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   3582篇
  免费   235篇
  3817篇
  2023年   23篇
  2022年   40篇
  2021年   77篇
  2020年   53篇
  2019年   56篇
  2018年   94篇
  2017年   75篇
  2016年   135篇
  2015年   187篇
  2014年   199篇
  2013年   258篇
  2012年   293篇
  2011年   294篇
  2010年   176篇
  2009年   177篇
  2008年   212篇
  2007年   204篇
  2006年   174篇
  2005年   183篇
  2004年   163篇
  2003年   155篇
  2002年   145篇
  2001年   27篇
  2000年   31篇
  1999年   38篇
  1998年   25篇
  1997年   35篇
  1996年   33篇
  1995年   24篇
  1994年   30篇
  1993年   25篇
  1992年   15篇
  1991年   15篇
  1990年   10篇
  1989年   10篇
  1988年   10篇
  1987年   10篇
  1986年   7篇
  1985年   9篇
  1984年   10篇
  1983年   5篇
  1982年   7篇
  1980年   9篇
  1979年   4篇
  1978年   4篇
  1977年   4篇
  1976年   5篇
  1973年   7篇
  1971年   4篇
  1946年   5篇
排序方式: 共有3817条查询结果,搜索用时 15 毫秒
51.
The present zootherapeutic study describes the traditional knowledge related to the use of different animals and animal-derived products as medicines by the Saharia tribe reside in the Shahabad and Kishanganj Panchayat Samiti's of Baran district of Rajasthan, India. A field survey was conducted from April to June 2006 by performing interview through structured questionnaire with 21 selected respondents, who provided information regarding use of animals and their products in folk medicine. A total of 15 animal species were recorded and they are used for different ethnomedical purposes, including cough, asthma, tuberculosis, paralysis, earache, herpes, weakness, muscular pain etc. The zootherapeutic knowledge was mostly based on domestic animals, but some protected species like the peacock (Pavo cristatus,), hard shelled turtle (Kachuga tentoria), sambhar (Cervus unicolor) were also mentioned as medicinal resources. We would suggest that this kind of neglected traditional knowledge should be included into the strategies of conservation and management of faunistic resources. Further studies are required for experimental validation to confirm the presence of bioactive compounds in these traditional remedies and also to emphasize more sustainable use of these resources.  相似文献   
52.
Sco proteins are widespread proteins found in eukaryotic as well as in many prokaryotic organisms. The 3D structure of representatives from human, yeast, and Bacillus subtilis has been determined, showing a thioredoxin-like fold. Sco proteins have been implicated mainly as copper transporters involved in the assembly of the CuA cofactor in cytochrome c oxidase. Some mutations have been identified in humans that lead to defective cytochrome c oxidase formation and thus to fatal illnesses. However, it appears that the physiological function of Sco proteins goes beyond assembly of the CuA cofactor. Extensive analysis of completely sequenced prokaryotic genomes reveals that 18% of them contain either Sco proteins but not CuA-containing proteins or vice versa. In addition, in several cases, multiple Sco-encoding genes occur even if only a single potential Sco target is encoded in the genome. Genomic context analysis indeed points to a more general role for Sco proteins in copper transport, also to copper enzymes lacking a CuA cofactor. To obtain further insight into the possible role of Sco in the assembly of other cofactors, a search for Cox11 proteins, which are important for CuB biosynthesis, was also performed. A general framework for the action of Sco proteins is proposed, based on the hypothesis that they can couple metal transport and thiol/disulfide-based oxidoreductase activity, as well as select between either of these two cellular functions. This model reconciles the variety of experimental observations made on these proteins over the years, and can constitute a basis for further studies.  相似文献   
53.
Personal exposure assessment is a challenging task that requires both measurements of the state of the environment as well as the individual's movements. In this paper, we show how location data collected by smartphone applications can be exploited to quantify the personal exposure of a large group of people to air pollution. A Bayesian approach that blends air quality monitoring data with individual location data is proposed to assess the individual exposure over time, under uncertainty of both the pollutant level and the individual location. A comparison with personal exposure obtained assuming fixed locations for the individuals is also provided. Location data collected by the Earthquake Network research project are employed to quantify the dynamic personal exposure to fine particulate matter of around 2500 people living in Santiago (Chile) over a 4‐month period. For around 30% of individuals, the personal exposure based on people movements emerges significantly different over the static exposure. On the basis of this result and thanks to a simulation study, we claim that even when the individual location is known with nonnegligible error, this helps to better assess personal exposure to air pollution. The approach is flexible and can be adopted to quantify the personal exposure based on any location‐aware smartphone application.  相似文献   
54.

