全文获取类型
收费全文 | 51134篇 |
免费 | 4754篇 |
国内免费 | 7973篇 |
出版年
2024年 | 142篇 |
2023年 | 710篇 |
2022年 | 1795篇 |
2021年 | 2814篇 |
2020年 | 2141篇 |
2019年 | 2602篇 |
2018年 | 2319篇 |
2017年 | 1803篇 |
2016年 | 2435篇 |
2015年 | 3577篇 |
2014年 | 4249篇 |
2013年 | 4384篇 |
2012年 | 5327篇 |
2011年 | 4817篇 |
2010年 | 3072篇 |
2009年 | 2797篇 |
2008年 | 3083篇 |
2007年 | 2683篇 |
2006年 | 2366篇 |
2005年 | 1926篇 |
2004年 | 1585篇 |
2003年 | 1456篇 |
2002年 | 1187篇 |
2001年 | 747篇 |
2000年 | 645篇 |
1999年 | 589篇 |
1998年 | 372篇 |
1997年 | 322篇 |
1996年 | 293篇 |
1995年 | 249篇 |
1994年 | 219篇 |
1993年 | 151篇 |
1992年 | 166篇 |
1991年 | 138篇 |
1990年 | 99篇 |
1989年 | 97篇 |
1988年 | 69篇 |
1987年 | 53篇 |
1986年 | 58篇 |
1985年 | 71篇 |
1984年 | 31篇 |
1983年 | 37篇 |
1982年 | 39篇 |
1981年 | 24篇 |
1980年 | 11篇 |
1979年 | 21篇 |
1978年 | 10篇 |
1974年 | 9篇 |
1973年 | 11篇 |
1971年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
目的:探究类风湿性关节炎伴间质性肺病中肿瘤标志物对肺功能的影响。方法:选取2011年3月至2013年3月我院收治的类风湿性关节炎患者88例,根据其是否伴有ILD,分为RA组53例和RA-ILD组35例。检测两组肺功能指标用力肺活量(FVC)、1s用力呼气容积(FEV1)、最大通气量百分比(MVV)、一氧化碳弥散量(DLCO),肿瘤标志物癌胚抗原CEA、癌抗原125(CA125)、癌抗原199(CA199)及抗环胍氨酸肽抗体(抗CCP抗体)的值,并利用统计学方法分析肿瘤标记物与肺功能指标、抗CCP抗体的相关性。结果:RA.ILD组FVC、FEV1、MVV、DLCO均比RA组低,CEA、CA125、CA199均比RA组高,结果比较差异显著具有统计学意义(P〈0.05)。但两组抗CCP抗体含量相比却无明显差异,不具有统计学意义(P〉0.05)。相关性分析显示,CEA与FVC、FEV1、MVV、DLCO呈负相关(P〈0.05),而CA125、CA199却与肺功能指标无相关性,CEA、CA125、CA199与抗CCP抗体均无相关性(P〉0.05)。结论:RA-ILD的肺功能指标均有明显下降,而肿瘤标志物表达水平却明显增高,CEA对肺功能损害影响较大,却与关节损害的关系不大,这为临床对类风湿性关节炎伴间质性肺病早诊断、早治疗提供了依据。 相似文献
992.
西瓜DUS测试标准品种SSR指纹图谱构建及应用 总被引:6,自引:0,他引:6
本研究采用代表最大限度西瓜遗传多样性的SSR核心引物组合,分析了西瓜DUS测试指南中的24份标准品种遗传多样性与核酸指纹。以基于重测序获得的SNP标记构建的17份西瓜材料的系统发育树为参照,对24份标准品种进行了遗传多样性分析,在遗传相似系数0.80处将24份标准品种分为3大类群,分析表明:核酸指纹分类比传统形态学分类更为准确。采用二维(QR)编码构建了西瓜24份标准品种的SSR指纹图谱,并利用本技术以保护品种“京欣2号”与对照品种“京欣1号”为例,进行了DUS分子鉴定测试,共扩增32个SSR位点,“京欣1号”和“京欣2号”之间存在4个位点的差异,品种间遗传相似系数为0.89,比形态学鉴定的差异位点更多且更准。本研究建立的西瓜DUS标准品种SSR指纹图谱与分子检测技术,可以应用到西瓜品种DUS分子检测实践,同时也为西瓜品种纯度与真实性鉴定及遗传背景分析提供了技术方案。 相似文献
993.
994.
