全文获取类型
收费全文 | 75395篇 |
免费 | 1843篇 |
国内免费 | 11087篇 |
出版年
2022年 | 452篇 |
2021年 | 659篇 |
2020年 | 618篇 |
2019年 | 1232篇 |
2018年 | 1586篇 |
2017年 | 981篇 |
2016年 | 1089篇 |
2015年 | 1229篇 |
2014年 | 2152篇 |
2013年 | 3046篇 |
2012年 | 2138篇 |
2011年 | 1801篇 |
2010年 | 1475篇 |
2009年 | 2265篇 |
2008年 | 2422篇 |
2007年 | 3075篇 |
2006年 | 3141篇 |
2005年 | 3152篇 |
2004年 | 3286篇 |
2003年 | 2992篇 |
2002年 | 2868篇 |
2001年 | 2588篇 |
2000年 | 1952篇 |
1999年 | 2244篇 |
1998年 | 1962篇 |
1997年 | 1502篇 |
1996年 | 1473篇 |
1995年 | 1523篇 |
1994年 | 1602篇 |
1993年 | 1444篇 |
1992年 | 1246篇 |
1991年 | 1236篇 |
1990年 | 1030篇 |
1989年 | 868篇 |
1988年 | 909篇 |
1987年 | 712篇 |
1986年 | 636篇 |
1985年 | 2119篇 |
1984年 | 3147篇 |
1983年 | 2063篇 |
1982年 | 2472篇 |
1981年 | 2097篇 |
1980年 | 1986篇 |
1979年 | 1749篇 |
1978年 | 1576篇 |
1977年 | 1451篇 |
1976年 | 1321篇 |
1975年 | 1113篇 |
1974年 | 1105篇 |
1973年 | 1040篇 |
排序方式: 共有10000条查询结果,搜索用时 671 毫秒
41.
George John Acton 《Phytochemistry》1974,13(8):1303-1310
The light-dependent increment in RNase activity (which is ribosome bound in cell extracts) is distributed as a gradient increasing from base to hook of lupin hypocotyls. No evidence was found of non-specific or of specific activation of pre-formed enzyme molecules following isolation, either before or after (latent activity) destruction of particles. The autodegradation capacity of ribosomes isolated from irradiated cells was almost double that of ribosomes from etiolated tissue. It is proposed that association between the bulk of the light-controlled RNase fraction and lupin ribosomes results from binding of soluble protein. It is not clear whether binding is specific or an artifact of isolation. 相似文献
42.
The interrelation was studied between the phototransient absorbing maximally at 412 nm (M412) and light-induced proton release under steady-state conditions in aqueous suspensions of ‘purple membrane’ derived from Halobacterium halobium. The decay of M412 was slowed down by the simultaneous application of the ionophoric antibiotics valinomycin and beauvericin. The former had only slight activity alone and the latter was effective only in conjunction with valinomycin. The steady-state concentration of M412 which was formed on illumination was a direct function of the concentration of valinomycin. Maximum stabilization of M412 was obtained when the valinomycin was approximately equimolar with the bacteriorhodopsin. Addition of salts to the medium increased the number of protons released per molecule of M412 without affecting the level of M412 which was produced by continuous illumination. The effectiveness of the salts in this respect depended on the nature of the cation. Ca2+ and their antagonists La3+ and ruthenium red were found to have especially high affinity for the system. The extent of light-induced acidification could not be enhanced by increasing the pH of the medium from 6.5 to 7.8. The possible mechanism of action of the ionophores and of the cations on the photocycle and on the proton cycle is discussed. 相似文献
43.
Volatiles from the epicuticular wax of watercress were collected by ether washing and examined using gas chromatographic and mass spectrometric analysi 相似文献
44.
Nabiel A.M. Saleh Zeinab A.R. El-karemy Ragaa M.A. Mansour Abdel-Aziz A. Fayed 《Phytochemistry》1983,22(11):2501-2505
The flavonoids of five Geranium, fourteen Erodium and four Monsonia species were studied. Quercetin was the most common aglycone with lesse 相似文献
45.
