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   723篇
  免费   33篇
  756篇
  2023年   2篇
  2022年   8篇
  2021年   11篇
  2020年   9篇
  2019年   13篇
  2018年   17篇
  2017年   6篇
  2016年   25篇
  2015年   19篇
  2014年   26篇
  2013年   48篇
  2012年   55篇
  2011年   46篇
  2010年   21篇
  2009年   23篇
  2008年   41篇
  2007年   42篇
  2006年   36篇
  2005年   28篇
  2004年   31篇
  2003年   47篇
  2002年   31篇
  2001年   13篇
  2000年   6篇
  1999年   13篇
  1998年   11篇
  1997年   6篇
  1996年   12篇
  1995年   10篇
  1994年   2篇
  1993年   5篇
  1992年   9篇
  1991年   8篇
  1990年   9篇
  1989年   5篇
  1988年   5篇
  1987年   8篇
  1986年   6篇
  1985年   3篇
  1983年   4篇
  1982年   3篇
  1980年   6篇
  1979年   2篇
  1976年   2篇
  1974年   2篇
  1973年   4篇
  1972年   3篇
  1965年   4篇
  1931年   1篇
  1905年   1篇
排序方式: 共有756条查询结果,搜索用时 0 毫秒
151.
Summary The cell subpopulations in the haemolymph ofPlanorbarius corneus were distinguished by means of flow cytometry. An antibody againstn-acetylmuramic acid was prepared and used as a cellular marker to recognize the cell types forming the subpopulations. The spreading haemocytes showed a positive reaction for anti-n-acetylmuramic acid; round haemocytes gave a negative reaction.  相似文献   
152.
Folate metabolism, also known as one-carbon metabolism, is required for several cellular processes including DNA synthesis, repair and methylation. Impairments of this pathway have been often linked to Alzheimer’s disease (AD). In addition, increasing evidence from large scale case-control studies, genome-wide association studies, and meta-analyses of the literature suggest that polymorphisms of genes involved in one-carbon metabolism influence the levels of folate, homocysteine and vitamin B12, and might be among AD risk factors. We analyzed a dataset of 30 genetic and biochemical variables (folate, homocysteine, vitamin B12, and 27 genotypes generated by nine common biallelic polymorphisms of genes involved in folate metabolism) obtained from 40 late-onset AD patients and 40 matched controls to assess the predictive capacity of Artificial Neural Networks (ANNs) in distinguish consistently these two different conditions and to identify the variables expressing the maximal amount of relevant information to the condition of being affected by dementia of Alzheimer’s type. Moreover, we constructed a semantic connectivity map to offer some insight regarding the complex biological connections among the studied variables and the two conditions (being AD or control). TWIST system, an evolutionary algorithm able to remove redundant and noisy information from complex data sets, selected 16 variables that allowed specialized ANNs to discriminate between AD and control subjects with over 90% accuracy. The semantic connectivity map provided important information on the complex biological connections among one-carbon metabolic variables highlighting those most closely linked to the AD condition.  相似文献   
153.
A 5-HT1A pharmacophore has been obtained employing a set of rigid templates encompassing the 5-HT1A structure. The use of rigid templates allowed us to overcome the discrepancy found when flexible structures where the energy of the active conformers are sometimes higher than the global minimum energy are used. On the basis of the results herein reported the three-dimensional requirements necessary for the binding interaction have been defined within this set of molecules. In this study forbidden zones of the receptor have been characterised. The pharmacophore model derived places some agonist/antagonist pharmacophore models appeared in the literature.  相似文献   
154.
155.
Agrobacterium rhizogenes transformed and control roots of the tetraploid potato cv. Bintje were compared. Transformed roots were obtained after infection by A. rhizogenes 15834 or 1855. Both in leaf and stem segments, more roots were formed at the basal side of the segments, indicative for a polarity in root formation. As compared to control roots the transformed roots are characterized by smaller and more densely stained cells, a zone of cell division, and smaller statoliths. These characteristics are correlated with vigorous growth, high branching incidence and diminished geotropism. The plant regeneration procedure according to Ooms et al. [1] was modified. The transformed roots required less 2,4-D than control roots for the induction of shoot-competent calli. The callus and shoot induction phases were reduced from 8 and 6 weeks to 3 and 3 weeks, respectively. Upon induction, 25%, 58% and 61% of the root clones originating from tuber, stem and leaf, respectively, produced shoots, whereas all of the control roots produced shoots. Shoot outgrowth occurred on liquid MS medium in the absence of hormones.Abbreviations Ri-root Agrobacterium rhizogenes transformed root - BAP benzylaminopurine - IAA indoleacetic acid - GA3 gibberellic acid - NAA naphthaleneacetic acid - 2,4-D 2,4 dichlorophenoxyacetic acid  相似文献   
156.
