全文获取类型
收费全文 | 161585篇 |
免费 | 2122篇 |
国内免费 | 541篇 |
专业分类
化学 | 89799篇 |
晶体学 | 2439篇 |
力学 | 6381篇 |
综合类 | 4篇 |
数学 | 16500篇 |
物理学 | 49125篇 |
出版年
2021年 | 1364篇 |
2020年 | 1578篇 |
2019年 | 1730篇 |
2018年 | 2007篇 |
2017年 | 1972篇 |
2016年 | 3127篇 |
2015年 | 2103篇 |
2014年 | 2883篇 |
2013年 | 6911篇 |
2012年 | 5863篇 |
2011年 | 7151篇 |
2010年 | 4835篇 |
2009年 | 4757篇 |
2008年 | 6599篇 |
2007年 | 6293篇 |
2006年 | 6179篇 |
2005年 | 5670篇 |
2004年 | 5031篇 |
2003年 | 4562篇 |
2002年 | 4427篇 |
2001年 | 5766篇 |
2000年 | 4137篇 |
1999年 | 3245篇 |
1998年 | 2262篇 |
1997年 | 2366篇 |
1996年 | 2234篇 |
1995年 | 2059篇 |
1994年 | 2022篇 |
1993年 | 1822篇 |
1992年 | 2298篇 |
1991年 | 2368篇 |
1990年 | 2195篇 |
1989年 | 2139篇 |
1988年 | 2119篇 |
1987年 | 2132篇 |
1986年 | 1952篇 |
1985年 | 2438篇 |
1984年 | 2447篇 |
1983年 | 1942篇 |
1982年 | 1968篇 |
1981年 | 1796篇 |
1980年 | 1777篇 |
1979年 | 2063篇 |
1978年 | 2140篇 |
1977年 | 2081篇 |
1976年 | 2013篇 |
1975年 | 1884篇 |
1974年 | 1873篇 |
1973年 | 1899篇 |
1972年 | 1246篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
G. D. Krapivan N. I. Val'ter T. Ya. Kaklyugina V. G. Kul'nevich 《Chemistry of Heterocyclic Compounds》1994,30(3):289-295
Halogen in positions 3 and 5 of the furan ring in ftirfurylidenedioxanediones is readily replaced by dithiocarbonate, dithiocarbatnate, dithiophosphate, thiocyanate, and azide anions, and by thiourea, and secondary and tertiary amines. The conformation of the initial halogen derivative is retained in the substitution products.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 327–334, March, 1994. 相似文献
42.
M. A. Mikhaleva B. M. Bolotin T. A. Kizner E. S. Serebrykova 《Chemistry of Heterocyclic Compounds》1994,30(1):79-81
We have synthesized 5-alkyl(alkoxy)-2-(o-lzydroxy-p-alkoxyphenyl)pyrimidines and considered the effect of the OH group on the inesomorphism. We have found that in binuclear o-hydroxyarylpyrimidines, an ortho OH group forming an intramolecular hydrogen bond increases Tmp, inhibits the appearance of nematic properties, and promotes the appearance of a smectic A.Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 30, No. 1, pp. 90–92, January, 1994. 相似文献
43.
N. I. Khamidov B. T. Kadyrov N. T. Ul'chenko A. Sh. Isamukhamedov A. I. Glushenkova 《Chemistry of Natural Compounds》1994,30(4):430-433
The phsicochemical indices and the fatty-acid and triacylglycerol compositions of cottonseed and palm oils, of cottonseed
oil hydrogenate, and of compositions based on them have been determined with the aid of IR and UV spectroscopies, GLC analysis,
and chemical transformations. The compositions and amounts of the main classes of lipids in the initial oils and the hydrogenate
have been studied. It has been found that in the process of hydrogenation the amount of oxygenated components falls.
The work was conducted with the financial support of the Uzbek Fund for Fundamental Investigations. 相似文献
44.
S. O. Kolusheva B. A. Salakhutdinov T. F. Aripov L. P. Vernon 《Chemistry of Natural Compounds》1994,29(4):523-525
It has been shown by the ESR of spin probes that thionin initially interacts with with negatively charged membranes electrostatically and then passes into the membranes to a depth comparable with the length of the hydrophobic sections of the protein loops.Institute of Bioorganic Chemistry, Academy of Sciences of the Republic of Uzbekistan, Tashkent. Brigham Young University, Provo, Utah, USA. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 594–597, July–August, 1993. 相似文献
45.
T. A. Beu 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1993,27(3):263-266
New analytical formulas for the torsionL-tensor are reported, which are used in molecular normal mode analysis calculations for the nonlinear transformation of the force constants from internal coordinates to normal coordinates. The proposed formalism exhibits a relative simplicity as compared to previous reported results. Sample calculations for methanol and hydrazine are presented. 相似文献
46.
Partially supported by NSF Grants. 相似文献
47.
48.
Summary The main purpose of this paper is to introduce the concepts of η-sets, ηζ-sets,η-continuity and ηζ-continuity and to obtain
a decomposition of continuity. 相似文献
49.
The paper mentioned above is a contribution of the authors to Volume 18 (2002) of this journal, see . Recently, J. Domsta pointed out to us that the proof of Theorem 4.2 in that paper contains an error. The purpose of this
addendum is to present a correct argument for it. 相似文献
50.
Wolfram Bremser Roland Becker Heinrich Kipphardt Petra Lehnik-Habrink Ulrich Panne Antje Töpfer 《Accreditation and quality assurance》2006,11(10):489-495
ISO Guide 35 deals with RM stability issues and scrutinizes the evaluation of stability testing results under the assumption that either there is no trend at all (a rather rare situation), or any observed deterministic change is insignificant and thus can be neglected. However, market demands for reliable reference materials are obviously not limited to stable or at least seemingly stable materials. In many analytical applications, analytes and measurands under consideration are known, or at least suspected, to be unstable on time scales that may vary widely from measurand to measurand. The Federal Institute for Materials Research and Testing (BAM) has developed (and successfully uses) an integrated approach in its certification practice. The approach is based on an initial stability study and subsequent post-certification monitoring. Data evaluation is model-based and takes advantage of all information collected in the stability testing scheme(s). It thus allows one to deal with any kind of instability observed, to assess limiting time intervals at any stress condition in the range tested, to estimate a final expiry date for materials with detected instabilities or the maximum admissible re-testing interval for seemingly stable materials, and to assess maximum admissible stress loads during delivery of the material to the customer. The article describes (and exemplifies) typical study layout, the model selection, and the integrated data assessment. 相似文献