全文获取类型
收费全文 | 10314篇 |
免费 | 1752篇 |
国内免费 | 2012篇 |
专业分类
化学 | 8149篇 |
晶体学 | 143篇 |
力学 | 526篇 |
综合类 | 207篇 |
数学 | 1313篇 |
物理学 | 3740篇 |
出版年
2024年 | 10篇 |
2023年 | 96篇 |
2022年 | 167篇 |
2021年 | 225篇 |
2020年 | 284篇 |
2019年 | 363篇 |
2018年 | 262篇 |
2017年 | 273篇 |
2016年 | 412篇 |
2015年 | 466篇 |
2014年 | 555篇 |
2013年 | 761篇 |
2012年 | 862篇 |
2011年 | 963篇 |
2010年 | 848篇 |
2009年 | 819篇 |
2008年 | 924篇 |
2007年 | 884篇 |
2006年 | 845篇 |
2005年 | 658篇 |
2004年 | 568篇 |
2003年 | 520篇 |
2002年 | 491篇 |
2001年 | 387篇 |
2000年 | 280篇 |
1999年 | 213篇 |
1998年 | 160篇 |
1997年 | 112篇 |
1996年 | 108篇 |
1995年 | 89篇 |
1994年 | 80篇 |
1993年 | 69篇 |
1992年 | 63篇 |
1991年 | 52篇 |
1990年 | 44篇 |
1989年 | 26篇 |
1988年 | 26篇 |
1987年 | 25篇 |
1986年 | 17篇 |
1985年 | 17篇 |
1984年 | 6篇 |
1983年 | 16篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1973年 | 3篇 |
1970年 | 3篇 |
1959年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
The asymmetric domino Michael-S(N)2 reaction of various 1,3-dicarbonyl compounds to α-bromonitroalkenes is described for the first time, employing readily available cinchona-derived bifunctional thioureas as organocatalysts. The novel transformations were highly regio-, chemo-, diastereo-, and enantioselective, which simultaneously gave the chiral tricyclic 2,3-dihydrofurans, bicyclic 2,3-dihydrofurans, and tetrasubstituted 2,3-dihydrofurans with two vicinal chiral carbon centers. 相似文献
994.
Gang Liu Tian‐Jun Wu Dr. Yuan‐Ping Ruan Prof. Pei‐Qiang Huang Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(19):5755-5768
The asymmetric total synthesis of natural azasugars (+)‐castanospermine, (+)‐7‐deoxy‐6‐epi‐castanospermine, and synthetic (+)‐1‐epi‐castanospermine has been accomplished in nine to ten steps from a common chiral building block (S)‐ 8 . The method features a powerful chiral relay strategy consisting of a highly diastereoselective vinylogous Mukaiyama‐type reaction with either chiral or achiral aldehydes (≥95 % de; de=diastereomeric excess) and a diastereodivergent reduction of tetramic acids, which allows formation of three continuous stereogenic centers with high diastereoselectivities. The method also provides a flexible access to structural arrays of 5‐(α‐hydroxyalkyl)tetramic acids, such as 17/34 , and 5‐(α‐hydroxyalkyl)‐4‐hydroxyl‐2‐pyrrolidinones, such as 18 and 25/35 a . The method constitutes the first realization of the challenging chiral synthons A and D and thus of the conceptually attractive retrosynthetic analysis shown in Scheme 1 in a highly enantioselective manner. 相似文献
995.
采用甲基丙烯酸二甲氨基乙酯的溴代丁烷季铵盐和硅烷偶联剂KH570的共聚物作为感湿聚合物,并向该聚合物中掺杂LiCl、CaCl2、FeCl33种不同的盐类,制备了高分子电阻型湿敏元件,系统研究了聚合物浓度、无机盐的种类和浓度对元件湿敏性能的影响。结果表明,在33%~95%RH湿度范围内,元件显示出较高的灵敏度(b为-0.043 8~-0.038 8)和较好的线性(R为-0.994 8~-0.981 6),且阻抗随聚合物浓度的增加而下降,但响应变慢;掺杂LiCl和CaCl2可使元件阻抗变小,掺杂FeCl3却使元件阻抗增大;在1×10-2mol/L的最佳LiCl掺杂浓度下,元件具有最好的灵敏度(b=-0.044 6)和最短的脱湿时间(20 s)。 相似文献
996.
997.
本文讨论一类非线性Schrdinger方程-ε~2△v+V(z)v=K(x)v~p,x∈R~N,v∈W~(1,2)(R~N),v(x)>0,势函数V(x)有正下界和在无穷远处为零两种情形.通过强最大值原理我们证明方程的基态解关于充分小的ε>0一致集中. 相似文献
998.
Zhi-gang Yu Zhi Qin Hong-rui Ji Xia Du Yan-hui Chen Ping Pan Heng Wang Yu-yong Liu 《Chromatographia》2010,72(11-12):1073-1081
A method for the simultaneous determination of 11 triazine herbicides residues in river water has been developed. It involves solid-phase extraction (SPE) pretreatment step and rapid resolution liquid chromatography-tandem mass spectrometry (RRLC-MS-MS). In the SPE pretreatment step, the adsorptive performance of MWCNTs material as SPE adsorbent and the elution capability of five kinds of solvents were investigated; in the LC separation step, a rapid resolution high throughput LC column, was used and the gradient elution mode adopted. The linear correlation coefficients (r 2) of the method for 11 target analytes varied between 0.9930 and 0.9980, the mean recoveries were in the range of 73.0 and 98.0% with relative standard deviations (RSD) 2.6 ~ 4.2%, the method detection limits (MDL) were all below 0.1 ng L?1. An expanded uncertainty of not more than 20% was estimated for each analyte at the spiked concentration of 4.0 μg L?1. The proposed method was applied to the determination of the residue concentrations of 11 pollutants in Songhuajiang River water. 相似文献
999.
A planar transition metal complex Cu(L)2 (L = (E)-benzyl-2-(4-nitrobenzylidene)-hydrazinecarbodithioate) has been prepared and determined by X-ray single-crystal diffraction. The crystal belongs to the monoclinic system,space group P21/c with a = 6.7101(11),b = 16.952(3),c = 13.962(3) ,β = 92.458(4)°,V = 1586.7(5) 3,Z = 4,Mr = 724.33,Dc = 1.516 g·m-3,μ = 0.998 mm-1,F(000) = 742,S = 1.021,R = 0.0634 and wR = 0.1077 for 813 observed reflections with Ⅰ 2σ(Ⅰ) and 205 parameters. In the molecular structure of the title complex,the copper atom exhibits a slightly distorted square-planar geometry in which the basal plane is defined by two N and two S atoms from two bidentate ligands. The complex was evaluated for its antitumor activity against two kinds of cell lines (MKN45 and HepG2) by MTT method. The preliminary bioassay indicates that the complex exhibits weak antitumor activity. 相似文献
1000.
Solvothermal reaction of [WS4]2-with CuCN and trithiocyanuric acid(L1) in orga-nic solvents gave rise to a new W/Cu/S polymer with a 2D anionic network,namely [Et4N]2[WS4Cu3(C3N3S3H1.5)2](1).The anionic layer of 1 is constructed by the T-shaped {WS4Cu3} subunits as nodes and L1 as linkers and features a(4,4) topology.Both 1 and its isomorphous compound [Et4N]2[MoS4Cu3(C3N3S3H1.5)2](2) have been fully characterized by X-ray crystal analysis,IR and microanalyses.Compounds 1 and 2 show optical transitions with band gaps of 2.17 and 1.84 eV,respectively. 相似文献