全文获取类型
收费全文 | 23451篇 |
免费 | 497篇 |
国内免费 | 574篇 |
专业分类
化学 | 13164篇 |
晶体学 | 216篇 |
力学 | 1610篇 |
综合类 | 18篇 |
数学 | 3662篇 |
物理学 | 5852篇 |
出版年
2021年 | 287篇 |
2020年 | 383篇 |
2019年 | 438篇 |
2018年 | 591篇 |
2017年 | 532篇 |
2016年 | 713篇 |
2015年 | 397篇 |
2014年 | 644篇 |
2013年 | 1141篇 |
2012年 | 875篇 |
2011年 | 921篇 |
2010年 | 837篇 |
2009年 | 805篇 |
2008年 | 851篇 |
2007年 | 849篇 |
2006年 | 609篇 |
2005年 | 525篇 |
2004年 | 576篇 |
2003年 | 588篇 |
2002年 | 617篇 |
2001年 | 519篇 |
2000年 | 379篇 |
1999年 | 298篇 |
1998年 | 285篇 |
1997年 | 272篇 |
1996年 | 252篇 |
1993年 | 248篇 |
1992年 | 249篇 |
1991年 | 252篇 |
1990年 | 270篇 |
1989年 | 275篇 |
1985年 | 274篇 |
1984年 | 297篇 |
1983年 | 262篇 |
1982年 | 276篇 |
1981年 | 245篇 |
1980年 | 267篇 |
1979年 | 310篇 |
1978年 | 338篇 |
1977年 | 323篇 |
1976年 | 406篇 |
1975年 | 362篇 |
1974年 | 395篇 |
1973年 | 400篇 |
1972年 | 376篇 |
1971年 | 334篇 |
1970年 | 320篇 |
1969年 | 299篇 |
1968年 | 253篇 |
1967年 | 254篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
Activated carbon production from almond shells using phosphoric acid activation agent was achieved by applying both conventional heating and microwave heating in succession. The morphology and surface properties of activated carbon were studied using thermogravimetric and differential gravimetric analysis, Fourier-transform infrared spectroscopy, scanning electron microscopy, and Brunauer–Emmett–Teller analysis. A surface area of 1128 m2/g was achieved by optimizing the microwave power (500?W), microwave application time (15?minutes), conventional heating time (45?minutes), conventional heating temperature (500?°C), and the phosphoric acid:sample ratio (0.7:1). An adsorption capacity of methylene blue of 148?mg/g and an iodine value of 791?mg/g was obtained for the prepared activated carbon. 相似文献
13.
Stadnyk V. Yo. Shchepanskyi P. A. Rudysh M. Ya. Kogut Z. A. 《Journal of Applied Spectroscopy》2021,88(4):831-837
Journal of Applied Spectroscopy - The temperature dependence of the refractive indices of K2SO4 with copper impurity was investigated. It was found that introduction of the copper impurity leads to... 相似文献
14.
In this study, stoichiometric protonation constants of L-tyrosine, L-cysteine, L-tryptophane, L-lysine, and L-histidine, and
their methyl and ethyl esters in water and ethanol–water mixtures of 30, 50, and 70% ethanol (v/v), were determined potentiometrically
using a combined pH electrode system calibrated as the concentration of hydrogen ion. Titrations were performed at 25∘C and the ionic strength of the medium was maintained at 0.10 mol⋅L−1 using sodium chloride. Protonation constants were calculated by using the BEST computer program. The effect of solvent composition
on the protonation constants is discussed. The log10 K2 values of esters generally decreased with increasing ethanol content. However, the log10 K1 values of the esters of L-tyrosine, L-cysteine, and L-tryptophane were found to increase with increasing ethanol content
in contrast those of L-lysine and L-histidine esters. 相似文献
15.
Ya. V. Fattakhov M. F. Galyautdinov T. N. L’vova I. B. Khaibullin 《Technical Physics》1997,42(12):1457-1459
The first results regarding the formation of a two-dimensional periodic structure of local melting regions on a silicon surface
upon pulsed light irradiation are presented. The conditions are established, and the mechanism of the formation of such structures
is discussed.
Zh. Tekh. Fiz. 67, 97–99 (December 1997) 相似文献
16.
Ya. Stradyn 《Chemistry of Heterocyclic Compounds》1994,30(3):377-379
17.
G. D. Krapivan N. I. Val'ter T. Ya. Kaklyugina V. G. Kul'nevich 《Chemistry of Heterocyclic Compounds》1994,30(3):289-295
Halogen in positions 3 and 5 of the furan ring in ftirfurylidenedioxanediones is readily replaced by dithiocarbonate, dithiocarbatnate, dithiophosphate, thiocyanate, and azide anions, and by thiourea, and secondary and tertiary amines. The conformation of the initial halogen derivative is retained in the substitution products.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 327–334, March, 1994. 相似文献
18.
19.
V. N. Plugar' Ya. V. Rashkes A. Ovezdurdyev I. D. Sham'yanov 《Chemistry of Natural Compounds》1994,29(4):462-466
The main directions of fragmentation and the EI of six pseudoguaianolides related to carpesiolin have been studied. It has been established that acylation of the OH group at C-6 suppresses the selective breakdown of the guaiane skeleton, while the simultaneous presence of AcO groups at C-2 and C-4 favors the formation of a number of characteristic ions. The hydrogenation of the exomethylene group has no appreciable influence on direction of fragmentation.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 530–535, July–August, 1993. 相似文献
20.
M. S. Tashmukhamedov O. K Zakirova Sh. Ya. Mirzaakhmedov Sh. I. Salikhov I. T. Yakubov M. M. Rakhimov 《Chemistry of Natural Compounds》1994,30(1):97-100
Phospholipase A2 has been isolated fromthe venom of he Central Asian green toad Bufo viridis in the electroophoretically homogeneous state for the first time by biospecific absorption chromatography. The affinity sorbent used was Affi-Gel 10 with covalently bound phosphatidylserine (PDS). The chemical inertness of the bound PDS to the hydrolytic action of phospholipase A2 and its high tendency to form biospecific complexes have been shown. Some biochemical characteristics of the enzyme isolated have been studied: influence of the pH and of the Ca2+ concentration and dependence of activity on substrate concentration.A. S. Sadykov Institute of Bioorganic Chemistry, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax 627071. Tashkent State University, fax 462472. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 105–109, January–February, 1994. 相似文献