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   688篇
  免费   68篇
  2022年   9篇
  2021年   8篇
  2020年   4篇
  2019年   10篇
  2018年   17篇
  2017年   16篇
  2016年   17篇
  2015年   25篇
  2014年   36篇
  2013年   45篇
  2012年   41篇
  2011年   49篇
  2010年   34篇
  2009年   20篇
  2008年   43篇
  2007年   28篇
  2006年   31篇
  2005年   25篇
  2004年   21篇
  2003年   23篇
  2002年   22篇
  2001年   21篇
  2000年   20篇
  1999年   16篇
  1998年   12篇
  1997年   10篇
  1996年   9篇
  1995年   6篇
  1994年   5篇
  1993年   4篇
  1992年   10篇
  1991年   6篇
  1990年   9篇
  1989年   10篇
  1987年   3篇
  1986年   11篇
  1984年   10篇
  1983年   4篇
  1982年   3篇
  1981年   3篇
  1978年   4篇
  1976年   3篇
  1974年   4篇
  1973年   4篇
  1972年   3篇
  1971年   3篇
  1969年   3篇
  1968年   4篇
  1939年   6篇
  1938年   11篇
排序方式: 共有756条查询结果,搜索用时 15 毫秒
101.
In the broader context of research on the Sicilian Porcellio imbutus-complex, the postmarsupial development of Porcellio siculoccidentalis Viglianisi, Lombardo & Caruso, 1992 was studied in detail. This research was conducted in the laboratory under controlled conditions, allowing us to follow the stages of development, from the formation of the marsupium in ovigerous females until the larval stages and development of the seventh pair of legs. The timing of developmental stages and the morphological modifications of appendages in the postmarsupial manca stages (M I-M III) are described. The manca stage M I had a duration of about one hour. Ovigerous females were collected and reared separately, and the number of parturial molts in the absence of males was counted. The results showed a maximum of four successive parturial molts. Fecundity and fertility were evaluated as the number of eggs and embryos, respectively, inside the marsupium of the ovigerous females. Both parameters were positively correlated with the size of the females. The maximum numbers of eggs and embryos in the marsupium were 113 and 141, respectively. Data describing the total number of postmarsupial mancas released per month indicated that the highest release occurred in April.  相似文献   
102.
Quantitative ultrasound (US) elastography (Q-USE), able to evaluate tissue stiffness has been indicated as a new diagnostic tool to differentiate benign from malignant thyroid lesions. Aim of this prospective study, conducted at the Department of Surgical Sciences, of the “Sapienza” University of Rome, was to evaluate the diagnostic accuracy of Q-USE, compared with US parameters, in thyroid nodules with indeterminate cytology (Thy3).The case study included 140 nodules from 140 consecutive patients. Patient’s thyroid nodules were evaluated by Q-USE, measuring the strain ratio (SR) of stiffness between nodular and surrounding normal thyroid tissue, and conventional US parameters prior fine-needle aspiration cytology. Those with Thy3 diagnosis were included in the study. Forty of the nodules analyzed harbored a malignant lesion. Q-USE demonstrated that malignant nodules have a significant higher stiffness with respect to benign one and an optimun SR cut-off value of 2.05 was individuated following ROC analysis. Univariate analysis showed that hypoechogenicity, irregular margins and SR >2.05 associated with malignancy, with an accuracy of 67.2%, 81,0% and 89.8%, respectively. Data were unaffected by nodule size or thyroiditis. These findings were confirmed in multivariate analysis demonstrating a significant association of the SR and the irregular margins with thyroid nodule’s malignancy. In conclusion, we demonstrated the diagnostic utility of Q-USE in the differential diagnosis of thyroid nodules with indeterminate cytology that, if confirmed, could be of major clinical utility in patients’ presurgical selection.  相似文献   
103.
Isopropanol (IPA) is widely used in household applications and constitutes a leading cause of acute alcohol intoxication second only to ethanol. Although the effects of ethanol on the immune system have been extensively studied, far fewer data are available on IPA. Given the structural similarity between the two molecules, we hypothesized that IPA could as well have immunomodulatory properties. We report here that acute IPA exposure is detrimental to human T lymphocyte and NK cell activity in vitro in concentrations as low as 0.08-0.16% (13-26 mM). IPA treatment did not affect receptor-mediated early signaling but had a reproducible and dose-dependent effect on the nuclear translocation of NFAT and AP-1. Furthermore, we show in a model of acute IPA intoxication that animals became immunosuppressed as judged by their reduced ability to release IL-2 and IFN-gamma in the serum in response to staphylococcal enterotoxin B. This effect was also associated to the down-regulation of TNF-alpha production and was sufficiently strong to rescue susceptible animals from enterotoxin-induced toxic shock. Our results suggest that IPA is potentially immunosuppressive to the adaptive and innate immune system and have broad significance given the exposure of the general population to this ubiquitous chemical.  相似文献   
104.
105.
106.
