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   4362篇
  免费   334篇
  国内免费   3篇
  4699篇
  2022年   35篇
  2021年   47篇
  2020年   50篇
  2019年   60篇
  2018年   84篇
  2017年   71篇
  2016年   74篇
  2015年   111篇
  2014年   172篇
  2013年   255篇
  2012年   263篇
  2011年   304篇
  2010年   184篇
  2009年   143篇
  2008年   174篇
  2007年   217篇
  2006年   198篇
  2005年   161篇
  2004年   151篇
  2003年   136篇
  2002年   115篇
  2001年   126篇
  2000年   131篇
  1999年   101篇
  1998年   50篇
  1997年   42篇
  1996年   47篇
  1995年   41篇
  1994年   35篇
  1993年   34篇
  1992年   74篇
  1991年   90篇
  1990年   88篇
  1989年   84篇
  1988年   44篇
  1987年   63篇
  1986年   70篇
  1985年   74篇
  1984年   66篇
  1983年   43篇
  1982年   47篇
  1981年   34篇
  1980年   25篇
  1979年   33篇
  1978年   30篇
  1977年   32篇
  1976年   24篇
  1975年   21篇
  1974年   23篇
  1972年   26篇
排序方式: 共有4699条查询结果,搜索用时 15 毫秒
71.
By providing a source of α-smooth muscle actin (α-SMA)-expressing myofibroblasts, microvascular pericytes contribute to the matrix remodeling that occurs during tissue repair. However, the extent to which pericytes may contribute to the fibroblast phenotype post-repair is unknown. In this report, we test whether pericytes isolated from human placenta can in principle become fibroblast-like. Pericytes were cultured in vitro for 11 passages. The Affymetrix mRNA expression profile of passage 2 and passage 11 pericytes was compared. The expression of type I collagen, thrombospondin and fibronectin mRNAs was induced by passaging pericytes in culture. This induction of a fibroblast phenotype was paralleled by induction of connective tissue growth factor (CTGF/CCN2) and type I collagen protein expression and the fibroblast marker ASO2. These results indicate that, in principle, pericytes have the capacity to become fibroblast-like and that pericytes may contribute to the population of fibroblasts in a healed wound.  相似文献   
72.
The effect of dimethoate on gingival and uteral collagen crosslinking was studied in normal and high protein diets fed female albino rats. The gingival and uteral samples were collected from all the groups of rats and percent reversibility of neutral salt soluble collagen gel and the solubility of insoluble collagen in KCNS or urea were determined. The analysis of gingival and uteral samples showed alpha 1 and alpha 2 sub units of neutral salt soluble collagen appreciably increased beta chains and aldehyde content significantly decreased in dimethoate treated animals compared to controls. The results indicate that due to the effect of dimethoate, the crosslinking and maturation of collagen are impaired.  相似文献   
73.
74.
The aim of this study was to evaluate the effects of summer and winter seasons on antioxidant status, body reserve mobilization and biomarkers of stress in Hariana and Sahiwal cows. Twelve lactating cows (six of each Hariana and Sahiwal cows) were included in summer (May to July) and winter season (November to January) study. Microclimatic observations were recorded on daily basis during the experimental period. In both seasons, blood samples were collected at fortnightly intervals for analysis of total antioxidant activity, non-esterified fatty acids (NEFA), β-Hydroxybutyric acid (BHBA), heat shock protein 70 and 90 (HSP70 and HSP90). Antioxidant activity reduced significantly (p < 0.05) in Hariana cattle during summers as compared to winters; whereas, seasonal variation exerts no effect on antioxidant activity in Sahiwal. Blood NEFA concentration was similar among both the breeds over both the seasons but reduced significantly (p < 0.05) during summer season as compared to winters in both the breeds. BHBA concentration was significantly higher (p < 0.05) in Hariana cows than Sahiwal cows during winters, however, no effect on BHBA level was observed during summer season in both the breeds. Significantly, lower plasma cortisol level (p < 0.05) was found during winter season in Sahiwal as well as Hariana cows. Further, Sahiwal exhibited lower plasma cortisol as compared to Hariana in both the seasons. HSP 70 and 90 showed non-significant differences between breeds within both the seasons. However, significantly, lower plasma HSP 70 levels (p < 0.05) were reported during winter season in Sahiwal as well as in Hariana cows. Results of present study revealed that indigenous Sahiwal is more heat tolerant as compared to Hariana breed.  相似文献   
75.
The water-soluble bisphosphine, 1,2-bis(bis(hydroxymethyl)phosphino)ethane (1), was synthesized in near quantitative yield by the reaction of bisphosphine, H2PCH2CH2PH2, with an aqueous formaldehyde in the presence of K2PtCl4. The reaction of this water-soluble bisphosphine 1 with cis-Pt(COD)Cl2 affords the mononuclear bischelate complex, [Pt{(HOH2C)2PCH2CH2P(CH2OH)2}2](Cl)2 (2), in near quantitative yield. The new ligand and complex have been characterized spectroscopically and the structure of the metal complex, 2, was determined by X-ray crystallography. The Pt(II) complex 2 crystallizes in the orthorhombic space group Pbca(a=14.623(1), B=16.216(2), C=9.319(4) Å) with Z=4. The final R value is 0.024.  相似文献   
76.
