全文获取类型
收费全文 | 55914篇 |
免费 | 4502篇 |
国内免费 | 3484篇 |
专业分类
63900篇 |
出版年
2024年 | 129篇 |
2023年 | 622篇 |
2022年 | 1449篇 |
2021年 | 2412篇 |
2020年 | 1628篇 |
2019年 | 2053篇 |
2018年 | 2209篇 |
2017年 | 1833篇 |
2016年 | 2399篇 |
2015年 | 2862篇 |
2014年 | 3620篇 |
2013年 | 3927篇 |
2012年 | 4576篇 |
2011年 | 4310篇 |
2010年 | 2996篇 |
2009年 | 2610篇 |
2008年 | 3083篇 |
2007年 | 2809篇 |
2006年 | 2444篇 |
2005年 | 2062篇 |
2004年 | 1984篇 |
2003年 | 1840篇 |
2002年 | 1529篇 |
2001年 | 1116篇 |
2000年 | 922篇 |
1999年 | 717篇 |
1998年 | 461篇 |
1997年 | 384篇 |
1996年 | 355篇 |
1995年 | 366篇 |
1994年 | 331篇 |
1993年 | 256篇 |
1992年 | 360篇 |
1991年 | 329篇 |
1990年 | 255篇 |
1989年 | 247篇 |
1988年 | 166篇 |
1987年 | 215篇 |
1986年 | 188篇 |
1985年 | 179篇 |
1984年 | 156篇 |
1983年 | 135篇 |
1982年 | 109篇 |
1981年 | 106篇 |
1980年 | 82篇 |
1979年 | 94篇 |
1978年 | 98篇 |
1977年 | 84篇 |
1973年 | 80篇 |
1972年 | 81篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
P73 is a structural and functional homologue of p53, and plays an important role in regulating cell cycle and apoptosis. A
potentially functional polymorphism (designated as p73 G4C14-to-A4T14) has been identified in a region in exon 2 of the p73 gene, which may theoretically form a stem-loop structure and thereby affect p73 expression. Several investigations have reported the correlation between p73 G4C14-to-A4T14 polymorphism and cancer risk.
However, the results are inconclusive. To further assess the association between p73 polymorphism and cancer risk, we performed
meta-analysis of the data sets obtained from 26 individual studies involving 8,148 cancer patients and 8,150 controls. The
association between p73 G4C14-to-A4T14 polymorphism and cancer risk was determined by crude odd ratios (OR) with 95% CI (confidential
interval). AT-allele carriers were found to have a significantly increased risk of cervical cancer (AT/GC vs. GC/GC, OR = 1.63,
95% CI = 1.14–2.33; AT/AT + AT/GC vs. GC/GC, OR = 1.49, 95% CI = 1.05–2.10), colorectal cancer (AT/AT vs. AT/GC + GC/GC, OR = 1.98,
95% CI = 1.25–3.12), head and neck cancer (AT/AT + AT/GC vs. GC/GC, OR = 1.44, 95% CI = 1.06–1.96) and other cancers (AT/AT
vs. GC/GC, OR = 1.78, 95% CI = 1.24–2.57; AT/AT vs. AT/GC + GC/GC, OR = 1.80, 95% CI = 1.26–2.56). In the stratified analysis
of ethnicity, a significantly elevated cancer risk was found in Caucasians (AT/AT + AT/GC vs. GC/GC, OR = 1.18, 95% CI = 1.08–1.30;
allele AT vs. allele GC, OR = 1.15, 95% CI = 1.06–1.24). No significant association of p73 polymorphism with the cancer risk
of smoking was detected by stratified analysis by smoking status. Together, our data suggest that the p73 G4C14-to-A4T14 may
be a risk factor of cancer especially in Caucasians. 相似文献
152.
