全文获取类型
收费全文 | 115740篇 |
免费 | 2460篇 |
国内免费 | 3686篇 |
出版年
2024年 | 44篇 |
2023年 | 322篇 |
2022年 | 610篇 |
2021年 | 1197篇 |
2020年 | 884篇 |
2019年 | 1075篇 |
2018年 | 12661篇 |
2017年 | 11213篇 |
2016年 | 8325篇 |
2015年 | 2076篇 |
2014年 | 2134篇 |
2013年 | 2219篇 |
2012年 | 6482篇 |
2011年 | 14797篇 |
2010年 | 13238篇 |
2009年 | 9427篇 |
2008年 | 11116篇 |
2007年 | 12570篇 |
2006年 | 1357篇 |
2005年 | 1389篇 |
2004年 | 1764篇 |
2003年 | 1724篇 |
2002年 | 1381篇 |
2001年 | 657篇 |
2000年 | 539篇 |
1999年 | 361篇 |
1998年 | 256篇 |
1997年 | 216篇 |
1996年 | 191篇 |
1995年 | 112篇 |
1994年 | 159篇 |
1993年 | 111篇 |
1992年 | 125篇 |
1991年 | 116篇 |
1990年 | 75篇 |
1989年 | 53篇 |
1988年 | 57篇 |
1987年 | 46篇 |
1986年 | 21篇 |
1985年 | 27篇 |
1984年 | 25篇 |
1983年 | 35篇 |
1982年 | 18篇 |
1980年 | 10篇 |
1972年 | 251篇 |
1971年 | 279篇 |
1965年 | 21篇 |
1962年 | 24篇 |
1944年 | 12篇 |
1940年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
941.
Fang-ping Wang Guo-ping Zhan Yu-ren Jiang Jing-nan Guo Zhi-gang Yin Rui Feng 《Journal of molecular modeling》2013,19(8):3135-3142
The adsorption behaviors of three carboxyl hydroxamic acids on diaspore (010) and kaolinite (001) have been studied by density functional theory (DFT) and molecular dynamics (MD) method. The results indicated that carboxyl hydroxamic acids could adsorb on diaspore surface by ionic bonds and hydrogen bonds, and adsorb on kaolinite surface by hydrogen bonds. The models of carboxyl hydroxamic acids adsorbed on diaspore and kaolinite surfaces are proposed. Figure
Carboxyl hydroxamic acids with different number of polar groups on the surfaces of diaspore (010) and kaolinite (001) 相似文献
942.
Recent technological advances in Global Positioning System (GPS) telemetry have allowed the production of lightweight devices suitable for use on small mammals. We evaluated the use of GPS bugs on the European hedgehog (Erinaceus europaeus) in a series of static and field tests. Static tests were conducted in five different rural habitats, affording different degrees of obstruction to satellites. GPS bug performance was good in all habitats (fix success rate (FSR): median ≥?66.8 %; location error (LE): mean ≤?13.5 m), except woodland (FSR?=?37.7 %; LE?=?15.6 m), with performance highest in the open pasture habitat (FSR?=?100 %; LE?=?6.4 m). Field tests revealed mean FSR was high (84.6 %), with the use of nesting habitats, the probable cause of most failed fixes. Despite being more expensive, GPS bugs require less survey effort and substantially lower labour costs with unlimited longevity permitting re-use in multiple seasons. We recommend the use of GPS bugs in the spatial ecological study of any small mammal in a rural environment, providing accurate and unbiased movement data. Further performance testing is recommended before deployment on species inhabiting forested habitats where reduced FSR and high LE support the alternative use of very high frequency tracking. 相似文献
943.
