全文获取类型
收费全文 | 147372篇 |
免费 | 31379篇 |
国内免费 | 10148篇 |
专业分类
化学 | 120760篇 |
晶体学 | 1264篇 |
力学 | 8938篇 |
综合类 | 533篇 |
数学 | 14536篇 |
物理学 | 42868篇 |
出版年
2024年 | 653篇 |
2023年 | 5364篇 |
2022年 | 4917篇 |
2021年 | 6283篇 |
2020年 | 8178篇 |
2019年 | 6217篇 |
2018年 | 5451篇 |
2017年 | 3789篇 |
2016年 | 10137篇 |
2015年 | 9893篇 |
2014年 | 10470篇 |
2013年 | 12413篇 |
2012年 | 12299篇 |
2011年 | 10685篇 |
2010年 | 9568篇 |
2009年 | 9302篇 |
2008年 | 7493篇 |
2007年 | 6705篇 |
2006年 | 5568篇 |
2005年 | 4659篇 |
2004年 | 3445篇 |
2003年 | 2712篇 |
2002年 | 2449篇 |
2001年 | 2020篇 |
2000年 | 1780篇 |
1999年 | 2097篇 |
1998年 | 1868篇 |
1997年 | 1801篇 |
1996年 | 1964篇 |
1995年 | 1635篇 |
1994年 | 1542篇 |
1993年 | 1374篇 |
1992年 | 1166篇 |
1991年 | 1050篇 |
1990年 | 846篇 |
1989年 | 638篇 |
1988年 | 577篇 |
1987年 | 480篇 |
1986年 | 453篇 |
1985年 | 414篇 |
1984年 | 346篇 |
1977年 | 337篇 |
1976年 | 397篇 |
1975年 | 488篇 |
1974年 | 516篇 |
1972年 | 387篇 |
1971年 | 375篇 |
1970年 | 554篇 |
1969年 | 437篇 |
1968年 | 466篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
The inhomogeneous Dirichlet problems concerning divergence form elliptic equations are studied. Optimal regularity requirements on the coefficients and domains for the W1,p theory, 1 < p < ∞, are obtained. The principal coefficients are supposed to be in the John‐Nirenberg space with small BMO seminorms. The domain is a Reifenberg domain. These conditions for the W1,p theory not only weaken the requirements on the coefficients but also lead to a more general geometric condition on the domains. In fact, these domains might have fractal dimensions. © 2004 Wiley Periodicals, Inc. 相似文献
33.
Dr. Konrad Natterer 《Monatshefte für Chemie / Chemical Monthly》1885,6(1):519-522
Ohne Zusammenfassung 相似文献
34.
35.
Herein we report a new method to collect a qualified infrared spectrum of a solute in solution by two solvent cells with different thickness during background single-beam spectrum scanning. By collecting the background spectrum with two cells (two stages), we successfully achieved accurate solvent compensation between a sample and a reference, namely, the solvent amounts in the sample and background measurements could become congruent. Therefore, the solvent bands were thoroughly suppressed in the infrared spectrum and a qualified spectrum of the solute was obtained. 相似文献
36.
Akira Yanagisawa Prof. Dr. Takahiro Suzuki Takanori Koide Shogo Okitsu Takayoshi Arai Prof. Dr. 《化学:亚洲杂志》2008,3(10):1793-1800
A Barbier‐type regioselective propargylation of aldehydes and ketones with (3‐bromobut‐1‐ynyl)trimethylsilane has been achieved using reactive barium as a low‐valent metal in THF. Especially in the case of ketones, the corresponding homopropargylic alcohols form almost exclusively. In the reaction of α,β‐unsaturated carbonyl compounds, only 1,2‐adducts have been observed. This method is also applicable to propargylation of imines, and the corresponding homopropargylic amines are obtained regiospecifically in good yields with diastereomeric ratios of up to 87:13. 相似文献
37.
Silica@copper (SiO2@Cu) core–shell nanoparticles were synthesized and well characterized by XRD, TEM, AFM, XPS, UV/Vis, TGA–MS, and ICP–AES techniques. The synthesized SiO2@Cu core–shell nanoparticles were employed as catalysts for the conjugate addition of amines to α,β‐unsaturated compounds in water to obtain β‐amino carbonyl compounds in excellent yields in shorter reaction times. Furthermore, the catalyst works well for hetero‐Michael addition reactions of heteroatom nucleophiles such as thiols to α,β‐unsaturated compounds. As the reaction is performed in water, it allows for easy recycling of the catalyst with consistent activity. 相似文献
38.
A two-step swelling procedure was adopted to synthesize mono-dispersed and highly cross-linked poly (St-divinylbenzene) particles
with PSt micro-spheres (1.80 μm in diameter). The PSt micro-spheres were prepared by a dispersion polymerization method and
used as seeds. The effects of monomer concentration, ratio of ethanol to water, swelling reagents, crosslinking reagents,
swelling temperature and agitation speed on particle size were investigated in detail. The morphologies and size distributions
of these micro-spheres were examined by SEM and particle size analysis (PSA). The T
g of the micro-spheres was measured by DSC. The results indicate that the particles (6.20 μm in diameter) exhibit excellent
mono dispersed property and high crosslinking degree when the concentration of the swelling reagent was 25%, the concentration
of the crosslinking reagents was 23%, the swelling temperature was 30°C and the stirring speed was 150 r/min.
__________
Translated from Chinese Journal of Applied Chemistry, 2007, 24(11): 1289–1294 相似文献
39.
40.
Chengzhi Qi Mingyang Wang Qihu Qian Jianjie Chen 《Moscow University Mechanics Bulletin》2008,63(5):113-121
The formation mechanisms for the structural hierarchy in geological media are discussed. It is shown that the formation of such a hierarchy is caused by certain external and internal circumstances. The first ones consist in the fact that, because of external actions, the Earth’s poles continuously execute the translational and rotational motions responsible for a regular structure of rock fracture and for the appearance of the scale factor √2. The second ones consist in the fact that, under the action of many random factors and because of external actions, during the formation of geological media there appear dissipative structures and, hence, some self-similar fractal structures are formed. 相似文献