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   1784篇
  免费   91篇
  国内免费   5篇
  2022年   6篇
  2021年   24篇
  2020年   4篇
  2019年   13篇
  2018年   14篇
  2017年   16篇
  2016年   33篇
  2015年   39篇
  2014年   47篇
  2013年   168篇
  2012年   111篇
  2011年   121篇
  2010年   71篇
  2009年   78篇
  2008年   114篇
  2007年   109篇
  2006年   113篇
  2005年   123篇
  2004年   111篇
  2003年   98篇
  2002年   90篇
  2001年   12篇
  2000年   13篇
  1999年   21篇
  1998年   16篇
  1997年   25篇
  1996年   15篇
  1995年   23篇
  1994年   20篇
  1993年   14篇
  1992年   16篇
  1991年   14篇
  1990年   11篇
  1989年   5篇
  1988年   6篇
  1987年   11篇
  1986年   10篇
  1985年   9篇
  1984年   10篇
  1983年   10篇
  1982年   20篇
  1981年   16篇
  1980年   12篇
  1979年   7篇
  1978年   10篇
  1976年   8篇
  1975年   8篇
  1974年   8篇
  1973年   5篇
  1972年   7篇
排序方式: 共有1880条查询结果,搜索用时 31 毫秒
141.
After the discovery of interleukin-2 (IL-2), lymphokine-activated killer (LAK) cells, tumor-infiltrating lymphocytes (TILs), and cytotoxic T lymphocytes (CTLs) sensitized with the mixed lymphocyte-tumor culture (MLTC) system have been conducted in adoptive immunotherapy (AIT) trials during past 15 years. Although the overall response rate of tumor shrinkage was marginal (9%), locoregional administration of TILs for malignant effusions was effective (77%) for a decrease or disappearance of the effusions even in terminally-ill patients, resulting in an improvement of QOL. Recent advances for molecular understanding of antigen presentation and recognition have promoted us to enhance the efficacy of AIT by using cultured dendritic cells (DCs) for generating antigen-specific CTLs in vitro. The peptide-pulsed DC-activated killer (PDAK) cells showed tumor recognition against antigen-expressing cells, and were efficiently propagated with the IL2 plus immobilized anti-CD3 antibody (IL-2/CD3) culture system. Clinical trials using PDAK cells against patients with lung metastases are now progressed, in which peptides suitable for generating CTLs were chosen in individual patients using the method designated as host-oriented peptide evaluation (HPOE) approach. Moreover, DCs were introduced with tumor-derived RNA, which was amplified with the T7 promoter system, and then were used for stimulating lymphocytes. The tumor RNA-introduced DC-activated killer (TRiDAK) cells showed tumor-specific interferon-gamma spots even in a patient in whom we failed to generate PDAK cells using DCs and peptides, suggesting that the clinical trial of AIT using TRiDAK cells is warranted for the treatment of patients with metastatic cancer. Thus, more understanding of antigen-presentation and -recognition mechanisms and immune regulation systems may promote clinical applications of AIT to establish a novel modality of cancer treatment.  相似文献   
142.
Fatty acid chain elongation is a crucial step in the biosynthesis of long chain fatty acids. An essential reaction in the elongation process is condensation of malonyl-CoA with acyl-CoA, which is catalyzed by beta-ketoacyl-CoA synthase (KCS) in plants. We have isolated and characterized the MpFAE3 gene, one of the KCS gene family in the liverwort Marchantia polymorpha. Transgenic M. polymorpha plants overexpressing MpFAE3 accumulate fatty acids 18:0, 20:0, and 22:0. In these plants, the amount of 16:0 is reduced to 50% of wild type. In a heterologous assay, transgenic methylotrophic yeast expressing the MpFAE3 gene accumulates fatty acid 18:0 and generates several longer fatty acids which are not detectable in the control, accompanied by a decrease of 16:0. These observations indicate that the MpFAE3 protein is preferentially involved in the elongation of 16:0 to 18:0 and also in the subsequent steps of 18:0 to 20:0 and 20:0 to 22:0 in M. polymorpha.  相似文献   
143.
