全文获取类型
收费全文 | 31315篇 |
免费 | 1743篇 |
国内免费 | 4577篇 |
专业分类
化学 | 27719篇 |
晶体学 | 589篇 |
力学 | 201篇 |
综合类 | 164篇 |
数学 | 4020篇 |
物理学 | 4942篇 |
出版年
2024年 | 32篇 |
2023年 | 235篇 |
2022年 | 450篇 |
2021年 | 546篇 |
2020年 | 601篇 |
2019年 | 1623篇 |
2018年 | 796篇 |
2017年 | 1573篇 |
2016年 | 980篇 |
2015年 | 879篇 |
2014年 | 1185篇 |
2013年 | 2719篇 |
2012年 | 1770篇 |
2011年 | 2065篇 |
2010年 | 1567篇 |
2009年 | 1793篇 |
2008年 | 2022篇 |
2007年 | 2103篇 |
2006年 | 1945篇 |
2005年 | 1684篇 |
2004年 | 1641篇 |
2003年 | 1334篇 |
2002年 | 1101篇 |
2001年 | 909篇 |
2000年 | 898篇 |
1999年 | 688篇 |
1998年 | 630篇 |
1997年 | 540篇 |
1996年 | 502篇 |
1995年 | 489篇 |
1994年 | 378篇 |
1993年 | 332篇 |
1992年 | 315篇 |
1991年 | 229篇 |
1990年 | 156篇 |
1989年 | 124篇 |
1988年 | 111篇 |
1987年 | 68篇 |
1986年 | 71篇 |
1985年 | 89篇 |
1984年 | 60篇 |
1983年 | 37篇 |
1982年 | 74篇 |
1981年 | 61篇 |
1980年 | 40篇 |
1979年 | 60篇 |
1978年 | 40篇 |
1977年 | 30篇 |
1976年 | 20篇 |
1973年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
71.
72.
许多乙酰芳胺类化合物具有优异的生物活性,例如除草剂苯噻草胺,可抑制细胞生长和分裂,防除稻田中禾本科杂草[1];杀菌剂甲霜灵可防治作物霜霉病[2]。本文将具有多种生物活性的嘧啶基团引入到乙酰芳胺结构中[3],合成下列10个未见文献报道的标题化合物Ⅰ,通... 相似文献
73.
74.
The response to Hg(II) of a thin all-solid-state Te-doped silver chalcogenide membrane, described by the general formula Ag2 + δSe1 − xTex, which has been electrochemically prepared following a previously proposed approach, has been investigated. The kinetics of formation of the membrane's secondary dynamic response to Hg(II) has been successfully combined with the precise timing and transient signal, typical for flow-injection (FI) measurements, in developing a sensitive and reliable mercury FI detector. Under optimized stream conditions it exhibits a linear Nernstian response, with a double slope of the calibration graph of 59 mV dec−1, over the mercury(II) concentration range 10−6 − 10−3 M, the typical sample throughput amounting to about 70 samples per hour. The observed chemical amplification of the signal is due to the specificity of the processes dominating the initial step in formation of the steady-state signal of the membrane to mercury. The analytical performance of the Hg(II) FI detector, as regards sensitivity, reproducibility, selectivity and long-term stability has been thoroughly investigated. The exact procedure for membrane electrodeposition is given and the potential of the proposed approach as a cost-effective way for preparing chalcogenides of unique structure and properties has been outlined in the above context. 相似文献
75.
76.
4-Vinylphenols, useful compounds for industrial applications, were obtained by decarboxylation of 4-hydroxycinnamic acids under microwave irradiation in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as base and basic aluminum oxide as solid support. The reactions were fast (15-30 min). The selective extraction of the final products with ethyl acetate avoids chromatographic purifications. The conversions are quantitative and the yields are satisfactory. Only the unstable 4-vinylcatechol was obtained in moderate yield. This procedure was successfully extended to a natural sample of ferulic acid extracted from wheat bran to get the corresponding 4-vinylguaiacol, a FEMA GRAS (Flavor and Extract Manufacturer's Association; General Regarded as Safe) approved flavoring agent. 相似文献
77.
We construct cellular homotopy theories for categories of simplicial presheaves on small Grothendieck sites and discuss applications to the motivic homotopy category of Morel and Voevodsky. 相似文献
78.
79.
80.
Several Pd-catalyzed reactions were explored to further functionalize the bromo-substituted 4-amino-1,2,4,5-tetrahydro-2-benzazepin-3-one scaffold (Aba). We report in this paper suitable reaction conditions for Suzuki, Buchwald-Hartwig, and Heck reactions. The substitution pattern of the starting aminobenzazepinone turned out to be crucial for the success of these transition metal-catalyzed reactions, which often required modifications of standard literature procedures. The Pd-catalyzed methods provide access to novel substitution patterns of the Aba scaffold. 相似文献