全文获取类型
收费全文 | 23347篇 |
免费 | 2427篇 |
国内免费 | 3538篇 |
专业分类
29312篇 |
出版年
2024年 | 89篇 |
2023年 | 385篇 |
2022年 | 936篇 |
2021年 | 1378篇 |
2020年 | 1073篇 |
2019年 | 1257篇 |
2018年 | 1164篇 |
2017年 | 871篇 |
2016年 | 1084篇 |
2015年 | 1561篇 |
2014年 | 1849篇 |
2013年 | 1814篇 |
2012年 | 2131篇 |
2011年 | 1992篇 |
2010年 | 1298篇 |
2009年 | 1121篇 |
2008年 | 1277篇 |
2007年 | 1116篇 |
2006年 | 997篇 |
2005年 | 831篇 |
2004年 | 838篇 |
2003年 | 780篇 |
2002年 | 725篇 |
2001年 | 484篇 |
2000年 | 381篇 |
1999年 | 348篇 |
1998年 | 244篇 |
1997年 | 175篇 |
1996年 | 160篇 |
1995年 | 152篇 |
1994年 | 116篇 |
1993年 | 108篇 |
1992年 | 97篇 |
1991年 | 72篇 |
1990年 | 72篇 |
1989年 | 71篇 |
1988年 | 46篇 |
1987年 | 39篇 |
1986年 | 34篇 |
1985年 | 20篇 |
1984年 | 23篇 |
1983年 | 20篇 |
1982年 | 22篇 |
1981年 | 16篇 |
1980年 | 8篇 |
1979年 | 7篇 |
1977年 | 5篇 |
1975年 | 4篇 |
1972年 | 3篇 |
1958年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
Tai‐Wen Lin Chi‐Chih Chen Shu‐Mei Wu Yu‐Ching Chang Yi‐Chuan Li Yu‐Wang Su Chwan‐Deng Hsiao Hsin‐Yang Chang 《The Plant journal : for cell and molecular biology》2019,99(1):128-143
In mammals and yeast, tail‐anchored (TA) membrane proteins destined for the post‐translational pathway are safely delivered to the endoplasmic reticulum (ER) membrane by a well‐known targeting factor, TRC40/Get3. In contrast, the underlying mechanism for translocation of TA proteins in plants remains obscure. How this unique eukaryotic membrane‐trafficking system correctly distinguishes different subsets of TA proteins destined for various organelles, including mitochondria, chloroplasts and the ER, is a key question of long standing. Here, we present crystal structures of algal ArsA1 (the Get3 homolog) in a distinct nucleotide‐free open state and bound to adenylyl‐imidodiphosphate. This approximately 80‐kDa protein possesses a monomeric architecture, with two ATPase domains in a single polypeptide chain. It is capable of binding chloroplast (TOC34 and TOC159) and mitochondrial (TOM7) TA proteins based on features of its transmembrane domain as well as the regions immediately before and after the transmembrane domain. Several helices located above the TA‐binding groove comprise the interlocking hook‐like motif implicated by mutational analyses in TA substrate recognition. Our data provide insights into the molecular basis of the highly specific selectivity of interactions of algal ArsA1 with the correct sets of TA substrates before membrane targeting in plant cells. 相似文献
122.
Adenosine is a major local regulator of tissue function and industrially useful as precursor for the production of medicinal nucleoside substances. High-throughput screening of adenosine overproducers is important for industrial microorganism breeding. An enzymatic assay of adenosine was developed by combined adenosine deaminase (ADA) with indophenol method. The ADA catalyzes the cleavage of adenosine to inosine and NH3, the latter can be accurately determined by indophenol method. The assay system was optimized to deliver a good performance and could tolerate the addition of inorganic salts and many nutrition components to the assay mixtures. Adenosine could be accurately determined by this assay using 96-well microplates. Spike and recovery tests showed that this assay can accurately and reproducibly determine increases in adenosine in fermentation broth without any pretreatment to remove proteins and potentially interfering low-molecular-weight molecules. This assay was also applied to high-throughput screening for high adenosine-producing strains. The high selectivity and accuracy of the ADA assay provides rapid and high-throughput analysis of adenosine in large numbers of samples. 相似文献
123.
Spirulina platensis was cultivated in a bench-scale airlift photobioreactor using synthetic wastewater (total nitrogen 412 mg L(-1), total phosphorous 90 mg L(-1), pH 9-10) with varying ammonia/total nitrogen ratios (50-100% ammonia with balance nitrate) and hydraulic residence times (15-25 d). High average biomass density (3500-3800 mg L(-1)) and productivity (5.1 g m(-2) d(-1)) were achieved when ammonia was maintained at 50% of the total nitrogen. Both high ammonia concentrations and mutual self-shading, which resulted from the high biomass density in the airlift reactor, were found to partially inhibit the growth of S. platensis. The performance of the airlift bioreactor used in this study compared favorably with other published studies. The system has good potential for treatment of high strength wastewater combined with production of algae for biofuels or other products, such as human and animal food, food supplements or pharmaceuticals. 相似文献
124.
