全文获取类型
收费全文 | 7312篇 |
免费 | 498篇 |
国内免费 | 3篇 |
出版年
2023年 | 41篇 |
2022年 | 63篇 |
2021年 | 117篇 |
2020年 | 113篇 |
2019年 | 95篇 |
2018年 | 210篇 |
2017年 | 195篇 |
2016年 | 275篇 |
2015年 | 413篇 |
2014年 | 443篇 |
2013年 | 523篇 |
2012年 | 631篇 |
2011年 | 582篇 |
2010年 | 367篇 |
2009年 | 302篇 |
2008年 | 469篇 |
2007年 | 417篇 |
2006年 | 420篇 |
2005年 | 392篇 |
2004年 | 366篇 |
2003年 | 297篇 |
2002年 | 282篇 |
2001年 | 63篇 |
2000年 | 47篇 |
1999年 | 45篇 |
1998年 | 39篇 |
1997年 | 39篇 |
1996年 | 35篇 |
1995年 | 35篇 |
1994年 | 26篇 |
1993年 | 35篇 |
1992年 | 33篇 |
1991年 | 19篇 |
1990年 | 30篇 |
1989年 | 19篇 |
1988年 | 15篇 |
1987年 | 14篇 |
1986年 | 14篇 |
1985年 | 21篇 |
1984年 | 16篇 |
1983年 | 22篇 |
1982年 | 18篇 |
1981年 | 18篇 |
1980年 | 15篇 |
1979年 | 20篇 |
1978年 | 18篇 |
1976年 | 13篇 |
1975年 | 27篇 |
1974年 | 19篇 |
1973年 | 17篇 |
排序方式: 共有7813条查询结果,搜索用时 15 毫秒
61.
Silvia M.C. Dias João B. Fernandes José G.S. Maia Otto R. Gottlieb Hugo E. Gottlieb 《Phytochemistry》1982,21(7):1737-1740
The trunk wood of an Amazonian Aniba (Lauraceae) species contains, besides dillapiol and the benzodioxane-type neolignan eusiderin, four bicyclo(3.2.1)octanoid neolignans. These comprise representatives of the canellin-type: the known methoxycanellin-A and the novel compounds characterized as (1R, 3S, 4S, 5S, 6S, 7R)-1-allyl-4-hydroxy-3, 5-dimethoxy-7-methyl-6-(3′-methoxy-4′, 5′-methylenedioxyphenyl)-8-oxo-bicyclo(3.2.1)octane; (1R, 3S, 4S, 5S, 6S, 7R)-1-allyl-4-hydroxy-3, 5-dimethoxy-7-methyl-6-(3′, 4′, 5′-trimethoxyphenyl)-8-oxobicyclo(3.2.1)octane and (1R, 4R, 5R, 6S, 7R, 8S)-1-allyl-4, 8-dihydroxy-5-methoxy-7-methyl-6-(3′-methoxy-4′,5′-methylenedioxyphenyl)-3-oxobicyclo(3.2.1)octane. 相似文献
62.
At concentrations inhibitory to the elongation of corn (Zea mays L.) roots, the auxins, indole-3-acetic acid (IAA) and α-naphthaleneacetic acid (α-NAA), cause an increase in the pH of the
bathing medium; this increase occurs with an average latent period shorter than the latent period for the inhibitory effect
of these auxins on elongation. Indole-2-carboxylic acid, an inactive structural analogue of IAA, and β-naphthaleneacetic acid,
an inactive analogue of α-NAA, affect neither growth nor the pH of the medium. Since acid pH is known to promote and basic
pH to inhibit root elongation, the data are consistent with the hypothesis that hormone-induced modification of cell-wall
pH plays a role in the control of elongation of roots, as has been proposed for elongation of stems and coleoptiles. 相似文献
63.
