首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1266篇
  免费   63篇
  国内免费   4篇
  1333篇
  2023年   7篇
  2022年   18篇
  2021年   26篇
  2020年   22篇
  2019年   13篇
  2018年   35篇
  2017年   30篇
  2016年   57篇
  2015年   37篇
  2014年   67篇
  2013年   75篇
  2012年   87篇
  2011年   59篇
  2010年   49篇
  2009年   40篇
  2008年   54篇
  2007年   50篇
  2006年   48篇
  2005年   58篇
  2004年   36篇
  2003年   25篇
  2002年   31篇
  2001年   28篇
  2000年   29篇
  1999年   24篇
  1997年   14篇
  1996年   16篇
  1995年   6篇
  1994年   11篇
  1993年   7篇
  1992年   13篇
  1991年   13篇
  1990年   14篇
  1989年   12篇
  1988年   16篇
  1987年   10篇
  1986年   18篇
  1985年   16篇
  1984年   20篇
  1983年   7篇
  1982年   6篇
  1981年   6篇
  1979年   9篇
  1978年   10篇
  1977年   8篇
  1974年   9篇
  1973年   9篇
  1972年   6篇
  1971年   12篇
  1970年   10篇
排序方式: 共有1333条查询结果,搜索用时 15 毫秒
11.
Assam hill goat (Capra hircus) is a prolific local goat in India. bone morphogenetic protein receptor (BMPR1B) gene was studied as a candidate gene for the prolificacy of goats. The objective of the present study was to detect the incidence of mutation in the exonic region of BMPR1B gene of Assam hill goat. Total 90 blood samples were collected randomly from different parts of Assam and genomic DNA were extracted using phenol–chloroform method. The quantity and quality of extracted DNA was examined by spectrophotometry and gel electrophoresis, respectively. PCR amplicon showed a product of 140 bp fragment of BMPR1B gene. The purified product upon digestion with AvaII showed monomorphic banding pattern and revealed wild type alleles with AA genotype. Nucleotide sequencing showed one new mutation 773 (G→C) which is found to be unique in Assam hill goat. Construction of tree at nucleotide level generates from the present experiment lies in common cluster which differs from the other breeds of goat. The analysis of polymorphism for BMPR1B in Assam hill goat indicates that the genetic factor responsible for prolificacy or multiple kidding rates is not related to the reported mutated alleles of BMPR1B gene. Therefore, attempts to be made to detect other SNPs for BMPR1B gene or otherwise effort should be made towards other fecundity gene which might be responsible for the prolificacy of Assam hill goat.  相似文献   
12.
Neurotrophins support neuronal survival and axonal regeneration after injury. To test whether local expression of Neurotrophin-3 (NT-3) would elicit axonal regeneration we lesioned the corticospinal tract (CST) at the level of the hindbrain and measured the number of axons that would grow from the unlesioned CST to the contralateral side where NT-3 was over expressed at the lumbar level of the spinal cord. An adenoviral vector that carried the rat NT-3 gene and the NGF signal peptide driven by the EF1α promoter (Adv.EF-NT-3) was used. This model enabled us to test the effects of NT-3 on axonal regeneration without confounding injury processes. Biotinylated dextran amine (BDA) was injected into the rat cortex on unlesioned side to mark CST axons 10 days postlesion. Adenoviral vectors (1 × 109 pfu, Adv.EF-NT-3 or Adv.EF-LacZ) were delivered to lumbar spinal cord by retrograde transport from the sciatic nerve 4 days later. Histological examination 3 weeks later revealed that more BDA-labelled axons had grown from the unlesioned CST to the denervated side at the lumbar level. Morphometric measurements showed that a significantly larger number of BDA-labelled CST axons ( p  < 0.001) were present in the animals that were treated with Adv.EF-NT-3 than those treated with Adv.EF-LacZ. These data demonstrate that local expression of NT-3 will support axonal regeneration in the injured spinal cord without adverse effects and suggest that gene delivery of neurotrophins may be an effective strategy for nervous system repair after injury.
Acknowledgements:   Funded by NIH Grant NS35280 and by Mission Connect of the TIRR Foundation.  相似文献   
13.
Direct photoaffinity labeling of tubulin with guanosine 5'-triphosphate   总被引:6,自引:0,他引:6  
J P Nath  G R Eagle  R H Himes 《Biochemistry》1985,24(6):1555-1560
Irradiation of tubulin in the presence of [3H]GTP or [3H]GDP at 254 nm led to the covalent incorporation of nucleotide into the protein. The specific nature of the labeling was shown in the following manner: with tubulin depleted of exchangeable nucleotide, the amount of labeling increased to a plateau value as the [3H]GTP concentration was increased, with saturation being reached at a ratio of approximately 1.5; the same amount of labeling was obtained with GTP/tubulin ratios of 1 and 100; [3H]GMP was not incorporated into the dimer, nor did GMP inhibit the incorporation of [3H]GTP; [3H]ATP was not incorporated; [3H]GTP incorporation did not occur into denatured tubulin or into serum albumin. When [alpha-32P]GTP was used in the irradiation experiments, sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the carboxymethylated protein demonstrated that the incorporated label was associated with the beta subunit. The radiation treatment did cause changes in the tubulin molecule resulting in a decrease in assembly competence and in sulfhydryl groups, but these effects were minimized when a large excess of GTP was present during irradiation. Labeling of tubulin in the assembled state was much less than that observed in the free state.  相似文献   
14.
