 | 11篇 |
1991年 | 19篇 |
1990年 | 12篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 7篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 5篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1947年 | 1篇 |
1946年 | 1篇 |
排序方式: 共有1948条查询结果,搜索用时 15 毫秒
991.
Photonic crystal fibers are a new class of single-material optical fibers with wavelength-scale air holes running down the
entire fiber length. Photonic crystal fibers were first developed in 1996 and have subsequently been the focus of increasing
scientific and technological interest in the field of fiber optics. The manufacturing, principles, basic properties, and some
applications of photonic crystal fibers are briefly described in this paper. A review of our recent work on the nonlinear
effects in photonic crystal fibers is presented, and special emphasis is placed on such effects as supercontinuum generation,
frequency conversion, and solitons observed when femtosecond light pulses propagate in these fibers. 相似文献
992.
Excited state absorption and stimulated emission of Nd3+ in crystals. Part 2: YVO4, GdVO4, and Sr5(PO4)3F 总被引:1,自引:0,他引:1
L. Fornasiero S. Kück T. Jensen G. Huber B.H.T. Chai 《Applied physics. B, Lasers and optics》1998,67(5):549-553
3+ ion in the crystals YVO4, GdVO4, and Sr5(PO4)3F. The measurements were performed in the spectral region of the main laser transitions 4F3/2→4I9/2, 4F3/2→4I11/2, and 4F3/2→4I13/2by a continuous wave pump and probe technique. The calibrated gain and ESA spectra are presented and possible implications
of ESA on the laser performance are estimated. It is shown that ESA can be a small loss factor to the laser emission near
1060 nm but does considerably diminish the effective emission cross sections near 1340 nm especially in Nd:YVO4 and Nd:GdVO4.
Received: 29 January 1998/Revised version: 8 May 1998 相似文献
993.
本文对新疆的十字花科9属9种杂草种子形状、大小、颜色及内部特征进行了描述,对种子外形、种皮进行电镜扫描,发现种皮微形态特征在种与种之间有明显的差异,并根据种皮微形态特征编制了分种检索表. 相似文献
994.
995.
Polymer microspheres are obtained by the dropwise addition of a precipitant, containing a polymeric stabilizer, into a polymer solution, containing a polymeric stabilizer. The polymer and stabilizer concentrations, the stirring speed, and the precipitation temperature determine the size and size uniformity of the microspheres. Seven polymer microspheres of polyimide, poly(ether imide), poly(ether ketone), poly(phenylene oxide), polysulfone, poly(vinylidene fluoride), and cellulose diacetate have been prepared with dimethylacetamide as the solvent, with water as the precipitant, and with poly(vinyl alcohol) as the stabilizer. The size and size uniformity of the obtained microspheres are d = 2.3–25.7 μm and ? = 0.15–0.50, respectively (? = σ/d, where ? is the dispersion coefficient, d is the average diameter, and σ is the standard deviation of the diameter). © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 159–165, 2003 相似文献
996.
997.
998.
beta-Hydroxypropionic acid- and hydroxyacetic acid-uroporphyrin I have been isolated from the urine of a patient with congenital erythropoietic porphyria by reversed phase high performance liquid chromatography. The compounds were characterized by their chemical behaviour and confirmed by liquid secondary ion mass spectrometry. 相似文献
999.
1000.
推导出利用embedded-atommethodEAM势表达的力学稳定性判据给出了相应的数值方法,并且提出了确定势函数的适用范围的理论判据。根据该理论肯定了A.Voter等给出的镍原子间的EAM势的可靠性,并计算了镍单晶体的力学性质。计算表明:单轴外力沿[100]方向加载在镍单晶体上,在压应力作用下,晶体结构发生转变,产生两个不稳定的新结构相bcc和bct相在张应力作用下,镍单晶发生均匀形变,当形变量达10.51%时材料断裂,相应的理论拉伸强度值为1.46×10~(11)dyn·cm~(-2)。由这些计算
关键词: 相似文献