全文获取类型
收费全文 | 85742篇 |
免费 | 6423篇 |
国内免费 | 3467篇 |
出版年
2023年 | 1307篇 |
2022年 | 1481篇 |
2021年 | 2485篇 |
2020年 | 2912篇 |
2019年 | 3748篇 |
2018年 | 3258篇 |
2017年 | 2428篇 |
2016年 | 2434篇 |
2015年 | 2692篇 |
2014年 | 4780篇 |
2013年 | 5929篇 |
2012年 | 3658篇 |
2011年 | 4751篇 |
2010年 | 4263篇 |
2009年 | 4014篇 |
2008年 | 4221篇 |
2007年 | 4349篇 |
2006年 | 3733篇 |
2005年 | 3547篇 |
2004年 | 3284篇 |
2003年 | 2754篇 |
2002年 | 2287篇 |
2001年 | 1685篇 |
2000年 | 1335篇 |
1999年 | 1483篇 |
1998年 | 1293篇 |
1997年 | 1177篇 |
1996年 | 1136篇 |
1995年 | 1121篇 |
1994年 | 1073篇 |
1993年 | 930篇 |
1992年 | 870篇 |
1991年 | 781篇 |
1990年 | 629篇 |
1989年 | 583篇 |
1988年 | 543篇 |
1987年 | 480篇 |
1986年 | 447篇 |
1985年 | 590篇 |
1984年 | 752篇 |
1983年 | 574篇 |
1982年 | 664篇 |
1981年 | 528篇 |
1980年 | 531篇 |
1979年 | 402篇 |
1978年 | 308篇 |
1977年 | 288篇 |
1976年 | 277篇 |
1975年 | 205篇 |
1974年 | 199篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
Intra‐cohort cannibalism is an example of a size‐mediated priority effect. If early life stages cannibalize slightly smaller individuals, then parents face a trade‐off between breeding at the best time for larval growth or development and predation risk from offspring born earlier. This game‐theoretic situation among parents may drive adaptive reproductive phenology toward earlier breeding. However, it is not straightforward to quantify how cannibalism affects seasonal egg fitness or to distinguish emergent breeding phenology from alternative adaptive drivers. Here, we devise an age‐structured game‐theoretic mathematical model to find evolutionary stable breeding phenologies. We predict how size‐dependent cannibalism acting on eggs, larvae, or both changes emergent breeding phenology and find that breeding under inter‐cohort cannibalism occurs earlier than the optimal match to environmental conditions. We show that emergent breeding phenology patterns at the level of the population are sensitive to the ontogeny of cannibalism, that is, which life stage is subject to cannibalism. This suggests that the nature of cannibalism among early life stages is a potential driver of the diversity of reproductive phenologies seen across taxa and may be a contributing factor in situations where breeding occurs earlier than expected from environmental conditions. 相似文献
73.
Alexander V. Kirdyanov Eugene A. Vaganov Malcolm K. Hughes 《Trees - Structure and Function》2007,21(1):37-44
We propose a technique for separating the climatic signal which is contained in two tree-ring parameters widely used in dendroclimatology.
The method is based on the removal of the relationship between tree-ring width (TRW) and maximum latewood density (MXD) observed
for narrow tree rings from high latitudes. The new technique is tested on data from three larch stands located along the northern
timberline in Eurasia. Correlations were calculated between the temperatures of pentads (five consecutive days), TRW chronologies
and MXD chronologies calculated according to the standard and proposed methods. The analysis confirms the great importance
of summer temperature for tree radial growth and tree-ring formation. TRW is positively correlated with the temperature of
four to eight pentads (depending on the region) at the beginning of the growth season, but MXD as obtained by the standard
technique is correlated with temperature over a much longer period. For maximum density series from which the relationship
between MXD and TRW has been removed (MXD′), there is a clear correlation with temperatures in the second part of the growing
season. These results are consistent with the known dynamics of tree-ring growth in high latitudes and mechanisms of tree-ring
formation. 相似文献
74.
75.
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
76.
77.
Benjamin S. Johnson Lexie Chafin Daniela Farkas Jessica Adair Ajit Elhance Laszlo Farkas Joseph S. Bednash James D. Londino 《Molecular & cellular proteomics : MCP》2022,21(7):100256
Identifying protein–protein and other proximal interactions is central to dissecting signaling and regulatory processes in cells. BioID is a proximity-dependent biotinylation method that uses an “abortive” biotin ligase to detect proximal interactions in cells in a highly reproducible manner. Recent advancements in proximity-dependent biotinylation tools have improved efficiency and timing of labeling, allowing for measurement of interactions on a cellular timescale. However, issues of size, stability, and background labeling of these constructs persist. Here we modified the structure of BioID2, derived from Aquifex aeolicus BirA, to create a smaller, highly active, biotin ligase that we named MicroID2. Truncation of the C terrminus of BioID2 and addition of mutations to alleviate blockage of biotin/ATP binding at the active site of BioID2 resulted in a smaller and highly active construct with lower background labeling. Several additional point mutations improved the function of our modified MicroID2 construct compared with BioID2 and other biotin ligases, including TurboID and miniTurbo. MicroID2 is the smallest biotin ligase reported so far (180 amino acids [AAs] for MicroID2 versus 257 AAs for miniTurbo and 338 AAs for TurboID), yet it demonstrates only slightly less labeling activity than TurboID and outperforms miniTurbo. MicroID2 also had lower background labeling than TurboID. For experiments where precise temporal control of labeling is essential, we in addition developed a MicroID2 mutant, termed lbMicroID2 (low background MicroID2), that has lower labeling efficiency but significantly reduced biotin scavenging compared with BioID2. Finally, we demonstrate utility of MicroID2 in mass spectrometry experiments by localizing MicroID2 constructs to subcellular organelles and measuring proximal interactions. 相似文献
78.
《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
79.
80.
Binding of B‐cell maturation antigen to B‐cell activating factor induces survival of multiple myeloma cells by activating Akt and JNK signaling pathways
下载免费PDF全文
![点击此处可从《Cell biochemistry and function》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Xianjuan Shen Yuehua Guo Jing Qi Wei Shi Xinhua Wu Shaoqing Ju 《Cell biochemistry and function》2016,34(2):104-110
B‐cell maturation antigen (BCMA) is expressed on normal and malignant plasma cells and represents a potential target for therapeutic intervention. In this study, we characterized the mechanism underlying the protein kinase B (Akt) and c‐Jun N‐terminal kinase (JNK) pathways and BCMA interactions in regulating multiple myeloma (MM) cell survival. It was found that the expression levels of B cell‐activating factor (BAFF) and BCMA were increased in MM cells as compared with those in normal controls. The proliferation of U266 cells was induced by recombinant human BAFF (rhBAFF) and could also be decreased by BCMA siRNA. The expression of Bcl‐2 protein was up‐regulated, and Bax protein was down‐regulated after rhBAFF treatment, which could be reversed by BCMA siRNA. Similarly, the protein p‐JNK and p‐Akt were activated by rhBAFF and could be changed by BCMA siRNA. In addition, the BCMA mRNA and protein expression levels were decreased after treatment with Akt and JNK pathway inhibitors. These results suggest that Akt and JNK pathways are involved in the regulation of BCMA. A novel BAFF/BCMA signalling pathway in MM may be a new therapeutic target for MM. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献