全文获取类型
收费全文 | 511650篇 |
免费 | 3185篇 |
国内免费 | 939篇 |
专业分类
化学 | 240803篇 |
晶体学 | 7295篇 |
力学 | 28417篇 |
综合类 | 9篇 |
数学 | 79272篇 |
物理学 | 159978篇 |
出版年
2020年 | 4531篇 |
2019年 | 5397篇 |
2018年 | 12527篇 |
2017年 | 12919篇 |
2016年 | 12653篇 |
2015年 | 5508篇 |
2014年 | 9201篇 |
2013年 | 18909篇 |
2012年 | 17520篇 |
2011年 | 25113篇 |
2010年 | 17828篇 |
2009年 | 18094篇 |
2008年 | 23371篇 |
2007年 | 25515篇 |
2006年 | 15564篇 |
2005年 | 16859篇 |
2004年 | 14383篇 |
2003年 | 13842篇 |
2002年 | 12870篇 |
2001年 | 12066篇 |
2000年 | 9836篇 |
1999年 | 7174篇 |
1998年 | 6505篇 |
1997年 | 6413篇 |
1996年 | 6068篇 |
1995年 | 5211篇 |
1994年 | 5323篇 |
1993年 | 5312篇 |
1992年 | 5493篇 |
1991年 | 5883篇 |
1990年 | 5755篇 |
1989年 | 5788篇 |
1988年 | 5500篇 |
1987年 | 5517篇 |
1986年 | 5224篇 |
1985年 | 6372篇 |
1984年 | 6739篇 |
1983年 | 5621篇 |
1982年 | 6017篇 |
1981年 | 5602篇 |
1980年 | 5243篇 |
1979年 | 5867篇 |
1978年 | 6122篇 |
1977年 | 6171篇 |
1976年 | 6250篇 |
1975年 | 5861篇 |
1974年 | 5726篇 |
1973年 | 6046篇 |
1972年 | 4655篇 |
1971年 | 4175篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
The microwave subsidiary absorption threshold in tangentially magnetized yttrium-iron-garnet (YIG) films was measured as a function of the static magnetic field, film thickness and decrease in the 0.3–3 μm range is observed. The effect is explained quantitatively by using modified Damon-Eshbach dispersion relations which take into account exchange interactions.
The effect of temperature on hcrit, the smallest threshold field amplitude, in the 250<T< 450 K temperature range can be expressed by an empirical relationship hcrit Ms(T)-1.6 where Ms is the saturation magnetization. This hcrit vs Ms relationship is similar to that obtained for the magnetization dependence of parallel pump thresholds in Li-Ti ferrite compounds. 相似文献
972.
973.
Ulenikov O. N. Tolchenov R. N. Melekhina E. N. Koivusaari M. Alanko S. Anttila R. 《Journal of Molecular Spectroscopy》1995,170(2)
High resolution Fourier transform spectra of deuterated hydrogen sulfide have been recorded in the region 2400-3000 cm−1. Rotational structures of the ν1 + ν2, ν2 + ν3 bands of D232S, of the ν3 and ν1 + ν2 bands of HD32S, and of the ν1 + ν2 band of HD34S were analyzed. Band centers and rotational, centrifugal distortion, and resonance parameters were obtained, which reproduce the initial values of the upper energy levels within a mean accuracy of 1.39 × 10−4 cm−1 for the states (110) and (011) of D232S, 1.61 × 10−4 cm−1 and 1.82 × 10−4 cm−1 for the states (001) and (110) of HD32S, and 2.09 × 10−4 cm−1 for the state (110) of HD34S, respectively. 相似文献
974.
