全文获取类型
收费全文 | 1300篇 |
免费 | 45篇 |
国内免费 | 3篇 |
专业分类
化学 | 877篇 |
晶体学 | 24篇 |
力学 | 20篇 |
数学 | 49篇 |
物理学 | 378篇 |
出版年
2021年 | 7篇 |
2020年 | 8篇 |
2019年 | 13篇 |
2018年 | 11篇 |
2017年 | 7篇 |
2016年 | 19篇 |
2015年 | 24篇 |
2014年 | 27篇 |
2013年 | 64篇 |
2012年 | 64篇 |
2011年 | 50篇 |
2010年 | 36篇 |
2009年 | 43篇 |
2008年 | 69篇 |
2007年 | 84篇 |
2006年 | 65篇 |
2005年 | 69篇 |
2004年 | 82篇 |
2003年 | 52篇 |
2002年 | 51篇 |
2001年 | 38篇 |
2000年 | 40篇 |
1999年 | 23篇 |
1998年 | 13篇 |
1997年 | 14篇 |
1996年 | 19篇 |
1995年 | 22篇 |
1994年 | 19篇 |
1993年 | 17篇 |
1992年 | 17篇 |
1991年 | 12篇 |
1990年 | 13篇 |
1989年 | 11篇 |
1988年 | 18篇 |
1987年 | 12篇 |
1986年 | 17篇 |
1985年 | 28篇 |
1984年 | 24篇 |
1983年 | 8篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 12篇 |
1979年 | 16篇 |
1978年 | 9篇 |
1977年 | 13篇 |
1976年 | 5篇 |
1975年 | 13篇 |
1974年 | 8篇 |
1972年 | 8篇 |
1966年 | 4篇 |
排序方式: 共有1348条查询结果,搜索用时 15 毫秒
151.
152.
This paper introduces an elasto-plastic joint element characterised by strain hardening and softening in the analysis of dynamic
soil-structure interaction. The phenomena of separation and sliding on the contact surface between soil and structure can
be better simulated and the process can also be described. The interaction problems in a typical soil-structure system are
analyzed in terms of elasto-plastic joint element as well as elastic ones. The results show that the elasto-plastic joint
element is much better than the elastic one in modelling, especially in that the relative displacements accross the joint
element can be much greater than that of the elastic case. Separation and sliding are not only related to the coefficient
of friction and cohesion but also to their changes with plastic volumetric strain.
The project is supported by the Sciences Foundation of the Chinese Academy of Sciences and the Disaster Provention Institute
of Kyoto University (Japan). 相似文献
153.
Paulo H. P. Macaúbas Hideo Kawamoto Masaoki Takahashi Kenzo Okamoto Toshikazu Takigawa 《Rheologica Acta》2007,46(7):921-932
Shape recovery of a droplet of liquid crystalline polymer (LCP) hydroxypropylcellulose in a matrix of poly(dimethyl siloxane) subjected to a step shear strain has been studied via optical microscopy. Just after application of a large strain, the LCP droplet shape is flat ellipsoid, and then the droplet takes cylindrical shape and band texture perpendicular to the flow direction appears. The band texture fades away before emergence of poly-domain structure. In the final process with the shape of spheroid, poly-domain structure recovers very slowly. Except for the final process, the shape change is identical with that of isotropic droplet at strains smaller than 3, when the LCP viscosity in Region II is taken as an equivalent viscosity for normalization. For a 20:80 blend, the excess relaxation modulus is calculated based on the Doi-Ohta theory, taking account of the distribution of droplet size and compared with experimental modulus data. 相似文献
154.
155.
Dr. Akihiro Takada Hiroaki Fujiwara Dr. Kenji Sugimoto Dr. Hirofumi Ueda Prof. Dr. Hidetoshi Tokuyama 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(46):16400-16403
The total synthesis of (?)‐isoschizogamine was accomplished, featuring the construction of the quaternary carbon center by the modified Johnson–Claisen rearrangement in basic media and the facile assembly of the key tetracyclic quinolone intermediate through a cascade cyclization. The characteristic cyclic aminal was constructed by late‐stage C?H functionalization at the position adjacent to the lactam nitrogen using a combination of CrO3 and nBu4NIO4 and subsequent Bi(OTf)3‐mediated cyclization. 相似文献
156.
