全文获取类型
收费全文 | 13927篇 |
免费 | 427篇 |
国内免费 | 902篇 |
出版年
2023年 | 107篇 |
2022年 | 196篇 |
2021年 | 248篇 |
2020年 | 178篇 |
2019年 | 204篇 |
2018年 | 181篇 |
2017年 | 166篇 |
2016年 | 227篇 |
2015年 | 266篇 |
2014年 | 613篇 |
2013年 | 828篇 |
2012年 | 638篇 |
2011年 | 618篇 |
2010年 | 490篇 |
2009年 | 575篇 |
2008年 | 663篇 |
2007年 | 693篇 |
2006年 | 640篇 |
2005年 | 671篇 |
2004年 | 598篇 |
2003年 | 541篇 |
2002年 | 484篇 |
2001年 | 330篇 |
2000年 | 293篇 |
1999年 | 343篇 |
1998年 | 284篇 |
1997年 | 310篇 |
1996年 | 281篇 |
1995年 | 297篇 |
1994年 | 287篇 |
1993年 | 290篇 |
1992年 | 255篇 |
1991年 | 212篇 |
1990年 | 186篇 |
1989年 | 182篇 |
1988年 | 170篇 |
1987年 | 171篇 |
1986年 | 129篇 |
1985年 | 217篇 |
1984年 | 187篇 |
1983年 | 136篇 |
1982年 | 184篇 |
1981年 | 142篇 |
1980年 | 123篇 |
1979年 | 117篇 |
1978年 | 60篇 |
1977年 | 65篇 |
1976年 | 54篇 |
1974年 | 26篇 |
1973年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
142.
Expression and stability of amplified genes encoding 5-enolpyruvylshikimate-3-phosphate synthase in glyphosate-tolerant tobacco cells 总被引:10,自引:0,他引:10
Yunxia Wang James D. Jones Stephen C. Weller Peter B. Goldsbrough 《Plant molecular biology》1991,17(6):1127-1138
Two distinct cDNAs for 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) were obtained from a glyphosate-tolerant tobacco cell line. The cDNAs were 89% identical and the predicted sequences of the mature proteins were greater than 83% identical with EPSPS proteins from other plants. Tobacco EPSPS proteins were more similar to those from tomato and petunia than Arabidopsis. One cDNA clone, EPSPS-1, represented a gene that was amplified in glyphosate-tolerant cells, while the gene for EPSPS-2 was unaltered in these cells. Consequently, EPSPS-1 mRNA was more abundant in tolerant than unselected cells, whereas EPSPS-2 mRNA was at relatively constant levels in these cell lines. Exposure of unselected cells and tobacco leaves to glyphosate produced a transient increase in EPSPS mRNA. However, glyphosate-tolerant cells containing amplified copies of EPSPS genes did not show a similar response following exposure to glyphosate. A significant proportion of the EPSPS gene amplification was maintained when tolerant cells were grown in the absence of glyphosate for eight months. Plants regenerated from these cells also contained amplified EPSPS genes. 相似文献
143.
Isolation and characterization of a cDNA clone encoding the anti-viral protein from Phytolacca americana 总被引:6,自引:0,他引:6
Phytolacca anti-viral protein (PAP) was purified from Phytolacca leaves and the N-terminal was sequenced. A cDNA library was made from mRNAs isolated from Phytolacca leaves and cDNA clones for PAP were identified using oligonucleotide probes derived from the N-terminal amino acid sequence. The PAP-cDNA clone was sequenced from both directions. The predicted amino acid sequence of PAP was compared with the amino acid sequences of other ribosome-inactivating proteins. The identities of these proteins to PAP ranged from 29 to 38%, and a region was found in each with a sequence similar to the PAP sequence (AIQMVSEAARFKYI). Southern blot analysis indicates that PAP is encoded by a multi-gene family.Abbreviations MAP
Mirabilis jalapa anti-viral protein
- PAP
Phytolacca anti-viral protein
- SO6
30 kDa ribosome-inactivating protein from the seeds of Saponaria officinalis 相似文献
144.
