全文获取类型
收费全文 | 3508篇 |
免费 | 230篇 |
国内免费 | 364篇 |
出版年
2024年 | 9篇 |
2023年 | 54篇 |
2022年 | 72篇 |
2021年 | 125篇 |
2020年 | 124篇 |
2019年 | 130篇 |
2018年 | 104篇 |
2017年 | 100篇 |
2016年 | 119篇 |
2015年 | 118篇 |
2014年 | 194篇 |
2013年 | 234篇 |
2012年 | 153篇 |
2011年 | 189篇 |
2010年 | 149篇 |
2009年 | 195篇 |
2008年 | 173篇 |
2007年 | 191篇 |
2006年 | 201篇 |
2005年 | 176篇 |
2004年 | 137篇 |
2003年 | 160篇 |
2002年 | 132篇 |
2001年 | 111篇 |
2000年 | 88篇 |
1999年 | 86篇 |
1998年 | 73篇 |
1997年 | 56篇 |
1996年 | 55篇 |
1995年 | 47篇 |
1994年 | 36篇 |
1993年 | 39篇 |
1992年 | 44篇 |
1991年 | 25篇 |
1990年 | 21篇 |
1989年 | 24篇 |
1988年 | 20篇 |
1987年 | 12篇 |
1986年 | 14篇 |
1985年 | 15篇 |
1984年 | 16篇 |
1983年 | 14篇 |
1982年 | 15篇 |
1981年 | 12篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1974年 | 6篇 |
排序方式: 共有4102条查询结果,搜索用时 937 毫秒
141.
142.
Adaptation to any given environment may be accompanied by a cost in terms of reduced growth in the ancestral or some alternative environment. Ecologists explain the cost of adaptation through the concept of a trade‐off, by which gaining a new trait involves losing another trait. Two mechanisms have been invoked to explain the evolution of trade‐offs in ecological systems, mutational degradation, and functional interference. Mutational degradation occurs when a gene coding a specific trait is not under selection in the resident environment; therefore, it may be degraded through the accumulation of mutations that are neutral in the resident environment but deleterious in an alternative environment. Functional interference evolves if the gene or a set of genes have antagonistic effects in two or more ecologically different traits. Both mechanisms pertain to a situation where the selection and the alternative environments are ecologically different. To test this hypothesis, we conducted an experiment in which 12 experimental populations of wild yeast were each grown in a minimal medium supplemented with a single substrate. We chose 12 different carbon substrates that were metabolized through similar and different pathways in order to represent a wide range of ecological conditions. We found no evidence for trade‐offs between substrates on the same pathway. The indirect response of substrates on other pathways, however, was consistently negative, with little correlation between the direct and indirect responses. We conclude that the grain of specialization in this case is the metabolic pathway and that specialization appears to evolve through mutational degradation. 相似文献
143.
Genetic mutation analysis at early stages of cell line development using next generation sequencing
下载免费PDF全文
![点击此处可从《Biotechnology progress》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Chapman Wright Joost Groot Samantha Swahn Helen McLaughlin Mei Liu Chongfeng Xu Chao Sun Eric Zheng Scott Estes 《Biotechnology progress》2016,32(3):813-817
A central goal for most biopharmaceutical companies is to reduce the development timeline to reach clinical proof of concept. This objective requires the development of tools that ensure the quality of biotherapeutic material destined for the clinic. Recent advances in high throughput protein analytics provide confidence in our ability to assess productivity and product quality attributes at early stages of cell line development. However, one quality attribute has, until recently, been absent from the standard battery of analytical tests facilitating informed choices early in cell line selection: genetic sequence confirmation. Techniques historically used for mutation analysis, such as detailed mass spectrometry, have limitations on the sample number and turnaround times making it less attractive at early stages. Thus, we explored the utility of Next‐Generation Sequencing (NGS) as a solution to address these limitations. Amplicon sequencing is one such NGS technique that is robust, rapid, sensitive, and amenable to multiplexing, all of which are essential attributes for our purposes. Here we report a NGS method based upon amplicon sequencing that has been successfully incorporated into our cell line development workflow alongside other high‐throughput protein analytical assays. The NGS method has demonstrated its value by identifying at least one Chinese hamster ovary (CHO) clone expressing a variant form of the biotherapeutic in each of the four clinical programs in which it has been utilized. We believe this sequence confirmation method is essential to safely accelerating the time to clinical proof of concept of biotherapeutics, and guard against delays related to sequence mutations. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:813–817, 2016 相似文献
144.
