全文获取类型
收费全文 | 22185篇 |
免费 | 1522篇 |
国内免费 | 992篇 |
专业分类
24699篇 |
出版年
2024年 | 53篇 |
2023年 | 295篇 |
2022年 | 631篇 |
2021年 | 1014篇 |
2020年 | 674篇 |
2019年 | 901篇 |
2018年 | 889篇 |
2017年 | 679篇 |
2016年 | 958篇 |
2015年 | 1335篇 |
2014年 | 1511篇 |
2013年 | 1753篇 |
2012年 | 1950篇 |
2011年 | 1821篇 |
2010年 | 1017篇 |
2009年 | 908篇 |
2008年 | 1012篇 |
2007年 | 928篇 |
2006年 | 847篇 |
2005年 | 726篇 |
2004年 | 633篇 |
2003年 | 527篇 |
2002年 | 475篇 |
2001年 | 309篇 |
2000年 | 320篇 |
1999年 | 284篇 |
1998年 | 175篇 |
1997年 | 161篇 |
1996年 | 181篇 |
1995年 | 162篇 |
1994年 | 136篇 |
1993年 | 102篇 |
1992年 | 152篇 |
1991年 | 150篇 |
1990年 | 124篇 |
1989年 | 97篇 |
1988年 | 98篇 |
1987年 | 101篇 |
1986年 | 70篇 |
1985年 | 89篇 |
1984年 | 50篇 |
1983年 | 53篇 |
1982年 | 27篇 |
1981年 | 26篇 |
1980年 | 24篇 |
1979年 | 35篇 |
1978年 | 28篇 |
1977年 | 20篇 |
1975年 | 29篇 |
1974年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Zenghong Ma Wei Cai Lei Wang Chenglin Du Weiwei Luo Linyu Niu Shuqing Xue Mengxin Ren Xinzheng Zhang Jingjun Xu 《Plasmonics (Norwell, Mass.)》2016,11(6):1481-1486
Magnetic hot spots, which implies confinements and enhancements of magnetic fields, are demonstrated in graphene junctions (GJs) in the mid-infrared range. The appearance of magnetic hot spots in GJs comes from the conduction currents in the junction. In further, the extinction resonance peaks suffer blue shift, along with the increases in the magnetic fields inside junction area, when the junction width reduces. In opposite to the circumstances for electric field enhancements, neither magnetic field enhancements nor resonance frequency of GJs is perturbed by the intrinsic nonlocal electronic response of graphene. Such nonlocality immunized magnetic enhancement could be explained by the polarization dependent property of nonlocal effect. 相似文献
92.
93.
Marianna Małek Bożena Bogusz Paulina Mrowiec Mariusz Szuta Maciej Opach Iwona Skiba-Kurek Paweł Nowak Karolina Klesiewicz Alicja Budak Elżbieta Karczewska 《Revista iberoamericana de micología》2018,35(3):140-146
Background
Fungal rhinosinusitis has become an increasingly recognized disease, being Aspergillus species responsible for most of the cases. Its diagnosis is quite difficult because of the non-specific symptoms and low sensitivity of the current diagnostic methods.Aims
An Aspergillus-specific nested polymerase chain reaction (PCR) assay using biopsy specimens taken from the maxillary sinuses was performed in order to assess its usefulness. Conventional diagnostic methods (histology and culture) were also carried out.Methods
A case–control study was performed in the Institute of Stomatology, Jagiellonian University in Kraków, between 2011 and 2014. The case group consisted of 21 patients with suspected rhinosinusal mycetoma while the control group included 46 patients with no suspicion of fungal rhinosinusitis. The two-step PCR assay amplified an Aspergillus specific portion of the 18S rRNA gene. Interval estimation of sensitivity, specificity, positive (PPV) and negative (NPV) predictive values were calculated to assess the diagnostic test performance. The agreement between the PCR and the other tests was evaluated using the Kappa coefficient (k).Results
Ninety percent of the samples obtained from patients diagnosed with mycetoma yielded positive PCR results. The PCR showed almost perfect concordance with histology (k = 0.88). Sensitivity, specificity, PPV and NPV estimates were 90%; 95% CI: (55.5–99.7%), 98.3%; 95% CI: (90.9–100%), 90%; 95% CI: (55.5–99.7%) and 98.3%; 95% CI: (90.9–100%), respectively. One clinical sample showed growth of Aspergillus fumigatus and positive PCR despite the negative histological examination.Conclusions
Nested PCR assay is a promising diagnostic tool to evaluate the presence of Aspergillus in the tissue of maxillary sinus from patients with suspicion of sinus aspergillosis. 相似文献94.
Chun-Xiang Fu De-Xiu Zhao Xiao-Feng Xue Zhi-Ping Jin Feng Shan Ma 《Process Biochemistry》2005,40(12):3789-3794
Agrobacterium rhizogenes-mediated genetic transformation of Saussurea involucrata was investigated. Four bacterial strains, A4, LBA 9402, R1000 and R1601 and three explant types, leaf blade, petiole and root, were examined. Over 100 hairy root lines were successfully established with strains R1601, R1000 and LBA9402, but none with A4. The highest transformation efficiency of 67% was achieved by using strain R1601 with root explants. One hairy root line isolated from this combination, HR1601-1, produced up to 43.5 ± 1.13 mg syringin g−1 dw, which is about 50-fold higher than that in the wild type plants.Two other lines, HR1000-1 and HRLBA9402-1, isolated from R1000- and LBA9402-transformed roots, respectively, also displayed high capacity of syringin production, being 32.5 ± 3.08 and 39.7 ± 1.37 mg syringin g−1 dw. These three lines were characterized in detail. Polymerase chain reaction analyses confirmed these root lines were of A. rhizogenes origin. 相似文献
95.