Physiological changes induced by chromium stress in plants: an overview   总被引:1,自引:0,他引:1  
This article presents an overview of the mechanism of chromium (Cr) stress in plants. Toxic effects of Cr on plant growth and development depend primarily on its valence state. Cr(VI) is highly toxic and mobile whereas Cr(III) is less toxic. Cr-induced oxidative stress involves induction of lipid peroxidation in plants that cause severe damage to cell membranes which includes degradation of photosynthetic pigments causing deterioration in growth. The potential of plants with the adequacy to accumulate or to stabilize Cr compounds for bioremediation of Cr contamination has gained engrossment in recent years.  相似文献   
15.
This article describes the phytochemical study of Cannabis sativa roots from northeastern Brazil. The dried plant material was pulverized and subjected to exhaustive maceration with ethanol at room temperature, obtaining the crude ethanolic extract (Cs-EEBR). The volatile compounds were analyzed by gas chromatography coupled with mass spectrometry (GC/MS), which allowed to identify 22 compounds by comparing the linear retention index (LRI), the similarity index (SI) and the fragmentation pattern of the constituents with the literature. By this technique the major compounds identified were: friedelan-3-one and β-sitosterol. In addition, two fractions were obtained from Cs-EEBR by classical column chromatography and preparative thin layer chromatography. These fractions were analyzed by NMR and IR and together with the mass spectrometry data allowed to identify the compounds: epifriedelanol, friedelan-3-one, β-sitosterol and stigmasterol. The study contributed to the phytochemical knowledge of Cannabis sativa, specifically the roots, as there are few reports on the chemical constituents of this part of the plant.  相似文献   
16.
In vertebrates, the nuclear pore complex (NPC), the gate for transport of macromolecules between the nucleus and the cytoplasm, consists of approximately 30 different nucleoporins (Nups). The Nup and SUMO E3-ligase Nup358/RanBP2 are the major components of the cytoplasmic filaments of the NPC. In this study, we perform a structure-function analysis of Nup358 and describe its role in nuclear import of specific proteins. In a screen for nuclear proteins that accumulate in the cytoplasm upon Nup358 depletion, we identified proteins that were able to interact with Nup358 in a receptor-independent manner. These included the importin α/β-cargo DBC-1 (deleted in breast cancer 1) and DMAP-1 (DNA methyltransferase 1 associated protein 1). Strikingly, a short N-terminal fragment of Nup358 was sufficient to promote import of DBC-1, whereas DMAP-1 required a larger portion of Nup358 for stimulated import. Neither the interaction of RanGAP with Nup358 nor its SUMO-E3 ligase activity was required for nuclear import of all tested cargos. Together, Nup358 functions as a cargo- and receptor-specific assembly platform, increasing the efficiency of nuclear import of proteins through various mechanisms.  相似文献   
17.
18.
A unicyanobacterial isolate of cyanobacterium, identified as Microcystis Ku2, produced a mammalian elastase-inhibitory lipid derivative. Protease inhibitors in cyanobacteria are unequivocally peptides. Since this metabolite appeared in lipid phase, we worked on a hypothesis that whether metabolite other than peptides could be responsible for the characteristic inhibition. It was purified by saponification and reverse phase column chromatography. The resulting compound was tentatively characterized as a glycolipid with structure of sulfated di-pentose derivative of ceramide (MW = 956 Da). The apparent IC50 for elastase was 1.3 μM.  相似文献   
19.
Peroxiredoxins (Prx) are ubiquitous thiol-dependent peroxidases capable of reducing a broad range of toxic peroxides and peroxinitrites. A cysteinyl residue of peroxiredoxins reacts with the peroxides as primary catalytic center and oxidizes to sulfenic acid. The regeneration of the reduced form of Prx is required as a next step to allow its entry into next catalytic cycle. Several proteins, such as thioredoxin, glutaredoxin, cyclophilin, among others, are known to facilitate the regeneration of the reduced (catalytically active) form of Prx in plants. Based on the cysteine residues conserved in the deduced amino acid sequence and their catalytic mechanisms, four groups of peroxiredoxins have been distinguished in plants, namely, 1-Cys Prx, 2-Cys Prx, Type II Prx and Prx Q. Peroxiredoxins are known to play an important role in combating the reactive oxygen species generated at the level of electron transport activities in the plant exposed to different types of biotic and abiotic stresses. In addition to their role in antioxidant defense mechanisms in plants, they also modulate redox signaling during development and adaptation. Besides these general properties, peroxiredoxins have been shown to protect DNA from damage in vitro and in vivo. They also regulate metabolism in thylakoids and mitochondria. The present review summarizes the most updated information on the structure and catalysis of Prx and their functional importance in plant metabolism.  相似文献   
20.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号