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   4041篇
  免费   254篇
  国内免费   8篇
  2024年   7篇
  2023年   39篇
  2022年   116篇
  2021年   163篇
  2020年   164篇
  2019年   263篇
  2018年   231篇
  2017年   158篇
  2016年   189篇
  2015年   194篇
  2014年   281篇
  2013年   352篇
  2012年   369篇
  2011年   339篇
  2010年   185篇
  2009年   150篇
  2008年   166篇
  2007年   197篇
  2006年   142篇
  2005年   116篇
  2004年   85篇
  2003年   105篇
  2002年   85篇
  2001年   18篇
  2000年   15篇
  1999年   17篇
  1998年   15篇
  1997年   16篇
  1996年   8篇
  1995年   9篇
  1994年   7篇
  1993年   4篇
  1992年   11篇
  1991年   6篇
  1990年   5篇
  1989年   5篇
  1988年   9篇
  1987年   6篇
  1986年   7篇
  1984年   9篇
  1983年   7篇
  1980年   2篇
  1979年   4篇
  1977年   2篇
  1976年   2篇
  1975年   5篇
  1972年   2篇
  1970年   2篇
  1966年   3篇
  1961年   2篇
排序方式: 共有4303条查询结果,搜索用时 125 毫秒
71.

Background

Light-emitting diode fluorescence microscopy (LED-FM) has been shown to be more sensitive than conventional bright field microscopy using Ziehl-Neelsen (ZN) stain in detecting sputum smear positive tuberculosis in controlled laboratory conditions. In 2012, Auramine O staining based LED-FM replaced conventional ZN microscopy in 200 designated microscopy centres (DMC) of medical colleges operating in collaboration with India’s Revised National Tuberculosis Control Programme. We aimed to assess the impact of introduction of LED-FM services on sputum smear positive case detection under program conditions.

Methods

This was a before and after comparison study. In 15 randomly selected medical college DMCs, all presumptive TB patients who underwent sputum smear examination in the years 2011 (before LED-FM) and 2012 (after LED-FM) were compared. An additional 15 comparable DMCs that implemented conventional ZN sputum smear microscopy were also selected for comparison between 2011 and 2012.

Results

The proportion of presumptive TB patients (PTP)found sputum smear positive increased by 30%- from 13.6% (3432/25159) in 2011 to 17.8% (4706/26426) in 2012 (P value <0.01) in the sites that implemented LED-FM microscopy, whereas in DMCs where the ZN staining procedure is followed the proportion of sputum smear positive had remained unchanged (13.0%versus 12.6%;P value0.31).

