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   1846篇
  免费   72篇
  2022年   5篇
  2021年   20篇
  2020年   13篇
  2019年   9篇
  2018年   17篇
  2017年   19篇
  2016年   24篇
  2015年   51篇
  2014年   61篇
  2013年   132篇
  2012年   86篇
  2011年   104篇
  2010年   66篇
  2009年   71篇
  2008年   102篇
  2007年   95篇
  2006年   97篇
  2005年   93篇
  2004年   90篇
  2003年   89篇
  2002年   90篇
  2001年   30篇
  2000年   48篇
  1999年   37篇
  1998年   19篇
  1997年   33篇
  1996年   21篇
  1995年   29篇
  1994年   24篇
  1993年   19篇
  1992年   20篇
  1991年   20篇
  1990年   29篇
  1989年   21篇
  1988年   30篇
  1987年   27篇
  1986年   19篇
  1985年   27篇
  1984年   14篇
  1983年   10篇
  1982年   12篇
  1981年   18篇
  1980年   12篇
  1979年   12篇
  1978年   13篇
  1977年   8篇
  1973年   5篇
  1972年   4篇
  1971年   4篇
  1969年   3篇
排序方式: 共有1918条查询结果,搜索用时 359 毫秒
81.
82.
The role of macrophage lipoprotein lipase (LpL) in the development of atherosclerosis and adiposity was examined in macrophage LpL knockout (MLpLKO) mice. MLpLKO mice were generated using cre-loxP gene targeting. Loss of LpL in macrophages did not alter plasma LpL activity or lipoprotein levels. Incubation of apolipoprotein E (ApoE)-deficient β-VLDL with peritoneal macrophages from ApoE knockout mice lacking macrophage LpL (MLpLKO/ApoEKO) led to less cholesteryl ester formation than that found with ApoEKO macrophages. MLpLKO/ApoEKO macrophages had reduced intracellular triglyceride levels, with decreased CD36 and carnitine palmitoyltransferase-1 mRNA levels compared with ApoEKO macrophages, when incubated with VLDL. Although both MLpLKO/ApoEKO and ApoEKO mice developed comparable hypercholesterolemia in response to feeding with a Western-type diet for 12 weeks, atherosclerosis was less in MLpLKO/ApoEKO mice. Epididymal fat mass and gene expression levels associated with inflammation did not differ between the two groups. In conclusion, macrophage LpL plays an important role in the development of atherosclerosis but not adiposity.  相似文献   
83.
Filaggrin protein is synthesized in the stratum granulosum of the skin and contributes to the formation of the human skin barrier. Profilaggrin is cleaved by proteolytic enzymes and converted to functional filaggrin, but its processing mechanism remains not fully elucidated. Kallikrein-related peptidase 5 (KLK5) is a major serine protease found in the skin, which is secreted from lamellar granules following its expression in the stratum granulosum and activated in the extracellular space of the stratum corneum. Here, we searched for profilaggrin-processing protease(s) by partial purification of epidermal extracts and found KLK5 as a possible candidate. We used high performance liquid chromatography coupled with electrospray tandem mass spectrometry to show that KLK5 cleaves profilaggrin. Furthermore, based on a proximity ligation assay, immunohistochemistry, and immunoelectron microscopy analysis, we reveal that KLK5 and profilaggrin co-localize in the stratum granulosum in human epidermis. KLK5 knockdown in normal cultured human epidermal keratinocytes resulted in higher levels of profilaggrin, indicating that KLK5 potentially functions in profilaggrin cleavage.  相似文献   
84.
We investigated the prevalence of Legionella species isolated from puddles on asphalt roads. In addition, we carried out sequence-based typing (SBT) analysis on the genetic relationship between L. pneumophila serogroup 1 (SG 1) isolates from puddles and from stock strains previously obtained from sputum specimens and public baths. Sixty-nine water samples were collected from puddles on roads at 6 fixed locations. Legionella species were detected in 33 samples (47.8%) regardless of season. Among the 325 isolates from puddles, strains of L. pneumophila SG 1, a major causative agent of Legionnaires'' disease, were the most frequently isolated (n = 62, 19.1%). Sixty-two isolates of L. pneumophila SG 1 from puddles were classified into 36 sequence types (STs) by SBT. ST120 and ST48 were identified as major STs. Environmental ST120 strains from puddles were found for the first time in this study. Among the 14 STs of the clinical isolates (n = 19), 4 STs (n = 6, 31.6%), including ST120, were also detected in isolates from puddles on roads, and the sources of infection in these cases remained unclear. The lag-1 gene, a tentative marker for clinical isolates, was prevalent in puddle isolates (61.3%). Our findings suggest that puddles on asphalt roads serve as potential reservoirs for L. pneumophila in the environment.  相似文献   
85.
86.