The single photon response in vertebrate phototransduction is highly reproducible despite a number of random components of the activation cascade, including the random activation site, the random walk of an activated receptor, and its quenching in a random number of steps. Here we use a previously generated and tested spatiotemporal mathematical and computational model to identify possible mechanisms of variability reduction. The model permits one to separate the process into modules, and to analyze their impact separately. We show that the activation cascade is responsible for generation of variability, whereas diffusion of the second messengers is responsible for its suppression. Randomness of the activation site contributes at early times to the coefficient of variation of the photoresponse, whereas the Brownian path of a photoisomerized rhodopsin (Rh*) has a negligible effect. The major driver of variability is the turnoff mechanism of Rh*, which occurs essentially within the first 2-4 phosphorylated states of Rh*. Theoretically increasing the number of steps to quenching does not significantly decrease the corresponding coefficient of variation of the effector, in agreement with the biochemical limitations on the phosphorylated states of the receptor. Diffusion of the second messengers in the cytosol acts as a suppressor of the variability generated by the activation cascade. Calcium feedback has a negligible regulatory effect on the photocurrent variability. A comparative variability analysis has been conducted for the phototransduction in mouse and salamander, including a study of the effects of their anatomical differences such as incisures and photoreceptors geometry on variability generation and suppression.  相似文献   
107.
Viral hemorrhagic fever is a clinical syndrome that poses serious global health threat. Among the causative agents, dengue virus (DV) has the highest incidence rate and its infection is the major cause of viral hemorrhagic fever in the world. Although the pathophysiological mechanisms of DV-induced diseases are not yet understood, it is well accepted that liver is a site of viral replication. In this study, we used proteomics to analyze infection of a hepatic cell lineage, HepG2, with DV, focusing on the secreted proteins. 1D-electrophoresis and liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) were used, allowing the identification of a total of 107 proteins, among which 35 were found only in control secretome and 24 only in infected cells secretome. To validate these data, we performed 2D-eletrophoresis followed by MALDI-TOF/TOF, resulting in the identification of 20 proteins, 8 of them confirming LC-MS/MS results. We discuss the results obtained taking into account the proteins previously described in the secretome of HepG2 cells, proteins present in human plasma and proteins of interest for dengue pathogenesis. Altogether the data presented here provide clues for the progress in the understanding of the role of liver secretion in the progression of the disease.  相似文献   
108.
A basic peroxidase from wheat kernel with antifungal activity.   总被引:1,自引:0,他引:1  
A basic heme-peroxidase (WP1) was purified to homogeneity from wheat (Triticum aestivum) kernels. The protein was not glycosylated and exhibited a molecular mass of 36 kDa and a pI of 8.0. The N-terminal amino acid sequence revealed a very high similarity with a wheat flour peroxidase allergen associated with baker's asthma. WPI showed indole-3-acetic acid oxidase activity in the presence of Mn2+ and phenolic cofactors. Antifungal assays performed in vitro towards phytopathogenic fungi indicated that WP1 was active in inhibiting germ tube elongation. This first report on antifungal properties of a heme-peroxidase gives experimental support to the idea that peroxidases play a defensive role against invading pathogens.  相似文献   
109.
BACKGROUND: We studied polycystic ovarian syndrome (PCOS) in fifty 25- to 37-year-old women who failed to conceive with clomiphene citrate treatment. METHODS: Twenty patients were submitted to treatment with low-dose (75 IU) urinary FSH (uFSH) in order to achieve ovulation and 30 patients were treated with recombinant FSH (rFSH) according to the same protocol. RESULTS: Ovulation was achieved in 75 and 97% of the cycles after uFSH and rFSH, respectively (p < 0.02). The length of treatment needed to achieve ovulation, the number of ampules given and dose per kilogram were significantly lower in the rFSH group. Mild ovarian hyperstimulation syndrome (OHSS) was observed in 9 uFSH cycles, whereas only 1 of the women treated with rFSH developed an OHSS (1/38 vs. 9/36; p < 0.01). CONCLUSION: rFSH is more efficient than uFSH in inducing ovulation in PCOS patients. The high prevalence of ovulatory cycles using a lower dose guaranteed greater safety of treatment and significantly reduced the incidence of OHSS.  相似文献   
110.
This work deals with biogenic amine production by yeast strains isolated from grapes and wines. A total of 50 strains were tested for their capacity to produce biogenic amines in wine. In general, all the species produced very low or non-detectable amounts of histamine, whereas methylamine and agmatine were formed by all the species considered. The highest concentration of total biogenic amines was formed by Brettanomyces bruxellensis, with an average value of 15 mg/l, followed by Saccharomyces cerevisiae with an average of 12.14 mg/l. The other species formed less than 10 mg of total biogenic amines per litre. Wines fermented with the most fermentative strains of S. cerevisiae species had the highest contents of ethanolamine, from 2.3 to 16 mg/l, and of agmatine, from 3.1 to 7.5 mg/l. The strains of the other species, which exhibited a low fermentative ability, Kloeckera apiculata, B. bruxellensis and Metschnikowia pulcherrima, varied in the production of agmatine and phenylethylamine. A significant variability in the production of cadaverine was characteristic of Candida stellata strains, which varied also in ethanolamine production. Our results emphasize the importance of using selected strains of S. cerevisiae, not only for the expression of desirable technological traits, but also to avoid potentially negative effects on human health. Therefore, the characterization of strains of S. cerevisiae for the 'production of biogenic amines' becomes of applicative interest.  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