The intestinal cell types of the pulmonate gastropodPlanorbarius corneus were studied using histochemical, immunocytochemical and ultrastructural procedures. Supporting cells, mucous cells and gland cells were observed in the intestine epithelium. The supporting cells seem to be involved in absorption process, showing endocytosis vesicles, evidence of lysosomal activity and storage of reserve materials. The presence of epithelial cells specialized in secretion indicates that digestive enzymes may be produced. Indeed, immunoreactive alpha-amylase molecules have been demonstrated. Some gland cells showed the ultrastructural features of invertebrate and vertebrate enteroendocrine cells and were also positive to vertebrate anti-insulin, anti-gastrin and anti-serotonin antibodies.  相似文献   
157.
158.
Li  Cui  Wang  Peng  Lombi  Enzo  Wu  Jingtao  Blamey  F. Pax C.  Fernández  Victoria  Howard  Daryl L.  Menzies  Neal W.  Kopittke  Peter M. 《Plant and Soil》2018,425(1-2):309-319
Plant and Soil - Arabidopsis thaliana is the model plant that is mainly used in studying cellulose and hemicellulose (CH) biosynthesis. Unfortunately, A. thaliana does not associate with mycorrhiza...  相似文献   
159.
The antitumor and antimetastatic activity of dacarbazine (DTIC) alone or in combination with cyclophosphamide (CY) was tested in C57BL/6 mice bearing Lewis lung carcinoma (3LL). Treatment with both agents significantly reduced tumor growth and the number of metastases. These effects were associated with marked changes of the biochemical and immunological properties of drug-treated 3LL cells, i.e. (a) reduction of 6 integrin expression, (b) increased susceptibility to natural immunity in vivo, as measured in terms of rapid clearance from mouse lungs of prelabeled 3LL cells injected i.v. and (c) increased immunogenicity, as assessed by T-cell-mediated immune responses (i.e. graft rejection by intact syngeneic mice, and frequency of specific CTL precursors recognizing DTIC/CY-treated cancer cells). The immunotherapeutic advantage afforded by increased immunosensitivity and immunogenicity of 3LL cells exposed to DTIC+CY appears to be markedly reduced in vivo by the profound immunodepressive effects of these drugs. Within this context, addition of interleukin-2 was found to increase the antitumor and antimetastatic activity of this chemotherapeutic regimen. The present study shows, for the first time in a solid tumor model, that a biological response modifier increases the antitumor efficacy of drugs that are able to affect the immunological properties of cancer cells.  相似文献   
160.
The efficiency of HIV-1 specific transfer factor (TF) administration, combined with Zidovudine (ZDV), in asymptomatic persistent generalised lymphadenopaty, or AIDS related complex (ARC) patients was evaluated. Twenty patients were randomly assigned to receive only ZDV (1st group) or ZDV together with HIV-1-specific TF (2nd group). HIV-1-specific TF was administered orally at 2 × 107 cell equivalent daily for 15 days, and thereafter once a week for up to 6 months. There were no significant differences between the two groups in clinical evolution, red blood cells, haemoglobin, lymphocytes, CD20 subset, transaminases,β-2-microglobulin, p24 antigen. White blood cells, CD8 lymphocytes as well as IL-2 levels increased in the second group, while the CD4 subset increased in the first group. The combination treatment with ZDV and TF appeared to be safe and well tolerated. Furthermore, levels of serum cytokines were investigated in 10 patients (8 asymptomatic and 2 ARC) treated with ZDV, and compared with 5 patients of the 2nd group (3 asymptomatic and 2 ARC) treated with ZDV plus HIV-1-specific TF. Peripheral lymphocytes, CD4, CD8 subsets, IL-2, TNFα, IL-6, p24 antigen, IL-2 soluble lymphocyte receptors (sR), CD4sR, CD8sR and ß-2-microglobulin were evaluated at the baseline and at the 3rd month. The CD4 subset was not significantly different in the two groups, whilst IL-2 increased in the 2nd group receiving ZDV plus TF, suggesting an activation of the Th1 secretion pattern.  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