全文获取类型
收费全文 | 15219篇 |
免费 | 1453篇 |
国内免费 | 2001篇 |
专业分类
18673篇 |
出版年
2024年 | 48篇 |
2023年 | 226篇 |
2022年 | 438篇 |
2021年 | 719篇 |
2020年 | 540篇 |
2019年 | 675篇 |
2018年 | 671篇 |
2017年 | 531篇 |
2016年 | 677篇 |
2015年 | 992篇 |
2014年 | 1209篇 |
2013年 | 1229篇 |
2012年 | 1493篇 |
2011年 | 1342篇 |
2010年 | 854篇 |
2009年 | 782篇 |
2008年 | 914篇 |
2007年 | 784篇 |
2006年 | 747篇 |
2005年 | 558篇 |
2004年 | 499篇 |
2003年 | 441篇 |
2002年 | 356篇 |
2001年 | 187篇 |
2000年 | 175篇 |
1999年 | 144篇 |
1998年 | 128篇 |
1997年 | 88篇 |
1996年 | 88篇 |
1995年 | 72篇 |
1994年 | 75篇 |
1993年 | 59篇 |
1992年 | 83篇 |
1991年 | 59篇 |
1990年 | 71篇 |
1989年 | 53篇 |
1988年 | 47篇 |
1987年 | 39篇 |
1986年 | 44篇 |
1985年 | 39篇 |
1984年 | 58篇 |
1983年 | 41篇 |
1982年 | 39篇 |
1981年 | 47篇 |
1980年 | 31篇 |
1979年 | 28篇 |
1978年 | 26篇 |
1977年 | 25篇 |
1975年 | 33篇 |
1974年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Nguyen Thi Quynh Mai Nguyen Thi Kim Thu Le Dac Tuyen Truong Chi Lam Vu Dinh Lam Nguyen Thi Quynh Hoa 《Plasmonics (Norwell, Mass.)》2021,16(5):1583-1592
Plasmonics - Developing a simple structure using low-cost material that enables both large-scale fabrication and broadband absorption response is highly desirable but very challenging for achieving... 相似文献
72.
炎症反应以炎症因子为代表,是骨关节炎(osteoarthritis,OA)中软骨下骨发生病变的重要机制。炎症因子半乳糖凝集素?3(galectin?3,Gal?3)会引起软骨下骨OA样变,但机制尚不清楚。利用因膝关节OA行全膝关节置换患者的胫骨平台标本,培养成骨细胞。分别在正常氧和缺氧条件下用Gal?3处理成骨细胞后,检测骨钙素、ERRα和Sirtuin 1的表达情况。同时,给予矿化液培养的成骨细胞以Gal?3处理,28 d后使用茜素红染色检测成骨细胞矿化程度并进行定量分析。结果显示,Gal?3抑制成骨细胞骨钙素的表达,在缺氧条件下诱导ERRα和Sirtuin1的表达,在正常氧条件下Gal?3促进OA成骨细胞的矿化。正常氧条件下,Gal?3可以诱导OA成骨细胞的异常矿化,缺氧条件下Gal?3促进成骨,表明Gal?3在OA成骨细胞的矿化中扮演重要角色。 相似文献
73.
Britt-Marie Sundblad Sven-Arne Jansson Lennarth Nystr?m Peter Arvidsson Bo Lundb?ck Kjell Larsson 《PloS one》2013,8(12)
Background
Little is known about the management of patients suffering from chronic obstructive pulmonary disease (COPD) during the last years of life. The aim of the study was to describe how management of COPD is performed in Sweden during the last two years of life.Methods
From the nationwide Cause of Death register all individuals with COPD as the underlying cause of death during two years were identified in one sparsely and one densely populated area of Sweden. Data were collected from medical records using a pre-defined protocol, especially developed for this purpose.Results
Of 822 individuals with COPD as underlying cause of death, medical records from 729 were available. The COPD diagnosis was based on lung function measurements in approximately half of the patients and median age at COPD diagnosis was 74 years (range 34-95). Women died at younger age, median 78 years (range 52-96) than did men (80 years (51-99)). The median survival time from diagnosis to death was 6 years in men and women in both areas. Among women and men 8.3% and 4.3% were never smokers, respectively. The structure of COPD management differed between the two areas, with utilization of physiotherapists, dieticians and working therapists being more used in the northern area, likely because of differences in accessibility to care institutions.Conclusions
In Sweden COPD is mostly diagnosed late in life and often not verified by lung function measurements. Opposite to the general population, women with COPD die at a lower age than men. 相似文献74.