The transient recoverable deformation ratio after melt elongation at various elongational rates and maximum elongations was
investigated for pure polystyrene and for a 85 wt.% polystyrene/15 wt.% linear low density polyethylene (PS/LLDPE 85:15) blend
at a temperature of 170 oC. The ratio p of the zero shear rate viscosity of LLDPE to that of PS is p = 0.059 ≈ 1:17. Retraction of the elongated LLDPE droplets back to spheres and end-pinching is observed during recovery.
A simple additive rule is applied in order to extract the contribution of the recovery of the elongated droplets from the
total recovery of the blend. In that way, the recoverable portion of the PS/LLDPE blend induced by the interfacial tension
is determined and compared with the results of a theory based on an effective medium approximation. The effective medium approximation
reproduces well the time scale of the experimental data. In addition, the trends that the recoverable deformation increases
with elongational rate and maximum elongation are captured by the theoretical approach. 相似文献
157.
Radiation emitted from the shock layer generated around a hypersonic flight model is experimentally investigated by using a ballistic range (two-stage light-gas gun). A polyethylene projectile of 1.2 cm in diameter is launched in this facility at the velocity of 5 km/sec (M=15), and the emission from the induced shock layer around the projectile is observed with a spectroscope. As a result, molecular band-spectra from NO and N2 are detected along with those from carboncontaining molecules. Total emission power is measured with a diode-type powermeter. In addition, dimension effect of the flight model is theoretically and numerically examined, and a scaling law on thermochemical structure of the shock layer is developed. It shows that the thickness of thermal boundary-layer formed on the model surface does not follow the conventional scaling law based on the reaction distance and on the energy relaxation distance. Finally, the radiative field around the projectile is numerically computed, and the total power emitted from the shock layer is estimated. From the comparison between computed and measured results, the validity of the calculation model is discussed. 相似文献
158.
Summary When a d.c. and a h.f. field are perpendicularly superposed in a electrical discharge (p 10–10–4 mm Hg), three types of discharge can exist, classified from the standpoint of d.c. conduction: (1) d.c. glow type, d.c.-dominant discharge with additional ionization by h.f. field; (2) space chargelimited type, the same as the conduction in the floating double probe in a plasma produced by h.f. field; (3) an intermediate stage between the first and second types, herein referred to as transition type. According to our analysis of the transition type at low pressure, the value of in high electric fields can be deduced from the measurement. 相似文献
159.
Rapid detection of trace level anabolic steroids in urine is highly desirable to monitor the consumption of performance enhancing anabolic steroids by athletes. The present article describes a novel strategy for identifying the trace anabolic steroids in urine using Leidenfrost phenomenon assisted thermal desorption (LPTD) coupled to dielectric barrier discharge (DBD) ionization mass spectrometry. Using this method the steroid molecules are enriched within a liquid droplet during the thermal desorption process and desorbed all-together at the last moment of droplet evaporation in a short time domain. The desorbed molecules were ionized using a dielectric barrier discharge ion-source in front of the mass spectrometer inlet at open atmosphere. This process facilitates the sensitivity enhancement with several orders of magnitude compared to the thermal desorption at a lower temperature. The limits of detection (LODs) of various steroid molecules were found to be in the range of 0.05–0.1 ng mL−1 for standard solutions and around two orders of magnitude higher for synthetic urine samples. The detection limits of urinary anabolic steroids could be lowered by using a simple and rapid dichloromethane extraction technique. The analytical figures of merit of this technique were evaluated at open atmosphere using suitable internal standards. The technique is simple and rapid for high sensitivity and high throughput screening of anabolic steroids in urine. 相似文献
160.
Atsushi TakemuraYasushi Katagiri Kenshu Fujiwara Hidetoshi Kawai Takanori Suzuki 《Tetrahedron letters》2011,52(11):1222-1224
The synthesis of the C22-C37 segment of prorocentin, isolated from the dinoflagellate Prorocentrum lima, was achieved. Because the relative stereochemical relationship between C26 and other stereocenters (C28/C31/C32 established as R*/R*/R*) in the C22-C37 region of natural prorocentin has not yet been determined, both epimers at C26 of the C22-C37 segment were selectively constructed. The synthesis was based on a 5-exo epoxide ring opening reaction to form an oxolane (E-ring), Brown asymmetric methallylation to install the C26-stereocenter, acryloylation of the resulting alcohol, and ring-closing olefin metathesis to establish the Z-olefin at C23/C24. 相似文献