Strong invaders are strong defenders – implications for the resistance of invaded communities
下载免费PDF全文
![点击此处可从《Ecology letters》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Anna Henriksson David A. Wardle Johan Trygg Sebastian Diehl Göran Englund 《Ecology letters》2016,19(4):487-494
Many ecosystems receive a steady stream of non‐native species. How biotic resistance develops over time in these ecosystems will depend on how established invaders contribute to subsequent resistance. If invasion success and defence capacity (i.e. contribution to resistance) are correlated, then community resistance should increase as species accumulate. If successful invaders also cause most impact (through replacing native species with low defence capacity) then the effect will be even stronger. If successful invaders instead have weak defence capacity or even facilitative attributes, then resistance should decrease with time, as proposed by the invasional meltdown hypothesis. We analysed 1157 introductions of freshwater fish in Swedish lakes and found that species’ invasion success was positively correlated with their defence capacity and impact, suggesting that these communities will develop stronger resistance over time. These insights can be used to identify scenarios where invading species are expected to cause large impact. 相似文献
145.
Allen Herbst Jonathan Wanagat Nashwa Cheema Kevin Widjaja Debbie McKenzie Judd M. Aiken 《Aging cell》2016,15(6):1132-1139
With age, somatically derived mitochondrial DNA (mtDNA) deletion mutations arise in many tissues and species. In skeletal muscle, deletion mutations clonally accumulate along the length of individual fibers. At high intrafiber abundances, these mutations disrupt individual cell respiration and are linked to the activation of apoptosis, intrafiber atrophy, breakage, and necrosis, contributing to fiber loss. This sequence of molecular and cellular events suggests a putative mechanism for the permanent loss of muscle fibers with age. To test whether mtDNA deletion mutation accumulation is a significant contributor to the fiber loss observed in aging muscle, we pharmacologically induced deletion mutation accumulation. We observed a 1200% increase in mtDNA deletion mutation‐containing electron transport chain‐deficient muscle fibers, an 18% decrease in muscle fiber number and 22% worsening of muscle mass loss. These data affirm the hypothesized role for mtDNA deletion mutation in the etiology of muscle fiber loss at old age. 相似文献
146.
147.
Min Ni Kai‐Zun Xu Jiang‐Hai Tian Jing‐Sheng Hu Bin Xue Wei‐De Shen Bing Li 《Archives of insect biochemistry and physiology》2016,93(2):110-118
The main mechanism of toxicity of organophosphate (OP) and carbamate (CB) insecticides is their irreversible binding and inhibition of acetylcholinestrase (AChE), encoded by ace1 (acetylcholinestrase gene 1), leading to eventual death of insects. Mutations in AChE may significantly reduce insects susceptibility to these pesticides. Bombyx mori is an important beneficial insect, and no OP‐ or CB‐resistant strains have been generated. In this study, wild‐type ace1 (wace1) and mutant ace1 (mace1) were introduced into BmN cells, confirmed by screening and identification. The expression of wace1 and mace1 in the cells was confirmed by Western blot and their expression levels were about 21‐fold higher than the endogenous ace1 level. The activities of AChE in wace1 and mace1 transgenic cells were 10.6 and 20.2% higher compared to control cells, respectively. mace1 transgenic cells had higher remaining activity than wace1 transgenic cells under the treatment of physostigmine (a reversible cholinesterase inhibitor) and phoxim (an OP acaricide). The results showed that ace1 transgene can significantly improve ace1 expression, and ace1 mutation at a specific site can reduce the sensitivity to AChE inhibitors. Our study provides a new direction for the exploration of the relationship between AChE mutations and drug resistance. 相似文献
148.