Vitamin D3 deficiency was found to be tightly linked to many health problems including metabolic syndrome, cancer, cardiovascular diseases, and type 2 diabetes mellitus. In our study, we tested the possible antidiabetic effects of one of vitamin D3 analogs, alfacalcidol, solely or in a combination with metformin on type 2 diabetic rats. Type 2 diabetic model rats were induced by feeding high-fat diet for 4 weeks followed by intraperitoneal injection of streptozotocin. In addition to the control group, the diabetic rats were divided into four groups: untreated, metformin-treated, alfacalcidol-treated, and combination-treated group (metformin?+?alfacalcidol) for 4 weeks. The level of fasting blood glucose, fasting serum insulin, homeostatic model of insulin resistance, serum lipid profile, liver enzymes, calcium, phosphorus, and 25-hydroxyvitamin D3 were also determined. Besides, sterol regulatory element binding protein-1c (SREBP-1c) and vitamin D receptors (VDR) gene expression at mRNA and protein levels were evaluated. The level of significance was fixed at P?≤?0.05 for all statistical tests. Alfacalcidol, solely or combined with metformin, significantly ameliorated glucose homeostasis and lipid profile parameters (P?<?0.001) with a neutral effect on calcium and phosphorus levels. Significant downregulation of mRNA expression of SREBP-1c in the liver, white as well as brown adipose tissues (P?<?0.001) and different patterns of mRNA expression of VDR gene in pancreas and white adipose tissue were observed in rats treated with alfacalcidol solely or in combination with metformin. Vitamin D3 analogs can modulate glucose parameters and lipid metabolism in a diabetic rat model and it provides additional protective effects when combined with metformin.

  相似文献   
55.
In characterizing mutants and covalently inhibited complexes of Fusarium solani cutinase, which is a 197-residue lipolytic enzyme, 34 variant structures, crystallizing in 8 different crystal forms, have been determined, mostly at high resolution. Taking advantage of this considerable body of information, a structural comparative analysis was carried out to investigate the dynamics of cutinase. Surface loops were identified as the major flexible protein regions, particularly those forming the active-site groove, whereas the elements constituting the protein scaffold were found to retain the same conformation in all the cutinase variants studied. Flexibility turned out to be correlated with thermal motion. With a given crystal packing environment, a high flexibility turned out to be correlated with a low involvement in crystal packing contacts. The high degree of crystal polymorphism, which allowed different conformations with similar energy to be detected, made it possible to identify motions which would have remained unidentified if only a single crystal form had been available. Fairly good agreement was found to exist between the data obtained from the structural comparison and those from a molecular dynamics (MD) simulation carried out on the native enzyme. The crystallographic approach used in this study turned out to be a suitable tool for investigating cutinase dynamics. Because of the availability of a set of closely related proteins in different crystal environments, the intrinsic drawback of a crystallographic approach was bypassed. By combining several static pictures, the dynamics of the protein could be monitored much more realistically than what can be achieved on the basis of static pictures alone. Proteins 26:442–458 © 1996 Wiley-Liss, Inc.  相似文献   
56.
57.
In the 1997-1998 and 1998-1999 school years we measured head dimensions of 1600 boys from 6 to 13 years attending elementary and middle schools in towns of the Cagliari area (Sardinia, Italy). For each age, we compared the mean values for circumference, length and width of the head with Canadian standards, widely used by Sardinian pediatricians. The t-test shows that the means of the three variables are significantly lower in the Cagliari boys than in their Canadian contemporaries, with the exception of head circumference in 6 and 7 year-olds, and of head width in 10 year-olds. Therefore, it is necessary to produce specific growth charts for circumference, length and width of the head of Sardinian children rather than evaluate their growth using standards of populations with different ethnic, geographical and socio-economic backgrounds.  相似文献   
58.
59.
The AGAMOUS (AG) gene is necessary for stamen and carpel development and is part of a monophyletic clade of MADS-box genes that also includes SHATTERPROOF1 (SHP1), SHP2, and SEEDSTICK (STK). Here, we show that ectopic expression of either the STK or SHP gene is sufficient to induce the transformation of sepals into carpeloid organs bearing ovules. Moreover, the fact that these organ transformations occur when the STK gene is expressed ectopically in ag mutants shows that STK can promote carpel development in the absence of AG activity. We also show that STK, AG, SHP1, and SHP2 can form multimeric complexes and that these interactions require the SEPALLATA (SEP) MADS-box proteins. We provide genetic evidence for this role of the SEP proteins by showing that a reduction in SEP activity leads to the loss of normal ovule development, similar to what occurs in stk shp1 shp2 triple mutants. Together, these results indicate that the SEP proteins, which are known to form multimeric complexes in the control of flower organ identity, also form complexes to control normal ovule development.  相似文献   
60.
We describe the molecular mechanisms of apoptosis and its relationships with hematologic malignancies, stressing the concept that, both positive and negative deregulation of apoptosis, may be involved in hematologic human diseases. So, this fundamental process must be balanced by so far unknown mechanisms, involving caspases (cysteine proteases, cleaving the protein substrate after an aspartate residue). These, so far known, ten proteases, are interconnected in a molecular cascade, initiated by the release of cytochrome C from mitochondrial membranes and its interaction with APAF-1 (the homolog of the Caenorhabditis e. CED-4) and with caspase 9, that initiates the proteolitic cascade (1,2). The conclusion is that apoptosis is a very important process, but yet poorly known in molecular details, in spite of the efforts of many scientists. Even the role of bcl-2, the main gene protecting from apoptosis, is still unknown. We close this chapter with a list of ten different technical approaches that can be useful tools to study apoptosis, and tracing the molecular principles on which they are based.  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