Guo-Hong Yu Lin-Lin Jiang Xue-Feng Ma Zhao-Shi Xu Meng-Meng Liu Shu-Guang Shan Xian-Guo Cheng 《PloS one》2014,9(10)
Zinc finger proteins were involved in response to different environmental stresses in plant species. A typical Cys2/His2-type (C2H2-type) zinc finger gene GmZF1 from soybean was isolated and was composed of 172 amino acids containing two conserved C2H2-type zinc finger domains. Phylogenetic analysis showed that GmZF1 was clustered on the same branch with six C2H2-type ZFPs from dicotyledonous plants excepting for GsZFP1, and distinguished those from monocotyledon species. The GmZF1 protein was localized at the nucleus, and has specific binding activity with EP1S core sequence, and nucleotide mutation in the core sequence of EPSPS promoter changed the binding ability between GmZF1 protein and core DNA element, implying that two amino acid residues, G and C boxed in core sequence TGACAGTGTCA possibly play positive regulation role in recognizing DNA-binding sites in GmZF1 proteins. High accumulation of GmZF1 mRNA induced by exogenous ABA suggested that GmZF1 was involved in an ABA-dependent signal transduction pathway. Over-expression of GmZF1 significantly improved the contents of proline and soluble sugar and decreased the MDA contents in the transgenic lines exposed to cold stress, indicating that transgenic Arabidopsis carrying GmZF1 gene have adaptive mechanisms to cold stress. Over-expression of GmZF1 also increased the expression of cold-regulated cor6.6 gene by probably recognizing protein-DNA binding sites, suggesting that GmZF1 from soybean could enhance the tolerance of Arabidopsis to cold stress by regulating expression of cold-regulation gene in the transgenic Arabidopsis. 相似文献
153.
Joe F. Bozeman III Shauhrat S. Chopra Philip James Sajjad Muhammad Hua Cai Kangkang Tong Maya Carrasquillo Harold Rickenbacker Destenie Nock Weslynne Ashton Oliver Heidrich Sybil Derrible Melissa Bilec 《Journal of Industrial Ecology》2023,27(2):382-394
Now is the time to refocus efforts in urban research and design. A changing climate and extreme weather events are presenting unique challenges to urban systems around the world. These challenges illuminate the social barriers that accompany disruptive events such as resource inequities and injustices. In this perspective, we provide three research priorities for just and sustainable urban systems that help to address these matters. The three research priorities are: (1) social equity and justice, (2) circularity, and (3) digital twins. Conceptual context and future research directions are provided for each. For social equity and justice, the future directions are mandatory equity analysis and inclusionary practices, understanding and reconciling historical injustices, and intentional integration with diverse community stakeholders. For circularity applications, they are better metrics for integration, more robust evaluation frameworks, and dynamic modeling at multiple spatial and temporal scales. Future directions for digital twins include developing principles to reduce complexity, integrating model and system components, and reducing barriers to data access. These research priorities are core to meeting several of the United Nations Sustainable Development Goals (i.e., 1—No Poverty, 8—Decent Work and Economic Growth, 10—Reduced Inequalities, and 11—Sustainable Cities and Communities). Useful social and technical matters are discussed throughout, where we highlight the importance of prioritizing localized research efforts, provide guidance for community-engaged research and co-development practices, and explain how these priorities interact to align with the evolving field of industrial ecology. 相似文献
154.
I. O. Vassilieva Yu. A. Negulyaev I. I. Marakhova S. B. Semenova 《Cell and Tissue Biology》2008,2(6):584-589
The recent cloning of the special calcium channels TRPV5 and TRPV6 (transient receptor potential vanilloid channels) has provided a molecular basis for studying previously unidentified calcium influx channels in electrically nonexcitable cells. In the present work using RT-PCR, we obtained the endogenous expression of mRNAs of genes trpv5 and trpv6 in lymphoblast leukemia Jurkat cells and in normal human T lymphocytes. Additionally, by immunoblotting, the presence of the channel-forming TRPV5 proteins has been shown both in the total lysate and in crude membrane fractions from Jurkat cells and normal T lymphocytes. The use of immunoprecipitation revealed TRPV6 proteins in Jurkat cells, whereas in normal T lymphocytes, this protein was not detected. The expression pattern and the selective Ca2+ permeation properties of TRPV5 and TRPV6 channels indicate the important role of these channels in Ca2+ homeostasis, as well as most likely in malignant transformation of blood cells. 相似文献
155.