Structural mutation analysis of PTEN and its genotype‐phenotype correlations in endometriosis and cancer
下载免费PDF全文
![点击此处可从《Proteins》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The phosphatase and tensin homolog deleted on chromosome ten (PTEN) gene encodes a tumor suppressor phosphatase that has recently been found to be frequently mutated in patients with endometriosis, endometrial cancer and ovarian cancer. Here, we present the first computational analysis of 13 somatic missense PTEN mutations associated with these phenotypes. We found that a majority of the mutations are associated in conserved positions within the active site and are clustered within the signature motif, which contain residues that play a crucial role in loop conformation and are essential for catalysis. In silico analyses were utilized to identify the putative effects of these mutations. In addition, coarse‐grained models of both wild‐type (WT) PTEN and mutants were constructed using elastic network models to explore the interplay of the structural and global dynamic effects that the mutations have on the relationship between genotype and phenotype. The effects of the mutations reveal that the local structure and interactions affect polarity, protein structure stability, electrostatic surface potential, and global dynamics of the protein. Our results offer new insight into the role in which PTEN missense mutations contribute to the molecular mechanism and genotypic‐phenotypic correlation of endometriosis, endometrial cancer, and ovarian cancer. Proteins 2016; 84:1625–1643. © 2016 Wiley Periodicals, Inc. 相似文献
149.
Role of W181 in modulating kinetic properties of Plasmodium falciparum hypoxanthine guanine xanthine phosphoribosyltransferase
下载免费PDF全文
![点击此处可从《Proteins》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Hypoxanthine‐guanine‐xanthine phosphoribosyltransference (HGXPRT), a key enzyme in the purine salvage pathway of the malarial parasite, Plasmodium falciparum (Pf), catalyses the conversion of hypoxanthine, guanine, and xanthine to their corresponding mononucleotides; IMP, GMP, and XMP, respectively. Out of the five active site loops (I, II, III, III', and IV) in PfHGXPRT, loop III' facilitates the closure of the hood over the core domain which is the penultimate step during enzymatic catalysis. PfHGXPRT mutants were constructed wherein Trp 181 in loop III' was substituted with Ser, Thr, Tyr, and Phe. The mutants (W181S, W181Y and W181F), when examined for xanthine phosphoribosylation activity, showed an increase in Km for PRPP by 2.1‐3.4 fold under unactivated condition and a decrease in catalytic efficiency by more than 5‐fold under activated condition as compared to that of the wild‐type enzyme. The W181T mutant showed 10‐fold reduced xanthine phosphoribosylation activity. Furthermore, molecular dynamics simulations of WT and in silico W181S/Y/F/T PfHGXPRT mutants bound to IMP.PPi.Mg2+ have been carried out to address the effect of the mutation of W181 on the overall dynamics of the systems and identify local changes in loop III'. Dynamic cross‐correlation analyses show a communication between loop III' and the substrate binding site. Differential cross‐correlation maps indicate altered communication among different regions in the mutants. Changes in the local contacts and hydrogen bonding between residue 181 with the nearby residues cause altered substrate affinity and catalytic efficiency of the mutant enzymes. Proteins 2016; 84:1658–1669. © 2016 Wiley Periodicals, Inc. 相似文献
150.
Ras/Raf/MEK/ERK 通路是调节细胞生长与增殖的重要信号传导通路。在Ras/Raf/MEK/ERK 通路中某些成员的突变往往与恶性肿瘤的发生密切相关。B-Raf 激酶是该通路中Raf 家族最重要的亚型,其主要突变形式B-RafV600E 在黑色素瘤等多种肿瘤中高度表达。选择性B-RafV600E 抑制剂vemurafenib 和dabrafenib 的上市使得晚期黑色素瘤的治疗进入新纪元,但是耐药性和副作用依然限制了二者的使用。综述目前Raf 激酶抑制剂耐药性与副作用产生机制以及Raf 激酶抑制剂的最新研究进展。 相似文献