We demonstrated that Mortierella alpina 1S-4 has two delta 6-desaturases, which are involved in the desaturation of linoleic acid to gamma-linolenic acid. For one of the two delta 6-desaturases, designated as delta 6I, gene cloning and its heterologous expression in a fungus, Aspergillus oryzae, has previously been reported. In addition, we indicated in this paper that there is an isozyme of the two delta 6-desaturases, designated as delta 6II, in M. alpina 1S-4. The predicted amino acid sequences of the Mortierella delta 6-desaturases were similar to those of ones from other organisms, i.e. borage and Caenorhabditis elegans, and had a cytochrome b5-like domain at the N-terminus, being different from the yeast delta 9-desaturase, which has the corresponding domain at the C-terminus. The full-length delta 6II cDNA was expressed in A. oryzae, resulting in the accumulation of gamma-linolenic acid (which was not detected in the control Aspergillus) up to 37% of the total fatty acids. The analysis of real-time quantitative PCR (RTQ-PCR) showed that the quantity of delta 6I RNA was 2.4-, 9-, and 17-fold higher than that of delta 6II RNA on 2, 3, and 4 days in M. alpina 1S-4, respectively. M. alpina 1S-4 is the first fungus to be confirmed to have two functional delta 6-desaturase genes.  相似文献   
144.
145.
We have identified a new Arabidopsis mutant, yore-yore (yre), which has small trichomes and glossy stems. Adhesion between epidermal cells was observed in the organs of the yre shoot. The cloned YRE had high homology to plant genes involved in epicuticular wax synthesis, such as ECERIFERUM1 (CER1) and maize GLOSSY1. The phenotype of transgenic plants harboring double-stranded RNA interference (dsRNAi) YRE was quite similar to that of the yre mutant. The amount of epicuticular wax extracted from leaves and stems of yre-1 was approximately one-sixth of that from the wild type. YRE promoter::GUS and in situ hybridization revealed that YRE was specifically expressed in cells of the L1 layer of the shoot apical meristem and young leaves, stems, siliques, and lateral root primordia. Strong expression was detected in developing trichomes. The trichome structure of cer1 was normal, whereas that of the yre cer1 double mutant was heavily deformed, indicating that epicuticular wax is required for normal growth of trichomes. Double mutants of yre and trichome-morphology mutants, glabra2 (gl2) and transparent testa glabra1 (ttg1), showed that the phenotype of the trichome structure was additive, suggesting that the wax-requiring pathway is distinct from the trichome development pathway controlled by GL2 and TTG1.  相似文献   
146.
147.
Sphingomonas paucimobilis SYK-6 transforms 2,2′-dihydroxy-3,3′-dimethoxy-5,5′-dicarboxybiphenyl (DDVA), a lignin-related biphenyl compound, to 5-carboxyvanillic acid via 2,2′,3-trihydroxy-3′-methoxy-5,5′-dicarboxybiphenyl (OH-DDVA) as an intermediate (15). The ring fission of OH-DDVA is an essential step in the DDVA degradative pathway. A 15-kb EcoRI fragment isolated from the cosmid library complemented the growth deficiency of a mutant on OH-DDVA. Subcloning and deletion analysis showed that a 1.4-kb DNA fragment included the gene responsible for the ring fission of OH-DDVA. An open reading frame encoding 334 amino acids was identified and designated ligZ. The deduced amino acid sequence of LigZ had 18 to 21% identity with the class III extradiol dioxygenase family, including the β subunit (LigB) of protocatechuate 4,5-dioxygenase of SYK-6 (Y. Noda, S. Nishikawa, K.-I. Shiozuka, H. Kadokura, H. Nakajima, K. Yano, Y. Katayama, N. Morohoshi, T. Haraguchi, and M. Yamasaki, J. Bacteriol. 172:2704–2709, 1990), catechol 2,3-dioxygenase I (MpcI) of Alcaligenes eutrophus JMP222 (M. Kabisch and P. Fortnagel, Nucleic Acids Res. 18:3405–3406, 1990), the catalytic subunit of the meta-cleavage enzyme (CarBb) for 2′-aminobiphenyl-2,3-diol from Pseudomonas sp. strain CA10 (S. I. Sato, N. Ouchiyama, T. Kimura, H. Nojiri, H. Yamane, and T. Omori, J. Bacteriol. 179:4841–4849, 1997), and 2,3-dihydroxyphenylpropionate 1,2-dioxygenase (MhpB) of Escherichia coli (E. L. Spence, M. Kawamukai, J. Sanvoisin, H. Braven, and T. D. H. Bugg, J. Bacteriol. 178:5249–5256, 1996). The ring fission product formed from OH-DDVA by LigZ developed a yellow color with an absorption maximum at 455 nm, suggesting meta cleavage. Thus, LigZ was concluded to be a ring cleavage extradiol dioxygenase. LigZ activity was detected only for OH-DDVA and 2,2′,3,3′-tetrahydroxy-5,5′-dicarboxybiphenyl and was dependent on the ferrous ion.Lignin is the most common aromatic compound in the biosphere, and the degradation of lignin is a significant step in the global carbon cycle. Lignin is composed of various intermolecular linkages between phenylpropanes and guaiacyl, syringyl, p-hydroxyphenyl, and biphenyl nuclei (5, 34). Lignin breakdown therefore involves multiple biochemical reactions involving the cleavage of intermonomeric