全文获取类型
收费全文 | 18973篇 |
免费 | 1612篇 |
国内免费 | 1528篇 |
专业分类
化学 | 5429篇 |
晶体学 | 90篇 |
力学 | 1412篇 |
综合类 | 491篇 |
数学 | 9035篇 |
物理学 | 5656篇 |
出版年
2023年 | 154篇 |
2022年 | 297篇 |
2021年 | 358篇 |
2020年 | 369篇 |
2019年 | 445篇 |
2018年 | 377篇 |
2017年 | 436篇 |
2016年 | 490篇 |
2015年 | 386篇 |
2014年 | 693篇 |
2013年 | 1081篇 |
2012年 | 733篇 |
2011年 | 940篇 |
2010年 | 994篇 |
2009年 | 1235篇 |
2008年 | 1177篇 |
2007年 | 1184篇 |
2006年 | 1102篇 |
2005年 | 883篇 |
2004年 | 746篇 |
2003年 | 736篇 |
2002年 | 691篇 |
2001年 | 591篇 |
2000年 | 549篇 |
1999年 | 498篇 |
1998年 | 435篇 |
1997年 | 356篇 |
1996年 | 323篇 |
1995年 | 245篇 |
1994年 | 217篇 |
1993年 | 171篇 |
1992年 | 186篇 |
1991年 | 124篇 |
1990年 | 107篇 |
1989年 | 97篇 |
1988年 | 79篇 |
1987年 | 79篇 |
1985年 | 466篇 |
1984年 | 326篇 |
1983年 | 258篇 |
1982年 | 244篇 |
1981年 | 177篇 |
1980年 | 155篇 |
1979年 | 171篇 |
1978年 | 103篇 |
1977年 | 107篇 |
1976年 | 99篇 |
1975年 | 97篇 |
1974年 | 129篇 |
1973年 | 137篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
53.
Summary The meaning of linear absorbing boundary conditions for periodic water waves in elliptical approaches is discussed. It is
found that the direction of propagation of the waves must be known for reliable boundary conditions and that the energy dissipation
of waves running parallel to a boundary in general cannot be modelled in the framework of a linear theory.
Work presented at the Euromech Colloquium 240 on ?Dispersive waves in dissipative fluids?, Bologna, August 30–September 2,
1988. 相似文献
54.
Summary We have estimated and measured the daily thermal expansion of an oceanographic platform. This has been found negligible as
far as the calibration of a satellite altimeter is concerned. 相似文献
55.
Kayll Lake 《General Relativity and Gravitation》2004,36(5):1159-1169
The norms associated with the gradients of the two non-differential invariants of the Kerr vacuum are examined. Whereas both locally single out the horizons, their global behavior is more interesting. Both reflect the background angular momentum as the volume of space allowing a timelike gradient decreases with increasing angular momentum becoming zero in the degenerate and naked cases. These results extend directly to the Kerr-Newman geometry. 相似文献
56.
Based on the beam coherence-polarization (BCP) matrix, the polarization property of coherent and incoherent Gaussian beam combinations is studied in detail. The general expressions for the degree of polarization P of the resulting beam in case of incoherent and coherent combinations are derived. It is shown that P is dependent on the incoherent or coherent combination, propagation distance, separation, azimuth of the polarization plane and numbers of beamlets in general. The irradiance distribution of the resulting beam for the coherent cases depends on the azimuth of the polarization plane of beamlets. However, for the incoherent case it does not. 相似文献
57.
58.
V. S. Gorelik P. P. Sverbil' A. B. Fadyushin V. V. Vasil'ev 《Journal of Russian Laser Research》2004,25(1):54-63
A possibility of application of semiconductor lasers of the visible range as exciting sources for Raman spectroscopy is studied. An experimental set-up for measuring Raman spectra of polycrystalline dielectrics and broad-gap semiconductors excited by a semiconductor laser with a wavelength of 640 nm was created. The conditions under which the spectral width of the lasing line of a semiconductor laser was within 10-3 cm-1 in the continuous mode with a power of 10 mW are realized. The characteristics of various types of exciting sources used in Raman spectroscopy are compared. The results of studies of the characteristic Raman spectra excited with a semiconductor laser in polycrystalline sulfur are presented. 相似文献
59.
Yuri M. Boiko Anders Bach Jørgen Lyngaae-Jørgensen 《Journal of Polymer Science.Polymer Physics》2004,42(10):1861-1867
Films of amorphous polystyrene (PS) with a weight-average molecular weight (Mw) of 225 × 103 g/mol were bonded in a T-peel test geometry, and the fracture energy (G) of a PS/PS interface was measured at the ambient temperature as a function of the healing time (th) and healing temperature (Th). G was found to develop with (th)1/2 at Th = Tg-bulk − 33 °C (where Tg-bulk is the glass-transition temperature of the bulk sample), and log G was found to develop with 1/Th at Tg-bulk − 43 °C ≤ Th ≤ Tg-bulk − 23 °C. The smallest measured value of G = 1.4 J/m2 was at least one order of magnitude larger than the work of adhesion required to reversibly separate the PS surfaces. These three observations indicated that the development of G at the PS/PS interface in the temperature range investigated (<Tg-bulk) was controlled by the diffusion of chain segments feasible above the glass-transition temperature of the interfacial layer, in agreement with our previous findings for fracture stress development at several polymer/polymer interfaces well below Tg-bulk. Close values of G = 8–9 J/m2 were measured for the symmetric interfaces of polydisperse PS [Mw = 225 × 103, weight-average molecular weight/number-average molecular weight (Mw/Mn) = 3] and monodisperse PS (Mw = 200 × 103, Mw/Mn = 1.04) after healing at Th = Tg-bulk − 33 °C for 24 h. This implies that the self-bonding of high-molecular-weight PS at such relatively low temperatures is not governed by polydispersity. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1861–1867, 2004 相似文献
60.
K. P. O. Mahesh M. Sivakumar Y. Yamamoto Y. Tsujita H. Yoshimizu S. Okamoto 《Journal of Polymer Science.Polymer Physics》2004,42(18):3439-3446
A crystalline δ form of a syndiotactic polystyrene (sPS) membrane was prepared from a solution of sPS (1 wt %) and p‐chlorotoluene (p‐CT) by a solution‐casting method. The mesophase (δ empty form) of sPS was obtained by the extraction of the guest solvent from the δ form of sPS by a stepwise solvent‐extraction method. The sPS/p‐CT mesophase membrane [p‐CT (A‐M)] was used for the sorption of 1 mol % p‐CT for different times and for the sorption of different concentrations of p‐CT, chlorobenzene (CB), p‐xylene (p‐X), toluene, and chloroform for 48 h. The presence of solvents in the sPS membrane was confirmed by IR analysis. A thermal study revealed that the sorption amount of 1 mol % p‐CT increased with increasing immersion time, and the sorption amounts of different solvents increased with increasing solvent concentration. Differential scanning calorimetry results showed that the desorption peak temperature increased as the amount of the solvent increased in the clathrated sPS membrane. Wide‐angle X‐ray diffraction results showed that 2θ at 8.25° was slightly shifted toward 8°, and there was no change in the peak position at 10° for p‐CT (A‐M), which was immersed in different solvents (1 mol %); however, the intensity of 2θ at 10° was not similar for all the samples. Among the solvents used for the sorption studies at 1 mol %, p‐CT (A‐M) could sorb more p‐CT and CB than p‐X, toluene, and chloroform. The solvent sorption isotherm was the Langmuir sorption mechanism. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3439–3446, 2004 相似文献