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   884篇
  免费   46篇
  国内免费   4篇
  2023年   1篇
  2022年   7篇
  2021年   7篇
  2020年   3篇
  2019年   10篇
  2018年   10篇
  2017年   17篇
  2016年   17篇
  2015年   18篇
  2014年   26篇
  2013年   60篇
  2012年   44篇
  2011年   74篇
  2010年   37篇
  2009年   36篇
  2008年   64篇
  2007年   66篇
  2006年   54篇
  2005年   64篇
  2004年   49篇
  2003年   53篇
  2002年   46篇
  2001年   6篇
  2000年   5篇
  1999年   8篇
  1998年   14篇
  1997年   14篇
  1996年   12篇
  1995年   11篇
  1994年   15篇
  1993年   10篇
  1992年   6篇
  1991年   3篇
  1990年   5篇
  1989年   8篇
  1988年   1篇
  1987年   4篇
  1986年   3篇
  1985年   3篇
  1984年   3篇
  1983年   12篇
  1982年   5篇
  1981年   6篇
  1980年   6篇
  1979年   5篇
  1978年   1篇
  1977年   1篇
  1975年   1篇
  1974年   2篇
  1971年   1篇
排序方式: 共有934条查询结果,搜索用时 15 毫秒
851.
Fifty-one human glycosyltransferases were expressed in Saccharomyces cerevisiae as immobilized enzymes and were assayed for enzymatic activities. The stem and catalytic regions of sialyl-, fucosyl-, galactosyl-, N-acetylgalactosaminyl-, and N-acetylglucosaminyltransferases were fused with yeast cell wall Pir proteins, which anchor glycosyltransferases at the yeast cell wall glucan. More than 75% of expressed recombinant glycosyltransferases retained their enzymatic activities in the yeast cell wall fraction and will be used as a human glycosyltransferase library. In increasing the enzymatic activities of immobilized glycosyltransferases, several approaches were found to be effective. Additional expression of yeast protein disulfide isomerase increased the expression levels and activities of polypeptide N-acetylgalactosaminyltransferases and other glycosyltransferases. PIR3 and/or PIR4 was more effective than PIR1 as a cell wall anchor when the Pir-glycosyltransferase fusions were expressed under the control of the constitutive glyceraldehyde-3-phosphate dehydrogenase promoter. Oligosaccharides such as Lewis x, Lewis y, and H antigen were successfully synthesized using this immobilized glycosyltransferase library, indicating that the Pir-fused glycosyltransferases are useful for the production of various human oligosaccharides.  相似文献   
852.
Erianthus arundinaceus, a warm-season perennial species in the Gramineae family, is currently being considered as a bioenergy crop candidate due to its capacity for high yields. Several experiments to explore this possibility have been conducted in Nasushiobara, Japan, where the mean minimum air temperature in January over the last three decades has been ??4.4 °C. Some accessions and breeding lines have demonstrated overwintering abilities, and annual dry matter yields of up to 52 t ha?1 were recorded in the 7th year after planting. Cutting to a 0.05-m height in February contributed more to subsequent regrowth and yield than did similar cutting in November. However, when performed in November, cutting to a 0.3-m height was more beneficial to subsequent regrowth and yield than cutting to a 0.05-m height. Allowing the foliage to run dry during winter led to a dry (approximately 70% dry matter ratio) biomass harvest in late winter. During winter, nutrient remobilization within the plants decreases nutrient removal from the soil. Although nitrogen fertilizer use efficiency was quite high (60%), only 20% of the nitrogen in an individual plant in the 2nd year after planting originated from fertilizer. This was likely due to a large amount of nitrogen obtained from non-fertilizer sources, i.e., soil and stored in the stubble from the previous harvest. Future experiments should focus on designing a fertilizer application program that could lead to sustainable and long-term high-yield E. arundinaceus biomass production in temperate zones.  相似文献   
853.
Dense granule protein 7 (NcGRA7) is a potent diagnostic antigen of Neospora caninum. Some studies have reported on the difficult expression, low yield, and variable degree of solubility of recombinant NcGRA7. We aimed to unravel the possible causes for these issues and tested NcGRA7 antigenicity in enzyme linked immunosorbent assays (ELISAs). The NcGRA7 coding sequence (217 amino acids) was split into five amino acid regions: NcGRA7m (27–217), NcGRA7m3 (27–160), NcGRA7m4 (27–135), NcGRA7m5 (161–190), and NcGRA7m6 (188–217). Three fragments, NcGRA7m, NcGRA7m3 and NcGRA7m4, exhibited high antigenic properties when tested against experimentally-infected mice and dog sera by ELISA. High levels of IgG2 antibodies against NcGRA7m3 were observed in field dog sera. In experimentally and naturally-infected cattle, the N. caninum-specific sera only reacted with NcGRA7m, indicating that this antigenic region differs among the three animal species. This study presents valuable information about the antigenic properties and topology of NcGRA7, and highlights its suitability for diagnostic purposes.  相似文献   
854.
855.
The molecular mechanisms of prion-induced cytotoxicity remain largely obscure. Currently, only a few cell culture models have exhibited the cytopathic changes associated with prion infection. In this study, we introduced a cell culture model based on differentiated neurosphere cultures isolated from the brains of neonatal prion protein (PrP)-null mice and transgenic mice expressing murine PrP (dNP0 and dNP20 cultures). Upon exposure to mouse Chandler prions, dNP20 cultures supported the de novo formation of abnormal PrP and the resulting infectivity, as assessed by bioassays. Furthermore, this culture was susceptible to various prion strains, including mouse-adapted scrapie, bovine spongiform encephalopathy, and Gerstmann-Sträussler-Scheinker syndrome prions. Importantly, a subset of the cells in the infected culture that was mainly composed of astrocyte lineage cells consistently displayed late-occurring, progressive signs of cytotoxicity as evidenced by morphological alterations, decreased cell viability, and increased lactate dehydrogenase release. These signs of cytotoxicity were not observed in infected dNP0 cultures, suggesting the requirement of endogenous PrP expression for prion-induced cytotoxicity. Degenerated cells positive for glial fibrillary acidic protein accumulated abnormal PrP and exhibited features of apoptotic death as assessed by active caspase-3 and terminal deoxynucleotidyltransferase nick-end staining. Furthermore, caspase inhibition provided partial protection from prion-mediated cell death. These results suggest that differentiated neurosphere cultures can provide an in vitro bioassay for mouse prions and permit the study of the molecular basis for prion-induced cytotoxicity at the cellular level.  相似文献   
856.
In the M/V “Louisa” case of 28 May 2013, the International Tribunal for the Law of the Sea held that it had no jurisdiction, even though it had established prima facie jurisdiction at the provisional measures stage. The M/V “Louisa” case thus gives rise to questions regarding the relationship between prima facie jurisdiction and jurisdiction on the merits. Moreover, the M/V “Louisa” Judgment also sheds some light on the applicability of the doctrine of abuse of rights provided in Article 300 of the UN Convention on the Law of the Sea.  相似文献   
857.
Abstract

