全文获取类型
收费全文 | 9757篇 |
免费 | 548篇 |
出版年
2022年 | 58篇 |
2021年 | 110篇 |
2020年 | 62篇 |
2019年 | 80篇 |
2018年 | 121篇 |
2017年 | 109篇 |
2016年 | 187篇 |
2015年 | 264篇 |
2014年 | 290篇 |
2013年 | 553篇 |
2012年 | 471篇 |
2011年 | 479篇 |
2010年 | 281篇 |
2009年 | 299篇 |
2008年 | 449篇 |
2007年 | 443篇 |
2006年 | 387篇 |
2005年 | 429篇 |
2004年 | 402篇 |
2003年 | 404篇 |
2002年 | 386篇 |
2001年 | 357篇 |
2000年 | 380篇 |
1999年 | 276篇 |
1998年 | 123篇 |
1997年 | 90篇 |
1996年 | 67篇 |
1995年 | 77篇 |
1994年 | 74篇 |
1993年 | 84篇 |
1992年 | 201篇 |
1991年 | 199篇 |
1990年 | 201篇 |
1989年 | 192篇 |
1988年 | 176篇 |
1987年 | 144篇 |
1986年 | 118篇 |
1985年 | 112篇 |
1984年 | 110篇 |
1983年 | 87篇 |
1982年 | 76篇 |
1981年 | 65篇 |
1979年 | 87篇 |
1978年 | 64篇 |
1977年 | 64篇 |
1976年 | 58篇 |
1975年 | 60篇 |
1974年 | 58篇 |
1973年 | 55篇 |
1972年 | 63篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
Takako S. Kaneko Mamiko Sato Masako Osumi Makoto Muroi Akira Takatsuki 《Plant cell reports》1996,15(6):409-413
Summary The effects of brefeldin A (BFA) on the secretion of acid phosphatase (APase) by tobacco protoplasts were investigated. Secretion of APase was inhibited by BFA in a dose-dependent manner, with a concomitant intracellular accumulation of the enzyme. The secreted APase was composed of two isoforms. BFA (10/ g/ml) inhibited the secretion of one of the isoforms without inhibiting that of the other, and this phenomenon explains the partial inhibition of APase secretion as a whole. The inhibition of APase secretion was accompanied by changes in the morphology of the Golgi apparatus and also by an increment in massdensity of cells.Abbreviations APase
acid phosphatase
- BFA
brefeldin A
- CHX
cycloheximide
- PAGE
polyacrylamide gel electrophoresis 相似文献
202.
The induction of phytochelatins (PCs) and their desglycyl peptides (both are referred to as class III metallothionein [CIIIMT]) by exposure to various metals (Ag+, As3+, As5+, Cd2+, Cu2+, Ga3+, Hg2+, In3+, Ni2+, Pb2+, Pd2+, Se4+, and Zn2+) and the metal composition in the CIIIMTs were investigated in root cultures of Rubia tinctorum L. All of these metal species induced PCs to various degrees when analyzed by the postcolumn derivatization high-performance liquid chromatography method. The desglycyl peptides of PCs often were also present. However, only Ag, Cd, and Cu were bound to the CIIIMTs that they induced when analyzed by the high-performance liquid chromatography-inductively coupled plasma-atomic emission spectrometry method. Cu was also bound to the CIIIMTs induced by Ag+, As3+, and Cd2+. After Ag+ exposure, an Fe peak that may be of Fe-CIIIMT was also observed. However, most of the metal species studied were not bound to the CIIIMTs that they induced. 相似文献
203.
204.
Gellan lyase was purified from the culture fluid of soil samples incubated in a medium containing gellan as a sole carbon source. The enzyme was a monomer with a molecular mass of 140 kDa and was most active at pH 7.5 and 45 degrees C. The enzyme was highly specific to gellan and lowered the viscosity of the polymer. 相似文献
205.
Hirobumi Suzuki Yasushi Sato Shizuo Fujiyama Nobuyoshi Ohba 《Biochemical genetics》1996,34(5-6):191-200
Japanese fireflies of the subfamily Luciolinae are biochemically analyzed using 13 allozymes, and the phylogenetic relationships obtained from this analysis are compared with their flash communication systems. As a result, the Japanese Luciolinae can be divided into three groups.Hotaria parvula andH. tsushimana together withLuciola yayeyamana andL. kuroiwae from the first group, and they use the same communication system.L. lateralis, Curtos okinawana, andC. costipennis make up the second group, and their communication systems are also the same.L. cruciata makes up the last one, and its communication system is different from the other fireflies of Luciolinae. Therefore, their taxonomical arrangement and communication systems are not congruent. However, the genetic similarity deduced by allozymic analysis of the members of the Japanese Luciolinae is highly consistent with their flash communication systems. 相似文献
206.
A rapidly frozen vitrified aqueous suspension of influenza A virus was observed by high resolution electron cryomicroscopy. The influenza particles were grouped into small (diameter < 150 nm) spherical particles with well organized interiors, large spherical ones with less internal organization, and filamentous ones. Envelopes of most of the large virus particles were phospholipid bilayers, and the chromatography fraction containing these large particles was largely devoid of viral activity. The envelopes of most of the filamentous and small spherical virus particles, on the other hand, gave a strange contrast which could be ascribed to a combination of a thin outer lipid monolayer and a 7.2 nm thick protein-containing inner layer. These latter particles represented most of the viral activity in the preparation. Densitometric traces of the near in-focus images confirmed these structural differences. Some viral envelope structures apparently intermediate between these two distinct types of membrane were also detected. A structural model of intact biologically active influenza virus particles was formulated from these results, together with computer simulations. 相似文献
207.
