全文获取类型
收费全文 | 10511篇 |
免费 | 297篇 |
国内免费 | 98篇 |
专业分类
化学 | 434篇 |
晶体学 | 11篇 |
力学 | 66篇 |
综合类 | 6篇 |
数学 | 9439篇 |
物理学 | 632篇 |
无线电 | 318篇 |
出版年
2023年 | 21篇 |
2022年 | 25篇 |
2021年 | 30篇 |
2020年 | 54篇 |
2019年 | 280篇 |
2018年 | 286篇 |
2017年 | 172篇 |
2016年 | 141篇 |
2015年 | 129篇 |
2014年 | 274篇 |
2013年 | 624篇 |
2012年 | 298篇 |
2011年 | 627篇 |
2010年 | 526篇 |
2009年 | 705篇 |
2008年 | 824篇 |
2007年 | 836篇 |
2006年 | 636篇 |
2005年 | 394篇 |
2004年 | 401篇 |
2003年 | 339篇 |
2002年 | 278篇 |
2001年 | 203篇 |
2000年 | 198篇 |
1999年 | 248篇 |
1998年 | 227篇 |
1997年 | 166篇 |
1996年 | 243篇 |
1995年 | 214篇 |
1994年 | 205篇 |
1993年 | 172篇 |
1992年 | 121篇 |
1991年 | 89篇 |
1990年 | 87篇 |
1989年 | 88篇 |
1988年 | 60篇 |
1987年 | 60篇 |
1986年 | 65篇 |
1985年 | 88篇 |
1984年 | 61篇 |
1983年 | 51篇 |
1982年 | 63篇 |
1981年 | 60篇 |
1980年 | 54篇 |
1979年 | 39篇 |
1978年 | 44篇 |
1977年 | 35篇 |
1976年 | 38篇 |
1975年 | 10篇 |
1974年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
291.
292.
V. G. Berezkin A. A. Korolev I. V. Malyukova R. G. Mardanov 《Russian Chemical Bulletin》1997,46(12):2064-2073
The effects of the carrier gas nature and pressure on the relative retention values of organic compounds were studied using
a series of capillary columns differing in the film thickness of the polar stationary phase (PEG-20M). Relative retention
depends linearly on the carrier gas pressure. This dependence becomes more pronounced in the following order of carrier gases:
helium < nitrogen < carbon dioxide. The limiting relative retention at a carrier gas pressure approaching zero rather than
relative retention values measured experimentally (relative retention time, Kovats retention index,etc.) is an invariant characteristic of a compound subjected to chromatography. For the carrier gases studied, the limiting retention
values almost does not depend on the nature of the carrier gas used. The limiting indicating the complex absorption-adsorption
nature of these parameters. Dissolution of a carrier gas in the stationary liquid phase has an effect on the relative retention.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2177–2186, December, 1997. 相似文献
293.
T. L. Clemens L. J. Fraher J. L. H. O'Riordan C. J. Little A. Dale 《Chromatographia》1980,13(3):141-144
Summary A simple, reproducible method for the biological synthesis of tritiated 24,25-dihydroxycholecalciferol, 25,26-dihydroxycholecalciferol and 1,25-dihydroxycholecalciferol is described. Kidney homogenates from both vitamin D deficient and replete chicks were usedin vitro to generate these dihydroxylated metabolites using 25 (23,24-3H) hydroxycholecalciferol as the substrate. Tritiated products were purified by Sephadex LH 20 chromatography followed by high-performance liquid chromatography; the identity of each metabolite was established by chromatography with authentic crystalline preparations.Presented at the Symposium organised by the Chromatography Discussion Group, held at Hatfield Lodge on 29 November 1979. 相似文献
294.