Reaction of 2′,5′-dichloro-2′,5′-dideoxyuridine (1) with ammonia and benzylamine afforded the corresponding 2-N-substituted 1-(5-chloro-5-deoxy-β-D-arabinofuranosyl)-isocytosine derivatives (2 and 10). Reaction of 1 with ammonia, methylamine, cyclohexylamine, and benzylamine followed by treatment with methanolic sodium methoxide gave the corresponding 2-N-substituted 1-(2,5-anhydro-β-D-arabino-furanosyl)isocytosine derivatives (6, 11, and 12).  相似文献   
858.

Background

No studies have evaluated whether administering intravenous lactated Ringer''s (LR) solution to patients with out-of-hospital cardiac arrest (OHCA) improves their outcomes, to our knowledge. Therefore, we examined the association between prehospital use of LR solution and patients'' return of spontaneous circulation (ROSC), 1-month survival, and neurological or physical outcomes at 1 month after the event.

Methods and Findings

We conducted a prospective, non-randomized, observational study using national data of all patients with OHCA from 2005 through 2009 in Japan. We performed a propensity analysis and examined the association between prehospital use of LR solution and short- and long-term survival. The study patients were ≥18 years of age, had an OHCA before arrival of EMS personnel, were treated by EMS personnel, and were then transported to hospitals. A total of 531,854 patients with OHCA met the inclusion criteria. Among propensity-matched patients, compared with those who did not receive pre-hospital intravenous fluids, prehospital use of LR solution was associated with an increased likelihood of ROSC before hospital arrival (odds ratio [OR] adjusted for all covariates [95% CI] = 1.239 [1.146–1.339] [p<0.001], but with a reduced likelihood of 1-month survival with minimal neurological or physical impairment (cerebral performance category 1 or 2, OR adjusted for all covariates [95% CI] = 0.764 [0.589–0.992] [p = 0.04]; and overall performance category 1 or 2, OR adjusted for all covariates [95% CI] = 0.746 [0.573–0.971] [p = 0.03]). There was no association between prehospital use of LR solution and 1-month survival (OR adjusted for all covariates [95% CI] = 0.960 [0.854–1.078]).

Conclusion

In Japanese patients experiencing OHCA, the prehospital use of LR solution was independently associated with a decreased likelihood of a good functional outcome 1 month after the event, but with an increased likelihood of ROSC before hospital arrival. Prehospital use of LR solution was not associated with 1-month survival. Further study is necessary to verify these findings. Please see later in the article for the Editors'' Summary  相似文献   
859.
Limited information is available about conformational differences between the abnormal isoform of prion protein (PrPSc) and cellular prion protein (PrPC) under native conditions. To clarify conformational differences between these two isoforms, PrP‐deficient mice were immunized with brain homogenates of normal and scrapie‐infected animals. All mice generated anti‐PrP antibodies. Peptide array analysis of these serum samples revealed a distinctive epitope of PrPSc consisting of QGSPGGN (PrP41–47) at the N‐terminus. This study demonstrated a conformational dissimilarity at the N‐terminus between PrPSc and PrPC, a finding that may provide novel information about conformational features of PrPSc.  相似文献   
860.
Equimolar aqueous solutions of d-glucose and n-butylamine were heated at 95°C for various times at pH 4, 6.5 and 11.48. The resulting brown solutions were extracted with ether. The volatile components in the ether extracts were analyzed by gas chromatography and gas chromatography-mass spectrometry, with a fused silica capillary column. The major components formed were identified as three alcohols, four N-butylpyrroles, N-butylacetamide, N-butylformamide, N-butylsuccinimide, one pyranone and 5-(hydroxymethyl)-2-furfural. In addition, eleven minor components were also identified. The relative amount of each component changed markedly with pH. At pH 4.0, higher-boiling heterocyclic compounds without C-C fission of glucose were largely formed, and at pH 11.48, lower-boiling fission compounds were mainly formed. Both were observed in the reaction at pH 6.5.  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