全文获取类型
收费全文 | 234583篇 |
免费 | 2349篇 |
国内免费 | 802篇 |
专业分类
化学 | 118089篇 |
晶体学 | 4006篇 |
力学 | 10796篇 |
综合类 | 1篇 |
数学 | 25682篇 |
物理学 | 79160篇 |
出版年
2020年 | 1858篇 |
2019年 | 2136篇 |
2018年 | 2810篇 |
2017年 | 2726篇 |
2016年 | 4004篇 |
2015年 | 2473篇 |
2014年 | 4050篇 |
2013年 | 10172篇 |
2012年 | 7696篇 |
2011年 | 9553篇 |
2010年 | 6784篇 |
2009年 | 6693篇 |
2008年 | 8809篇 |
2007年 | 8858篇 |
2006年 | 8395篇 |
2005年 | 7605篇 |
2004年 | 7003篇 |
2003年 | 6162篇 |
2002年 | 6105篇 |
2001年 | 7107篇 |
2000年 | 5382篇 |
1999年 | 4242篇 |
1998年 | 3574篇 |
1997年 | 3481篇 |
1996年 | 3306篇 |
1995年 | 3010篇 |
1994年 | 2961篇 |
1993年 | 3050篇 |
1992年 | 3157篇 |
1991年 | 3333篇 |
1990年 | 3087篇 |
1989年 | 3032篇 |
1988年 | 3067篇 |
1987年 | 2956篇 |
1986年 | 2800篇 |
1985年 | 3811篇 |
1984年 | 4005篇 |
1983年 | 3198篇 |
1982年 | 3410篇 |
1981年 | 3338篇 |
1980年 | 3230篇 |
1979年 | 3335篇 |
1978年 | 3422篇 |
1977年 | 3350篇 |
1976年 | 3448篇 |
1975年 | 3141篇 |
1974年 | 3150篇 |
1973年 | 3194篇 |
1972年 | 2235篇 |
1971年 | 1849篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
András Gy. Németh Renáta Szabó Dr. Attila Domján Prof. György M. Keserű Dr. Péter Ábrányi-Balogh 《ChemistryOpen》2021,10(1):16-27
The development of a new three-component chromatography-free reaction of isocyanides, amines and elemental sulfur allowed us the straightforward synthesis of thioureas in water. Considering a large pool of organic and inorganic bases, we first optimized the preparation of aqueous polysulfide solution from elemental sulfur. Using polysulfide solution, we were able to omit the otherwise mandatory chromatography, and to isolate the crystalline products directly from the reaction mixture by a simple filtration, retaining the sulfur in the solution phase. A wide range of thioureas synthesized in this way confirmed the reasonable substrate and functional group tolerance of our protocol. 相似文献
82.
Andrey Vyacheslavovich Vasilyev Valeriya Sergeevna Kuznetsova Tatyana Borisovna Bukharova Timofei Evgenevich Grigoriev Yuriy Dmitrievich Zagoskin Irina Alekseevna Nedorubova Igor Ivanovich Babichenko Sergey Nicolaevich Chvalun Dmitry Vadimovich Goldstein Anatoliy Alekseevich Kulakov 《Molecules (Basel, Switzerland)》2021,26(2)
Compositions based on chitosan/β-glycerophosphate hydrogels with highly porous polylactide granules can be used to obtain moldable bone graft materials that have osteoinductive and osteoconductive properties. To eliminate the influence of such characteristics as chain length, degree of purification, and molecular weight on a designed material, the one-stock chitosan sample was reacetylated to degrees of deacetylation (DD%) of 19.5, 39, 49, 55, and 56. A study of the chitosan/β-glycerophosphate hydrogel with chitosan of a reduced DD% showed that a low degree of deacetylation increased the MSCs (multipotent stromal cells) viability rate in vitro and reduced the leukocyte infiltration in subcutaneous implantation to Wistar rats in vivo. The addition of 12 wt% polylactide granules resulted in optimal composite mechanical and moldable properties, and increased the modulus of elasticity of the hydrogel-based material by approximately 100 times. Excessive filling of the material with PLA (polylactide) granules (more than 20%) led to material destruction at a ~10% strain. Osteoinductive and osteoconductive properties of the chitosan hydrogel-based material with reacetylated chitosan (39 DD%) and highly porous polylactide granules impregnated with BMP-2 (bone morphogenetic protein-2) have been demonstrated in models of orthotopic and ectopic bone formation. When implanted into a critical-size calvarial defect in rats, the optimal concentration of BMP-2 was 10 μg/mL: bone tissue areas filled the entire material’s thickness. Implantation of the material with 50 μg/mL BMP-2 was accompanied with excessive growth of bone tissue and material displacement beyond the defect. Significant osteoinductive and osteoconductive properties of the material with 10 μg/mL of BMP-2 were also shown in subcutaneous implantation. 相似文献
83.
Experimental Mechanics - Insufficient data are available to fully understand the effects of metal additive manufacturing (AM) defects for widespread adoption of the emerging technology.... 相似文献
84.
85.
Yablokov M. Yu. Shchegolikhin A. N. Lebedev O. V. Goncharuk G. P. Ozerin A. N. 《Russian Chemical Bulletin》2021,70(9):1816-1821
Russian Chemical Bulletin - Gradient polymer composites were prepared by melt-mixing of carbon black and polypropylene in a compounder and subsequent hot pressing of pellets. The thermally treated... 相似文献
86.
87.
Mathematical Notes - 相似文献
88.
Gelikonov G. V. Ksenofontov S. Yu. Shilyagin P. A. Gelikonov V. M. 《Radiophysics and Quantum Electronics》2019,62(3):228-236
Radiophysics and Quantum Electronics - We propose and experimentally test a numerical method for correction of the influence of fluctuations in the distance to objects during noncontact probing in... 相似文献
89.
A.G. Rousskikh A.V. Fedyunin A.P. Artyomov A.S. Zhigalin V.I. Oreshkin 《Current Applied Physics》2019,19(6):704-708
The aim of the study presented in this paper was to characterize quantitatively the erosion of aluminum cathodes in high-current vacuum arcs. The experimental setup comprised two current generators. The first one, capable of generating a current of amplitude up to 350 kA, was used to produce a plasma jet, that is, the object to be investigated. The second generator was used to produce a source of probe radiation for imaging the object under investigation in soft x rays of energy ?ν ≈ 0.5–3 keV. The findings of the study are based on experimental data obtained by electrophysical and radiographic methods. It has been shown that the cathode erosion rate in a high-current vacuum arc is a function of the charge passed through the cathode. 相似文献