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991.
Hideaki Fujiwara Atsuomi Kimura Yasuhiro Yanagawa Takashi Kamiya Mineyuki Hattori Takashi Hiraga 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2001,150(2):156
Size dependency of the relaxation time T1 was measured for laser-polarized 129Xe gas encapsulated in different sized cavities made by glass bulbs or gelatin capsules. The use of laser-polarized gas enhances the sensitivity a great deal, making it possible to measure the longer 129Xe relaxation time in quite a short time. The size dependency is analyzed on the basis of the kinetic theory of gases and a relationship is derived in which the relaxation rate is connected with the square inverse of the diameter of the cavity. Such an analysis provides a novel parameter which denotes the wall effect on the relaxation rate when a gas molecule collides with the surface once in a second. The relaxation time of 129Xe gas is also dependent on the material which forms the cavity. This dependency is large and the relaxation study using polarized 129Xe gas is expected to offer important information about the state of the matter of the cavity wall. 相似文献
992.
N. Yasuda K. Uchikawa K. Amemiya N. Watanabe H. Takahashi M. Nakazawa M. Yamamoto K. Ogura 《Radiation measurements》2001,34(1-6):45-49
As a frame work of the study for the latent track size measurement using atomic force microscope, we have measured the minute etch pits and the extremely small amount of bulk etch of CR-39 at the beginning of chemical etching, and obtained its growth curves in nanometer dimensions. The pieces of CR-39 were exposed to 6 MeV/nC and Fe ions with normal incidence angle and were etched in 70°C 7 N NaOH solution for 0.5,1,2,3,5 min. The diameters of latent track were estimated to be 17 nm for Fe ions and 8 nm for C ions, respectively. These values are comparable to the experimental data on the average ‘track core diameters’ that have been obtained by various experimental techniques. 相似文献
993.
消光系统在光脉动法颗粒粒径测量技术中是一个十分重要的物理量,但现有的消光系数处理方法有许多不完善的地方。本文用分段最小二乘法拟合消光系数曲线,给出相应的分段表达式。该方法简化了消光系统的计算过程,能够满足工程测量的精度要求,有助于光脉动法在线测量的实现。 相似文献
994.
RAJ P. Singh 《Journal of Electronic Materials》2001,30(12):1584-1594
The particle size, surface area, morphology, and purity of tantalum pentoxide are critical for some of its applications in
the manufacture of several, electronic products. Although the purity of different grades of Ta2O5, such as standard technical grade, carbide grade, and optical grade, have been well documented, there is no report on the
morphology and other surface characteristics of Ta2O5 powders. The objective of this paper is to review various methods and recent developments in the processing of tantalum oxide
powders. The other objective of this paper is to report on the morphology, particle size, and surface area of tantalum oxide
obtained from different methods of preparation. The work reported in this paper will be useful for researchers involved in
the development of tantalum-related electronic materials. 相似文献
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非平衡晶化控制水滑石晶粒尺寸 总被引:13,自引:0,他引:13
本文采用非平衡晶化法通过在晶化后期补加原料合成了一系列不同晶粒尺寸的水滑石(LDH)样品,研究表明:非平衡晶化法可在一定范围内调控LDH的粒径,所合成的LDH样品组成稳定,晶体结构完整。 相似文献
1000.
A Capacity Analysis for the IEEE 802.11 MAC Protocol 总被引:28,自引:0,他引:28
The IEEE 802.11 MAC protocol provides shared access to a wireless channel. This paper uses an analytic model to study the channel capacity – i.e., maximum throughput – when using the basic access (two-way handshaking) method in this protocol. It provides closed-form approximations for the probability of collision p, the maximum throughput S and the limit on the number of stations in a wireless cell.The analysis also shows that: p does not depend on the packet length, the latency in crossing the MAC and physical layers, the acknowledgment timeout, the interframe spaces and the slot size; p and S (and other performance measures) depend on the minimum window size W and the number of stations n only through a gap g=W/(n–1) – consequently, halving W is like doubling n; the maximum contention window size has minimal effect on p and S; the choice of W that maximizes S is proportional to the square root of the packet length; S is maximum when transmission rate (including collisions) equals the reciprocal of transmission time, and this happens when channel wastage due to collisions balances idle bandwidth caused by backoffs.The results suggest guidelines on when and how W can be adjusted to suit measured traffic, thus making the protocol adaptive. 相似文献