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   326篇
  免费   41篇
  国内免费   7篇
  374篇
  2024年   3篇
  2023年   5篇
  2022年   4篇
  2021年   9篇
  2020年   9篇
  2019年   11篇
  2018年   19篇
  2017年   9篇
  2016年   19篇
  2015年   17篇
  2014年   24篇
  2013年   27篇
  2012年   27篇
  2011年   25篇
  2010年   6篇
  2009年   18篇
  2008年   15篇
  2007年   10篇
  2006年   10篇
  2005年   10篇
  2004年   10篇
  2003年   4篇
  2002年   9篇
  2001年   7篇
  2000年   12篇
  1999年   6篇
  1997年   2篇
  1996年   2篇
  1995年   2篇
  1994年   2篇
  1993年   2篇
  1992年   2篇
  1991年   4篇
  1989年   2篇
  1985年   2篇
  1984年   4篇
  1980年   3篇
  1975年   1篇
  1974年   1篇
  1973年   5篇
  1972年   1篇
  1970年   1篇
  1969年   3篇
  1968年   1篇
  1967年   1篇
  1966年   1篇
  1965年   1篇
  1955年   1篇
  1948年   1篇
  1939年   1篇
排序方式: 共有374条查询结果,搜索用时 15 毫秒
31.
We studied two pathways that involve the transfer of persulfide sulfur in humans, molybdenum cofactor biosynthesis and tRNA thiolation. Investigations using human cells showed that the two-domain protein MOCS3 is shared between both pathways. MOCS3 has an N-terminal adenylation domain and a C-terminal rhodanese-like domain. We showed that MOCS3 activates both MOCS2A and URM1 by adenylation and a subsequent sulfur transfer step for the formation of the thiocarboxylate group at the C terminus of each protein. MOCS2A and URM1 are β-grasp fold proteins that contain a highly conserved C-terminal double glycine motif. The role of the terminal glycine of MOCS2A and URM1 was examined for the interaction and the cellular localization with MOCS3. Deletion of the C-terminal glycine of either MOCS2A or URM1 resulted in a loss of interaction with MOCS3. Enhanced cyan fluorescent protein and enhanced yellow fluorescent protein fusions of the proteins were constructed, and the fluorescence resonance energy transfer efficiency was determined by the decrease in the donor lifetime. The cellular localization results showed that extension of the C terminus with an additional glycine of MOCS2A and URM1 altered the localization of MOCS3 from the cytosol to the nucleus.  相似文献   
32.
The circulating population of peripheral T lymphocytes obtained from a blood sample can provide a large amount of information about an individual's medical status and history. Recent evidence indicates that the detection and functional characterization of antigen-specific T cell subsets within the circulating population may provide a diagnostic indicator of disease and has the potential to predict an individual's response to therapy. In this report, a microarray detection platform that combines grating-coupled surface plasmon resonance imaging (GCSPRI) and grating-coupled surface plasmon coupled emission (SPCE) fluorescence detection modalities were used to detect and characterize CD4(+) T cells. The microspot regions of interest (ROIs) printed on the array consisted of immobilized antibodies or peptide loaded MHC monomers (p/MHC) as T cell capture ligands mixed with additional antibodies as cytokine capture ligands covalently bound to the surface of a corrugated gold sensor chip. Using optimized parameters, an unlabeled influenza peptide reactive T cell clone could be detected at a frequency of 0.1% in a mixed T cell sample using GCSPRI. Additionally, after cell binding was quantified, differential TH1 cytokine secretion patterns from a T cell clone cultured under TH1 or TH2 inducing conditions was detected using an SPCE fluorescence based assay. Differences in the secretion patterns of 3 cytokines, characteristic of the inducing conditions, indicated that differences were a consequence of the functional status of the captured cells. A dual mode GCSPRI/SPCE assay can provide a rapid, high content T cell screening/characterization tool that is useful for diagnosing disease, evaluating vaccination efficacy, or assessing responses to immunotherapeutics.  相似文献   
33.
The aim of this study was to identify the main weed communities in Al-Jouf province in northern Saudi Arabia. Moreover, the composition and diversity of these communities were studied in relation to soil variables and crop type. Some 54 stands representing olive orchards, date palm orchards, wheat crop and watermelon crop were studied, using ten quadrats (1 × 1 m) per stand. A total of 71 species belonging to 22 families and 61 genera were observed. The classification of vegetation using the Two Way Indicator Species Analysis (TWINSPAN) resulted in the recognition of four vegetation groups representing wheat crop, orchards in winter season, orchards in summer season and watermelon crop. These results suggested the importance of both crop and season for the formation of weed community. Detrended Correspondence Analysis (DCA) showed that these groups are clearly distinguished by the first two DCA axes. The species richness was higher in both olive and date palm orchards than in wheat and watermelon crops. This pattern of species richness could be related to farm management practices and habitat micro-heterogeneity. Soil electrical conductivity, organic carbon and soil texture showed significant correlations with species richness and the cover values of some dominant species, suggesting the significant role of soil characteristics in weed community structure and diversity.  相似文献   
34.
