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   8992篇
  免费   637篇
  国内免费   468篇
  10097篇
  2024年   10篇
  2023年   81篇
  2022年   191篇
  2021年   325篇
  2020年   231篇
  2019年   265篇
  2018年   282篇
  2017年   231篇
  2016年   320篇
  2015年   461篇
  2014年   578篇
  2013年   638篇
  2012年   739篇
  2011年   703篇
  2010年   413篇
  2009年   371篇
  2008年   424篇
  2007年   416篇
  2006年   367篇
  2005年   359篇
  2004年   292篇
  2003年   299篇
  2002年   241篇
  2001年   195篇
  2000年   193篇
  1999年   162篇
  1998年   108篇
  1997年   102篇
  1996年   104篇
  1995年   101篇
  1994年   78篇
  1993年   78篇
  1992年   127篇
  1991年   101篇
  1990年   72篇
  1989年   72篇
  1988年   66篇
  1987年   49篇
  1986年   41篇
  1985年   53篇
  1984年   33篇
  1983年   24篇
  1982年   19篇
  1981年   10篇
  1979年   10篇
  1978年   6篇
  1977年   7篇
  1971年   7篇
  1970年   7篇
  1966年   7篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
The microRNAs (miRNAs) are involved in multiple pathological processes among various types of tumors. However, the functions of miRNAs in benign brain tumors are largely unexplored. In order to explore the pathogenesis of the invasiveness in non-functional pituitary adenoma (NFPA), the miRNAs expression profile was analyzed between invasive and non-invasive non-functional pituitary adenoma by miRNAs microarray. Six most significant differentially expressed miRNAs were identified including four upregulated miRNAs hsa-miR-181b-5p, hsa-miR-181d, hsa-miR-191-3p, and hsa-miR-598 and two downregulated miRNAs hsa-miR-3676-5p and hsa-miR-383. The functions and corresponding signaling pathways of differentially expressed miRNAs were investigated by bioinformatics techniques, including Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis. The result of GO analysis indicates regulation of voltage-gated potassium channel activity, positive regulation of sodium ion transport, positive regulation of GTPase activity, negative regulation of Notch signaling pathway, etc. KEGG pathway reveals a series of biological processes, including prolactin signaling pathway, endocrine and other factor-regulated calcium reabsorption, fatty acid metabolism, neuroactive ligand-receptor interaction, etc. The miRNAs hsa-miR-181a-5p was verified by quantitative real-time PCR, and the expression level was in accordance with the microarray result. Our result can provide the evidence on featured miRNAs which play a prominent role in pituitary adenoma as effective biomarkers and therapeutic targets in the future.  相似文献   
32.
新疆罗布麻生态类型及其纤维品质研究   总被引:7,自引:0,他引:7  
新疆塔里木河及叶尔羌河流域是我国能够提供商品精干罗布麻的主要地区。由于野生罗布麻生长高矮不一,形态各异,与其纤维品质的相关性较大。通过40个株号的罗布麻植株形态和纤维长度等的的测定,分析各类型罗布麻的纤维长度和罗布麻植株各部分纤维长度情况。研究结果表明:罗布红麻高杆类型主茎纤维最长,罗布麻放牧类型纤维最短。罗布麻植株各部分纤维长度是主茎上的大于分枝,主茎中部的最长,基部和梢部最短。为野生罗布麻资源开发利用提科学依据。  相似文献   
33.
A high throughput toxicity biosensor has been designed and constructed using recombinant Escherichia coli cells, containing stress specific promoters (recA, fabA, or katG) or constitutive promoters (lac) fused to luciferase genes originating from Vibrio fisheri. These genetically engineered cells were immobilized in 96 well plates. By optimizing cell immobilization conditions and the strains' response specificity to toxic chemicals, bioluminescent outputs decreased or increased dose-dependently upon adding test chemicals. However, to date the toxicity data obtained using this biosensor have not been compared with the results of other toxicity tests. Phenolics were chosen to evaluate the correlation between the LD50 and the EC50 (GC2) or EC120 (DPD2540) of Daphnia magna and E. coli, respectively. Toxicity data obtained from constitutive strains by bioluminescent level decrements were compared with the results from D. magna as a standard. LD50 values were used as parameters of D. magna toxicity and EC50 of EC120 values were used for the immobilized biosensor. In the DPD2540 test, phenolics, membrane damaging toxic chemicals, for testing immobilized stress specific bacterial strains trigger dose-dependant bioluminescence increase within specific concentration. Although the stress specific responsiveness from the strains could not be compared with D. magna's LD50 values, these responses offer additional information, such as upon the mode of toxic action in the sample, in addition to the cellular toxicity results as indicated by the EC50. This novel high throughput toxicity biosensor can be implemented to investigate the toxicity of any other soluble materials, and can be used as a standardization tool for the evaluation of toxicity.  相似文献   
34.
