全文获取类型
收费全文 | 29693篇 |
免费 | 903篇 |
国内免费 | 235篇 |
专业分类
化学 | 19257篇 |
晶体学 | 128篇 |
力学 | 648篇 |
综合类 | 1篇 |
数学 | 5385篇 |
物理学 | 3883篇 |
无线电 | 1529篇 |
出版年
2022年 | 159篇 |
2021年 | 322篇 |
2020年 | 375篇 |
2019年 | 342篇 |
2018年 | 303篇 |
2017年 | 311篇 |
2016年 | 642篇 |
2015年 | 667篇 |
2014年 | 707篇 |
2013年 | 1468篇 |
2012年 | 1492篇 |
2011年 | 1777篇 |
2010年 | 1004篇 |
2009年 | 883篇 |
2008年 | 1550篇 |
2007年 | 1547篇 |
2006年 | 1645篇 |
2005年 | 1456篇 |
2004年 | 1391篇 |
2003年 | 1135篇 |
2002年 | 1106篇 |
2001年 | 471篇 |
2000年 | 439篇 |
1999年 | 422篇 |
1998年 | 405篇 |
1997年 | 458篇 |
1996年 | 415篇 |
1995年 | 373篇 |
1994年 | 409篇 |
1993年 | 357篇 |
1992年 | 329篇 |
1991年 | 328篇 |
1990年 | 285篇 |
1989年 | 287篇 |
1988年 | 264篇 |
1987年 | 227篇 |
1986年 | 256篇 |
1985年 | 376篇 |
1984年 | 379篇 |
1983年 | 335篇 |
1982年 | 359篇 |
1981年 | 324篇 |
1980年 | 350篇 |
1979年 | 284篇 |
1978年 | 308篇 |
1977年 | 285篇 |
1976年 | 230篇 |
1975年 | 199篇 |
1974年 | 210篇 |
1973年 | 170篇 |
排序方式: 共有10000条查询结果,搜索用时 960 毫秒
171.
172.
Peter D. Verhaert Maria C. Prieto Conaway Tonya M. Pekar Ken Miller 《International journal of mass spectrometry》2007,260(2-3):177
Direct tissue imaging was performed on dissected insect tissue using a MALDI ion trap to visualize endogenous neuropeptides. Coupling tissue imaging to tandem MSn allows for the identification of previously known species and the ability to identify new ones by de novo sequencing, as searchable databases for insects are sparse. Direct tissue imaging is an attractive technique for the study of neuropeptides as minimal sample preparation is required prior to mass spectrometry. We successfully identified neuropeptides present in the corpora cardiaca and allata of Acheta domesticus (the house cricket). Diagnostic fragments at low m/z were used to distinguish between lipids and neuropeptides. The distribution of peptides appears to be more differentially localized than that of phospholipids, which seem to be more evenly distributed within the tissue. 相似文献
173.
问:我们了解到,长电在十多年前还是一个资不抵债、名不见经传的小企业,如今的长电不但成功上市,还在集成电路和半导体分立器件器件装业树立了一个行业领先者的形象,而且其各项技术经济指标在国内同类企业中名列前茅,对此,请问您如何评价您所创业的这个企业和团队. 相似文献
174.
175.
The melting behaviour, some phase boundaries and the lattice parameters in the region of the NiAs-type phase in the ternary system cobalt-antimony-tellurium have been determined by differential thermal analysis and X-ray diffraction. A projection of the liquidus surface and the phase relationships in different sections with constant antimony/tellurium ratios are presented. The peculiar variation of the lattice parameters with the composition of the nonstoichiometric NiAs-type phase is discussed in terms of the defect structure.Dedicated to Prof. K. L. Komarek on the occasion of his 65th birthday 相似文献
176.
What is the maximum number of unit distances between the vertices of a convex n-gon in the plane? We review known partial results for this and other open questions on multiple occurrences of the same interpoint distance in finite planar subsets. Some new results are proved for small n. Challenging conjectures, both old and new, are highlighted. 相似文献
177.
Katalytische Epoxidierung und 1,2‐Dihydroxylierung von Olefinen mit Bispidin‐Eisen(II)/H2O2‐Systemen
178.
Marko D. Mihovilovic Bernhard Müller Markus Spina Arjumand I. Durrani Peter Stanetty Georg Dazinger Karl Kirchner 《Monatshefte für Chemie / Chemical Monthly》2006,137(6):785-794
Summary. Recombinant Escherichia coli overexpressing Pseudomonas sp. NCIMB 9872 cyclopentanone monooxygenase (CPMO, EC 1.14.13.16) and Acinetobacter sp. NCIMB 9871 cyclohexanone monooxygenase (CHMO, EC 1.14.13.22) have been utilized in whole-cell Baeyer-Villiger biotransformations of prochiral bicycloketones. A significant difference in substrate acceptance and stereoselectivity was
observed for bicyclo[3.3.0] and bicyclo[4.3.0] substrates. A plausible mechanism of these transformations was established
by means of high level DFT/B3LYP calculations suggesting an essential difference in electronic requirements for a successful
enzymatic conversion, which was similarly encountered in recombinant whole-cell mediated biooxidations. Some of the lactones
produced in the biocatalytic Baeyer-Villiger oxidation represent key intermediates for the synthesis of indole alkaloids. 相似文献
179.
180.
J. Peter H. Pabon 《Journal of voice》1991,5(3)
A phonetogram is a plot of the dynamic range of the voice as a function of fundamental frequency. Traditionally, the phonetogram only records the sound-pressure level (SPL) of the threshold of phonation and the upper limit in SPL the voice can reach with sustained phonation as a function of the fundamental frequency (F0). In this study, the phonetogram is extended by including acoustic voice-quality parameters. Three additional parameters are tested: jitter, shimmer, and crest factor. For each individual voice, the variation in the three parameters is evaluated over the entire phonetogram area. By averaging individual phonetograms, standard or norm phonetograms are obtained revealing general patterns in voice-quality variation. These patterns reflect the complex relations between F0, SPL, and the acoustic voice-quality parameters just mentioned. Jitter and shimmer distributions over the phonetogram show that large variations in perturbation values can be expected when production conditions are altered. Highest perturbation values are found for the low F0 and low SPL phonations. For all voices, a gradual decrease of the crest factor is found with increasing F0, reflecting the degrading of spectral complexity with F0. The crest-factor parameter can also be used to mark those areas in the phonetogram where the fundamental dominates the waveform and where flow control is the main SPL regulating mechanism in voice production. The strong quality variations within the phonetogram stress the need for accurate control of F0 and SPL in objective voice-quality measurement. 相似文献