Mrs. J. Van Vossel-Daeninck K. Dierickx F. Vandesande A. Van Vossel 《Cell and tissue research》1981,218(1):7-12
Summary The hypothalamic magnocellular preoptic nucleus of Rana temporaria was studied at the electron-microscopic level with the use of the unlabeled antibody peroxidase-antiperoxidase complex (PAP) technique. The magnocellular preoptic nucleus of R. temporaria contains at least three different types of neurons: (1) Vasotocinergic neurons, (2) mesotocinergic neurons, and (3) neurons that contain either somatostatin or an immunologically related peptide. The present results are in complete agreement with those of previous immunocytochemical studies conducted at the light microscopic level. 相似文献
64.
Dr. N. Goossens Dr. S. Blähser A. Oksche F. Vandesande K. Dierickx 《Cell and tissue research》1977,184(1):1-13
Summary The results of an immunohistochemical investigation of the hypothalamo-neurohypophysial system in several species of birds have shown that: (1) mesotocin and vasotocin are synthesized in separate neurons; (2) in all species investigated the distribution of mesotocinergic and vasotocinergic perikarya follows a common pattern; (3) the external zone of the avian anterior median eminence contains exclusively vasotocinergic nerve fibers, originating in supraoptic and ventral paraventricular regions; (4) the distribution of immunoreactive elements in the neural lobe shows a definite species-dependent pattern. 相似文献
65.
Marden A. de Alvarenga Raimundo Braz Fo Otto R. Gottlieb João P. de P. Dias Aderbal F. Magalhães Eva G. Magalhães Gouvan C. de Magalhães Mauro T. Magalhães José G.S. Maia Raquel Marques Anita J. Marsaioli Antônio A.L. Mesquita Anselmo A. de Moraes Alaide B. de Oliveira Geovane G. de Oliveira Gentil Pedreira Sebastião K. Pereira Sonildes L.V. Pinho Celira C. Santos 《Phytochemistry》1978,17(3):511-516
Wood samples, infested by fungi during storage, were shown to contain, besides the known 5-methyl-mellein, additional (3R)-8-hydroxy-3-methyl-3,4-dihydroisocoumarins substituted by 7-methyl, 5-formyl, 5-carboxy, 5-hydroxy, 5-methoxy, 6-methoxy-5-methyl and 6,7-dimethoxy-5-methyl groups, as well as 6-formyl-7-hydroxy-5-methoxy-4-methylphthalide. Several 2-methylchromanones were synthesized in order to show that this class of compounds can be distinguished from 3-methyl-3,4-dihydroisocoumarins by MS. 相似文献
66.
Stop-flow techniques were used to examine the rapid axonal transport of norepinephrine in rabbit sciatic nerves. When the midpoint of a nerve incubated in vitro was cooled to 2°C while the remainder was kept at 37°C, norepinephrine accumulated proximal to the cooled region at a rate corresponding to an average transport velocity between 5 and 6 mm/hr in a distal direction. Since only about half of the norepinephrine appeared to be free to move, the mean velocity of the moving fraction was probably twice as great. No norepinephrine accumulated distal to a broad cooled region under conditions in which there would have been a significant accumulation of dopamine-β-hydroxylase activity. Therefore, unlike dopamine-β-hydroxylase, norepinephrine may not be subject to rapid retrograde transport. When nerves that had been locally cooled for 1.5 hr were rewarmed uniformly to 37°C, a wave of norepinephrine moved exclusively in a distal direction. The peak of this wave moved at a velocity of 12.2 ± 0.5 mm/hr or 293 ± 12 mm/day; the front of the wave moved at about 18 mm/hr. or 430 mm/day; and the tail probably moved faster than 6 mm/hr. This spectrum of velocities was virtually identical to the one displayed by the wave of dopamine-β-hydroxylase activity that was generated under the same conditions. Our results are consistent with the conclusion that all axonal structures containing norepinephrine also contain dopamine-β-hydroxylase, but they are not consistent with the converse. 相似文献
67.