Jianmei Luo Meiling Chi Hongyu Wang Huanhuan He Minghua Zhou 《Bioprocess and biosystems engineering》2013,36(12):1889-1896
A convenient and promising alternative to surface modification of carbon mesh anode was fulfilled by electrochemical oxidation in the electrolyte of nitric acid or ammonium nitrate at ambient temperature. It was confirmed that such an anode modification method was low cost and effective not only in improving the efficiency of power generation in microbial fuel cells (MFCs) for synthetic wastewater treatment, but also helping to reduce the period for MFCs start-up. The MFCs with anode modification in electrolyte of nitric acid performed the best, achieving a Coulombic efficiency enhancement of 71 %. As characterized, the electrochemical modification resulted in the decrease of the anode potential and internal resistance but the increase of current response and nitrogen-containing and oxygen-containing functional groups on the carbon surface, which might contribute to the enhancement on the performances of MFCs. 相似文献
944.
In our previous study, we used a comparative proteomic approach based on 2DE to profile dynamic proteomes of cotton fibers and found 235 protein spots differentially expressed during the elongation process ranging from 5 to 25 days post‐anthesis. Of them, only 106 differentially expressed proteins (DEPs) were identified by MS due to database limitations at the time. In the present work, we successfully identified the remaining 129 DEPs from the same experimental system using high‐resolution MS with an updated database. Bioinformatic analysis revealed that proteins involved in carbohydrate and protein metabolism, transport, and redox homeostasis are the most abundant, and glycolysis was found to be the most significantly regulated process during fiber elongation. Our high‐confidence reference dataset, composed of 235 DEPs, provides a valuable resource for future studies on the molecular mechanism of cotton fiber elongation. 相似文献
945.
目的:探讨胆管结石合并胆管癌的临床特征及诊治方法。方法:回顾性分析2000年1月-2009年12月我院收治的胆管结石合并胆管癌16例患者的临床病理资料。结果:胆管癌的发生率占同期胆管结石患者的3.1%,其临床表现以右上腹疼痛及反复的胆管炎发作为主,但缺乏特异性。术前胆管癌组患者AKP、γ-GT均有不同程度升高,ALT升高12例,总胆红素升高9例,与非胆管癌组相比,AKP、γ-GT、ALT、TBIL均显著升高(P〈0.01),且胆管癌组术前血清CA19-9及CEA显著高于非胆管癌组(P〈0.01),而两组间CA125及AFP水平比较无显著差异(P〉0.05)。16例患者中可进行手术治疗10例;其中根治性手术8例,姑息性手术2例。8例根治性手术患者的1、3年生存率分别为78.6%和36.4%;2例姑息性手术患者1、3年生存率分别为50.0%和0%,两组比较具有显著性差异(P〈0.05)。结论:胆管结石合并胆管癌的临床表现缺乏特异性,患者的疗效较差,对血清CA19-9和CEA显著升高者应行病理活检确诊,治疗手段应该力争实行根治性切除,有助于提高患者的生存期。 相似文献
946.
947.
Tianjiao Lyu Nan Jia Jieyu Wang Xiaohui Yan Yinhua Yu Zhen Lu Robert C Bast Jr Keqin Hua Weiwei Feng 《Epigenetics》2013,8(12):1330-1346
The initiation of angiogenesis can mark the transition from tumor dormancy to active growth and recurrence. Mechanisms that regulate recurrence in human cancers are poorly understood, in part because of the absence of relevant models. The induction of ARHI (DIRAS3) induces dormancy and autophagy in human ovarian cancer xenografts but produces autophagic cell death in culture. The addition of VEGF to cultures maintains the viability of dormant autophagic cancer cells, thereby permitting active growth when ARHI is downregulated, which mimics the “recurrence” of growth in xenografts. Two inducible ovarian cancer cell lines, SKOv3-ARHI and Hey-ARHI, were used. The expression level of angiogenesis factors was evaluated by real-time PCR, immunohistochemistry, immunocytochemistry and western blot; their epigenetic regulation was measured by bisulfite sequencing and chromatin immunoprecipitation. Six of the 15 angiogenesis factors were upregulated in dormant cancer cells (tissue inhibitor of metalloproteinases-3, TIMP3; thrombospondin-1, TSP1; angiopoietin-1; angiopoietin-2; angiopoietin-4; E-cadherin, CDH1). We found that TIMP3 and CDH1 expression was regulated epigenetically and was related inversely to the DNA methylation of their promoters in cell cultures and in xenografts. Increased H3K9 acetylation was associated with higher TIMP3 expression in dormant SKOv3-ARHI cells, while decreased H3K27me3 resulted in the upregulation of TIMP3 in dormant Hey-ARHI cells. Elevated CDH1 expression during dormancy was associated with an increase in both H3K4me3 and H3K9Ac in two cell lines. CpG demethylating agents and/or histone deacetylase inhibitors inhibited the re-growth of dormant cancer cells, which was associated with the re-expression of anti-angiogenic genes. The expression of the anti-angiogenic genes TIMP3 and CDH1 is elevated during dormancy and is reduced during the transition to active growth by changes in DNA methylation and histone modification. 相似文献
948.
