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   2875篇
  免费   203篇
  国内免费   1篇
  3079篇
  2024年   6篇
  2023年   27篇
  2022年   89篇
  2021年   117篇
  2020年   91篇
  2019年   115篇
  2018年   140篇
  2017年   104篇
  2016年   157篇
  2015年   192篇
  2014年   193篇
  2013年   256篇
  2012年   296篇
  2011年   261篇
  2010年   161篇
  2009年   116篇
  2008年   132篇
  2007年   118篇
  2006年   100篇
  2005年   102篇
  2004年   76篇
  2003年   62篇
  2002年   60篇
  2001年   10篇
  2000年   8篇
  1999年   10篇
  1998年   14篇
  1997年   7篇
  1996年   5篇
  1995年   3篇
  1994年   7篇
  1993年   8篇
  1992年   2篇
  1991年   4篇
  1989年   3篇
  1986年   4篇
  1985年   1篇
  1984年   1篇
  1983年   1篇
  1982年   3篇
  1981年   2篇
  1979年   1篇
  1978年   2篇
  1977年   1篇
  1976年   1篇
  1974年   1篇
  1973年   2篇
  1967年   1篇
  1962年   2篇
  1960年   1篇
排序方式: 共有3079条查询结果,搜索用时 15 毫秒
11.
This study evaluated the effect of crude protein (CP) reduction in four diets (156, 139, 132, and 127 g Kg-1 DM) maintaining constant metabolizable protein (188 g/day) on the follicular fluid and cumulus-oocyte complexes of mid-lactating Girolando cows. Twenty-two Girolando cows with average of 21.55 ±3.19 L daily milk yield, 105.30 ±22.62 days in lactation and 3.22 ±0.03 body condition score were selected. To reduce CP in diets and maintain constant metabolizable protein, urea and soybean meal were gradually replaced by lignosulfonate-treated soybean meal (SoyPass®, Cargill), resulting in an increase in rumen-undegradable protein and a reduction in rumen degradable protein. A linear and quadratic reduction was observed in the plasma and follicular fluid urea nitrogen concentration following CP reduction, with the most intense reduction occurring in the 127 g Kg-1 DM group (p<0.001). As CP reduced, there was a tendency for a linear increase in the follicular growth rate (P=0.0696), on the number and proportion of viable oocytes (P<0.09), and also a linear increase for the number (P=0.0397) and proportion (P<0.09) of grade I viable oocytes. Plus, there was a linear effect for the number of cumulus oophorus cells. Cows fed with the lowest amount of CP had cumulus-oocyte complexes with higher numbers of cumulus oophorus cells (P=0.0238). Also, the reduction of diet crude protein was followed by a decrease in the probability of oocytes’ DNA degradation. In conclusion, the reduction of CP in the diet of mid-lactating Girolando cows, reduces urea nitrogen concentration in both blood plasma and follicular fluid, and, as a consequence, increases the viability of oocytes and the number of cumulus oophorus cells while reducing oocytes’ DNA degradation of follicular included cumulus-oocyte complex. The reduction on dietary CP may improve in vivo oocytes’ embryo development impacting fertility of lactating dairy cows.  相似文献   
12.
13.
? Premise of the study: Microsatellite markers were developed for the population genetic analyses of the neotropical tree Dipteryx alata (Fabaceae). ? Methods and Results: Microsatellites were developed from a genomic shotgun library. Polymorphism at each microsatellite loci was analyzed based on 94 individuals from three populations. Eight loci amplified successfully and presented one to 10 alleles, and expected heterozygosities ranged from 0.097 to 0.862. Four loci also amplified in Pterodon emarginatus and presented similar polymorphism. ? Conclusion: The eight microsatellite primer pairs are potentially suitable for population genetic studies and successfully amplified in another Fabaceae species.  相似文献   
14.
Identification of tissue-specific microRNAs from mouse   总被引:76,自引:0,他引:76  
MicroRNAs (miRNAs) are a new class of noncoding RNAs, which are encoded as short inverted repeats in the genomes of invertebrates and vertebrates. It is believed that miRNAs are modulators of target mRNA translation and stability, although most target mRNAs remain to be identified. Here we describe the identification of 34 novel miRNAs by tissue-specific cloning of approximately 21-nucleotide RNAs from mouse. Almost all identified miRNAs are conserved in the human genome and are also frequently found in nonmammalian vertebrate genomes, such as pufferfish. In heart, liver, or brain, it is found that a single, tissue-specifically expressed miRNA dominates the population of expressed miRNAs and suggests a role for these miRNAs in tissue specification or cell lineage decisions. Finally, a miRNA was identified that appears to be the fruitfly and mammalian ortholog of C. elegans lin-4 stRNA.  相似文献   
15.
