全文获取类型
收费全文 | 64815篇 |
免费 | 1959篇 |
国内免费 | 1379篇 |
专业分类
化学 | 32560篇 |
晶体学 | 1086篇 |
力学 | 3451篇 |
综合类 | 89篇 |
数学 | 5421篇 |
物理学 | 25546篇 |
出版年
2022年 | 581篇 |
2021年 | 615篇 |
2020年 | 675篇 |
2019年 | 693篇 |
2018年 | 795篇 |
2017年 | 667篇 |
2016年 | 1171篇 |
2015年 | 951篇 |
2014年 | 1334篇 |
2013年 | 2964篇 |
2012年 | 2845篇 |
2011年 | 3507篇 |
2010年 | 2539篇 |
2009年 | 2585篇 |
2008年 | 3174篇 |
2007年 | 2979篇 |
2006年 | 2817篇 |
2005年 | 2502篇 |
2004年 | 2300篇 |
2003年 | 2046篇 |
2002年 | 1997篇 |
2001年 | 3230篇 |
2000年 | 2335篇 |
1999年 | 1745篇 |
1998年 | 1202篇 |
1997年 | 1157篇 |
1996年 | 954篇 |
1995年 | 840篇 |
1994年 | 762篇 |
1993年 | 654篇 |
1992年 | 988篇 |
1991年 | 987篇 |
1990年 | 877篇 |
1989年 | 768篇 |
1988年 | 748篇 |
1987年 | 806篇 |
1986年 | 672篇 |
1985年 | 901篇 |
1984年 | 837篇 |
1983年 | 576篇 |
1982年 | 569篇 |
1981年 | 537篇 |
1980年 | 497篇 |
1979年 | 624篇 |
1978年 | 651篇 |
1977年 | 662篇 |
1976年 | 575篇 |
1975年 | 483篇 |
1974年 | 523篇 |
1973年 | 450篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
The coordination chemistry of beryllium with particular emphasis on chelates under physiological or near physiological conditions is surveyed. Hard donors such as oxygen are emphasized; equilibrium data and formation constants are reported as an indication of the strength of the complex. 相似文献
32.
33.
Y Sonoda K Ichinose T Yoshimura Y Sato T Sasaki 《Chemical & pharmaceutical bulletin》1991,39(1):100-103
Lanosterol derivatives with a functional group at C-32 have been synthesized from 3 beta-acetoxylanostan-7 alpha-ol. The key reaction of the synthesis is the hypoiodite reaction of 3 beta-acetoxylanostan-7 alpha-ol. In vitro antitumor activity testing of the lanosterol derivatives revealed that 3 beta-hydroxylanost-7-en-32-oic acid has antineoplastic activity. 相似文献
34.
K. Y. Lin 《Journal of statistical physics》1987,49(1-2):269-279
The spontaneous magnetization of the Ising model on a 4–8 lattice with six different coupling constants and two different magnetic moments is studied. A formula for the spontaneous magnetization is proposed. The result agrees with the exact low-temperature series expansions up to the 12th order. 相似文献
35.
K Kawasaki T Tsuji K Hirase M Miyano Y Imoto M Iwamoto 《Chemical & pharmaceutical bulletin》1991,39(3):584-589
N-Terminal tripeptide analogs of fibrin alpha-chain were synthesized and their inhibitory effect on fibrinogen/thrombin clotting was examined. A new water-soluble active ester, 3-pyridinium ester, was used for the synthesis. Among the synthetic peptides, H-Gly-Pro-Arg-hexamethyleneimine exhibited the highest inhibitory effect on fibrinogen-thrombin clotting. 相似文献
36.
The mode of action of the anti-complementary acidic heteroglycans, AAF-IIb-2 and IIb-3 which consisted of rhamnogalacturonan core and arabinogalactan moieties, purified from the leaves of Artemisia princeps PAMP (Japanese name = Gaiyo) were investigated. The anti-complementary activities of AAF-IIb-2 and IIb-3 were reduced partially in the absence of Ca2+ ions. A marked consumption of C4 was observed to have occurred when serum was incubated with both polysaccharides in the presence of Ca2+ ions. AAF-IIb-2 showed more potent C4 consumption than IIb-3. After the incubation of the serum with AAF-IIb-2 in the absence of Ca2+ ions, a cleavage of C3 in the serum was detected by immunoelectrophoresis. AAF-IIb-2 showed more significant consumption of the complement than IIb-3 when rabbit erythrocytes were used in the assay system in the absence of Ca2+ ions. These results indicate that AAF-IIb-2 activates the complement via both the alternative and classical pathways, whereas IIb-3 mainly activates the complement via the classical pathway. The absorption of serum with Protein A-Sepharose results in a decrease of the activity of AAF-IIb-2 and IIb-3. However, the decrease of the activity was restored by the replacement of the immunoglobulin G (IgG) fraction after its recovery from the Protein A-Sepharose. These results suggest that IgG dependent mechanisms are both involved in the anti-complementary activity of AAF-IIb-2 and IIb-3. 相似文献
37.
The object of this note is to prove the followingTheorem Let{a_n}and{b_n}be sequences of real numbers such that0<∑∑a_n~2<+∞and0<∑b_n~2<+∞.Then we have the inequalitysum from m=1 to∞sum from n=1 to∞a_mb_n/m+n<{sum from n=1 to∞(π-θ/n~(1/2)a_n~2}~1/2{sum from n=1 to∞(π-θ/n~(1/2)b_n~2}~1/2 (1)whereθ=3/2~(1/2)-1=1.121320343. 相似文献
38.
J Szeman H Ueda J Szejtli E Fenyvesi Y Machida T Nagai 《Chemical & pharmaceutical bulletin》1987,35(1):282-288
39.
A new type of THz waveguides, which employs a solid polyethylene rod as the core and polyethylene tubes in a periodic array of square lattice as the cladding, is proposed. Optical properties of this new THz waveguide, especially in dispersion, confinement loss and single mode property, are investigated in detail with the plane wave expansion method and the beam propagation method. Numerical results demonstrate that the new THz waveguide can reach not only low dispersion but also low confinement loss at single mode propagation. Therefore, the square lattice structure is a better candidate as THz waveguides than the triangular ones. 相似文献
40.
L. Tong Y. Tian Q. Y. Wang Y. S. Ling 《International Journal of Infrared and Millimeter Waves》2006,27(9):1307-1314
The paper introduces a special system calibration technology in s-parameters measurement of microwave and millimeter wave
devices. The 8-term errors module is built by analyzing the signals flowing in the measurement system. Then the calibration
technology using non-standard kits is designed on the base. Finally, the experiment using the calibration technology is introduced. 相似文献