linkages, demethylations, hydroxylations, side-chain modifications, and aromatic ring fission (10, 11, 19, 40).Soil bacteria are known to display ample metabolic versatility toward aromatic substrates. Sphingomonas paucimobilis SYK-6 (formerly Pseudomonas paucimobilis SYK-6) has been isolated with 2,2′-dihydroxy-3,3′-dimethoxy-5,5′-dicarboxybiphenyl (DDVA) as a sole carbon and energy source. This strain can also grow on syringate, 3-O-methylgallic acid (3OMGA), vanillate, and other dimeric lignin compounds, including β-aryl ether, diarylpropane (β-1), and phenylcoumaran (15). Analysis of the metabolic pathway has indicated that the dimeric lignin compounds are degraded to protocatechuate or 3OMGA (15) and that these compounds are cleaved by protocatechuate 4,5-dioxygenase encoded by ligAB (30). Among the dimeric lignin compounds, the degradation of β-aryl ether and the biphenyl structure is the most important, because β-aryl ether is most abundant in lignin (50%) and the biphenyl structure is so stable that its decomposition should be rate limiting in lignin degradation. We have already characterized the β-etherase and Cα-dehydrogenase genes (2326) (ligFE and ligD, respectively) involved in the degradation of β-aryl ether. In this study, we focused on the genes responsible for the degradation of DDVA in SYK-6.In the proposed DDVA metabolic pathway of S. paucimobilis SYK-6 illustrated in Fig. Fig.1A,1A, DDVA is first demethylated to produce the diol compound 2,2′,3-trihydroxy-3′-methoxy-5,5′-dicarboxybiphenyl (OH-DDVA). OH-DDVA is then degraded to 5-carboxyvanillic acid (5-CVA), and this compound is converted to 3OMGA (15). The resulting product is cleaved by protocatechuate 4,5-dioxygenase. A ring cleavage enzyme for OH-DDVA has been thought to be involved in this pathway because the production of 5-CVA from OH-DDVA resembles the formation of benzoic acid from biphenyl by 2,3-dihydroxybiphenyl through the sequential action of a meta cleavage enzyme and a meta-cleavage compound hydrolase (Fig. (Fig.1B)1B) (1, 9, 13, 18, 21, 28). Open in a separate windowFIG. 1(A) Proposed metabolic pathway for DDVA by S. paucimobilis SYK-6. (B) Pathway for the conversion of 2,3-dihydroxybiphenyl (2,3-DHBP) to benzoate by the polychlorinated biphenyl-degrading bacteria. The proposed DDVA metabolic pathway follows the previous one (15). Enzymes: LigZ, OH-DDVA oxygenase; LigAB, protocatechuate 4,5-dioxygenase; BphC, 2,3-dihydroxybiphenyl 1,2-dioxygenase; BphD, 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoic acid hydrolase. TCA, tricarboxylic acid.In this study, we isolated the ligZ gene encoding a ring cleavage enzyme for OH-DDVA. The nucleotide sequence of the gene was determined, and the ligZ gene product was characterized.  相似文献   
148.
We tested whether the cultural background of raters influenced ratings of chimpanzee personality. Our study involved comparing personality and subjective well‐being ratings of 146 chimpanzees in Japan that were housed in zoos, research institutes, and a retirement sanctuary to ratings of chimpanzees in US and Australian zoos. Personality ratings were made on a translated and expanded version of a questionnaire used to rate chimpanzees in the US and Australia. Subjective well‐being ratings were made on a translated version of a questionnaire used to rate chimpanzees in the US and Australia. The mean interrater reliabilities of the 43 original adjectives did not markedly differ between the present sample and the original sample of 100 zoo chimpanzees in the US. Interrater reliabilities of these samples were highly correlated, suggesting that their rank order was preserved. Comparison of the factor structures for the Japanese sample and for the original sample of chimpanzees in US zoos indicated that the overall structure was replicated and that the Dominance, Extraversion, Conscientiousness, and Agreeableness domains clearly generalized. Consistent with earlier studies, older chimpanzees had higher Dominance and lower Extraversion and Openness scores. Correlations between the six domain scores and subjective well‐being were comparable to those for chimpanzees housed in the US and Australia. These findings suggest that chimpanzee personality ratings are not affected by the culture of the raters. Am. J. Primatol. 71:283–292, 2009. © 2009 Wiley‐Liss, Inc.  相似文献   
149.

