全文获取类型
收费全文 | 9981篇 |
免费 | 1978篇 |
国内免费 | 3424篇 |
专业分类
化学 | 6894篇 |
晶体学 | 440篇 |
力学 | 656篇 |
综合类 | 339篇 |
数学 | 1564篇 |
物理学 | 5490篇 |
出版年
2024年 | 24篇 |
2023年 | 93篇 |
2022年 | 391篇 |
2021年 | 344篇 |
2020年 | 375篇 |
2019年 | 318篇 |
2018年 | 396篇 |
2017年 | 508篇 |
2016年 | 379篇 |
2015年 | 474篇 |
2014年 | 640篇 |
2013年 | 875篇 |
2012年 | 764篇 |
2011年 | 883篇 |
2010年 | 847篇 |
2009年 | 902篇 |
2008年 | 1002篇 |
2007年 | 857篇 |
2006年 | 854篇 |
2005年 | 663篇 |
2004年 | 529篇 |
2003年 | 439篇 |
2002年 | 426篇 |
2001年 | 406篇 |
2000年 | 483篇 |
1999年 | 265篇 |
1998年 | 137篇 |
1997年 | 114篇 |
1996年 | 132篇 |
1995年 | 77篇 |
1994年 | 104篇 |
1993年 | 86篇 |
1992年 | 74篇 |
1991年 | 58篇 |
1990年 | 56篇 |
1989年 | 55篇 |
1988年 | 50篇 |
1987年 | 32篇 |
1986年 | 31篇 |
1985年 | 28篇 |
1984年 | 32篇 |
1983年 | 23篇 |
1982年 | 24篇 |
1981年 | 23篇 |
1980年 | 23篇 |
1979年 | 17篇 |
1978年 | 14篇 |
1977年 | 9篇 |
1975年 | 6篇 |
1959年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
高抗冲聚丙烯序列结构的综合表征 总被引:3,自引:0,他引:3
用高分辨^13C NMR、FTIR等手段获得了高抗冲聚丙烯的组成和序列分布等链结构方面的信息。用DSC、WAXD等方法研究了它们的结晶行为、熔融转变及晶体结构,多种方法相结合有效地表征了高抗冲聚丙烯的序列结构。 相似文献
72.
73.
74.
考虑二阶非线性椭圆型微分方程∑^n_{i,j}∂/∂x_i{A_{i,j}(x,y)∂/∂x_j}+q(x)f(y)=0 (E),其中q(x)在外区域 Ω∈R\+n上变号. 利用偏Riccati变换和积分平均技巧, 建立了方程(E)所有解振动的充分准则. 相似文献
75.
阐述了双反函数、自双反函数和多数函数的定义,提出了自双反函数的性质.根据上述定义利用布尔代数中的基本概念、定理和公式证明了这些性质,展示了自双反函数在RM展开系数图(bj图)中的特点,讨论了自双反函数在函数分类中的应用. 相似文献
76.
ZHANG Zhi-Li WANG Hong-Tao WANG Xiao-Wei MA Xiao-Yan LIU Jun-Yi R.J. Griff B.T. Golding 《有机化学》2003,23(Z1):10-10
Cobalamin-dependent methionine synthase plays a crucial role in folate metabolism and such would appear to be an excellent target for rational antifolate drug design. However, to date, no anticancer agents directed at this enzyme are available, but the enzyme is efficiently and specifically inhibited by N2O and this has proven invaluable for evaluating the biochemical consequence of enzyme inhibition and for mechanistic studies. [1,2] 2,5-Diamino-4-oxo-6-(3-butenyl) pyrimidine, a key intermediate in synthetic inhibitors of methionine synthase, was first synthesized using γbutenyl-β-ketoester and guanidine carbonate (Scheme 1). [3] 相似文献
77.
Triterpenoid Constituents of Huperzia miyoshiana 总被引:1,自引:0,他引:1
Thirteen triterpenoids, including three new ones, miyoshianois A (1), B (2) and C (3), were isolated from Huperzia miyoshiana. The structures of these new compounds were established as 3-O-dihydroferuloyltohogenol (1), 16-oxo-3β,21β-dihydrox-y-serrat-14-en-24-ferulate (2) and 16-oxo-3a, 21β-dihydroxy-serrat-14-en-24-ferulate (3), respectively, on the basis of their spectroscopic analysis. 相似文献
78.
Possible triggering of solar activity to big earthquakes (Ms ≥ 8) in faults with near west-east strike in China 总被引:1,自引:0,他引:1
HAN Yanben GUO Zengjian WU Jinbing & MA Lihua . National Astronomical Observatories Chinese Academy of Sciences Beijing China . Earthquake Research Institute of Lanzhou CSB Lanzhou China Correspondence should be addressed to Han Yanben 《中国科学G辑(英文版)》2004,(2)
A big earthquake (Ms = 8.1) occurred at western Kunlun Mts gap on November 14, 2001. It is the biggest earthquake in China in the past 50 years and the only one with a magnitude bigger than 8 in China after Dangxiong Earthquake (M = 8) in Tibet in 1951. The big earthquake has drawn wide attention of scientists in seismological, geophysical, geological and astro-geodynamic circles. Scientists are interested in the occurrence regularity of the very big earthquakes and try to find out the fac… 相似文献
79.
Three Stilbene Tetramers from the Roots of Caragana sinica 总被引:3,自引:0,他引:3
Three stilbene tetramers, carasinols A-C (1-3), along with three known substances, leachianol C, cararosinol A and stenophyllol B, were isolated from the roots of Caragana sinica. Their structures were elucidated by spectroscopy. It was found that compounds isolated except for stenophyllol B stimulated the proliferation of cultured osteoblasts. 相似文献
80.
In this paper, based on known crystal structures of square pyramid (SP) and trigonal bipyramid (TBP) penta coordinated phosphorus compounds containing amino acid side chains, such as amino, carboxyl, hydroxyl or thiol, a software for survey the P(5)-structure of phosphorylated proteins was derived. By this software, it was found that 382 of 398 phosphorus related kinases (96%) from current PDB could go through the penta-coordinated phosphorus transition state or intermediate. 相似文献