Liang Ma Meixiang Xu Julia R. Forman Jane Clarke Andres F. Oberhauser 《The Journal of biological chemistry》2009,284(47):32942-32949
Mutations in polycystin-1 (PC1) can cause autosomal dominant polycystic kidney disease, which is a leading cause of renal failure. The available evidence suggests that PC1 acts as a mechanosensor, receiving signals from the primary cilia, neighboring cells, and extracellular matrix. PC1 is a large membrane protein that has a long N-terminal extracellular region (about 3000 amino acids) with a multimodular structure including 16 Ig-like polycystic kidney disease (PKD) domains, which are targeted by many naturally occurring missense mutations. Nothing is known about the effects of these mutations on the biophysical properties of PKD domains. Here we investigate the effects of several naturally occurring mutations on the mechanical stability of the first PKD domain of human PC1 (HuPKDd1). We found that several missense mutations alter the mechanical unfolding pathways of HuPKDd1, resulting in distinct mechanical phenotypes. Moreover, we found that these mutations also alter the thermodynamic stability of a structurally homologous archaeal PKD domain. Based on these findings, we hypothesize that missense mutations may cause autosomal dominant polycystic kidney disease by altering the stability of the PC1 ectodomain, thereby perturbing its ability to sense mechanical signals. 相似文献
96.
N-乙酰氨基葡萄糖化在信号转导中的作用 总被引:2,自引:0,他引:2
蛋白质磷酸化在生命活动以及信号转导过程中的重要作用已经被研究证实,但不少研究发现在大多数核,胞液蛋白质上不仅存在磷酸化动态修饰,还存在广泛的动态N-乙酰氨基葡萄糖修饰,N-乙酰氨基葡萄糖基转移酶和N-乙酰氨基葡萄糖基酶以类似于蛋白质激酶和磷酸酶的方式调节蛋白质是否发生N-乙酰氨基葡萄糖化。N-乙酰氨基葡萄糖化蛋白质主要分布在细胞核与胞液,其生理功能涉及细胞基本生命活动和调节信号传递。N-乙酰氨基葡萄糖的作用基础与阻断或影响蛋白质的磷酸化有关。 相似文献
97.
98.
Identification of domain required for catalytic activity of auxilin in supporting clathrin uncoating by Hsc70 总被引:1,自引:0,他引:1
Ma Y Greener T Pacold ME Kaushal S Greene LE Eisenberg E 《The Journal of biological chemistry》2002,277(51):49267-49274
During clathrin-mediated endocytosis Hsc70, supported by the J-domain protein auxilin, uncoats clathrin-coated vesicles. Auxilin contains both a clathrin-binding domain and a J-domain that binds Hsc70, and it has been suggested that these two domains are both necessary and sufficient for auxilin activity. To test this hypothesis, we created a chimeric protein consisting of the J-domain of auxilin linked to the clathrin-binding domain of the assembly protein AP180. This chimera supported uncoating, but unlike auxilin it acted stoichiometrically rather than catalytically because, like Hsc70, it remained associated with the uncoated clathrin. This observation supports our proposal that Hsc70 chaperones uncoated clathrin by inducing formation of a stable Hsc70-clathrin-AP complex. It also shows that Hsc70 acts by dissociating individual clathrin triskelions rather than cooperatively destabilizing clathrin-coated vesicles. Because the chimera lacks the C-terminal subdomain of the auxilin clathrin-binding domain, it seemed possible that this subdomain is required for auxilin to act catalytically, and indeed its deletion caused auxilin to act stoichiometrically. In contrast, deletion of the N-terminal subdomain weakened auxilin-clathrin binding and prevented auxilin from polymerizing clathrin. Therefore the C-terminal subdomain of the clathrin-binding domain of auxilin is required for auxilin to act catalytically, whereas the N-terminal subdomain strengthens auxilin-clathrin binding. 相似文献
99.
Three-dimensional quantitative structure–activity relationship (3D-QSAR) studies were performed on a series of substituted 1,4-dihydroindeno[1,2-c]pyrazoles inhibitors, using molecular docking and comparative molecular field analysis (CoMFA). The docking results from GOLD 3.0.1 provide a reliable conformational alignment scheme for the 3D-QSAR model. Based on the docking conformations and alignments, highly predictive CoMFA model was built with cross-validated q 2 value of 0.534 and non-cross-validated partial least-squares analysis with the optimum components of six showed a conventional r 2 value of 0.911. The predictive ability of this model was validated by the testing set with a conventional r 2 value of 0.812. Based on the docking and CoMFA, we have identified some key features of the 1,4-dihydroindeno[1,2-c]pyrazoles derivatives that are responsible for checkpoint kinase 1 inhibitory activity. The analyses may be used to design more potent 1,4-dihydroindeno[1,2-c]pyrazoles derivatives and predict their activity prior to synthesis. 相似文献
100.
A thermophilic bacterial strain GXN151 which could degrade Avicel efficiently was isolated and identified as Bacillus licheniformis. A genomic library of GXN151 was constructed and two novel endoglucanase genes designated cel9A and cel12A were isolated by screening the library on carboxylmethyl cellulase indicator plates. The analysis of amino acid sequences deduced from the genes indicated that Cel9A consisted of a catalytic domain belonging to glycosyl hydrolase family 9, a linker domain, and a carbohydrate binding module family 3 from N-terminal to C-terminal; Cel12A had only one catalytic domain belonging to glycosyl hydrolase family 12. The combinations of Cel9A and Cel12A produced by the recombinant E. coli exhibited synergistic action against substrates of carboxylmethyl cellulose as well as Avicel. 相似文献