Background

The number of elderly patients with maxillofacial trauma is rapidly increasing due to active lifestyles and longevity. Shimane prefecture has the fastest growing proportion of elderly individuals in Japan. The aim of this study was to reveal the distinctive features and treatment modes of mandibular fracture treatment mode in patients requiring hospitalization at the Department of Oral and Maxillofacial Surgery, Shimane University Hospital, Japan.

Patients and Methods

Patient age, sex, period between injury and first consultation, years since injury, cause of injury, fracture site, treatment, and duration of hospitalization were evaluated. Univariate Poisson regression, relative risk with 95% confidence interval based on the Wald test, Fisher’s exact test, and Kruskal-Wallis test were used to explore associations among clinical and demographic variables.

Results

In total, 305 patients were diagnosed with and hospitalized for mandibular fracture from 1980 to 2010. Younger age increased the risk for mandibular fracture. Incidence was higher in males than females, particularly in the young, but the male to female ratio decreased with age. The period until first hospital consultation decreased progressively over the study period. Fall was a much more frequent cause in patients aged ≥60 than in those aged <60 years. Mandibular fracture with condyle, symphysis, and angle involvement were most common and were associated with sex, age, and treatment mode. Length of hospitalization has decreased since 1980.

Conclusion

In our department, patients aged ≥60 years accounted for a greater proportion of mandibular fracture cases than in many previous studies, reflecting the greater proportion of elderly residents in Shimane prefecture.  相似文献   
150.
TAE226, a bis-anilino pyrimidine compound, has been developed as an inhibitor of focal adhesion kinase (FAK) and insulin-like growth factor-I receptor (IGF-IR). In this study, we investigated the effect of TAE226 on non-small-cell lung cancer (NSCLC), especially focusing on the EGFR mutational status. TAE226 was more effective against cells with mutant EGFR, including the T790M mutant, than against cells with wild-type one. TAE226 preferentially inhibited phospho-EGFR and its downstream signaling mediators in the cells with mutant EGFR than in those with wild-type one. Phosphorylation of FAK and IGF-IR was not inhibited at the concentration at which the proliferation of EGFR-mutant cells was inhibited. Results of the in vitro binding assay indicated significant differences in the affinity for TAE226 between the wild-type and L858R (or delE746_A750) mutant, and the reduced affinity of ATP to the L858R (or delE746_A750) mutant resulted in good responsiveness of the L858R (or delE746_A750) mutant cells to TAE226. Of interest, the L858R/T790M or delE746_A750/T790M mutant enhanced the binding affinity for TAE226 compared with the L858R or delE746_A750 mutant, resulting in the effectiveness of TAE226 against T790M mutant cells despite the T790M mutation restoring the ATP affinity for the mutant EGFR close to that for the wild-type. TAE226 also showed higher affinity of about 15-fold for the L858R/T790M mutant than for the wild-type one by kinetic interaction analysis. The anti-tumor effect against EGFR-mutant tumors including T790M mutation was confirmed in mouse models without any significant toxicity. In summary, we showed that TAE226 inhibited the activation of mutant EGFR and exhibited anti-proliferative activity against NSCLCs carrying EGFR mutations, including T790M mutation.  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