全文获取类型
收费全文 | 1197篇 |
免费 | 43篇 |
国内免费 | 5篇 |
专业分类
化学 | 813篇 |
晶体学 | 5篇 |
力学 | 48篇 |
数学 | 108篇 |
物理学 | 271篇 |
出版年
2023年 | 5篇 |
2022年 | 10篇 |
2021年 | 23篇 |
2020年 | 25篇 |
2019年 | 20篇 |
2018年 | 17篇 |
2017年 | 12篇 |
2016年 | 23篇 |
2015年 | 25篇 |
2014年 | 29篇 |
2013年 | 61篇 |
2012年 | 70篇 |
2011年 | 77篇 |
2010年 | 34篇 |
2009年 | 39篇 |
2008年 | 79篇 |
2007年 | 65篇 |
2006年 | 83篇 |
2005年 | 71篇 |
2004年 | 57篇 |
2003年 | 62篇 |
2002年 | 54篇 |
2001年 | 10篇 |
2000年 | 16篇 |
1999年 | 11篇 |
1998年 | 15篇 |
1997年 | 8篇 |
1996年 | 20篇 |
1995年 | 18篇 |
1994年 | 16篇 |
1993年 | 12篇 |
1992年 | 10篇 |
1991年 | 9篇 |
1990年 | 8篇 |
1989年 | 11篇 |
1988年 | 8篇 |
1987年 | 9篇 |
1985年 | 9篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 10篇 |
1981年 | 5篇 |
1980年 | 11篇 |
1979年 | 12篇 |
1978年 | 12篇 |
1977年 | 8篇 |
1976年 | 14篇 |
1975年 | 4篇 |
1973年 | 10篇 |
1970年 | 3篇 |
排序方式: 共有1245条查询结果,搜索用时 171 毫秒
81.
82.
This paper studies the propagation of pulse-like solutions of semilinear hyperbolic equations in the limit of short wavelength. The pulses are located at a wavefront Σ?{φ=0} where φ satisfies the eikonal equation and dφ lies on a regular sheet of the characteristic variety. The approximate solutions are uεapprox=U (t, x, φ(t, x)/ε) where U(t, x, r) is a smooth function with compact support in r. When U satisfies a familiar nonlinear transport equation from geometric optics it is proved that there is a family of exact solutions uεexact such that uεapprox has relative error O(ε) as ε→0. While the transport equation is familiar, the construction of correctors and justification of the approximation are different from the analogous problems concerning the propagation of wave trains with slowly varying envelope. 相似文献
83.
Li N Tan WG Tsang RY Tyrrell DL Dovichi NJ 《Analytical and bioanalytical chemistry》2002,374(2):269-273
We report an accurate and reproducible DNA quantitation method using the polymerase chain reaction (PCR). The amount of PCR product is monitored after each PCR cycle by capillary electrophoresis. To ensure accurate quantitation, a non-amplified internal standard is added to each PCR-amplified electrophoresis sample to correct for variations in injection volume. Quantitation of the sample is based on the number of cycles necessary to generate a predetermined amount of PCR product. Duck hepatitis B virus genome was used as a model in this study. The genome was quantified with a linear relationship between cycle number and logarithm of sample DNA for amounts of sample DNA between 30 and 3.1 x 10(8) copies ( r(2)>0.999). The relative standard deviation for the corrected capillary electrophoresis signal was 2.7%, while the relative standard deviation for the overall assay was 3.0%. Results from a single-blind study generated a relative error of 1.3%. 相似文献
84.
Gao J Strässler C Tahmassebi D Kool ET 《Journal of the American Chemical Society》2002,124(39):11590-11591
We report on a new class of water-soluble fluorescent molecules (polyfluors) that are composed of multiple individual fluorophores assembled on a DNA-like backbone. Four fluorophore deoxyribosides were synthesized, and these individual molecules were assembled into oligofluor strings on a DNA synthesizer. A library of 256 tetrafluors was generated by split and pool methods on polystyrene beads. Images of the library under a fluorescence microscope revealed at least 40-50 different hues and intensities. Selected tetrafluors were resynthesized in pure form in solution and displayed properties, such as large Stokes shifts, that individual fluorophores do not have. 相似文献
85.
86.
Superior laryngeal nerve paresis and paralysis 总被引:1,自引:0,他引:1
Gürsel Dursun Robert Thayer Sataloff Joseph R. Spiegel Steven Mandel Reinhardt J. Heuer Deborah Caputo Rosen 《Journal of voice》1996,10(2):206-211
Superior laryngeal nerve paresis and paralysis are relatively common but often difficult to diagnose with certainty. They are most commonly caused by viral infections, though other etiologies must be considered. A thorough history and physical examination, including strobovideolaryngoscopy and laryngeal electromyography, are needed for definitive diagnosis. It is essential to establish the diagnosis accurately to differentiate an apparent superior laryngeal nerve paresis from other conditions, such as myasthenia gravis. Laryngeal electromyography is used to confirm clinical impressions, as a guide for therapy, and as one measure of recovery. In our experience, accurate and early diagnosis assure the best phonatory outcome by directing therapy that will prevent or eliminate compensatory vocal abuses, which may themselves lead to even more serious vocal injury. 相似文献
87.
Scrambling of the carbon atoms in benz[a]anthracene between positions 5 and 6 has been shown to occur at high temperatures; a mechanism involving thermal generation of a carbene is proposed. 相似文献
88.
Youval Shvo Yigal Blum Deborah Reshef Marit Menzin 《Journal of organometallic chemistry》1982,226(1):C21-C24
Ru3(CO)12 acts as a homogeneous catalyst precursor for the transformation of αω-diols to polyesters and lactones. 相似文献
89.
Wing Tsang 《国际化学动力学杂志》1978,10(1):41-66
Tertiary-amyl amine has been decomposed in single-pulse shock-tube experiments. Rate expressions for several of the important primary steps are This leads to D(CH3? H) – D(NH2? H) = ?10.5 kJ and D[(CH3)3C? H] – D[(CH3)2NH2C? H] = + 6 kJ. The present and earlier comparative rate single-pulse shock-tube data when combined with high-pressure hydrazine decomposition results-(after correcting for fall off effects through RRKM calculations) gives where kr(…) is the recombination rate involving the appropriate radicals. This suggests that in this context amino radical behavior is analogous to that of alkyl radicals. If this agreement is exact, then Rate expressions for the primary step in the decomposition of a variety of primary amines have been computed. In the case of benzyl amine where data exist the agreement is satisfactory. The following differences in bond energies have been estimated: 相似文献
90.
Wing Tsang 《国际化学动力学杂志》1978,10(6):599-617
Cyclopentane has been decomposed in comparative-rate single-pulse shock-tube experiments. The pyrolytic mechanism involves isomerization to 1-pentene and also a minor pathway leading to cyclopropane and ethylene. This is followed by the decomposition of 1-pentene and cyclopropane. The rate expressions over the temperature range of 1000°–1200° K are Details of the cyclopentane decomposition processes are considered, and it appears that if the trimethylene radical is an intermediate, then ΔHf(trimethylene) ≤ 280 kJ/mol at 300°K. 相似文献