全文获取类型
收费全文 | 19707篇 |
免费 | 739篇 |
国内免费 | 77篇 |
专业分类
化学 | 15757篇 |
晶体学 | 121篇 |
力学 | 307篇 |
数学 | 2525篇 |
物理学 | 1813篇 |
出版年
2023年 | 161篇 |
2022年 | 143篇 |
2021年 | 888篇 |
2020年 | 504篇 |
2019年 | 554篇 |
2018年 | 440篇 |
2017年 | 363篇 |
2016年 | 732篇 |
2015年 | 653篇 |
2014年 | 712篇 |
2013年 | 1282篇 |
2012年 | 1355篇 |
2011年 | 1504篇 |
2010年 | 940篇 |
2009年 | 851篇 |
2008年 | 1257篇 |
2007年 | 1210篇 |
2006年 | 1059篇 |
2005年 | 916篇 |
2004年 | 770篇 |
2003年 | 614篇 |
2002年 | 596篇 |
2001年 | 256篇 |
2000年 | 193篇 |
1999年 | 151篇 |
1998年 | 159篇 |
1997年 | 136篇 |
1996年 | 174篇 |
1995年 | 121篇 |
1994年 | 102篇 |
1993年 | 102篇 |
1992年 | 86篇 |
1991年 | 100篇 |
1990年 | 76篇 |
1989年 | 98篇 |
1988年 | 78篇 |
1987年 | 67篇 |
1986年 | 73篇 |
1985年 | 101篇 |
1984年 | 98篇 |
1983年 | 55篇 |
1982年 | 90篇 |
1981年 | 73篇 |
1980年 | 72篇 |
1979年 | 58篇 |
1978年 | 59篇 |
1977年 | 46篇 |
1976年 | 40篇 |
1975年 | 23篇 |
1963年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 498 毫秒
81.
Marta Gimnez-Pedrs Ali Aghmiz Carmen Claver Anna M. Masdeu-Bult Denis Sinou 《Journal of molecular catalysis. A, Chemical》2003,200(1-2):157-163
High linear alkenes (1-octene and 1-decene) have been hydroformylated using water-soluble rhodium complexes associated with sulfonated diphosphines in the presence of ionic surfactants or methanol. In all cases, the hydroformylation activities were higher than in experiments without additives. The selectivity in aldehydes was higher when we used cetyltrimethylammonium hydrogensulfate (CTAHSO4) as the surfactant or methanol as the co-solvent. 相似文献
82.
83.
Most operational models in atmospheric physics, meteorology and climatology nowadays adopt spherical geodesic grids and require “ad hoc” developed interpolation procedures. The author does a comparison between chosen representatives of linear, distance-based and cubic interpolation schemes outlining their advantages and drawbacks in this specific application field. Numerical experiments on a standard test problem, while confirming a good performance of linear and distance-based schemes in a single interpolation step, also show their minor accuracy with respect to the cubic scheme in the more realistic simulation of advection of a meteorological field. 相似文献
84.
Giovanni Tartarini Alessandra Lena Davide Passaro Lorenzo Rosa Stefano Selleri Pier Faccin Enrico Maria Fabbri 《Optical and Quantum Electronics》2006,38(9-11):869-876
A comprehensive numerical tool has been developed for the evaluation of the performances of Radio over Fiber (RoF) links intended for wireless signal distribution.At the transmitter end an appropriate set of rate equations allows to model the optical source as a solitary laser or as an appropriately injection locked laser. The optical channel is modeled putting into account the combined effect of fiber dispersion, laser source non ideal performances (e.g. non-linear effects, frequency chirp), and quadratic detection of the receiving photodiode. The simulation model developed can be a useful tool at the design stage allowing a preliminary evaluation of the characteristics of real RoF links. 相似文献
85.
We show that every arithmetically Cohen-Macaulay two-codimensional subscheme ofP
n can be deformed to a reduced union of two-codimensional linear subvarieties. This problem (classical for curves with the name of Zeuthen problem) was solved for curves by F.Gaeta. 相似文献
86.
87.
6-Thia-l-aza-5λ5-phosphabicyclo[3.2.0]hept-3-enes and Isothiocyanatophosphine-sulfides from (Methylidenamino)phosphines, Carbon Disulfide, and Acetylene- or Ethylene Derivatives (Methylidenamino)phosphines react with carbon disulfide to 1,3,2-thiazaphosphete derivatives 2 . Acetylenedicarboxylates give with 2 6-thia-l-aza-5λ5-phosphabicyclo[3.2.0]hept-3-enes 4a , b , and acrylates yield isothio-cyanatophosphin-sulfides 5a – c . The structures of 4a and 5a are proven by an X-ray diffraction analysis. 相似文献
88.
89.
Maria Benedetta Fadda Nicoletta Curreli Raffaello Pompei Antonio Rescigno Augusto Rinaldi Enrico Sanjust 《Applied biochemistry and biotechnology》1994,44(3):263-270
A highly active thermostable β-glucosidase was purified to homogeneity from a strain ofTrichoderma sp. The enzyme was an extracellular glycoprotein and showed hydrolytic activity toward several β-glucosides.
Cellobiose was found to be the substrate of choice for this enzyme. This finding could suggest future technological applications
of the purified protein. 相似文献
90.
Maria Carmelita Kasuya 《Journal of fluorine chemistry》2007,128(5):562-565
A series of fluorinated galactosides, dodecyl 2-deoxy-2-fluoro-β-d-galactopyranoside (2F Gal), dodecyl 4-deoxy-4-fluoro-β-d-galactopyranoside (4F Gal) and dodecyl 6-deoxy-6-fluoro-β-d-galactopyranoside (6F Gal), was chemically synthesized and introduced to B16 cells to serve as scaffolds for cellular enzyme glycosylation. Results showed that the presence of fluorine exercised significant effects on cell viability. Among the fluorinated galactosides used, 2F Gal was glycosylated to afford a GM4 analogue. 相似文献