We compare blood pressure and hypertension between adult men on the USA mainland and in Puerto Rico born during 1886-1930 to test hypotheses about the link between cardiovascular health and large socioeconomic and political changes in society: (a) 8853 men surveyed in Puerto Rico in 1965 and (b) 1449 non-Hispanic White men surveyed on the mainland during 1971-1975. Systolic and diastolic blood pressure and hypertension were regressed separately on demographic and socioeconomic variables and cardiovascular risk factors. Mainland men not taking anti-hypertensive medication showed statistically significant improvements in systolic blood pressure and hypertension at the beginning of the century and men in Puerto Rico showed improvements in diastolic blood pressure but only during the last two quinquenniums. An average man born on the mainland during the last birth quinquennium (1926-1930) had 7.4-8.7 mmHg lower systolic blood pressure and was 61% less likely to have systolic hypertension than one born before 1901. On average Puerto Rican men born during 1921-1925 had approximately 1.7 mmHg lower diastolic blood pressure than men born before 1901. Analyses of secular trends in cardiovascular health complements analyses of secular trends in anthropometric indicators and together provide a fuller view of the changing health status of a population.  相似文献   
16.
17.
An antifungal protein from Helianthus annuus L. seeds (Ha-AP10) has been purified to homogeneity and characterized. Ha-AP10 purification was performed by gel filtration, cation exchange chromatography and reverse phase HPLC. Its molecular mass was estimated to be 10 kDa and western blot analyses suggest that it has an extracellular location. The N-terminal sequence of Ha-AP10 showed strong homology to some plant lipid-transfer proteins (LTPs). Antifungal tests have demonstrated that Ha-AP10 exerts a fungistatic effect. It completely inhibits the germination of spores of the fungal pathogen Fusarium solani f. sp. eumartii at a concentration of 40 μg ml−1 and produces a 50% growth inhibition at 6.5 μg ml−1 (0.65 μ M ). These data place Ha-AP10 among the most potent antifungal LTPs described so far.  相似文献   
18.
Candidiasis is the most common opportunistic yeast infection. Candida species and other microorganisms are involved in this complicated fungal infection, but Candida albicans continues to be the most prevalent. In the past two decades, it has been observed an abnormal overgrowth in the gastrointestinal, urinary and respiratory tracts, not only in immunocompromised patients, but also related to nosocomial infections and even in healthy individuals. There is a widely variety of causal factors that contribute to yeast infection which means that candidiasis is a good example of a multifactorial syndrome. Due to rapid increase in the incidence in these infections, this is the subject of numerous studies. Recently, the focus of attention is the treatment and, above all, the prevention of those complications. The diagnosis of candidiasis could become quite complicated. Prevention is the most effective “treatment,” much more than eradication of the yeast with antifungal agents. There are several aspects to consider in the daily routine that can provide a strength protection. However, a therapeutic approach is necessary when the infection is established, and therefore, other alternatives should be explored. This review provides an overview on predisposition factors, prevention and diagnosis of candidiasis, highlighting alternative approaches for candidiasis treatment.  相似文献   
19.
In the present study we analyzed medicinal and edible plant utilization in Cuyin Manzano, a small rural population located near the Andean forests of Argentina. We also studied where and when plant knowledge was learned, who the principal transmitters were, and how people were taught. The participants were interviewed individually and at random, by means of a semi-structured questionnaire. Interviews were carried out in 16 families in order to examine the present use of wild plants. The inhabitants of Cuyin Manzano cited 87 plants: 63 medicinal and 24 edible species. They mentioned on average 31 ± 10 species per person. Similar patterns of plant use were found in young and old people alike, irrespective of gender. Learning about useful plants took place at an early age as a result of family tradition. This local knowledge is acquired and taught “by doing,” and is mostly transmitted vertically through family dissemination. Wild plant learning implies the acquisition of plants' physical and functional features as well as their environmental characteristics.  相似文献   
20.
Bacteriophage replication requires specific host‐recognition. Some siphophages harbour a large complex, the baseplate, at the tip of their non‐contractile tail. This baseplate holds receptor binding proteins (RBPs) that can recognize the host cell‐wall polysaccharide (CWPS) and specifically attach the phage to its host. While most phages possess a dedicated RBP, the phage J‐1 that infects Lactobacillus casei seemed to lack one. It has been shown that the phage J‐1 distal tail protein (Dit) plays a role in host recognition and that its sequence comprises two inserted modules compared with ‘classical’ Dits. The first insertion is similar to carbohydrate‐binding modules (CBMs), whereas the second insertion remains undocumented. Here, we determined the structure of the second insertion and found it also similar to several CBMs. Expressed insertion CBM2, but not CBM1, binds to L. casei cells and neutralize phage attachment to the bacterial cell wall and the isolated and purified CWPS of L. casei BL23 prevents CBM2 attachment to the host. Electron microscopy single particle reconstruction of the J‐1 virion baseplate revealed that CBM2 is projected at the periphery of Dit to optimally bind the CWPS receptor. Taken together, these results identify J‐1 evolved Dit as the phage RBP.  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