V. S. Kirilyuk 《Journal of Mathematical Sciences》1995,77(6):3486-3488
We consider an elastic isotropic material containing a fibrous inclusion or a void subject to loads. We study the possibility
of increasing the strength of the material using “control action.” As examples of such actions we consider an additional external
load, application of pressure in the cavities (voids), and variation of the temperature of uniform heating of the medium with
the inclusions. Studies are carried out for two-dimensional problems of linear elasticity theory. From the class of all possible
actions we single out a subclass leading to states of equal strength along the phase interface. We study the efficiency of
these types of action and show that in certain cases they lead to a manifold increase in the strength of the material. We
give the results of numerical studies.
Translated fromTeoreticheskaya i Prikladnaya Mekhanika, No. 24, 1993, pp. 15–19. 相似文献
975.
Zhai X. Garate E. Prohaska R. Benford G. Fisher A. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1993,21(1):142-150
Experimental studies of a plasma-filled X -band backward-wave oscillator (BWO) are presented. Depending on the background gas pressure, microwave frequency upshifts of up to 1 GHz appeared along with an enhancement by a factor of 7 in the total microwave power emission. The bandwidth of the microwave emission increased from ⩽0.5 GHz to 2 GHz when the BWO was working at the RF power enhancement pressure region. The RF power enhancement appeared over a much wider pressure range in a high beam current case (10-100 mT for 3 kA) than in a lower beam case (80-115 mT for 1.6 kA). The plasma-filled BWO has higher power output than the vacuum BWO over a broader region of magnetic guide field strength. Trivelpiece-Gould modes (T-G modes) are observed with frequencies up to the background plasma frequency in a plasma-filled BWO. Mode competition between the T-G modes and the X -band Tm01 mode prevailed when the background plasma density was below 6×1011 cm-3 . At a critical background plasma density of ≃8×1011 cm-3 power enhancement appeared in both X -band and the T-G modes. Power enhancement of the S -band in this mode collaboration region reached up to 8 dB. Electric fields measured by the Stark-effect method were as high as 34 kV/cm while the BWO power level was 80 MW. These electric fields lasted throughout the high-power microwave pulse 相似文献
976.
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, No. 4, pp. 108–112, July–August, 1993. 相似文献
977.
978.
V. O. Kur'yanov T. F. Zhelobetskaya A. E. Zemlyakov V. Ya. Chirva 《Chemistry of Natural Compounds》1993,29(1):103-106
The synthesis has been effected of derivatives of MDP having a spacer with an amino or carboxy group. The final stage of the synthesis was the condensation of Boc-L-Ala-D-iGln with 6-aminohexanol (followed by the two-stage replacement of the hydroxy by an azido group) or with benzyl 6-aminohexanoate.Simferopol' State University. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 122–125, January–February, 1993. 相似文献
979.
A PULSED LASER AND PULSE RADIOLYSIS STUDY OF AMPHIPHILIC CHLOROPHYLL DERIVATIVES WITH PDT ACTIVITY TOWARD MALIGNANT MELANOMA 总被引:1,自引:0,他引:1
L. Fiedor A. A. Gorman I. Hamblett V. Rosenbach-Belkin Y. Salomon A. Scherz I. Tregub 《Photochemistry and photobiology》1993,58(4):506-511
Two amphiphilic derivatives of chlorophyll, which have high potential as photodynamic therapy sensitizers for malignant melanoma have been investigated by a combination of laser flash photolysis and pulse radiolysis. It is shown that direct excitation of monomeric forms of these molecules in both hydrophilic and hydrophobic environments produces significant yields of the corresponding triplet states, which have been characterized in terms of spectral and kinetic parameters. In both environments, scavenging of the triplets by oxygen produces singlet oxygen, O2 (l Δ8 ), with essentially unit efficiency as evidenced by time-resolved IR luminescence measurements. 相似文献
980.
O. A. Rakitin E. A. Khaibullina T. I. Godovikova V. A. Ogurtsov L. I. Khimel'nitskii 《Chemistry of Heterocyclic Compounds》1993,29(8):952-954
Previously unreported furoxanenitrolic acids have been synthesized.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1117–1119, August, 1993. 相似文献