全文获取类型
收费全文 | 11818篇 |
免费 | 2121篇 |
国内免费 | 1395篇 |
专业分类
化学 | 8038篇 |
晶体学 | 162篇 |
力学 | 823篇 |
综合类 | 105篇 |
数学 | 1250篇 |
物理学 | 4956篇 |
出版年
2024年 | 39篇 |
2023年 | 279篇 |
2022年 | 467篇 |
2021年 | 542篇 |
2020年 | 499篇 |
2019年 | 506篇 |
2018年 | 430篇 |
2017年 | 385篇 |
2016年 | 623篇 |
2015年 | 590篇 |
2014年 | 702篇 |
2013年 | 840篇 |
2012年 | 1071篇 |
2011年 | 1034篇 |
2010年 | 803篇 |
2009年 | 737篇 |
2008年 | 720篇 |
2007年 | 641篇 |
2006年 | 650篇 |
2005年 | 567篇 |
2004年 | 371篇 |
2003年 | 309篇 |
2002年 | 312篇 |
2001年 | 236篇 |
2000年 | 212篇 |
1999年 | 211篇 |
1998年 | 177篇 |
1997年 | 204篇 |
1996年 | 180篇 |
1995年 | 162篇 |
1994年 | 138篇 |
1993年 | 97篇 |
1992年 | 88篇 |
1991年 | 79篇 |
1990年 | 79篇 |
1989年 | 69篇 |
1988年 | 53篇 |
1987年 | 29篇 |
1986年 | 44篇 |
1985年 | 32篇 |
1984年 | 18篇 |
1983年 | 15篇 |
1982年 | 15篇 |
1981年 | 7篇 |
1980年 | 9篇 |
1975年 | 7篇 |
1973年 | 4篇 |
1972年 | 7篇 |
1965年 | 6篇 |
1964年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Abe K Abt I Ash WW Aston D Bacchetta N Baird KG Baltay C Band HR Barakat MB Baranko G Bardon O Barklow T Bazarko AO Ben-David R Benvenuti AC Bienz T Bilei GM Bisello D Blaylock G Bogart JR Bolton T Bower GR Brau JE Breidenbach M Bugg WM Burke D Burnett TH Burrows PN Busza W Calcaterra A Caldwell DO Calloway D Camanzi B Carpinelli M Cassell R Castaldi R Castro A Cavalli-Sforza M Church E Cohn HO Coller JA Cook V Cotton R Cowan RF Coyne DG D'Oliveira A Damerell CJ Dasu S De Sangro R De Simone P 《Physical review D: Particles and fields》1994,50(9):5580-5590
32.
33.
A practical synthetic route to 4-acetylisocoumarins and the first total synthesis of AGI-7 (5) and sescandelin (4) are described. The readily available homophthalate 8 was transformed to the vinylogous amide ester 13 in high overall yield. Upon treatment of 13 with refluxing aqueous formic acid, the desired 4-acetylisocoumarin (5) and its regioisomer 3-methyl-4-formylisocoumarin (17) were produced in a 3:1 ratio. After separation of the desired product (5) from the unwanted minor isomer, the enantioselective reduction of AGI-7 by borane in the presence of Corey's (S)-oxazaborolidine reagent afforded (+)-sescandelin (4) with a 93% ee. 相似文献
34.
Two novel metal-organic frameworks (MOFs) [Zn(TITMB)(OAc)](OH).8.5H(2)O (1) and [Ag(TITMB)N(3)].H(2)O (2) [TITMB = 1,3,5-tris(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene, OAc = acetate anion] were synthesized and their structures were determined by X-ray crystallography. Complex 1 crystallizes in tetragonal space group P(-)4 with a = 23.2664(7) and c = 11.9890(3) A and Z = 8. 1 has a one-dimensional tubelike structure with large inner pore size of approximately 17 A. Complex 2 crystallizes in monoclinic space group C2 with a = 20.7193(10), b = 11.5677(8), and c = 12.2944(6) A, beta = 125.5770(10) degrees, and Z = 4. 2 consists of two-dimensional honeycomb networks that interpenetrate each other to generate a polycatenated structure. In these two complexes, both zinc(II) and silver(I) atoms are four-coordinated with the same tetrahedral coordination geometry. The topologies of 1 and 2 are predominated by the conformations of TITMB, which are cis, trans, trans in 1 and cis, cis, cis in 2, respectively. 相似文献
35.
36.
A new highly sensitive and selective chromogenic reagent, 2-(2,5-disulfonic-4-methoxyphenylazo)-7-(2-hydroxyl-5-carboxylphenylazo)-1,8-dihydroxynaphthalene-3,6-disulfonic
acid (1), was synthesized and applied to the spectrophotometric determination of trace thorium. In 5 mL of a 6 M perchloric acid
medium, which greatly increases the selectivity, thorium reacts with 1 to form a 1: 2 green complex, having a sensitive absorption peak at 670 nm. Under optimal conditions, Beer’s law is obeyed
over the range from 0 to 0.8 μg/mL Th(IV) and the apparent molar absorptivity is 2.09 × 105 L/mol cm. It is found that, uranium(VI), Ti(IV), heavy rare earths, and most of other common metal ions do not interfere.
The method has been tested on the determination of thorium in food samples with satisfactory results.
The text was submitted by the authors in English. 相似文献
37.
38.
Density functional theory (PBE and B3LYP) was used to study asymmetric hydrogenations of alkenes catalyzed by an iridium imidazolylidine oxazoline complex. The calculation predicts that the alkene preferentially coordinates to the site trans to the carbene. The coordinated alkene then reacts first with the H2 ligand, then with the hydride to form alkane. Finally, the alkane is released by equilibrating with extrinsic H2 and alkene. Enantioface selectivities for hydrogenations of trisubstituted alkenes seem to be driven primarily by steric interactions with the adamantyl part of the ligand; only the smallest substituents can adopt a site close to it. Application of this theoretical model leads to correct predictions regarding the experimentally observed sense and magnitude of the enantioselectivities. 相似文献
39.
Determination of dispersity of crushed granite 总被引:1,自引:0,他引:1
Summary Experimental crushed granite column breakthrough curves, using 99Tc as spike tracer and 3H as invariant tracer, were analyzed by different linear regression techniques. Dispersity of crushed granite and the retardation factor of 99TcO4- on the crushed granite were determined simultaneously by one linear regression. Dispersity of crushed granite was also obtained with 3H as invariant tracer by the other linear regression. The dispersities found by spike source and invariant source methods are compared. Experimental results show that the dispersity found by the spike source method is close to that found by the invariant source method. This indicates that dispersity is only a characteristic of the dispersion medium. 相似文献
40.
James V. Crivello Mingxin Fan 《Journal of polymer science. Part A, Polymer chemistry》1992,30(1):31-39
In the presence of Si? H containing cocatalysts, dicobaltoctacarbonyl has been found to very efficiently catalyze the ring-opening polymerization of cyclic ethers, especially epoxides, as well as certain vinyl monomers. The reaction conditions employed are very similar to those used in Co2(CO)8 catalyzed hydrogenation and hydrosilylation reactions. Detailed investigations have been carried out to elucidate the nature of the active species for this catalytic system. A cationic mechanism is proposed based on the experimental results of those investigations. 相似文献