全文获取类型
收费全文 | 28982篇 |
免费 | 1107篇 |
国内免费 | 148篇 |
专业分类
化学 | 20345篇 |
晶体学 | 257篇 |
力学 | 607篇 |
数学 | 3693篇 |
物理学 | 5335篇 |
出版年
2023年 | 187篇 |
2022年 | 161篇 |
2021年 | 389篇 |
2020年 | 534篇 |
2019年 | 508篇 |
2018年 | 340篇 |
2017年 | 298篇 |
2016年 | 801篇 |
2015年 | 687篇 |
2014年 | 815篇 |
2013年 | 1346篇 |
2012年 | 1737篇 |
2011年 | 1966篇 |
2010年 | 1135篇 |
2009年 | 969篇 |
2008年 | 1616篇 |
2007年 | 1527篇 |
2006年 | 1527篇 |
2005年 | 1407篇 |
2004年 | 1249篇 |
2003年 | 959篇 |
2002年 | 985篇 |
2001年 | 504篇 |
2000年 | 451篇 |
1999年 | 423篇 |
1998年 | 406篇 |
1997年 | 357篇 |
1996年 | 348篇 |
1995年 | 312篇 |
1994年 | 337篇 |
1993年 | 337篇 |
1992年 | 297篇 |
1991年 | 224篇 |
1990年 | 253篇 |
1989年 | 226篇 |
1988年 | 236篇 |
1987年 | 223篇 |
1986年 | 202篇 |
1985年 | 310篇 |
1984年 | 283篇 |
1983年 | 220篇 |
1982年 | 225篇 |
1981年 | 236篇 |
1980年 | 220篇 |
1979年 | 215篇 |
1978年 | 249篇 |
1977年 | 222篇 |
1976年 | 180篇 |
1974年 | 188篇 |
1973年 | 161篇 |
排序方式: 共有10000条查询结果,搜索用时 416 毫秒
91.
As pan of a biomimetic approach towards me marine triterpene teurilene (2), the synthesis of the chiral diepoxide 3 is described. Aiming at the synthesis of the squalene tetraepoxide 1, double Sharpless epoxidation led to the intermediate bisglycidic alcohol 7 being subject to a stereochemical analysis. 相似文献
92.
93.
94.
O. Dumbrajs M. Thumm J. Pretterebner D. Wagner 《International Journal of Infrared and Millimeter Waves》1992,13(6):825-840
Mode conversion at discontinuities of an ordinary gyrotron cavity is examined. It is shown how the production of unwanted spurious modes can be reduced substantially by introducing smooth transition regions between the individual parts of the cavity. The cavity of the 140 GHz KfK gyrotron operating in the TE10,4 mode is used as an example. Cavity and adjacent tapered output waveguide are optimized as a single unit. 相似文献
95.
Simon Thomas 《Archive for Mathematical Logic》1998,37(7):483-493
We study the relationship between the cofinality of the infinite symmetric group and the cardinal invariants and . In particular, we prove the following two results.
Theorem 0.1
It is consistent with
ZFC
that there exists a simple
$P_{\omega_{1}}$
-point and that
$c(Sym(\omega)) = \omega_{2} = 2^{\omega}$
.
Theorem 0.2
If there exist both a simple
$P_{\omega_{1}}$
-point and a
$P_{\omega_{2}}$
-point, then
$c(Sym(\omega)) = \omega_{1}$
.
Received: 7 March 1996 相似文献
96.
An improved method including extraction procedures is presented for the analysis of nucleotides in suspension-cultivated animal cells. Quantification was performed by ion-pair high-performance liquid chromatography after perchloric acid extraction. It was found that the amount of perchloric acid taken for extraction influenced the yield and that cell washing procedures caused deterioration of the analysis results for triphosphates. More than thirty nucleotides and sugar-nucleotides were separated within 25 min using a Supelcosil reversed-phase column (3 microns) with tetrabutylammonium hydrogensulphate as pairing agent and methanol-pH gradient elution. Cultivated hybridoma cells showed variations in intracellular nucleotide concentrations as well as relative amounts during different growth phases, which could reflect the physiological state of a cell culture. 相似文献
97.
We consider a spatially distributed hybrid system consisting of a convection/reaction system in which the reaction switches discontinuously in time between modes, independently at each spatial point on reaching “switching thresholds”. The model involves a novel formulation for evolution of the free boundary between the modal regions. 相似文献
98.
99.
We give combinatorial proofs that certain families of differences of products of Schur functions are monomial-positive. We
show in addition that such monomial-positivity is to be expected of a large class of generating functions with combinatorial
definitions similar to Schur functions. These generating functions are defined on posets with labelled Hasse diagrams and
include for example generating functions of Stanley's (P,ω)-partitions.
T.L. was supported in part by NSF DMS-0600677. 相似文献
100.
Hyperfine Interactions - The YFe4Al8 and ErFe4Al8 intermetallics were studied by57Fe Mössbauer spectroscopy between 2 K and room temperature. The spectra are consistent with iron occupying 8f... 相似文献