Eunice Sok Ping Leong Yan Jun Liu Chan Choy Chum Jing Hua Teng 《Plasmonics (Norwell, Mass.)》2013,8(2):1221-1226
Optical magnetic responses were demonstrated in subwavelength Ag–MgF2–Ag grating structures for transverse magnetic-polarized light. The subwavelength Ag–MgF2–Ag grating structures were fabricated using e-beam lithography followed by a lift-off process. By fixing the Ag–MgF2–Ag strip dimension, the effect of the stripe width on the magnetic resonances was compared for two different grating pitches. With further reduced grating pitch, we pushed the optical magnetic resonances to near UV (deep blue). Numerical simulations confirmed our experimental observations and were in good agreement with the experimental results. 相似文献
995.
Excitation of surface plasmons in metallic nanoparticles is a promising method for increasing the light absorption in solar cells and hence the cell photocurrent. Comprehensive optimization of a nanoparticle fabrication process for enhanced performance of polycrystalline silicon thin-film solar cells is presented. Three factors were studied: the Ag precursor film thickness, annealing temperature and time. The thickness of the precursor film was 10, 14 and 20 nm; annealing temperature was 190, 200, 230 and 260 °C; and annealing time was varied between 20 and 95 min. Performance enhancement due to light-scattering by nanoparticles was calculated by comparing absorption, short-circuit current density and energy conversion efficiency in solar cells with and without nanoparticles formed under different process conditions. Nanoparticles formed from 14-nm-thick Ag precursor film annealed at 230 °C for 53 min result in the highest absorption enhancement in the 700–1,100 nm wavelength range, in the highest enhancement of total short-circuit current density. The highest photocurrent enhancement was 33.5 %, which was achieved by the cell with the highest absorption enhancement in the 700–1,100 nm range. The plasmonic cell efficiency of 5.32 % was achieved without a back reflector and 5.95 % with the back reflector; which is the highest reported efficiency for plasmonic thin-film solar cells. 相似文献
996.
Jun Qian Chen-xu Liu Wu-deng Wang Jing Chen Yu-dong Li Jing-jun Xu Qian Sun 《Plasmonics (Norwell, Mass.)》2013,8(2):955-962
The optical responses of metal nanoparticles induced by subtle variations in geometry, especially by the rounding of the edges and corners, have generated great interest at present due to the requirement of fabricating refined structures of metal nanoparticles and theoretical simulations of the real particles. We study the effect of both inner and outer edge rounding on the optical properties of gold nanobox and gold nanobox dimer with small interparticle distances by using the discrete dipole approximation method. The shift of extinction peaks, the electric field distribution, and the variation of refractive index sensitivities by changing the curvature of the inner and outer edges of gold nanobox are investigated. We demonstrate that the optical properties of nanobox are more sensitive to the outer edge rounding than the inner edge rounding. By edge rounding of two very close gold nanoboxes, the blue shift of the dipolar and the quadrupolar plasmonic resonances of nanobox dimer are shown. Comparing with the inner edge rounding of nanobox dimer, we find that rounding of the outer edges causes the larger shift of the quadrupolar mode and approximate shift of the dipole mode. 相似文献
997.
Jing Rao Sergey Varlamov Jongsung Park Svetlana Dligatch Anatoli Chtanov 《Plasmonics (Norwell, Mass.)》2013,8(2):785-791
Surface plasmonic-enhanced light trapping from metal nanoparticles is a promising way of increasing the light absorption in the active silicon layer and, therefore, the photocurrent of the silicon solar cells. In this paper, we applied silver nanoparticles on the rear side of polycrystalline silicon thin film solar cell and systematically studied the dielectric environment effect on the absorption and short-circuit current density (Jsc) of the device. Three different dielectric layers, magnesium fluoride (MgF2, n?=?1.4), tantalum pentoxide (Ta2O5, n?=?2.2), and titanium dioxide (TiO2, n?=?2.6), were investigated. Experimentally, we found that higher refractive index dielectric coatings results in a redshift of the main plasmonic extinction peak and higher modes were excited within the spectral region that is of interest in our thin film solar cell application. The optical characterization shows that nanoparticles coated with highest refractive index dielectric TiO2 provides highest absorption enhancement 75.6 %; however, from the external quantum efficiency characterization, highest short-circuit current density Jsc enhancement of 45.8 % was achieved by coating the nanoparticles with lower refractive index MgF2. We also further optimize the thickness of MgF2 and a final 50.2 % Jsc enhancement was achieved with a 210-nm MgF2 coating and a back reflector. 相似文献
998.
