全文获取类型
收费全文 | 267724篇 |
免费 | 2381篇 |
国内免费 | 622篇 |
专业分类
化学 | 142188篇 |
晶体学 | 4166篇 |
力学 | 11937篇 |
综合类 | 9篇 |
数学 | 29524篇 |
物理学 | 82903篇 |
出版年
2019年 | 2297篇 |
2018年 | 3124篇 |
2017年 | 3117篇 |
2016年 | 4499篇 |
2015年 | 2665篇 |
2014年 | 4293篇 |
2013年 | 10698篇 |
2012年 | 8103篇 |
2011年 | 9928篇 |
2010年 | 7101篇 |
2009年 | 6897篇 |
2008年 | 9340篇 |
2007年 | 9540篇 |
2006年 | 8909篇 |
2005年 | 8086篇 |
2004年 | 7439篇 |
2003年 | 6748篇 |
2002年 | 6673篇 |
2001年 | 7341篇 |
2000年 | 5679篇 |
1999年 | 4369篇 |
1998年 | 3863篇 |
1997年 | 3850篇 |
1996年 | 3584篇 |
1995年 | 3337篇 |
1994年 | 3494篇 |
1993年 | 3188篇 |
1992年 | 3667篇 |
1991年 | 3672篇 |
1990年 | 3599篇 |
1989年 | 3459篇 |
1988年 | 3569篇 |
1987年 | 3464篇 |
1986年 | 3286篇 |
1985年 | 4362篇 |
1984年 | 4635篇 |
1983年 | 3873篇 |
1982年 | 4005篇 |
1981年 | 3933篇 |
1980年 | 3912篇 |
1979年 | 3877篇 |
1978年 | 4191篇 |
1977年 | 4107篇 |
1976年 | 4173篇 |
1975年 | 3849篇 |
1974年 | 3893篇 |
1973年 | 4050篇 |
1972年 | 2851篇 |
1971年 | 2378篇 |
1970年 | 2177篇 |
排序方式: 共有10000条查询结果,搜索用时 578 毫秒
281.
A. Nikakhtar A. Nasehzadeh G. A. Mansoori 《Journal of the Iranian Chemical Society》2006,3(2):161-167
A thermodynamic cycle for the nanoclusteration between DNA and dendronized polymer is proposed and electrostatic free energies of a series of DNA- dendronized polymer nanoclusteration processes are calculated. The free energies for assembling fixed charges and mobile ions, and the bending energies of the DNA chain wrapped around the dendronized polymer are taken into consideration. The free energies of nanoclusteration are calculated for a number of nanoclusters with different conformations at constant temperature and constant ionic strength. The effects of temperature and ionic strength on the free energy of nanoclusteration and stability of their conformations are also investigated. 相似文献
282.
G. Scorza Dragoni 《Annali di Matematica Pura ed Applicata》1940,19(1):45-49
Sunto. L'A., riferendosi alle trasformazioni topologiche di un cerchio, dimostra un'estensione di un noto teorema relativo all'esistenza
di punti uniti nelle trasformazioni considerate. 相似文献
283.
J.-C. Thomas L. Achouri J. Äystö R. Béraud B. Blank G. Canchel S. Czajkowski P. Dendooven A. Ensallem J. Giovinazzo N. Guillet J. Honkanen A. Jokinen A. Laird M. Lewitowicz C. Longour F. de Oliveira Santos K. Peräjärvi M. Stanoiu 《The European Physical Journal A - Hadrons and Nuclei》2004,21(3):419-435
284.
285.
G.P. Romanelli D. Bennardi D.M. Ruiz G. Baronetti H.J. Thomas 《Tetrahedron letters》2004,45(48):8935-8939
Substituted coumarins are synthesized from phenols and β-ketoesters by the Pechmann reaction, using a Wells-Dawson heteropolyacid (H6P2W18O62·24H2O) as catalyst by a solvent-free procedure. This one requires low reaction times, 130 °C temperature and as little as 1 mol % of Wells-Dawson acid, obtaining good to excellent yields of coumarins. The catalyst showed to be reusable with no differences in the yields. The results are compared with those of the reactions performed in toluene solution. The presented synthetic procedure is a convenient, clean and fast alternative for synthesizing 4-substituted coumarins (17 examples). 相似文献
286.
G. Tóth 《Journal of Radioanalytical and Nuclear Chemistry》1989,137(4):259-264
The distribution of mono- poly- and unlabelled protein molecules in the radiolabelling mixture was calculated from probability point of view as a function of the radioiodine/protein ratio. 相似文献
287.
L. Ya. Yukel'son I. I. Parilis G. L. Bussel' D. Kh. Khamidov 《Chemistry of Natural Compounds》1989,25(6):698-704
On the basis of a computer analysis of four classes of toxic polypeptides, generalized primary structures of each class have been obtained which can be used for planning the synthesis of biologically active compounds. 相似文献
288.
S. P. Tretyakova Yu. S. Zamyatnin V. N. Kovantsev Yu. S. Korotkin V. L. Mikheev G. A. Timofeev 《Zeitschrift für Physik A Hadrons and Nuclei》1989,333(4):349-353
The emission of Ne and Mg nuclei was detected in the spontaneous decay of234U with probabilities of, respectively, (3.9 ±1.0) × 10?13 and (2.3 ±0.7) × 10?13 relative toα-decay. The upper limits of this kind of decay for235U and236U have been established. Systematics of half-lives for cluster emission are found to be similar to the Geiger-Nuttall dependence forα-decay. Some evidence for the presence of hindrance to cluster emission from the odd-mass nuclei233U and235U is obtained. 相似文献
289.
290.
The precision of intensity modulated fiber optic sensor systems mainly is restricted by the attenuation characteristics of the analog fiber optical data link. Special encoding and referencing schemes are used to overcome this data link dependence. In this paper encoding and referencing principles for optical sensors are outlined and compared. Especially the two wavelengths referencing and the optical delay line processing techniques are discussed in more detail and results are presented. 相似文献