全文获取类型
收费全文 | 1007篇 |
免费 | 69篇 |
国内免费 | 1篇 |
出版年
2023年 | 15篇 |
2022年 | 24篇 |
2021年 | 36篇 |
2020年 | 12篇 |
2019年 | 21篇 |
2018年 | 25篇 |
2017年 | 22篇 |
2016年 | 32篇 |
2015年 | 60篇 |
2014年 | 50篇 |
2013年 | 84篇 |
2012年 | 75篇 |
2011年 | 99篇 |
2010年 | 29篇 |
2009年 | 47篇 |
2008年 | 50篇 |
2007年 | 42篇 |
2006年 | 46篇 |
2005年 | 24篇 |
2004年 | 43篇 |
2003年 | 22篇 |
2002年 | 26篇 |
2001年 | 23篇 |
2000年 | 30篇 |
1999年 | 21篇 |
1998年 | 10篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 7篇 |
1992年 | 10篇 |
1991年 | 11篇 |
1990年 | 12篇 |
1989年 | 9篇 |
1988年 | 10篇 |
1987年 | 8篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1979年 | 1篇 |
1976年 | 2篇 |
1974年 | 1篇 |
排序方式: 共有1077条查询结果,搜索用时 218 毫秒
51.
In conifers, the cytochrome P450 monooxygenase of the CYP720B family plays an important role in the synthesis of diterpene resin acids, which are specialised metabolites of the oleoresin defence. We isolated CYP720B19 from Pinus armandi and found that it belongs to the CYP720B family. The CYP720B19 open reading frame of 1467 bp encodes a protein of 488 amino acid residues with high similarity to abietadienol/abietadienal oxidase. Differential expression of the CYP720B19 gene significantly changed when plants were inoculated with the fungus Leptographium qinlingensis, mechanically wounded, or treated with methyl jasmonate (MeJa) and Tween at 4 days and 8 days. Increased expression of the CYP720B19 gene after these treatments suggested that the gene was involved in pine defence against inoculation by L. qinlingensis, MeJa treatment and mechanical injury. 相似文献
52.
Tran Cuong Manh Van Pham Hai Nguyen Hien Thuy Nguyen Thuy Thi Vu Lam Dinh Do Tung Hoang 《Plasmonics (Norwell, Mass.)》2019,14(6):1587-1592
Plasmonics - Since the metamaterial perfect absorber (MPA) is composed of electromagnetic resonance structures, the main operational mechanism of the MPA is electromagnetic resonance. In this work,... 相似文献
53.
54.
Shafket Rasool Doan Van Vu Chang Eun Song Hang Ken Lee Sang Kyu Lee Jong‐Cheol Lee Sang‐Jin Moon Won Suk Shin 《Liver Transplantation》2019,9(21)
The room temperature (RT) processability of the photoactive layers in polymer solar cells (PSCs) from halogen‐free solvent along with their highly reproducible power conversion efficiencies (PCEs) and intrinsic thickness tolerance are extremely desirable for the large‐area roll‐to‐roll (R2R) production. However, most of the photoactive materials in PSCs require elevated processing temperatures due to their strong aggregation, which are unfavorable for the industrial R2R manufacturing of PSCs. These limiting factors for the commercialization of PSCs are alleviated by synthesizing random terpolymers with components of (2‐decyltetradecyl)thiophen‐2‐yl)naphtho[1,2‐c:5,6‐c′]bis[1,2,5]thiadiazole and bithiophene substituted with methyl thiophene‐3‐carboxylate (MTC). In contrast to the temperature‐dependent PNTz4T polymer, the resulting random terpolymers (PNTz4T‐MTC) show better solubility, slightly reduced crystallinity and aggregation, and weaker intermolecular interaction, thus enabling PNTz4T‐MTC to be processed at RT from a halogen‐free solvent. Particularly, the PNTz4T‐5MTC‐based photoactive layer exhibits an excellent PCE of 9.66%, which is among the highest reported PCEs for RT and ecofriendly halogen‐free solvent processed fullerene‐based PSCs, and a thickness tolerance with a PCE exceeding 8% from 100 to 520 nm. Finally, large‐area modules fabricated with the PNTz4T and PNTz4T‐5MTC polymer have shown 4.29% and 6.61% PCE respectively, with an area as high as 54.45 cm2 in air. 相似文献
55.
Epithelial-vascular cross talk mediated by VEGF-A and HGF signaling directs primary septae formation during distal lung morphogenesis 总被引:1,自引:0,他引:1
There is increasing evidence that epithelial-vascular interactions are essential for tissue patterning. Here we identified components of the molecular cross talk between respiratory epithelial cells and pulmonary capillaries necessary for the formation of the gas exchange surface of the lung. Selective inactivation of the Vegf-A gene in respiratory epithelium results in an almost complete absence of pulmonary capillaries, demonstrating the dependence of pulmonary capillary development on epithelium-derived Vegf-A. Deficient capillary formation in Vegf-A deficient lungs is associated with a defect in primary septae formation, a morphogenetic process critical for distal lung morphogenesis, coupled with suppression of epithelial cell proliferation and decreased hepatocyte growth factor (Hgf) expression. Lung endothelial cells express Hgf, and selective deletion of the Hgf receptor gene in respiratory epithelium phenocopies the malformation of septae, confirming the requirement for epithelial Hgf signaling in normal septae formation and suggesting that Hgf serves as an endothelium-derived factor that signals to the epithelium. Our findings support a mechanism for primary septae formation dependent on reciprocal interactions between respiratory epithelium and the underlying vasculature, establishing the dependence of pulmonary capillary development on epithelium-derived Vegf-A, and identify Hgf as a putative endothelium-derived factor that mediates the reciprocal signaling from the vasculature to the respiratory epithelium. 相似文献
56.