Hanna G. Budayeva Arundhati Sengupta-Ghosh Lilian Phu John G. Moffat Gai Ayalon Donald S. Kirkpatrick 《Molecular & cellular proteomics : MCP》2022,21(4):100221
Muscle-specific receptor tyrosine kinase (MuSK) agonist antibodies were developed 2 decades ago to explore the benefits of receptor activation at the neuromuscular junction. Unlike agrin, the endogenous agonist of MuSK, agonist antibodies function independently of its coreceptor low-density lipoprotein receptor–related protein 4 to delay the onset of muscle denervation in mouse models of ALS. Here, we performed dose–response and time-course experiments on myotubes to systematically compare site-specific phosphorylation downstream of each agonist. Remarkably, both agonists elicited similar intracellular responses at known and newly identified MuSK signaling components. Among these was inducible tyrosine phosphorylation of multiple Rab GTPases that was blocked by MuSK inhibition. Importantly, mutation of this site in Rab10 disrupts association with its effector proteins, molecule interacting with CasL 1/3. Together, these data provide in-depth characterization of MuSK signaling, describe two novel MuSK inhibitors, and expose phosphorylation of Rab GTPases downstream of receptor tyrosine kinase activation in myotubes. 相似文献
46.
Feral and laboratory flocks of rock doves () show a pattern of grouped sequential exploitation when simultaneously presented with two dispersed, depleting patches of seed. This behavior contrasts with the ideal free distribution pattern shown when patches are small and concentrated. Grouped sequential exploitation consists of two phases: all pigeons first land together and feed at one patch, then leave one by one for the other patch. Departure times of individuals for the second patch are correlated with feeding rate at patch 1, which is in turn correlated with position in the dominance hierarchy. The decision to switch from patch 1 to patch 2 improves individual feeding rates in all cases, but is done slightly later than it should according to optimal foraging theory. 相似文献
47.
48.
D E Bowman 《Biochemical and biophysical research communications》1979,87(1):78-84
The oxidized B chain of insulin was used as a simple model for further consideration of limited proteolysis with low substrate:enzyme ratios. With low B chain:trypsin ratios, the ordinarily slower cleavage rate of the -Lys29-Ala30 bond essentially equaled the cleavage saturation rate of the -Arg22-Gly23 bond. This led to the disappearance of octapeptide which ordinarily forms most rapidly. Heptapeptide and alanine, formed mainly by cleavage of the octapeptide, decreased somewhat at high enzyme relative levels. Trypsin added to B chain formed a single chromatographic peak. 相似文献
49.
Shigeo Koyasu Makoto Asada Akio Fukuda Yoshimi Okada 《Journal of molecular biology》1981,153(2):471-475
The mode of polymerization of two species of flagellins, flagellin A and flagellin B, in polar flagella of Caulobacter crescentus was examined. By immunological staining we found that 1 to 1.2 μm of the portion of the flagellar filament proximal to the cell was composed of flagellin B, whereas about 5 μm of the distal portion was composed of flagellin A. This result, together with the previous observation that a flagellin B-less mutant cannot form normal flagella but instead forms stubs in spite of their high level of flagellin A synthesis, indicates that flagellin B is very important for the formation of complete flagella and/or for the initiation of filament formation from the hook. 相似文献
50.
Lens includes L.
culinaris subsp. culinaris (the cultivated lentil) and several wild species distributed from the Mediterranean region to western Asia. We compared sequence
variation in the ITS region among species of Lens in an effort to end persisting uncertainty regarding the phylogeny of the genus. The parsimony analysis revealed a single
minimum-length tree with a topology congruent with patterns derived by previous studies of nuclear and chloroplast DNA RFLPs.
The basal and highly divergent status of the L. nigricans clade is depicted, and the progenitor-derivative relationship between L. culinaris subsp. orientalis and L. culinaris subsp. culinaris is reaffirmed. Resolution in the tree was improved by combining the ITS data set with a pre-existing set of chloroplast DNA
restriction site data obtained from the same group of samples.
Received May 8, 2000 Accepted October 26, 2001 相似文献