The silkworm, Bombyx mori, is an important economic insect for its production of silk. The larvae of many lepidopteran insects are major agricultural pests and often silkworm is explored as a model organism for other lepidopteran pest species. The hemolymph of caterpillars contains a lot of nutrient and immune components. In this study, we applied liquid chromatography–tandem mass spectrometry to gain a better understanding of the larval hemolymph proteomics in B. mori. We identified 752 proteins in hemolymph collected from day-4 fourth instar and day-7 fifth instar. Nearly half the identified proteins (49 %) were predicted to function as binding proteins and 46 % were predicted to have catalytic activities. Apolipophorins, storage proteins, and 30K proteins constituted the most abundant groups of nutrient-storage proteins. Of them, 30K proteins showed large differences between fourth instar larvae and fifth instar larvae. Besides nutrient-storage proteins, protease inhibitors are also expressed very highly in hemolymph. The analysis also revealed lots of immunity-related proteins, including recognition, signaling, effectors and other proteins, comprising multiple immunity pathways in hemolymph. Our data provide an exhaustive research of nutrient-storage proteins and immunity-related proteins in larval hemolymph, and will pave the way for future physiological and pathological studies of caterpillars.  相似文献   
35.
36.
37.
Abstract: It is well documented that nerve growth factor (NGF) plays an important role in maintaining functions of cholinergic basal forebrain neurons. In the present study, we tested the hypothesis that cholinergic activity controls NGF levels in cholinoceptive neurons of the cerebral cortex and hippocampus. To address that question, we used both cholinergic deafferentation of cerebral cortex and hippocampus by cholinergic immunolesion with 192IgG-saporin and chronic pharmacological treatment of sham-treated and immunolesioned rats with the cholinergic agonist pilocarpine and the cholinergic antagonist scopolamine. We observed an increase in NGF protein levels in the cortex and hippocampus after cholinergic immunolesions and also after muscarinic receptor blockade by chronic intracerebroventricular scopolamine infusion in sham-treated rats after 2 weeks. There was no further increase in the accumulation of NGF after scopolamine treatment of immunolesioned rats. Chronic infusion of pilocarpine had no effect on cortical and hippocampal NGF protein levels in sham-treated rats. In rats with cholinergic immunolesions, however, pilocarpine did prevent the lesion-induced accumulation of NGF. There was no effect of cholinergic lesion and drug treatment on cortical or hippocampal NGF mRNA levels, consistent with the importance of NGF retrograde transport as opposed to its de novo synthesis. This study provides strong evidence for the hypothesis that there is cholinergic control of cortical and hippocampal NGF protein but not mRNA levels in adult rats.  相似文献   
38.
The continuous chain of residues (Thr7 to Ala12) of Loop1 of Fas2 (F1) and its interaction with the peripheral binding sites (Tyr70-Val71) of AChE (P1) has been studied. Our results suggest that the flexibility of Loop1 might be caused by either the partially protonated guanidine group of Arg11 under experimental conditions or by the interaction with the negatively charged center of substrates. The binding energy of F1-P1 is predicted to be -16.6 kcal/mol at the B3LYP/6-311G(d,p) level, which is assumed to originate from one isolated O7...HN10 H-bond, one possible O10...HC71 unconventional O...HC type H-bonding, and the improved pi-bonding cooperativity around the peptide group of the AChE segment Tyr70-Val71. The classical Kitaura-Morokuma energy decomposition analysis, the NPA charge analysis, and the AIM analysis consistently reveal that the peptide group in segment P1 is more polarizable, which might play the key role in the interactions between F1 and P1. The PCM solvent effect corrected results reveal decrease of the interaction energy of the considered model. The importance of Thr8 of Fas2 in the P-site binding of AChE is also concluded. Site-directed mutations on either the Fas2 residue of Thr8 or the AChE residue of Tyr70 are expected to alter the binding behavior of the Loop1 of Fas2 with AChE.  相似文献   
39.
Castration-resistant progression of prostate cancer after androgen deprivation therapies remains the most critical challenge in the clinical management of prostate cancer. Resurgent androgen receptor (AR) activity is an established driver of castration-resistant progression, and upregulation of the full-length AR (AR-FL) and constitutively-active AR splice variants (AR-Vs) has been implicated to contribute to the resurgent AR activity. We reported previously that ginsenoside 20(S)-protopanaxadiol-aglycone (PPD) can reduce the abundance of both AR-FL and AR-Vs. In the present study, we further showed that the effect of PPD on AR expression and target genes was independent of androgen. PPD treatment resulted in a suppression of ligand-independent AR transactivation. Moreover, PPD delayed castration-resistant regrowth of LNCaP xenograft tumors after androgen deprivation and inhibited the growth of castration-resistant 22Rv1 xenograft tumors with endogenous expression of AR-FL and AR-Vs. This was accompanied by a decline in serum prostate-specific antigen levels as well as a decrease in AR levels and mitoses in the tumors. Notably, the 22Rv1 xenograft tumors were resistant to growth inhibition by the next-generation anti-androgen enzalutamide. The present study represents the first to show the preclinical efficacy of PPD in inhibiting castration-resistant progression and growth of prostate cancer. The findings provide a rationale for further developing PPD or its analogues for prostate cancer therapy.  相似文献   
40.
The expression level of a gene is often used as a proxy for determining whether the protein or RNA product is functional in a cell or tissue. Therefore, it is of fundamental importance to understand the global distribution of gene expression levels, and to be able to interpret it mechanistically and functionally. Here we use RNA sequencing (RNA‐seq) of mouse Th2 cells, coupled with a range of other techniques, to show that all genes can be separated, based on their expression abundance, into two distinct groups: one group comprised of lowly expressed and putatively non‐functional mRNAs, and the other of highly expressed mRNAs with active chromatin marks at their promoters. These observations are confirmed in many other microarray and RNA‐seq data sets of metazoan cell types.  相似文献   
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