Jing Lu Mingxin Wen Yurong Huang Xiuquan He Yunshan Wang Qi Wu Zengchun Li Andres Castellanos-Martin Mar Abad Juan J. Cruz-Hernandez Cesar A. Rodriguez Jesus Perez-Losada Jian-Hua Mao Guangwei Wei 《Epigenetics》2013,8(6):571-583
Recently, it has been suggested that C2ORF40 is a candidate tumor suppressor gene in breast cancer. However, the mechanism for reduced expression of C2ORF40 and its functional role in breast cancers remain unclear. Here we show that C2ORF40 is frequently silenced in human primary breast cancers and cell lines through promoter hypermethylation. C2ORF40 mRNA level is significantly associated with patient disease-free survival and distant cancer metastasis. Overexpression of C2ORF40 inhibits breast cancer cell proliferation, migration and invasion. By contrast, silencing C2ORF40 expression promotes these biological phenotypes. Bioinformatics and FACS analysis reveal C2ORF40 functions at G2/M phase by downregulation of mitotic genes expression, including UBE2C. Our results suggest that C2ORF40 acts as a tumor suppressor gene in breast cancer pathogenesis and progression and is a candidate prognostic marker for this disease. 相似文献
999.
Yehui Zhou Jing Lan Wei Wang Qin Shi Yang Lan Zhiyi Cheng Honggeng Guan 《Journal of molecular histology》2013,44(5):555-563
E3 ubiquitin ligases regulate a variety of biological processes through the ubiquitin–proteasome system, together with ubiquitin activating enzyme E1 and ubiquitin-conjugating enzyme E2. Previous studies have demonstrated that zinc and ring finger 3 (ZNRF3), which belongs to the E3 ubiquitin ligases family is involved in the Wnt signalling pathway, which plays an important role in causing cancer. However, the expression and function of ZNRF3 in human gastric adenocarcinoma still remains unclear. Immunohistochemical and western blot analysis showed a significant down-regulation of ZNRF3 protein in gastric adenocarcinoma tissues compared with adjacent normal gastric tissues. In addition, there was a correlation between the down-regulation of ZNRF3 and poor tissue differentiation in gastric adenocarcinoma. To investigate the potential function of ZNRF3 in cell proliferation and apoptosis, a gastric cell line SGC7901 was employed. The over-expression of wild-type ZNRF3, which was accomplished by the transient transfection of recombinant pEGFP-ZNRF3 (or empty plasmids as control) into the cell line SGC7901, was confirmed by western blot analysis. Flow-cytometry-based and Cell Counting Kit-8 assays showed that over-expression of wt ZNRF3 induced apoptosis and suppressed proliferation. ZNRF3-overexpressing gastric cells displayed partly attenuated protein levels of beta-catenin and TCF-4 compared with those transfected with the empty plasmid. Our study demonstrates a novel gastric adenocarcinoma suppressor and reveals that ZNRF3 inhibits gastric cancer cell growth and promotes the cell apoptosis by affecting the Wnt/beta-catenin/TCF signalling pathway. 相似文献
1000.
Jian Chen Feihui Zou Hongran Fu Hui Mao Mingjie Gong Lanchun Ni Xide Xu Jinlong Shi Kaifu Ke Maohong Cao Fei Zhou Wei Shi 《Journal of molecular histology》2013,44(3):271-283
Traumatic brain injury (TBI) triggers a complex series of neurochemical and signaling changes that lead to neuronal dysfunction and overreactive astrocytes. In the current study, we showed that interactions between SCYL1-bp1 and Pirh2 are involved in central nervous system (CNS) injury and repair. Western blot and immunohistochemical analysis of an acute traumatic brain injury model in adult rats revealed significantly increased levels of SCYL1-bp1 and Pirh2 in the ipsilateral brain cortex, compared to contralateral cerebral cortex. Immunofluorescence double-labeling analyses further revealed that SCYL1-bp1 is mainly co-expressed with NeuN. Terminal deoxynucleotidyl transferase-mediated biotinylated-dUTP nick-end labeling staining data supported the involvement of SCYL1-bp1 and Pirh2 in neuronal apoptosis after brain injury. We additionally examined the expression profiles of active caspase-3, which were altered in correlation with the levels of SCYL1-bp1 and Pirh2. Notably, both SCYL1-bp1 and Pirh2 were colocalized with active caspase-3, and all three proteins participated in neuronal apoptosis. Immunoprecipitation experiments further revealed interactions of these proteins with each other in the pathophysiology process. To our knowledge, this is the first study to report interactions between SCYL1-bp1 and Pirh2 in traumatic brain. Our data collectively indicate that SCYL1-bp1 and Pirh2 play important roles in CNS pathophysiology after TBI. 相似文献