Using geometry optimization and DFT method at the B3LYP/6-31G* level of theory for C30H20, an equilibrium geometry is identified that has the form of polyhedral hydrocarbon with five carbon–carbon single bonds linking a dodecahedrane cage and a pentaprismane cage. Thus, this molecule is a tri-cage molecule with two pentaprismane cages and one dodecahedrane cage. Vibrational frequencies and the infrared spectrum are computed at the same level of theory. The heat of formation for C30H20 has been estimated in this paper. The heat of formation of C30H20 as well as the vibrational analysis indicates that this molecule enjoys sufficient stability to allow for its experimental preparation. 相似文献
295.
Helmut Karzel 《Aequationes Mathematicae》1978,17(1):83-90
A permutation set (M, I) consisting of a setM and a set of permutations ofM, is calledsymmetric, if for any two permutations, the existence of anx M with (x) (x) and
–1
(x) =
–1
(x) implies
–1
=
–1
, andsharply 3-transitive, if for any two triples (x
1,x
2,x
3), (y
1,y
2,y
3) M
3 with|{x
1,x
2,x
3
}| = |{y
1,y
2,y
3
}| = 3 there is exactly one permutation with(x
1) =y
1,(x
2) =y
2,(x
3) =y
3. The following theorem will be proved.THEOREM.Let (M, ) be a sharply 3-transitive symmetric permutation set with |M|3, such that contains the identity. Then is a group and there is a commutative field K such that and the projective linear group PGL(2, K) are isomorphic. 相似文献
296.
A highly sensitive and specific enzyme-linked immunosorbent assay (ELISA) method has been developed for the determination of 20(S)-protopanaxatriol (PPT), one of the major aglycones of dammarane-type ginseng saponins. Polyclonal antibodies raised against ginsenoside F1 (GF1)-bovine serum albumin showed high reactivities to PPT and GF1, whereas they exhibited minor or even no cross-reactivities to other ginsenosides and protopanaxadiol (0.19%). The working range of this method extends from 50 pg ml−1 to 20 ng ml−1 of PPT. The assay reported here has been validated against an HPLC technique using PPT-containing samples and was shown to correlate closely (γ=0.993). This ELISA could be a useful tool for the determination of PPT contained in biological fluids and plant materials. 相似文献
297.
16R-Bromopregnane-3S,20S-diol reacted with potassium t-butoxide to afford androst-16-en-3S-ol in a moderate yield via fragmentation reaction. The latter is a key intermediate for the synthesis of 5α-androst-16-en-3-one, as boar sex pheromone, and other steroidal drugs. In addition, 16R,20S-epoxypregnane-3S-ol was also obtained as a major product by changing the reaction solvent. 相似文献
298.
The convergence of the class of direct interpolatory iterationsI
n
for a simple zero of a non-linear operatorF in a Banach space of finite or infinite dimension is studied.A general convergence result is established and used to show that ifF is entire the radius of convergence goes to infinity withn while ifF is analytic in a ball of radiusR the radius of convergence increases to at leastR/2 withn.The research was supported in part by the National Science Foundation under Grant MCS 75-222-55 and the office of Naval Research under Contract N00014-76-C-0370, NR 044-422. 相似文献
299.
Defining achoice as a mapping of the subsets of a setX into their respective subsets, a one-to-one (and naturally) corresponding binary operation,sequential choice, is identified under which the power set ofX is closed as achoice groupoid. A complete logical diagram is given, exhibiting all the implications between conjunctions of the seven conditions: (1) idempotence, (2) consistency, (3) absorbence, and (4) homomorphism of a choice, and (5) commutativity, (6) associativity, and (7) path-independence of the corresponding sequential choice. 相似文献
300.
Shie-Shien Yang 《Annals of the Institute of Statistical Mathematics》1981,33(1):463-470
Summary Let (X
1,Y
1), (X
2,Y
2),…, (X
n,Y
n) be i.i.d. as (X, Y). TheY-variate paired with therth orderedX-variateX
rn is denoted byY
rn and terms the concomitant of therth order statistic. Statistics of the form
are considered. The asymptotic normality ofT
n is established. The asymptotic results are used to test univariate and bivariate normality, to test independence and linearity
ofX andY, and to estimate regression coefficient based on complete and censored samples. 相似文献