全文获取类型
收费全文 | 16623篇 |
免费 | 2714篇 |
国内免费 | 1983篇 |
专业分类
化学 | 11865篇 |
晶体学 | 168篇 |
力学 | 1028篇 |
综合类 | 162篇 |
数学 | 1972篇 |
物理学 | 6125篇 |
出版年
2024年 | 58篇 |
2023年 | 338篇 |
2022年 | 599篇 |
2021年 | 644篇 |
2020年 | 671篇 |
2019年 | 641篇 |
2018年 | 579篇 |
2017年 | 536篇 |
2016年 | 754篇 |
2015年 | 800篇 |
2014年 | 941篇 |
2013年 | 1205篇 |
2012年 | 1409篇 |
2011年 | 1456篇 |
2010年 | 1025篇 |
2009年 | 949篇 |
2008年 | 1060篇 |
2007年 | 982篇 |
2006年 | 867篇 |
2005年 | 729篇 |
2004年 | 570篇 |
2003年 | 460篇 |
2002年 | 453篇 |
2001年 | 396篇 |
2000年 | 318篇 |
1999年 | 340篇 |
1998年 | 301篇 |
1997年 | 222篇 |
1996年 | 253篇 |
1995年 | 255篇 |
1994年 | 211篇 |
1993年 | 179篇 |
1992年 | 142篇 |
1991年 | 166篇 |
1990年 | 156篇 |
1989年 | 126篇 |
1988年 | 100篇 |
1987年 | 87篇 |
1986年 | 66篇 |
1985年 | 69篇 |
1984年 | 28篇 |
1983年 | 39篇 |
1982年 | 27篇 |
1981年 | 21篇 |
1980年 | 14篇 |
1979年 | 12篇 |
1978年 | 8篇 |
1977年 | 11篇 |
1975年 | 7篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
A sensitive, rapid and selective liquid chromatography negative electrospray ionization tandem mass spectrometry [LC-(-)ESI-MS-MS] method has been developed and validated for the simultaneous quantification of budesonide (BUD) and its major metabolites, 6beta-hydroxybudesonide (OH-BUD) and 16alpha-hydroxyprednisolone (OH-PRED) in human plasma. The method was validated over a linear range from 0.1 to 10 ng/mL for all three analytes using a solid-phase extraction procedure with 9-fluoro-hydrocortisone as the internal standard. The between-day and within-day coefficients of variation for all compounds were < or =20% at the concentrations of lower limit of quantification and < or =15% at other quality control concentrations. The utility of this assay was demonstrated by monitoring BUD, OH-BUD and OH-PRED plasma concentrations in one healthy subject for 24 h following a 3 mg oral dose of budesonide, administered as a pH modified release capsule (Budenofalk) to healthy volunteers. 相似文献
33.
A chain of vertex-linked "bare" nido-Ge(9)(2-) clusters (shown in the picture) is featured by the novel polymeric Zintl anion formed from the binary alloy "KGe(4)", ethylenediamine, and [18]crown-6. The polymerization of nido-Ge(9)(4-) clusters is counterintuitive to known two-electron oxidation behavior of nido clusters and the existence of the isolated closo-Ge(9)(2-) ion. The novel semiconducting cluster "wire" establishes direct structural and mechanistic links between molecular Zintl cluster ions with the extended structures of Zintl phases and elemental nanophase materials. 相似文献
34.
A diastereoselective and modular approach to the synthesis of the 3-hydroxymethyl-2,3,5,6,7,7a-hexahydro-1H-pyrrolizine-1,2,7-triol structure, characteristic of several natural pyrrolizidine natural products, has been developed. This approach culminated in the synthesis of (-)-7-epiaustraline and (+)-1,7-diepiaustraline. The oxazolidinone group has been found to be a useful protecting group in the RCM reaction and, as part of a pyrrolo[1,2-c]oxazol-3-one ring system, has functioned as a stereo- and regio-directing group in a key diastereoselective cis-dihydroxylation reaction and a regioselective nucleophilic ring-opening of a S,S-dioxo-dioxathiole. 相似文献
35.
Min Ming Tang 《Journal of Mathematical Analysis and Applications》1977,57(2):368-381
In this paper we study the behavior of solutions of some quasilinear parabolic equations of the form as t → ∞. In particular, the solutions of these equations will decay to zero as t → ∞ in the L∞ norm. 相似文献
36.
The definition of bond index introduced by Ehrenson, and written in terms of bond order and overlap integrals, has been applied to a series of nitriles. A good correlation between heats of formation and a linear equation in the indices for each bond present is obtained. This was extended to include the results for a set of hydrocarbons. 相似文献
37.
A sensitive and selective method using liquid chromatography with electrospray ionization mass spectrometric detection was
developed for the quantification of bilobalide and ginkgolides in canine plasma. The analytes were extracted with diethyl
ether-dichloromethane-isopropanol (6:3:1, v/v) after spiking the samples with daidzein (internal standard). The lower limit
of quantification (LLOQ) of the method was 2.5 μg L−1 for ginkgolide B and 10.0 μg L−1 for bilabolide, ginkgolide A and ginkgolide C. The accuracy of the method was within 15% of the actual values over a wide
range of plasma concentrations. The intra-day and inter-day precision was better than 15% (R.S.D.). Finally, the LC-ESI-MS
method was successfully applied to study the pharmacokinetics of ginkgolides and bilabolide after administration of Ginkgo biloba extracts to dogs. 相似文献
38.
The structures of B32 and B32H2–32 with Ih symmetry have been investigated by means of ab initio calculations at STO-3G level. The relationship between molecular orbitals of them has been analyzed and their bonding properties have been discussed. Then the possibility of their existence, as well as the similarity and difference between B32 (B32H2–32) and C60 (C60H60) have been inferred. 相似文献
39.
Yu Tang 《Tetrahedron letters》2006,47(23):3823-3825
5-Endo iodocyclization of various β,γ-unsaturated amides proceeded smoothly to give the corresponding conjugated iminolactones exclusively in satisfactory yields with the use of tBuOCl and I2 as the reagents, which proved to be much advantageous over the conventional I2/NaHCO3. 相似文献
40.
Lipophilic crown ether carboxylic acids such as 2-(sym-dibenzo-16-crown-5-oxy)stearic acid with a cavity size comparable to the ionic radius of rare-earth elements are selective chelation agents for preconcentration and separation of lanthanides from natural waters for NAA. Interfering matrix elements such as sodium and bromine can be simultaneously eliminated during the extraction. The lanthanides can be back-extracted into a dilute acid solution for NAA, thus providing a large preconcentration factor. This two-step extraction method appears suitable for the determination of lanthanides in natural waters and in biological samples. 相似文献