JAK2 associates with the beta c chain of the receptor for granulocyte-macrophage colony-stimulating factor, and its activation requires the membrane-proximal region. 总被引:32,自引:10,他引:22
下载免费PDF全文
![点击此处可从《Molecular and cellular biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
F W Quelle N Sato B A Witthuhn R C Inhorn M Eder A Miyajima J D Griffin J N Ihle 《Molecular and cellular biology》1994,14(7):4335-4341
The high-affinity receptor for granulocyte-macrophage colony-stimulating factor (GM-CSF) consists of a unique alpha chain and a beta c subunit that is shared with the receptors for interleukin-3 (IL-3) and IL-5. Two regions of the beta c chain have been defined; these include a membrane-proximal region of the cytoplasmic domain that is required for mitogenesis and a membrane-distal region that is required for activation of Ras, Raf-1, mitogen-activated protein kinase, and S6 kinase. Recent studies have implicated the cytoplasmic protein tyrosine kinase JAK2 in signalling through a number of the cytokine receptors, including the IL-3 and erythropoietin receptors. In the studies described here, we demonstrate that GM-CSF stimulation of cells induces the tyrosine phosphorylation of JAK2 and activates its in vitro kinase activity. Mutational analysis of the beta c chain demonstrates that only the membrane-proximal 62 amino acids of the cytosolic domain are required for JAK2 activation. Thus, JAK2 activation is correlated with induction of mitogenesis but does not, alone, activate the Ras pathway. Carboxyl truncations of the alpha chain, which inactivate the receptor for mitogenesis, are unable to mediate GM-CSF-induced JAK2 activation. Using baculovirus-expressed proteins, we further demonstrate that JAK2 physically associates with the beta c chain but not with the alpha chain. Together, the results further support the hypothesis that the JAK family of kinase are critical to coupling cytokine binding to tyrosine phosphorylation and ultimately mitogenesis. 相似文献
208.
209.
A genomic clone for the cyc07 gene, which is expressed specifically at the S phase during the cell cycle in synchronous cultures of periwinkle (Catharanthus roseus) cells, was isolated. Determination of the nucleotide sequence of the clone revealed that the cyc07 gene consists of seven exons separated by six introns. Genomic Southern analysis indicated that the cyc07 gene is present as a single copy per haploid genome in periwinkle. Expression of related genes was detected in a wide range of other plants. Transgenic Arabidopsis plants were generated that expressed the gene for -glucuronidase (GUS) under the control of the promoter of the cyc07 gene. The tissue-specific pattern of expression directed by the promoter was investigated by analysis of GUS activity. Histochemical tests demonstrated that 589 bp of the 5-upstream sequence of the cyc07 gene could direct specifical expression of the GUS reporter gene in meristematic tissues in transgenic plants. The spatial pattern of expression directed by the promoter was closely correlated with meristematic activity and cell proliferation, suggesting an association between the function of the cyc07 gene and cell proliferation. 相似文献
210.
Keisuke Tsutsumi Masami Niwa Naoki Kitagawa Sei-ich Yamaga Takeo Anda †Akihiko Himeno ‡Takaya Sato Humayun Khalid Kohtaro Taniyama Shobu Shibata 《Journal of neurochemistry》1994,63(6):2240-2247
Abstract: We identified and characterized 125I-endothelin-1 (125I-ET-1) binding sites in tumor capillaries isolated from human glioblastomas, using the quantitative receptor autoradiographic technique with pellet sections. Quantification was done using the computerized radioluminographic imaging plate system. High-affinity ET receptors were localized in capillaries from glioblastomas and the surrounding brain tissues (KD = 4.7 ± 1.0 × 10?10 and 1.6 ± 0.3 × 10?10M, respectively; Bmax = 161 ± 38 and 140 ± 37 fmol/mg, respectively; mean ± SEM, n = 5). BQ-123, a selective antagonist for the ETA receptor, potently competed for 125I-ET-1 binding to sections of the microvessels with IC50 values of 5.1 ± 0.3 and 5.1 ± 1.5 nM, and 10?6M BQ-123 displaced 84 and 58% of ET binding to capillaries from tumors and brains, respectively. In addition, competition curves obtained in the presence of increasing concentrations of ET-3 showed two components (IC50 = 5.7 ± 2.5 × 10?10 and 1.4 ± 0.2 × 10?6M for tumor microvessels, 1.8 ± 0.6 × 10?10 and 1.1 ± 0.3 × 10?6M for brain microvessels, respectively). Our results indicate that (a) the method we used is simple and highly sensitive for detecting and characterizing various receptors in tumor capillaries, especially in the case of a sparse specimen, and (b) capillaries in glioblastomas express specific high-affinity ET binding sites, candidates for biologically active ET receptors, which predominantly belong to the ETA subtype. 相似文献