“Nagashima-type” palmoplantar keratosis (NPPK) is an autosomal recessive nonsyndromic diffuse palmoplantar keratosis characterized by well-demarcated diffuse hyperkeratosis with redness, expanding on to the dorsal surfaces of the palms and feet and the Achilles tendon area. Hyperkeratosis in NPPK is mild and nonprogressive, differentiating NPPK clinically from Mal de Meleda. We performed whole-exome and/or Sanger sequencing analyses of 13 unrelated NPPK individuals and identified biallelic putative loss-of-function mutations in SERPINB7, which encodes a cytoplasmic member of the serine protease inhibitor superfamily. We identified a major causative mutation of c.796C>T (p.Arg266) as a founder mutation in Japanese and Chinese populations. SERPINB7 was specifically present in the cytoplasm of the stratum granulosum and the stratum corneum (SC) of the epidermis. All of the identified mutants are predicted to cause premature termination upstream of the reactive site, which inhibits the proteases, suggesting a complete loss of the protease inhibitory activity of SERPINB7 in NPPK skin. On exposure of NPPK lesional skin to water, we observed a whitish spongy change in the SC, suggesting enhanced water permeation into the SC due to overactivation of proteases and a resultant loss of integrity of the SC structure. These findings provide an important framework for developing pathogenesis-based therapies for NPPK.  相似文献   
87.
We have previously shown that methionine–heme iron coordination is perturbed in domain-swapped dimeric horse cytochrome c. To gain insight into the effect of methionine dissociation in dimeric cytochrome c, we investigated its interaction with cyanide ion. We found that the Soret and Q bands of oxidized dimeric cytochrome c at 406.5 and 529 nm redshift to 413 and 536 nm, respectively, on addition of 1 mM cyanide ion. The binding constant of dimeric cytochrome c and cyanide ion was obtained as 2.5 × 104 M?1. The Fe–CN and C–N stretching (ν Fe–CN and ν CN) resonance Raman bands of CN?-bound dimeric cytochrome c were observed at 443 and 2,126 cm?1, respectively. The ν Fe–CN frequency of dimeric cytochrome c was relatively low compared with that of other CN?-bound heme proteins, and a relatively strong coupling between the Fe–C–N bending and porphyrin vibrations was observed in the 350–450-cm?1 region. The low ν Fe–CN frequency suggests weaker binding of the cyanide ion to dimeric cytochrome c compared with other heme proteins possessing a distal heme cavity. Although the secondary structure of dimeric cytochrome c did not change on addition of cyanide ion according to circular dichroism measurements, the dimer dissociation rate at 45 °C increased from (8.9 ± 0.7) × 10?6 to (3.8 ± 0.2) × 10?5 s?1, with a decrease of about 2 °C in its dissociation temperature obtained with differential scanning calorimetry. The results show that diatomic ligands may bind to the heme iron of dimeric cytochrome c and affect its stability.  相似文献   
88.
The esterification rates (ratio of the concentration of an acid in the neutral ethyl ester form to total concentration of the acid) of main organic acids in wines were determined to study the extent of ethyl ester formation of organic acids. The esterification rates ranged from zero to 24.6%. The averaged values of table wines were from 6 to 16% for acetic and lactic acid, from 0.3 to 3.6% for succinic and malic acid, and from zero to 0.1% for tartaric acid. Sherries had higher esterification rates, about 1.6 to 6 times larger, than table wines. It was found that storage time and temperature influence the formation of ethyl esters, and it was suggested that the aging period required for the ester equilibrium is about one year for acetic and lactic acid, and more than two years for succinic, malic and tartaric acid. The possibility and the procedure to control wine quality during the aging process were discussed.  相似文献   
89.
Experiments were done to investigate the volatile components in botrytized grape must and transformation of terpenoids in terpene-supplemented grape must by Botrytis cinerea. Twenty-eight compounds were identified in the volatile concentrate of botrytized must with a combined gas chromatograph-mass spectrometer. No terpenoids were detected in the concentrate. Linalool or terpinen-4-ol decreased a lot when Botrytis cinerea was cultured in the must with these terpenes for 15 days. In linalool-supplemented botrytized must 9 identified and 3 unidentified terpenes were found, while only geranial was detected in terpinen-4-ol-supplemented botrytized must. Botrytis cinerea did not produce terpenoid in grape must without terpenes, but transformed linalool added to grape must into some other monoterpenes.  相似文献   
90.
Several analogs of abscisic acid (ABA) were prepared and their biological activities were assayed. Among the compounds tested, 5-(l, 2-epoxy-2, 6, 6-trimethyl-l-cyclohexyl)-, 5-(l-hydroxy-2, 6, 6-trimethyl-2-cyclohexen-l-yl)- and 5-(l-hydroxy-2-methylene-6, 6-dimethyl-l-cyclohexyl)-3-methyl-cis, trans-2, 4-pentadienoic esters (V, IX, XXIII and XXV) were found to be potent plant growth inhibitors. Their activities were superior or comparable to that of ABA.  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