75.
Yuwon Park Nam‐Soon Choi Sangjin Park Seung Hee Woo Soojin Sim Bo Yun Jang Seung M. Oh Soojin Park Jaephil Cho Kyu Tae Lee 《Liver Transplantation》2013,3(2):206-212
Remarkable improvements in the electrochemical performance of Si materials for Li‐ion batteries have been recently achieved, but the inherent volume change of Si still induces electrode expansion and external cell deformation. Here, the void structure in Si‐encapsulating hollow carbons is optimized in order to minimize the volume expansion of Si‐based anodes and improve electrochemical performance. When compared to chemical etching, the hollow structure is achieved via electroless etching is more advanced due to the improved electrical contact between carbon and Si. Despite the very thick electrodes (30 ~ 40 μm), this results in better cycle and rate performances including little capacity fading over 50 cycles and 1100 mA h g?1 at 2C rate. Also, an in situ dilatometer technique is used to perform a comprehensive study of electrode thickness change, and Si‐encapsulating hollow carbon mitigates the volume change of electrodes by adoption of void space, resulting in a small volume increase of 18% after full lithiation corresponding with a reversible capacity of about 2000 mA h g?1. 相似文献
76.
Zhangwei Wang Bin Li Shishan Yu Xuewen Lai Bo Liu Jie Chen Toshimitsu Hayashi 《Phytochemistry letters》2013,6(3):461-466
Chemical investigation of the aqueous extract of the aerial portion of Sibiraea angustata led to the isolation of eight new monoterpene acylglucosides named sibiraglucoside A–H (1–8) and two known monoterpenes, sibiraic acid (9) and sibiskoside (10). Their structures were elucidated through extensive spectroscopic data analysis (including 1D and 2D NMR and HRESIMS experiments) and compared to literature data. In the in vitro bioassay, all of the compounds showed moderate hypolipidemic effects. 相似文献
77.
Qiang Wang Bo Xiang Wei Deng Junyao Wu Mingli Li Xiaohong Ma Yingcheng Wang Lijun Jiang Grainne McAlonan Siew E. Chua Pak C. Sham Xun Hu Tao Li 《PloS one》2013,8(9)
Reduced Gray matter (GM) volume is a core feature of schizophrenia. Mapping genes that is associated with the heritable disease-related phenotypes may be conducive to elucidate the pathogenesis of schizophrenia. This study aims to identify the common genetic variants that underlie the deficits of GM volume in schizophrenia. High-resolution T1 images and whole genome genotyping data were obtained from 74 first-episode treatment-naïve patients with schizophrenia and 51 healthy controls in the Mental Health Centre of the West China Hospital, Sichuan University. All participants were scanned using a 3T MR imaging system and were genotyped using the HumanHap660 Bead Array. Reduced GM volumes in three brain areas including left hOC3v in the collateral sulcus of visual cortex (hOC3vL), left cerebellar vermis lobule 10 (vermisL10) and right cerebellar vermis lobule 10 (vermisR10) were found in patients with schizophrenia. There was a group by genotype interaction when genotypes from genome-wide scan were subsequently considered in the case-control analyses. SNPs from three genes or chromosomal regions (TBXAS1, PIK3C2G and HS3ST5) were identified to predict the changes of GM volume in hOC3vL, vermisL10 and vermisR10. These results also highlighted the usefulness of endophenotype in exploring the pathogenesis of neuropsychiatric diseases such as schizophrenia although further independent replication studies are needed in the future. 相似文献
78.