Some properties of the β-N-acetyl-D-hexosaminidase purified from intercellular fluid of tomato leaves after the plant was systematically infected by TMV (tobacco mosaic virus) were studied. When pNP β-D-GlcNAc (p nitrophenyl-N-aeetyl β-D-glucosaminide) or pNP β-D- GalNAc (p-nitrophenyl-N-acetyl-β-D galactosaminide) was used as the substrate, it showed the optical pH between 4. 8--5.0 and optical temperature between 44— 47℃. Studies of thermostabillty indicated that the enzyme had a biphasic denaturation curve. Using pNP-β-D-GIcNAc or pNP-β-D GalNAc as the substrate, the Km value of the enzyme was 0. 36 and 0. 67 mmol/L respectively. N acetyi-D glucosamine and N acetyl-D-galactosamine were competitive inhibitors of the enzyme activities. Ag+ and Hg2+ were sensitive inhibitors and Fe2+ . Fe3+ and Cu2+ were also inhibitors enzyme activities. 相似文献
156.
157.
Ishizuka Y Takasugi K Tsutsumi Y Kanazawa K Nemoto T Kiyoshi T Nakanishi H 《Carbohydrate research》2005,340(7):1343-1350
1H NMR spectra of G1-alpha-CD and G1-beta-CD were recorded using a spectrometer equipped with a 21.6 T magnet. An ultra-high magnetic field was effective for detecting 1H NMR signals with a small difference in chemical shifts. Introducing a glucosyl group onto CDs as a branch caused deformation of equilibrated 1H signals of cyclodextrin. Particularly, 1H signals in branched glucose were shifted greatly. 相似文献
158.
Food restriction (FR) is hypothesized to decrease body fat content of an animal and thus prevent obesity. However, the response of energy budget to a continuous (CFR) or discontinuous FR (DFR) remains inconsistent. In the present study, effects of CFR or DFR and refeeding on energy budget and behavior were examined in male Swiss mice. CFR significantly decreased the energy expenditure associated with basal metabolic rate (BMR) and activity behavior, but not sufficiently to compensate for energy deficit and thus resulted in lower body mass and fat content. DFR mice had a significantly higher food intake on ad libitum days and showed increases in BMR and activity after 4 weeks’ DFR, which might resulted in lower body mass and less body fat than controls. After being refed ad libitum, both CFR and DFR mice had similar body mass, BMR, and behavioral patterns to controls but had 95% and 75% higher fat content. This suggested that not only CFR but also DFR would be a significant factor in the process of obesity for animals that were refed ad libitum. It also indicated that food restriction interrupted many times by periods of ad libitum feeding had the same long-term effects like continuous underfeeding. 相似文献
159.
P. O. Tsvetkov A. A. Kulikova F. Devred E. Yu. Zernii D. Lafitte A. A. Makarov 《Molecular Biology》2011,45(4):641-646
Vinca-alkaloids, such as vinblastine, and some of their derivatives, for example vinorelbine, are widely used in clinical therapy of leukemia and several types of tumors. Their effects are associated with the disfunctioning of the mitotic spindle, which leads to mitosis blockage and a shutting down of the cell cycle. Their primary target is tubulin; however, recent research has shown that some of the vinca-alkaloids inhibit calmodulin binding to its targets. Vinca-alkaloids binding with other proteins could be responsible for their efficiency and neuroprotection. Here, we investigated the thermodynamics of vinorelbine interactions with calmodulin and tubulin. It was determined that, unlike the other vinca-alkaloids, both vinorelbine binding sites are located in the C-domain of calmodulin and they are characterized by association constants of 4.0 × 105 and 5.4 × 104 M−1. At the same time, the thermodynamics of vinorelbine binding to tubulin are not much different from that of other vinca-alkaloids. These results will allow us to get a better insight on the reaction mechanisms of vinca-alkaloids on a secondary protein target. 相似文献
160.