Conclusion

Use of LED-FM significantly increased the proportion of smear positive cases among presumptive TB patients under routine program conditions in high workload laboratories. The study provides operational evidence needed to scale-up the use of LED-FM in similar settings in India and beyond.  相似文献   
72.
ErbB-3 (HER-3) receptor is involved in tumor progression and resistance to therapy. Development of specific inhibitors impairing the activity of ErbB-3 is an attractive tool for cancer therapeutics. MP-RM-1, a murine monoclonal antibody targeting human ErbB-3, has shown anticancer activity in preclinical models. With the aim to provide novel candidates for clinical use, we have successfully generated a humanized version of MP-RM-1. The humanized antibody, named EV20, abrogates both ligand-dependent and ligand-independent receptor signaling of several tumor cell types, strongly promotes ErbB-3 down-regulation, and efficiently and rapidly internalizes into tumor cells. Furthermore, treatment with EV20 significantly inhibits growth of xenografts originating from prostatic, ovarian, and pancreatic cancers as well as melanoma in nude mice. In conclusion, we provide a novel candidate for ErbB-3-targeted cancer therapy.  相似文献   
73.
The structural, elastic and electronic properties of lutatium-pnictides (LuN, LuP, LuAs, LuSb, and LuBi) were analyzed by using full-potential linearized augmented plane wave within generalized gradient approximation in the stable rock-salt structure (B1 phase) with space group Fm-3m and high-pressure CsCl structure (B2 phase) with space group Pm-3m. Hubbard-U and spin-orbit coupling were included to predict correctly the semiconducting band gap of LuN. Under compression, these materials undergo first-order structural transitions from B1 to B2 phases at 241, 98, 56.82, 25.2 and 32.3 GPa, respectively. The computed elastic properties show that LuBi is ductile by nature. The electronic structure calculations show that LuN is semiconductor at ambient conditions with an indirect band gap of 1.55 eV while other Lu-pnictides are metallic. It was observed that LuN shows metallization at high pressures. The structural properties, viz, equilibrium lattice constant, bulk modulus and its pressure derivative, transition pressure, equation of state, volume collapse, band gap and elastic moduli, show good agreement with available data.
Figure
Equation of state of Lu-pnictides  相似文献   
74.
Salicylic acid (SA) is a prominent signaling molecule during biotic and abiotic stresses in plants biosynthesized via cinnamate and isochorismate pathways. Cinnamate 4-hydroxylase (C4H) and isochorismate synthase (ICS) are the main enzymes in phenylpropanoid and isochorismate pathways, respectively. To investigate the actual roles of these genes in resistance mechanism to environmental stresses, here, the coding sequences of these enzymes in safflower (Carthamus tinctorius), as an oilseed industrial medicinal plant, were partially isolated and their expression profiles during salinity stress, wounding, and salicylic acid treatment were monitored. As a result, safflower ICS (CtICS) and C4H (CtC4H) were induced in early time points after wounding (3–6 h). Upon salinity stress, CtICS and CtC4H were highly expressed for the periods of 6–24 h and 3–6 h after treatment, respectively. It seems evident that ICS expression level is SA concentration dependent as if safflower treatment with 1 mM SA could induce ICS much stronger than that with 0.1 mM, while C4H is less likely to be so. Based on phylogenetic analysis, safflower ICS has maximum similarity to its ortholog in Vitis vinifera up to 69%, while C4H shows the highest similarity to its ortholog in Echinacea angustifolia up to 96%. Overall, the isolated genes of CtICS and CtC4H in safflower could be considered in plant breeding programs for salinity tolerance as well as for pathogen resistance.  相似文献   
75.
Highlights? Nondiabetic LRP6 mutation carriers are hyperinsulinemic and insulin resistant ? IR expression is reduced in skeletal muscles of the LRP6 mutation carriers ? Wnt/LRP6 regulate the insulin receptor and IGFR expression ? The LRP6 mutation reduces TCF7L2-dependent IR expression and enhances mTOR activity  相似文献   
76.
The effect of oral administration of different doses of hydroalcoholic extract of silymarin on body weight, glucose concentration and indicators of oxidative stress superoxide dismutase (SOD), glutathione peroxidase (GPX), catalase (CAT) and malondialdehyde (MDA) was investigated in the present study. Fifty adult male Wistar rats were used. The animals were divided into five groups and oral route of administration was used in control group (0.9 %, NaCl), control group patients (0.9 %, NaCl), diabetic group (100 mg/kg, silymarin), diabetic group (125 mg/kg, silymarin), diabetic group (250 mg/kg, silymarin) for 14 days with gavage. Diabetes was induced by a single injection of streptozotocin (45 mg/kg, i.p.). Before and 3 days after injection, and at 7 and 14 days of treatment, the fasting glucose level and weight were measured. At the end of 14 days, animals were anesthetized with ether and blood samples were taken by heart puncture and were analyzed for oxidative stress indicators. The results showed that hydroalcoholic extract of silymarin can increase the average body weight and decrease glucose and, at the end of 14 days, decrease MDA level and increase the level of antioxidant enzymes (SOD, GPX, CAT) in red blood cells in a dose-dependent manner (P < 0.05). In conclusion, the hydroalcoholic extract of silymarin has an overall beneficial effect on body weight, glucose level and oxidative stress. Therefore, silymarin may reduce oxidative stress via increasing antioxidant enzyme activity.  相似文献   
77.
As an enzyme acting at the junction of gluconeogenic pathway, phosphoenolpyruvate carboxykinase (PEPCK) controls substrate flow from Krebs cycle toward glucose production. Therefore, it would be advantageous to design effective inhibitors to inactivate PEPCK in diabetes mellitus and other abnormalities caused by insulin resistance. Such inhibitors may compensate the metabolic consequences of ex-activity of PEPCK at these conditions. Understanding the mechanism by which inhibitors exert their effect on enzyme activity is of great interest for designing stronger inhibitors. In the present work, molecular dynamic simulations were used to study enzyme-inhibitor interactions. Our results indicate that inhibitors of PEPCK with their short chains interact with enzyme active site through non-covalent interactions of electrostatic and hydrogen bond nature. The data also show that inhibitors neither reach a stable state in their binding site nor make static complex with the enzyme active site. Instead, they interact with functional groups of active site residues in a dynamic fashion. In this way, oxalate and sulfoacetate carrying two negative groups of higher charge density and optimum spacing from each other, show more dynamic behavior (lower stability in their binding site) and more inhibitory effects than other inhibitors used (phosphonoformate, phosphoglycolate and 3-phosphonopropionate).  相似文献   
78.
Three new phenolic compounds, sorlanin (4-(3-(hydroxymethyl)-5-methoxy-7-phenyl-2,3-dihydrobenzo[b][1,4]dioxin-2-yl)-2-methoxyphenol, 1), sorbanin (2-((3,5-dimethoxy-[1,1′-biphenyl]-4-yl)oxy)-1-(4-hydroxy-3-methoxyphenyl)propane-1,3-diol, 2) and sorbalanin (4-(3-(hydroxymethyl)-5,6-dimethoxy-2,3-dihydrobenzo[b][1,4]dioxino[2,3-g]benzofuran-2-yl)-2-methoxyphenol, 3), together with eight known compounds, polystachyol (4), isolariciresinol (5), dihydrodehydrodiconiferyl alcohol (6), tuberculatin (7), ovafolinin E (8), aucuparin (9), 2′-methoxyaucuparin (10), and tetracosyl-3-(3,4-dihydroxyphenyl)acrylate (11), were isolated from Sorbus lanata. The structures of these phytoconstituents were elucidated through extensive spectroscopic techniques, including UV, IR, 1D and 2D NMR, ESI-MS and HRESI-MS experiments. All the compounds except 9 and 10 were isolated for the first time from the genus Sorbus. The isolated compounds were also tested in DPPH radical scavenging reaction where compounds 6, 7, 10 and 11 showed significant activities with IC50 values of 9.2, 11.7, 23.0 and 33.7 μM, respectively.  相似文献   
79.
80.
Biological Trace Element Research - In low-income and middle-income countries such as Iran, smoking is becoming increasingly popular, especially among young people. This has led to additional...  相似文献   
[首页] « 上一页 [3] [4] [5] [6] [7] 8 [9] [10] [11] [12] [13] 下一页 » 末  页»
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