全文获取类型
收费全文 | 32482篇 |
免费 | 1431篇 |
国内免费 | 5023篇 |
专业分类
化学 | 30227篇 |
晶体学 | 338篇 |
力学 | 85篇 |
综合类 | 253篇 |
数学 | 5683篇 |
物理学 | 2350篇 |
出版年
2024年 | 47篇 |
2023年 | 293篇 |
2022年 | 871篇 |
2021年 | 799篇 |
2020年 | 834篇 |
2019年 | 965篇 |
2018年 | 839篇 |
2017年 | 936篇 |
2016年 | 1064篇 |
2015年 | 1021篇 |
2014年 | 1266篇 |
2013年 | 2720篇 |
2012年 | 2097篇 |
2011年 | 1843篇 |
2010年 | 1617篇 |
2009年 | 1952篇 |
2008年 | 2067篇 |
2007年 | 2247篇 |
2006年 | 2015篇 |
2005年 | 1812篇 |
2004年 | 1638篇 |
2003年 | 1304篇 |
2002年 | 1116篇 |
2001年 | 826篇 |
2000年 | 834篇 |
1999年 | 722篇 |
1998年 | 594篇 |
1997年 | 590篇 |
1996年 | 581篇 |
1995年 | 543篇 |
1994年 | 468篇 |
1993年 | 395篇 |
1992年 | 367篇 |
1991年 | 250篇 |
1990年 | 206篇 |
1989年 | 221篇 |
1988年 | 155篇 |
1987年 | 122篇 |
1986年 | 90篇 |
1985年 | 107篇 |
1984年 | 91篇 |
1983年 | 53篇 |
1982年 | 84篇 |
1981年 | 61篇 |
1980年 | 37篇 |
1979年 | 45篇 |
1978年 | 40篇 |
1977年 | 24篇 |
1976年 | 26篇 |
1975年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Marina DellaGreca 《Tetrahedron》2006,62(12):2877-2882
Examination of the hydroalcoholic extract of the leaves of Aptenia cordifolia has afforded three cinnamic acid amides and two lignanamides. Structures were established on the basis of spectroscopic data, including 2D-NMR analyses. 相似文献
142.
Andrea Loi 《Differential Geometry and its Applications》2006,24(3):311-319
In this paper we study the Calabi diastasis function of Hermitian symmetric spaces. This allows us to prove that if a complete Hermitian locally symmetric space (M,g) admits a Kähler immersion into a globally symmetric space (S,G) then it is globally symmetric and the immersion is injective. Moreover, if (S,G) is symmetric of a specified type (Euclidean, noncompact, compact), then (M,g) is of the same type. We also give a characterization of Hermitian globally symmetric spaces in terms of their diastasis function. Finally, we apply our analysis to study the balanced metrics, introduced by Donaldson, in the case of locally Hermitian symmetric spaces. 相似文献
143.
Common fixed-point results are established for a new class of noncommuting selfmaps. We apply them to obtain several invariant approximation results which unify, extend, and complement well-known results. 相似文献
144.
脑细胞激活素药物的化学成分分析 总被引:1,自引:0,他引:1
采用日本岛津LC-60A型高压液相色谱仪和美国P-E3030型原子吸收分光光度计,对该药进行了氨基酸、维生素和化学元素的含量测定。结果表明,该药含有18种氨基酸,不少于3种维生素和20几种化学元素,为进一步改进该药物的合理配制方法和临床应用提供了参考数据。 相似文献
145.
146.
Given an integer n ≥ 2, let λ(n) := (log n)/(log γ(n)), where γ(n) = Π
p|n p, stand for the index of composition of n, with λ(1) = 1. We study the distribution function of (λ(n) – 1) log n as n runs through particular sets of integers, such as the shifted primes, the values of a given irreducible cubic polynomial
and the shifted powerful numbers.
Research supported in part by a grant from NSERC.
Research supported by the Applied Number Theory Research Group of the Hungarian Academy of Science and by a grant from OTKA.
Professor M.V. Subbarao passed away on February 15, 2006.
Received: 3 March 2006 Revised: 28 October 2006 相似文献
147.
This paper examines the steady state behaviour of a batch arrival queue with two phases of heterogeneous service along and Bernoulli schedule vacation under multiple vacation policy, where after two successive phases service or first vacation the server may go for further vacations until it finds a new batch of customer in the system. We carry out an extensive stationary analysis of the system, including existence of stationary regime, queue size distribution of idle period process, embedded Markov chain steady state distribution of stationary queue size, busy period distribution along with some system characteristics. 相似文献
148.
The toxicity of inorganic trivalent arsenic for living organisms is reduced by in vivo methylation of the element. In man, this biotransformation leads to the synthesis of monomethylarsonic (MMA) and dimethylarsinic (DMA) acids, which are efficiently eliminated in urine along with the unchanged form (Asi). In order to document the methylation process in humans, the kinetics of Asi, MMA and DMA elimination were studied in volunteers given a single dose of one of these three arsenicals or repeated doses of Asi. The arsenic methylation efficiency was also assessed in subjects acutely intoxicated with arsenic trioxide (As2O3) and in patients with liver diseases. Several observations in humans can be explained by the properties of the enzymic systems involved in the methylation process which we have characterized in vitro and in vivo in rats as follows: (1) production of Asi metabolites is catalyzed by an enzymic system whose activity is highest in liver cytosol; (2) different enzymic activities, using the same methyl group donor (S-adenosylmethionine), lead to the production of mono- and di-methylated derivatives which are excreted in urine as MMA and DMA; (3) dimethylating activity is highly sensitive to inhibition by excess of inorganic arsenic; (4) reduced glutathione concentration in liver moderates the arsenic methylation process through several mechanisms, e.g. stimulation of the first methylation reaction leading to MMA, facilitation of Asi uptake by hepatocytes, stimulation of the biliary excretion of the element, reduction of pentavalent forms before methylation, and protection of a reducing environment in the cells necessary to maintain the activity of the enzymic systems. 相似文献
149.
V. I. Saloutin I. T. Bazyl' Z. E. Skryabina P. N. Kondrat'ev O. N. Chupakhin 《Russian Chemical Bulletin》1994,43(2):279-282
Reactions of pentafluorobenzoylpyruvic acid with amines afford the respective enamines. The intramolecular cyclization of the latter results inN-substituted 4-quinolone-2-carboxylic acids. Ammonia and triethylamine favor the cyclization of pentafluorobenzoylpyruvic acid to 2-carboxychromone.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 299–302, February, 1994. 相似文献
150.
L. T. Eremenko L. B. Romanova M. E. Ivanova I. L. Eremenko S. E. Nefedov Yu. T. Struchkov 《Russian Chemical Bulletin》1994,43(4):619-623
An effective method of esterification of 1,4-cubanedicarboxylic acid with alkylsulfuric acids is proposed. The derivatives of alkanols with substantially different pKa Valus are obtained in high yields. Molecular structures of the esters obtained are confirmed by various methods. The X-ray study showed a remarkable effect of the nature of an alkyl radical on the geometry of the cubane core.Translated fromIzyestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp.668–672, April, 1994.The authors thank Dr. G. V. Lagodzinskaya for analyzing the NMR spectra and for useful discussions. 相似文献