A microarray (LungCaGxE), based on Illumina BeadChip technology, was developed for high-resolution genotyping of genes that are candidates for involvement in environmentally driven aspects of lung cancer oncogenesis and/or tumor growth. The iterative array design process illustrates techniques for managing large panels of candidate genes and optimizing marker selection, aided by a new bioinformatics pipeline component, Tagger Batch Assistant. The LungCaGxE platform targets 298 genes and the proximal genetic regions in which they are located, using ∼13,000 DNA single nucleotide polymorphisms (SNPs), which include haplotype linkage markers with a minimum allele frequency of 1% and additional specifically targeted SNPs, for which published reports have indicated functional consequences or associations with lung cancer or other smoking-related diseases. The overall assay conversion rate was 98.9%; 99.0% of markers with a minimum Illumina design score of 0.6 successfully generated allele calls using genomic DNA from a study population of 1873 lung-cancer patients and controls.  相似文献   
77.
Previous studies of Ehrlichia chaffeensis infection in the mouse have demonstrated that passive transfer of polyclonal Abs from resistant immunocompetent mice to susceptible SCID mice ameliorated infection and disease, even when Abs were administered during established infection. To identify particular Abs that could mediate bacterial clearance in vivo, E. chaffeensis-specific mAbs were generated and administered to infected SCID mice. Bacterial infection in the livers was significantly lowered after administration of either of two Abs of different isotypes (IgG2a and IgG3). Moreover, repeated administration of one Ab (Ec56.5; IgG2a) rescued mice from an otherwise lethal infection for at least 5 wk. Both protective Abs recognized the E. chaffeensis major outer membrane protein (OMP)-1g. Further studies revealed that both Abs recognized closely related epitopes within the amino terminus of the first hypervariable region of OMP-1g. Analyses of human sera showed that E. chaffeensis-infected patients also generated serological responses to OMP-1g hypervariable region 1, indicating that humans and mice recognize identical or closely related epitopes. These studies demonstrate that OMP-specific mAbs can mediate bacterial elimination in SCID mice, and indicate that Abs, in the absence of cell-mediated immunity, can play a significant role in host defense during infection by this obligate intracellular bacterium.  相似文献   
78.
Genetic analysis of temperature-sensitive male sterilty in rice   总被引:1,自引:0,他引:1  
The present study of genetic analysis is an attempt to precisely characterize diverse temperature-sensitive genic male-sterile (TGMS) lines so as to explore the possibilities of utilizing the most promising in large-scale hybrid seed production. Genetical studies revealed that the TGMS segregants derived from crosses involving TGMS lines ID24 and SA2 expressed differential fertility levels at low-temperature conditions. A majority of these progenies expressed transgressive segregation towards either sterility of fertility, causing instability of sterility and low reversibilty of fertility which may be due to large numbers of single-locus QTLs and their epistatic interactions. We identified two putative genes imparting temperature-sensitive male sterility after observing crosses involving diverse TGMS sources. To identify suitable molecular markers closely linked to the trait we used RAPD, AFLP and microsatellites which generated polymorphism through bulked segregant analysis. AFLP analysis using a smaller genome kit resulted in enormous polymorphism, out of which the combination EAA/MCAG amplified a 330-bp fragment, which closely segregated with the gene at a distance of 5.3 cM. This fragment was eluted for cloning and from the sequence a STS primer (TS200) was developed which produced a dominant polymorphism specific to TGMS. The microsatellite RM257, located earlier on chromosome 9, was linked with the TGMS trait in SA2 at a distance of 6.2 cM. RM257 produced a codominant polymorphism with 145-bp (sterile) and 132-bp (fertile) products. Both individually and collectively, the markers TS200 and RM257 located on either side of the TGMS locus are very useful for marker-assisted selection. Received: 10 April 1999 / Accepted: 29 July 1999  相似文献   
79.
In this paper, we study various lossless compression techniques for electroencephalograph (EEG) signals. We discuss a computationally simple pre-processing technique, where EEG signal is arranged in the form of a matrix (2-D) before compression. We discuss a two-stage coder to compress the EEG matrix, with a lossy coding layer (SPIHT) and residual coding layer (arithmetic coding). This coder is optimally tuned to utilize the source memory and the i.i.d. nature of the residual. We also investigate and compare EEG compression with other schemes such as JPEG2000 image compression standard, predictive coding based shorten, and simple entropy coding. The compression algorithms are tested with University of Bonn database and Physiobank Motor/Mental Imagery database. 2-D based compression schemes yielded higher lossless compression compared to the standard vector-based compression, predictive and entropy coding schemes. The use of pre-processing technique resulted in 6% improvement, and the two-stage coder yielded a further improvement of 3% in compression performance.  相似文献   
80.
A series of 2,5-diaryloxadiazole linked pyrrolo[2,1-c][1,4]benzodiazepine conjugates have been prepared and evaluated for their anticancer activity. These conjugates have shown promising activity with GI50 values ranging from <0.1 to 0.29 μΜ. It is observed that some of these conjugates particularly 4a, 4d, 4i and 4l exhibit significant anticancer activity. Some detailed biological assays relating to the cell cycle aspects associated to Bax and caspases have been examined with a view to understand the mechanism of action of these conjugates.  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