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排序方式: 共有991条查询结果,搜索用时 15 毫秒
101.
102.
S. A. Dodds T. L. Estle G. A. Gist Qiuan Zhu S. L. Rudaz D. P. Spencer E. J. Ansaldo J. H. Brewer D. R. Noakes R. Keitel 《Hyperfine Interactions》1986,32(1-4):869-872
Magnetic resonance of a spin system which is acted upon by a large near-resonance oscillating magnetic field transverse to
a static field has been studied experimentally and theoretically for many years. The technique of DEMUR (Double Electron Muon
Resonance) has many advantages for such studies. This paper will describe the results of an experiment to study the precession
of the muonium triplet near magnetic resonance using DEMUR. 相似文献
103.
104.
105.
Spencer P. Kuo 《Shock Waves》2007,17(4):225-239
Two types of plasma spikes, generated by on-board 60 Hz periodic and pulsed dc electric discharges in front of two slightly
different wind tunnel models, were used to demonstrate the non-thermal plasma techniques for shock wave mitigation. The experiments
were conducted in a Mach 2.5 wind tunnel. (1) In the periodic discharge case, the results show a transformation of the shock
from a well-defined attached shock into a highly curved shock structure, which has increased shock angle and also appears
in diffused form. As shown in a sequence with increasing discharge intensity, the shock in front of the model moves upstream
to become detached with increasing standoff distance from the model and is eliminated near the peak of the discharge. The
power measurements exclude the heating effect as a possible cause of the observed shock wave modification. A theory using
a cone model as the shock wave generator is presented to explain the observed plasma effect on shock wave. The analysis shows
that the plasma generated in front of the model can effectively deflect the incoming flow; such a flow deflection modifies
the structure of the shock wave generated by the cone model, as shown by the numerical results, from a conic shape to a curved
one. The shock front moves upstream with a larger shock angle, matching well with that observed in the experiment. (2) In
the pulsed dc discharge case, hollow cone-shaped plasma that envelops the physical spike of a truncated cone model is produced
in the discharge; consequently, the original bow shock is modified to a conical shock, equivalent to reinstating the model
into a perfect cone and to increase the body aspect ratio by 70%. A significant wave drag reduction in each discharge is inferred
from the pressure measurements; at the discharge maximum, the pressure on the frontal surface of the body decreases by more
than 30%, the pressure on the cone surface increases by about 5%, whereas the pressure on the cylinder surface remains unchanged.
The energy saving from drag reduction is estimated to make up two-thirds of the energy consumed in the electric discharge
for the plasma generation. The measurements also show that the plasma effect on the shock structure lasts much longer than
the discharge period.
相似文献
相似文献
106.
Synthesis of an [(NHC)2Pd(SiMe3)2] Complex and Catalytic cis‐Bis(silyl)ations of Alkynes with Unactivated Disilanes 下载免费PDF全文
Melvyn B. Ansell Dr. Debbie E. Roberts Prof. F. Geoffrey N. Cloke Dr. Oscar Navarro Dr. John Spencer 《Angewandte Chemie (International ed. in English)》2015,54(19):5578-5582
The novel complex cis‐[(ITMe)2Pd(SiMe3)2 (ITMe=1,3,4,5‐tetramethylimidazol‐2‐ylidene) has been synthesized by mild oxidative cleavage of Me3SiSiMe3 using [(ITMe)2Pd0]. The use of this complex as precatalyst for the cis‐bis(silyl)ation of alkynes using unactivated disilanes is reported. 相似文献
107.
Computational studies of the interaction of 1,1-dimethylallyl cation with benzene reveal that its potential energy surface has a rich complexity. The lowest energy π-complex, which involves binding of both ends of the cation to the benzene ring, is calculated to be 4.5 kcal mol−1 lower in energy than its related σ-complex. The results provide further support for the idea that π complexation of carbocations is stronger over the periphery of aromatic systems, and offer insight into why biological reactions involving this type of carbocation do not lead via σ-complex formation to electrophilic substitution of the aromatic rings in proteins. 相似文献
108.
John Spencer Hiren PatelSamantha K. Callear Simon J. ColesJohn J. Deadman 《Tetrahedron letters》2011,52(45):5905-5909
A library of pyridines and pyrimidines has been synthesised in excellent yields employing microwave and flow chemistry methodologies. Work-up bottlenecks have been facilitated substantially by the use of supported reagents and many of the final compounds have been studied in the solid state by single crystal X-ray diffraction. 相似文献
109.
110.
Kuemin C Stutz R Spencer ND Wolf H 《Langmuir : the ACS journal of surfaces and colloids》2011,27(10):6305-6310
Capillary assembly was explored for the precise placement of 25 nm × 70 nm colloidal gold nanorods on prestructured poly(dimethylsiloxane) template surfaces. The concentration of nanorods and cationic surfactant cetyltrimethylammonium bromide (CTAB), the template wettability, and most critically the convective transport of the dispersed nanorods were tuned to study their effect on the resulting assembly yield. It is shown that gold nanorods can be placed into arrayed 120-nm diameter holes, achieving assembly yields as high as 95% when the local concentration of nanorods at the receding contact line is sufficiently high. Regular arrays of gold nanorods have several benefits over randomly deposited nanorod arrangements. Each assembled nanorod resides at a precisely defined location and can easily be found for subsequent characterization or direct utilization in a device. The former is illustrated by collecting scattering spectra from single nanorods and nanorod dimers, followed by subsequent SEM characterization without the need for intricate registration schemes. 相似文献