全文获取类型
收费全文 | 75564篇 |
免费 | 5506篇 |
国内免费 | 3578篇 |
出版年
2024年 | 144篇 |
2023年 | 1152篇 |
2022年 | 1936篇 |
2021年 | 2506篇 |
2020年 | 2374篇 |
2019年 | 2649篇 |
2018年 | 2622篇 |
2017年 | 1898篇 |
2016年 | 1897篇 |
2015年 | 2401篇 |
2014年 | 4431篇 |
2013年 | 5594篇 |
2012年 | 3313篇 |
2011年 | 4479篇 |
2010年 | 3432篇 |
2009年 | 3871篇 |
2008年 | 3944篇 |
2007年 | 4017篇 |
2006年 | 3630篇 |
2005年 | 3273篇 |
2004年 | 2919篇 |
2003年 | 2439篇 |
2002年 | 2171篇 |
2001年 | 1490篇 |
2000年 | 1269篇 |
1999年 | 1290篇 |
1998年 | 1193篇 |
1997年 | 1033篇 |
1996年 | 995篇 |
1995年 | 911篇 |
1994年 | 840篇 |
1993年 | 753篇 |
1992年 | 659篇 |
1991年 | 612篇 |
1990年 | 492篇 |
1989年 | 445篇 |
1988年 | 409篇 |
1987年 | 387篇 |
1986年 | 344篇 |
1985年 | 476篇 |
1984年 | 666篇 |
1983年 | 498篇 |
1982年 | 547篇 |
1981年 | 396篇 |
1980年 | 405篇 |
1979年 | 326篇 |
1978年 | 254篇 |
1977年 | 200篇 |
1976年 | 167篇 |
1975年 | 146篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
Charles E. Wenner John C. Cheney L. David Tomei 《Journal of cellular biochemistry》1981,15(2):161-168
The introduction of either PGF2α (10?7 M) or TPA (10?7 M) stimulated, ouabain-sensitive 86Rb+ influx at 30 min in postconfluent 3T3-4 mouse fibroblast cultures by 117% and 124%, respectively. Both TPA and PGF2α at these concentrations stimulated the incorporation of 3H-TdR into DNA. TPA had the greatest stimulatory effect, which was similar to that obtained with 10% fetal calf serum. In accord with the idea that modulation of membrane processes such as Na+/K+ pump activity in fibroblasts may reflect important events related to the initiation of DNA synthesis, it was observed that in both 3T3-4 and C3H-1 0T½ cells there were parallel increases in 3H-TdR incorporation and ouabain-sensitive 86Rb+ influxes with 10?7 M TPA, whereas PGF2α stimulated a significant increase in 3H-TdR incorporation in 3T3-4 but not C3H-10T½ cells and only marginal increases in ouabain-sensitive 86Rb+ influx in both. Therefore, although there appears to be a close correlation between Na+/K+ pump activation and subsequent S-phase entry following TPA stimulation, a similar correlation for PGF2α cannot be confirmed. 相似文献
63.
64.
《Developmental cell》2022,57(18):2221-2236.e5
- Download : Download high-res image (185KB)
- Download : Download full-size image
65.
The distribution of vitamin K epoxidase activity in rough and smooth microsomes has been studied and compared to the prothrombin precursor and vitamin K-dependent carboxylase activity. All three activities were high in rough microsomes as compared to the low levels found in smooth microsomes. The results are in agreement with the suggestion that there might be a linkage between the vitamin K-dependent carboxylation and epoxidation reaction in vivo. 相似文献
66.
《Bioscience, biotechnology, and biochemistry》2013,77(10):1763-1765
We previously isolated a Serratia marcescens O5: HI Z-54 strain which produces a new reddish-violet pigment, a peptide- ferropyrimine complex. This study showed that polymyxin B enhances the formation of the pigment about threefold. This occurs because polymyxin B in the medium causes the formation of an iron-polymyxin B complex which imposes a low iron stress on the bacteria and, in turn, enhances pigment production. This shows that polymyxin B is both a membrane-disrupting and ionophoric antibiotic. 相似文献
67.
1. Ship‐induced waves can affect the physical characteristics of lake and river shorelines, and laboratory studies have shown effects on littoral invertebrates. Here, we explored whether these effects could be observed under field conditions along a natural lake shore affected by wave sequences (trains) produced by boats. 2. Individuals of five invertebrate species (Bithynia tentaculata, Calopteryx splendens, Dikerogammarus villosus, Gammarus roeselii, Laccophilus hyalinus) were exposed to waves with increasing shear stress in five habitats differing in structural complexity. 3. Detachment of invertebrates increased with increasing shear stress and was best modelled using sigmoid response curves. Habitat structural complexity mitigated the effects of shear stress, and detachment rate was influenced more by habitat type than by species. A threshold (90% of the individual invertebrates unaffected) stress level of 0.64 N m?2 was found for a structurally complex reed habitat, compared to 0.37 N m?2 for a simple sand habitat. 4. Shear stress associated with wave trains created by recreational boating at a distance of 35 m from the shore and at a speed of 11 km h?1 resulted in 45% detachment of littoral invertebrates. Decreasing the boat‐to‐shore distance to 20 m increased wave shear stress by 30% and invertebrate detachments up to 75%. 5. Disturbance of littoral habitats and invertebrate assemblages are widespread in inland waters used for recreational and/or commercial navigation. Our findings show that the integrity of littoral zones of navigable surface waters could be much improved by implementing management measures such as physically protecting complex habitats with dense reed belts and tree roots, and reducing boat speeds and increasing their minimum shoreline distance. 相似文献
68.
《Cell reports》2020,30(6):1835-1847.e9
- Download : Download high-res image (127KB)
- Download : Download full-size image
69.
Harry Le Vine Pedro Cuatrecasas 《Biochimica et Biophysica Acta (BBA)/General Subjects》1981,672(3):248-261
A cytosolic, macromolecular factor required for the cholera toxin-dependent activation of pigeon erythrocyte adenylate cyclase and cholera toxin-dependent ADP-ribosylation of a membrane-bound 43 000 dalton polypeptide has been purified 1100-fold from horse erythrocyte cytosol using organic solvent precipitation and heat treatment. This factor, 13 000 daltons, does not absorb to anionic or cationic exchange resins, is sensitive to trypsin or 10% trichloroacetic acid and is not extractable by diethyl ether. Activation of adenylate cyclase by cholera toxin requires the simultaneous presence of ATP (including possible trace GTP), NAD+, dithiothreitol, cholera toxin, membranes and the cytosolic macromolecular factor. Reversal of cholera toxin activation of adenylate cyclase, and of the toxin-dependent ADP-ribosylation, requires the presence of the cytosolic factor. The ability of the purified cytosolic factor to influence the hormonal sensitivity of liver membrane adenylate cyclase may provide clues to its physiological functions. 相似文献
70.