Malaria signature on human genome is marked by several gene polymorphisms. HemoglobinAS (HbAS) is known to protect against severe malaria, but barely proved to protect against uncomplicated malaria (UM). Similarly, the influence of FcγRIIa-RH131 polymorphism on malaria is controversial. Polymorphisms in both genes were examined and levels of IgG subclasses against four malaria antigens were measured for 250 Fulani’s from Daraweesh, eastern Sudan. Morbidity data for up to nine years was available for 214 donors. Number of malaria episodes experienced by each individual during the study period was used as indicator for susceptibility to UM. PCR and RFLP were used for donors DNA genotyping and ELISA for antibodies measurement. Results revealed that neither FcγRIIa-RH131 alleles/genotypes nor HbAA/AS was significantly associated with malaria morbidity or with levels of IgG to test antigens. Both polymorphisms were in Hardy–Weinberg Equilibrium, interestingly, there was strong association between the two polymorphisms (linkage disequilibrium – LD) with D′ = 0.89. The association between the two polymorphisms was confirmed by analysis of independent material from a neighboring village. In conclusion, in Daraweesh both FcγRIIa-RH131 and HbAA/AS genotypes, independently or together, were not major markers for UM susceptibility, however, marked LD was observed between the two polymorphisms.  相似文献   
35.
MA Nasr  CJ Nicol  JC Murrell 《PloS one》2012,7(8):e42420
The European ban on battery cages has forced a change towards the use of non-cage or furnished cage systems, but unexpectedly this has been associated with an increased prevalence of keel bone fractures in laying hens. Bone fractures are acutely painful in mammals, but the effect of fractures on bird welfare is unclear. We recently reported that keel bone fractures have an effect on bird mobility. One possible explanation for this is that flying becomes mechanically impaired. However it is also possible that if birds have a capacity to feel pain, then ongoing pain resulting from the fracture could contribute to decreased mobility. The aim was to provide proof of concept that administration of appropriate analgesic drugs improves mobility in birds with keel fracture; thereby contributing to the debate about the capacity of birds to experience pain and whether fractures are associated with pain in laying hens. In hens with keel fractures, butorphanol decreased the latency to land from perches compared with latencies recorded for these hens following saline (mean (SEM) landing time (seconds) birds with keel fractures treated with butorphanol and saline from the 50, 100 and 150 cm perch heights respectively 1.7 (0.3), 2.2 (0.3), p = 0.05, 50 cm; 12.5 (6.6), 16.9 (6.7), p = 0.03, 100 cm; 20.6 (7.4), 26.3 (7.6), p = 0.02 150 cm). Mobility indices were largely unchanged in birds without keel fractures following butorphanol. Critically, butorphanol can be considered analgesic in our study because it improved the ability of birds to perform a complex behaviour that requires both motivation and higher cognitive processing. This is the first study to provide a solid evidential base that birds with keel fractures experience pain, a finding that has significant implications for the welfare of laying hens that are housed in non-cage or furnished caged systems.  相似文献   
36.
Cystinuria (OMIM 220100) is an inborn congenital disorder characterised by a defective cystine metabolism resulting in the formation of cystine stones. Among the heterogeneous group of kidney stone diseases, cystinuria is the only disorder which is exclusively caused by gene mutations. So far, two genes responsible for cystinuria have been identified: SLC3A1 (chromosome 2p21) encodes the heavy subunit rBAT of a renal b0,+ transporter while SLC7A9 (chromosome 19q12) encodes its interacting light subunit b0,+AT. Mutations in SLC3A1 are generally associated with an autosomal-recessive mode of inheritance whereas SLC7A9 variants result in a broad clinical variability even within the same family. The detection rate for mutations in these genes is larger than 85%, but it is influenced by the ethnic origin of a patient and the pathophysiological significance of the mutations. In addition to isolated cystinuria, patients suffering from the hypotonia-cystinuria syndrome have been reported carrying deletions including at least the SLC3A1 and the PREPL genes in 2p21. By extensive molecular screening studies in large cohort of patients a broad spectrum of mutations could be identified, several of these variants were functionally analysed and thereby allowed insights in the pathology of the disease as well as in the renal trafficking of cystine and the dibasic amino acids. In our review we will summarize the current knowledge on the physiological and the genetic basis of cystinuria as an inborn cause of kidney stones, and the application of this knowledge in genetic testing strategies.  相似文献   
37.
T. Skhiri  L. Gaha  M. Nasr 《Andrologie》1991,1(1):40-41
A sample of 22 consultants for sterility has been studied. Sterility is badly accepted; it is felt as a narcissic wound, keeping on a depressive mood, with loss of the spirit of initiative. The multiplication of examinations and visits to doctors is a current consequence inspite of the results of complementary examinations. The means of reparation and compensation are very much restricted. Insemination is refused in 77% of the cases. Adoption causes many cultural problems. For the majority of consultants resorting to religion results in resignation more than acceptation  相似文献   
38.
39.
Summary At high salinities and high temperatures, the growth rate of Pterocladia was high, the tips of branch initials were dilated and holdfasts broadened. By the end of the fourth week bleaching of the whole plant was complete.Under low salinities and low temperatures, the rate of vegetative growth was decreased, the cuticle was thin and food reserve was centrally accumulated in the cells.Under high salinities and low temperatures, the rate of growth was greatly reduced and cells were devoid of food reserve. Defoliation of lateral branches was frequent.Under low salinities and high temperatures, the rate of growht was rather high and cells were relatively large.  相似文献   
40.
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