全文获取类型
收费全文 | 2684篇 |
免费 | 432篇 |
国内免费 | 158篇 |
专业分类
化学 | 371篇 |
晶体学 | 10篇 |
力学 | 1112篇 |
综合类 | 23篇 |
数学 | 155篇 |
物理学 | 1603篇 |
出版年
2024年 | 4篇 |
2023年 | 19篇 |
2022年 | 47篇 |
2021年 | 55篇 |
2020年 | 65篇 |
2019年 | 69篇 |
2018年 | 67篇 |
2017年 | 62篇 |
2016年 | 99篇 |
2015年 | 80篇 |
2014年 | 126篇 |
2013年 | 184篇 |
2012年 | 156篇 |
2011年 | 205篇 |
2010年 | 129篇 |
2009年 | 184篇 |
2008年 | 135篇 |
2007年 | 161篇 |
2006年 | 155篇 |
2005年 | 142篇 |
2004年 | 129篇 |
2003年 | 113篇 |
2002年 | 124篇 |
2001年 | 88篇 |
2000年 | 92篇 |
1999年 | 79篇 |
1998年 | 59篇 |
1997年 | 66篇 |
1996年 | 36篇 |
1995年 | 46篇 |
1994年 | 57篇 |
1993年 | 50篇 |
1992年 | 37篇 |
1991年 | 30篇 |
1990年 | 31篇 |
1989年 | 19篇 |
1988年 | 18篇 |
1987年 | 8篇 |
1986年 | 10篇 |
1985年 | 10篇 |
1984年 | 10篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有3274条查询结果,搜索用时 15 毫秒
101.
102.
根据气体幼力学中一维定常等熵等流的基本方程组,得出的一维定常等熵管流的速度变化与管截面变化关系式,定性一讨论了一维定常等熵管流的截面变化对气流速度的影响。 相似文献
103.
This paper describes some of the aspects necessary for the design and use of tube chain conveyors. It is based on the reports of experienced experts and recent tube chain conveyor experimental results. The aim of the research work is the formulation of general technical regulations for tube chain conveyors. Theoretical models were developed, which allow the calculation of the motion resistances in all parts of the conveyor by the use of empirical extracted correction factors. Specially designed measurement equipment enabled the measurement of the important chain tractive force from the closed tube system. The measurements show the influence of the major operational parameters and the bulk solid properties. 相似文献
104.
Jakob J. Keller 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1996,47(6):821-836
Introducing a vector potential, that is based on a pair of stream functions, and a velocity potential, antisymmetric equations for the stream functions are derived with the help of a variational principle. It is found that the equations are in a suitable form to investigate flows with helical symmetry, and, for example, to connect upstream axisymmetric flows with downstream helical flows. The special case of a transition from an upstream solid-body vortex to a downstream helical flow is investigated in detail. Furthermore, the stream-function equations are particularly useful to investigate general small-amplitude inertia waves on vortex flows. Time-dependent helical flows that are time-independent in a suitably rotating frame of reference can also be discussed with the proposed method. 相似文献
105.
R. J. Emrich 《Shock Waves》1996,5(6):327-339
Recollections of activities in the Physics Department of Princeton University leading to the construction and use of the SHOCK
TUBE are recorded. Walker Bleakney was the leader of these activities from 1940 to 1979, and his methods and attitude are
described. Original interferograms made at Princeton show some results obtained. 相似文献
106.
107.
团簇结构测量是团簇科学研究中的一个重要课题。文章对近几年发展的注入离子漂移管技术进行了详细介绍与分析,该技术是上前测量团簇结构近似程度最高的技术,已在C,Si,Ge及Al等原子团簇的结构研究中获得广泛应用,并取得了许多重要结果。 相似文献
108.
de Swiet TM 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2005,174(2):331-334
For many applications, reducing sample resistance, rather than increasing probe Q or filling factor, is the only way to further improve the signal-to-noise ratio of cryogenically cooled NMR probes. In this paper, bounds are calculated for the minimum sample resistance that can be achieved for various sample geometries. The sample resistance of 100 mM NaCl in H(2)O in 5 mm sample tubes was measured on a 600 MHz cold probe to be within 14% of the optimum value. The minimum sample resistance can however be lowered by altering the tube cross section. Rectangular tubes oriented with the long axis along the RF magnetic field are particularly favourable. 相似文献
109.
We describe the construction and operation of a variable temperature (VT) system for a high field fast magic angle spinning (MAS) probe. The probe is used in NMR investigations of biological macromolecules, where stable setting and continuous measurement of the temperature over periods of several days are required in order to prevent sample overheating and degradation. The VT system described is used at and below room temperature. A vortex tube is used to provide cooling in the temperature range of -20 to 20 degrees C, while a liquid nitrogen-cooled heat exchanger is used below -20 degrees C. Using this arrangement, the lowest temperature that is practically achievable is -140 degrees C. Measurement of the air temperature near the spinning rotor is accomplished using a fiber optic thermometer that utilizes the temperature dependence of the absorption edge of GaAs. The absorption edge of GaAs also has a magnetic field dependence that we have measured and corrected for. This dependence was calibrated at several field strengths using the well-known temperature dependence of the (1)H chemical shift difference of the protons in methanol. 相似文献
110.
This paper describes an acoustic method for inducing rotating vortex flows in microchannels. An ultrasonic crystal is used to create an acoustic standing wave field in the channel and thus induce a Rayleigh flow transverse to the laminar flow in the channel. Mixing in microchannels is strictly diffusion-limited because of the laminar flow, a transverse flow will greatly enhance mixing of the reactants. This is especially evident in chemical microsystems in which the chemical reaction is performed on a solid phase and only one reactant is actually diffusing. The method has been evaluated on two different systems, a mixing channel with two parallel flows and a porous silicon micro enzyme reactor for protein digestion. In both systems a significant increase of the mixing ratio is detected in a narrow band of frequency for the actuating ultrasound. 相似文献