全文获取类型
收费全文 | 5221篇 |
免费 | 650篇 |
国内免费 | 404篇 |
专业分类
化学 | 1201篇 |
晶体学 | 39篇 |
力学 | 597篇 |
综合类 | 124篇 |
数学 | 2184篇 |
物理学 | 2130篇 |
出版年
2024年 | 15篇 |
2023年 | 40篇 |
2022年 | 114篇 |
2021年 | 107篇 |
2020年 | 160篇 |
2019年 | 158篇 |
2018年 | 153篇 |
2017年 | 151篇 |
2016年 | 177篇 |
2015年 | 149篇 |
2014年 | 244篇 |
2013年 | 451篇 |
2012年 | 284篇 |
2011年 | 322篇 |
2010年 | 262篇 |
2009年 | 335篇 |
2008年 | 326篇 |
2007年 | 322篇 |
2006年 | 290篇 |
2005年 | 292篇 |
2004年 | 241篇 |
2003年 | 230篇 |
2002年 | 208篇 |
2001年 | 154篇 |
2000年 | 154篇 |
1999年 | 130篇 |
1998年 | 132篇 |
1997年 | 128篇 |
1996年 | 72篇 |
1995年 | 83篇 |
1994年 | 80篇 |
1993年 | 50篇 |
1992年 | 45篇 |
1991年 | 42篇 |
1990年 | 30篇 |
1989年 | 19篇 |
1988年 | 24篇 |
1987年 | 13篇 |
1986年 | 17篇 |
1985年 | 14篇 |
1984年 | 9篇 |
1983年 | 2篇 |
1982年 | 14篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1978年 | 2篇 |
1977年 | 6篇 |
1976年 | 2篇 |
1959年 | 4篇 |
排序方式: 共有6275条查询结果,搜索用时 15 毫秒
101.
102.
Mohammad Mehdi Khodaei Davood Kordestani 《Phosphorus, sulfur, and silicon and the related elements》2013,188(11):2403-2405
Abstract Direct conversion of acylals to the corresponding bisulfites can be easily performed in the presence of bismuth (III) nitrate pentahydrate in ethanol at room temperature in good yields. 相似文献
103.
Evgeniy A. Losev Elena Boldyreva 《Acta Crystallographica. Section C, Structural Chemistry》2019,75(3):313-319
A cocrystal and a molecular salt of β‐alanine and dl ‐tartaric acid, C3H8NO2+·C4H4O6?, of the same chemical composition, were studied over a wide temperature range by single‐crystal and powder X‐ray diffraction. Neither the interconversion between the two phases nor any polymorphic transitions were observed in the temperature range from 100 K to the melting points. This contrasts with the solvent‐mediated phase transition from the salt to the cocrystal in a slurry that has been documented earlier. 相似文献
104.
Guoxing Yin Tingting Niu Ting Yu Yabing Gan Xinyu Sun Peng Yin Haimin Chen Youyu Zhang Haitao Li Shouzhuo Yao 《Angewandte Chemie (International ed. in English)》2019,58(14):4557-4561
Studying numerous biologically important species simultaneously is crucial to understanding cellular functions and the root causes of related diseases. Direct visualization of endogenous biothiols in biological systems is of great value to understanding their biological roles. Herein, a novel multi‐signal fluorescent probe was rationally designed and exploited for the simultaneous sensing of homocysteine (Hcy), cysteine (Cys), and glutathione (GSH) using different emission channels. This probe was successfully applied to the simultaneous discrimination between and visualization of endogenous Hcy, Cys, GSH, and their transformation in living cells. 相似文献
105.
Chiral derivatives of trans-1,2-diaminocyclohexane with different N,N-dialkyl groups in well-defined orientations have been synthesized, and applied as catalysts for the asymmetric aldol reaction between a variety of aldehydes and ketones. Enantiomeric catalyst 1j catalyzed the reaction in ethanol and provided excellent diastereoselectivity and enantioselectivity. Significantly, simple replacement of organic solvents with water switched the products of the aldol reactions from anti to syn configuration. Such catalytic reactions led to the products with anti to syn diastereoselectivity up to 99:1 in ethanol, while in water gave the products with syn to anti diastereoselectivity up to 99:1. 相似文献
106.
107.
Jungui DaiShujun Zhang Jun-ichi SakaiJiao Bai Yoshiki OkuMasayoshi Ando 《Tetrahedron letters》2003,44(5):1091-1094
Three C-14 oxygenated taxanes, 2α,5α,10β,14β-tetraacetoxytaxa-4(20),11-diene (1), 2α,5α,10β-triacetoxy-14β-(2-methylbutyryloxy)taxa-4(20),11-diene (2), and yunanaxane (3), major products of callus cultures of Taxus spp., were regio- and stereoselectively hydroxylated at the 7β position by a fungus, Absidia coerulea IFO 4011. Intriguingly, when 1 was co-administered with β-cyclodextrin and incubated with the fungus cell cultures, three other compounds 5α,9α,10β,13α-tetraacetoxytaxa-4(20),11-dien-14β-ol (7), 5α,9α,10β,13α-tetraacetoxytaxa-4(20),11-dien-1β-ol (8) and 5α,9α,10β,13α-tetraacetoxy-11(15→1) abeotaxa-4(20),11-dien-15-ol (9) were obtained. 相似文献
108.
109.
以天然产物齐墩果酸为母体,设计合成齐墩果酸衍生物,采用计算机辅助药物设计,对C-3、C-28位结构改造,设计合成12个未见文献报道的靶向VEGFR受体抑制剂; 采用噻唑蓝(MTT)法,用人肝癌细胞(HepG2)和乳腺癌细胞(MCF-7)对其进行初步体外抗肿瘤活性筛选;其结构经1H-NMR、13C-NMR谱确证。活性测试得出化合物I7、II1与阳性对照药相比有较强抑制作用,其抗肿瘤活性高于母体OA,分子对接结果显示I7和II1 与 VEGFR 受体具有较好的结合能力,值得进一步研究。 相似文献
110.
Summary A simple and general scheme to exploit any discrete point group symmetry in two-electron integral transformations is introduced. It has been implemented together with integral pre-screening techniques in direct two-electron integral transformations. Its application has also been extended to subsequent MO integral processing steps like MP2 or solution of the coupled-perturbed Hartree-Fock equations (CPHF). Timings for representative applications are presented. 相似文献