Jean F. Emly Wendy A. Ratcliffe Elaine Green Sarah J. Bowden David A. Heath Ann Blight Susan Hughes John G. Ratcliffe 《生物化学与生物物理学报:疾病的分子基础》1992,1180(1):58-64
The molecular forms of parathyroid hormone-related protein (PTHRP) in conditioned media from the BEN human lung cancer cell line, rat parathyroid cells (PT-r) and human keratinocytes were studied by gel-filtraton chromatography with assay of PTHRP by immunoassays and bioassay. Immunoreactivity (1–86 and 1–34) and bioactivity (1–34) in conditioned media eluted as a coincident major peak (approx. molecular mass 19–22 kDa) and there was evidence of amino-terminal species in the molecular mass range 10–16 kDa in BEN and keratinocyte media. Western blotting of PTHRP affinity purified by monoclonal antibodies directed at regions 1–34 or 37–67, identified a major species in all cell cytosols and media with an apparent molecular mass of 24–25 kDa, consistently slighty larger than recombinant PTHRP(1–141) (mobility of 21 kDa) which may represent an intact or native form of PTHRP. Additional amino-terminal species were identified in medium from keratinocytes (16 and 7 kDa), BEN cells (18 and 14 kDa) and PT-R cells (17 kDa), suggesting that processing occurs at the C-terminus and within the mid-region to form a range of amino-terminal fragments. 相似文献
145.
Ignacio R. Rodriguez Pedro Gonzales J. Samuel Zigler Teresa Borrás 《生物化学与生物物理学报:疾病的分子基础》1992,1180(1):44-52
A congenital cataract present in guinea pigs provided a unique opportunity to study a hereditary lens diseases at the molecular level. ζ-crystallin, one of the most abundant guinea pig lens proteins, was found to be altered in the lens of cataractous animals. Several ζ-crystallin cDNA clones were isolated from a cataractous lens library and found to contain a 102-bp deletion towards the 3′ end of the coding region. The deletion does not interfere with the reading frame but results in a protein 34 amino acids shorter. Sequence analysis of a normal genomic ζ-crystallin clone revealed that the missing 102-bp fragment corresponds to an entire exon (exon 7). PCR analysis of the genomic DNA isolated from cataractous animals showed that exon 7, though missing from the mRNA, is intact in the cataractous genome. Further sequence analysis of the α-crystallin gene disclosed a dinucleotide delection of the universal AG at the acceptor splice-site of intron 6 of the mutant gene. The presence of this mutation results in the skipping of exon 7 during the mRNA processing which in turn results in the altered ζ-crystallin protein. This if the first time a genomic mutation in an enzyme/crytallin gene has been directly linked to a congenital cataract. 相似文献
146.
147.
Xiao-yan Ding Wallace L. McKeehan Jianming Xu Horst Grunz 《Development genes and evolution》1992,201(6):334-339
Summary Mesoderm formation is a result of cell-cell interactions between the vegetal and animal hemisphere and is thought to be mediated by inducing peptide growth factors including members of the FGF and TGF superfamilies. Our immunochemical study analyses the distribution of FGF receptors coded by the human flg gene during embryogenesis of Xenopus laevis. Immunostaining was detected in the dorsal and ventral ectoderm and also in the marginal zone of early cleavage, blastula and gastrula stages. Signals were very strong in the mid and late blastula (stage 8 and 9) and declined slightly in the early gastrula (stage 10). A dramatic decrease was observed up to the late gastrula (stage 11+). In stage 13 embryos, immunostaining was only found in cells around the blastopore. Isolated ectoderm cultured in vitro showed a similar temporal expression and decrease of the signal as the normal embryos. These results indicate that receptor expression is independent of the interaction of the animal cells with the vegetal part of the embryo. Of interest is the fact that the signal cannot only be found at or near the cell surface but also within the cell. This suggests the presence of an intracellular isoform of the receptor resulting from the endogenous expression of splice variants and the internalization of transmembrane receptor. Taken together our results suggest that the loss of competence (for bFGF around stage 10) is not directly correlated with the presence of receptors. The possible roles of heparan sulphate glucosaminoglycans (low affinity receptors) and control mechanisms in the intracellular signalling pathway downstream of the receptor level should be taken into consideration. 相似文献
148.
An alternative procedure to obtain the parameters of Monod's growth model in batch culture is presented. It is based on the integral kinetic analysis methodology, employs a one-dimensional Golden Section search optimization method and is implemented on a spread-sheet programme. The procedure is discussed in detail and is illustrated by analysis of batch substrate consumption data by an aerobic bacterial consortium. 相似文献
149.
提出一个改进的下丘脑-垂体-甲状腺轴的数学模型.该模型既考虑了此分泌调节系统各激素之间的激活和反馈作用,也考虑了甲状腺激素与蛋白质结合的动力学过程.由该模型推导的结果与实验结果符合得很好. 相似文献
150.