全文获取类型
收费全文 | 23359篇 |
免费 | 4607篇 |
国内免费 | 2673篇 |
专业分类
化学 | 8807篇 |
晶体学 | 537篇 |
力学 | 2376篇 |
综合类 | 330篇 |
数学 | 2762篇 |
物理学 | 15827篇 |
出版年
2024年 | 46篇 |
2023年 | 228篇 |
2022年 | 658篇 |
2021年 | 719篇 |
2020年 | 697篇 |
2019年 | 616篇 |
2018年 | 650篇 |
2017年 | 903篇 |
2016年 | 1051篇 |
2015年 | 890篇 |
2014年 | 1259篇 |
2013年 | 1905篇 |
2012年 | 1555篇 |
2011年 | 1575篇 |
2010年 | 1423篇 |
2009年 | 1510篇 |
2008年 | 1433篇 |
2007年 | 1480篇 |
2006年 | 1418篇 |
2005年 | 1274篇 |
2004年 | 1259篇 |
2003年 | 1073篇 |
2002年 | 942篇 |
2001年 | 796篇 |
2000年 | 778篇 |
1999年 | 699篇 |
1998年 | 574篇 |
1997年 | 474篇 |
1996年 | 414篇 |
1995年 | 320篇 |
1994年 | 281篇 |
1993年 | 274篇 |
1992年 | 223篇 |
1991年 | 165篇 |
1990年 | 154篇 |
1989年 | 152篇 |
1988年 | 150篇 |
1987年 | 106篇 |
1986年 | 99篇 |
1985年 | 70篇 |
1984年 | 49篇 |
1983年 | 24篇 |
1982年 | 52篇 |
1981年 | 44篇 |
1980年 | 33篇 |
1979年 | 37篇 |
1978年 | 29篇 |
1977年 | 18篇 |
1976年 | 15篇 |
1974年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
The mechanism of X-ray waveguide-resonance propagation or the radiation superstream model, which can become the ground of X-ray nanophotonics, is discussed briefly. Some attention is devoted to features consideration of the simplest devices characterized by the waveguide-resonance transportation of X-ray beams. The experimental data showing the user possibilities of a simplest waveguide-resonators application for diffractometry are presented. We discuss the main reasons to improve the metrological characteristics for total reflection X-ray fluorescence (TXRF) analytical method in case when the target exciting beam is formed by a waveguide-resonator. Some problems appearing during the waveguide-resonator application are formulated. 相似文献
72.
The 57Fe Mössbauer effect study at 5.0 K and in an external magnetic field of 9.0 T on a high-quality stable decagonal quasicrystal Al65Co15Cu19.9Fe0.1 is presented. It is shown that the iron atoms are located in two distinct classes of sites. The values of the principal component of the electric field gradient tensor and the asymmetry parameter at these sites are, respectively, ?1.90(10)?×?1021 V/m2, 0.97(15) and ?3.95(12)?×?1021 V/m2, 0.00(17). 相似文献
73.
In this paper, the effect of cubic zinc metaborate Zn4O(BO2)6 on the sintering of MnZn-ferrites for medium frequency power applications is investigated. Zinc metaborate is synthesized in the laboratory using zinc oxide and boric acid as metal precursors. As observed, when zinc metaborate is added to the MnZn-ferrites at an optimum amount of 0.02 wt%, it significantly enhances densification and therefore allows, for a given density, reduction of the firing temperature by almost 200 °C. MnZn-ferrites exhibiting power losses of 70 mW/cm3 (measured at a frequency of 400 kHz, magnetic field 50 mT and temperature of 90 °C) are synthesized from conventionally milled powders with average particle diameter 0.6 μm, compacted and fired at 1100 °C. Identical experiments conducted under the same conditions on specimens without zinc metaborate additions revealed power losses greater than 300 mW/cm3, because of insufficient densification. 相似文献
74.
S. C. Tiwari 《Foundations of Physics Letters》2006,19(1):51-62
Advances in gauge theories and unified theories have not thrown light on the meaning of electron. The problem of the origin
of electronic charge is made precise, new insights gained from Weyl space are summarized, and the origin of charge in terms
of fractional spin is suggested. A new perspective on the abelian Chern-Simons theory is presented to explain charge. 相似文献
75.
ZnO naorods on ZnO-coated seed substrates were fabricated by solution chemical method from Zn(NO3)2/NaOH under assisted electrical field. The working mechanism of electrical field was analyzed and the factors affecting the rod growth such as potential, precursor concentration and growth temperature were elucidated. The structural and optical properties are characterized by SEM, TEM, XRD, HRTEM and UV-vis. The results indicated that the nanorods have wurtzite structure without electrical field and are primarily of zincite structure under electrical field; when the electrical field is 1.1-1.3 V, not only the elevation of ion diffusion and adsorption lower the crystallite/solution interfacial energy and then the crystal nucleation barrier by increasing charge intensity, but also the production of H+ through oxidation of OH− increases properly the degree of solution supersaturation near the substrate, and thus lowers the activation energy. Both the two processes do favor to rod growth. With increasing precursor concentration in this system, the average diameter and length of ZnO nanorods increase, leading to decreasing of optical transmittance. The maximum rod growth rate at given concentration of Zn2+ occurs at a specific temperature. 相似文献
76.
核磁共振成像一维空间编码教学实验 总被引:2,自引:2,他引:0
利用梯度磁场实现检测信号的空间编码,是核磁共振成像(MRI)的关键技术.本文采用ccc系列样品将二维问题简化为一维,使用超小型教学用核磁共振成像仪进行了一维空间编码实验研究,并对实验过程及实验结果进行了计算模拟和分析. 相似文献
77.
78.
79.
本文根据汉寿县1960─1988年洪涝灾害资料,应用加权列联表分析法,与前期气候因子建立洪涝趋势预测模式。最后对1989─1990年洪涝试报,取得了满意的效果。 相似文献
80.