Ma Z Liu T Li X Zhou T Xiao L Que H Tian D Jing S Liu S 《Cellular and molecular neurobiology》2006,26(3):277-288
Spinal cord injury (SCI) initiates a cascade of events and these responses to injury are likely to be mediated and reflected by changes in mRNA concentrations. As a step towards understanding the complex mechanisms underlying repair and regeneration after SCI, the gene expression pattern was examined 4.5 days after complete transection at T8-9 level of rat spinal cord. Improved subtractive hybridization was used to establish a subtracted cDNA library using cDNAs from normal rat spinal cord as driver and cDNAs from injured spinal cord as tester. By expressed sequence tag (EST) sequencing, we obtained 73 EST fragments from this library, representing 40 differentially expressed genes. Among them, 32 were known genes and 8 were novel genes. Functions of all annotated genes were scattered in almost every important field of cell life such as DNA repair, detoxification, mRNA quality control, cell cycle control, and signaling, which reflected the complexity of SCI and regeneration. Then we verified subtraction results with semiquantitative RT-PCR for eight genes. These analyses confirmed, to a large extent, that the subtraction results accurately reflected the molecular changes occurring at 4.5 days post-SCI. The current study identified a number of genes that may shed new light on SCI-related inflammation, neuroprotection, neurite-outgrowth, synaptogenesis, and astrogliosis. In conclusion, the identification of molecular changes using improved subtractive hybridization may lead to a better understanding of molecular mechanisms responsible for repair and regeneration after SCI. 相似文献
125.
1999、2000年3~6月,对辽宁省朝阳县树俩型苍鹭孵化习性和育雏习性进行观察。苍鹭孵化以雌鸟为主,两性轮流孵化,孵化期24~27天,平均孵化率93.5%;雏鸟为晚成鸟,育雏期40~50天左右,育雏过程分育雏初期、中期、末期三阶段;雏鸟的食物以鱼类、蚌类为主。 相似文献
126.
Ya‐Yun Zuo Huan‐Huan Ma Wen‐Jie Lu Xing‐Liang Wang Shu‐Wen Wu Ralf Nauen Yi‐Dong Wu Yi‐Hua Yang 《Insect Science》2020,27(4):791-800
Insect ryanodine receptors (RyRs) are the targets of diamide insecticides. Two point mutations G4946E and I4790M (numbering according to Plutella xylostella, PxRyR) in the transmembrane domain of the insect RyRs associated with diamide resistance have so far been identified in three lepidopteran pests, P. xylostella, Tuta absoluta and Chilo suppressalis. In this study, we identified one of the known RyR target site resistance mutations (I4790M) in a field‐collected population of Spodoptera exigua. The field‐collected WF population of S. exigua exhibited 154 fold resistance to chlorantraniliprole when compared with the susceptible WH‐S strain. Sequencing the transmembrane domains of S. exigua RyR (SeRyR) revealed that the resistant WF strain was homozygous for the I4743M mutation (corresponding to I4790M in PxRyR), whereas the G4900E allele (corresponding to G4946E of PxRyR) was not detected. The 4743M allele was introgressed into the susceptible WH‐S strain by crossing WF with WH‐S, followed by three rounds of backcrossing with WH‐S. The introgressed strain 4743M was homozygous for the mutant 4743M allele and shared about 94% of its genetic background with that of the recipient WH‐S strain. Compared with WH‐S, the near‐isogenic 4743M strain showed moderate levels of resistance to chlorantraniliprole (21 fold), cyantraniliprole (25 fold) and flubendiamide (22 fold), suggesting that the I4743M mutation confers medium levels of resistance to all three diamides. Genetic analysis showed diamide resistance in the 4743M strain was inherited as an autosomal and recessive trait. Results from this study have direct implications for the design of appropriate resistance monitoring and management practices to sustainably control S. exigua. 相似文献
127.
Valle M Zavialov A Li W Stagg SM Sengupta J Nielsen RC Nissen P Harvey SC Ehrenberg M Frank J 《Nature structural biology》2003,10(11):899-906
Aminoacyl-tRNAs (aa-tRNAs) are delivered to the ribosome as part of the ternary complex of aa-tRNA, elongation factor Tu (EF-Tu) and GTP. Here, we present a cryo-electron microscopy (cryo-EM) study, at a resolution of approximately 9 A, showing that during the incorporation of the aa-tRNA into the 70S ribosome of Escherichia coli, the flexibility of aa-tRNA allows the initial codon recognition and its accommodation into the ribosomal A site. In addition, a conformational change observed in the GTPase-associated center (GAC) of the ribosomal 50S subunit may provide the mechanism by which the ribosome promotes a relative movement of the aa-tRNA with respect to EF-Tu. This relative rearrangement seems to facilitate codon recognition by the incoming aa-tRNA, and to provide the codon-anticodon recognition-dependent signal for the GTPase activity of EF-Tu. From these new findings we propose a mechanism that can explain the sequence of events during the decoding of mRNA on the ribosome. 相似文献
128.
129.
Zechang Xin Duguang Li Feiyu Mao Yan Du Xiaodong Wang Peng Xu Zhennan Li Jianjun Qian Jie Yao 《Journal of cellular physiology》2020,235(11):8416-8423
Plastin-3 plays a key role in cancer cell proliferation and invasion, but its prognostic value in pancreatic cancer (PACA) remains poorly defined. In this study, we show that PLS3 messenger RNA is overexpressed in PACA tissue compared with normal tissue. We accumulated 207 cases of PACA specimens to perform immunohistochemical analysis and demonstrated that PLS3 levels correlate with T-classification (p < .001) and pathology (p < .001). Furthermore, overall survival rates (p < .001) in tumors with high PLS3 expression were poor, as assessed through Kaplan–Meier survival analysis. PLS3 was found to be an independent prognostic factor for PACA through multivariate Cox regression analysis. Moreover, we found that PLS3 enhances the proliferation and invasion of tumor cells as assessed through Cell Counting Kit-8, wounding healing assays, and Transwell assays. The upregulation of PLS3 also led to enhanced phosphatidylinositol-3 kinase/protein kinase B signaling in PACA cells. These data suggest that PLS3 is a biomarker to estimate PACA progression and represents a molecular target for PACA therapy. 相似文献
130.