全文获取类型
收费全文 | 4382篇 |
免费 | 72篇 |
国内免费 | 10篇 |
专业分类
化学 | 3117篇 |
晶体学 | 20篇 |
力学 | 68篇 |
数学 | 932篇 |
物理学 | 327篇 |
出版年
2019年 | 34篇 |
2016年 | 71篇 |
2015年 | 51篇 |
2014年 | 34篇 |
2013年 | 113篇 |
2012年 | 89篇 |
2011年 | 140篇 |
2010年 | 102篇 |
2009年 | 114篇 |
2008年 | 140篇 |
2007年 | 139篇 |
2006年 | 146篇 |
2005年 | 132篇 |
2004年 | 104篇 |
2003年 | 101篇 |
2002年 | 104篇 |
2001年 | 55篇 |
2000年 | 72篇 |
1999年 | 61篇 |
1998年 | 59篇 |
1997年 | 56篇 |
1996年 | 71篇 |
1995年 | 79篇 |
1994年 | 59篇 |
1993年 | 68篇 |
1992年 | 95篇 |
1991年 | 95篇 |
1990年 | 78篇 |
1989年 | 71篇 |
1988年 | 61篇 |
1987年 | 65篇 |
1986年 | 68篇 |
1985年 | 84篇 |
1984年 | 90篇 |
1983年 | 84篇 |
1982年 | 81篇 |
1981年 | 107篇 |
1980年 | 61篇 |
1979年 | 80篇 |
1978年 | 74篇 |
1977年 | 92篇 |
1976年 | 65篇 |
1975年 | 79篇 |
1974年 | 85篇 |
1973年 | 64篇 |
1972年 | 55篇 |
1971年 | 48篇 |
1970年 | 37篇 |
1967年 | 31篇 |
1962年 | 29篇 |
排序方式: 共有4464条查询结果,搜索用时 15 毫秒
981.
We have examined the influence of parametric noise on the solution behavioru(t, x) of a nonlinear initial value() problem arising in cell kinetics. In terms of ensemble statistics, the eventual limiting solution mean
and variance
are well-characterized functions of the noise statistics, and
and
depend on . When noise is continuously present along the trajectory,
and
are independent of the noise statistics and . However, in their evolution toward
and
, both
u
(t, x) and
u
2
(t, x) depend on the noise and. 相似文献
982.
983.
Helmut Schmidhammer Karin Mayer-Valkanover Michaela Walla-Kugler 《Helvetica chimica acta》1990,73(7):1986-1990
Starting from 5-methyl-oxycodone ( 6 ), 5-methylnaloxone ( 4 ), and 5-methylnaltrexone ( 5 ) have been prepared in several steps. Both 4 and 5 behaved as partial agonists in the AcOH writhing agonism and antagonism test in mice. 相似文献
984.
Anton Pachinger Elisabeth Eisner Claudia Tertsch Helmut Begutter Hubert Klus 《Journal of separation science》1992,15(5):302-304
A gas chromatographic method with alkali flame ionization detection is described for the determination of residue levels (0.1 μg/I and below) of deethylatrazine and deisopropylatrazine in drinking and ground water. Confirmation of the identities of the compounds is achieved by trifluoroacetylation, reaction conditions for which are presented. 相似文献
985.
Intramolecular [n.n]paracyclophane quinhydrones with two oligo= oxaalkylene bridges 2a–e (m = 0,1,2,3 and 4, resp.) have been synthesized. The selective double complexation of these compounds with metal cations of suitable size (e.g. 7) is indicated by remarkable enhancements of the intensity of charge-transfer absorptions. 相似文献
986.
Solid-phase synthesis of fullerene-peptides 总被引:1,自引:0,他引:1
Pantarotto D Bianco A Pellarini F Tossi A Giangaspero A Zelezetsky I Briand JP Prato M 《Journal of the American Chemical Society》2002,124(42):12543-12549
The solid-phase synthesis of peptides (SPPS) containing [60]fullerene-functionalized amino acids is reported. A new amino acid, fulleropyrrolidino-glutamic acid (Fgu), is used for the SPPS of a series of analogues of different length based on the natural Leu(5)-Enkephalin and on cationic antimicrobial peptides. These fullero-peptides were prepared on different solid supports to analyze the influence of the resin on the synthesis. Optimized protocols for the coupling and deprotection procedures were determined allowing the synthesis of highly pure peptides in sufficient quantities for evaluation of biological activities. In particular, to avoid side reactions of the fullerene moiety with bases and nucleophiles, the removal of the protecting groups was performed under inert conditions (nitrogen or argon in the dark). We have encountered serious problems with the recovery of the crude compounds, especially when Fgu was inserted in the proximity of the resin core as fullero-peptides tend to remain embedded inside the resin. Eventually, all of the fullero-peptides were easily purified, and the cationic peptides were tested for their antimicrobial activities. They displayed a specific activity against the Gram-positive bacterium S. aureus and also lysed erythrocytes. The availability of a fullero-amino acid easily useable in the SPPS of fullero-peptides may thus open the way to the synthesis of new types of biologically active oligomers. 相似文献
987.
A mechanistically unprecedented situation characterizes the gas‐phase ion chemistry of Ni(C,H3,O)+ when reacted under thermal, single‐collision conditions with ethane. A dehydrogenation channel leading to Ni(C3,H7,O)+ is to 90% preceded by a complete loss of positional identity of all nine H‐atoms of the encounter complex (‘scrambling’), whereas ca. 10% of the reaction exhibit a selective C? H bond activation of the alkane. In addition, a degenerate H exchange between ethane and the (C,H3,O) unit occurs as a side reaction, the mechanistic details of which remain unknown for the time being. 相似文献
988.
989.
Wolfgang Hanefeld Martin Schlitzer Norbert Debski Helmut Euler 《Journal of heterocyclic chemistry》1996,33(4):1143-1146
3-Aminorhodanine 2 was reacted with cyclic anhydrides yielding 3-(2,5-dioxopyrrolidin-1-yl), 3-(2,6-dioxopiperidin-1-yl), and 3-(1,3-dioxoisoindolin-2-yl)rhodanine 6-8 , which in turn were condensated in 5 position with several aldehydes yielding the new rhodanine derivatives 9-11 . 相似文献
990.
Ursula Schmid Heinz Heimgartner Hans Schmid Peter Schnholzer Helmut Link Karl Bernauer 《Helvetica chimica acta》1975,58(7):2222-2227
Structure of a Stable Dipolar Compound from 2,2-Dimethyl-3-dimethylamino-2H-azirine and Benzoylisothiocyanate. Benzoylisothiocyanate and 2,2-dimethyl-3-dimethylamino-2H-azirine ( 1 ) react to given the dipolar compound 4,4-dimethyl-2-thiazolin-5-dimethylimminium-2-benzcarboxamidate ( 2 ), whose structure has been proved by X-ray analysis. Compound 2 , upon addition of water, yields the thiourea derivative 3 , whereas by acid catalyzed hydrolysis the thiazolinone derivative 4 is formed. The dipolar structure 2 is also existent in organic solvents like dimethylsulfoxide or chloroform. 相似文献