Jo Ann Render 《Development genes and evolution》1983,192(3-4):120-129
Summary The embryo ofSabellaria cementarium (Polychaeta) forms a polar lobe at each of the first two cleavage divisions which becomes absorbed into one of the blastomeres at the end of the division. Lobe removal experiments show that the polar lobe preceding first cleavage is necessary for the development of the apical tuft and the posttrochal region of the trochophore larva. The polar lobe preceding second cleavage is smaller than the first polar lobe and is necessary only for post-trochal region development. In blastomere isolation experiments, isolates containing the C but not the D blastomere form apical tufts. Isolates containing the D but not the C blastomere do not form apical tufts. When the polar lobe preceding second cleavage is removed and the C and D blastomeres are separated and raised in isolation, each can form an apical tuft. When the second cleavage is equalized with sodium dodecyl sulfate (SDS) such that both the C and the D blastomeres receive second polar lobe material, no apical tuft is formed. These results suggest that apical tuft determinants are distributed to both the C and D blastomeres at second cleavage but that the second polar lobe contains an inhibitor for apical tuft formation which is shunted to the D blastomere after the completion of second cleavage. 相似文献
68.
Françoise Phan-Dinh-Tuy Anne Weber Joëlle Henry Dominique Cottreau Axel Kahn 《Analytical biochemistry》1982,127(1):73-80
Electrophoresis on cellulose acetate strips was used to analyze protein kinases from normal rat liver. In addition to already well-characterized cAMP-dependent protein kinases type I and II and cAMP-independent casein kinases I and II, this method enabled the detection of several supplementary bands corresponding to kinases which were investigated according to their substrate specificity, activation by cAMP, and inhibition by the specific inhibitor of the catalytic subunit of cAMP-dependent protein kinases or by heparin. Using this rapid, sensitive, and resolutive electrophoretic method, different isozyme patterns could be obtained starting from minute amounts of different types of biological material. 相似文献
69.
Jan J. B. Boesen Sandrine Stuivenberg Corné H. M. Thyssens Henk Panneman Firouz Darroudi Paul H. M. Lohman Jo W. I. M. Simons 《Molecular & general genetics : MGG》1992,234(2):217-227
Summary Cells of the mouse T-lymphoma line GRSL13 were treated with 8-methoxy-psoralen plus longwave ultraviolet light (PUVA) under conditions where the biological effects are mainly due to non-persistent DNA crosslinks (PUVA-CL treatment). Fluctuation analysis showed that PUVA-CL treatment resulted in an enhancement of the mutation rate in the progeny of treated cells, which persisted until the eleventh generation after treatment. Since only 5 cross-links are available to account for 52 mutational events observed in the coding region, about 90% of the induced mutational events must have been untargeted. This was confirmed by molecular analysis of these mutations, which showed that 53% of the point mutations arose at sites which are not a target for psoralens. This supports the hypothesis that stress responses may give rise to untargeted mutagenesis. Further support for this hypothesis is provided by the observation that 8-methoxy-psoralen (8-MOP) or UVA alone (both of which are known to induce many pleiotropic effects) each acted as indirect mutagen by enhancing the mutation rate 2–4 fold in the progeny of treated cells. 相似文献
70.
Darja Barlič Maganja Borut Štrukelj Jože Pungerčar Franc Gubenšek Vito Turk Igor Kregar 《Plant molecular biology》1992,20(2):311-313
A genomic DNA clone encoding an aspartic proteinase inhibitor of potato was isolated from a lambda EMBL3 phage library using the aspartic proteinase inhibitor cDNA as a hybridization probe. The gene has all characteristic sequences normally found in eucaryotic genes. Typical CAAT and TATA box sequences were found in the 5-upstream region. In this part are also two putative regulatory AGGA box sequences located. In the genomic sequence there are no intron sequences interrupting the coding region. An open reading frame of the gene encodes a precursor protein of 217 amino acids which shows high percent identity with the aspartic proteinase inhibitor cDNA. 相似文献