全文获取类型
收费全文 | 10745篇 |
免费 | 173篇 |
国内免费 | 183篇 |
出版年
2024年 | 12篇 |
2023年 | 163篇 |
2022年 | 173篇 |
2021年 | 267篇 |
2020年 | 334篇 |
2019年 | 484篇 |
2018年 | 464篇 |
2017年 | 218篇 |
2016年 | 243篇 |
2015年 | 213篇 |
2014年 | 864篇 |
2013年 | 1272篇 |
2012年 | 506篇 |
2011年 | 789篇 |
2010年 | 594篇 |
2009年 | 525篇 |
2008年 | 472篇 |
2007年 | 527篇 |
2006年 | 417篇 |
2005年 | 365篇 |
2004年 | 256篇 |
2003年 | 197篇 |
2002年 | 168篇 |
2001年 | 36篇 |
2000年 | 32篇 |
1999年 | 22篇 |
1998年 | 24篇 |
1997年 | 16篇 |
1996年 | 15篇 |
1994年 | 16篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1991年 | 13篇 |
1990年 | 12篇 |
1989年 | 9篇 |
1987年 | 9篇 |
1985年 | 106篇 |
1984年 | 178篇 |
1983年 | 128篇 |
1982年 | 132篇 |
1981年 | 117篇 |
1980年 | 116篇 |
1979年 | 93篇 |
1978年 | 75篇 |
1977年 | 88篇 |
1976年 | 88篇 |
1975年 | 80篇 |
1974年 | 58篇 |
1973年 | 70篇 |
1972年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
91.
Isopongaglabol and 6-methoxyisopongaglabol, two new hydroxyfuranoflavones, together with two furanoflavones 5-methoxyfurano(8,7-4″,5″)flavone and 5-methoxy-3′,4′-methylenedioxyfurano(8,7-4″,5″)flavone, two simple flavones, desmethoxykanugin and fisetin tetramethyl ether, a chromenoflavanone, ovalichromene B, two triterpenes, cycloart-23-ene-3β,25-diol and friedelin, and β-sitosterol-β-d-glucoside were isolated from the petrol and CHCl3 extracts of the flowers of Pongamia glabra. The structures of isopongaglabol and 6-methoxyisopongaglabol have been established as 4′-hydroxyfurano(8,7-4″,5″)flavone and 4′-hydroxy-6-methoxyfurano(8,7-4″,5″)flavone, respectively, on the basis of the spectral evidence and they have been confirmed by synthesis. 相似文献
92.
Ferdinand Bohlmann Naleen Borthakur Robert M. King Harold Robinson 《Phytochemistry》1982,21(7):1793-1794
Calea reticulata afforded in addition to known compounds two new sesquiterpenes. These were germacrane and eudesmane derivatives, identified as germacra-4(15),5,10(14)-trien-1-one and 6-epi-β-verbesinol coumarate, respectively. 相似文献
93.
The aerial parts of Passiflora serratodigitata yielded 5,7-dihydroxy-4-phenylcoumarin, its 7-β-glucoside and the known C-glycosylflavones 2″-xylosylvitexin, 2″-xylosylisovitexin, vitexin, isovitexin, a vicenin, and orientin. The known flavone chrysin was also isolated. This is the first report of neoflavonoids in the family Passifloraceae. 相似文献
94.
A particulate enzymatic preparation, extracted from fenugreek seedlings (Trigonella foenum-graecum) catalyses the transfer of mannose from guanosine diphosphate-[U-14C]mannose and its incorporation into an alkali-soluble polysaccharide. Chemical and enzymatic study of this polysaccharide reveals the presence of only one type of osidic linkage, namely β-(1 → 4)-s-mannopyranosyl. The influence of some factors on this biosynthesis was studied, as well as the MW of the polysaccharide and the existence of an endogenous acceptor. 相似文献
95.
For the purpose of describing the pathway by which estrogens are synthesized in the rhesus monkey () corpus luteum (CL), CL were obtained during the midluteal phase of the menstrual cycle and fragments incubated with equimolar amounts of [7-3H]pregnenolone plus [4-14C]progesterone. Metabolites including 3H-progesterone, 3H, 14C-20α-dihydroprogesterone, 3H, 14C-17-hydroxyprogesterone, 3H-estrone and 3H-estradiol-17β appeared in the medium during the first 20 minutes of incubation, 3H, 14C-Androstenedione was not consistently noted until after 60 minutes. Despite the fact that the 14C/3H-17-hydroxyprogesterone ratio quickly approached a constant value in the medium, 14C-estrogens were not detected in the medium or tissue fragments suggesting that progesterone was not a principal precursor for estrogen synthesis. As evidenced by the observation that the 14C/3H-progesterone ratio was significantly higher in luteal fragments than the 17-hydroxyprogesterone ratio, 17-hydroxyprogesterone appeared to be synthesized from pregnenolone both by way of progesterone and by another route which did not include progesterone. C21- and C18-Steroids were more concentrated in tissue fragments after 120 minutes of incubation than in the medium indicating that these steroids were sequestered by luteal tissue. 相似文献
96.
97.
98.
3-(2-Carboxyethyl)thymine (3-CET) was synthesized from β-propiolactone (BPL) and dThd5′P at pH 9.0–9.5 via the intermediate 3-(2-carboxyethyl)thymidine-5′-monophosphoric acid (3-CEdThd5′P). 3-CEdThd5′P was converted to 3-CET by hydrolysis in 1.5 N HCl at 100°C for 2 h. The structure of 3-CET was assigned on the basis of UV spectra, electron impact (EI) and isobutane chemical ionization mass spectra and the EI mass spectrum of a trimethylsilyl derivative of 3-CET. BPL was reacted in vitro with calf thymus DNA at pH 7.5. 100 A units of BPL-reacted DNA yielded, following perchloric acid hydrolysis and preparative paper chromatography, 3 A units of 3-CET. Reaction of BPL with the phosphodiester thymidylyl-(3′-5′)thymidine gave 3-(2-carboxyethyl)thymidylyl-(3′-5′)-3-(2-carboxyethyl)thymidine (~3%). Phosphotriester formation was not detected. 相似文献
99.
Cationized ferritin was found to inhibit the lateral mobility of intramembrane proteins in turkey erythrocyte membranes and the activation of adenylate cyclase by the (?)-epinephrine-bound β-adrenergic receptor. It was observed that cationized ferritin has only a small direct effect on the β-receptor and on the adenylate cyclase moiety. It is concluded that the cationized ferritin-induced inhibition of the hormone-dependent cyclase activity results from the inhibition of the lateral mobility of the receptor and therefore a decrease in the bimolecular rate of interaction between the receptor and the enzyme. 相似文献
100.
K. Watanabe S. Hakomori M.E. Powell M. Yokota 《Biochemical and biophysical research communications》1980,92(2):638-646
Two amphipathic protein fractions soluble in organic solvents as well as in water have been isolated from the ganglioside fraction of bovine erythrocyte membranes by successive chromatography in chloroform-methanol mixture on DEAE-Sephadex, silicic acid, and α-hydroxypropylated Sephadex G50 (LH60) columns. These two fractions contained a similar low molecular weight protein but with distinctively different amino acid composition. One of these proteins has been characterized by having a strong Paul-Bunnell antigen activity and had a binding affinity to ganglioside. A similar protein without Paul-Bunnell antigen activity was isolated as the major ganglioside-associated protein. 相似文献