Tsikas D Thum T Becker T Pham VV Chobanyan K Mitschke A Beckmann B Gutzki FM Bauersachs J Stichtenoth DO 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2007,851(1-2):229-239
Dimethylamine [DMA, (CH(3))(2)NH)] is abundantly present in human urine. Main sources of urinary DMA have been reported to include trimethylamine N-oxide, a common food component, and asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide (NO) synthesis. ADMA is excreted in the urine in part unmetabolized and in part after hydrolysis to DMA by dimethylarginine dimethylaminohydrolase (DDAH). Here we describe a GC-MS method for the accurate and rapid quantification of DMA in human urine. The method involves use of (CD(3))(2)NH as internal standard, simultaneous derivatization with pentafluorobenzoyl chloride and extraction in toluene, and selected-ion monitoring of m/z 239 for DMA and m/z 245 for (CD(3))(2)NH in the electron ionization mode. GC-MS analysis of urine samples from 10 healthy volunteers revealed a DMA concentration of 264+/-173 microM equivalent to 10.1+/-1.64 micromol/mmol creatinine. GC-tandem MS analysis of the same urine samples revealed an ADMA concentration of 27.3+/-15.3 microM corresponding to 1.35+/-1.2 micromol/mmol creatinine. In these volunteers, a positive correlation (R=0.83919, P=0.0024) was found between urinary DMA and ADMA, with the DMA/ADMA molar ratio being 10.8+/-6.2. Elevated excretion rates of DMA (52.9+/-18.5 micromol/mmol creatinine) and ADMA (3.85+/-1.65 micromol/mmol creatinine) were found by the method in 49 patients suffering from coronary artery disease, with the DMA/ADMA molar ratio also being elevated (16.8+/-12.8). In 12 patients suffering from end-stage liver disease, excretion rates of DMA (47.8+/-19.7 micromol/mmol creatinine) and ADMA (5.6+/-1.5 micromol/mmol creatinine) were found to be elevated, with the DMA/ADMA molar ratio (9.17+/-4.2) being insignificantly lower (P=0.46). Between urinary DMA and ADMA there was a positive correlation (R=0.6655, P<0.0001) in coronary artery disease, but no correlation (R=0.27339) was found in end-stage liver disease. 相似文献
57.
Marijana Vučinić Ivana Hajzler Jelena Terzin Katarina Nenadović Ljiljana Janković Eva Voslarova 《Anthrozo?s》2019,32(1):129-139
The objective of the research was to determine the profile of reptile owners (n = 238) in terms of their socio-demographic characteristics and evaluations of veterinarians’ expertise. Reptile owners living in four non-EU Balkan countries (Bosnia and Herzegovina, Macedonia, Montenegro, and Serbia) were randomly selected from two social networks. Statistically significant differences were found in snake, lizard, and turtle owners (p < 0.05) in terms of gender, employment status, and monthly earnings. Male owners of reptiles were slightly more numerous (52%) compared with female owners (48%). Sixty-four percent of reptile owners were over 20 years old. The unemployed reptile owners (16%) were about five times fewer in number compared with those who studied at university and those who were employed. Forty-one percent of reptile owners declared high monthly incomes. Forty percent of reptile owners never contacted and had no experience with veterinarians. Fifty-eight percent of reptile owners contacted or visited veterinarians due to the medical condition of their animals, 14% of them contacted veterinarians for advice on reptile keeping, and only 6% did so for a preventive veterinary examination. Forty-seven percent of reptile owners were satisfied with veterinary services. The importance of the results of this survey is that they can provide a basis for adopting legislation on the ownership of reptiles as pet animals, together with being a baseline for monitoring subsequent changes in interest in these animals as pets. The results also identify the need for more dedication from veterinarians in educating reptile owners, and for necessary adjustments in veterinary education. 相似文献
58.
59.
OSP/claudin-11 forms a complex with a novel member of the tetraspanin super family and beta1 integrin and regulates proliferation and migration of oligodendrocytes 下载免费PDF全文
Tiwari-Woodruff SK Buznikov AG Vu TQ Micevych PE Chen K Kornblum HI Bronstein JM 《The Journal of cell biology》2001,153(2):295-305
Oligodendrocyte-specific protein (OSP)/claudin-11 is a major component of central nervous system myelin and forms tight junctions (TJs) within myelin sheaths. TJs are essential for forming a paracellular barrier and have been implicated in the regulation of growth and differentiation via signal transduction pathways. We have identified an OSP/claudin-11-associated protein (OAP)1, using a yeast two-hybrid screen. OAP-1 is a novel member of the tetraspanin superfamily, and it is widely expressed in several cell types, including oligodendrocytes. OAP-1, OSP/claudin-11, and beta1 integrin form a complex as indicated by coimmunoprecipitation and confocal immunocytochemistry. Overexpression of OSP/claudin-11 or OAP-1 induced proliferation in an oligodendrocyte cell line. Anti-OAP-1, anti-OSP/claudin-11, and anti-beta1 integrin antibodies inhibited migration of primary oligodendrocytes, and migration was impaired in OSP/claudin-11-deficient primary oligodendrocytes. These data suggest a role for OSP/claudin-11, OAP-1, and beta1 integrin complex in regulating proliferation and migration of oligodendrocytes, a process essential for normal myelination and repair. 相似文献
60.