Yu-Jue Wang Wen Liu Chi Chen Li-Meng Yan Jun Song Kun-Yuan Guo Gang Wang Qing-Hong Wu Wei-Wang Gu 《PloS one》2013,8(3)
Background
The radiation-induced energy metabolism dysfunction related to injury and radiation doses is largely elusive. The purpose of this study is to investigate the early response of energy metabolism in small intestinal tissue and its correlation with pathologic lesion after total body X-ray irradiation (TBI) in Tibet minipigs.Methods and Results
30 Tibet minipigs were assigned into 6 groups including 5 experimental groups and one control group with 6 animals each group. The minipigs in these experimental groups were subjected to a TBI of 2, 5, 8, 11, and 14 Gy, respectively. Small intestine tissues were collected at 24 h following X-ray exposure and analyzed by histology and high performance liquid chromatography (HPLC). DNA contents in this tissue were also examined. Irradiation causes pathologic lesions and mitochondrial abnormalities. The Deoxyribonucleic acid (DNA) content-corrected and uncorrected adenosine-triphosphate (ATP) and total adenine nucleotides (TAN) were significantly reduced in a dose-dependent manner by 2–8 Gy exposure, and no further reduction was observed over 8 Gy.Conclusion
TBI induced injury is highly dependent on the irradiation dosage in small intestine and inversely correlates with the energy metabolism, with its reduction potentially indicating the severity of injury. 相似文献79.
Fusheng Jiang Weiping Li Yanfen Huang Yitao Chen Bo Jin Nipi Chen Zhishan Ding Xinghong Ding 《PloS one》2013,8(2)
This study was carried out to evaluate the utilization probability of the fibrous root part (FRP) of Bletilla striata, which was usually discarded and harvesting pseudobulb part (PSP). The chemical composition, total phenolic content, DPPH radical scavenging activity, Ferric-reducing antioxidant power and tyrosinase inhibition activity were compared between FRP and PSP. Antioxidant and pro-oxidant effect as well as antitumor effect of the extract of FRP and PSP were analyzed by in vitro cell system as well. Thin layer chromatography and high performance liquid chromatography analysis indicated that the chemical compositions in the two parts were similar, but the content in FRP was much higher than PSP. Meanwhile, the FRP extracts showed higher phenolic content, stronger DPPH scavenging activity, Ferric-reducing antioxidant capacity and tyrosinase inhibition activity. Sub-fraction analysis revealed that the distribution characteristic of phenolic components and other active constituents in FRP and PSP were consistent, and mainly deposited in chloroform and acetoacetate fractions. Especially, the chloroform sub-fraction (sch) of FRP showed extraordinary DPPH scavenging activity and tyrosinase inhibition activity, with IC50 0.848 mg/L and 4.3 mg/L, respectively. Besides, tyrosinase inhibition activity was even stronger than the positive compound arbutin (31.8 mg/L). Moreover, In vitro cell system analysis confirmed that FRP extract exerts comparable activity with PSP, especially, the sub-fraction sch of FRP showed better antioxidant activity at low dosage and stronger per-oxidant activity at high dosage, and both sch of FRP and PSP can dose-dependent induce HepG2 cells apoptosis, which implied tumor therapeutic effect. Considering that an additional 0.3 kg FRP would be obtained when producing 1.0 kg PSP, our work demonstrated that FRP is very potential to be used together with PSP. 相似文献
80.
Turtle barnacles are common epibionts on marine organisms. Chelonibia testudinaria is specific on marine turtles whereas C. patula is a host generalist, but rarely found on turtles. It has been questioned why C. patula, being abundant on a variety of live substrata, is almost absent from turtles. We evaluated the genetic (mitochondrial COI, 16S and 12S rRNA, and amplified fragment length polymorphism (AFLP)) and morphological differentiation of C. testudinaia and C. patula from different hosts, to determine the mode of adaptation exhibited by Chelonibia species on different hosts. The two taxa demonstrate clear differences in shell morphology and length of 4–6th cirri, but very similar in arthropodal characters. Moreover, we detected no genetic differentiation in mitochondrial DNA and AFLP analyses. Outlier detection infers insignificant selection across loci investigated. Based on combined morphological and molecular evidence, we proposed that C. testudinaria and C. patula are conspecific, and the two morphs with contrasting shell morphologies and cirral length found on different host are predominantly shaped by developmental plasticity in response to environmental setting on different hosts. Chelonibia testudinaria is, thus, a successful general epibiotic fouler and the phenotypic responses postulated can increase the fitness of the animals when they attach on hosts with contrasting life-styles. 相似文献