Rui Zhang Zhigang Meng Tao Zhou Yong Deng Li Feng Yuan Wang Guoqing Sun Sandui Guo Maozhi Ren 《Plant signaling & behavior》2013,8(11)
FKBP12 encodes a prolyl isomerase and highly conserved in eukaryotic species. In yeasts and animals, FKBP12 can interact with rapamycin and FK506 to form rapamycin-FKBP12 and FK506-FKBP12 complex, respectively. In higher plants, FKBP12 protein lost its function to bind rapamycin and FK506. Early studies showed that yeast and human FKBP12 protein can restore the rapamycin sensitivity in Arabidopsis, but the used concentration is 100–1000 folds higher than that in yeast and animals. High concentration of drugs would increase the cost and cause the potential secondary effects on plant growth and development. Here we further discovered that BP12 plants generated in our previous study are hypersensitive to rapamycin at the concentration as low as that is effective in yeast and animals. It is surprising to observe that WT and BP12 plants are not sensitive to FK506 in normal growth condition. These findings advance the current understanding of rapamycin-TOR signaling in plants. 相似文献
949.
Tommaso Iannitti Mohamed Elhensheri Ali Ö. Bingöl Beniamino Palmieri 《Journal of molecular histology》2013,44(2):191-201
Osteoarthritis is a degenerative joint disease mostly occurring in the knee and commonly seen in middle-aged and elderly adults. Intra-articular injection of hyaluronic acid has been widely used for treatment of knee osteoarthritis. The aim of this study was to evaluate the efficacy of intra-articular injection of a novel highly cross-linked hyaluronic acid, alone or in combination with ropivacaine hydrochloride and triamcinolone acetonide, on knee articular cartilage in a rabbit model of collagenase-induced knee osteoarthritis. After induction of experimental osteoarthritis by intra-articular injection of collagenase, adult New Zealand white rabbits (n = 12) were divided into 3 groups. Group 1 (control group) received 0.3 ml phosphate buffered saline into the right knee joint. Group 2 received 0.3 ml cross-linked hyaluronic acid (33 mg/ml) into the right knee joint. Group 3 received a mixture of 0.15 ml cross-linked hyaluronic acid (33 mg/ml), 0.05 ml ropivacaine hydrochloride 1 % and 0.1 ml triamcinolone acetonide (10 mg/ml) into the right knee joint. Intra-articular injections were given 4 weeks after first collagenase injection and were administered once a week for 3 weeks. Gross pathology and histological evaluation of rabbits’ knee joints were performed after 16 weeks following initial collagenase injection. Histological analysis of sections of right knee joints at lesion sites showed a significant decrease in Mankin’s score in groups treated with hyaluronic acid alone or in combination with ropivacaine hydrochloride and triamcinolone acetonide versus control group (p < 0.05 and p < 0.01 respectively). This evidence was consistent with strong articular degenerative changes in control right knee joints (grade III osteoarthritis), while the treated groups revealed less severe articular degenerative changes (grade II osteoarthritis). The present results show that cross-linked hyaluronic acid, alone or in combination with ropivacaine hydrochloride and triamcinolone acetonide, produces a significant improvement in knee articular cartilage degeneration in a rabbit model of collagenase-induced osteoarthritis. 相似文献
950.